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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 9 • Date Sept. 2004

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Displaying Results 1 - 23 of 23
  • IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

    Page(s): 1 - 2
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  • IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society

    Page(s): 3
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  • IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society

    Page(s): 4
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  • Table of contents

    Page(s): 5 - 6
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  • Information for contributors with multimedia addition

    Page(s): 1041 - 1045
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  • A multimedia example

    Page(s): 1046
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  • Effects of piezoelectric coupling on energy mapping of thickness-shear modes

    Page(s): 1047 - 1049
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  • AMCXO and its test system

    Page(s): 1050 - 1053
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB) |  | HTML iconHTML  

    In this paper, we introduce a novel temperature compensated crystal oscillator - analog memory compensated crystal oscillator (AMCXO), a microcomputer compensated crystal oscillator (MCXO) based on an analogue approach, and we compare the performance between MCXO and AMCXO, arid analyze the necessity of developing AMCXO. Both AMCXO and MCXO, combined with their test systems, use computers to generate the control signals used for the compensated crystal oscillators according to temperature variation. However, the execution devices are much different from each other in the practical temperature compensated crystal oscillators. A MCXO uses a set of digital units, including a microprocessor, to realize the compensation. For it, equations or tables are used to express the relationship between the control signal and temperature. An AMCXO uses an analogue memory, which has the same functions as the digital units of MCXO. For AMCXO, a curve or figure based on the equations or tables is used to express the same relationship. Their test systems have obvious distinctions in temperature experiment, data acquisition, and processing. A better performance will be obtained by using a more complicated AMCXO test system, and the cost can be reduced at the same time. View full abstract»

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  • Spherical Bragg reflector resonators

    Page(s): 1054 - 1059
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (963 KB) |  | HTML iconHTML  

    In this paper we introduce the concept of the spherical Bragg reflector (SBR) resonator. The resonator is made from multiple layers of spherical dielectric, loaded within a spherical cavity. The resonator is designed to concentrate the energy within the central region of the resonator and away from the cavity walls to minimize conductor losses. A set of simultaneous equations is derived, which allows the accurate calculation of the dimensions of the layers as well as the frequency. The solution is confirmed using finite-element analysis. A Teflon-free space resonator was constructed to prove the concept. The Teflon SBR was designed at 13.86 GHz and exhibited a Q-factor of 22,000, which agreed well with the design values. This represents a factor of 3.5 enhancement over a resonator limited by the loss-tangent of Teflon. Similarly, SBR resonators constructed with low-loss materials could achieve Q-factors of the order of 300,000. View full abstract»

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  • Modeling of wave propagation in layered piezoelectric media by a recursive asymptotic method

    Page(s): 1060 - 1071
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB) |  | HTML iconHTML  

    In this paper, a simple asymptotic method to compute wave propagation in a multilayered general anisotropic piezoelectric medium is discussed. The method is based on explicit second and higher order asymptotic representations of the transfer and stiffness matrices for a thin piezoelectric layer. Different orders of the asymptotic expansion are obtained using Pade approximation of the transfer matrix exponent. The total transfer and stiffness matrices for thick layers or multilayers are calculated with high precision by subdividing them into thin sublayers and combining recursively the thin layer transfer and stiffness matrices. The rate of convergence to the exact solution is the same for both transfer and stiffness matrices; however, it is shown that the growth rate of the round-off error with the number of recursive operations for the stiffness matrix is twice that for the transfer matrix; and the stiffness matrix method has better performance for a thick layer. To combine the advantages of both methods, a hybrid method which uses the transfer matrix for the thin layer and the stiffness matrix for the thick layer is proposed. It is shown that the hybrid method has the same stability as the stiffness matrix method and the same round-off error as the transfer matrix method. The method converges to the exact transfer/stiffness matrices essentially with the precision of the computer round-off error. To apply the method to a semispace substrate, the substrate was replaced by an artificial perfect matching layer. The computational results for such an equivalent system are identical with those for the actual system. In our computational experiments, we have found that the advantage of the asymptotic method is its simplicity and efficiency. View full abstract»

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  • Experimental investigation of computed tomography sound velocity reconstruction using incomplete data

    Page(s): 1072 - 1081
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2451 KB) |  | HTML iconHTML  

