[ieee 2011 ieee 17th international symposium for design and technology in electronic packaging...

2011 IEEE 17th

International Symposium for Design and Technology in Electronic Packaging (SIITME)

978-1-4577-1277-7/11/$26.00 ©2011 IEEE 133 20-23 Oct 2011, Timisoara, Romania

On Pinnae Design and Fabrication Technology

Silviu Epure and Dorel Aiordachioaie

Electronics and Telecommunication Department

“Dunarea de Jos” University

Galati, Romania

Abstract— The paper presents a design and fabrication

technology of the pinnae, i.e. external ear in the context of

biomimetic sonar heads building for in air sonar applications.

The basic steps and formula of the design process are described

followed by a description of the fabrication technology for

various sizes and shapes of pinnae. The experimental

measurements are focused on voltage sensibility and pattern

directivity in horizontal and vertical planes. The results show a

voltage gain of parabolic pinnae and a narrow beam in pattern

directivity of the ultrasonic bio-mimetic transducers, which

makes them suitable for using in image generation applications.

The work is important because uses a simple technology to make

almost any kind of artificial bio-mimetic shapes of pinnae.

Keywords-pinnae; directivity design; technology; bio-mimetism;

signal processing; sonar; ultrasonic transducers.

I. INTRODUCTION

Many biological studies show the importance of the pinnae in environment living and exploration of animals. The most relevant example is the case of bats. The external shape of the ear has a lot of non-uniformities and the surface is slightly mobile and flexible. Such set of features provides a sensibility of hearing and the possibility to precisely localize various targets on the hunting field.

Sonar based navigation of autonomous vehicles tries to mimic the behavior of such animals, and the first think is to implement the shape of the external ear of bat into robotic sonar. The idea is not new. As example, [3] and [8] made simulation and experiments regarding the shape of external ear. Simulation based studies show that the best shape of artificial made pinnae is the paraboloid, in fact a portion of the paraboloid. May be the best example of such intensive work to mimic and to understand the functions and the limits of the external ear, some time called pinnae, was under CIRCE research project, [7]. The paper is part of the adbiosonar research project, [1], with the main goal to design sonar heads under biomimetic and adaptive behavior constraints. The paper describes the results of the design, built and measurements processes of external ears, which are called pinnae.

The basic necessary knowledge in designing the artificial pinnae is coming from elementary geometry and it is presented in section II for completeness. Section III describes the proposed technology to build artificial pinnae. Section IV presents and discusses the results of experimental measurements, mainly for directivity purposes.

II. BASIC KNOWLEDGE TO DESIGN PINNAE

The position of the focus of a parabolic dish antenna (or parabolic reflector) is found in terms of the diameter of the dish and its depth. We first write the equation of the parabola so that the focal distance (distance from vertex to focus) appears in the equation. Fig. 1 below shows a parabola, its focus F at ),0( f

and its directrix at ky . Using the definition of the parabola,

i.e. any point M(x,y) on the parabola is equidistant from the focus and the directrix, we may write the equation:

222 )(),( fyxFMDist

and

22 )(),( kydirectrixMDist

Figure 1. Schematic for parabola equation

Figure 2. Computation of the focus point

The focus coordinate f and the coordinate of directrix k are related by a link imposing the condition:

The work was supported by the CNMP research grant no 12079 / 2008 – Adaptive bio-mimetic sonar heads for autonomous vehicle - ADBIOSONAR

under PNCDI-II. Available at , http://www.adbiosonar.ugal.ro

2011 IEEE 17th



kfkfyx 020

For the 3D space, under the system xOyz, with Oz as symmetry axis, we have a surface based on equation

fyxfkkfyxz 22 222222

as it is represented in figure (3.a) and (3.b).

(a) (b)

Figure 3. Partial representation of the 3D paraboloid with f=d/2

Note: Fig. 2 presents a parabola with three parameters: D- diameter of the dish; d – depth of the dish; f – coordinate of the focus. If we want to compute the coordinate of focus f by imposing a geometric shape of the reflector (i.e. d and D), then

d

D

d

D

y

xf

164

4/

4

222

The above formula helps in positioning the feed of the parabolic antennas as it gives the focal distance f. Of course, in practice, the shape of the dish is not a perfect parabola and therefore small adjustments are needed when positioning the feed.

By imposing a focus point at the middle of the depth, and on Oy axis, a dependency equation is obtained as

ddD 8284.28

which is graphically represented in Fig. 4, right side. As design example, let us consider 0.1dH cm, so the focus is at half

distance 0.50 cm. Then, 82.282.2 dHDH cm and

82.282.2 dVDV cm -> 41.12/ DV cm. The technical

sheet of the pinna is presented in Fig. 5.

