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2008 IEEE International Ultrasonics Symposium (IUS)
Beijing International Convention Center (BICC)
Beijing, China, November 2-5, 2008 (View: Conf. Photos/Videos and 
Beijing Photos 
)
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Sponsored by the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society |
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Invited Talks (21 in Total)
Topics of Invited Talks (Please Click on the Links to Jump to the Talks):
Notes: To quickly find where the invited talks are scheduled in the conference technical program, please check the Condensed Program and the Floor Plan. You could also see more details of the technical program in the Full Program (Program Book), Abstract Book, and Meeting Planner. (Please use the labels such as "1I-3" to locate the corresponding sessions).
Group 1: Medical Ultrasonics:
Talk #1.1:
Title: Functional imaging of the heart
Jan D'hooge (Presenter), Piet Claus, Jens-Uwe Voigt, and Frank Rademakers, Department of Cardiovascular diseases, Catholic University of Leuven, Leuven, Belgium.
Abstract:
Background, Motivation and Objective:
The function of the heart is to eject blood into the aorta/pulmonary artery during systole (i.e. systolic function) and to refill with blood during diastole (i.e. diastolic function). The heart is able to do so by active contraction and relaxation of the heart muscle (i.e. the myocardium) resulting in changes in wall and cavity dimensions. This in turn results in cavity pressure changes accelerating the blood in or out of the ventricular cavity.
Ultrasound (US) imaging has been the modality of choice for the non-invasive assessment of cardiac function. Traditionally, Mor B-mode derived volume-changes are measured to assess systolic function while blood flow patterns measured using Doppler techniques are used as an index for diastolic function.
Technological developments in ultrasound imaging have resulted in new methodologies for the quantification of cardiac function.
Statement of Contribution/Methods:
US approaches for the quantification of cardiac function can be categorized into methods that assess properties of the myocardium and methods that asses characteristics of the blood flow.
In the former approaches, myocardial motion and deformation imaging has taken an important role. Although the original methods were based on Doppler imaging, later developments allowed to measure motion and deformation within the image plane (2D) and recently also in 3D (using volumetric US). These methods have enabled assessing ventricular twist/untwist characteristics ?the latter being an interesting parameter for diastolic function. The above measurements in combination with mechanical models of the heart allow estimating the force regionally developed by the cardiac muscle.
Besides of these mechanistic approaches, acoustic properties of the myocardium have also been studied to functionally characterize the heart. Integrated backscatter and its cyclic variation have shown to be of interest in a large number of studies.
3D US systems have allowed a better characterization of ventricular volume changes which has led to the introduction of several new functional parameters.
Color Doppler M-mode imaging of blood flow can be used to estimate intra-ventricular pressure gradients which in turn have been correlated to cardiac function. More recently, speckle tracking approaches have also been applied to characterize (2D) blood flow patterns within the ventricle. It might be an important new approach.
Results:
In this review lecture, the above described techniques will be presented from a technical point of view together with the experimental validation and/or clinical findings already available. Pros and contras of the approaches will be discussed.
Discussion and Conclusions:
Developments in cardiac US have driven new methodologies to more accurately quantify cardiac function. They provide us with tools to better understand cardiac (patho)-physiology and, as such, better diagnose and treat the individual patient.
Talk #1.2:
Title: Supersonic Shear Wave Elasticity Imaging
*Mathias Fink (Presenter), *Mickael Tanter, **Jeremy Bercoff, and **Jacques Souquet, *ESPCI, Laboratoire Ondes et Acoustique, Paris, France. **Supersonic Imagine, Aix en Provence, France.
Abstract:
Background, Motivation and Objective:
This lecture presents a review of the applications of Supersonic Shear Imaging (SSI)modality.
Statement of Contribution/Methods:
This technique is based on the combination of a dynamic radiation force induced in tissue by a set of ultrasonic beams and an ultrafast imaging sequence (5000 Images/s) capable of catching in real time the propagation of resulting shear waves. A shear source moving at a supersonic speed is remotely induced in tissues by the use of a special transmit beamforming sequence. It radiated quasi-plane shear waves propagating in a Mach cone. The local shear wave velocity is recovered using a time of fligth technique and enables the two dimensionnal (2D) maping of shear elasticity. This imaging modality is implemented on conventional probes driven by dedicated ultrafast echographic platforms. Consequently, it can be performed during a standard echographic exam.
Results:
The preliminary clinical results demonstrate the clinical feasibility of this new elastography technique in providing quantitative assesment of relative stiffness of breast tissues. Experimental results will emphasize the potential of this elastography technique for many others potential applications such as liver, cardiovascular, opthalmologic and muscular applications.
Discussion and Conclusions:
Beyond elasticity imaging, a complete in vivo assessment of tissue rheology can be performed using this approach. Dispersion effects affecting the propagation of visco-elastic waves in soft tissues are a key to understanding the rheological behavior of human tissues. New signal processing approaches based on the Supersoinic shear imaging modality were also developed and introduce a new concept of shear wave spectroscopy that could potentially become a great tool in tissue characterization and medical diagnosis.
Talk #1.3:
Title: Micro-ultrasound Takes Off (In the Biological Sciences)
F. Stuart Foster, Imaging Research, Sunnybrook Health Sciences Centre and University of Toronto, Toronto, Ontario, Canada.
Abstract:
Background, Motivation and Objective:
Disease models in the mouse have become a central part of modern biomedical research. The next major project following the sequencing of the mouse genome is the coordinated and systematic knocking out of each of the mouse’s ~ 30,000 genes and the discovery of the phenotypes associated with these mutations. In addition, subtle gene variations that predispose individuals to disease will be studied in ever increasing numbers. The National Institutes of Health in the United States and other international organizations are betting 100’s of millions of dollars that this will lead to critical discoveries needed along the path to better healthcare. Imaging will play a major role in this enterprise and ultrasound will take its rightful seat at the table. The successful development of high frequency mechanical sector imaging has led to an entirely new community of ultrasound users whose backgrounds are not necessarily in imaging or medicine. They are physiologists, cell and molecular biologists, developmental biologists, and animal scientists.
Statement of Contribution/Methods:
This talk will describe the path of instrument and applications development for high frequency “micro-ultrasound?for mice. Basic imaging, Doppler, and contrast imaging modes will be reviewed and the current state of the art in high frequency imaging of the mouse will be discussed.