    An approach for reconstructing the sound velocity distribution in the breast was previously proposed and verified by simulations, and the present study investigated the approach experimentally. The experimental setup comprised a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom containing objects with differing physical properties, and a computer. The array system was used to collect channel data for simultaneous B-mode image formation and limited-angle tomographic sound velocity reconstruction. The phantom was constructed from materials mimicking the following tissues in the breast: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. The sound velocities in these materials matched those in the corresponding real tissues. The imaging setup is similar to that of X-ray mammography, in which a linear array is placed at the top of the breast and a metal plate is placed at the bottom for reflecting sound waves. Thus, both B-mode images and the sound velocity distribution can be acquired using the same setup. An algorithm based on a convex programming formulation was used to reconstruct the sound velocity images. By scanning the phantom at different positions, nine cases were evaluated. In each of the nine cases, the image object comprised a background (glandular tissue) and one or three regions of interest (fat, tumor, or cyst). The sound velocity was accurately estimated in the nine cases evaluated, with sound velocity errors being less than 5 m/s in 8 of 11 regions of interest. Thus, obtaining the sound velocity distribution is feasible with a B-mode imaging setup using linear arrays. Knowledge of the sound velocity distribution in the breast can be used to complement B-mode imaging and to enhance the detection of breast cancer. View full abstract»

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  • Direct sampled I/Q beamforming for compact and very low-cost ultrasound imaging

    Page(s): 1082 - 1094
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1400 KB) |  | HTML iconHTML  

    A wide variety of beamforming approaches are applied in modern ultrasound scanners, ranging from optimal time domain beamforming strategies at one end to rudimentary narrowband schemes at the other. Although significant research has been devoted to improving image quality, usually at the expense of beamformer complexity, we are interested in investigating strategies that sacrifice some image quality in exchange for reduced cost and ease in implementation. This paper describes the direct sampled in-phase/quadrature (DSIQ) beamformer, which is one such low-cost, extremely simple, and compact approach. DSIQ beamforming relies on phase rotation of I/Q data to implement focusing. The I/Q data are generated by directly sampling the received radio frequency (RF) signal, rather than through conventional demodulation. We describe an efficient hardware implementation of the beam-former, which results in significant reductions in beam-former size and cost. We present the results of simulations and experiments that compare the DSIQ beamformer to more conventional approaches, namely, time delay beamforming and traditional complex demodulated I/Q beam-forming. Results that show the effect of an error in the direct sampling process, as well as dependence on signal bandwidth and system f number (f#) are also presented. These results indicate that the image quality and robustness of the DSIQ beamformer are adequate for low end scanners. We also describe implementation of the DSIQ beamformer in an inexpensive hand-held ultrasound system being developed in our laboratory. View full abstract»

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  • Sound speed estimation using automatic ultrasound image registration

    Page(s): 1095 - 1106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (685 KB) |  | HTML iconHTML  

    A mismatch between the sound speed assumed for beamforming and scan conversion and the true sound speed in the tissue to be imaged can lead to significant defocusing and some geometric distortions in ultrasound images. A method is presented for estimating the average sound speed based on detection of these distortions using automatic registration of overlapping, electronically steered images. An acrylamide gel phantom containing vaporized dodecafluoropentane droplets as point targets was constructed to evaluate the technique. Good agreement (rms deviation <0.4%) was found between the sound speeds measured in the phantom using a reference pulse-echo technique and the image-based sound speed estimates. A significant improvement in accuracy (rms deviation <0.1%) was achieved by including the simulated sound field of the probe rather than assuming straight acoustic beams and propagation according to ray acoustics. View full abstract»

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  • Directional synthetic aperture flow imaging

    Page(s): 1107 - 1118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3053 KB) |  | HTML iconHTML  

    A method for flow estimation using synthetic aperture imaging and focusing along the flow direction is presented. The method can find the correct velocity magnitude For any flow angle, and full color flow images can be measured using only 32 to 128 pulse emissions. The approach uses spherical wave emissions with a number of defocused elements and a linear frequency-modulated pulse (chirp) to improve the signal-to-noise ratio. The received signals are dynamically focused along the flow direction and these signals are used in a cross-correlation estimator for finding the velocity magnitude. The flow angle is manually determined from the B-mode image. The approach can be used for both tissue and blood velocity determination. The approach was investigated using both simulations and a flow system with a laminar flow. The flow profile was measured with a commercial 7.5 MHz linear array transducer. A plastic tube with an internal diameter of 17 mm was used with an EcoWatt 1 pump generating a laminar, stationary flow. The velocity profile was measured for flow angles of 90 and 60 degrees. The RASMUS research scanner was used for acquiring radio frequency (RF) data from 128 elements of the array, using 8 emissions with 11 elements in each emission. A 20-/spl mu/s chirp was used during emission. The RF data were subsequently beamformed off-line and stationary echo canceling was performed. The 60-degree flow with a peak velocity of 0.15 m/s was determined using 16 groups of 8 emissions, and the relative standard deviation was 0.36% (0.65 mm/s). Using the same setup for purely transverse flow gave a standard deviation of 1.2% (2.1 mm/s). Variation of the different parameters revealed the sensitivity to number of lines, angle deviations, length of correlation interval, and sampling interval. An in vivo image of the carotid artery and jugular vein of a healthy 29-year-old volunteer was acquired. A full color flow image using only 128 emissions could be made with a high-velocity p- - recision. View full abstract»

