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Showing papers in "IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control in 1993"


Journal ArticleDOI
TL;DR: An overview of time-domain techniques that have appeared in the literature over the past few years is presented, and their potential advantages over Doppler are examined, and the individual techniques are compared.
Abstract: The Doppler technique has traditionally been the method used to extract motion information from ultrasonic echoes reflected by moving tissues. The Doppler technique has been around for a long time, and has been extensively reviewed and analyzed in the literature. Recently, time-domain methodologies for estimating tissue motion have gained in popularity. Time-domain methods have advantages over Doppler methods in many applications, and as of yet have not been comprehensively reviewed. An overview of time-domain techniques that have appeared in the literature over the past few years is presented. Their potential advantages over Doppler are examined, and the individual techniques are compared. >

340 citations


Journal ArticleDOI
TL;DR: The development of ultrasound backscatter microscopy is described together with initial clinical and biological applications and the development of new high sensitivity transducers in the 40-100-MHz range now permits visualization of tissue structures with resolution approaching 20 mu m and a maximum penetration of approximately 4 mm.
Abstract: The development of ultrasound backscatter microscopy (UBM) is described together with initial clinical and biological applications. UBM is essentially an extension of the powerful B-mode backscatter methods developed for clinical imaging in the 3-10-MHz frequency range. The development of new high sensitivity transducers in the 40-100-MHz range now permits visualization of tissue structures with resolution approaching 20 mu m and a maximum penetration of approximately 4 mm. The performance characteristics and trade-offs of these new polymer and ceramic devices are reviewed, and the implementation of high-frequency imaging systems is described. Initial clinical applications of UBM include ophthalmic, skin, and intravascular imaging. Examples of images and progress in these areas are presented. The biological application of UBM is illustrated by studies of drug uptake in living tumor spheroids. Significant increases in backscatter levels resulting from drugs targeting oxic and hypoxic cell populations are demonstrated. >

208 citations


Journal ArticleDOI
TL;DR: A simple physical model of 1-3 composite piezoelectrics that was advanced for the material properties relevant to thickness-mode oscillations is extended to address the hydrostatic response.
Abstract: A simple physical model of 1-3 composite piezoelectrics that was advanced for the material properties relevant to thickness-mode oscillations is extended to address the hydrostatic response. The model is valid when the lateral spatial scale of the composite is sufficiently fine that the composite can be treated as an effective homogeneous medium. Expressions are derived for the composite's material parameters in terms of the volume fraction of piezoelectric ceramic and the properties of the constituent piezoelectric ceramic and passive polymer. The results are similar to those derived by Haun and Newnham (1983, 1986) using a parallel-series connectivity model. The model is illustrated by analyzing composites made from conventional PZT5 and anisotropic modified lead titanate piezoelectric ceramics. For PZT5, the composite structure enhances its hydrostatic charge coefficient, hydrostatic voltage coefficient, hydrophone figure of merit, and hydrostatic coupling coefficient, while three of these quantities fall short of their pure ceramic values in the modified lead titanate composites. The shortfall is due to an enhanced composite that arises from lateral stress on the polymer being transferred to a longitudinal stress along the ceramic rods by the Poisson effect in the polymer, thus producing a charge through the ceramic's d/sub 33/. >

183 citations


Journal ArticleDOI
TL;DR: An autoregressive (AR) spectral estimation method is compared with a conventional fast Fourier transform (FFT)-based approach for this task and offers promise for enhanced spatial resolution and accuracy in ultrasonic tissue characterization and nondestructive evaluation of materials.
Abstract: The problem of estimation of mean scatterer spacing in an object containing regularly spaced structures is addressed. An autoregressive (AR) spectral estimation method is compared with a conventional fast Fourier transform (FFT)-based approach for this task. Regularly spaced structures produce a periodicity in the power spectrum of ultrasonic backscatter. This periodicity is manifested as a peak in the cepstrum. A phantom was constructed for comparison of the two methods. It contained regularly spaced nylon filaments. It also contained randomly positioned glass spheres that produced incoherent backscatter. In an experiment in which this target was interrogated using broadband ultrasound, the AR spectral estimate offered considerable improvement over the FFT when the analysis gate length was on the order of the structural dimension. Advantages included improved resolution, reduction in bias and variance of scatterer spacing estimates, and greater resistance to ringing artifacts. Data were also acquired from human liver in vivo. AR spectral estimates on human data exhibited a decreased dependence on gate length. These results offer promise for enhanced spatial resolution and accuracy in ultrasonic tissue characterization and nondestructive evaluation of materials. >

