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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 6 • Date Nov. 1997

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Displaying Results 1 - 25 of 31
  • Comments on real-space Green's function of an isolated point-charge in an unbounded anisotropic medium

    Publication Year: 1997 , Page(s): 1179 - 1180
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (158 KB)  

    The electric potential of an isolated point-charge in an unbounded anisotropic dielectric can be derived by an approach which merely involves a coordinate transformation and the knowledge of the solution to the corresponding isotropic problem. View full abstract»

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  • Dynamic shear piezoelectricity of poly(vinylidene fluoride) thin films

    Publication Year: 1997 , Page(s): 1181 - 1188
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (861 KB)  

    The shear wave properties of stretched and polarized PVDF thin films have been studied under application of a high frequency electric field parallel to the film surface. It has been found that the piezoelectric constants d/sub 15/ and d/sub 24/ do not act effectively under conditions of thickness resonance, in contrast with their large static values. This result is in severe disagreement with the symmetry predictions and raises the necessity for thorough investigation of the contribution of the amorphous phase as well as the collective behaviour of piezoelectric crystallites. View full abstract»

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  • Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound vibrational modes

    Publication Year: 1997 , Page(s): 1189 - 1197
    Cited by:  Papers (18)  |  Patents (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (995 KB)  

    Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound vibrational modes were studied. The transducers consist of coaxially segmented, longitudinally and tangentially polarized piezoelectric ceramic rings, a back metal cylinder, and a front exponential solid metal horn. Based on the plane-wave approximation, the equivalent circuits of the longitudinal and torsional vibrations in the sandwiched transducer were obtained and the resonance frequency equations of the transducer in longitudinal and torsional vibrations were derived. By means of choosing the radius decay coefficient of the front exponential horn, the longitudinal and torsional vibrations are made to resonate at the same frequency in the transducer. Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound modes were designed and fabricated according to the frequency equations. It is demonstrated that the measured resonance frequencies of the transducers are in good agreement with the theoretical results, and the measured resonance frequencies of the transducers in longitudinal and torsional vibration modes are also in good agreement with each other. Theoretical and experimental results show that this kind of transducer can be used in ultrasonic welding, ultrasonic machining, ultrasonic motors, and other ultrasonic applications which need large displacement amplitudes. View full abstract»

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  • Measurement of X-ray intensity in the medical diagnostic range by a ferroelectric detector

    Publication Year: 1997 , Page(s): 1198 - 1203
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB)  

    A pyroelectric detector is described for measuring the energy fluence rate (intensity) of X-ray pulses with duration from 0.8 to 6 seconds in the diagnostic energy range from 50 to 140 kVp corresponding to an equivalent photon energy of 29 to 45 keV. Detector response to a radiation pulse conforms to theoretical prediction based upon thermal and electrical analysis and is linear with energy fluence rate of the radiation over the range studied. The detector is small, inexpensive, rugged, and simple to construct. View full abstract»

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  • Modeling of piezoelectric multilayer ceramics using finite element analysis

    Publication Year: 1997 , Page(s): 1204 - 1214
    Cited by:  Papers (21)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1820 KB)  

    For medical ultrasound imaging, 2-D array transducers have greater versatility than linear arrays. Unfortunately, the tiny array elements in a 2-D array have poor signal-to-noise ratio (SNR). We have previously shown that SNR is increased in 2-D array transducers made from piezoelectric multilayer ceramics. Conventional one-dimensional models provide accurate results when comparing multilayer ceramic performance relative to single layer transducers. However, these models are not accurate when comparing simulations directly to measurements. Because multilayer ceramics have a complex structure, a 3-D model, such as finite element analysis, is needed for accurate simulations. We modeled four arrays that were previously fabricated: a single layer and multilayer 1 MHz, 2-D array element, and a single layer and multilayer 2.25 MHz, 1.5-D array element that can focus and steer in azimuth but only steer in the elevation dimension. We compared the simulated and measured impedance plots for each transducer. The finite element analysis plots accurately predicted the impedance for each vibration mode. On the other hand, the one dimensional KLM transmission line model could simulate only the thickness mode vibrations and the results were inaccurate compared to measurements. We also simulated the transmit output pressure for the 2.25 MHz arrays and compared the results to measurements. The simulated pressure vs. time plots and their spectra were accurate when compared to measurements. Finally, we obtained a series of images that show the impulse response vibrations for the 2.25 MHz, arrays. These animations show the vibration modes in the complex multilayer ceramic structure. Measurements were not available to confirm the animations. Our results show that finite element analysis in three dimensions is a valuable tool to predict the performance of multi-layer transducers. View full abstract»

