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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 4 • Date July 1996

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Displaying Results 1 - 25 of 30
  • IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society Distinguished Lecturer Award: The Se

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  • Achievement Award of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society

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  • 1994 Outstanding Paper Award of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society

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  • Finite element simulation of piezoelectric vibrator gyroscopes

    Page(s): 509 - 518
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    A finite element approach to the simulation of piezoelectric vibrator gyroscopes is presented for characteristic prediction. The formulation is given including the effect of Coriolis force due to rotation for a piezoelectric thin plate, which is considered to be two-dimensional in plane vibration. For numerical examples, the gyroscopes of a thin square plate, and a cross-bar and a ring built in the plate are considered, which pave the way for the development of the gyroscopes of monolithic configuration. The effect of the rotation on the modal shapes, the resonant frequencies, and the transmission characteristics are discussed demonstrating the sensing capability against the rotation. View full abstract»

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  • Characterization of optoacoustic surgical devices

    Page(s): 519 - 526
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    Describes a measurement technique specially developed to characterize optoacoustic sources. The technique provides a convenient baseline for a comparison of different surgical ultrasonic systems utilizing optoacoustic and ultrasonic transducers. In addition, it provides a well-defined tool to optimize the performance of a variety of designs. Attention is focused on the laser-assisted devices in which appropriately delivered light energy is converted into acoustic shock wave. A meaningful comparison of such devices with other therapeutic equipment designed for a direct interaction with tissue requires knowledge of energy needed for a successful surgical treatment. It is demonstrated that knowledge of the key shock wave parameters allows the total acoustic energy associated with the shock wave to be determined. The procedure developed to calculate this energy is discussed and it is shown that the value of this energy can be conveniently used as an indicator of efficacy of an optoacoustic converter in a clinical environment. The influence of the performance of the polyvinylidene fluoride (PVDF) hydrophone probes on the measurement results was also analyzed. It was determined that when appropriately selected, the wide-band PVDF probes are well suited for characterization of the optoacoustic devices in the frequency range 1-100 MHz. The characterization procedure developed is applicable to surgical ultrasonic systems including conventional and laser-assisted phacoemulsifiers. View full abstract»

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  • Multistrip couplers for surface acoustic wave sensor application

    Page(s): 527 - 530
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    We present a new surface acoustic wave gas sensor utilizing a multistrip coupler on LiNbO/sub 3/ and LiTaO/sub 3/ substrates and using copper phthalocyanine as a sensor layer for NO/sub 2/. The sensor signal originates from surface conductivity changes induced by the adsorbed NO/sub 2/. This variation in conductivity leads to a changing coupling efficiency of the multistrip coupler and thus to variations in the insertion loss of the device. Rayleigh and shear wave devices with operating frequencies of 170 and 243 MHz have been tested. A sensitivity of better than 1 ppb NO/sub 2/ in air was achieved. View full abstract»

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  • High-frequency ultrasonic cleaning tank utilizing oblique incidence

    Page(s): 531 - 535
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    Transmission characteristics of a double-structured tank, used for high-frequency (1 MHz range) ultrasonic cleaning of semiconductor wafers and substrates, were improved by utilizing oblique incidence of ultrasonic waves. As the sound transmittivity through a plate in water varies with the angle of incidence, the bottom of the Pyrex glass inner container was slanted at the angle where strong transmission occurred. In the slant-bottom container, an intensive and uniform sound pressure distribution was measured with a polyvinylidene fluoride (PVDF) hydrophone probe. In comparison with the conventional horizontal-bottom container, it was shown that the distributions as well as amplitude of sound pressure were remarkably improved by slanting the bottom of the inner container at the proper angle. View full abstract»

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  • High-frequency membrane hydrophone

