Research ArticleCorn Husk Fiber-Polyester Composites as Sound AbsorberNonacoustical and Acoustical Properties
Nasmi Herlina Sari1 I N G Wardana2 Yudy Surya Irawan2 and Eko Siswanto2
1Department of Mechanical Engineering Faculty of Engineering Mataram University Nusa Tenggara Barat Indonesia2Department of Mechanical Engineering Faculty of Engineering Brawijaya University East Java Indonesia
Correspondence should be addressed to Nasmi Herlina Sari nherlinasariunramacid
Received 13 December 2016 Accepted 29 January 2017 Published 19 February 2017
Academic Editor Marc Thomas
Copyright copy 2017 Nasmi Herlina Sari et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
This study investigates the acoustical and nonacoustical properties of composites using corn husk fiber (CHF) and unsaturatedpolyester as the sound-absorbing materials The influence of the volume fraction of CHF on acoustic performance wasexperimentally investigated In addition the nonacoustical properties such as air-flow resistivity porosity and mechanicalproperties of composites have been analyzedThe results show that the sound absorptions at low frequencies are determined by thenumber of lumens in fiber particularly the absorption coefficient which increases the amount of fiber For high-frequency soundthe absorption coefficient is determined by the arrangement of fibers in the composite An absorption coefficient is close to zerowhen the fibers are arranged in a conventional pattern however when they are arranged in a random pattern a high absorptioncoefficient can be obtainedThe bond interface between the fiber and resin enhances its mechanical properties which increases thelongevity of the composite panel
1 Introduction
Noise pollution and waste management are two problemsthat need to be solved in modern societies The use of newlydeveloped alternative materials to absorb the noise consid-erably minimizes these problems Hence the inexpensiveeasily created thin and lightweight composite materials thatcan absorb soundwaves in broader frequency fields are highlydesirable
The fibrous sound-absorbing materials have been exten-sively investigated [1ndash5] Biot studies [1 2] provide anapproach for the propagation of elastic waves in the fluidmedium-saturated porous material at high and low frequen-cies where factors such as pore geometry fluid and mediumhaving comparable densities are required to be consideredDelany and Bazley [3] developed a simple model for estimat-ing the sound of absorption coefficients and characteristics ofimpedance of different types of fibrous absorbent materialsLee and Chen [4] developed Acoustic Transmission Analysis(ATA) model to estimate the acoustic absorption of a mul-tilayer absorbers Attenborough [5] developed a model for
estimating the acoustical characteristics of fibrous absorbentssoils and sands using flow resistivity formulae
The polymer has been widely utilized as a matrix in fibercomposites because it is easily formed from a material thathas physical and acoustical properties [6ndash13] Veerakumarand Selvakumar [6] studied acoustic properties for compositemade from kapok fiber with polypropylene fiber which werefound to demonstrate good sound absorption behavior inthe frequency range 250ndash2000Hz Jailani et al [7] studiedon panels made from coconut coir fibers which have beenconducted to analyze compression effect of the panel onthe acoustic performance The coir fiber panel is a goodsound absorber at 15ndash5 kHz Zulkifli et al [8] investigated theeffect of the porous layer backing and a perforated panel onthe sound absorption coefficient of coconut coir fiber Theyindicated that increasing the thickness material of the panelwill improve the sound absorption ability especially in thelow-frequency range at 600ndash2400Hz Chen et al [9] studiedthe sound-absorbing properties of ramie fiber-reinforcedpolylactic acidmaterials Putra et al [10] studied the potentialof waste fibers from paddy mixed with polyurethane as
HindawiAdvances in Acoustics and VibrationVolume 2017 Article ID 4319389 7 pageshttpsdoiorg10115520174319389
2 Advances in Acoustics and Vibration
acoustic material and found that the absorption coefficientis greater than 05 from 1 kHz and can reach the averagevalue of 08 above 25 kHz Bastos et al [11] developedvegetable fibers coconut palm sisal and acaı as sound-absorbing panels Measurement scale reverberation chamberexposed promising results from acoustic performance forall panels Flammability odor fungal growth and agingtests have been performed on samples to identify theirpractical ability Koizumi et al [12] developed bamboo fiberas sound-absorbing material They reported that the bamboofiber material has equivalent acoustics properties with glasswool Jayamani and Hamdan [13] studied sound absorp-tion coefficient of urea-formaldehyde and polypropylenemixed with kenaf fiber They reported that the kenaf fiberreinforced with polypropylene demonstrates higher soundabsorption coefficients than kenaf fiber reinforced with urea-formaldehyde These previous studies represented that abetter understanding of the microstructure and physicalparameters of a material could help in developing high-performance acoustic materials
This study primarily investigates the effect of addingcorn husk fibers (CHFs) on acoustical and nonacousticsproperties of polyester composites In addition the effects offiber content on the tensile properties and microstructuresvia SEM have been analyzed The results of this study couldcontribute to engineering applications especially as soundabsorbers
2 Materials and Methods
21 Materials and Sample Preparation CHF is the mainraw material used in this study The fiber contains 4615cellulose 3379 hemicellulose and 392 lignin It has beentreated with 5 sodium hydroxide (NaOH) for 2 h Thescheme of reaction is given as follows
CHF minusOH + NaOH 997888rarr CHF minusO-Na+ +H2O (1)
Chemical reactions have been removing impurities on thefiber surface The CHF was rinsed five times with mineralwater in other to remove NaOH sticking from the fibersurfaces They were dried in natural sunlight to remove anyresidual moisture and were then preserved in a dry box witha humidity of 40 The chemical contents of treated CHFare 5437 cellulose 2237 hemicellulose and 564 ligninThe average of diameter of a single CHF is 0133 plusmn 003mmmeasured by a Mitutoyo digital micrometer
Theunsaturated polyester resin 2250 BW-EXhas a viscos-ity of 6ndash8 poise (25∘C) the tensile strength of 88 Kgmm2a tensile modulus of 500Kgmm2 the flexural strength of25 Kgmm2 and elongation of 23
The weight of polyester resin and CHFs were measuredbefore processing so as to determine the volume fractionof CHFs and polyester in the resulting composite Thecomposition of different sound absorbers is summarized inTable 1 The mixtures were hot pressed at 100∘C and 03MPafor 4min into a round mold with a diameter of 32mmfollowed by cooling to room temperature at 5MPa to obtaina round shape to fit in the impedance tube during the sound
Table 1 The composition of the composite (mean values in volumefraction)
Sample CHF () Polyester resin ()PF-E 20 80PF-G 40 60PF-H 50 50PF-I 60 40PF-K 70 30PF-M 80 20
absorption test All the absorbermaterials were obtainedwitha diameter of 29mm and thickness of 20mm Six differentsamples were used for acoustical and porosity tests
22 Porosity The connected porosity of composite samplewas nonacoustically measured using the method of watersaturation used by Vasina et al [14] All the samples weredried at 105∘C for 24 h Subsequently they were weighedbefore being left in a vacuum vessel to saturate under waterthe density of water is 120588
119908= 1000Kgsdotmminus3 After 24 h they
were carefully removed and weighed again The porosity wascomputed using 120576 = 119881
119886119881119904 where 119881
119886is the volume of the
composite occupied by the water and119881119904is the total volume of