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  • Axial strain calculation using a low-pass digital differentiator in ultrasound elastography

    Page(s): 1119 - 1127
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3610 KB) |  | HTML iconHTML  

    In ultrasound elastography, tissue axial strains are calculated from the gradient of the estimated axial displacements. However, the common differentiation operation amplifies the noises in the displacement estimation, especially at high frequencies. In this paper, a low-pass digital differentiator (LPDD) is proposed to calculate the axial strain from the estimated tissue displacement. Several LPDDs that have been well developed in the field of digital signal processing are presented. The corresponding performances are compared qualitatively and quantitatively in computer simulations and in preliminary phantom and in vitro experiments. The results are consistent with the theoretical analysis of the LPDDs. View full abstract»

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  • Estimation of surface pose with a physically-based ultrasonic image model

    Page(s): 1128 - 1136
    Multimedia
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (698 KB) |  | HTML iconHTML  

    State-of-the-art approaches to shape analysis in medical images use a variety of sophisticated models for object shape. We have developed an image model that permits the application of these approaches to ultrasonic images, with detailed methods for representing rough surfaces. Our physically-based, probabilistic image model incorporates the combined effects of the system point-spread function (PSF), the tissue microstructure, and the gross tissue shape. At each image pixel, the amplitude mean and variance are computed directly from the model, characterizing the combined influence of shape, microstructure, and system PSF. Calculation of the SNR/sub 0/ is used to further classify each pixel as Rayleigh- or non-Rayleigh-distributed. This characterization was used here to generate a data likelihood representing any set of images of a given surface by a probability density conditioned on the surface pose, or rotation and translation. The utility of this likelihood was demonstrated by applying maximum likelihood estimation to infer the pose of a cadaveric vertebra from simulated images of its surface. Successful results were achieved using derivative-based optimization algorithms for a data set of only three images. With a quasi-Newton BFGS algorithm, error in 15 of 20 trials was less than 0.4 degrees in rotation and 0.2 mm in translation. Estimation was inaccurate in only 1 of 20 trials. These results illustrate the potential of a physically-based image model in a rigorous approach to image analysis and also serve as an example of quantitative assessment of the model via performance in a specific application. View full abstract»

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  • Contrast echocardiography for pulmonary blood volume quantification

    Page(s): 1137 - 1147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB) |  | HTML iconHTML  

    Pulmonary blood volume quantification is important both for diagnosis and for monitoring of the circulatory system. It requires employment of transpulmonary indicator dilution techniques, which are very invasive due to the need for double catheterization. This paper presents a new minimally invasive technique for blood volume quantification. An ultrasound contrast agent bolus is injected peripherally and detected by an ultrasound transducer in the central circulation. Several echocardiographic views permit simultaneous detection of contrast in different cardiac cavities and central vessels, and acoustic backscatter measurements produce multiple indicator dilution curves (IDCs). Contrast mean-transit-time differences are derived from the IDC analysis and multiplied times cardiac output for the assessment of blood volumes between different detection sites. For pulmonary blood volume estimates, the right ventricle and the left atrium IDCs are measured. The mean transit time of the IDC is estimated by specific modelling. The Local Density Random Walk and the First Passage Time models were tested for IDC interpolation and interpretation. The system was validated in vitro for a wide range of flows. The results show very accurate volume measurements. The volume estimate determination coefficient is greater than 0.999 for both model fits. A preliminary study in patients shows promising results. View full abstract»

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  • The RF-powered surface wave sensor oscillator - a successful alternative to passive wireless sensing

    Page(s): 1148 - 1156
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (963 KB) |  | HTML iconHTML  