    Page(s): 536 - 544
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    A membrane hydrophone with a 37-/spl mu/m diameter spot poled electrode has been fabricated on a 4-/spl mu/m-thick film of the piezoelectric copolymer, polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), and initially characterized. The hydrophone has an effective spot size of less than 100 /spl mu/m, an on-membrane +7-dB gain buffer amplifier, and a -3-dB bandwidth of 150 MHz. The acoustic properties of the hydrophone were investigated with a transducer equivalent circuit model, the electric fringe fields due to poling were characterized with a finite difference electrostatic field model, and the effective spot diameters 2a/sub 3/ and 2a/sub 6/ were estimated. Measurements on the bandwidth, effective spot size, and sensitivity are presented. This hydrophone appears suitable for the characterization of both the frequency and spatial parameters of high-frequency transducers such as intravascular ultrasound (IVUS) catheter transducers operating in the 10-40 MHz range. View full abstract»

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  • A 100-MHz ultrasound imaging system for dermatologic and ophthalmologic diagnostics

    Page(s): 545 - 552
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    A major design problem concerning high-frequency broad-band ultrasound imaging systems is caused by the strong dispersive attenuation of the tissue, which gives rise to images with inhomogeneous resolution and poor signal to noise ratio (SNR). To address the noise problem, strongly focused transducers with high energy density in a narrow focal region are utilized, which also provide more isotropic images due to improved lateral resolution. To account for the short depth of the focal area two suitable imaging conceptions are used: 1) synthetic aperture concept and 2) B/D-scan concept. To avoid the inhomogeneity of the images, different transmitter signals for each depth are applied, which are pseudoinversely prefiltered according to the transfer function of the tissue. To gain signal energy required for inverse filtering, a pulse compression technique with nonlinearly frequency modulated chirp signals is utilized. These procedures have been implemented in an ultrasound imaging system, which has been developed in the authors' laboratory for eye and skin examinations, It can be used with transducers in a frequency range from 20 to 250 MHz. View full abstract»

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  • Micromachined piezoelectric force sensors based on PZT thin films

    Page(s): 553 - 559
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    A micromachined lead zirconate titanate (PZT) force sensor for scanning force microscope (SFM) is conceptualized by its piezoelectricity. The fabrication procedure is interpreted, and mechanical characteristics of the micromachined PZT force sensors with various lengths are studied in this paper. A compact SFM is constructed by using the piezoelectric PZT sensor. A very clear image is taken by this SFM. The current study of the micromachined PZT force sensor can be considered as a breakthrough of design of SFM as well as a good example of integrated piezoelectric microdevices. View full abstract»

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  • Disposable PVDF ultrasonic transducers for nondestructive testing applications

    Page(s): 560 - 568
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    Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant /spl epsi//sub r/, dielectric loss tangent tan /spl delta//sub e/, electromechanical coupling constant k/sub t/, mechanical quality factor Q/sub m/, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80/spl deg/C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested. View full abstract»

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  • Acoustic transfer function of the clamp-on flowmeter

    Page(s): 569 - 575
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    An angular spectrum approach is used to derive the acoustic transfer function of the clamp-on flowmeter. The flowmeter factor is calculated as a function of the position of the transducers by numerical evaluation of the transmission function. This method enables high measurement accuracy even in the case of the practically unavoidable mispositioning of the transducers. Simulations and measurement results show the influence of the transducer aperture and the pipe wall on the flowmeter factor. View full abstract»

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  • Acquisition and stereoscopic visualization of three-dimensional ultrasonic breast data

    Page(s): 576 - 580
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    A motorized mechanical setup has been designed to provide a series of two-dimensional (2-D) parallel echographic slices of the breast from the regular translation of a linear phased array transducer. During the acquisition step, the breast is compressed between a plane support and a plexiglass plate to avoid breast motions. A stereoscopic computer graphic method has been developed for the visualization of such three-dimensional (3-D) ultrasonic data. Experiments on an agar gel phantom and on in vivo female breasts have been performed. View full abstract»

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  • Flaw identification from time and frequency features of ultrasonic waveforms

