Showing papers in "IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control in 1990"

Simulation of piezoelectric devices by two- and three-dimensional finite elements

Abstract: A method for the analysis of piezoelectric media based on finite-element calculations is presented in which the fundamental electroelastic equations governing piezoelectric media are solved numerically The results obtained by this finite-element calculation scheme agree with theoretical and experimental data given in the literature The method is applied to the vibrational analysis of piezoelectric sensors and actuators with arbitrary structure Natural frequencies with related eigenmodes of those devices as well as their responses to various time-dependent mechanical or electrical excitations are computed The theoretically calculated mode shapes of piezoelectric transducers and their electrical impedances agree quantitatively with interferometric and electric measurements The simulations are used to optimize piezoelectric devices such as ultrasonic transducers for medical imaging The method also provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoelectric media >

Ultrasonic imaging of internal vibration of soft tissue under forced vibration

Abstract: An imaging system that can display both the amplitude and phase maps of internal vibration in soft tissues for forced low-frequency vibration is described. In this method, low-frequency sinusoidal vibration of frequency under several hundred hertz is applied from the surface of the sample and the resulting movement in it is measured from the Doppler frequency shift of the simultaneously transmitted probe ultrasonic waves. Basic experiments are carried out by using 3.0-MHz ultrasonic waves. The two-dimensional maps of the amplitude and phase of internal vibration are shown, and the velocities of vibration are measured for some samples as well as in vivo. >

Matrix methods applied to acoustic waves in multilayers

Abstract: Matrix methods for analyzing the electroacoustic characteristics of anisotropic piezoelectric multilayers are described. The conceptual usefulness of the methods is demonstrated in a tutorial fashion by examples showing how formal statements of propagation, transduction, and boundary-value problems in complicated acoustic layered geometries such as those which occur in surface acoustic wave (SAW) devices, in multicomponent laminates, and in bulk-wave composite transducers are simplified. The formulation given reduces the electroacoustic equations to a set of first-order matrix differential equations, one for each layer, in the variables that must be continuous across interfaces. The solution to these equations is a transfer matrix that maps the variables from one layer face to the other. Interface boundary conditions for a planar multilayer are automatically satisfied by multiplying the individual transfer matrices in the appropriate order, thus reducing the problem to just having to impose boundary conditions appropriate to the remaining two surfaces. The computational advantages of the matrix method result from the fact that the problem rank is independent of the number of layers, and from the availability of personal computer software that makes interactive numerical experimentation with complex layered structures practical. >

Ultrasonic nondiffracting transducer for medical imaging

Abstract: The nondiffracting J/sub 0/ Bessel beam is evaluated, and its application to medical imaging is suggested. Computer simulations and experimental results for a ten-ring annular Bessel shaded transducer are described. Both continuous-wave (CW) and pulse-wave (PW) excitations are shown and compared to conventional Gaussian beams. The nondiffracting beam has about 1.27-nm radius main lobe with a 20-cm depth of field compared to the Gaussian transducer of the same size with a 1.27-mm radius main lobe at a focus of 12 cm and 2*4-cm depth of field. The side lobes of the nondiffracting beam are the same as the J/sub 0/ Bessel function. The effects of heterogeneity due to tissue on the nondiffracting beam and on the focused Gaussian beam are also reported. >

Flow velocity profile via time-domain correlation: error analysis and computer simulation

Abstract: An ultrasonic human-blood-flow velocity profile measurement method using time-domain correlation of consecutive echo pairs has been developed. The time shift between a pair of range gated echoes is estimated by searching for the shift that results in the maximum correlation. The time shift indicates the distance a group of scatterers has moved, from which flow velocity is estimated. The basis for the computer simulations and error analyses of the scheme includes a band-passed white Gaussian noise signal model for an echo from a scattering medium, the estimate of flow velocity from both a single scatterer and multiple scatterers, and a derived precision estimation. The error analysis via computer simulation includes an evaluation of errors associated with the correlation method. For a uniform flow velocity profile, beamwidth modulation represents the greatest error source. However, for a nonuniform flow velocity profile, the jitter caused by a small flow velocity gradient can exceed the other error sources. A detailed computer simulation evaluated the interdependencies of window length, beam width, vessel diameter, and viewing angle on the estimation of flow velocity. >