    A novel, passive wireless surface acoustic wave (SAW) sensor providing a highly coherent measurand proportional frequency, frequency modulated (FM) with identification (ID) data and immune to interference with multiple-path signals is described. The sensor is appropriate for bandwidth-limited applications requiring high-frequency accuracy. It comprises a low-power oscillator, stabilized with the sensing SAW resonator and powered by the rectified radio frequency (RF) power of the interrogating signal received by an antenna on the sensor part. A few hundred microwatts of direct current (DC) power are enough to power the sensor oscillator and ID modulation circuit and achieve stable operation at 1.0 and 2.49 GHz. Reliable sensor interrogation was achieved over a distance of 0.45 m from a SAW-based interrogation unit providing 50 mW of continuous RF power at 915 MHz. The -30 to -35 dBm of returned sensor power was enough to receive the sensor signal over a long distance and through several walls with a simple superheterodyne FM receiver converting the sensor signal to a low measure and proportional intermediate frequency and retrieving the ID data through FM detection. Different sensor implementations, including continuous and pulsed power versions and the possibility of transmitting data from several measurands with a single sensor, are discussed. View full abstract»

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  • Dyadic Green's functions of a laminar plate

    Page(s): 1157 - 1164
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    We introduce the concept of dyadic Green's functions of a laminar plate. These functions generalize classical Green's functions. In addition to relating displacements and stresses at the surface of a medium, they relate these quantities at both the top and the bottom surfaces of a medium of finite thickness and infinite extent in the transverse directions. We describe here the calculation of these functions in the spectral domain and provide some academic examples demonstrating their interest. View full abstract»

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  • Idealized analysis of SAW longitudinally coupled resonator filters

    Page(s): 1165 - 1170
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (491 KB) |  | HTML iconHTML  

    A surface acoustic wave (SAW) longitudinally coupled resonator (LCR) filter consists of either two or three interdigital transducers located between two strongly reflecting gratings. The behavior of this structure is, in general, very complex because the transducers are of the single-electrode type, which gives strong electrode reflections. It is shown here that, for the filter passband, a number of realistic assumptions can be used to derive a very simple set of approximate relations for the device Y-matrix. The simplifications involve reciprocity, symmetry, and power conservation. The theory also uses the necessary fact that each grating, combined with its adjacent transducer, must have high directivity so that application of a voltage results in wave generation primarily toward the center of the device. For a three-transducer device, it is shown using symmetry that the central transducer behaves as if it were transparent, despite having strong electrode reflections. Hence, the device behaves as a single resonant cavity. The simple Y-matrix formulae are shown to agree very well with accurate results obtained by a coupling-of-modes (COM) analysis for both types of device. They also lead to simple formulae for the electrical loading required to obtain a flat, low-loss filter response. Equivalent circuits also are discussed. View full abstract»

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  • A new-style, slotted-cymbal transducer with large displacement and high energy transmission

    Page(s): 1171 - 1177
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1293 KB) |  | HTML iconHTML  

    The cymbal transducer had more improved performances than the moonie transducer, but as with the moonie end caps, flexural motion of the cymbal end caps would cause high-tangential stresses, which could lead to loss of mechanical output energy. So, a new-style design, called slotted-cymbal transducer, is presented in this paper. The slotted-cymbal transducer released the tangential stresses by adopting a new-style, radial-slotted cymbal end caps. Through theoretical calculation and finite element analysis in collaboration with measurements, the slotted-cymbal transducer was demonstrated to possess high performances of displacement and energy transmission. This design would decrease the fundamental resonance frequencies of systems by different numbers of slots, and it would have more potential applications of low frequency and large displacement. View full abstract»

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  • Finite-element analysis of material and parameter effects in laser-based thermoelastic ultrasound generation

    Page(s): 1178 - 1186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1139 KB) |  | HTML iconHTML  

    Laser-based, thermoelastic transduction methods have potential in very high frequency (>50 MHz), high-density two-dimensional (2-D) arrays for a variety of very high-resolution superficial imaging applications, including in vivo tissue sectioning. Previous studies of these transducers generally have been based on experimental measurements or theoretical analyses using various simplifying assumptions. These theoretical models are mostly 1-D and best matched to simple geometries with a minimum number of component materials. In this work, we use a new thermoelastic solver in a commercially available finite-element analysis (FEA) software package to analyze multidimensional effects in laser-based devices of arbitrary geometry with the potential for use with arbitrary material properties. The FEA approach was verified first against experimental data. Thereafter, we explored the impact of various design variables, including laser spot size and laser penetration depth. View full abstract»

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  • Time-scale removal of "wall thump" in Doppler ultrasound signals: a simulation study

    Page(s): 1187 - 1192
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB) |  | HTML iconHTML  

    A novel approach for blood and wall signal separation in Doppler ultrasound is proposed in the wavelet time-scale domain. The Doppler signals of different clutter-to-blood ratios from a femoral artery were simulated and used in the experiments. Compared with the conventional high-pass filtering and the signal separation in the spectrogram, the new method delivers improved performance for "wall thump" removal with minimal loss of low-flow signal. 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