S-MRUT: Sectored-Multi Ring Ultrasonic Transducer for selective powering of brain implants

One of the main challenges of the current ultrasonic transducers for powering brain implants is the complexity of focusing ultrasonic waves in various axial and lateral directions. The available transducers usually use electrically controlled phased array for beamforming the ultrasonic waves, which increases the complexity of the system even further. In this paper, we propose a straightforward solution for selective powering of brain implants to remove the complexity of conventional phased arrays. Our approach features a Sectored-Multi Ring Ultrasonic Transducer (S-MRUT) on a single piezoelectric sheet, specifically designed for powering implantable devices for optogenetics in freely moving animals. The proposed uni-directional S-MRUT is capable of focusing the ultrasonic waves on brain implants located at different depths and regions of the brain. The S-MRUT is designed based on Fresnel Zone Plate (FZP) theory, simulated in COMSOL, and fabricated with microfabrication process. The acoustic profile of the seven different configurations of the SMRUT were measured using a hydrophone with the total number of 7436 grid points. The measurements show the ability of the proposed S-MRUT to sweep the focus point of the acoustic waves in the axial direction in depths of 1 – 3mm, which is suitable for powering implants in the striatum of the mouse. Furthermore, the proposed S-MRUT demonstrates a steering area with the average radius of 0:862mm, and 0:678mm in experiments, and simulations, respectively. The S-MRUT is designed with the size of 3.8 × 3.8 × 0.5mm3 and the weight of 0:054gr, showing that it is compact and light enough to be worn by a mouse. Finally, the S-MRUT was tested in our measurement setup, where it successfully transfers sufficient power to a 2:8mm3 optogentic stimulator to turn on a microLED on the stimulator

Ultrasonic augers for improved transport of granular materials

This paper explores the superposition of ultrasonic vibration on vertical rotating augers in a variety of granular media. Ultrasonic vibration is known to facilitate direct penetration of granular media, and it is anticipated that any related reduction in the torque requirements of a rotating system might improve augering performance. Experimental results suggest that, compared to the non-ultrasonic scenario, ultrasonically assisted augering significantly promotes the flow of granular media, while moderately reducing the torque required to operate the device. Furthermore, it was discovered that particle size, helix angle, and auger speed all affect the performance of the auger in different ways as the ultrasonic amplitude is adjusted

