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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 6 • Date Nov. 1999

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Displaying Results 1 - 25 of 33
  • Simulation and experimental characterization of a 2-D capacitive micromachined ultrasonic transducer array element

    Publication Year: 1999 , Page(s): 1337 - 1340
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (147 KB)  

    In this letter, a 400-/spl mu/m/spl times/400-/spl mu/m 2-D capacitive micromachined ultrasonic transducer (cMUT) array element is experimentally characterised, and the results are found to be in good agreement with theoretical predictions. As a receiver, the transducer has a 1.8/spl times/10/sup -7/ nm//spl radic/(Hz) displacement sensitivity, and, as a transmitter, it produces 16.4 kPa/V of output pressure at the transducer surface at 3 MHz. The transducer also has more than 100% fractional bandwidth around 3 MHz, which makes it suitable for ultrasound imaging. View full abstract»

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  • Tunable optical oscillator based on a DFB-MQW laser and a fiber loop reflector

    Publication Year: 1999 , Page(s): 1341 - 1342
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (82 KB)  

    In this paper, we report experimental results on the frequency control of an optical oscillator based on a single-cavity DFB-MQW laser and a fiber loop reflector. Self-pulsation frequency can be controlled by changing the step amplitude of the laser bias current. View full abstract»

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  • Constitutive equations of symmetrical triple layer piezoelectric benders

    Publication Year: 1999 , Page(s): 1343 - 1351
    Cited by:  Papers (46)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB)  

    Piezoelectric triple layer benders, with a structure of two piezoelectric top and bottom layers sandwiched by a non-piezoelectric elastic central layer, are one of the most commonly used piezoelectric devices. In this paper, we present the derivation of the constitutive equations of a symmetrical triple layer piezoelectric bender under different excitation conditions. The constitutive equations are presented by a 4/spl times/4 matrix with an external moment M, an external tip force F, a uniform load p, and an applied electric voltage V as the extensive parameters, with the generated tip angular deflection (slope) /spl alpha/, tip deflection /spl delta/, volume displacement v, and electric charge Q as the internal parameters. Further analysis on the electromechanical behavior of the triple layer piezoelectric bender can be made on the constitutive equations. View full abstract»

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  • Finite element analysis of a deformable array transducer

    Publication Year: 1999 , Page(s): 1352 - 1363
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    Deformable array transducers have previously been described to implement 2-D phase aberration correction of near-field aberrators with only a 1/spl times/N or 2/spl times/N array configuration. This transducer design combines mechanical phase correction using an actuator with electronic phase correction for a 2-D correction with significantly fewer elements than a full 2-D array. We have previously reported the fabrication and results of a 1/spl times/32 deformable array fabricated with a RAINBOW (Reduced And INternally Biased Wafer) actuator. Because of the complicated construction of deformable arrays, we propose to use finite element analysis (FEA) as a design tool for array development. In this paper, we use 2-D and 3-D FEA to model the experimental results of the deformable array as the first step toward development of a design tool. Because the deformable array combines a mechanical actuator with a medical ultrasound transducer, improvement in performance must consider both the ultrasound characterization along with the low frequency actuator characterization. For the ultrasound characterization, time domain FEA simulations of electrical vector impedance accurately predicted the measurements of single array elements. Additionally, simulations of pulse-echo sensitivity and bandwidth were also well matched to measurements. For the low frequency actuator characterization, time domain simulation of the low frequency vector impedance accurately predicted measurement and confirmed the fundamental flexure resonance of the cantilever configuration at 1.3 kHz. Frequency domain FEA included thermal processing effects and predicted actuator curvature arising during fabrication. Finally, frequency domain FEA simulations of voltage-induced displacement accurately predicted measured displacement. View full abstract»

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  • Theory and analysis of electrode size optimization for capacitive microfabricated ultrasonic transducers

    Publication Year: 1999 , Page(s): 1364 - 1374
    Cited by:  Papers (45)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Theoretical analysis and computer simulations of capacitive microfabricated ultrasonic transducers indicate that device performance can be optimized through judicious patterning of electrodes. The conceptual basis of the analysis is that electrostatic force should be applied only where it is most effective, such as at the center of a circular membrane. If breakdown mechanisms are ignored, an infinitesimally small electrode with an infinite bias voltage results in the optimal transducer. A more realistic design example compares the 3-dB bandwidths of a fully metalized transducer and a partially metalized transducer, each tuned with a lossless Butterworth network. It is found that the bandwidth of the optimally metalized device is twice that of the fully metalized device. View full abstract»