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  • Diffraction of two optical beams by a SAW in an isotropic solid

    Publication Year: 1997 , Page(s): 1215 - 1218
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (366 KB)  

    This paper for the first time explores the diffraction of two spatially separated parallel light beams by reflection from a SAW, propagating in isotropic semi-space. In the analysis the attenuation and dispersion of SAW, the interference of light beams and scattering by different sites of acoustic wave are considered. The analytical expressions predict low-frequency oscillation of the resulting diffracted fields as observed in previous experiments. Using measurements of period oscillation of diffracted intensity vs. SAW frequency, the SAW dispersion curve and phase and group velocities were determined. View full abstract»

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  • Precise interferometric AO method for SAW velocity measurements in an anisotropic solid

    Publication Year: 1997 , Page(s): 1219 - 1223
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    We suggest an original method utilizing a two beam optical interferometer for the accurate SAW velocity measurements in an anisotropic solid. Namely, two parallel and spatially separated optical beams are diffracted from different points along the path of SAW propagation. Then at the output of the interferometer light beams of different orders (0, /spl plusmn/1) reflecting from the surface with SAW are combined in pairs to create the interference patterns. Measurement of the interference pattern's intensity oscillations versus the SAW frequency gives all needed information to determine the phase and the group SAW velocities and their dispersion. Experimental software includes: statistical data accumulation with auto correction of the interferometer phase change caused by a change of the external conditions, and Fourier analysis of interferometer signal spectrum with the use of generalized variables taking into account the SAW dispersion. The experimental error depends on the experimental peculiarities and is about 0.5 m/s for the phase velocity and 3 m/s for the group velocity. The method is tested by SAW velocity measurements on ST-quartz with a thin film of Al. View full abstract»

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  • Principles of local sound velocity and attenuation measurements using transmission acoustic microscope

    Publication Year: 1997 , Page(s): 1224 - 1231
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (898 KB)  

    Fundamentals of transmission acoustic microscopy as applied to measurements of sound velocities and attenuation in thin specimens and films are discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving lenses in the two-lens focusing system of the transmission microscope. It is proposed to measure the A(z) dependence twice: initially without a specimen, and then in the presence of it. When a specimen is absent, maximum of the A(z)-curve arises in the confocal position of the lenses. In the presence of an object, the main peak of the curve is shifted, and its magnitude diminishes. Measuring the changes makes it possible to determine local values of sound velocities and attenuation. For data interpretation a theory of formation of the output signal in the two-lens focusing system was developed. The relationship between the peak shift and the ratio of sound velocities in a specimen and a couplant contains a correction depending on beam angle aperture. View full abstract»

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  • Characterization and imaging of SAW grooved transducer acoustic field by SLAM

    Publication Year: 1997 , Page(s): 1232 - 1238
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1365 KB)  

    Quantitative characterization of the surface acoustic field radiated forward, backward, and in orthogonal directions by the grooved transducer, implemented onto a glass substrate, is accomplished by a scanning laser acoustic microscope (SLAM) operating at 31 MHz. The surface acoustic wave (SAW) amplitude is measured as a function of the number of grooves and the position of the bulk acoustic wave (BAW) transducer. The number of the operating grooves efficiently contributing to the SAW response is estimated. Remarkable reflection of the SAW beam between two identical gratings is observed. View full abstract»

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  • Impact of new high stability frequency standards on the performance of the NIST AT1 time scale

    Publication Year: 1997 , Page(s): 1239 - 1244
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (713 KB)  

