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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 6 • Date Nov. 1998

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Displaying Results 1 - 17 of 17
  • A swept-scanning mode for estimation of blood velocity in the microvasculature

    Page(s): 1437 - 1440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB)  

    In contrast to previous systems in which an ultrasonic pulse was repeatedly directed to a discrete line of sight, a new method has been developed to continuously scan over a region in order to rapidly assess blood velocities in superficial small blood vessels. Using this technique, which we call swept-scan, a high frequency transducer can rapidly translate across a region of interest, and sensitive maps of blood velocity in small blood vessels can be constructed. This system has been applied to flow mapping in the anterior segment of the eye, which is clinically significant in cases of trauma and glaucoma. No previous imaging technique has been capable of estimating blood velocities within this region in a clinically useful manner. With this new technique, each 2-D scan of the eye can be obtained in an interval on the order of 1 second, and blood flow through the iris and ciliary body can be detected in vessels as small as 40 microns. A major implication of this new technique is that a wall filter can be applied continuously to the return from all regions, thus eliminating the transient response that occurs along each line of sight in traditional Doppler systems. View full abstract»

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  • An explanation for the anomalous ultrasonic slow wave in underwater sand

    Page(s): 1441 - 1443
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    An explanation is given for the propagation time of the well-known anomalous ultrasonic slow wave observed in water-saturated sand using a three-layer elastic model. The rapid increase of elastic properties of sand with depth causes conversion of near-grazing underwater acoustic waves into multiple coupled shear and compressional waves. View full abstract»

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  • Novel pyroelectric sensor materials

    Page(s): 1444 - 1452
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    Ceramic compositions of barium strontium titanium oxide (BSTO) have been formulated for applications as pyroelectric sensor materials. The material has been fabricated in tape-cast and thin film forms. In general, the materials demonstrated high pyroelectric coefficients (p) accompanied with low dielectric constant and low dissipation factor. The compositions of the tape-cast and thin film specimens examined in this paper include a well-known commercially adopted Ba/sub 0.64/Sr/sub 0.36/TiO/sub 3/ as well as a composition suggested in the literature, and a patented composition with the addition of MgO to BSTO is investigated. Doping BSTO with MgO has been shown to reduce the dielectric constant and loss tangent (over a very wide frequency range from 100 Hz-10 GHz) of the material and thereby increase the pyroelectric figure of merit. This article will discuss the processing, material characterization, pyroelectric coefficient, and pyroelectric figure-of-merit of the above mentioned BSTO compositions. View full abstract»

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  • Dynamics of an ultrasonic transducer used for wire bonding

    Page(s): 1453 - 1460
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB)  

    The vibration displacement distributions along a transducer used in ultrasonic wire bonding were measured using a heterodyne interferometer, and many nodes and anti-nodes were found. A mechanical finite element method (FEM) was used to compute the resonant frequencies and vibration mode shapes. The displacement distributions of the dominant 2nd axial mode agreed well with the measured values. Undesirable nonaxial modes, including the higher order flexural and torsional modes, also were excited at frequencies very close to the working frequency (2nd axial mode) of the transducer. Hence, the measured displacements were the resultant of all the allowable modes being excited. However, the excitation of these nonaxial modes were small enough not to affect the formation of consistent and high quality wire bonds. Results of the present study were used to determine a suitable location for installing a piezoelectric sensor to monitor the bond quality. View full abstract»

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  • The diffraction response interpolation method

    Page(s): 1461 - 1475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (637 KB)  

    Computer modeling of the output voltage in a pulse-echo system is computationally very demanding, particularly when considering reflector surfaces of arbitrary geometry. A new, efficient computational tool, the diffraction response interpolation method (DRIM), for modeling of reflectors in a fluid medium, is presented. The DRIM is based on the velocity potential impulse response method, adapted to pulse-echo applications by the use of acoustical reciprocity. Specifically, the DRIM operates by dividing the reflector surface into planar elements, finding the diffraction response at the corners of the elements, calculating the response integrated over the surface element by time-domain convolutions with analytically determined filters, and summing the responses from the individual surface elements. As the method is based on linearity, effects such as shadowing, higher-order diffraction, nonlinear propagation, cannot be directly incorporated in the modeling. The DRIM has been compared to other modeling tools when possible. Excellent agreement between the results obtained with the DRIM and the alternative techniques have been found, and the DRIM offers reductions in computation time in the range from 30 to 400 times. Experimental results obtained using a planar circular transducer together with cylindrical reflectors were compared to DRIM results and fairly good agreement was observed. View full abstract»

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  • The modulational method of quartz crystal oscillator frequency stabilization

    Page(s): 1476 - 1484
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB)  