Experimental and finite element modelling of ultrasonic cutting of food

In recent years ultrasonic cutting has become an established technology in a variety of industries including the food processing industry to cut a variety of materials. An ultrasonic cutting system consists of a generator, transducer and either a single or multiple blade cutting devices tuned to a specific mode of vibration, commonly the longitudinal mode, between 20 and 100 kHz. High power ultrasonic cutting device design has traditionally relied on the cut requirements of the product, the use of empirical approaches where ultrasonic cutting system parameters such as cutting speed, frequency of vibration, mode of vibration, blade tip amplitude, gain and cutting orientation are determined from experimental and experience of the tool designers. Finite element (FE) models have also been used to predict the vibrational behaviour of the cutting tool. However, the performance of an ultrasonic device critically relies on the interaction of the cutting tool and material to be cut. Currently the interaction between the resonant blade and the material to be cut is neglected but the cutting mechanism at the interface is of significant importance and knowledge of this mechanism would be of considerable benefit to designers when developing ultrasonic cutting blade concepts and processing requirements. Simulations of the cutting process would also enable designers to conduct parametric studies quickly using computational methods instead of conducting lengthy, laborious experimental tests. The research reported in this thesis provides an insight into the requirements of the tool-material interaction to allow optimal cutting parameters to be estimated as an integral part of designing cutting blades for use in the food industry. A methodology is proposed for modelling the interaction between the resonant blade and the material to be cut using the finite element method, to gain an understanding of the cutting mechanism. The effect of ultrasonic cutting parameters, such as resonant frequency, mode of vibration, blade tip sharpness, cutting force, cutting speed, blade tip amplitude and are also investigated. Knowledge of the temperature distribution at the interface between the resonant blade and the substrate material would also be of benefit as currently experimental determination of the temperature at the interface is impractical using current measuring systems. Two thermo-mechanical FE models of ultrasonic cutting are developed which simulate the cutting tool and material interaction to allow cutting parameters to be derived numerically to enhance cutting blade design. The FE models incorporate experimentally derived mechanical and thermal properties of the common engineering thermoset Perspex and also of the following food materials; toffee, cheese, chocolate and jelly. The combined thermo-stress FE model allows the temperature at the cut interface to be determined under various loading conditions and provides a method for investigating the effects of blade design on temperature at the blade-material interface. Estimations of accurate mechanical and thermal properties of foodstuffs for inclusion in the FE models are determined experimentally using materials testing techniques such as tension and compression tests. Ultrasonic cutting blades are designed using finite element analysis and experimental investigations are performed on an ultrasonic cutting rig to validate the FE models. Two different generic 2D modelling approaches to simulate ultrasonic cutting are presented. One uses the debond method in ABAQUS standard and the alternative uses the element erosion method in ABAQUS explicit. Progression of the element erosion method into a 3D model is also presented with the intension of improving the accuracy of the modelling technique and to offer the flexibility to model complex geometries or cutting orientations. The models are presented and validated experimentally against a common engineering material, Perspex, and parametric studies are presented and discussed for the food materials; toffee, cheese, chocolate and jelly. For accurate modelling of any process, accurate material data is required and for common engineering materials such as Perspex accurate data is readily available in the literature. For food products however, the mechanical and thermal properties are not readily available and are often batch dependent. Methodologies for testing and determining the mechanical and thermal properties of two selected food materials, toffee and cheese, are also presented and the results from these experimental tests are incorporated in the finite element models to simulate the food materials during ultrasonic cutting. Models of ultrasonic cutting are for both single layer materials and also for multi layer material architectures

Investigating the effect of ultrasonic consolidation on shape memory alloy fibres