    The recent addition of new commercial high stability frequency standards to the National Institute of Standards and Technology (NIST) real time AT1 time scale has resulted in significant improvements in the performance of the scale. The frequency stability of the scale at one day has increased by a factor of 2 to 4/spl times/10/sup -15/ and the stability at 100 days has improved to approximately 1/spl times/10/sup -15/. As a result UTC (NIST) has been kept within 50 ns of UTC (Coordinated Universal Time) for the last year. Further improvements are anticipated as more high performance clocks are added to the AT1 ensemble. View full abstract»

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  • Enhanced compressibility tomography

    Publication Year: 1997 , Page(s): 1245 - 1252
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1907 KB)  

    We are interested here in the inversion of data leading to high quality imaging of physical parameters. We deal with ultrasonic diffraction tomography and first show how far field diffraction measurements of an incident plane wave give access to the spatial Fourier transform of a composite object. In the case of an acoustic model (soft tissues), this object is characterized by two parameters, e.g., the compressibility and density, each being affected by its own point spread function. The development of quantitative imaging proceeds from the separation of each parameter contribution. This can be done by measuring the scattered field over an arc for several transmitter positions around the object. This allows us, under specified conditions, to reconstruct either the compressibility, or the velocity, or the impedance maps. We have focused on compressibility imaging for which we propose a novel algorithm based on a redundant reconstruction procedure. We present tomograms of biological phantoms obtained with our experimental set-up. View full abstract»

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  • Correlation receivers using Laguerre filter banks for modelling narrowband ultrasonic echoes and estimating their time-of-flights

    Publication Year: 1997 , Page(s): 1253 - 1263
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1112 KB)  

    A class of baseband correlation receivers is developed for estimating the time-of-flight of a narrowband signal. In contrast to conventional correlation receivers that contain a perfectly known replica of the signal, the signal shape is unknown to the proposed receiver. A parametric model of the signal envelope is therefore built, concurrently with the process of time-of-flight estimation. The identification of the model parameters can be pursued by assuming that a few signal constraints are satisfied at the time instant of signal onset: the constraints concern the value of the signal envelope and of its first time derivative. The correlation receivers perform a series expansion of the signal envelope by a set of Laguerre basis functions; the outputs of the Laguerre filter bank that computes the running Laguerre transform are used to build a parametric model of the unknown envelope and to estimate its time-of-flight. Simple variations of the correlation receivers are proposed, which differ from each other in the use they make of the signal constraints. The correlation receivers are applied to process narrowband echoes from in-air ultrasonic sensors. Potential applications are object identification and surface profiling in the robotic field. Computer simulations and experiments using a simple pulse-echo sensor system are presented. View full abstract»

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  • A preliminary evaluation of the effects of primary and secondary radiation forces on acoustic contrast agents

    Publication Year: 1997 , Page(s): 1264 - 1277
    Cited by:  Papers (77)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2738 KB)  

    Primary and secondary radiation forces result from pressure gradients in the incident and scattered ultrasonic fields. These forces and their dependence on experimental parameters are described, and the theory for primary radiation force is extended to consider a pulsed traveling wave. Both primary and secondary radiation forces are shown to have a significant effect on the flow of microbubbles through a small vessel during insonation. The primary radiation force produces displacement of microspheres across a 100 micron vessel radius for a small transmitted acoustic pressure. The displacement produced by primary radiation force is shown to display the expected linear dependence on the pulse repetition frequency and a nonlinear dependence on transmitted pressure. The secondary radiation force produces a reversible attraction and aggregation of microspheres with a significant attraction over a distance of approximately 100 microns. The magnitude of the secondary radiation force is proportional to the inverse of the squared separation distance, and thus two aggregates accelerate as they approach one another. We show that this force is sufficient to produce aggregates that remain intact for a physiologically appropriate shear rate. Brief interruption of acoustic transmission allows an immediate disruption of the aggregate. View full abstract»

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  • Characteristics of acoustic streaming created and measured by pulsed Doppler ultrasound

    Publication Year: 1997 , Page(s): 1278 - 1285
    Cited by:  Papers (17)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1045 KB)  