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  • Curved PVDF airborne transducer

    Publication Year: 1999 , Page(s): 1375 - 1386
    Cited by:  Papers (19)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    In the application of airborne ultrasonic ranging measurement, a partially cylindrical (curved) PVDF transducer can effectively couple ultrasound into the air and generate strong sound pressure. Because of its geometrical features, the ultrasound beam angles of a curved PVDF transducer can be unsymmetrical (i.e., broad horizontally and narrow vertically). This feature is desired in some applications. In this work, a curved PVDF air transducer is investigated both theoretically and experimentally. Two resonances were observed in this transducer. They are length extensional mode and flexural bending mode. Surface vibration profiles of these two modes were measured by a laser vibrometer. It was found from the experiment that the surface vibration was not uniform along the curvature direction for both vibration modes. Theoretical calculations based on a model developed in this work confirmed the experimental results. Two displacement peaks were found in the piezoelectric active direction of PVDF film for the length extensional mode; three peaks were found for the flexural bending mode. The observed peak positions were in good agreement with the calculation results. Transient surface displacement measurements revealed that vibration peaks were in phase for the length extensional mode and out of phase for the flexural bending mode. Therefore, the length extensional mode can generate a stronger ultrasound wave than the flexural bending mode. The resonance frequencies and vibration amplitudes of the two modes strongly depend on the structure parameters as well as the material properties. For the transducer design, the theoretical model developed in this work can be used to optimize the ultrasound performance. View full abstract»

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  • An investigation of the effects of material anisotropy and heterogeneity on pulsed, laser-generated acoustic signals

    Publication Year: 1999 , Page(s): 1387 - 1395
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB)  

    Point-source and line-source models for the laser ultrasonic source in materials exhibiting transverse isotropy are applied to the specific problem of laser generation and ultrasonic propagation in unidirectional, polymer matrix composite materials. Comparing experiment and theory, it is shown that these composite materials exhibit homogeneous behavior, at the frequencies investigated, for ultrasonic wave propagation perpendicular to the fiber direction. For ultrasonic propagation in the fiber direction, ultrasonic dispersion, resulting from the inhomogeneous nature of the composite, affects the laser ultrasonic signal. View full abstract»

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  • Thermal transient model of a crystal resonator employing thickness-shear vibrations

    Publication Year: 1999 , Page(s): 1396 - 1406
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (341 KB)  

    This paper presents an improved model of thermally induced frequency transients in vacuum-enclosed thickness-shear mode quartz crystal resonators. The response times to temperature changes for different parts of the resonator and resulting thermal dynamic coefficients are examined and are related to Ballato's coefficient through a function defined by the resonator design, dependent on thermal response times only. A method is worked out for response time calculations for the different contributions to the static and dynamic temperature behavior of general and anharmonic modes. The model has been used to examine thermally induced frequency transients of the AT-cut resonator h/sub 513/ anharmonic mode excited by the modulational method within an ovenized Colpitts oscillator. A good agreement is shown between the predicted curves and experimental data over a variety of temperature ranges. View full abstract»

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  • Wavelet transform-based strain estimator for elastography

    Publication Year: 1999 , Page(s): 1407 - 1415
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    A new signal processing algorithm based on a wavelet transform (WT) is proposed for instantaneous strain estimation in acoustic elastography. The proposed estimator locally weighs ultrasonic echo signals acquired before tissue compression by a Gaussian window function and uses the resulting waveform as a mother wavelet to calculate the WT of the postcompression signal. From the location of the WT peak, strain is estimated in the time-frequency domain. Because of the additive noise in signals and the discrete sampling, errors are commonly made in estimating the strain. Statistics of these errors are analyzed theoretically to evaluate the performance of the proposed estimator. The strain estimates are found to be unbiased, but error variances depend on the signal properties (echo signal-to-noise ratio and bandwidth), signal processing parameter (time-bandwidth product), and the applied strain. The results are compared with those obtained from the conventional strain estimator based on time-delay estimates. The proposed estimator is shown to offer strain estimates with greater precision and potentially higher spatial resolution, dynamic range, and sensitivity at the expense of increased computation time. View full abstract»