    Page(s): 592 - 600
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    Time and frequency features have been used with classification algorithms to distinguish between ultrasonic echoes from flaws in pipes and ultrasonic echoes from various geometric configurations of weld root and counterbore. Waveforms containing reflections from known geometries and from flaws were obtained and sets of features were defined using a k-nearest neighbor approach to separate waveforms into classes. Two independent databases containing various flaws and pipe geometries were used to determine these feature sets. From these databases, optimal feature sets were found to separate counterbore waveforms from crack waveforms. Optimal feature sets were also found to distinguish between waveforms from counterbore, waveforms containing both counterbore and root echoes, and waveforms from flaws. The best feature sets used with the classifier algorithms could separate waveforms from the same database with accuracy in the 92-97% range and with high confidence., Another database was obtained from pipe structures in a nuclear power plant to provide a field test of the method. When applied to this database, the same classifier algorithms and feature sets used with the other databases either resulted in a comparable percentage of correct decisions, but with low confidence, or could not classify anywhere from 79 to 88% of the waveforms. Spatial parameters based on averaging feature vectors in axial and circumferential directions were also defined and used for classification. These classifications had higher accuracy but lower confidence levels than the classifications based on individual waveforms. View full abstract»

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  • Development and application of mass sensors based on flexural resonances in alumina beams

    Page(s): 601 - 608
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    New mass sensors are described, which are based on the change in the flexural resonant frequencies of ceramic cantilever beams subject to piezoelectric excitation. The devices have been fabricated by screen-printing and firing a PZT-based paste on 96% alumina substrates with the methods of thick film technology and are, therefore, low cost and easy to manufacture. Inserted in an electronic feedback loop sustaining and tracking oscillations at one of the resonant frequencies, the sensors work as resonant microbalances with frequency output and can be employed for gravimetric chemical measurements. The beams have been implemented in two different sizes and, as a consequence, operated at different frequencies (about 82 and 149 kHz), in order to vary the mass sensitivity. The sensors' manufacturing and theory of operation are illustrated, and experimental results on their characterization are reported. For the two sensor sizes, mass sensitivities of about -280 and -1200 Hz/mg have been measured, in agreement with theoretical predictions. The influence of temperature has been investigated showing that, for slow thermal drifts, a satisfying degree of compensation can be achieved with a differential configuration. The devices have been successfully applied as sorption sensors for the measurement of air relative humidity (RH) by sensitizing the beams' surface with hydrophilic polymeric coatings. On the basis of past investigations, poly(N-vinylpyrrolidinone) and poly(ethyleneglycol) have been adopted as coating materials, obtaining respective frequency shifts of about 500 and 1400 Hz for RH ranging from 12 to 85%. View full abstract»

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  • Multilayer piezoelectric resonators for medical ultrasound transducers

    Page(s): 620 - 622
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    Multilayer piezoelectric resonators were fabricated and the dependence of the electrical impedance and the coupling coefficient were measured as a function of the number of layers, for N=1, /spl middot//spl middot//spl middot/, 20 layers. The magnitude of the electrical impedance followed the theoretical predicted 1/N/sup 2/ relation, and the coupling coefficient, K/sub t/, remained relatively constant out to N=15 layers. These cofired resonators are suitable for medical ultrasound transducers. View full abstract»

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  • Reduction of cavitation using pseudorandom signals [therapeutic US]

    Page(s): 623 - 625
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    It is known that the scattering of ultrasound by cavitation bubbles reduces the efficiency of treatment by high-intensity focused ultrasound. In the authors' experiments striving to reduce grating lobe levels of annular arrays they observed less microbubble formation at the focus of the transducer when pseudorandom phase-modulated CW signals were used rather than single-frequency CW signals. To confirm this unexpected result, the authors performed an experiment in a solution of luminol which is known to be a cavitation detector. A 5-cm diameter spherical transducer (1.1 MHz center frequency and 0.6 MHz bandwidth), focused at 197 mm was used. The ratio of the sonoluminescence intensity produced by a single-frequency signal to that produced by a pseudorandom phase-modulated signal increased with the intensity of the applied held and attained a value of nearly 50 for an intensity of 4.6 W cm/sup -2/. View full abstract»