Results:
Examples of functional imaging of inflammation, cardiovascular disease, and tumour microcirculation will be used to illustrate the potential and limitations of the current technology. Potential for molecular imaging will be explored in a melanoma xenograft model in which the expression pattern of VEGFR-2 is studied. In contrast imaging, performance improvements will require optimization of the microbubbles themselves, a better understanding of microbubble interactions at high frequencies in both the bound and unbound state, and improved capabilities for nonlinear excitation.
Discussion and Conclusions:
One of the barriers to development of micro-ultrasound imaging has always been the lack of high frequency arrays. This barrier is about to disappear. The latest results on the development of composite materials, high frequency linear arrays, and beamformers will be presented. These devices will dominate the next generation of micro-ultrasound imaging systems. Speculation on the future of micro-ultrasound technology and applications will be discussed.
Talk #1.4:
Title: Ultrasonic Imaging of 3-Dimensional Propagation of Electric Excitation and Vibrations in Human Heart
*Hiroshi Kanai (Presenter), **Junya Ohkohchi, and **Hideyuki Hasegawa, *Department of Electronic Engineering, Tohoku University, Sendai, Miyagi, Japan. **Graduate School of Biomedical Engineering, Tohoku University, Sendai, Miyagi, Japan.
Abstract:
Background, Motivation and Objective:
If the heart wall vibration caused as the response to the electric excitation is visualized using transcutaneous ultrasound, regional physiological properties in action potential and mechanical properties of the viscoelasticity can be noninvasively revealed. We have already found that the pulsive vibration is excited on the myocardium 15 ms after the electrical stimulation to an isolated heart [Acoustical Science and Technology 24, 17 (2003)]. Base on the fact, we have transcutaneously detected the propagation of minute vibration caused just around R-wave of the electrocardiogram (ECG). However, such visualization was limited to 2-dimentional (2D) plane obtained by scanning the ultrasonic beams. In this study, the propagation of the vibrations caused just around R-wave of ECG is visualized in 3-dimentional (3D) space.
Statement of Contribution/Methods:
Since the propagation speed is several m/s along the heart wall, the necessary temporal resolution is at least 2 ms for the visualization. In our previous study, using a sparse sector scan in 2D plane [IEEE Trans. UFFC. 51, 1931 (2005)], the vibration waves were measured almost simultaneously at about 10,000 points set in the heart wall at a high frame rate but the scanning direction was limited to 10-16. Thus, there is no space to detect the RF data in 3D space with high temporal resolution. In this study, therefore, the multiple 2D data are acquired during consecutive several cardiac cycles and the propagation properties in 3D space are reconstructed. The probe on the chest wall is rotated intermittingly by 15 degrees at each of the relaxation periods during the consecutive 13 cardiac cycles, and RF data are acquired in the 2D plane by sparse scan in 16 directions. Since the direction of the ultrasonic beam at the center of the 2D planes is common in the data acquisition, it is easy to synchronize the time of each cardiac cycle precisely using the detected vibrations, and then the propagation of the vibration of the myocardium can be reconstructed in 3D space.
Results:
The method was noninvasively applied to healthy subjects. The consecutive spatial distributions of the spatially interpolated phase of the waves reveal wave propagation along the heart wall. Just after the Q-wave of the ECG, the propagation started at the center of the interventricular septum, where Purkinje fiber contacts with the myocardium, to the base side and apical side of the heart. Its propagation speed was slow (1 m/s), which shows the propagation of electrical excitation. After the R-wave of the ECG, other pulsive waves started to propagate from the base to the apex. Since its speed was several m/s for about 50 Hz but there was dispersion, this is the shear wave caused by the mitral-valve closure.
Discussion and Conclusions:
The method noninvasively reveals the propagation of electrical conduction wave by measuring regional myocardial response to it in human heart, which will be a novel tissue characterization of the heart.
Talk #1.5:
Title: Deconvolution and elastography based on 3D ultrasound
Richard Prager (Presenter), Andrew Gee, Graham Treece, Joel Lindop, and Nick Kingsbury, Department of Engineering, University of Cambridge, United Kingdom.
Abstract:
Background, Motivation and Objective:
This talk is in two parts and addresses two ways of getting more information out of the RF signal from a 3D mechanically-swept medical ultrasound scanner. The first topic is the use of non-blind deconvolution to improve the
clarity of the data, particularly in the direction perpendicular to the individual B-scans. The second topic is strain imaging. We present a robust and efficient approach to the estimation and display of axial strain information.
Statement of Contribution/Methods:
For deconvolution, we calculate an estimate of the point-spread function at each depth in the image using Field II. This is used as part of an EM framework in which the ultrasound scatterer field is modelled as the product of (a) a piece-wise smooth and (b) a fine-grain varying function. In the E step, a Wiener filter is used to estimate the scatterer field based on an assumed piece-wise smooth component. In the M step, wavelet denoising is used to estimate the piece-wise smooth component from the scatterer field.
For strain imaging we use a quasi-static approach with efficient phase-based algorithms. Our contributions lie in robust and efficient 3D displacement tracking, point-wise quality-weighted averaging, and a stable display that shows not only strain but also an indication of the quality of the data at each point in the image. This enables clinicians to see where the strain estimate is meaningful and where it is mostly noise.
Results:
For deconvolution we will present in-vivo and in-vitro images and simulations with quantitative performance measures. For example, with the blurred 3D data taken as 0dB, we get an improvement of 5.68dB with a Wiener filter alone, 5.90dB with ForWaRD and 7.45dB with our EM algorithm. For strain imaging we will show images based on 2D and 3D data and show how full 3D analysis can be performed in about 20 seconds on a typical computer. We will also present initial results of our clinical study to explore the applications of our system in our local hospital.
Discussion and Conclusions:
We have shown that it is possible to use fast phase-based algorithms to provide accurate, stable images. With appropriate point-wise persistence, sufficiently clear and stable images can be presented in real-time to be of clinical interest. Our study of deconvolution with a spatially-varying point-spread function indicates that such algorithms may soon be fast enough to be a cost effective way of improving medical ultrasound images.
Talk #1.6:
Title: Ultrasound Particle Velocimetry: an Emerging Technique in Cardiology
*Hairong Zheng (Presenter) and **Robin Shandas, *Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China. **University of Colorado at Boulder, Boulder, CO, USA.