    Self measurement of acoustic streaming by Doppler ultrasound could be used to evaluate properties of fluids such as viscosity or the coagulation of blood. To characterize acoustic streaming caused by pulsed ultrasonic beams, Doppler signal processing was used to measure streaming velocity under a variety of conditions in vitro using blood and water. Velocities as high as 5 mm/s were measured in blood at the diagnostic power levels (3.5 mW) used in 20 MHz catheter velocimetry. It was found that streaming decreases with distance due to absorption and beam spreading, increases with applied acoustic power, and decreases with increased viscosity during blood coagulation. However, the increase in velocity with acoustic power is nonlinear with an exponent of 0.67 for water and 1.42 for blood even though the radiation force as measured by deflection of a suspended transducer is linear with power. The time constant of streaming to a step change in acoustic power is 80 ms in blood and 200 ms in water. It is concluded that streaming is measurable in pulsed Doppler beams, that it could produce artifacts or unintended effects, and that it could be used to characterize fluid properties and to detect coagulation of whole blood. View full abstract»

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  • Three-dimensional tissue motion and its effect on image noise in elastography

    Publication Year: 1997 , Page(s): 1286 - 1296
    Cited by:  Papers (36)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1730 KB)  

    In elastography both high correlation coefficient between pre- and post-compression RF signals and high applied strain are required to achieve the best quality in elastograms. Because the elastogram is computed using a 1-D cross-correlation technique applied to a 1-D ultrasound signal, it is assumed that tissue motion occurs only within the axis of compression (axis of the acoustic wave propagation), or at least that the scatterers remain within the acoustic beam during tissue motion. In practice, soft tissues are incompressible and, therefore, the lateral and elevational (out-of-plane) tissue strains are 50% of the applied strain. Therefore, tissue scatterers may move across the beam due to the applied compression. In this paper we address the degradation of the elastographic quality due to the lateral and elevational motion of the scatterers in uniformly elastic media. A full 3-D model predicting the correlation coefficient as measured using 1-D cross-correlations is proposed. It is shown that the signal-to-noise ratio in elastograms (SNR/sub e/) is nonstationary, and that it depends on the beamwidth and on the applied strain. In order to achieve a higher stationary SNR/sub e/, it is proposed to confine the tissue in the lateral direction. Phantom experiments are used to corroborate the theoretical developments. View full abstract»

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  • Application of the photo-elastic method to measurement of dynamic stress distribution for NS-GT cut quartz crystal resonators

    Publication Year: 1997 , Page(s): 1297 - 1303
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB)  

    NS-GT cut quartz crystal resonators are widely used as a frequency standard element in consumer products and communication equipment. The vibration mode of the resonators was analyzed by the finite element method (FEM) because they have a complicated shape. As a result, an asymmetrical vibration mode at the main resonant frequency has been obtained by the FEM simulation. But, it is necessary to confirm the asymmetrical vibration mode experimentally because it is just a simulation. In this paper, stress distributions of the NS-GT cut quartz crystal resonators are measured experimentally by using a dynamic photo-elastic method when the resonators are vibrating in the resonant frequency; thereafter, vibration modes of the NS-GT cut resonators are estimated with the experimental data of the stress distributions. This experiment for the NS-GT cut quartz crystal resonators exposes the existence of a twisted asymmetrical vibration mode at the main resonant frequency, with the magnitude of the twisted vibration in proportion to thickness of the resonators. View full abstract»

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  • An elasticity microscope. Part I: Methods

    Publication Year: 1997 , Page(s): 1304 - 1319
    Cited by:  Papers (48)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2493 KB)  

    An elasticity microscope images tissue stiffness at fine resolution. Possible applications include dermatology, ophthalmology, pathology, and tissue engineering. In addition, if the resolution approaches cellular dimensions, then this system may be very useful in understanding tissue micromorphology. Elasticity images can be reconstructed from displacement and strain fields measured throughout the specimen during controlled external loading. High frequency ultrasound is used to obtain these images by tracking coherent speckle motion during deformation. In this paper, methods are presented to track speckle in two dimensions with near unity correlation coefficients using a high frequency, single element focused transducer. These techniques include improved means for speckle tracking. Procedures to control boundary conditions for consistent specimen deformation and scanning techniques required to obtain a plane-strain state in the imaging plane are also discussed. To test these methods, a 50 MHz elasticity microscope was constructed. View full abstract»

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  • An elasticity microscope. Part II: Experimental results

    Publication Year: 1997 , Page(s): 1320 - 1331
    Cited by:  Papers (26)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3264 KB)  