PC software for SAW propagation in anisotropic multilayers

Abstract: A software package that provides an interactive and graphical environment for surface acoustic wave (SAW) and plate-mode propagation studies in arbitrarily oriented anisotropic and piezoelectric multilayers is described. The software, which runs on an IBM PC with math coprocessor, is based on a transfer-matrix formulation for calculating the characteristics of SAW propagation in multilayers that was originally written for a mainframe computer. The menu-driven software will calculate wave velocities and field variable variations with depth for any desired propagation direction: the graphics capability provides a simultaneous display of slowness or velocity and of SAW Delta v/v coupling constant curves, and their corresponding field profiles in either polar or Cartesian coordinates, for propagation in a selected plane or as a function of one of the Euler angles. The program generates a numerical data file containing the calculated velocities and field profile data. Examples illustrating the usefulness of the software in the study of various SAW and plate structures are presented. >

Volumetric blood flow via time-domain correlation: experimental verification

Abstract: A novel ultrasonic volumetric flow measurement method using time-domain correlation of consecutive pairs of echoes has been developed. An ultrasonic data acquisition system determined the time shift between a pair of range gated echoes by searching for the time shift with the maximum correlation between the RF sampled waveforms. Experiments with a 5-MHz transducer indicate that the standard deviation of the estimate of steady fluid velocity through 6-mm-diameter tubes is less than 10% of the mean. Experimentally, Sephadex (G-50; 20-80 mu m dia.) particles in water and fresh porcine blood have been used as ultrasound scattering fluids. Two-dimensional (2-D) flow velocity can be estimated by slowly sweeping the ultrasonic beam across the blood vessel phantom. Volumetric flow through the vessel is estimated by integrating the 2-D flow velocity field and then is compared to hydrodynamic flow measurements to assess the overall experimental accuracy of the time-domain method. Flow rates from 50-500 ml/min have been estimated with an accuracy better than 10% under the idealized characteristics used in this study, which include straight circular thin-walled tubes, laminar axially-symmetric steady flow, and no intervening tissues. >

Finite-element analysis of vibrational modes in piezoelectric ceramic disks

Abstract: The natural vibrational modes of axially symmetric piezoelectric ceramic disks have been calculated by the finite-element method. The disks are of the type used as active elements in compressional wave ultrasonic transducers, and are electrically polarized in thickness with full electrodes on the disk's major faces. To optimize disk geometry for ultrasonic transducer application, the dependence of the vibrational modes on the disk diameter-to-thickness ratio for ratios from 0.2 (a tall cylinder) to 10.0 (a thin disk) has been studied. Series and parallel resonance frequencies for each of the modes are determined through an eigenfrequency analysis, and effective electromechanical coupling coefficients are calculated. The modal displacement fields in the disk are calculated to determine the physical nature of each mode. An analysis of the complete spectrum of piezoelectrically active modes as a function of diameter-thickness ratio is presented for the ceramic PZT-5H, including and identification of radial, edge, length expander, thickness shear, and thickness extensional vibrations. From this analysis, optimal diameter-to-thickness ratios for good transducer performance are discussed. >

Embedded fiber-optic Fabry-Perot ultrasound sensor

Abstract: A fiber-optic ultrasound sensor is presented. The sensor consists of a continuous length of single-mode optical fiber with a built-in Fabry-Perot interferometer. The acoustic pressure produces changes in the index of refraction along the interferometer cavity through the strain-optic effect, thus modulating the reflected power of the light propagating in the fiber. The dielectric internal mirrors that form the interferometer are fabricated by joining a fiber coating with a TiO/sub 2/ film at one end to an uncoated fiber by electric arc fusion splicing. Experimental results have been obtained for sensors embedded in plastic and graphite composite materials, using ultrasound waves in the range from 100 kHz to 5 MHz. Values for the optical phase shift amplitude as large as 0.5 rad were obtained at an acoustic frequency of 200 kHz for a 1.1-cm-long interferometer embedded in plastic. >

Experimental results with a real-time adaptive ultrasonic imaging system for viewing through distorting media

Abstract: An online adaptive phased-array ultrasonic imaging system capable of markedly improving the detectability of targets viewed through inhomogeneous media is described. An online adaptive phase correction technique implemented on a research phased-array scanner is described. The theoretical basis for this technique is presented by describing the relationship between the magnitude of phase aberrations and the regional brightness of speckle and pointlike targets. The system currently generates a corrected image in approximately 0.1 s and utilizes no prior knowledge of the aberrating media or the target. The adaptive imaging algorithm uses regional target brightness as a quality factor. The results of in vitro tests with this system using electronic and physical aberrators for both diffuse and pointlike targets are presented. >

Spectral characterization of tissues microstructure by ultrasounds: a stochastic approach