Abstract:
Background, Motivation and Objective:
Development and progression of vascular atherosclerosis and aneurysms are modulated by local hemodynamics such as wall shear stress and blood flow recirculation. However, current non-invasive imaging techniques either cannot resolve the multi-component nature of such flows or are too cumbersome for routine clinical use. We have recently developed a novel contrast-based echo particle image velocimetry technique (Echo PIV) to quantify complex blood flow vectors noninvasively. The method is angle independent, possesses excellent spatial and temporal resolution, and is simpler to use than MRI velocimetry. Here we examine the utility of this method to characterize hemodynamics around carotid plaques and abdominal aortic aneurysms using in vitro phantoms.
Statement of Contribution/Methods:
A custom-designed Echo PIV system, including a 7.5 MHz 128-element linear array transducer, custom-designed firing sequences, and a velocimetry algorithm for analyzing the backscattered radio-frequency (RF) data, was used along with commercially available ultrasound contrast microbubbles to obtain velocity vectors through models of carotid stenosis and abdominal aortic aneurysms. Both steady and pulsatile flows were used.
Results:
Echo PIV was able to resolve and quantify the complex hemodynamics around carotid plaques and abdominal aortic aneurysms, including proximal flow velocity vectors and distal vortex recirculation patterns. The method was also capable of producing time-resolved multi-component velocity, shear stress and vorticity maps. Good agreement between peak velocities found by Echo PIV and those measured by conventional ultrasound Doppler was also found.
Discussion and Conclusions:
The Echo PIV method provides an easy, direct and accurate means of quantitatively yet non-invasively characterizing complex vascular hemodynamics with comparable spatial resolution and superior temporal resolution to MRI velocimetry.
Talk #2.1:
Title: New Developments in Ultrasonic Gas Analysis and Flowmetering
Saul Jacobson, 403 Huon Road, TAS 7004, Australia.
Abstract:
Background, Motivation and Objective:
Ultrasonic methods have important advantages in the measurement of gas flow, including the ability to measure almost any gas or gas mixture over a wide pressure range and turndown ratio. Ultrasonic gas flowmeters also are capable of measuring bi-directional flow and may be non-intrusive with no pressure loss. In certain cases the sensors may even be clamped on the outside of the pipe. Traditionally the Transit-time method has been used, but more recently interesting developments in Tag Cross-correlation have yielded promising results, particularly for low-pressure clamp-on applications. Ultrasonic flowmeters for gas have been commercially available since the 1980s, and they are widely accepted today for flaregas and stackgas monitoring and for a wide variety of industrial and fuel gas measurements. Highly accurate multi-path meters are approved and commonly used for custody transfer measurement of natural gas. In addition to the many advantages ultrasonic methods have in the measurement of the gas flowrate, ultrasonic propagation characteristics of the gas may also be measured to determine properties of the gas, such as its molecular weight, density or energy content.
Statement of Contribution/Methods:
Soundspeed, in conjunction with temperature and pressure measurement were first used in the 1980s to determine the molecular weight and derive the mass flowrate of flaregas. Ultrasonic flowmeters for custody transfer natural gas gained acceptance in the 1990s with the publication of the American Gas Association AGA-9 report, which includes guidelines on the measurement and use of the gas soundspeed. More recently gas soundspeed and other properties such as attenuation have been used for the analysis of binary gases and pseudo-binary gases such as breathing gases, biogas, landfill gas, and process gases. Acoustic impedance has been measured and used to determine the density of high pressure gases.
Results:
This paper reviews the methods to analyze binary, ternary and multi-component gases as well as presenting some new results from work conducted by the author and colleagues for biogas, consising primarily of methane and carbon dioxide at 100% RH.
Discussion and Conclusions:
A review of the literature finds ultrasonic methods to be an effective means of gas flow measurement and analysis for many applications. The authors experiments found good correlation between ultrasonic methods and gas chromatography for the analysis of “simulated?as well as real biogas.
Talk #2.2:
Title: Invariants of the time reversal operator and ultrasonic applications
Claire Prada (Presenter) and Mathias Fink, Laboratoire Ondes et Acoustique, CNRS, Universit?Paris 7, ESPCI, Paris, France.
Abstract:
Background, Motivation and Objective:
It is well known that acoustic time reversal mirrors own outstanding focussing properties in complex media. Used in the pulse echo mode, the time reversal process can be iterated to achieve selective focusing on the most reflective point among a set of scatterers or to enhance and extract the echo from a defect in a noisy structure.
Statement of Contribution/Methods:
The iterative time reversal process can be described by the Time Reversal Operator. This process has an ensemble of invariants that can be determined from the measurement of the array inter-element impulse responses and the singular value decomposition of corresponding array response matrix. The determination and analysis of these invariants is the object of the D.O.R.T. method (French acronym for Decomposition of the Time Reversal Operator). It can be used to separate the echoes of several scatterers in an inhomogeneous medium. It also enables the separation of the radiation modes of a solid scatterer, like, for example, the various Lamb waves circumnavigating a hollow cylinder, leading to its characterization. Furthermore, when an estimate of the medium’s Green function is available, high resolution and low noise images can be achieved using the back-propagation of the dominant invariants.
Results:
This presentation will provide an overview of the different results obtained with the DORT method in the context of non detructive evaluation. Different improvements of the method will be shown, like the acquisition of the array response matrix using the Hadamard basis or focussed transmissions, or the coding of the inter-element impulse responses on 1-bit with little loss of information. Several examples of invariants of the time reversal operator and applications to the detection and characterization of solid scatterers will be presented.
Discussion and Conclusions:
The DORT method is a powerfull tool that can be used as a complement to conventional beamforming imaging technique. Furthermore, it allows detection and focusing through aberrating media where conventional beamforming fails.
Talk #2.3:
Title: Ultra High Frequency Acoustic Wave Detection of HIV Antibody
*Michael Thompson (Presenter) and **Scott Ballantyne, *Chemistry, University of Toronto, Toronto, Ontario, Canada. **Maple Biosciences, Toronto, Ontario, Canada.