the composite The volume of water can be computed using119881119908= (1198982minus1198981)120588119908 where119898
2and119898
1are the wet and the dry
masses of the composite (Kg) respectively
23 Air-Flow Resistivity There are several empirical andsemiempirical equations in the literature that can be used toestimate the flow resistivity of absorber materials based uponfiber radius and material porosity or the bulk density of thematerials [14ndash16] The air-flow resistivity of the samples usedin this study is expressed in [16]
119877 =68120583 (1 minus 120576)1296
11988621205763 (2)
where 120583 is the viscosity of air (184 times 10minus5 Pasdots) 120576 is theporosity and 119886 is the radius of the fiber
24 Tortuosity The following empirical formula was used tocalculate tortuosity (120590) in terms of porosity The tortuosity isexpressed in [5]
120590 = 1 +(1 minus 120576)
(2120576) (3)
25 Sound Absorption Measurement The acoustic proper-ties of the composite sample were measured using a two-microphone transfer-function method according to ASTME-1050-98ISO 10534-2 standards The testing apparatus waspart of complete acoustic material testing system Bruel ampKjaer (type 4206 Bruel amp Kjaeligr) as it is seen in Figure 1A small tube setup was employed to measure differentacoustical parameters in the frequency range of 100Hzndash64 kHz At one end of the tube a loudspeaker was situated
Advances in Acoustics and Vibration 3
Power amplifierAcoustic material test
Computer
Loudspeaker
Microphones
Sample
Incident signal
Reflected signal
(100Hzndash64kHz)Impedance tube kit
Figure 1 Impedance tube kit (type 4206 Bruel amp Kjaeligr)
to act as a sound source and the test material was placedat the other end to measure sound absorption propertiesTwo acoustic microphones (type 4187 Bruel amp Kjaeligr) werelocated in front of the sample to record the incident soundfrom the loudspeaker and the reflected sound from thematerial The recorded signals in the analyzer in terms of thetransfer function between the microphones were processedusing Bruel amp Kjaeligr material testing software to obtain theabsorption coefficient of the sample under test Each set of theexperiment was repeated three times in order to have averagemeasurements
26 Mechanical Properties The tensile and Youngrsquos modu-lus were determined using a Tensilon RTG-1310 universaltesting machine with a load cell of 10 kN All the samplesof composites were tested after conditioning for 24 h in astandard testing atmosphere of 70 relative humidity and28∘CAccording to theASTMD3039 standard a gauge lengthof 150mm and a crosshead speed of 5mmmin were usedfor tensile testing The sample size was 250mm times 254mmtimes 6mm In total 21 samples were tested for each samplecondition and the average and standard deviation values werereported
27 Scanning Electron Microscope The surface morphologiesof composites were observed using an Inspect-S50 scanningelectronmicroscope with field emission gun An acceleratingvoltage of 10 kV was used to collect SEM images on thesurface of the sample The morphologies of the compositeswere observed and analyzed via SEM at room temperatureBefore testing the samples were sliced and mounted ontoSEM stubs using double-sided adhesive tape They weregold sputtered for 5min to a thickness of approximately
10 nm under pressure of 01 torr and 18mA current to makethe sample conductive SEM micrographs were recorded atdifferent magnifications to ensure clear images
3 Results and Discussion
31 Nonacoustic Composites Properties Large differenceswere observed in nonacoustical properties of the compositesamples because of their different microstructures as aresult of the addition of the CHF in the polyester Thisdiversity is very interesting because it provides differentporous microstructures and consequently different acousticproperties Porosity tortuosity and flow resistivity values arelisted in Table 2
Increasing the amount of fiber volume fraction in thepolyester resin increases the porosity and decreases bothtortuosity and air-flow resistivity in the absorbent material(seen Table 2) The porosity value of the sample PF-M was08267 whichwas higher than those of the other samples usedin this study The presence of lumen in the fiber indicatesthat the porosity of the sample increases when the number offibers increases (Figure 2) In other words the lower value ofporosity and higher value of the flow resistivity of the samplecan be attributed to the higher volume fraction of polyesterresin
All the composite samples demonstrate an open porestructure wherein the pores are interconnected This is oneof the most important factors for noise absorption becausesuch a structure decreases air-flow resistivity and thus thedissipation of the wave energy in the pores In these samplesthe multiscale fiber structure with the lumen inside fiberbundle has a pore shape and the pore size can differ by severalorders of magnitude (Figures 2(a) and 2(b))
4 Advances in Acoustics and Vibration
Table 2 Nonacoustical properties of samples
Sample Thickness (mm) Density (Kgsdotm3) Porosity120576
Air-flow resistivity R (Pasdotssdotmminus2) Tortuosity120590
PF-E 20 6405 06474 44980 1272PF-G 20 3834 07053 29353 1208PF-H 20 3041 07247 25424 1190PF-I 20 2441 07457 21576 1171PF-K 20 1980 07582 19568 1160PF-M 20 1583 07954 14435 1128
(a) (b)
Figure 2 SEM photomicrographs of corn husk fibers 5 NaOH treated (a) surface and (b) cross-sectional features
PF-M
PF-H PF-I
PF-K
Polyester
PF-E
PF-G
1000 2000 3000 4000 5000 60000Frequency (Hz)
00
02
04
06
08
10
Soun
d ab
sorp
tion
coeffi
cien
t
Figure 3 The sound absorption coefficients of composite samples
32 Acoustical Properties The normal sound absorptionproperties for all samples of CHF-polyester composites aregraphically illustrated in Figure 3 The zero value in the 119910-axis indicates perfect sound reflection and the value of oneimplies complete sound absorption These results show thatall composite samples demonstrated an increase in soundabsorption coefficient in the range of 1 kHzndash25 kHz This isbecause lumen inside the fiber bundle increases the amount
of fiber which results in high absorption coefficient Theadditional thermal energy is dissipated more rapidly due tothe increased frictional surface area The sound absorptioncoefficient of the PF-M sample is therefore correspondinglyhigher than those of the other samples The sound wavespropagate vibration energy through the air spaces in theindividual lumina inside the fiber A part of this sound energyis converted into heat in the lumina which is then absorbedby the surrounding walls The larger the air cavities andlumina inside the fiber the longer the wavelength of thesound that is absorbed somore dominant at low frequenciesSEM micrograph analysis (Figures 6(a) 6(c) 6(e) 6(g) 6(i)and 6(k)) illustrates that there are many lumens inside thefiber and continuous channels in the porous structure ofpolyester composites
At frequencies above 2 kHz the sound absorption capa-bility of PF-E PF-G PF-I and PF-K samples decreasesThe decrease caused by the interface of the fiberresin andorderly fiber arrangement that cause the higher value ofthe flow resistivity of the sample makes movements of thesound difficult to pass through the samples An absorptioncoefficient is close to zero when the fibers are arranged in aconventional pattern SEM micrographs (Figure 6) illustratethat there is a distinct interface between fibers and resin inall samples Interface surfaces between fibers and resin of PF-E PF-G PF-I and PF-K samples (Figures 6(b) 6(d) 6(h)
Advances in Acoustics and Vibration 5
PF-GPolyester
PF-E
PF-I
PF-K
PF-HPF-M
1000 2000 3000 4000 5000 60000Frequency (Hz)
05
101520253035404550
Real
par
t of i
mpe
danc
e rat
io
Figure 4 The real part of the impedance ratio of different samples