Figure 4. Computation of the focus position knowing the width (D) and

depth (d) of the dish

Figure 5. Technical sheet of the ear

III. TECHNOLOGY TO BUILD PINNAE

Pinnae are to be build from low temperature heat moldable sheet of plastic material (high density polyethylene, polypropylene etc.).

In a temperature controlled oven, the plastic sheet is placed between two plaster molds, as in Fig.6; temperature is then slowly risen until molds fit together. The oven is then cooled to room temperature and the pinnae are cut out. The temperature profile is strongly dependent on the type of plastic material used, but it is influenced too by the mass of the molds and humidity. In our case it was determined by trial and error that risen the temperature from 25 to 110°C in 30 minutes offers the best results.

The two plaster molds represents each face of the paraboloid to be obtained, so these parts needs to me manufactured as closely possible to the mathematic equation of the desired surface. Fig. 6 shows these two surfaces of the pinnae, internal and external, respectively.

Figure 6. Details of fabrication process: (a); (b); (c)

A milling machine, controlled by computer was used to manufacture these molds. The necessary files for milling path are in g-code language and are generated from Matlab. The line structure of the file is as

G01 X x_value Y y_value Z z_value

Depending on the resolution of the surface the file could have up to 150.000–160.000 lines.

pas_x = 0.1;%required for quantization

pas_y = 0.1;

2011 IEEE 17th



pas_z = 0.1;

...

fid = fopen('ear_int.txt','wt');

xxmd = zeros(length(xv), length(yv));

for j = 1:length(xv),

for i = 1:length(yv),

xxmd(i,j) = xxm(i,j);

fprintf(fid,'G01 X %4.2f Y %4.2f Z

%4.2f \n', i*pas_x, j*pas_y, xxmd(i,j))

end;

end;

fclose(fid);

Quantization step for the surface is chosen as a compromise among smoothness of the molds, size of the milling bit, size of the output files and milling duration.

Syntax of the g-code resulted file is:

G21 (measurements unit -mm)

G90 (absolute coordinate positioning)

M03 (start spindle)

G01 X 0.50 Y 0.50 Z 0.00

...

G01 X 28.00 Y 16.00 Z -2.35

G01 X 28.00 Y 16.50 Z -2.78

G01 X 28.00 Y 17.00 Z -3.15

....

G01 X 40.50 Y 40.50 Z 0.00

M05 (stop spindle)

M02 (end of program)

where G01 control the machine to go to the following coordinates in straight line, starting from the actual position.

Using the molds in Fig. 6, two pinnae are simultaneously obtained. Some examples of such pinnae are presented in Fig.7: a) the smallest pinnae tested (D = 2 cm), b) intermediate size, c) big size (D = 8 cm). A quick qualitative test to check for proper shape is to place a light source in front of the pinnae and observe where the light is focused, Fig. 7.

Figure 7. Quick test for focal point

As seen in Fig. 8, each ear of the sonar head consist in the pinnae, the transducer and the extruded polystyrene base support. This material was chosen because of its property to

absorb high frequency sounds, so no significant reflections of the input beam will occur from the base of the pinnae.

Figure 8. Physical shapes used in biomimetic sonar heads

Given the fact that the transducer used in our experiments is in fact the active element from commercial 40 kHz transducers (8 mm diameter piezo), it is expected that smaller dimensions of the pinnae to lead to wider directivity chart. This effect is due to the transducer receiving the ultrasounds even if there is no perfect focalization.

Further measurements are necessary to study the directivity chart of the pinnae, both in horizontal and vertical planes, as it is described in the next section.

IV. RESULTS OF EXPERIMENTAL MEASUREMENTS

A. Experimental setup

The ears constructed as previous presented have been analyzed both for gain and directivity. Measurement have been made on a 4D positioning system, where the emitter can be position in XYZ axes and the receiver can be horizontally rotated. The voltage from the receiver transducer was amplified (five times), rectified, filtered and then transferred to the computer via an ADC circuit. Amplifier’s and precision rectifier’s schematics are classical and will not be presented here. Analog to digital conversion and communication with the PC are implemented in a microcontroller. The numerical values of the amplitude are available in Matlab for further processing. Three distinct situations were analyzed: transducer with no pinnae, small pinnae and big pinnae.