This research was driven by the capability of the Ultrasonic Consolidation (UC) manufacturing process to create smart metal matrix composites for use within high value engineering sectors, such as aerospace. The UC process is a hybrid additive/subtractive manufacturing process that embeds fibres into metal matrices via the exploitation of a high plastic flow, low temperature phenomenon encountered at ultrasonic frequency mechanical vibrations. The research concerned an investigation of the use of the UC process for embedding Nickel-Titanium alloy (NiTi) shape memory alloy (SMA) fibres into Aluminium (Al) matrices which could potentially be used as vibration damping structures, stress state variable structures, as well as other future smart material applications. It was hypothesised that the fibre volume fraction within a UC matrix was limited due to a reduction in foil/foil bonding, caused by increased fibre numbers, as opposed to the total level of plastic flow of the matrix material being insufficient to accommodate the increased fibre numbers. This hypothesis was tested by increasing the NiTi SMA fibre volume fraction, within an Al 3003 (T0) metal matrix, beyond that of previous UC work. The metal matrix and the fibre matrix interface of these samples was then microscopically analysed and the overall UC sample integrity was tested via mechanical peel testing. It was found that a fibre volume fraction of ~9.8% volume (30 X Ø100 µm SMA fibres) was the maximum achievable using an Al 3003 (T0) 100 µm thick foil material and conventional UC fibre embedding. A revised hypothesis was postulated that the interlaminar structure created during UC was affected by the process parameters used. This interlaminar structure contained areas of un-bonded foil and the increase of UC process parameters would reduce this area of un-bonded foil. Areas of this interlaminar structure were also thought to have undergone grain refinement which would have created harder material areas within the structure. It was suggested that maximum plastic flow of the matrix had not been reached and thus the use of larger diameter NiTi SMA fibres were embedded to increase the effective SMA fibre volume fraction within Al 3003 (T0) UC samples. It was suggested that the embedding of SMA fibres via UC had an abrasive effect on the SMA fibres and the SMA fibres had an effect on the Al 3003 (T0) microstructure. It was further suggested that the activation of UC embedded SMA fibres would reduce the strength of the fibre/matrix interface and the matrix would impede the ability of the SMA fibres to contract causing a forceful interaction at the fibre to matrix interface, weakening the UC structure. The investigation to test the revised hypothesis was broken down into three sections of study. Study 1 was a methodology to determine the characteristics of the interlaminar surface created via UC and how this surface affected the nature of the consolidated sample. UC samples of Al 3003 (T0) were manufactured using a range of process parameters. The analysis involved optical microscopy to determine the UC weld density and the interlaminar surface; mechanical peel testing to quantify the interlaminar bond strength; white light interferometry to measure the interlaminar surface profile and microhardness measurements to determine the hardness of the interlaminar material. Study 2 was a methodology to allow the analysis of the microstructural and mechanical interactions at the fibre/matrix interface, post-UC. Al 3003 (T0) samples were manufactured via UC using a range of process parameters with various NiTi SMA fibre diameters embedded. The analysis involved using mechanical peel testing to determine the interlaminar bond strength; optical microscopy to determine the level of fibre encapsulation; scanning electron microscopy and focussed ion beam analysis to analyse the fibre and matrix grain structures and microscopic interactions. Study 3 was a methodology to investigate the fibre usage as would be expected from envisaged applications of an SMA containing metal matrix composite. Samples were manufactured using a range of UC process parameters with various SMA fibre diameters embedded and the embedded SMA fibres were subjected to different extension/contraction cycle numbers. The analysis involved using mechanical peel testing to determine the interlaminar bond strength; optical microscopy to determine the level of fibre encapsulation and the interlaminar effect of fibre activation; fibre pullout testing to measurement the strength of the fibre/matrix interaction and load rate testing of the activated SMA fibres to monitor performance. The interlaminar surface was found to affect the strength and density of interlaminar bonding during the UC process and the use of higher UC process parameters affected this interlaminar structure. Levels of un-bonded material were found within the interlaminar structure and these levels were found to decrease with increasing sonotrode amplitude and pressure with reducing speed. It was suggested that a specifically texture sonotrode could be developed to modify the interlaminar structure to the requirements of the intended sample application. The measurement of the interlaminar material hardness was unsuccessful and future work would likely require a different methodology to measuring this. The work identified a grain refining effect of the embedded SMA fibres on the Al 3003 (T0) matrix material, (grain sizes were reduced from ~15 µm to <1 µm within 20 µm of the SMA fibres), as well as localised damage caused by the UC process to the SMA fibres. The performance of the activated SMA fibres established that this damage did not prohibit the ability of the SMAs to function however the compressive nature of the Al 3003 (T0) matrix was identified as reducing the ability of the SMA fibres to contract. Additionally it was found that the activation of SMA fibres within an Al 3003 (T0) matrix resulted in a reduction of the fibre/matrix interface strength which allowed fibres to be pulled from the composite with greater ease (a loss of ~80% was encountered after a single activation and extension cycle). The use of larger SMA fibre diameters allowed for the fibre volume fraction to be increased however the activation of these SMA fibres had a delaminating effect on the Al 3003 (T0) structure due to the size of the radial expansion of the SMA fibre. The work furthered the understanding of the effect of UC on SMA fibres and highlighted the importance of the interlaminar surface in UC and that to increase the SMA fibre volume fraction to a useable level (25-50%) then an alternative fibre embedding method within UC is required. The fibre/matrix interface interactions during SMA activation have implications in the ability of UC SMA embedded smart metal matrix composites to function successfully due to weakening effects on fibre matrix interface strength and the ability to achieve SMA fibre activation within the metal matrix

Microfabricated liquid density sensors using polyimide-guided surface acoustic waves