153 citations


Journal ArticleDOI
TL;DR: An overview of surface acoustic wave filter techniques available for different applications is given, and for many devices the theoretical frequency response is presented along with the measurement curve.
Abstract: An overview of surface acoustic wave (SAW) filter techniques available for different applications is given. Techniques for TV IF applications are outlined, and typical structures are presented. This is followed by a discussion of applications for SAW resonators. Low-loss devices for mobile communication systems and pager applications are examined. Tapped delay lines (matched filters) and convolvers for code-division multiaccess (CDMA) systems are also covered. Although simulation procedures are not considered, for many devices the theoretical frequency response is presented along with the measurement curve. >

99 citations


Journal ArticleDOI
TL;DR: The manner in which the stability and accuracy of these devices impact the performance of military communication, navigation, surveillance, electronic warfare, missile guidance, and identification-friend-or-foe systems is discussed.
Abstract: The application of frequency control and timing devices in modern military electronics systems is reviewed. The manner in which the stability and accuracy of these devices impact the performance of military communication, navigation, surveillance, electronic warfare, missile guidance, and identification-friend-or-foe (IFF) systems is discussed. >

98 citations


Journal ArticleDOI
TL;DR: In this paper, a method for the determination of the mutual admittance between the grating electrodes is presented, and an analytical expression for the contribution of surface acoustic waves (SAWs) is proposed.
Abstract: The coupling problem between electrodes due to the propagation of acoustic waves in a periodic metal grating on a piezoelectric substrate is theoretically studied. A method for the determination of the mutual admittance between the grating electrodes is presented, and an analytical expression for the contribution of surface acoustic waves (SAWs) is proposed. The SAW characteristic parameters are determined with a numerical technique that is able to deal with a leaky SAW as well as a true SAW (conventional Rayleigh type or Bleustein-Gulyaev type). Using this technique, the SAWs' contribution to the mutual admittance can be removed, and the analysis of other contributions becomes possible. In particular, the amplitude decay rate of the residual mutual admittance with electrode separation gives information about the propagation of the surface skimming bulk waves (SSBWs). The method presented is applied to several currently used material-cut configurations. >

93 citations


Journal ArticleDOI
TL;DR: A method for calculating the load characteristics of a traveling-wave-type ultrasonic motor (TWUM) and the numerically calculated load characteristics are shown to agree well with the measured ones, confirming the validity of the method.
Abstract: A method for calculating the load characteristics of a traveling-wave-type ultrasonic motor (TWUM) is proposed. A systematic method using an equivalent circuit is suggested for estimating the performance of the motor, including its electrical and the mechanical parts. In the proposed method, a governing equation for the motor is derived to describe the relation between the applied voltage at an electrical terminal, vibration velocities, and the external forces at mechanical terminals of a vibrator. A method for estimating the forces between the rotor and the vibrator of the motor is presented and used to calculate the load characteristics. The numerically calculated load characteristics are shown to agree well with the measured ones, confirming the validity of the method. >

88 citations


Journal ArticleDOI
TL;DR: The technique is initially developed for transmission, but its extension to reception and pulse-echo conditions is discussed, demonstrating the feasibility of the technique.
Abstract: A type of transducer composed of several active piezoelectric layers is described. These layers are independently stimulated electrically to achieve performance, in terms of sensitivity and bandwidth, not available in conventional, single active layer designs. A straightforward modeling technique is employed for predicting the performance of these transducers and for determining the optimal excitation characteristics. The technique is initially developed for transmission, but its extension to reception and pulse-echo conditions is discussed. A selection of experimental results demonstrates the feasibility of the technique. >