    A new trend in self-contained (without the use of quantum discriminators) frequency stabilization of an oven controlled crystal oscillator (OCXO) and frequency standard is proposed and discussed. The method developing the trend is called a modulational method and is based on the use of the reference properties of crystal resonator natural bulk vibrations (double-frequency and multi-frequency oscillators are not used in this case). The concept is based on dynamic modulation characteristics of an oscillator, and basic relationships are found for their calculation. The construction principles of the frequency control systems are formulated substantiating mathematically the essence of the method. Basic ratios of modulating signals are determined, the solution of which shows only a slight influence of the modulation signal on the Allan variance and spectral density of an OCXO. The results of the method's practical use are considered. Their subject is the OCXO with the oven system adapted to the ambient temperature and crystal frequency standard with aging rate compensation. View full abstract»

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  • Imaging strongly scattering media using a multiple frequency distorted Born iterative method

    Page(s): 1485 - 1496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    The distorted Born iterative (DBI) method is a powerful approach for solving the inverse scattering problem for ultrasound tomographic imaging. This method alternates between solving the inverse scattering problem for the scattering function and the forward scattering problem for the total field and the inhomogeneous Green's function. The algorithm is initialized using the basic Born inverse solution. One fundamental problem is the algorithm diverges for strongly scattering media. This is caused by the limitation of the Born assumption in estimating the initial step of the algorithm. We present a multiple frequency DBI approach to alleviate this problem, thus extending the applicability of the DBI method to the level of dealing with biological tissue. In this multiple frequency approach, a low frequency DBI-based solution, is used to initialize the algorithm at higher frequencies. The low frequency allows convergence of the algorithm to a contrast level that is close to the true level, however, with a poor spatial resolution. The high frequency improves the spatial resolution while preserving convergence because the difference between the true contrast and the initial contrast is relatively small. We present numerical simulations that demonstrate the ability of this method to reconstruct strongly scattering regions. View full abstract»

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  • Modeling of highly loaded 0-3 piezoelectric composites using a matrix method

    Page(s): 1497 - 1505
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    A model previously developed for pure 0-3 connectivity piezocomposites has been extended to 3-3 connectivity. This matrix method allows the prediction of the effective electroelastic moduli of a piezocomposite according to its connectivity. It is used to optimize composite performance by choosing the optimal constituents for each phase. A simple combination of the results for 0-3 and 3-3 connectivities allows the effective proportion of 3-3 connectivity to be defined in highly loaded 0-3 piezocomposites. This theoretical analysis has been used to evaluate effective proportions of 3-3 connectivity in five composite samples. The values obtained are shown to be a function of the ceramic volume fraction and fabrication process. The results of this study were used to optimize the fabrication process. View full abstract»

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  • SAW device applications of longitudinal leaky surface waves on lithium tetraborate

    Page(s): 1506 - 1516
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    The possibility of high frequency SAW device applications of longitudinal leaky surface waves (LLSW) on lithium tetraborate (Li/sub 2/B/sub 4/O/sub 7/; LBO) is investigated in this paper. An electrical equivalent circuit model (ECM) is extended in order to consider effects of bulk wave scattering for the LLSWs. The equivalent circuit parameters used in the extended ECM for designing the LLSW devices are directly determined from numerically calculated dispersion curves. For applications of the LLSW, high frequency SAW filters on LBO with the Euler angles (0/spl deg/, 47.3/spl deg/, 90/spl deg/) are demonstrated. As examples of the high frequency devices, 1.5 GHz and 1.2 GHz SAW filters using the mode are designed by using the extended ECM, and fabricated by using conventional patterning processes. One is for the filter of the global positioning system (GPS), another is for the 1.2 GHz band data transmission radio system in Japan. As a result, low loss SAW filters can be obtained easily without submicron fabrication techniques by using the LLSWs on LBO. Furthermore, the frequency response calculated by the extended ECM are in a good agreement with the experiments. View full abstract»

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  • US backscatter and attenuation 30 to 50 MHz and MR T2 at 3 Tesla for differentiation of atherosclerotic artery constituents in vitro

    Page(s): 1517 - 1525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB)  

    This study compares quantitative characterization of atherosclerotic artery constituents by high resolution estimates of ultrasonic attenuation, ultrasonic attenuation-compensated backscatter, and magnetic resonance transverse relaxation time. Atherosclerotic human arteries were studied in vitro at 37/spl deg/C. Backscattered radio frequency signals were acquired with a 50 MHz backscatter acoustic microscope. Ultrasonic parametric images were constructed from the integrated (30 to 50 MHz) backscatter and attenuation obtained using FFT methods with diffraction correction and a multinarrow-band attenuation algorithm. Parametric magnetic resonance images were constructed from calculated values of the transverse relaxation time T2 determined from an 8 echo-single-slice sequence at 3 Tesla. In a total of 54 regions of interest, average values of integrated attenuation, integrated backscatter compensated for the attenuation between the artery surface and the scattering volume, and the transverse relaxation time were correlated with local tissue composition as assessed by histology. Results show that ultrasound and magnetic resonance techniques offer complementary approaches for characterization of plaque composition. View full abstract»