Abstract:
Background, Motivation and Objective:
Screening and detection of HIV disease in patients requires assaying of blood or serum samples for antibody. For rapid screening, the detection of only one antibody is required, but for confirmation of the presence of the disease up to 10 are mandatory. Such assays are highly time consuming and costly, and involve significant skilled labour. It is the specific overall objective of this project to develop an electronic signalling approach to the detection of HIV in biological fluids. The technology incorporates a biosensor methodology which will be designed for the clincal laboratory. The basis is ultra high frequency acoustic wave technology
Statement of Contribution/Methods:
Our contribution has three distinct but connected goals. First we have developed a flow through system which incorporates a bulk acoustic wave sensor in an analytical configuration. The sensor is a conventional 20 MHz quartz device which is excited not by the usual electrode technique, but by a flat spiral coil. Secondary electric fields drive the device up to the 50th harmonic thus generating high sensitivity. The second crucial aspect of the project is the attachment of antibody probes to the device surface. These probes which are based on peptide structures bind antibody which is then detected by the sensor. We have designed and developed new linking agents for attaching probes at optimum surface density but also that avoid the vexing non-specific adsorption
problem. The thired part of the work involves the use of the whole configuration to analyse real samples such as human serum
Results:
We have demonstrated that the sensor can be operated with facility in a flow-injection apparatus. The faces of the device must be extremely parallel and have optimum surface physical nature as shown by AFM. XPS and other surface techniques have been used widely to demonstrate the presence of peptide probes on the quartz surface. The linkers are based on customized silane chemistry and constitute new molecules for the surface bioanalytical chemist. The binding of antibody in the flow system yields signals in the thousands of Hz. In serum we can acheive ratios of signal over nonspecific adsorptive noise at up 5 to 1.
Discussion and Conclusions:
The system described above is being developed for commercial application in the clinical lab. Required for the future is the design and implementation of a multiplexed system involving series or parallel flow. Also the prototype instrument requires significant design engineering for non-technical users. The instrument will then be tested in the clinical environment
Talk #3.1:
Title: Piezoelectric MEMS for Audio Signal Transduction, Microfluidic Management, Resonant Mass Sensing, and Movable Surface Micromachined Structures
Eun Kim, Electrical Engineering - Electrophysics, University of Southern California, Los Angeles, CA, USA.
Abstract:
Background, Motivation and Objective:
This paper describes (1) piezoelectric microphone and microspeaker, (2) micromachined self-focusing acoustic transducers for liquid droplet-ejection, mixing, pumping and transporting, (3) resonant mass sensors based on film bulkacoustic resonators (FBAR), and (4) piezoelectrically actuated mirror array and tunable capacitor.
First presented will be micromachined microphones and microspeakers that consume very low power, and are small, rugged and highly sensitive. The microphones and microspeakers are built on micromachined diaphragms with a piezoelectric ZnO, and have large dynamic range, no need to have a polarization voltage, and no major performance/reliability problem due to water condensation. The fabrication processes for the transducers are relatively simple and very robust. We have incorporated various types of diaphragms that are cantilever-like, bimorph-type, containing partially-etched holes, corrugated, dome-shaped, etc.
Another line of presentation will be on microfluidic mixers, pumps, transporters and ejectors based on the self-focusing acoustic-wave transducer (SFAT). All the transducers are powered by a piezoelectric film or substrate, and are inherently fast, consume low power, and require no heat. The SFATs do not require any nozzle or acoustic lens, and their fabrications are very simple. Moreover, the SFAT ejector (unlike a nozzle-based ejector) can eject liquid droplets at any oblique angle, and does not have to be moved to ink a spot with different liquids. We have integrated a 2-D ejector array with microchannels, chambers and other microfluidic components on a single silicon chip for a small, portable, affordable DNA synthesis system.
Also described will be FBAR-based highly sensitive, resonant mass sensors that can operate in vapor and liquid. In vapor, the sensor based on an FBAR with Q of about 500 at 1 GHz can detect a mass change of 10-9g/cm2 on its surface. The following FBAR-based sensors will briefly be described: mercuric ion sensor, DNA hybridization sensor, explosivevapor- trace detector, and a 1.5mm long, 250?m wide and 15?m thick polymer probe with an FBAR mass sensor at its tip.
Finally presented will be a piezoelectrically actuated array of cantilevers/bridges (whose facets can accurately be controlled by electrical voltage) for tunable capacitors, RF switches and projection displays. Through the implementation of a simply-supported bridge driven by two 100-?m-long ZnO-actuated cantilevers, a compact surface-micromachined tunable capacitor has been fabricated on a single chip without any warping, and shown to be capable of a 1,400% continuous tuning from 0.13 pF to 1.82 pF. Also shown will be a cantilever array with a pixel size of 100x100 ?m2 that was developed for a projection display. A piezoelectric ZnO film was used to produce 0.116?V vertical deflection of the cantilever.
Statement of Contribution/Methods:
None.
Results:
None.
Discussion and Conclusions:
None.
Talk #3.2:
Title: Applications of Sonic Waves in the Estimation of Petrophysical, Geophysical and Geomechanical Properties of Subsurface Rocks
*Bikash Sinha and **Vivian Pistre (Presenter), *Mathematics and Modeling, Schlumberger-Doll Research, Cambridge, MA, USA. **Well Placement and Safety, Schlumberger Beijing Geoscience Centre, Beijing, China.
Abstract:
Background, Motivation and Objective:
Sonic waves play an important role in estimating rock properties that are crucial in an efficient and safe production of oil and gas wells. An acoustic source in a fluid-filled borehole can generate both nondispersive headwaves as well as relatively stronger borehole guided modes. Processing of waveforms recorded with adequate spatial sampling yields sonic velocities in the surrounding formation over the receiver aperture. These velocities are then transformed into elastic moduli of the propagating medium. Elastic moduli of the formation provide many useful petrophysical, geophysical and geomechanical attributes of porous rocks that constitute hydrocarbon bearing formations. Petrophysical attributes of hydrocarbon bearing formations include porosity, pore pressure, and fluid mobility. Geophysical attributes of the formation deal with anisotropy characterization of formations on a seismic scale. Geomechanical properties of rock consists of estimating in situ formation stresses and strengths as a function of radial position away from the borehole surface.
Statement of Contribution/Methods:
Compressional velocity through a porous rock has been used to estimate porosity using Wyllie time-average equation whereby an interval transit time is decomposed into transit times in the solid and fluid components of the composite structure. Rock porosity can then be estimated using compressional velocity of the rock matrix and pore fluid in conjunction with measured velocity in the composite structure. There are well established correlations that help identify formation lithology in terms of the compressional to shear velocity ratio or the Poisson's ratio of the material. Plots of compressional to shear velocity ratio against compressional transit time help identify intervals containing limestone, dolomite, salt and quartz.