and 6(j) resp) are quite dense and contain orderly fiberbundles arrangement Interface strength not only influencescomposite mechanical property but also influences soundabsorption quality When sufficient amount of resin is usedthe interface area between the fibers and the resin is smoothand strong (Figures 6(a) and 6(b)) When the incidentsound waves are continuously transmitted onto a compositeinterface the sound waves will be reflected and refractedand the acoustic damping phenomena will consume a smallamount of energy reducing heat losses and thus obtaining alower absorption coefficient at high frequencies This wouldalso explain why the sound absorption of PF-E is lower thanthose of sample patterns of composites which are similar
Sample pure polyester resin (PE) had the absorption coef-ficient under 02 Althoughpolyestermay be a valuable optionin noise absorption applications these results discourage itsuse as a sound-absorbing material
Figure 3 also shows that the PF-H and PF-M samplesdemonstrated the ability to absorb sound at high frequenciesabove 4 kHz This is due to the random distribution of thefiber The random distribution of the fibers in the fibrousabsorbent materials allows the sound waves to hit the lumenof the fiber bundle and strengthen the sound absorptioneffect a high absorption coefficient can be obtained SEMmicrographs (Figures 6(e) 6(f) 6(k) and 6(l)) illustrate therandom distribution of the fibers in PF-H and PF-M samples
Figures 4 and 5 show that the real part is the resistanceassociated with energy losses and the imaginary part is thereactance associated with phase changes respectively In thiscase we can observe a better performance of PF-H and PF-Msamples than other materials studied Increasing the amountof fiber reduces the number of impedance values andmaterialstiffnessThe reduced impedance values increase the fractionof wave energy that can be transmitted through the sample
Furthermore sound absorption at lower frequencies(over 10ndash2 kHz) is desirable for automotive applicationsbecause of this frequency range according to noise from thewind engine running tires road and conversation therebymaking CHF-polyester composites a promising candidate forautomotive interior sound absorption
PF-G
Polyester
PF-E
PF-H
PF-M
PF-I
PF-K
1000 2000 3000 4000 5000 60000Frequency (Hz)
minus20
minus10
0
10
20
30
Imag
inar
y pa
rt o
f im
peda
nce r
atio
Figure 5 The imaginary part of the impedance ratio of samples
33 Mechanical Properties Theoretically there should be aninteraction between hydrophobic polyester and hydrophiliccellulose The disappearance of the noncellulose material onthe surface of the fiber enables surface interaction with thepolyester matrix The void fraction is mainly formed becausethe composites have not been consolidated (not sufficientlypressed to form a contiguous solid structure) in order tomanufacture composites
Figures 7 and 8 show that the increase in the fibervolume fraction leads to increase in the tensile strength valueand Youngrsquos modulus of the composite from 1881 plusmn 85to 2573 plusmn 319MPa The increase in mechanical strengthcan be attributed to the bond interface between the fibersand resin The mechanical properties of the PF-M sample(or composite sample with 20 resin and 80 CHF) aretherefore correspondingly higher than those of the othersamples
For PF-H sample there was a 1253 decrease in thetensile strength values with a strength value of 2040 plusmn11MPa The probability of the overlapping of multiple CHFin composite samples thereby causes the weaker transferenceof load between fiber and matrix occurring due to thepoor interfacial adhesion causing lowering in the mechanicalproperties However the value of the modulus of elasticityof the sample PF-H is higher than that of the material usedin this study contributing to the sound absorption of thesample
The tensile strength value of the PF-E sample is the lowercompared to other samples This is due to the fiber volumefraction less than the other samples The tensile strength ofthe fiber of 23743MPa is higher than the tensile strength ofthe resin
4 Conclusions
In this study a CHF-polyester sound absorber was proposedand the sound absorption capability of the material wassignificantly enhanced through the simple method Thepresence of a number of lumen structures in the fiber bundlefacilitates sound absorption at low frequencies in the range
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
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2 Advances in Acoustics and Vibration
acoustic material and found that the absorption coefficientis greater than 05 from 1 kHz and can reach the averagevalue of 08 above 25 kHz Bastos et al [11] developedvegetable fibers coconut palm sisal and acaı as sound-absorbing panels Measurement scale reverberation chamberexposed promising results from acoustic performance forall panels Flammability odor fungal growth and agingtests have been performed on samples to identify theirpractical ability Koizumi et al [12] developed bamboo fiberas sound-absorbing material They reported that the bamboofiber material has equivalent acoustics properties with glasswool Jayamani and Hamdan [13] studied sound absorp-tion coefficient of urea-formaldehyde and polypropylenemixed with kenaf fiber They reported that the kenaf fiberreinforced with polypropylene demonstrates higher soundabsorption coefficients than kenaf fiber reinforced with urea-formaldehyde These previous studies represented that abetter understanding of the microstructure and physicalparameters of a material could help in developing high-performance acoustic materials
This study primarily investigates the effect of addingcorn husk fibers (CHFs) on acoustical and nonacousticsproperties of polyester composites In addition the effects offiber content on the tensile properties and microstructuresvia SEM have been analyzed The results of this study couldcontribute to engineering applications especially as soundabsorbers
2 Materials and Methods
21 Materials and Sample Preparation CHF is the mainraw material used in this study The fiber contains 4615cellulose 3379 hemicellulose and 392 lignin It has beentreated with 5 sodium hydroxide (NaOH) for 2 h Thescheme of reaction is given as follows
CHF minusOH + NaOH 997888rarr CHF minusO-Na+ +H2O (1)
Chemical reactions have been removing impurities on thefiber surface The CHF was rinsed five times with mineralwater in other to remove NaOH sticking from the fibersurfaces They were dried in natural sunlight to remove anyresidual moisture and were then preserved in a dry box witha humidity of 40 The chemical contents of treated CHFare 5437 cellulose 2237 hemicellulose and 564 ligninThe average of diameter of a single CHF is 0133 plusmn 003mmmeasured by a Mitutoyo digital micrometer
Theunsaturated polyester resin 2250 BW-EXhas a viscos-ity of 6ndash8 poise (25∘C) the tensile strength of 88 Kgmm2a tensile modulus of 500Kgmm2 the flexural strength of25 Kgmm2 and elongation of 23
The weight of polyester resin and CHFs were measuredbefore processing so as to determine the volume fractionof CHFs and polyester in the resulting composite Thecomposition of different sound absorbers is summarized inTable 1 The mixtures were hot pressed at 100∘C and 03MPafor 4min into a round mold with a diameter of 32mmfollowed by cooling to room temperature at 5MPa to obtaina round shape to fit in the impedance tube during the sound
Table 1 The composition of the composite (mean values in volumefraction)
Sample CHF () Polyester resin ()PF-E 20 80PF-G 40 60PF-H 50 50PF-I 60 40PF-K 70 30PF-M 80 20
absorption test All the absorbermaterials were obtainedwitha diameter of 29mm and thickness of 20mm Six differentsamples were used for acoustical and porosity tests
22 Porosity The connected porosity of composite samplewas nonacoustically measured using the method of watersaturation used by Vasina et al [14] All the samples weredried at 105∘C for 24 h Subsequently they were weighedbefore being left in a vacuum vessel to saturate under waterthe density of water is 120588
119908= 1000Kgsdotmminus3 After 24 h they
were carefully removed and weighed again The porosity wascomputed using 120576 = 119881