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  • Microwave interferometry: application to precision measurements and noise reduction techniques

    Page(s): 1526 - 1536
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB)  

    A concept of interferometric measurements has been applied to the development of ultra-sensitive microwave noise measurement systems. These systems are capable of reaching a noise performance limited only by the thermal fluctuations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of conventional systems and has allowed the first experimental evidence of the intrinsic phase fluctuations in microwave isolators and circulators. Microwave frequency discriminators with interferometric signal processing have proved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave oscillators with a phase noise spectral density of order -150 dBc/Hz at 1 kHz Fourier frequency, without the use of cryogenics. Another possible application of the interferometric noise measurements systems include "flicker noise-free" microwave amplifiers and advanced two oscillator noise measurement systems. View full abstract»

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  • Changes in the echoes from ultrasonic contrast agents with imaging parameters

    Page(s): 1537 - 1548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    Current harmonic imaging scanners transmit a narrowband signal that limits spatial resolution in order to differentiate the echoes from tissue from the echoes from microbubbles. Because spatial resolution is particularly important in applications, including mapping vessel density in tumors, we explore the use of wideband signals in contrast imaging. It is first demonstrated that microspheres can be destroyed using one or two pulses of ultrasound. Thus, temporal signal processing strategies that use the change in the echo over time can be used to differentiate echoes from bubbles and echoes from tissue. Echo parameters, including intensity and spectral shape for narrowband and wideband transmission, are then evaluated. Through these experiments, the echo intensity received from bubbles after wideband transmission is shown to be at least as large as that for narrowband transmission, and can be larger. In each case, the echo intensity increases in a nonlinear fashion in comparison with the transmitted signal intensity. Although the echo intensity at harmonic multiples of the transmitted wave center frequency can be larger for narrowband insonation, echoes received after wideband insonation demonstrate a broadband spectrum with significant amplitude over a very wide range of frequencies. View full abstract»

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  • Development of a PVDF membrane hydrophone for use in air-coupled ultrasonic transducer calibration

    Page(s): 1549 - 1558
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (331 KB)  

    This work describes the use of a polyvinylidene fluoride (PVDF) membrane hydrophone for application in air-coupled transducer calibration. A one-dimensional theoretical analysis is used to demonstrate the potential and performance of PVDF as a hydrophone material over the frequency range 100 kHz to 5 MHz included in the evaluation is the influence of deposited metallic electrode layers on the sensitivity of the material. Experimental validation over the restricted range 400 kHz to 1 MHz is provided by a coplanar 0.028 mm thick membrane hydrophone in conjunction with a custom built 1-3 piezocomposite transmitter. Calibration of the membrane hydrophone is performed by employing a standard hydrophone that has been calibrated to a primary standard in a water medium. Justification for such an approach is presented within the theoretical analysis which provides a close correlation with experimental data. The generation of Lamb waves at critical angles in the PVDF and their subsequent influence on the directional response of membrane hydrophones operating in air is also addressed. A method for partial suppression of the Lamb waves, based around perforation of the membrane (either in whole or in part), is evaluated experimentally with reasonable results. View full abstract»

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  • A SAW resonator filter using longitudinal and transverse modes

    Page(s): 1559 - 1564
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    A SAW resonator filter using not only transverse but also longitudinal modes is presented. The design principle permits to construct four-pole filters without cascading or parallel connection. The input and output transducers arranged side by side have equal construction characterized by unsymmetrical withdrawing weighting. Neighboring disturbing longitudinal modes are suppressed due to weighting determined by an iterative procedure. The successful application of the principle to a device is demonstrated by experimental measurements. View full abstract»

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  • A deconvolution filter for improvement of time-delay estimation in elastography

    Page(s): 1565 - 1572
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (390 KB)  

    In elastography, tissue under investigation is compressed, and the resulting strain is estimated from the gradient of displacement estimates. Therefore, it is important to accurately estimate the displacements (time-delay) for good quality elastograms. A principal source of error in time-delay estimation in elastography is the decorrelation of the echo signal due to tissue compression (decorrelation noise). Temporal stretching of the postcompression signals has been shown to reduce the decorrelation noise at small strains. In this article, we present a deconvolution filter that reduces the decorrelation even further when applied in conjunction with signal stretching. The performance of the proposed filter is evaluated using simulated data. View full abstract»

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  • 1998 Index: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

    Page(s): 1579 - 1598
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    Freely Available from IEEE

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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