88 citations


Journal ArticleDOI
TL;DR: A simple equivalent circuit is introduced that expresses the unique operation mechanism of the hybrid transducer-type motor and a numerical simulation based on the model enables them to predict the motor characteristics such as the maximum torque and the no-load revolution speed.
Abstract: The authors present a design method for a hybrid transducer-type ultrasonic motor (HTUSM) for practical use. They introduce a simple equivalent circuit that expresses the unique operation mechanism of the hybrid transducer-type motor. A numerical simulation based on the model enables them to predict the motor characteristics such as the maximum torque and the no-load revolution speed. In addition, for the purpose of efficient design and physical interpretation of the phenomena, they discuss analytically the maximum torque of a special case and develop two design charts for the prediction of the no-load speed of the motor. >

71 citations


Journal ArticleDOI
TL;DR: The development of a dual-mode thickness-shear quartz pressure sensor to meet the demanding performance requirements of oil-field applications is discussed and pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in/sup 2/) at 175 degrees C is obtained.
Abstract: The development of a dual-mode thickness-shear quartz pressure sensor to meet the demanding performance requirements of oil-field applications is discussed. The objective was to develop a sensor with an operating pressure range of 0-103.42 MPa (0.15 000 lb/in/sup 2/), a temperature range of -10 to +175 degrees C, a pressure calibration accuracy of 6894.8 Pa (1 lb/in/sup 2/), and resolution of 68.95 Pa (0.01 lb/in/sup 2/) with 1-s counter gate time. Doubly rotated cuts with piezoelectric coupling to both the C-modes of vibration were investigated. A theoretical study and general design considerations in the development of such sensors are described. Experimental results were obtained for two sensor designs: one uses a cylindrical design with the SBTC-cut, and the other, called SPA, is a special resonator design vibrating around 5 MHz without any activity dips. Pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in/sup 2/) at 175 degrees C is obtained. Laboratory evaluation of the static and dynamic performances is discussed for the prototypes based on the SPA design. >

Journal ArticleDOI
TL;DR: A computationally efficient method for phase aberration correction in ultrasound imaging based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements is presented.
Abstract: A computationally efficient method for phase aberration correction in ultrasound imaging is presented. The method is based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements. Effects of averaging estimated aberration patterns over scan angle and truncation to a single bit wordlength are examined. Phase distortions due to near-field inhomogeneities are simulated using silicone rubber aberrators. Performance of the method is tested using experimental data. Simulation studies addressing different factors affecting efficiency of the method, such as the number of iterations, window length, and the number of scan angles used for averaging, are presented. Images of a standard resolution phantom are reconstructed and used for qualitative testing. >

Journal ArticleDOI
TL;DR: An adaptation to a data reduction method is outlined for determining backscatter coefficients, eta, when broad-bandwidth pulses are employed, although better accuracy is obtained for longer gate durations, particularly when the sample exhibits resonance peaks inBackscatter versus frequency.
Abstract: An adaptation to a data reduction method is outlined for determining backscatter coefficients, eta , when broad-bandwidth pulses are employed. The accuracy of these eta values is assessed with well-characterized phantoms, for which backscatter coefficients based on their physical properties have been independently calculated. One phantom produces Rayleigh-like scattering, where the backscatter coefficient varies smoothly with frequency over the analysis bandwidth. A second phantom exhibits local maxima and minima in the scattering function versus frequency due to the presence of millimeter-sized graphite gel spheres in a gel background. The method was found to produce accurate results using time gate durations as small as 2 mu s, although better accuracy is obtained for longer gate durations, particularly when the sample exhibits resonance peaks in backscatter versus frequency. Use of a Hamming window in place of a rectangular window extends the accuracy near the upper and lower limits of the frequency range. >