119886119881119904 where 119881
119886is the volume of the
composite occupied by the water and119881119904is the total volume of
the composite The volume of water can be computed using119881119908= (1198982minus1198981)120588119908 where119898
2and119898
1are the wet and the dry
masses of the composite (Kg) respectively
23 Air-Flow Resistivity There are several empirical andsemiempirical equations in the literature that can be used toestimate the flow resistivity of absorber materials based uponfiber radius and material porosity or the bulk density of thematerials [14ndash16] The air-flow resistivity of the samples usedin this study is expressed in [16]
119877 =68120583 (1 minus 120576)1296
11988621205763 (2)
where 120583 is the viscosity of air (184 times 10minus5 Pasdots) 120576 is theporosity and 119886 is the radius of the fiber
24 Tortuosity The following empirical formula was used tocalculate tortuosity (120590) in terms of porosity The tortuosity isexpressed in [5]
120590 = 1 +(1 minus 120576)
(2120576) (3)
25 Sound Absorption Measurement The acoustic proper-ties of the composite sample were measured using a two-microphone transfer-function method according to ASTME-1050-98ISO 10534-2 standards The testing apparatus waspart of complete acoustic material testing system Bruel ampKjaer (type 4206 Bruel amp Kjaeligr) as it is seen in Figure 1A small tube setup was employed to measure differentacoustical parameters in the frequency range of 100Hzndash64 kHz At one end of the tube a loudspeaker was situated
Advances in Acoustics and Vibration 3
Power amplifierAcoustic material test
Computer
Loudspeaker
Microphones
Sample
Incident signal
Reflected signal
(100Hzndash64kHz)Impedance tube kit
Figure 1 Impedance tube kit (type 4206 Bruel amp Kjaeligr)
to act as a sound source and the test material was placedat the other end to measure sound absorption propertiesTwo acoustic microphones (type 4187 Bruel amp Kjaeligr) werelocated in front of the sample to record the incident soundfrom the loudspeaker and the reflected sound from thematerial The recorded signals in the analyzer in terms of thetransfer function between the microphones were processedusing Bruel amp Kjaeligr material testing software to obtain theabsorption coefficient of the sample under test Each set of theexperiment was repeated three times in order to have averagemeasurements
26 Mechanical Properties The tensile and Youngrsquos modu-lus were determined using a Tensilon RTG-1310 universaltesting machine with a load cell of 10 kN All the samplesof composites were tested after conditioning for 24 h in astandard testing atmosphere of 70 relative humidity and28∘CAccording to theASTMD3039 standard a gauge lengthof 150mm and a crosshead speed of 5mmmin were usedfor tensile testing The sample size was 250mm times 254mmtimes 6mm In total 21 samples were tested for each samplecondition and the average and standard deviation values werereported
27 Scanning Electron Microscope The surface morphologiesof composites were observed using an Inspect-S50 scanningelectronmicroscope with field emission gun An acceleratingvoltage of 10 kV was used to collect SEM images on thesurface of the sample The morphologies of the compositeswere observed and analyzed via SEM at room temperatureBefore testing the samples were sliced and mounted ontoSEM stubs using double-sided adhesive tape They weregold sputtered for 5min to a thickness of approximately
10 nm under pressure of 01 torr and 18mA current to makethe sample conductive SEM micrographs were recorded atdifferent magnifications to ensure clear images
3 Results and Discussion
31 Nonacoustic Composites Properties Large differenceswere observed in nonacoustical properties of the compositesamples because of their different microstructures as aresult of the addition of the CHF in the polyester Thisdiversity is very interesting because it provides differentporous microstructures and consequently different acousticproperties Porosity tortuosity and flow resistivity values arelisted in Table 2
Increasing the amount of fiber volume fraction in thepolyester resin increases the porosity and decreases bothtortuosity and air-flow resistivity in the absorbent material(seen Table 2) The porosity value of the sample PF-M was08267 whichwas higher than those of the other samples usedin this study The presence of lumen in the fiber indicatesthat the porosity of the sample increases when the number offibers increases (Figure 2) In other words the lower value ofporosity and higher value of the flow resistivity of the samplecan be attributed to the higher volume fraction of polyesterresin
All the composite samples demonstrate an open porestructure wherein the pores are interconnected This is oneof the most important factors for noise absorption becausesuch a structure decreases air-flow resistivity and thus thedissipation of the wave energy in the pores In these samplesthe multiscale fiber structure with the lumen inside fiberbundle has a pore shape and the pore size can differ by severalorders of magnitude (Figures 2(a) and 2(b))
4 Advances in Acoustics and Vibration
Table 2 Nonacoustical properties of samples
Sample Thickness (mm) Density (Kgsdotm3) Porosity120576
Air-flow resistivity R (Pasdotssdotmminus2) Tortuosity120590
PF-E 20 6405 06474 44980 1272PF-G 20 3834 07053 29353 1208PF-H 20 3041 07247 25424 1190PF-I 20 2441 07457 21576 1171PF-K 20 1980 07582 19568 1160PF-M 20 1583 07954 14435 1128
(a) (b)
Figure 2 SEM photomicrographs of corn husk fibers 5 NaOH treated (a) surface and (b) cross-sectional features
PF-M
PF-H PF-I
PF-K
Polyester
PF-E
PF-G
1000 2000 3000 4000 5000 60000Frequency (Hz)
00
02
04
06
08
10
Soun
d ab
sorp
tion
coeffi
cien
t
Figure 3 The sound absorption coefficients of composite samples
32 Acoustical Properties The normal sound absorptionproperties for all samples of CHF-polyester composites aregraphically illustrated in Figure 3 The zero value in the 119910-axis indicates perfect sound reflection and the value of oneimplies complete sound absorption These results show thatall composite samples demonstrated an increase in soundabsorption coefficient in the range of 1 kHzndash25 kHz This isbecause lumen inside the fiber bundle increases the amount
of fiber which results in high absorption coefficient Theadditional thermal energy is dissipated more rapidly due tothe increased frictional surface area The sound absorptioncoefficient of the PF-M sample is therefore correspondinglyhigher than those of the other samples The sound wavespropagate vibration energy through the air spaces in theindividual lumina inside the fiber A part of this sound energyis converted into heat in the lumina which is then absorbedby the surrounding walls The larger the air cavities andlumina inside the fiber the longer the wavelength of thesound that is absorbed somore dominant at low frequenciesSEM micrograph analysis (Figures 6(a) 6(c) 6(e) 6(g) 6(i)and 6(k)) illustrates that there are many lumens inside thefiber and continuous channels in the porous structure ofpolyester composites
At frequencies above 2 kHz the sound absorption capa-bility of PF-E PF-G PF-I and PF-K samples decreasesThe decrease caused by the interface of the fiberresin andorderly fiber arrangement that cause the higher value ofthe flow resistivity of the sample makes movements of thesound difficult to pass through the samples An absorptioncoefficient is close to zero when the fibers are arranged in aconventional pattern SEM micrographs (Figure 6) illustratethat there is a distinct interface between fibers and resin inall samples Interface surfaces between fibers and resin of PF-E PF-G PF-I and PF-K samples (Figures 6(b) 6(d) 6(h)
Advances in Acoustics and Vibration 5
PF-GPolyester
PF-E
PF-I
PF-K
PF-HPF-M
1000 2000 3000 4000 5000 60000Frequency (Hz)
05
101520253035404550
Real
par
t of i
mpe
danc
e rat
io
Figure 4 The real part of the impedance ratio of different samples