    For pt.I see ibid., vol.44, no.6, pp.1304-19 (1997). Initial experimental results from a 50 MHz elasticity microscope are shown. Using methods discussed previously, we present measured displacement and normal axial strain fields from a tissue mimicking phantom. Results from this homogenous gel are compared to a finite element simulation of the deformation experiment. The spatial resolution is estimated to be approximately 52 /spl mu/m for axial displacements, and 71 /spl mu/m for normal axial strains. These estimates were further tested by imaging a phantom containing a hard cylindrical inclusion with cross-sectional diameter of 265 /spl mu/m. By examining the strain transition between regions in this image, the spatial resolution of the normal axial strain was verified to be at most 88 /spl mu/m. A typical experiment produces peak normal axial strain around 3%. These experiments demonstrate the potential of high frequency ultrasound as a means for elasticity microscopy. Preliminary deformation experiments are presented on porcine epidermis. View full abstract»

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  • An extended autocorrelation method for estimation of blood velocity

    Publication Year: 1997 , Page(s): 1332 - 1342
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1828 KB)  

    The conventional autocorrelation method (AM) to estimate the blood velocity for color flow imaging (CFI) is based on the phase estimation of the autocorrelation function. In this paper, a new extended autocorrelation method (EAM) that uses both phase and magnitude of the two dimensional (depth and temporal direction) autocorrelation function for estimating the blood velocity is presented. It is shown that the EAM has similar performance as the cross-correlation method (CCM). Both of them have smaller estimation variance than the AM and have the ability to estimate velocities beyond the Nyquist velocity, but the EAM is more computationally efficient than the CCM. A 2-D blood flow signal with rectilinear velocity including the transit time effect has also been simulated and the results are presented in this paper. For comparison, the EAM and the CCM have been applied to the simulated signals in which the flow velocities are up to four times the Nyquist velocity. The EAM has been further verified by experimental RF data from the subclavian artery. View full abstract»

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  • Acceleration sensitivity of surface wave resonators

    Publication Year: 1997 , Page(s): 1343 - 1347
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (585 KB)  

    In light of the substantial performance advantages of STW over SAW in various areas, theoretical and experimental studies of the acceleration sensitivities of STW and SAW resonators have been undertaken. The purpose of the studios has been to understand the fundamental nature of STW and SAW acceleration sensitivities, and to determine whether the performance advantages of STW seen in other areas extend to the case of acceleration sensitivity. The basic approach utilizes the perturbation theory developed by Tiersten to calculate the acceleration sensitivities of both STW and SAW resonators. The acceleration-induced bias is conveniently written in terms of acceleration-induced deformation gradients and factored elastic stiffness expressions. This representation clarifies important concepts regarding the frequency shift and the involved elastic constants, and provides the designer with insight into the basic nature of the problem. The dependencies of the normal acceleration sensitivities on substrate and mode shape parameters and the fundamental nature of plate flexure are discussed at length. The calculations compare favorably to recent experimental results. View full abstract»

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  • Development of the torque accumulation method for a torsional vibration system

    Publication Year: 1997 , Page(s): 1348 - 1354
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (866 KB)  

    This paper presents a new method to accumulate the output of several torsional transducers together into one output. The torsional transducers are connected around the circumference of a thick metal disk (the accumulator) in which the fundamental torsional mode is excited. The torque of each transducer is transmitted to the accumulator, and the accumulated torque appears on both the top and the bottom surfaces of the accumulator. The authors discuss the torque accumulation and the transformation mechanism analytically by using an equivalent electrical circuit model and obtaining the analytic expression of the torque factor, which represents the maximum output torque per unit voltage applied to the electrical port. In an experimental study, four Langevin torsional transducers 30 mm in diameter attached to an accumulator 100 mm in diameter was used as a prototype. The measured torque factor is found to be proportional to the number of connected transducers, and the calculated torque factor agrees well with the experimentally determined one. View full abstract»

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  • Phantom materials for elastography

    Publication Year: 1997 , Page(s): 1355 - 1365
    Cited by:  Papers (145)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1273 KB)  