Journal ArticleDOI
TL;DR: Multipoint foci have been synthesized by applying the pseudoinverse field conjugation method to a single ultrasonic transducer coupled to a polystyrene lens that is capable of generating strongly localized, controlled temperature fields for hyperthermia.
Abstract: Multipoint foci have been synthesized by applying the pseudoinverse field conjugation method to a single ultrasonic transducer coupled to a polystyrene lens. The lens design is based on phased array calculations are then fabricated on a computer-controlled milling machine. The measured beam patterns from the lenses agree closely with the beam patterns predicted by theory for the equivalent phased arrays. Temperature distributions from thermal modeling and those measured in tissue equivalent phantoms show that the lens system is capable of generating strongly localized, controlled temperature fields for hyperthermia. >

Journal ArticleDOI
TL;DR: Approximate formulas including losses to predict the electrical impedance of a thin unloaded piezoelectric plate around antiresonant frequencies of the thickness modes have been derived and it is shown that the theoretical impedance curves obtained with this model are in good agreement with measurements.
Abstract: Approximate formulas including losses to predict the electrical impedance of a thin unloaded piezoelectric plate around antiresonant frequencies of the thickness modes have been derived. To do so, a total loss factor is defined that includes both mechanical and electrical losses. Complex electrical impedance measurements on a lead metaniobate and four PZT-type materials between 2 and 50 MHz have been performed. The total loss factors were deduced from both the peak real impedance and from the -6 dB bandwidth of the real impedance peak. Results for fundamental and harmonic thickness modes on thin plates are discussed and the five materials are compared. It is found that for these piezoceramics the total loss factor is well approximated by a linear function of frequency. Finally, a frequency-dependent loss factor is included in the KLM equivalent circuit and it is shown that the theoretical impedance curves obtained with this model are in good agreement with measurements. >

Journal ArticleDOI
TL;DR: Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager, and can enhance detection of low contrast lesions using large phased-array apertures.
Abstract: In clinical applications using large apertures, a significant number of phased array elements may be blocked due to discontinuous acoustic windows into the body. These blocked elements produce undesired beamforming artifacts, degrading spatial and contrast resolution. To minimize these artifacts, an algorithm using multiple receive beams and the total-least-squares method is proposed. Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager. Combined with first-and second-order scatterer statistics derived from multiple receive beams, the algorithm is modified for blocked element compensation on distributed scattering sources. Results also indicate that compensated images are comparable to full array images, and that even full array images can be improved by removing undesired sidelobe contributions. This method, therefore, can enhance detection of low contrast lesions using large phased-array apertures. >

Journal ArticleDOI
TL;DR: A summation-subtraction method developed for decreasing the sidelobes is presented and the authors apply this technique to limited diffraction beams and obtain an analytic description.
Abstract: Conventional focused transducers have a sharp focal spot with low sidelobes, but they also have a short depth of field. Commercial medical scanners obtain increased depth of field by combining several images in a montage, each obtained at a different focal depth. Therefore, to get low sidelobes over a large depth of field several transmits must be used, which decrease the frame rate. Limited diffraction beams such as Bessel beams and X waves obtain good resolution over very large depth of field, but they have high sidelobes. A summation-subtraction method developed for decreasing the sidelobes is presented. The method requires three transmits, decreasing the frame rate to one third. The authors apply this technique to limited diffraction beams and obtain an analytic description. >

Journal ArticleDOI
TL;DR: In this article, the static equilibrium conditions for piezoelectric-ceramic-polymer composite structures are derived for a 2-2 composite of lamellar configuration, and the amplification factor is defined for the enhancement of the response of the active PEG ceramic resulting from this stress transfer.
Abstract: The static equilibrium conditions have been derived for piezoelectric-ceramic-polymer composite structures. Rigorous solutions are obtained for a 2-2 composite of lamellar configuration. Under a uniaxial stress or an electric field the strain profile becomes inhomogeneous due to different elastic stiffness of the two components (hard piezoelectric ceramics and soft polymer). The stress transfer between the two components is identified as due to an additional shear stress produced at the ceramic-polymer interface, and the amplification factor is defined for the enhancement of the response of the active piezoelectric ceramic resulting from this stress transfer. It is shown that this enhancement effect not only depends on the volume percentage of the active component but also on the aspect ratio of the two components. >