and 6(j) resp) are quite dense and contain orderly fiberbundles arrangement Interface strength not only influencescomposite mechanical property but also influences soundabsorption quality When sufficient amount of resin is usedthe interface area between the fibers and the resin is smoothand strong (Figures 6(a) and 6(b)) When the incidentsound waves are continuously transmitted onto a compositeinterface the sound waves will be reflected and refractedand the acoustic damping phenomena will consume a smallamount of energy reducing heat losses and thus obtaining alower absorption coefficient at high frequencies This wouldalso explain why the sound absorption of PF-E is lower thanthose of sample patterns of composites which are similar
Sample pure polyester resin (PE) had the absorption coef-ficient under 02 Althoughpolyestermay be a valuable optionin noise absorption applications these results discourage itsuse as a sound-absorbing material
Figure 3 also shows that the PF-H and PF-M samplesdemonstrated the ability to absorb sound at high frequenciesabove 4 kHz This is due to the random distribution of thefiber The random distribution of the fibers in the fibrousabsorbent materials allows the sound waves to hit the lumenof the fiber bundle and strengthen the sound absorptioneffect a high absorption coefficient can be obtained SEMmicrographs (Figures 6(e) 6(f) 6(k) and 6(l)) illustrate therandom distribution of the fibers in PF-H and PF-M samples
Figures 4 and 5 show that the real part is the resistanceassociated with energy losses and the imaginary part is thereactance associated with phase changes respectively In thiscase we can observe a better performance of PF-H and PF-Msamples than other materials studied Increasing the amountof fiber reduces the number of impedance values andmaterialstiffnessThe reduced impedance values increase the fractionof wave energy that can be transmitted through the sample
Furthermore sound absorption at lower frequencies(over 10ndash2 kHz) is desirable for automotive applicationsbecause of this frequency range according to noise from thewind engine running tires road and conversation therebymaking CHF-polyester composites a promising candidate forautomotive interior sound absorption
PF-G
Polyester
PF-E
PF-H
PF-M
PF-I
PF-K
1000 2000 3000 4000 5000 60000Frequency (Hz)
minus20
minus10
0
10
20
30
Imag
inar
y pa
rt o
f im
peda
nce r
atio
Figure 5 The imaginary part of the impedance ratio of samples
33 Mechanical Properties Theoretically there should be aninteraction between hydrophobic polyester and hydrophiliccellulose The disappearance of the noncellulose material onthe surface of the fiber enables surface interaction with thepolyester matrix The void fraction is mainly formed becausethe composites have not been consolidated (not sufficientlypressed to form a contiguous solid structure) in order tomanufacture composites
Figures 7 and 8 show that the increase in the fibervolume fraction leads to increase in the tensile strength valueand Youngrsquos modulus of the composite from 1881 plusmn 85to 2573 plusmn 319MPa The increase in mechanical strengthcan be attributed to the bond interface between the fibersand resin The mechanical properties of the PF-M sample(or composite sample with 20 resin and 80 CHF) aretherefore correspondingly higher than those of the othersamples
For PF-H sample there was a 1253 decrease in thetensile strength values with a strength value of 2040 plusmn11MPa The probability of the overlapping of multiple CHFin composite samples thereby causes the weaker transferenceof load between fiber and matrix occurring due to thepoor interfacial adhesion causing lowering in the mechanicalproperties However the value of the modulus of elasticityof the sample PF-H is higher than that of the material usedin this study contributing to the sound absorption of thesample
The tensile strength value of the PF-E sample is the lowercompared to other samples This is due to the fiber volumefraction less than the other samples The tensile strength ofthe fiber of 23743MPa is higher than the tensile strength ofthe resin
4 Conclusions
In this study a CHF-polyester sound absorber was proposedand the sound absorption capability of the material wassignificantly enhanced through the simple method Thepresence of a number of lumen structures in the fiber bundlefacilitates sound absorption at low frequencies in the range
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
Advances in Acoustics and Vibration 3
Power amplifierAcoustic material test
Computer
Loudspeaker
Microphones
Sample
Incident signal
Reflected signal
(100Hzndash64kHz)Impedance tube kit
Figure 1 Impedance tube kit (type 4206 Bruel amp Kjaeligr)
to act as a sound source and the test material was placedat the other end to measure sound absorption propertiesTwo acoustic microphones (type 4187 Bruel amp Kjaeligr) werelocated in front of the sample to record the incident soundfrom the loudspeaker and the reflected sound from thematerial The recorded signals in the analyzer in terms of thetransfer function between the microphones were processedusing Bruel amp Kjaeligr material testing software to obtain theabsorption coefficient of the sample under test Each set of theexperiment was repeated three times in order to have averagemeasurements
26 Mechanical Properties The tensile and Youngrsquos modu-lus were determined using a Tensilon RTG-1310 universaltesting machine with a load cell of 10 kN All the samplesof composites were tested after conditioning for 24 h in astandard testing atmosphere of 70 relative humidity and28∘CAccording to theASTMD3039 standard a gauge lengthof 150mm and a crosshead speed of 5mmmin were usedfor tensile testing The sample size was 250mm times 254mmtimes 6mm In total 21 samples were tested for each samplecondition and the average and standard deviation values werereported
27 Scanning Electron Microscope The surface morphologiesof composites were observed using an Inspect-S50 scanningelectronmicroscope with field emission gun An acceleratingvoltage of 10 kV was used to collect SEM images on thesurface of the sample The morphologies of the compositeswere observed and analyzed via SEM at room temperatureBefore testing the samples were sliced and mounted ontoSEM stubs using double-sided adhesive tape They weregold sputtered for 5min to a thickness of approximately
10 nm under pressure of 01 torr and 18mA current to makethe sample conductive SEM micrographs were recorded atdifferent magnifications to ensure clear images
3 Results and Discussion
31 Nonacoustic Composites Properties Large differenceswere observed in nonacoustical properties of the compositesamples because of their different microstructures as aresult of the addition of the CHF in the polyester Thisdiversity is very interesting because it provides differentporous microstructures and consequently different acousticproperties Porosity tortuosity and flow resistivity values arelisted in Table 2
Increasing the amount of fiber volume fraction in thepolyester resin increases the porosity and decreases bothtortuosity and air-flow resistivity in the absorbent material(seen Table 2) The porosity value of the sample PF-M was08267 whichwas higher than those of the other samples usedin this study The presence of lumen in the fiber indicatesthat the porosity of the sample increases when the number offibers increases (Figure 2) In other words the lower value ofporosity and higher value of the flow resistivity of the samplecan be attributed to the higher volume fraction of polyesterresin
All the composite samples demonstrate an open porestructure wherein the pores are interconnected This is oneof the most important factors for noise absorption becausesuch a structure decreases air-flow resistivity and thus thedissipation of the wave energy in the pores In these samplesthe multiscale fiber structure with the lumen inside fiberbundle has a pore shape and the pore size can differ by severalorders of magnitude (Figures 2(a) and 2(b))