Results, Discussion and Conclusions:
Recent applications of elastic moduli of rocks in a reasonably uniform lithology are in the estimation of fluid mobility in porous rocks; formation stresses; and fracture characterization. The presence of a fluid-filled borehole in a tectonically stressed formation causes both radial and azimuthal heterogeneities in rock stresses. Formation stresses are estimated using an acoustoelastic model based on nonlinear continuum mechanics. This model predicts crossing dipole dispersions to be an indicator of stress differential in the borehole cross-sectional plane. In-situ rock strength can be estimated using radial variations of shear velocities obtained from the inversion of borehole dispersions. Estimates of rock stresses and strength help maintain wellbore stability during drilling and production.
Talk #3.3:
Title: Interfacial Waves and Stability at the Frictional Sliding Interface between Two Solids
Yue-Sheng Wang, Institute of Engineering Mechanics, Beijing jiaotong University, Beijing, China.
Abstract:
Background, Motivation and Objective:
Interfacial waves play an important role in many fields such as geophysics, seismology and non-destructive evaluation, etc., and thus have received considerable attention. Most of the published papers are concerned with the welded interface. However, contact interfaces, smooth or frictional, are also common in practical cases. The slip dynamics and Rayleigh-Stoneley-wave theory involving frictional contact interfaces are attracting more and more scientists working with experimental, numerical and analytical tools.
Statement of Contribution/Methods:
In this paper, the theoretical study is presented on the interfacial waves and stability at a frictional interface between two anisotropic elastic or piezoelastic solids that are pressed together by remote pressure and meanwhile sheared by remote shearing traction and electric load. The external loads may or may not lead to steady rigid sliding between two solids. A perturbation field propagating steadily along the interface is examined by ignoring the details of the perturbation source. The local stick¨Cslip motion at the frictionally contact interface caused by the perturbed slip pulse is studied. The Stroh formalism, together with the concept of the surface impedance tensor is employed. The boundary value problem involving unknown slip/stick zones is cast to a Cauchy singular integral equation with an unknown integral interval.
Results:
By solving the singular integral equations analytically, the explicit expressions of interface waves, which could satisfy the boundary conditions and energy balance, are therefore obtained. The explicit solutions are obtained. The existence conditions are given. Particularly, the existence conditions and physical properties of interface waves have been further discussed based on numerical calculations for practical examples.
Discussion and Conclusions:
The results show: 1)Slip-stick frictional interface waves might exist in most material combinations. In some specific cases, the waves will involve 1/2 singularity at one end of slip zones while be bounded at the other end, which in the meantime requires enough large frictional coefficient. The wave speed ranges are related to the frictional coefficient. In more general cases, the interface waves will involved singularity weaker than 1/2 at one end of slip zones while be bounded at the other end. 2)Between the anisotropic elastic or piezoelastic media that are steadily frictionally sliding under the applied tractions, there will be no such interface waves that could change the stresses so as to cause the local slip motion at the interface, i.e., self-excited oscillations of instable interface waves will not transformed to the steady slip-stick motion at the interface without separation.
Talk #3.4:
Title: Theory, and Experimental Verifications of the Resonator Q and Equivalent Electrical Parameters due to Viscoelastic, Conductivity and Mounting Supports Losses
*Yook-Kong Yong (Presenter), *Mihir Patel, and **Masako Tanaka, *Civil and Environmental Engineering, Rutgers University, Piscataway, New Jersey, USA. **Epson Toyocom, Japan.
Abstract:
Background, Motivation and Objective:
Current finite element software does not allow for the calculation of a resonator Q without apriori assumptions of the resonator impedance or damping. A novel analytical/numerical method for calculating the resonator Q, and its equivalent electrical parameters due to viscoelastic, conductivity and mounting supports losses is presented. Hence the method presented will be quite useful for designing new resonators, and reducing their time and costs of prototyping. There is also a necessity for better and more realistic modeling of the resonators due to miniaturizations, and the rapid advances in frequency ranges in telecommunication.
Statement of Contribution/Methods:
We present new three-dimensional finite elements models of quartz resonators and aluminum nitrite SMR's with viscoelasticity, conductivity, and mounting support losses. For quartz the materials losses attributed to electrical conductivity and acoustic viscosity were obtained from Lee, Liu and Ballato[1], and Lamb and Richter[2], respectively. The losses at the mounting supports were modeled by perfectly matched layers (PML's). The theory for dissipative anisotropic piezoelectric solids given by Lee, Liu and Ballato [1] was formulated in a weak form for finite element applications. PML's were placed at the base of the mounting supports to simulate the energy losses to a semi-infinite base substrate. FE simulations were carried out for free vibrations and forced vibrations of AT-cut quartz resonators, and solidly mounted resonators (SMR’s). The FEM models for the SMR's employ periodic boundary conditions[3].
Results:
Results for quartz thickness shear AT-cut quartz resonators and SMR's are presented and compared with experimental data. Results for the resonator Q and the equivalent electrical parameters were compared with their measured values. Good comparisons were found. Results for low and high Q AT-cut quartz resonators compared well with their experimental values. FEM models with periodic boundary conditions were employed to calculate the Q of SMR’s operating in the range of 1.70 to 1.90 GHz. The Bragg layers of the SMR’s consist of three alternating layers of W and SiO2. The resonating element consisted of AlN piezoelectric film with Mo electrodes. Their Q and Keff values showed very good agreement with the measured data. The effect of thermal compensating oxide and Mo electrode resistance on the Q values was studied and compared with the measurement data.
Discussion and Conclusions:
Comparisons of the Q and other electrical parameters obtained from the free vibration analysis with their corresponding values from the forced vibration analysis were found to be in excellent agreement. The results were validated by good comparisons with their experimental values. The resulting FE model gives the Q value without prior assumptions of damping factors and impedance. A new method for estimating the Q directly from the frequency spectrum obtained for free vibrations was also presented.
Talk #4.1:
Title: SAW and BAW Technologies for RF Filter Applications: A Review of the Relative Strengths and Weaknesses
Robert Aigner, TriQuint Semiconductor, Apopka, Florida, USA.
Abstract:
Background, Motivation and Objective:
The first part of this paper aims to present facts and figures comparing SAW and BAW technologies with regard to
(a) process complexity / cost , size
(b) function, performance and fundamental limitations
(c) simulation methods and design flow
Based on the criteria above the application space for RF filters in wireless communication will be mapped and selected examples will be discussed in detail.