Abstract: A model of the echo formation process from tissues is suggested, in order to relate microstructural features to ultrasonic spectral signatures. The tissue is modeled as a collection of ideal randomly distributed scatterers, filtered by a time-invariant system representing the measurement apparatus and the average properties of the scattering medium, to obtain the backscattered signal. The gamma distribution has been assumed to describe the process, because it offers a flexible approach to approximating the parametric regularity of the scatterers. According to the model the spectral characteristics of the backscattered signal are strictly correlated with the spatial architecture and can be related to the gamma distribution parameters, i.e. interdistance and order. The model has been tested by simulating practical situations, in order to prove its validity and to test the procedure for estimating model parameters from actual data. The correspondence of experimental results obtained from tissues of different degrees of regularity with the simulated results confirms the effectiveness of the model for tissue characterization studies. >

Acoustic properties of particle/polymer composites for ultrasonic transducer backing applications

Abstract: The acoustic impedance and attenuation in composites made of particle fillers loaded in polymer matrices for transducer backing applications is investigated. The acoustic impedance of tungsten/vinyl composites was modeled, and an experimental matrix identifying variables that contribute to composite attenuation was established. The variable included the particle type, the particle size and volume fraction of a filler, the physical characteristics of the polymer matrix, and the processing route that determined the composite connectivity. Experimental results showed that with an increase in filler particle size or a decrease in volume fraction of filler, there is an increase in composite attenuation. Overall, the various types of filler, the polymer matrix, and the interface between the two contribute to attenuation in the composite, as confirmed by the acoustic properties and the microstructural analysis. >

Modeling phase noise in frequency dividers

Abstract: A theory for modeling noise in frequency dividers and the measurements to support the theory are presented. The most complete measurements were made on ECL (emitter-coupled logic) dividers for which the primary noise contributions were from additive output noise and sampled additive input noise. Output phase power spectral density due to the latter varies as the square of the input frequency and is inversely proportion to the output frequency. The third most significant contributor was sampled output noise. A summary of available noise data is also given. >

A linear piezoelectric stepper motor with submicrometer step size and centimeter travel range

Abstract: A linear stepper motor capable of submicrometer controlled movement has been constructed using the piezoelectric material lead zirconate titanate (PZT). This motor consists of a 25.4-mm*12.7-mm*1.6-mm piezoelectric driving element connected between a glider base and an attached load. The device is inset in a trench to constrain motion to one dimension. An electrode on the bottom of the glider is used with an electrode on the top of the trench to implement an electrostatic clamp. This clamp enables the stepper motor to climb slopes of up to 12 degrees , whereas without the clamp only slopes of 6 degrees or less are tolerated. A linear inertial sliding motion can be achieved by expanding and contracting the piezoelectric bar, but the addition of the electrostatic clamp enhances the movement capabilities of the glider by the periodic clamping and unclamping of the glider. Glider velocities of 5.7-476 mu m/s are measured by timing the movement of the glider over a 1.0-mm portion of the track through an optical microscope. Displacement steps of 0.07-1.1 mu m are calculated by dividing the measured glider velocity by the frequency of the applied voltage pulses. Displacement step size and glider velocity are controlled by the application of PZT extension voltages ranging from +or-(60-340) V. >

Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise

Abstract: Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering gallery mode sapphire ring resonator with Q of 2*10/sup 5/. The nature of the mode, which involves little metallic conduction, allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified with good agreement with calculated frequency predictions. Waveguide coupling parameters have been characterized for the principal (lowest frequency) mode family, for n=5 to n=10 full waves around the perimeter. For a 5-cm wheel resonator in a 7.6-cm container, Q-values of above 10/sup 5/ were found at room temperature for all of the modes in this sequence. Coupling Q-values for the same modes ranged from 10/sup 4/ (n=5) to 10/sup 5/ (n=10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n=10 (7.84-GHz) mode showed a 1/f/sup 3/ dependence for low offset frequencies, and a value of L(f)=-55 dB/Hz at an offset of 10 Hz from the carrier. The oscillator shows phase noise below the previously reported for any X-band source. >

Analysis of piezoelectric bulk-acoustic-wave resonators as detectors in viscous conductive liquids

Abstract: An analytical solution for the resonance condition of a piezoelectric quartz resonator with one surface in contact with a viscous conductive liquid is presented. The characteristic equation that describes the resonance condition and accounts for all interactions including acoustoelectric interactions with ions and dipoles in the solution is obtained in terms of the crystal and liquid parameters. A simple expression for the change in the resonance frequency is obtained. For viscous nonconductive solutions, the frequency change is reduced to a relationship in terms of the liquid density and viscosity. For dilute conductive liquid, the change in frequency is derived in terms of the solution conductivity and dielectric constant. The boundary conditions for the problem are defined with and without the electrical effects of electrodes. Experiments were conducted with various viscous and conductive chemical liquids using a fabricated miniature liquid flow cell containing an AT-cut quartz crystal resonator. The results, which show good agreement with the theory, on the use of quartz crystal resonators as conductivity and/or viscosity sensors are reported. >