4 Advances in Acoustics and Vibration
Table 2 Nonacoustical properties of samples
Sample Thickness (mm) Density (Kgsdotm3) Porosity120576
Air-flow resistivity R (Pasdotssdotmminus2) Tortuosity120590
PF-E 20 6405 06474 44980 1272PF-G 20 3834 07053 29353 1208PF-H 20 3041 07247 25424 1190PF-I 20 2441 07457 21576 1171PF-K 20 1980 07582 19568 1160PF-M 20 1583 07954 14435 1128
(a) (b)
Figure 2 SEM photomicrographs of corn husk fibers 5 NaOH treated (a) surface and (b) cross-sectional features
PF-M
PF-H PF-I
PF-K
Polyester
PF-E
PF-G
1000 2000 3000 4000 5000 60000Frequency (Hz)
00
02
04
06
08
10
Soun
d ab
sorp
tion
coeffi
cien
t
Figure 3 The sound absorption coefficients of composite samples
32 Acoustical Properties The normal sound absorptionproperties for all samples of CHF-polyester composites aregraphically illustrated in Figure 3 The zero value in the 119910-axis indicates perfect sound reflection and the value of oneimplies complete sound absorption These results show thatall composite samples demonstrated an increase in soundabsorption coefficient in the range of 1 kHzndash25 kHz This isbecause lumen inside the fiber bundle increases the amount
of fiber which results in high absorption coefficient Theadditional thermal energy is dissipated more rapidly due tothe increased frictional surface area The sound absorptioncoefficient of the PF-M sample is therefore correspondinglyhigher than those of the other samples The sound wavespropagate vibration energy through the air spaces in theindividual lumina inside the fiber A part of this sound energyis converted into heat in the lumina which is then absorbedby the surrounding walls The larger the air cavities andlumina inside the fiber the longer the wavelength of thesound that is absorbed somore dominant at low frequenciesSEM micrograph analysis (Figures 6(a) 6(c) 6(e) 6(g) 6(i)and 6(k)) illustrates that there are many lumens inside thefiber and continuous channels in the porous structure ofpolyester composites
At frequencies above 2 kHz the sound absorption capa-bility of PF-E PF-G PF-I and PF-K samples decreasesThe decrease caused by the interface of the fiberresin andorderly fiber arrangement that cause the higher value ofthe flow resistivity of the sample makes movements of thesound difficult to pass through the samples An absorptioncoefficient is close to zero when the fibers are arranged in aconventional pattern SEM micrographs (Figure 6) illustratethat there is a distinct interface between fibers and resin inall samples Interface surfaces between fibers and resin of PF-E PF-G PF-I and PF-K samples (Figures 6(b) 6(d) 6(h)
Advances in Acoustics and Vibration 5
PF-GPolyester
PF-E
PF-I
PF-K
PF-HPF-M
1000 2000 3000 4000 5000 60000Frequency (Hz)
05
101520253035404550
Real
par
t of i
mpe
danc
e rat
io
Figure 4 The real part of the impedance ratio of different samples
and 6(j) resp) are quite dense and contain orderly fiberbundles arrangement Interface strength not only influencescomposite mechanical property but also influences soundabsorption quality When sufficient amount of resin is usedthe interface area between the fibers and the resin is smoothand strong (Figures 6(a) and 6(b)) When the incidentsound waves are continuously transmitted onto a compositeinterface the sound waves will be reflected and refractedand the acoustic damping phenomena will consume a smallamount of energy reducing heat losses and thus obtaining alower absorption coefficient at high frequencies This wouldalso explain why the sound absorption of PF-E is lower thanthose of sample patterns of composites which are similar
Sample pure polyester resin (PE) had the absorption coef-ficient under 02 Althoughpolyestermay be a valuable optionin noise absorption applications these results discourage itsuse as a sound-absorbing material
Figure 3 also shows that the PF-H and PF-M samplesdemonstrated the ability to absorb sound at high frequenciesabove 4 kHz This is due to the random distribution of thefiber The random distribution of the fibers in the fibrousabsorbent materials allows the sound waves to hit the lumenof the fiber bundle and strengthen the sound absorptioneffect a high absorption coefficient can be obtained SEMmicrographs (Figures 6(e) 6(f) 6(k) and 6(l)) illustrate therandom distribution of the fibers in PF-H and PF-M samples
Figures 4 and 5 show that the real part is the resistanceassociated with energy losses and the imaginary part is thereactance associated with phase changes respectively In thiscase we can observe a better performance of PF-H and PF-Msamples than other materials studied Increasing the amountof fiber reduces the number of impedance values andmaterialstiffnessThe reduced impedance values increase the fractionof wave energy that can be transmitted through the sample
Furthermore sound absorption at lower frequencies(over 10ndash2 kHz) is desirable for automotive applicationsbecause of this frequency range according to noise from thewind engine running tires road and conversation therebymaking CHF-polyester composites a promising candidate forautomotive interior sound absorption
PF-G
Polyester
PF-E
PF-H
PF-M
PF-I
PF-K
1000 2000 3000 4000 5000 60000Frequency (Hz)
minus20
minus10
0
10
20
30
Imag
inar
y pa
rt o
f im
peda
nce r
atio
Figure 5 The imaginary part of the impedance ratio of samples
33 Mechanical Properties Theoretically there should be aninteraction between hydrophobic polyester and hydrophiliccellulose The disappearance of the noncellulose material onthe surface of the fiber enables surface interaction with thepolyester matrix The void fraction is mainly formed becausethe composites have not been consolidated (not sufficientlypressed to form a contiguous solid structure) in order tomanufacture composites
Figures 7 and 8 show that the increase in the fibervolume fraction leads to increase in the tensile strength valueand Youngrsquos modulus of the composite from 1881 plusmn 85to 2573 plusmn 319MPa The increase in mechanical strengthcan be attributed to the bond interface between the fibersand resin The mechanical properties of the PF-M sample(or composite sample with 20 resin and 80 CHF) aretherefore correspondingly higher than those of the othersamples
For PF-H sample there was a 1253 decrease in thetensile strength values with a strength value of 2040 plusmn11MPa The probability of the overlapping of multiple CHFin composite samples thereby causes the weaker transferenceof load between fiber and matrix occurring due to thepoor interfacial adhesion causing lowering in the mechanicalproperties However the value of the modulus of elasticityof the sample PF-H is higher than that of the material usedin this study contributing to the sound absorption of thesample
The tensile strength value of the PF-E sample is the lowercompared to other samples This is due to the fiber volumefraction less than the other samples The tensile strength ofthe fiber of 23743MPa is higher than the tensile strength ofthe resin
4 Conclusions
In this study a CHF-polyester sound absorber was proposedand the sound absorption capability of the material wassignificantly enhanced through the simple method Thepresence of a number of lumen structures in the fiber bundlefacilitates sound absorption at low frequencies in the range
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
4 Advances in Acoustics and Vibration
Table 2 Nonacoustical properties of samples
Sample Thickness (mm) Density (Kgsdotm3) Porosity120576
Air-flow resistivity R (Pasdotssdotmminus2) Tortuosity120590
PF-E 20 6405 06474 44980 1272PF-G 20 3834 07053 29353 1208PF-H 20 3041 07247 25424 1190PF-I 20 2441 07457 21576 1171PF-K 20 1980 07582 19568 1160PF-M 20 1583 07954 14435 1128
(a) (b)
Figure 2 SEM photomicrographs of corn husk fibers 5 NaOH treated (a) surface and (b) cross-sectional features
PF-M
PF-H PF-I
PF-K
Polyester
PF-E
PF-G
1000 2000 3000 4000 5000 60000Frequency (Hz)
00
02
04
06
08
10
Soun
d ab
sorp
tion