Statement of Contribution/Methods:
The second part of this paper will review how both technologies progressed in recent years and will focus on innovations. Both SAW and BAW keep pushing for better performance and at times compete with each other. Despite that there are surprisingly many areas where SAW and BAW face similar challenges on a path to improved performance and/or lower cost. Commonalities and areas where SAW and BAW learn from each other are:
(a) frequency correction “trimming?methods for yield improvement
(b) materials and processes for acoustic layers
(c) wafer-level-packaging
Results:
Results of research and development work at TriQuint in both SAW and BAW will be presented. The emphasis will be on temperature compensated (TC) filters and duplexers. TC SAW shows promise to fulfill demanding duplexer requirements for emerging mobile phone bands. Fully temperature compensated BAW filters enable to fix interference issues in emerging wireless applications.
Discussion and Conclusions:
The shockwave FBAR/BAW has generated inside the SAW community a few years ago has passed. It generated a lot of pressure while approaching and a lot of traction while dissipating. Several suppliers now have both technologies in their portfolio while others stick to either the one or the other. SAW is recovering lost market share based on cost advantages and innovations which aim to overcome their main weaknesses. BAW on the other side keeps pushing the performance envelope for filters with extreme specifications. In the history of electronics over the past 50 years there are many cases of a new technology challenging established technologies. Examples range from “Transistor vs. Vacuum tube?and “GaAs vs. Silicon?to “CMOS vs. Bipolar? Which of those best compares to “BAW vs. SAW?will be speculated about in the discussion.
Talk #4.2:
Title: Piezoelectric Boundary Wave Devices: Their Underlying Physics and Applications
*Ken-ya Hashimoto (Presenter), *Yiliu Wang, *Tatsuya Omori, *Masatsune Yamaguchi, **Michio Kadota, **Hajime Kando, and **Teruhisa Shibahara, *Dept. EEE, Chiba University, Chiba, Chiba, Japan. **Murata MFG, Co. Ltd., Yasu, Shiga, Japan.
Abstract:
Background, Motivation and Objective:
For SAW devices, bulky and expensive packaging has been one of the vital problems for their further miniaturization and price cuts. Piezoelectric boundary acoustic waves (PBAWs) have long been expected to be one of the possible solutions to break down this problem. Very recently, Kando, et al. proposed the SiO2 overlay/heavy grating electrode/rotated Y-cut LiNbO3 (rot. YX-LN) substrate structure for developing PBAW devices. The remarkable advantage of this device is that the cavity over the chip surface can completely be got rid of. This makes the packaging most simple and enables the packaged device size to be minimized, whilst the device fabrication process is almost identical with that for traditional SAW devices.
Statement of Contribution/Methods:
This paper reviews physical properties of PBAWs and their application to miniature and high performance RF filters/duplexers.
Results:
First, basic properties of PBAWs are discussed. It is shown that PBAWs are supported in various structures provided that highly piezoelectric material(s) are employed as structural member(s). For example, the Si/SiO2/IDT/rot. YX-LN structure supports PBAWs with a large electromechanical coupling factor and moderate temperature coefficient of velocity. In the structure, the PBAW energy is confined around the relatively thick SiO2 layer, where the wave velocity is relatively small. On the other hand, PBAWs are trapped near the electrode region in the SiO2/heavy grating electrode/rot. YX-LN structure. This means that PBAW properties in the structure are independent of the SiO2 layer thickness. This is a significant advantage for mass production. One may mind the fact with the structure, however, that the PBAW velocity should be smaller than the shear-wave velocity in SiO2, otherwise the PBAW becomes leaky. Rot. YX-LN possesses piezoelectric coupling with Rayleigh-type waves as well as SH-type waves. Responses associated with the former have to be suppressed completely for filter applications. It is discussed how these two waves are dependent on the substrate rotation angle, electrode thickness, and metallization ratio. The PBAW devices employing SiO2/Au electrodes/0-15°YX-LN are now being mass-produced. Because of the removed cavity from the chip surface, the packaged device size can be reduced dramatically. For example, a DMS filter based on PBAWs is developed for GSM900 Rx in a size of 0.8x0.6x0.25 mm3. The minimum insertion loss achieved in the passband (925-960 MHz) is 2.7dB (max), which is comparable to that of conventional SAW filters in a relatively large device size. The SiO2 layer is effective in achieving the improved temperature coefficient of frequency of -30 to -40 ppm/°C.
Discussion and Conclusions:
The PBAW devices for various standards such as GSM1800 and GSM1900 have already been developed and are being mass-produced.
Talk #4.3:
Title: A Review of the Recent Development of MEMS and Crystal Oscillators and Their Impacts on the Frequency Control Products Industry
C.S. Lam, Integrated Device Technology, Inc., Andover, MA, USA.
Abstract:
Background, Motivation and Objective:
Due to its high Q and temperature-stable properties, quartz crystal based oscillators are important clock sources in consumer, commercial, industrial, and military products The demand for quartz crystal resonators and oscillators continues to rise and the quartz crystal industry has made major progresses in miniaturization, performance enhancement, and cost reduction in the past ten years. The unique fabrication and encapsulation requirements though render quartz crystal resonators and oscillators difficult or close to impossible to be integrated onto the mature silicon based IC platforms. The recent technical breakthroughs of all silicon MEMS (Micro Electro Mechanical Systems) based resonators and oscillators seem to re-ignite the interest in displacing/replacing the quartz crystal technology and to open up again the prospect in clock source integration. Based on a 2006 review paper by the author[1], this paper expands on the subject by reviewing the development of all silicon MEMS oscillators and crystal oscillators in the past few years and commenting on what challenges they face in the highly competitive frequency control products industry. This paper will also touch on the recent development of CMOS oscillators (without moving parts) and piezoelectric-activated silicon MEMS resonators and oscillators.
[1] "An Assessment of the Recent Development of MEMS Oscillators as Compared with Crystal Oscillators," C.S. Lam, Piezoelectricity, Acoustic Waves and Device Applications- Proc. of the 2006 Symposium, Zhejiang University, China, 14~16 December 2006, ed. Ji Wang and Weiqiu Chen, pp. 308-315 (also in https://www.txccorp.com/download/tech_paper/2006-SPAWDA-3.pdf)
Statement of Contribution/Methods:
None.
Results:
None.
Discussion and Conclusions:
None.
Talk #5.1:
Title: PMN-PZT Single Crystals and Composites for Transducer Applications
Sung-Min Lee, Dong-Ho Kim, and Ho-Yong Lee (Presenter), Ceracomp Co., Ltd., Sunmoon University, Asan, Chungnam, South Korea.