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  • A network analyzer-based tissue characterization system

    Page(s): 626 - 627
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    A novel ultrasound tissue characterization system is described which utilizes a network analyzer, S-parameter test set, 180/spl deg/ hybrid junction, and a mock transducer circuit to exploit the wide-band potential of a commercial piezoelectric polymer transducer. The relatively short round-trip pulselength achieved using the system (70 ns in water) is compared to that obtained using a high-frequency pulser/receiver and the same transducer (130 ns in water). Finally, the in vitro acoustic response of a section of neonate porcine carotid artery obtained using the network analyzer-based system is reported, along with histologic results for the same vessel. View full abstract»

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  • A global system identification approach for the accurate parametric modeling of ultrasonic reflection and transmission experiments

    Page(s): 628 - 639
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    This paper presents a global system identification approach for the parametric modeling of both reflection and transmission experiments performed on a linear homogeneous visco-elastic material at normal incidence. It is shown that this global approach leads to improved estimates of the parameters occuring in the analytical model for the reflection and transmission coefficients of a visco-elastic plate immersed in water. The plane wave propagation model takes into account the absorption and dispersion in the material as well as an analytic diffraction correction for the beam spread. The proposed inverse procedure Is based on a maximum likelihood estimator. View full abstract»

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  • Experimental verification of the theory of elastic properties using scattering approximations in (0-3) connectivity composite materials

    Page(s): 640 - 645
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    New methods of estimating effective macroscopic elastic constants for inhomogeneous materials have recently been proposed using elastic-wave scattering theory. However, there are few experimental measurements which allow the validation of these models. The purpose of this paper is to verify if the scattering approximation theories allow prediction of the acoustic properties of epoxy composites containing tungsten powder for various particle sizes and various volume fractions of filler. The theoretical predictions are compared with the experimental results and the different models are discussed. View full abstract»

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  • Properties of interdigital transducers in relation to the substrate crystal symmetry

    Page(s): 646 - 653
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    Exclusively from the crystal symmetry, we obtain results concerning properties of interdigital transducers radiating Rayleigh waves along high-symmetrical crystal directions. Three cases of high-symmetrical directions are considered: the propagation direction is parallel to a rotation axis, perpendicular to a mirror plane, or parallel to a rotoinversion axis of the substrate crystal. In respect to the symmetry properties of the piezoelectric tensor related to a mirror operation on a plane perpendicular to the propagation direction, the three original cases can be concentrated in three symmetry cases. The crystal symmetry determines the properties of the piezoelectric tensor, and consequently the wave excitation by transducers. These considerations enable one to ascertain the positions of the transduction centers and the influence of internal reflections to the amplitude characteristics. Furthermore, we are able to discuss natural single-phase unidirectional transducer (NSPUDT) effects in layer structures, the old question "crossed-field or in-line model", and the existence of cross-coupling of waves, similar to multistrip couplers, in interdigital transducers (IDTs). The theoretical predictions are compared with our own and other authors' experimental results. View full abstract»

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  • Spectral velocity profiles for detailed ultrasound flow analysis

    Page(s): 654 - 659
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    The operation of a novel ultrasound multigate instrument capable of computing in real-time the fast Fourier transform (FFT) of Doppler signals detected from 64 equally spaced range cells is presented. The new system provides up to 50 velocity profiles per second, which are displayed in such a manner that information about the full spectral content of Doppler signals at all the investigated depths is continuously monitored over a PRF-wide frequency range which can be set arbitrarily between -PRF and +PRF. Experimental results are presented, which demonstrate that the true velocity profile can be accurately detected through the computation of "local" maximum velocities obtained by properly correcting the maximum frequency of each spectrum. There is also a discussion on how the results of multigate analysis are influenced by the sample volume length, a parameter which can be usually set by modifying the duration of the transmitted burst. In particular, it is shown that, in regions close to the vessel walls, the shear rate can be measured with a spatial resolution related to the spacing between subsequent range cells and not to the sample volume length. View full abstract»