coeffi
cien
t
Figure 3 The sound absorption coefficients of composite samples
32 Acoustical Properties The normal sound absorptionproperties for all samples of CHF-polyester composites aregraphically illustrated in Figure 3 The zero value in the 119910-axis indicates perfect sound reflection and the value of oneimplies complete sound absorption These results show thatall composite samples demonstrated an increase in soundabsorption coefficient in the range of 1 kHzndash25 kHz This isbecause lumen inside the fiber bundle increases the amount
of fiber which results in high absorption coefficient Theadditional thermal energy is dissipated more rapidly due tothe increased frictional surface area The sound absorptioncoefficient of the PF-M sample is therefore correspondinglyhigher than those of the other samples The sound wavespropagate vibration energy through the air spaces in theindividual lumina inside the fiber A part of this sound energyis converted into heat in the lumina which is then absorbedby the surrounding walls The larger the air cavities andlumina inside the fiber the longer the wavelength of thesound that is absorbed somore dominant at low frequenciesSEM micrograph analysis (Figures 6(a) 6(c) 6(e) 6(g) 6(i)and 6(k)) illustrates that there are many lumens inside thefiber and continuous channels in the porous structure ofpolyester composites
At frequencies above 2 kHz the sound absorption capa-bility of PF-E PF-G PF-I and PF-K samples decreasesThe decrease caused by the interface of the fiberresin andorderly fiber arrangement that cause the higher value ofthe flow resistivity of the sample makes movements of thesound difficult to pass through the samples An absorptioncoefficient is close to zero when the fibers are arranged in aconventional pattern SEM micrographs (Figure 6) illustratethat there is a distinct interface between fibers and resin inall samples Interface surfaces between fibers and resin of PF-E PF-G PF-I and PF-K samples (Figures 6(b) 6(d) 6(h)
Advances in Acoustics and Vibration 5
PF-GPolyester
PF-E
PF-I
PF-K
PF-HPF-M
1000 2000 3000 4000 5000 60000Frequency (Hz)
05
101520253035404550
Real
par
t of i
mpe
danc
e rat
io
Figure 4 The real part of the impedance ratio of different samples
and 6(j) resp) are quite dense and contain orderly fiberbundles arrangement Interface strength not only influencescomposite mechanical property but also influences soundabsorption quality When sufficient amount of resin is usedthe interface area between the fibers and the resin is smoothand strong (Figures 6(a) and 6(b)) When the incidentsound waves are continuously transmitted onto a compositeinterface the sound waves will be reflected and refractedand the acoustic damping phenomena will consume a smallamount of energy reducing heat losses and thus obtaining alower absorption coefficient at high frequencies This wouldalso explain why the sound absorption of PF-E is lower thanthose of sample patterns of composites which are similar
Sample pure polyester resin (PE) had the absorption coef-ficient under 02 Althoughpolyestermay be a valuable optionin noise absorption applications these results discourage itsuse as a sound-absorbing material
Figure 3 also shows that the PF-H and PF-M samplesdemonstrated the ability to absorb sound at high frequenciesabove 4 kHz This is due to the random distribution of thefiber The random distribution of the fibers in the fibrousabsorbent materials allows the sound waves to hit the lumenof the fiber bundle and strengthen the sound absorptioneffect a high absorption coefficient can be obtained SEMmicrographs (Figures 6(e) 6(f) 6(k) and 6(l)) illustrate therandom distribution of the fibers in PF-H and PF-M samples
Figures 4 and 5 show that the real part is the resistanceassociated with energy losses and the imaginary part is thereactance associated with phase changes respectively In thiscase we can observe a better performance of PF-H and PF-Msamples than other materials studied Increasing the amountof fiber reduces the number of impedance values andmaterialstiffnessThe reduced impedance values increase the fractionof wave energy that can be transmitted through the sample
Furthermore sound absorption at lower frequencies(over 10ndash2 kHz) is desirable for automotive applicationsbecause of this frequency range according to noise from thewind engine running tires road and conversation therebymaking CHF-polyester composites a promising candidate forautomotive interior sound absorption
PF-G
Polyester
PF-E
PF-H
PF-M
PF-I
PF-K
1000 2000 3000 4000 5000 60000Frequency (Hz)
minus20
minus10
0
10
20
30
Imag
inar
y pa
rt o
f im
peda
nce r
atio
Figure 5 The imaginary part of the impedance ratio of samples
33 Mechanical Properties Theoretically there should be aninteraction between hydrophobic polyester and hydrophiliccellulose The disappearance of the noncellulose material onthe surface of the fiber enables surface interaction with thepolyester matrix The void fraction is mainly formed becausethe composites have not been consolidated (not sufficientlypressed to form a contiguous solid structure) in order tomanufacture composites
Figures 7 and 8 show that the increase in the fibervolume fraction leads to increase in the tensile strength valueand Youngrsquos modulus of the composite from 1881 plusmn 85to 2573 plusmn 319MPa The increase in mechanical strengthcan be attributed to the bond interface between the fibersand resin The mechanical properties of the PF-M sample(or composite sample with 20 resin and 80 CHF) aretherefore correspondingly higher than those of the othersamples
For PF-H sample there was a 1253 decrease in thetensile strength values with a strength value of 2040 plusmn11MPa The probability of the overlapping of multiple CHFin composite samples thereby causes the weaker transferenceof load between fiber and matrix occurring due to thepoor interfacial adhesion causing lowering in the mechanicalproperties However the value of the modulus of elasticityof the sample PF-H is higher than that of the material usedin this study contributing to the sound absorption of thesample
The tensile strength value of the PF-E sample is the lowercompared to other samples This is due to the fiber volumefraction less than the other samples The tensile strength ofthe fiber of 23743MPa is higher than the tensile strength ofthe resin
4 Conclusions
In this study a CHF-polyester sound absorber was proposedand the sound absorption capability of the material wassignificantly enhanced through the simple method Thepresence of a number of lumen structures in the fiber bundlefacilitates sound absorption at low frequencies in the range
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
Advances in Acoustics and Vibration 5
PF-GPolyester
PF-E
PF-I
PF-K
PF-HPF-M
1000 2000 3000 4000 5000 60000Frequency (Hz)
05
101520253035404550
Real
par
t of i
mpe
danc
e rat
io
Figure 4 The real part of the impedance ratio of different samples
and 6(j) resp) are quite dense and contain orderly fiberbundles arrangement Interface strength not only influencescomposite mechanical property but also influences soundabsorption quality When sufficient amount of resin is usedthe interface area between the fibers and the resin is smoothand strong (Figures 6(a) and 6(b)) When the incidentsound waves are continuously transmitted onto a compositeinterface the sound waves will be reflected and refractedand the acoustic damping phenomena will consume a smallamount of energy reducing heat losses and thus obtaining alower absorption coefficient at high frequencies This wouldalso explain why the sound absorption of PF-E is lower thanthose of sample patterns of composites which are similar
Sample pure polyester resin (PE) had the absorption coef-ficient under 02 Althoughpolyestermay be a valuable optionin noise absorption applications these results discourage itsuse as a sound-absorbing material