Abstract:
Background, Motivation and Objective:
Crystallographically engineered Relaxor-PT single crystals, specifically PMN-PT and PZN-PT, offer very high piezoelectric and electromechanical coupling coefficients (d33>2,000 pC/N; k33>0.9), promising for next generation electromechanical devices such as ultrasonic transducers and actuators. However, these piezoelectric single crystals exhibit relatively low TC, TRT and EC, and thus have very limited usage range. In contrast to the growth of relaxor-PT single crystals, PZT and relaxor-PZTs can not be readily grown in single crystal form because of their incongruent melting behavior. Attempts to grow single crystals of PZT and relaxor-PZTs have been made by numerous researchers, resulting in crystallites too small (2 ~ 3 mm in size) to allow adequate property measurements. If PZT and relaxor-PZTs materials could be grown in single crystal form, PZT and realxor-PZT single crystals have been expected to have remarkable and wide range of dielectric and piezoelectric properties such as high K3T, TC, TRT and EC.
Statement of Contribution/Methods:
The solid-state crystal growth (SSCG) technique is to grow a single crystal in a polycrystalline precursor by continuous grain growth of an external seed single crystals without complete melting of major components. In the SSCG process, no melting of PZT is involved and thus the issue of incongruent melting can be avoided. It is also readily amenable to dopant modifications which give us the family of piezoelectrically "soft" and "hard" PZT and relaxor-PZT single crystals, similar to "soft" and "hard" ceramics we have today. In this investigation, undoped and doped MPB PMN-PZT single crystals were fabricated using the SSCG technique and their dielectric/piezoelectric properties characterized.
Results:
The undoped and doped (Fe-, Mn-, and In-) PMN-PZT single crystals of high TC (> 180~300oC) and EC (> 3.5~10 kV/cm) were sucessufully fabricated by the SSCG technique and their dielectric/piezoelectric properties characterized. Especially the temperature dependence of the piezoelectric/electromechanical properties, the dc bias effect on TRT (or the application usage temperature range), the high field unipolar strain, and the development of an internal bias were investigated and compared to PMN-PT single crystals. Piezoelectric single crystal-polymer composites were also prepared by using undoped and doped PMN-PZT single crystals and their dielectric/piezoelectric properties characterized.
Discussion and Conclusions:
Compared to PMN-PT single crystals, the high TC/EC PMN-PZT single crystals were found to exhibit a much wider usage range with respect to electric field as well as temperature, and thus are better candidates for application in transducers and actuators. Along with high TCs, the ability for dopant engineering using the SSCG technique has been demonstrated to piezoelectrically "harden" crystals (Qm = 500 ~1,000) via the development of an internal bias.
Talk #5.2:
Title: Vibration Mode and Relevant Ultrasonic Applications of Ferroelectric Single Crystals Pb(Mg1/3Nb2/3)O3-PbTiO3
Dan Zhou and Haosu Luo (Presenter), Shanghai Institute of Ceramics, CAS, Shanghai, China.
Abstract:
Background, Motivation and Objective:
Modern medical ultrasonic imaging relies almost exclusively on piezoelectric transducers to convert mechanical waves to electrical signals and vice versa. The vast majority of these devices incorporate a polycrystalline piezoelectric based on the composition Pb(Zr1-x, Tix)O3, generally known as PZT. These materials offer electromechanical properties k33 of 75% and piezoelectric properties d33 of 600 pC/N. Recently, much research work has been reported on the relaxor ferroelectric single crystals (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) with superior properties of k33 (~94%), d33 (>2000pC/N), etc. Such excellent performances will lead to large improvement of sensitivity and resolution in medical ultrasonic imaging systems.
Statement of Contribution/Methods:
The electromechanicl factors were measured according to IEEE standards by HP4194A impedance analyzer. The single element PMN-PT transducer was fabricated with the same structure as PZT transducer. The PMN-PT/Epoxy composites and array transducers were simulated with PiezoCAD.
Results:
The PMN-PT crystals were investigated of electromechanical factors k33, kt, k33' and piezoelectric constant d33, with different orientation and cuts for various medical ultrasonic applications. Based on the longitude extension mode (k33), the PMN-PT/Epoxy 1-3 composites were modeled and fabricated. The holistic kt (>90%) of the composites far exceeds that of the PZT ceramics (only ~50%). The relatively low acoustic impedance makes the acoustic matching to human tissue much easier. The results will be favorable for single element ultrasonic transducers, such as Doppler blood flow imaging applications. For medical linear and phase array transducers, the coupling factor k33' is a key indicator. The PMN-PT resonators of this vibration mode were studied systematically with orientations and poling conditions. The optimized cut type of PMN-PT for array applications was obtained with k33' of 92%, which is larger than that 70% of conventional PZT ceramics.
Then, ultrasonic transducer devices utilizing PMN-PT were investigated. The PMN-PT pulse wave 2MHz TCD probe was manufactured with 30% broader bandwidth and 4dB higher sensitivity compared with PZT probe. These enhanced performances were induced by relatively high kt (62%) and d33 of PMN-PT. The single element transducer based on PMN-PT/Epoxy 1-3 composites was simulated with broader bandwidth and higher echo response than PZT transducers. The PMN-PT 3.5MHz linear array transducer was also simulated with the similar effects.
Discussion and Conclusions:
The PMN-PT were investigated and optimized for various medical ultrasonic transducer applications. The ultrahigh piezoelectric and electromechanical constants were obtained in PMN-PT. Three types of fabricated or simulated medical transducers utilizing PMN-PT all show improved pulse length, bandwidth and sensitivity. So the next generation of high performance ultrasonic transducers is expected.
Talk #5.3:
Title: Piezoelectric Thin and Thick Films for Transducer Applications
*Wei Ren (Presenter), *Peng Lin, *Zheng Wang, *Xiaoqing Wu, *Peng Shi, *Xi Yao, **Qifa Zhou, **Dawei Wu, **Benpeng Zhu, and **K. Kirk
Shung, *Electronic Materials Research Laboratory, Xi'an Jiaotong University, Xi'an, Shanxi, China. **NIH Transducer Resource Center and Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
Abstract:
Background, Motivation and Objective:
In recent years, the demands for miniaturized devices integrated with microelectronics have increased significantly, leading to great interests in the design and fabrication of thin/thick film transducers. Lead zirconate titanate (PZT) is an attractive material for transducer applications due to its excellent electromechanical properties. Such devices often require crack-free films with thickness of 1~10 ?m. A polymer-assisted deposition and PZT powders/sol-gel solution composite thick films have been developed to prepare PZT thick films.