Journal ArticleDOI
TL;DR: In this article, the aging results for more than 40 oscillators, from a variety of sources, for periods ranging from 1 yr to more than 10 yr. The aging data were accumulated with an automated aging facility.
Abstract: The authors report aging results for more than 40 oscillators, from a variety of sources, for periods ranging from 1 yr to more than 10 yr. The aging data were accumulated with an automated aging facility. The oscillators that have been tested include temperature-compensated crystal oscillators (TCXOs) and oven-controlled crystal oscillators (OCXOs). The TCXOs were maintained in a controlled temperature environment. Several of the TCXOs were built for a gun-launched sensor application and have been shown to be capable of surviving more than 30000-g shock levels of 12-ms duration. The aging results for these ruggedized TXCOs are surprisingly good ( >

Journal ArticleDOI
TL;DR: An antialiasing algorithm is proposed that allows the source to be discretized with fewer sample points for a given accuracy than required with simple discretization techniques.
Abstract: The angular spectrum decomposition is evaluated in terms of plane wave angular range, angular resolution, and spatial aliasing error using two-dimensional FFT (2-D FFT). The algorithm makes possible the source plane decomposition of normal velocity and pressure fields radiated by transducers of arbitrary shape, with significantly faster results achievable for planar sources. Although the angular spectrum is equally applicable to fields far from the transducer, the efficient calculation is derived specifically for fields in or very close to the source plane. An antialiasing algorithm is proposed that allows the source to be discretized with fewer sample points for a given accuracy than required with simple discretization techniques. Guidelines for the selection of sampling interval, discretization size, etc. are developed on an application-specific basis and indicate the best ratio of numerical accuracy to computational cost. >

Journal ArticleDOI
TL;DR: The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight using a special filtering technique based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements is presented.
Abstract: The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight is presented. The flow meter under discussion uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone to measure high flow velocities, above 20 m/s. Because of the need for a pulse compression technique in the signal waveform design the technique of pulse compression and the choice of signal waveforms are discussed. The advantages and disadvantages of amplitude weighting vis-a-vis frequency domain manipulations of the waveforms are also discussed. To eliminate spurious times of flight, a special filtering technique is used, based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements. A summary of user experience with high-rangeability gas flow meters in use on different offshore platforms and in refineries is given. Long-term tests that examined the accuracy of the high-rangeability flow meter are also described. >

Journal ArticleDOI
TL;DR: A connection technique for two-dimensional array ultrasound transducers developed by combining a conductive lambda /4 mismatching layer with a multi-layer ceramic (MLC) connector using thick-film microelectronic technology is described.
Abstract: A connection technique for two-dimensional array ultrasound transducers developed by combining a conductive lambda /4 mismatching layer with a multi-layer ceramic (MLC) connector using thick-film microelectronic technology is described. The connector consists of 20 thick films of alumina and screen printed metallization with customized interconnections between the layers called vias. Ten ground layers are interleaved between ten signal layers to reduce elecrical crosstalk. A lambda /4 mismatching layer of conductive epoxy is bonded between each PZT element and the silver metal pad of the MLC connector to provide an effective low impedance backing. In the current configuration, a 16*16 transducer array, 0.6 mm element spacing, is expanded to a 16*16 grid of connector pins at a standard spacing of 2.5 mm. Vector impedance, sensitivity, bandwidth, interelement uniformity, and crosstalk are all in good agreement with arrays of conventional fabrication. However, an array with MLC connector can be fabricated more quickly independent of the number of elements. >