    Acoustic and mechanical properties are reported for gelatin materials used to construct tissue-like phantoms for elasticity imaging (elastography). A device and procedure for measuring elastic properties are described. The measured compression forces were comparable to results obtained from finite element analysis when linear elastic media are assumed. Also measured were the stress relaxation, temporal stability, and melting point of the materials. Aldehyde concentration was used to increase the stiffness of the gelatin by controlling the amount of collagen cross-linking. A broad range of tissue-like elastic properties was achieved with these materials, although gels continued to stiffen for several weeks. The precision for elastic modulus measurements ranged from less than 0.1% for 100 kPa samples to 8.9% for soft (<10 kPa), sticky samples. View full abstract»

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  • Phase aberration correction in two dimensions with an integrated deformable actuator/transducer

    Publication Year: 1997 , Page(s): 1366 - 1375
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1525 KB)  

    Two-dimensional arrays are required to implement two-dimensional phase aberration correction using traditional electronic correction techniques. A new transducer design, deformable in the elevation dimension, can be used to implement two-dimensional phase correction without using a full two-dimensional array. Phase correction in azimuth is achieved by altering the electronic phase delays of the elements. Phase correction in elevation is achieved by tilting the elements in elevation with piezoelectric actuators. Previously, such deformable arrays were fabricated by bonding PZT array elements to low frequency actuators. The construction of deformable arrays is simplified by using the actuator for both the element deflection and the generation of ultrasound. The new construction technique was used to fabricate a prototype 1/spl times/32 deformable array with a 3.5 MHz center frequency and an actuator flexure resonance of 3/spl deg/ at 1.3 kHz with a 300 Vpp sine wave. The prototype array was characterized and used to make B-scan images. Phase correction was simulated by tilting the elements on-line to alter the B-scan image and resulted in a cyst contrast reduction from 0.86 for the control to 0.76 with the elements tilted. Further characterization of the deformable array performance includes the frequency response of the actuator. Initial results from a 2/spl times/32 deformable array fabricated with the new construction technique are also presented. The 2/spl times/32 array configuration additionally offers the potential for on-line elevation focusing. View full abstract»

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  • Temperature coefficient of sensitivity dependence of the measurement error of quartz crystal resonators

    Publication Year: 1997 , Page(s): 1376 - 1381
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB)  

    This paper discusses the measurement error of quartz crystal resonators (QXRs) vs. the temperature coefficient of force sensitivity. Based on the analysis of the difference between the temperature coefficient of frequency and the temperature coefficient of force sensitivity, the measurement error formula is deduced. According to the error formula, the physical significance of the temperature coefficient of force sensitivity is explained, and the method of selecting a scale temperature is given. The measurement error formula has been verified recently by experimental results. To expand the selectable range of cut modes and to compare the performances of QXRs, the selecting principle of the best group of the angles of cut of quartz crystal plate, /spl theta/, /spl thetav/, and azimuth angle of applied force, /spl psi/ is given simultaneously. According to the measurement error formula and the selecting principle of the best group of the angles, the best azimuth angle of AT-cut used as force sensitive resonators is found through the analysis of the measurement error. This paper provides a theoretical basis on which the measurement accuracy of QXR force sensors can be improved. View full abstract»

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  • Two-dimensional ultrasonic flaw detection based on the wavelet packet transform

    Publication Year: 1997 , Page(s): 1382 - 1394
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2359 KB)  

    An important issue in ultrasonic nondestructive evaluation is the detection of flaw echoes in the presence of coherent background noise associated with the microstructure of materials. Many signal processing techniques have proven to be useful for this purpose, but fully 2-D flaw detection techniques remain desirable. In this paper, we describe a novel automatic flaw detection method based on the wavelet packet transform, which is particularly well adapted to B-scan image analysis. After a brief review of the essential elements of the theory of wavelets and wavelet packets, a detailed description of the method is provided. The detection process operates on a set of spatially oriented frequency channels, i.e., detail images, obtained from successive wavelet packet decompositions of the initial B-scan. A statistical selection procedure based on the modeling of the detail image histograms retains the useful information-bearing frequency channels. The flaw information is then extracted from these selected channels by means of a specific thresholding scheme. Some experimental detection results in B-scan images of austenitic stainless steel samples comprising artificial flaws are presented. 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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