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  • High frame rate imaging with a small number of array elements

    Publication Year: 1999 , Page(s): 1416 - 1421
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (285 KB)  

    Recently, a high frame rate imaging method has been developed to construct either 2-D or 3-D images (about 3750 frames or volumes/s at a depth of about 200 mm in biological soft tissues because only one transmission is needed). The signal-to-noise ratio (SNR) is high using this method because all array elements are used in transmission and the transmit beams do not diverge. In addition, imaging hardware with the new method can be greatly simplified. Theoretically, the element spacing (distance between the centers of two neighboring elements) of an array should be /spl lambda//2, where /spl lambda/ is the wavelength, to avoid grating lobes in imaging. This requires an array of a large number of elements, especially, for 3-D imaging in which a 2-D array is needed. In this paper, we study quantitatively the relationship between the quality of images constructed with the new method and the element spacing of array transducers. In the study, two linear arrays were used. One has an aperture of 18.288 mm, elevation dimension of 12.192 mm, a center frequency of 2.25 MHz, and 48 elements (element spacing is 0.381 mm or 0.591 /spl lambda/). The other has a dimension of 38.4 mm/spl times/10 mm, a center frequency of 2.5 MHz, and 64 elements (0.6 mm or 1.034 /spl lambda/ element spacing). Effective larger element spacings were obtained by combining signals from adjacent elements. Experiments were performed with both the new and the conventional delay-and-sum methods. Results show that resolution of constructed images is not affected by the reduction of a number of elements, but the contrast of images is decreased dramatically when the element spacing is larger than about 2.365 /spl lambda/ for objects that are not too close to the transducers. This suggests that an array of about 2.365 /spl lambda/ spacing can be used with the new method. This may reduce the total number of elements of a fully sampled 128/spl times/128 array (0.5 /spl lambda/ spacing) from 16384 to about 732 c- nsidering that the two perpendicular directions of a 2-D array are independent (ignoring the larger element spacing in diagonal directions of 2-D arrays). View full abstract»

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  • Modeling resonance tests for electrostrictive ceramics

    Publication Year: 1999 , Page(s): 1422 - 1430
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    The electromechanical coupling coefficient represents a useful figure-of-merit for comparing the quality of different electroactive materials. However, the coupling coefficient for an electrostrictive ceramic is not a unique material parameter, because it depends strongly on the applied DC bias field, AC field amplitude and frequency, and stress. These dependencies make direct comparison between electrostrictors and piezoelectrics somewhat ambiguous. In this paper, we developed a pair of coupling parameters for electrostrictors that were strictly material constants and completely characterized the material's electromechanical quality. We proposed relatively simple, inexpensive resonance testing to measure these new parameters from the electrical admittance of a vibrating electrostrictive rod. The electromechanical coupling coefficient for a specific loading condition is computed from these parameters, allowing direct comparison between electrostrictive and piezoelectric materials. View full abstract»

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  • Fast three-step method for shear moduli calculation from quartz crystal resonator measurements

    Publication Year: 1999 , Page(s): 1431 - 1438
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    Quartz crystal resonator measurements can be used for polymer material characterization. The non-gravimetric regime of these resonators is exploited: the electrical response of polymer-coated quartz resonators depends on the polymer shear modulus. Previously reported methods employ an electrical admittance analysis together with difficult and time-consuming data fitting procedures to calculate the film shear modulus. This contribution presents a fast and accurate three-step method for the calculation of complex shear moduli of polymer films from quartz crystal resonator measurements. In the first step, the acoustic load impedance is calculated from the electrical admittance of the quartz crystal. The key point of this method is the application of a family of approximations for the calculation of the shear modulus from the acoustic load impedance in the second step. In the third step, the best approximation is improved further in an iterative procedure. View full abstract»

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  • A smooth impact rotation motor using a multi-layered torsional piezoelectric actuator

    Publication Year: 1999 , Page(s): 1439 - 1445
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB)  