Journal ArticleDOI
TL;DR: A method is presented for implementing an optimal form of the Wiener filter that requires only estimates of the noise distribution parameters, and three estimation techniques, one a maximum-likelihood based method and the other two residual-sum-of-squares methods, are formulated and tested.
Abstract: Flaw signals measured in ultrasonic testing include the effects of the measurements system and are corrupted by noise The measurement system response is both bandlimited and frequency dependent within the bandwidth, resulting in measured signals which are blurred and distorted estimates of actual flaw signatures The Wiener filter can be used to estimate the flaw's scattering amplitude by removing the effect of the measurement system in the presence of noise A method is presented for implementing an optimal form of the Wiener filter that requires only estimates of the noise distribution parameters The theoretical error for scattering amplitude estimation, assuming various levels of available prior information, is analyzed Three estimation techniques, one a maximum-likelihood based method and the other two residual-sum-of-squares methods, are formulated and tested The results demonstrate that any of the three approaches could be used to optimally implement the alternative form of the Wiener filter with limited prior information >

Journal ArticleDOI
TL;DR: MLE results for 15 A-scans from stainless steel specimens with three different grain sizes indicate an average 6-dB signal-to-noise ratio (SNR) improvement in the coherent scatterer echo intensities for estimators using the SAC characterization as opposed to the PSD characterization.
Abstract: The effects of using spectral correlation in a maximum-likelihood estimator (MLE) for backscattered energy corresponding to coherent reflectors embedded in media of microstructure scatterers is considered. The spectral autocorrelation (SAC) function is analyzed for various scatterer configurations based on the regularity of the interspacing distance between scatterers. It is shown that increased regularity gives rise to significant spectral correlation, whereas uniform distribution of scatters throughout a resolution cell results in no significant correlation between spectral components. This implies that when a true uniform distribution for the effective scatterers exists, the power spectral density (PSD) is sufficient to characterize their echoes. However, as the microstructure scatterer distribution becomes more regular, SAC terms become more significant. MLE results for 15 A-scans from stainless steel specimens with three different grain sizes indicate an average 6-dB signal-to-noise ratio (SNR) improvement in the coherent scatterer (flat-bottom hole) echo intensities for estimators using the SAC characterization as opposed to the PSD characterization. >

Journal ArticleDOI
TL;DR: The results show that current diagnostic transducers heat more significantly at the transducer-tissue interface than at the focus, and the temperature rises for simultaneous multimode scanned beams are additive as the peak temperatures of each mode will occur on the surface.
Abstract: An acoustic-thermal model was developed for scanned diagnostic ultrasound in soft tissue. An adiabatic surface between the transducer and the skin was justified, and the model accounted for attenuation and focusing. The temperature along the central plane of the temporally averaged acoustic field was calculated by integration of line sources of heat that result from the tissue's absorption of ultrasound. The temperature profiles were calculated for 1400 transducers. The results show that current diagnostic transducers heat more significantly at the transducer-tissue interface than at the focus. The temperature rise in the focal region is typically less than 25% of that at the surface. The acoustic power per scan length that results in a 1 degrees C temperature rise at the surface is calculated as (210 mW-MHz/cm)/f. These results apply to both linear arrays and sectorlike scan formats. The temperature rises for simultaneous multimode scanned beams are additive as the peak temperatures of each mode will occur on the surface. Consideration was given to the surface boundary condition for such models. This boundary is considered adiabatic for calculation of heating due to acoustic absorption alone. Additional heating or cooling resulting from the transducer can then be superimposed on this solution. >

Journal ArticleDOI
Osamu Ohnishi1, Osamu Myohga1, Tadao Uchikawa1, M. Tamegai1, Inoue Takeshi1, Sadayuki Takahashi1 
TL;DR: It is found that the resonant frequencies for longitudinal mode and torsional mode could coincide with each other in the ultrasonic motor, according to finite element method analysis and experimental measurement.
Abstract: A piezoelectric ultrasonic motor, which uses longitudinal and torsional composite vibration, is examined in order to obtain high torque characteristics with small diameter. Piezoelectric ceramic elements, oscillating in both longitudinal and torsional modes, respectively, are used as piezoelectric stiffened modes having high electromechanical coupling factors k/sub 33/ and k/sub 15/, respectively. It is found that the resonant frequencies for longitudinal mode and torsional mode could coincide with each other in the ultrasonic motor, according to finite element method analysis and experimental measurement. The motor operating in both resonant vibrations indicated good performance. The 20-mm diameter motor exhibited 4 kgfcm maximum torque, 450 r/min maximum rotational speed, 40% maximum efficiency, and quick responsiveness, within 2.5 ms. >