Statement of Contribution/Methods:
PbZr0.52Ti0.48O3 (PZT) thin and thick films with thickness of 1~10 ?m have been prepared by a metallo-organic decomposition process modified by a polymer, poly(vinyl acetate) (PVAc). It?s found that with an increase of PVAc in PZT solutions, the single-layer thickness of PZT films increases from 0.07 ?m to 0.47 ?m. When PVAc-related organic compounds are decomposed, nano-sized pores are formed and provide space for the structural and stress relaxation. It prevents the crack formation and increases the uncracking critical thickness of PZT films.
In addition, PZT composite thick films up to 30 ?m-thick have been successfully prepared with a spin-coating of PZT powers/sol-gel composite solution. The electric properties of the films were evidently enhanced by infiltration of PZT solgel into composite films and optimization of PZT powders to PZT sol-gel mass ratio in composite solution. Transducer and array at a frequency high than 100 MHz have been fabricated using above PZT thick films by MEMS technology.
Results:
Dielectric, ferroelectric, and piezoelectric properties of PZT films have been thoroughly investigated. For PVAc modified PZT films, with the increase of the film thickness from 0.95 ?m to 9.9 ?m, the dielectric constant increases from 1070 to 1600, while the dielectric loss is in a range of 0.03~0.04 at 1 kHz. Remanent polarization increases from 36.1 ?C/cm2 to 55.3 ?C/cm2, while coercive field decreases from 57.3 kV/cm to 40.9 kV/cm. The piezoelectric coefficient d33 increases from 43.9 pm/V to 200 pm/V.
Discussion and Conclusions:
Using PZT thick films, high-frequency transducers and kerfless array at a frequency high than 100 MHz will be presented. Meanwhile, the effect of the residual stresses of PZT films on devices has been investigated.
Talk #5.4:
Title: The Physical Acoustics of Energy Harvesting
Stewart Sherrit, Advanced Technologies Group, Instrument Mechanical Engineering Section, Jet Propulsion Laboratory, Pasadena, CA, USA.
Abstract:
Background, Motivation and Objective:
Energy harvesting systems based on the transformation of acoustic vibrations into electrical energy are increasingly being used for niche applications due to the reduction in power consumption of modern day electronic systems. Typically these applications involve extracting energy at remote or isolated locations where local long term power is unavailable or inside sealed or rotating systems where cabling and electrical commutation are problematic. This paper will look at some of the limitations of these systems.
Statement of Contribution/Methods:
A variety of modes of harvesting electrical power from acoustic vibrations or impacts generated by machines, humans or nature will be presented. These modes can be configured to extract energy from longitudinal, transverse, bending, hydrostatic or shear waves at frequencies ranging from less than a Hz to 10’s of kHz. In order to aid in the design and optimization of these devices we have identified common elements of these systems.
Results:
These common elements are: the input mechanical power spectrum, the effective matching of mechnical loads, the conversion of the input mechanical energy into electrical energy using piezoelectric or biased electrostrictive transducers and matching the electrical load. Recent results on an acoustic electric feed-through device demonstrated 1 kW power conversions at power densities of 70 W/cm2 and 25 W/cm3 using a pre-stressed stacked PZT ceramics operating at 16 kHz with an efficiency of 84%. In addition a variety of circuits have been designed and are currently available to optimize the electrical impedance matching. These results suggest the conversion and the electrical matching are not the limiting elements of these devices and we will show that the main impediment to increased power is the vibration source amplitude, frequency, inertia and the size limitations of the energy harvesting systems or in the case of human powered systems the requirement that the device remains unobtrusive.
Discussion and Conclusions:
Although the power densities of these devices may be limited by the source and the matching of the mechanical loads there are plenty of applications that are feasible within the available power densities due to the wonders of CMOS.
Talk #5.5:
Title: Ultrasonic Thermoacoustic Energy Conversion
Orest G. Symko (Presenter) and Myra Flitcroft, Department of Physics, University of Utah, Salt Lake City, Utah, USA.
Abstract:
Background, Motivation and Objective:
When heat is applied to one end of a stack of plates inside an acoustic resonator, sound can be generated. This is the basis of a thermoacoustic engine called a prime mover. It consists of a resonator with a working gas, a cold heat exchanger next to the stack and a hot heat exchanger against the other end of the stack; heat is injected to the hot heat exchanger. The device is driven by a temperature gradient across the stack; above a critical gradient the onset for oscillations occurs. Being a resonant system the device size scales inversely with frequency. Certain applications have advantages in reducing device size and hence to operate in the ultrasonic range. The development of the technology dealing with this frequency range and device characteristics is presented here. By coupling a piezoelectric device to the thermoacoustic engine, conversion from heat to electricity is achieved. The unit makes a compact energy converter with essentially no parts. It can be used in energy conversion applications, especially waste heat to electricity conversion.
Statement of Contribution/Methods:
In developing such small devices for the ultrasonic range it is important to scale down the critical dimensions from working audio frequency devices. With air as the working fluid the resonator (? wave resonator) length is 4.1mm for an operating frequency of 21 kHz. Heat, generated by a flame or other source, is applied to the hot heat exchanger. Above a threshold temperature difference between the hot and cold heat exchangers, acoustic oscillations are generated. Coupled to a piezoelectric device; it converts sound to electricity. Thermal interaction between the sound field and the element of the stack provides the correct phasing for sound production. This is achieved when the condition ωτ ≈ 1 is met; ω is the angular frequency of the sound and τ is a thermal relaxation time given by d2 / 2α where d = an effective distance between stack elements and α = the thermal diffusivity.
Results:
Scaling down in size thermoacoustic engines from the audio range led to miniature engines. The devices radiated sound when the injected heat created a temperature gradient above threshold. For devices 4.1mm long sound was radiated at 21kHz. Depending on the alignment of the cold and the hot parts, the temperature difference across the stack for onset of oscillations ranged from 85ºC to 180ºC.
Sound intensities outside the resonator varied with the ΔT across the stack; they reached levels of over 140dB. Generated acoustic energy is converted to electricity by means of a piezoelectric element.
Discussion and Conclusions:
Since the acoustic devices are resonant systems, large power density can be achieved with ultrasonic devices for the 20kHz unit. At an acoustic intensity of 160dB, the power density would be ~2 Watts/cm3. To achieve high power levels, an array of such devices can be formed.
The results show the potential of a thermoacoustic-piezoelectric approach in the ultrasonic range for energy conversion from heat to electricity.
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