    A smooth impact rotation motor was fabricated and successfully operated using a torsional piezo actuator. Yoshida et al. reported a linear type smooth impact motor in 1997. This linear motor demonstrated a high output force and a long stroke. A superior feature of the smooth impact drive is a high positioning resolution compared with an impact drive. The positioning resolution of SIDM (smooth impact drive mechanism) is equal to the piezo displacement. The reported positioning resolution of the linear type was 5 nm. Our rotation motor utilized a torsional actuator containing multi-layered piezoelectric material. The torsional actuator was cylindrical in shape with an outer diameter of 15 mm, an inner diameter of 10 mm, and a length of 11 mm. Torsional vibration performance was measured with a laser Doppler vibrometer. The obtained torsional displacement agreed with the calculated values and was sufficient to drive a rotor. The rotor was operated with a saw-shaped input voltage (180 V; 8 kHz). The revolution direction was reversible. The maximum revolution speed was 27 rpm, and the maximum output torque was 56 gfcm. In general, smooth-impact drives do not show high efficiency; however, the level of efficiency of our results (max., 0.045%) could be increased by improving the contact surface material. In addition, we are studying quantitative consideration, for example, about the optimum pre-load or frictional force. View full abstract»

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  • Investigation on piezoelectric helix for use as a hydrophone

    Publication Year: 1999 , Page(s): 1446 - 1449
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    The piezoelectric helical spring is analyzed for use as a hydrophone. Because the polarity in the helix is arranged parallel to the electrode planes, the shear mode, g/sub 15/ can perform the elastoelectric conversion without any undesired couplings under hydrostatic condition. In this paper, the structural effects are modeled using the concept of stress amplifier. The gain factor, G, is defined as the ratio of the average stress in the piezoceramic to the detected pressure and, therefore, provides a G-fold increase in voltage responsivity. In addition, a solution for increasing the capacitance while maintaining the sensitivity is proposed. Numerical results showing high hydrostatic responsivities are given. View full abstract»

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  • Efficient transmit beamforming in pulse-echo ultrasonic imaging

    Publication Year: 1999 , Page(s): 1450 - 1458
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    A high performance ultrasound imaging system requires accurate control of the amplitude of the array elements, as well as of the time delays between them, both in the transmit and receive modes. In transmission, conventional array aperture windowing implies a different driving voltage for each element of the array, an expensive solution for systems with a large number of channels. In this paper, we present a simple, versatile, and inexpensive beamforming method that operates the aperture windowing in the transmit mode, simply controlling the lengths of the electric pulses driving the array elements. Computer simulations and experimental measurements are presented for different types of arrays. They confirm that the proposed beamforming technique improves the contrast resolution of the imaging system, reducing the off-axis intensity of the radiated field pattern. Moreover, the axial resolution is slightly enhanced, because the overall length of the transmitted ultrasonic pulse is reduced. View full abstract»

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  • Evaluation of the unscanned soft-tissue thermal index

    Publication Year: 1999 , Page(s): 1459 - 1476
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1947 KB)  

    The monopole-source solution was used to calculate the three-dimensional complex acoustic pressure field for focused circular apertures in a medium having homogeneous acoustic and thermal properties. The three source diameters were 1, 2, and 4 cm and the eight transmit f-numbers (ratio of the radius of curvature/source diameter) were 0.7, 1.0, 1.3, 1.6, 2.0, 3.0, 4.0, and 5.0. For these focused field geometries, eight ultrasonic frequencies were evaluated (1, 2, 3, 4, 5, 7, 9, and 12 MHz) from which the three-dimensional temperature distribution was calculated using the bio-heat transfer equation in homogeneous, perfused media (attenuation=absorption=0.3 dB/cm-MHz; perfusion length: 1.0 cm). For each of the 192 cases, the acoustic field was normalized to the derated spatial peak, temporal average intensity (I/sub SPTA.3/) of 720 mW/cm/sup 2/, the maximum value allowed by the FDA 510(k) diagnostic ultrasound equipment approval process. Using the normalized acoustic field, the axial temperature increase profiles and the maximum temperature increases (/spl Delta/T/sub max/) were determined for each case. Also, from the normalized acoustic field, the unscanned soft-tissue thermal index (TIS) was determined. In general, /spl Delta/T/sub max/, TIS, and source power increase with increasing transmit f-number, source diameter, or frequency. The TIS generally underestimates (is less than) /spl Delta/T/sub max/ for f-numbers /spl les/2, conditions for which /spl Delta/T/sub max//spl les/0.30/spl deg/C and TIS/spl les/0.40. This suggests that, for transmit f-numbers /spl les/2, TIS would not need to be displayed according to the ODS display requirements. With the exception of the longer-focus, larger-diameter, higher-frequency sources, TIS generally tracks /spl Delta/T/sub max/ for f-numbers /spl ges/3. These exceptions suggest a breakdown of the ODS procedures far calculating TIS. View full abstract»