Journal ArticleDOI
TL;DR: An asynchronous spread spectrum modem in the 2.45-GHz band has been implemented using an efficient ZnO-SiO/sub 2/-Si surface acoustic wave (SAW) convolver, based on a direct-sequence/code-shift-keying (DS/CSK) method for the modulation.
Abstract: An asynchronous spread spectrum (SS) modem in the 2.45-GHz band has been implemented using an efficient ZnO-SiO/sub 2/-Si surface acoustic wave (SAW) convolver. The modem, which can operate under full duplex transmission is based on a direct-sequence/code-shift-keying (DS/CSK) method for the modulation. Pseudonoise (PN) codes are chosen from a preferred pair of m-sequences of period 127, and the code rate is 14 MHz. The demodulation is carried out asynchronously, utilizing the coherent correlation characteristics of the SAW convolver. The main interference caused by a transmitted signal in the modem itself is effectively reduced by an RF isolator and the SS process gain. Adequate self-jamming rejection capability has been confirmed; a bit error rate of 10/sup -6/ is observed at -78.3 dB of a desired-to-undesired-signal ratio using an artificial transmission line. >

Journal ArticleDOI
TL;DR: Experimental results obtained in water as well as in air show that this optical heterodyne technique offers a very sensitive way of measuring ultrasonic pressures in the low megahertz range even for very low pressures.
Abstract: An optical heterodyne interferometer was used for measuring short ultrasonic pulses in fluids The optical phase shift of the probe beam, proportional to the acoustic pressure integrated along the light path, was demodulated quantitatively by electronic processing The detection sensitivities of 10/sup -3/ (Pa/ square root Hz) in water and 10/sup -4/ (Pa/ square root Hz) in air were deduced The experimental results obtained in water as well as in air show that this optical heterodyne technique offers a very sensitive way of measuring ultrasonic pressures in the low megahertz range even for very low pressures >

Journal ArticleDOI
TL;DR: The expressions of the inphase and quadrature components from the point of focusing are derived and analyzed in detail, and a scheme to eliminate the unwanted phase terms is proposed.
Abstract: The quadrature sampling technique as a means of detecting the envelope of RF waveform in the baseband is well known. If this technique is applied to a focused ultrasound imaging system using an array transducer, whether it is a synthetic or nonsynthetic focusing system, unwanted phase terms appear in the expressions of the inphase and quadrature components of the baseband signal when an appropriate delay time is introduced to each channel signal for the purpose of focusing. The expressions of the inphase and quadrature components from the point of focusing are derived and analyzed in detail, and a scheme to eliminate the unwanted phase terms is proposed. The resulting phase-error-free quadrature sampling technique is applied to the synthetic focusing system; a system block diagram together with the simulation and experimental results are presented. >

Journal ArticleDOI
TL;DR: The performance of a single-phase unidirectional transducers utilizing the internal reflections of floating electrodes of electrically open and shorted metal strips within an interdigital electrode structure (FEUDT: floating electrode unid Directional transducer) is analyzed using a coupled-mode theory.
Abstract: The performance of a single-phase unidirectional transducers utilizing the internal reflections of floating electrodes of electrically open and shorted metal strips within an interdigital electrode structure (FEUDT: floating electrode unidirectional transducer) is analyzed using a coupled-mode theory. All four independent parameters (the self and mutual coupling coefficient, the transduction coefficient, and the static capacitance) governing the coupling-mode equation with an electrical transduction term are analytically derived using extended Legendre polynomial expansions of electrical fields and perturbation analysis. Frequency response of radiation admittance and insertion loss, and SAW field distributions in a transducer are calculated from simple closed-form solutions of the coupled-mode equation. The shift effect of reflection and transduction centers due to the asymmetric electrode structure is clarified. Experimental results are given for test devices fabricated on a 128 degrees C YX LiNbO/sub 3/ substrate and compared with theoretical results. >