DEPARTMENT OF MECHANICAL ENGINEERING

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Llewellyn-Jones PhD Annual Review August 28, 2014

Figure 22: Optical Microscopy (Zeiss Axio Imager M2, 5⇥ objective) image of CNW’s with 2MHz standing wavefield applied, Colour Online

The spectra need correction for varying levels of noise (resulting from fluorescence) before the degreeof alignment of the fibres can be determined. A baseline correction for the spectra was performed. It wasthen assumed that the intensity of the peak at 2900cm�1 was invariant, which is a reasonable assumptionif the region of the sample analysed does not vary Wiley and Atalla [1987]. Having scaled the spectraaccordingly to normalise against this peak, the variation in the intensity of the peak at 1095cm�1 couldbe determined. The corrected and normalised spectra for each sample are shown in Figure 23. The peaksvisible in sample 1 at around 3100cm�1 are the result of high energy cosmic rays incident on the CCDarray.

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Figure 23: Corrected, normalised raman spectra of the two dried samples of aligned CNW’s. Colour Online

To clearly visualise the variation of the intensity of the peak with angle, a polar plot is used, with theangle between the light polarisation and the axis of the acoustic traps represented by ✓ and the intensityof the peak for that spectra represented by r. The results are shown in Figure 24. As the distance ofeach point from the origin represents the ratio between the intensity of two Raman shift peaks, the valueis dimensionless, and only the relative value of di↵erent points at di↵erent angles can be used. This givesa qualitative idea of the degree of alignment of the nanowhiskers in the sample, with a perfectly circularplot showing entirely random orientation of the local particles and a thin flat line representing perfect

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Trapping through ultrasonic/magnetic field

IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. , NO. , MARCH 2015 1

Counter-propagating wave acoustic particlemanipulation device for the effective manufacture of

composite materials.Marc-S. Scholz, Bruce W. Drinkwater, Thomas M. Llewellyn-Jones, and Richard S. Trask

Abstract—An ultrasonic particle manipulation device exhibit-

ing broad frequency band behaviour is explored experimentally

and characterised by two-dimensional finite element analysis

in terms of its acoustic properties. The device was used to

manipulate a variety of particles differing in size, shape, and

material composition inside a number of host fluids, whilst

monitoring the assembly path by high speed imaging. In water,

assembly times for isolated microscopic particles were recorded

to be of the order of several 100ms. Good agreement was found

with the theoretical assembly time of a 10 µm polystyrene

sphere, which was calculated from pressure and acoustic force

predictions made by finite element analysis. An evaluation of the

two-dimensional pressure map indicated the pressure distribution

to vary across the depth of the device with the maximum pressure

occurring near the substrate.

Index Terms—Acoustic radiation pressure, Acoustophoretic

force, Metamaterials, Particle manipulation, Ultrasonic assembly.

I. INTRODUCTION

Across a diverse range of applications, acoustic particlemanipulation techniques have already been employed to trapmicron- to millimeter-size objects and to form ordered arraysof particles. One area of developing interest is the ultrasonicassembly of polymer composite materials [1], [2], [3], [4], [5],[6], [7] and metamaterials [8], [9], [10].

Although acoustic manipulation has previously been demon-strated for both spherical and fibrous particles in polymericmatrix media including acrylics, agar, epoxy, polyester, andpolysiloxane, the repeatable manufacture of such specimens inan effective manner is still proving a challenge. For example,the removal of ultrasonically assembled composite samplesfrom inside the device’s manipulation cavity is often achievedonly with great difficulty, due to chemical bonding of the poly-mer to its surroundings. Furthermore, particle manipulationdevices typically operate across a narrow band of frequencies,thus limiting the number of predetermined patterns that canbe formed by a single device [11], [12], [13].

In this article, we aim to address both of the above issuesand analyse the performance of a counter-propagating wavedevice that enables the fast and reliable fabrication of thinlayers of anisotropic structural composite.

Manuscript received Thursday 26th March, 2015; revised.The authors are with the University of Bristol, Queen’s Building, University

Walk, Bristol, BS8 1TR, United Kingdom.

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Figure 1: Two-element ultrasonic device. (a) A pair of opposed parallelPZT transducers generates an acoustic standing wave field inside the centralcavity. (b) cross-sectional representation of the device by material layers: air(1), PMMA (5mm), H2O (9.025mm), PZT (0.975mm), PMMA (5mm),resin (30mm), PMMA (5mm), PZT (0.975mm), H2O (9.025mm), PMMA(5mm), air (1). (c) photograph of the device. Adapted from Scholz et al.[6], [7].

II. ULTRASONIC DEVICE

The design forming the basis of investigation to this article,is shown in Figure 1 and was previously described in [6]. Twoopposed parallel 0.975mm ⇥ 15mm ⇥ 2mm lead zirconatetitanate (PZT) transducers (Noliac NCE51) were separatedfrom a central 30mm⇥15mm⇥2mm manipulation cavity bya 5mm thick poly(methyl methacrylate) (PMMA) boundary,which served to protect the acoustic system from the resin

Field control for instantaneous alignment

Multi-lengthscale materials alignment

Cellulose whiskers

1mm Nickel coated Carbon

fibres

Self-healing capsules

✚ ✚ ! (1) Biological inspiration

(2) Controlled alignment of complex architectures

(3) 3D printing of novel material architectures

(Outcome) Morphogenesis of

advanced materials

Collagen – staggered fibrous profile

Cephapods – muscular hydostatic

Fellowship Vision: New modes of composite assembly, i.e. manufacturing as a growth process.

Controlled stiffness for morphing based on origami

Cellulose architecture remodelling

Ionoprinting of hydrogels for architectural reversible growth

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C! D!

Multi-materials for printing

Biology-3D Printing-FEA-Testing

!

Dynamic-Z 3D printing

Professor Richard Trask EPSRC Fellow & Professor in Advanced Materials