The simultaneous measurements of liquid density and refractive index on the same liquid sample are desirable. This thesis investigates the development of a micro- fabricated liquid density sensor that can be integrated into existing refractometers. A discussion of density sensing techniques and review of suitable sensors is given, leading to the choice of a Love mode surface acoustic wave (SAW) device. Love modes are formed by focussing the acoustic energy in a thin waveguide layer on a surface acoustic wave device. The horizontal-shear wave motion reduces attenuation in liquid environments, and the high surface energy density theoretically gives the highest sensitivity of all SAW devices. This study follows the development of a Love mode liquid density sensor using a polyimide waveguide layer. The novel use of polyimide offers simple and cheap fabrication, and theoretically gives a very high sensitivity to surface loading due to its low acoustic velocity. Love mode devices were fabricated with different polyimide waveguide thicknesses. The optimum thickness for a compromise between low loss and high sensitivity was 0.90 - 1.0 μm. These devices exhibited a linear shift in frequency with the liquid density-viscosity product for low viscosities. The response was smaller for high viscosities due to non-Newtonian liquid behaviour. Dual delay-line structures with a smooth 'reference' and corrugated 'sense' delay- lines were used to trap the liquid and separate the density from the density-viscosity product. A sensitivity up to 0.13 μgcm(^-3)Hz(^-1) was obtained. This is the highest density sensitivity obtained from an acoustic mode sensor. Experimental results show a zero temperature coefficient of frequency is possible using polyimide waveguides. These are the first Love mode devices that demonstrate temperature independence, highlighting the importance of polyimide as a new waveguide material

Development of High-speed Photoacoustic Imaging technology and Its Applications in Biomedical Research

Photoacoustic (PA) tomography (PAT) is a novel imaging modality that combines the fine lateral resolution from optical imaging and the deep penetration from ultrasonic imaging, and provides rich optical-absorption–based images. PAT has been widely used in extracting structural and functional information from both ex vivo tissue samples to in vivo animals and humans with different length scales by imaging various endogenous and exogenous contrasts at the ultraviolet to infrared spectrum. For example, hemoglobin in red blood cells is of particular interest in PAT since it is one of the dominant absorbers in tissue at the visible wavelength.The main focus of this dissertation is to develop high-speed PA microscopy (PAM) technologies. Novel optical scanning, ultrasonic detection, and laser source techniques are introduced in this dissertation to advance the performance of PAM systems. These upgrades open up new avenues for PAM to be applicable to address important biomedical challenges and enable fundamental physiological studies.First, we investigated the feasibility of applying high-speed PAM to the detection and imaging of circulating tumor cells (CTCs) in melanoma models, which can provide valuable information about a tumor’s metastasis potentials. We probed the melanoma CTCs at the near-infrared wavelength of 1064 nm, where the melanosomes absorb more strongly than hemoglobin. Our high-speed PA flow cytography system successfully imaged melanoma CTCs in travelling trunk vessels. We also developed a concurrent laser therapy device, hardware-triggered by the CTC signal, to photothermally lyse the CTC on the spot in an effort to inhibit metastasis.Next, we addressed the detection sensitivity issue in the previous study. We employed the stimulated Raman scattering (SRS) effect to construct a high-repetition-rate Raman laser at 658 nm, where the contrast between a melanoma CTC and the blood background is near the highest. Our upgraded PA flow cytography successfully captured sequential images of CTCs in mouse melanoma xenograft model, with a significantly improved contrast-to-noise ratio compared to our previous results. This technology is readily translatable to the clinics to extract the information of a tumor’s metastasis risks.We extended the Raman laser technology to the field of brain functional studies. We developed a MEMS (micro-electromechanical systems) scanner for fast optical scanning, and incorporated it to a dual-wavelength functional PAM (fPAM) for high-speed imaging of cerebral hemodynamics in mouse. This fPAM system successfully imaged transient changes in blood oxygenation at cerebral micro-vessels in response to brief somatic stimulations. This fPAM technology is a powerful tool for neurological studies.Finally, we explored some approaches of reducing the size the PAM imaging head in an effort to translate our work to the field of wearable biometric monitors. To miniaturize the ultrasonic detection device, we fabricated a thin-film optically transparent piezoelectric detector for detecting PA waves. This technology could enable longitudinal studies on free-moving animals through a wearable version of PAM