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  • Correlation processing for correction of phase distortions in subaperture imaging

    Publication Year: 1999 , Page(s): 1477 - 1488
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    Ultrasonic subaperture imaging combines synthetic aperture and phased array approaches and permits low-cost systems with improved image quality. In subaperture processing, a large array is synthesized using echo signals collected from a number of receive subapertures by multiple firings of a phased transmit subaperture. Tissue inhomogeneities and displacements in subaperture imaging may cause significant phase distortions on received echo signals. Correlation processing on reference echo signals can be used for correction of the phase distortions, for which the accuracy and robustness are critically limited by the signal correlation. In this study, we explore correlation processing techniques for adaptive subaperture imaging with phase correction for motion and tissue inhomogeneities. The proposed techniques use new subaperture data acquisition schemes to produce reference signal sets with improved signal correlation. The experimental test results were obtained using raw radio frequency (RF) data acquired from two different phantoms with 3.5 MHz, 128-element transducer array. The results show that phase distortions can effectively be compensated by the proposed techniques in real-time adaptive subaperture imaging. View full abstract»

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  • Design optimization of dome actuators

    Publication Year: 1999 , Page(s): 1489 - 1496
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB)  

    This paper reports the conceptual design, analysis, and modeling of the electromechanical behavior of dome actuators. The geometric parameters of the actuator (dome thickness, width, radius, and depth), poling direction, electric field, and material properties (elastic compliance, piezoelectric constants, and dielectric permittivity) have been taken into account in the modeling work. The results of the analysis indicate that a dome actuator with a tangentially alternating poling direction and electric field (Case C) exhibits much larger displacement and force responses than dome actuators with other poling directions and electric fields. The first mode of natural frequency of the Case C dome actuator also was investigated, and its predicted performance was compared with that of moonie and rainbow actuators. The findings of this research clearly demonstrate the merit of design optimization of electromechanical devices. View full abstract»

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  • Acoustic wave-based sensors using mode conversion in periodic gratings

    Publication Year: 1999 , Page(s): 1497 - 1503
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (194 KB)  

    Using periodic gratings etched into the surface of a piezoelectric plate, surface acoustic waves (SAW) can be converted into bulk waves and vice versa with high efficiency. If parallel grating structures are fabricated on opposite surfaces of a piezoelectric plate, a SAW also can be directed from one surface to the other. Using such structures, acoustic wave-based sensors can be designed that utilize SAW for the detection of chemical analytes on an electrode-free surface, i.e., the back surface. As a result, spurious sensor response and electrode aging that may occur when a chemical analyte comes in contact with the transducers are minimized. The design principles of these grating-based SAW sensors are explained, and the mass sensitivity is investigated using chemical vapor deposited thin polymer films, a type of material used in many practical chemical sensor applications. Experimental results are presented for the detection of nitrogen dioxide (NO/sub 2/) in sub-ppm concentrations. View full abstract»

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  • Absolute measurements of ultrasonic pressure by using high magnetic fields

    Publication Year: 1999 , Page(s): 1504 - 1511
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A hydrophone is introduced that exploits the emf signal generated in a conductor when sonicated in the presence of a uniform static magnetic field. The method uses a small metal coil or metal membrane as a hydrophone receiver. Acoustic signals at 748 kHz are introduced in 1.5 T and 4.7 T fields and recorded both through direct electrical contact with the hydrophone and via RF pick-up coils, allowing wireless placement of the hydrophone. Linear response Is confirmed over four orders of magnitude in the pressure amplitude. Waveforms determined from the detected voltage are shown to be in excellent agreement with those obtained using a calibrated polyvinylidene difluoride film, and absolute values correlate within 20%. The methods are conceptually suitable for use in the presence of the high and uniform field of commercial MR scanners. The hydrophone may appear particularly useful as a quality assurance device in therapeutic and diagnostic acoustic techniques that use MRI. View full abstract»

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  • The coupling-of-modes approach to the analysis of STW devices. II