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  • Markov models of specular and diffuse scattering in restoration of medical ultrasound images

    Page(s): 660 - 669
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    Observed medical ultrasound images are degraded representations of the true tissue reflectance. The specular reflections at boundaries between regions of different tissue types are blurred, and the diffuse scattering within such regions also contains speckle. This reduces the diagnostic value of such images. In order to remove both blur and speckle, the authors develop a maximum a posteriori deconvolution algorithm for two-dimensional (2-D) ultrasound radio frequency (RF) images based on a new Markov random field image model incorporating spatial smoothness constraints and physical models for specular reflections and diffuse scattering. During stochastic relaxation, the algorithm alternates steps of restoration and segmentation, and includes estimation of reflectance parameters. The smoothness constraints regularize the overall procedure, and the algorithm uses the specular reflection model to locate region boundaries. The resulting restorations of some simulated and real RF images are significantly better than those produced by Wiener filtering. View full abstract»

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  • Finite element analysis of multilevel acoustic Fresnel lenses

    Page(s): 670 - 677
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    Fresnel lenses have recently emerged as viable alternatives to conventional spherical lenses for focusing ultrasonic waves in acoustic microscopy systems. Although these lenses are relatively straightforward to manufacture, their bulk represents a major handicap. A remedy to this problem is to use multilevel acoustic Fresnel lenses. Multilevel lenses are surface relief structures that can be fabricated very precisely using existing VLSI semiconductor technology. However, accurate tools for designing lenses to achieve the desired efficiency and power specifications are not available. This paper presents a finite element study of multilevel acoustic Fresnel lenses. Results showing ultrasonic wave propagation through such surface relief structures together with the resulting diffraction profiles are presented. The high efficiency and focusing power of these lenses are also demonstrated. Simulation results together with a discussion on various multilevel lens design issues are presented. These results confirm the advantages of such lenses, and suggest that the finite element model can serve as a valuable tool for designing, simulating, and studying lens profiles prior to their fabrication. View full abstract»

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  • Characterization of air-coupled transducers

    Page(s): 678 - 689
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    This paper describes a theoretical and experimental study for determination of the through-air system impulse response and insertion loss with different air-coupled ultrasonic transducers. Wide-band piezopolymer transducers (PVDF) are employed in both transmission and reception modes and their behavior assessed by means of mathematical modeling and experiment. Specifically, a linear systems approach, modified to include the influence of attenuation in the propagation medium, was used to design suitable PVDF transducers for wide-band operation in air. Suitable devices were then manufactured for determination of the transmission and reception response characteristics of piezocomposite and electrostatic transducers when operating in the air environment. A range of transducers was evaluated, including 1-3 connectivity composites of different ceramic volume fraction and mechanical matching conditions, in addition to electrostatic devices of varying design. To complement the investigation, relative performances for narrow-band operation are also presented under transmission and transmit-receive conditions. Despite the obvious measurement difficulties, good agreement between theory and experiment was observed and the methodology is shown to provide a convenient and robust procedure for comparison of through-air transducers operating in the frequency range 50 KHz to 2 MHz. Although highly resonant, the most effective composite transducers under consideration demonstrate an improvement in two-way insertion loss of 22.4 dB and 11.5 dB over a corresponding electrostatic pair, under narrow-band and wide-band operation, respectively. View full abstract»

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Aims & Scope

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control focuses on the theory, design, and application on generation, transmission, and detection of bulk and surface mechanical waves.

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Editor-in-Chief
Steven Freear
s.freear@leeds.ac.uk