B. Voltage Sensibility Measurements

Emitter was placed at a distance of 50cm from the receiver and driven with continuous sinusoidal signal, 41 kHz, 10Vpp. In the case of receiver without pinnae, the electrical signal at the transducer was 100 mVpp. Using the small pinnae to concentrate the ultrasounds, signal’s amplitude raised to 170 mVpp; using the big pinnae, the amplitude reached 320 mVpp. Comparing with the situation of transducer without pinnae, we approximate 1.7 the gain of the small pinnae and 3.2 the gain of the big pinnae.

2011 IEEE 17th



C. Directivity characteristics

We obtained the transducers by cutting out the housing of a commercial 40 kHz transducer (MA40S5), [9], as in Fig.9 . So it was interesting to compare the characteristics of original, modified, and final receiver.

Figure 9. Original Murata transducer and the modified one.

The Fig. 10 presents the directivity charts, in horizontal plane for: a) original transducer with no pinnae; b) transducer without housing and with no pinnae; c) transducer with small pinnae and d) transducer with big pinnae.

Figure 10. Directivity charts, horizontal plane, various configurations

Figure 11. Directivity charts, vertical plane, various ears

It can be clearly observed that the bigger the ratio between size of the paraboloid and size of the transducer, the better directivity characteristic is obtained.

Given the fact that the resulting ear is not symmetrical in vertical plane (we only use one half of the paraboloid), it is expected that directivity chart in vertical plane to be asymmetrical as well. Fig. 11 presents these characteristics: a) ear without parabolic surface (transducer is sensible to sounds that touch vertically the ear), b) ear with small pinnae – two cases, c) ear with big pinnae – two cases. It can be observed that in the latest case, a secondary lobe is present at about 15 degree from horizontal plane.

V. CONCLUSIONS

A pinnae making process is presented, both from theoretical and practical point of views. Using mathematical tools (Matlab) the surface of the pinnae is designed. This surface is then digitized with a resolution good enough for milling the molds. Thermo-molding of a plastic sheet will lead to pinnae with desired 3D shape. This process was exemplified on a paraboloid shape for the pinnae, but can be applied for any surface. The ears that use the pinnae have been analyzed from the gain perspective, as well as the directivity in horizontal and vertical plane. The experimental measurements regarding the sensibility and directivity correspond with the theoretical computed values. Starting from a commercial ultrasonic transducer with a measured directivity lobe of about 80° (70° according to MA40S5 product page), a pinnae with 20° lobe was obtained. The ear based on these pinnae will allow higher angular resolution and higher sensitivity than a standard transducer, and it will be used in ultrasonic image generation processes.

REFERENCES

[1] Adbiosonar, Adaptive and biomimetic sonar heads for autonomous vehicles, CNMP research grant 12079/2008, http://www. adbiosonar.ugal.ro

[2] Honsberger, R. “Mathematical Gems III.“, Washington, DC: Math. Assoc. Amer., pp. 189-191, 1985

[3] Carmena, J. M., Kampchen, N., Kim, D., & Hallam, J. C. T., Artificial ears for a biomimetic sonar head: From multiple reflectors to surfaces. Artificial Life, 7(2), 147-169, 2001.

[4] Kampchen, N., Evolving pinna-like surfaces for a biomimetic sonar head, MSc in Artificial Intelligence Division of Informatics University of Edinburgh, UK, 2000.

[5] Herbert Peremans and Jonas Reijniers, The CIRCE Head: A Biomimetic Sonar System, W. Duch et al. (Eds.): ICANN 2005, LNCS 3696, Springer-Verlag Berlin Heidelberg, pp. 283–288, 2005.

[6] Martin K. Obrist M.K., Fenton M.B., Eger J. L. and Schlegel P.A., What Ears Do For Bats: A Comparative Study of Pinna Sound Pressure Transformation In Chiroptera, J. Exp. Biol. 180, 119-152, 1993.

[7] Herbert Peremans, The CIRCE (Chiroptera Inspired Robotic CEphaloid) project is a collaborative EU-project within the Proactive Initiative 2001 in Bionics entitled LIFE-LIKE PERCEPTION SYSTEMS (LPS). Available at http://www.ua.ac.be/main.aspx?c=.APL&n=40656, 2010.

[8] Carmena J.M., Kim D., and Hallam J.C.T., Designing artificial ears for animat echolocation. From Animals to Animats,vol 6. pp.73-80, J-A. Meyer et al. (Eds.), MIT Press, 2000.

[9] MA40S5 product page, http://search.murata.co.jp/Ceramy/Catalog Action.do?sHinnm=MA40S5&sNHinnm=MA40S5&sNhin_key=MA40S5&sLang=en&sParam=MA40S5

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