    Publication Year: 1999 , Page(s): 1512 - 1517
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    For pt. I see ibid., vol. 44, no. 3, p. 652-7 (1997). The method for analyzing surface transverse wave (STW) devices by using a coupling-of-modes (COM) formalism has been completed, covering the STW electromechanical coupling coefficient (ECC). An ECC analytical formula has been derived by fitting numerical results from STW effective permittivity analysis. The ECC exhibits frequency and mass-loading variation. Using this new result, a satisfactory agreement with available experimental frequency characteristics of STW two-port quartz resonators has been achieved, without the necessity of additional experimental information. In its present form, the method is self-consistent and applicable to arbitrary STW layouts. View full abstract»

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  • Electromechanical properties of lead zirconate titanate piezoceramics under the influence of mechanical stresses

    Publication Year: 1999 , Page(s): 1518 - 1526
    Cited by:  Papers (56)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    In lead zirconate titanate piezoceramics, external stresses can cause substantial changes in the piezoelectric coefficients, dielectric constant, and elastic compliance due to nonlinear effects and stress depoling effects. In both soft and hard PZT piezoceramics, the aging can produce a memory effect that will facilitate the recovery of the poled state in the ceramics from momentary electric or stress depoling. In hard PZT ceramics, the local defect fields built up during the aging process can stabilize the ceramic against external stress depoling that results in a marked increase in the piezoelectric coefficient and electromechanical coupling factor in the ceramic under the stress. Although soft PZT ceramics can be easily stress depoled (losing piezoelectricity), a DC bias electric field, parallel to the original poling direction, can be employed to maintain the ceramic poling state so that the ceramic can be used at high stresses without depoling. View full abstract»

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  • Volumetric ultrasound system for left ventricle motion imaging

    Publication Year: 1999 , Page(s): 1527 - 1538
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    An external ultrasound oscillating probe has been developed for the purpose of visualizing dynamically the left cardiac ventricle three-dimensional (3D) movements and deformations. The fundamental principle of this probe is to maintain in continuous oscillation a classical one-dimensional (1D) transducer array around its axis at a maximum oscillation rate of 3 degrees per millisecond. A global medical system, including hardware elements and a software package, has been designed for this application. A motorization set and electronic boards enable this new oscillating probe to be used with any recent echograph equipped with a cardiac module and an external triggering cineloop. Moreover, in order to obtain 3D/4D left ventricle movements from a set of 2D recorded images, a rendering method based on the 2D discrete Fourier transform is applied. Promising preliminary results have been obtained on some patients, and a clinical study on a great number of subjects (both healthy and heart complaint people) was carried out. View full abstract»

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  • Reflection of ultrasonic Lamb waves produced by thin conducting strips

    Publication Year: 1999 , Page(s): 1539 - 1544
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The reflection of ultrasonic Lamb waves produced by a periodic array of thin conducting strips deposited on a piezoelectric plate was investigated both theoretically and experimentally. A repetitively mismatched transmission line model was used to analyze the performance of the reflector. The reflection coefficient of a single strip is given by R/spl ap//spl Delta/v/v, where /spl Delta/v/v is the fractional change in velocity produced by electrical shorting of the propagation surface. An attractive property of Lamb waves is that they can provide a much higher value of /spl Delta/v/v than is possible with surface acoustic waves. Therefore, efficient Lamb wave reflectors can be realized with relatively few strips in the reflector. For example, reflection coefficient very close to unity, R/spl ap/0.98, has been obtained in a Lamb wave reflector consisting of just 12 strips on a Y-X lithium niobate plate. The reflector has been used to realize a unidirectional transducer (UDT). A Lamb wave delay line consisting of two UDTs shows insertion loss of less than 3 dB with fractional bandwidth greater than 7%. View full abstract»

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  • A Bayesian method for oscillator stability analysis

    Publication Year: 1999 , Page(s): 1545 - 1550
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (162 KB)  

    The power spectral density of frequency fluctuations of an oscillator is generally modeled as a sum of power laws with integer exponents (from -2 to +2). However, a power law with a fractional exponent may exist. We propose a method for measuring the level of such a noise process and determining the probability density of the exponent. This yields a criterion for compatibility with an integer exponent. This method is based on a Bayesian approach called the reference analysis of Bernardo-Berger. The application to a sequence of frequency measurement from a quartz oscillator illustrates this paper. 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