Figure 3 also shows that the PF-H and PF-M samplesdemonstrated the ability to absorb sound at high frequenciesabove 4 kHz This is due to the random distribution of thefiber The random distribution of the fibers in the fibrousabsorbent materials allows the sound waves to hit the lumenof the fiber bundle and strengthen the sound absorptioneffect a high absorption coefficient can be obtained SEMmicrographs (Figures 6(e) 6(f) 6(k) and 6(l)) illustrate therandom distribution of the fibers in PF-H and PF-M samples
Figures 4 and 5 show that the real part is the resistanceassociated with energy losses and the imaginary part is thereactance associated with phase changes respectively In thiscase we can observe a better performance of PF-H and PF-Msamples than other materials studied Increasing the amountof fiber reduces the number of impedance values andmaterialstiffnessThe reduced impedance values increase the fractionof wave energy that can be transmitted through the sample
Furthermore sound absorption at lower frequencies(over 10ndash2 kHz) is desirable for automotive applicationsbecause of this frequency range according to noise from thewind engine running tires road and conversation therebymaking CHF-polyester composites a promising candidate forautomotive interior sound absorption
PF-G
Polyester
PF-E
PF-H
PF-M
PF-I
PF-K
1000 2000 3000 4000 5000 60000Frequency (Hz)
minus20
minus10
0
10
20
30
Imag
inar
y pa
rt o
f im
peda
nce r
atio
Figure 5 The imaginary part of the impedance ratio of samples
33 Mechanical Properties Theoretically there should be aninteraction between hydrophobic polyester and hydrophiliccellulose The disappearance of the noncellulose material onthe surface of the fiber enables surface interaction with thepolyester matrix The void fraction is mainly formed becausethe composites have not been consolidated (not sufficientlypressed to form a contiguous solid structure) in order tomanufacture composites
Figures 7 and 8 show that the increase in the fibervolume fraction leads to increase in the tensile strength valueand Youngrsquos modulus of the composite from 1881 plusmn 85to 2573 plusmn 319MPa The increase in mechanical strengthcan be attributed to the bond interface between the fibersand resin The mechanical properties of the PF-M sample(or composite sample with 20 resin and 80 CHF) aretherefore correspondingly higher than those of the othersamples
For PF-H sample there was a 1253 decrease in thetensile strength values with a strength value of 2040 plusmn11MPa The probability of the overlapping of multiple CHFin composite samples thereby causes the weaker transferenceof load between fiber and matrix occurring due to thepoor interfacial adhesion causing lowering in the mechanicalproperties However the value of the modulus of elasticityof the sample PF-H is higher than that of the material usedin this study contributing to the sound absorption of thesample
The tensile strength value of the PF-E sample is the lowercompared to other samples This is due to the fiber volumefraction less than the other samples The tensile strength ofthe fiber of 23743MPa is higher than the tensile strength ofthe resin
4 Conclusions
In this study a CHF-polyester sound absorber was proposedand the sound absorption capability of the material wassignificantly enhanced through the simple method Thepresence of a number of lumen structures in the fiber bundlefacilitates sound absorption at low frequencies in the range
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
6 Advances in Acoustics and Vibration
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
(j) (k) (l)
Figure 6 Scanning electron microscope (SEM) images of surfaces of the samples and cross-sectional features of composite samples (a b)PF-E (c d) PF-G (e f) PF-H (g h) PF-I (i j) PF-K and (k l) PF-M
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
Advances in Acoustics and Vibration 7
PF-IPF-E PF-G PF-H PF-K PF-M000
500
1000
1500
2000
2500
3000
3500
Tens
ile st
reng
th (M
Pa)
Samples
1881
22952040
2368 2323 2573
Figure 7 Tensile strength of each sample
PF-IPF-E PF-G PF-H PF-K PF-MSamples
0
500
1000
1500
2000
2500
Mod
ulus
of E
lasti
city
(MPa
)
123149969
16957
1142913775 13299
Figure 8 Modulus of elasticity of each sample
of 1 kHzndash2 kHz The interface between the surface of thefiberresin and orderly arrangement of fibers within the resinof PF-E PF-G PF-I and PF-K samples caused a decrease inthe sound absorption properties at frequencies above 2 kHzHigh frequencies above 4 kHz (PF-H and P F-M samples) areobtained due to the random distribution of the fiber
Increased resin lowers friction between the fibers reduc-ing heat losses and subsequently its sound absorption coeffi-cient
All samples used in this study have the potential to beused as sound-absorbing materials These results indicatethat alternative high-performance sound-absorbing materi-als could be obtained using CHF which can solve environ-mental problems and reduce noise pollution
Competing Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid I Low-frequency rangerdquoThe Journal oftheAcoustical Society of America vol 28 no 2 pp 168ndash178 1956
[2] M A Biot ldquoTheory of propagation of elastic waves in a fluid-saturated porous solid II Higher frequency rangerdquoThe Journalof the Acoustical Society of America vol 28 no 2 pp 179ndash1911956
[3] M E Delany and E N Bazley ldquoAcoustical properties of fibrousabsorbentmaterialsrdquoApplied Acoustics vol 3 no 2 pp 105ndash1161969
[4] F-C Lee and W-H Chen ldquoAcoustic transmission analysis ofmulti-layer absorbersrdquo Journal of Sound and Vibration vol 248no 4 pp 621ndash634 2001
[5] K Attenborough ldquoAcoustical characteristics of rigid fibrousabsorbents and granularmaterialsrdquoThe Journal of the AcousticalSociety of America vol 73 no 3 pp 785ndash799 1983
[6] A Veerakumar and N Selvakumar ldquoA preliminary investiga-tion on kapokpolypropylene nonwoven composite for soundabsorptionrdquo Indian Journal of Fibre and Textile Research vol 37no 4 pp 385ndash388 2012
[7] M Jailani M Nor and R Zulkifli ldquoEffect of compression onthe acoustic absorption of coir fiberrdquoAmerica Journal of AppliedSciences vol 7 no 9 pp 1285ndash1290 2010
[8] R Zulkifli Zulkarnain and M J M Nor ldquoNoise control usingcoconut coir fiber sound absorber with porous layer backingand perforated panelrdquoAmerican Journal of Applied Sciences vol7 no 2 pp 260ndash264 2010
[9] D Chen J Li and J Ren ldquoStudy on sound absorption propertyof ramie fiber reinforced poly(L-lactic acid) composites mor-phology and propertiesrdquoComposites Part A Applied Science andManufacturing vol 41 no 8 pp 1012ndash1018 2010
[10] A Putra Y Abdullah H Efendy W M F W Mohamad andN L Salleh ldquoBiomass from paddy waste fibers as sustainableacoustic materialrdquo Advances in Acoustics and Vibration vol2013 Article ID 605932 7 pages 2013
[11] L P Bastos G D S V De Melo and N S Soeiro ldquoPanelsmanufactured from vegetable fibers an alternative approachfor controlling noises in indoor environmentsrdquo Advances inAcoustics and Vibration vol 2012 Article ID 698737 9 pages2012
[12] T Koizumi N Tsujiuchi and A Adachi ldquoThe development ofsound absorbing materials using natural bamboo fibersrdquo HighPerformance Structures and Materials vol 4 pp 157ndash166 2002
[13] E Jayamani and SHamdan ldquoSound absorption coefficients nat-ural fibre reinforced compositesrdquo Advanced Materials Researchvol 701 pp 53ndash58 2013
[14] M Vasina D C Hughes K V Horoshenkov and L LapcıkJr ldquoThe acoustical properties of consolidated expanded claygranulatesrdquo Applied Acoustics vol 67 no 8 pp 787ndash796 2006
[15] F P Mechel Formulas of Acoustics Springer Berlin Germany2nd edition 2008
[16] R Maderuelo-Sanz A V Nadal-Gisbert J E Crespo-Amorosand F Parres-Garcıa ldquoA novel sound absorber with recycledfibers coming from end of life tires (ELTs)rdquo Applied Acousticsvol 73 no 4 pp 402ndash408 2012
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpswwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of