Progress at NIST toward absolute frequency standards using stored ions

Abstract: Experiments directed toward the realization of frequency standards of high accuracy using stored ions are briefly summarized. In one experiment, an RF oscillator is locked to a nuclear spin-flip hyperfine transition (frequency approximately= 3.03*10/sup 8/ Hz) in /sup 9/Be/sup +/ ions that are stored in a Penning trap and sympathetically laser-cooled. Stability is better than 3*10/sup -12/ tau /sup -(1/2)/ and uncertainty in Doppler shifts is estimated to be less than 5*10/sup -15/. In a second experiment, a stable laser is used to probe an electric quadrupole transition (frequency approximately=1.07*10/sup 15/ Hz) in a single laser-cooled /sup 199/Hg/sup +/ ion stored in a Paul trap. The measured Q value of this transition is approximately 10/sup 13/. Future possible experiments are discussed. >

Experimental verification of the Kramers-Kronig relationship for acoustic waves

Abstract: A spectral technique for effectively and accurately measuring acoustic attenuation over a wide frequency range is reported. The spectral technique for phase measurement developed by W. Sachse and Y.H. Pao (1978) was used to determine the acoustic dispersion. For acoustic waves, a very simple and useful Kramers-Kronig relationship was previously derived by M. O'Donnell, E.T. Jaynes, and J.G. Miller (1981). The attenuation was calculated, using this relationship, from the measured dispersion and then compared with the attenuation that was measured independently. Dispersion was deduced from the measured attenuation and compared with the measured dispersion. The results of two highly attenuative specimens are presented. The agreement between the calculated attenuation and measured attenuation is excellent. The deduced dispersion also agrees well with the measured one. This agreement verifies the simple Kramers-Kronig relationship used. It further shows the accuracy of the spectral techniques for attenuation and dispersion measurements over a wide frequency range. >

Analysis of nonaxisymmetric vibration mode piezoelectric annular plate and its application to an ultrasonic motor

Abstract: The development of an ultrasonic motor using nonaxisymmetric vibration modes of a piezoelectric annular plate is described. A piezoelectric annular plate is analyzed to find its mode patterns, elliptic motions of displacement for the motor, and the distributions of the induced charge on the plate surface, and to calculate electromechanical coupling factors. On the basis of the analyzed results, motors using the annular plate have been built and their characteristics measured. The construction and characteristics of these motors are discussed. >

Optimizing ultrasonic transducers based on piezoelectric composites using a finite-element method

Abstract: A novel approach to understanding the vibratory behavior of composite piezoelectric materials is proposed. Elementary ceramic rods, and the effects of their width-to-thickness (W/T) ratio are studied. A model based on the finite-element methods is used. Some experimental results that agree well with the computed data are presented. Plots of resonant frequencies and coupling coefficients versus W/T are given that can be used in transducer design. >

Low-order AR models for mean and maximum frequency estimation in the context of Doppler color flow mapping

Abstract: Autoregressive (AR) techniques are investigated by developing mean and maximum frequency estimators suitable for use in Doppler color flow mapping systems, where they are most needed. The estimators are based on low-order (for computational efficiency) AR models applied to complex signals whose real and imaginary parts are the in-phase and quadrature components of the analytical Doppler signal, respectively. A large number of simulated data sequences generated by a sinusoidal computer model and having different number of samples, spectral shapes, bandwidths, and signal-to-noise ratios are used to examine the performance (bias and variance) of the estimators in a systematic manner. Comparisons are made with the established autocorrelation technique, whose output is shown to be identical to one of the AR mean frequency estimators described. >

Ultrasonic robot eyes using neural networks

Abstract: In order to construct a robot eye using ultrasonic waves in air, a system that combines existing acoustical holography with neural networks is devised. In this system, neural networks are used to reduce the vagueness of reconstruction from the acoustical holography. The system is able to identify objects and to reconstruct the acoustical images of objects using an array of only a small number of receivers. Some experimental results on identification and reconstruction using several kinds of metal plate objects are reported. >

The random phase transducer: a new technique for incoherent processing-basic principles and theory

Abstract: It is pointed out that speckle noise can be reduced through the use of incoherent processing techniques. The theoretical limit for the SNR improvement when incoherent processing techniques are used is studied. The study leads to the concept of information grains. A simple technique for incoherent processing that is easy to implement and that allows a good physical understanding of the limitations of incoherent processing of pulse-echo signals is also studied. This technique does not require the division of the receiving aperture into many small coherent subelements, the scanning of the field as in spatial compounding, or the use of low-sensitivity CdS transducers. It involves a single coherent transducer and a moving random phase screen placed in front of it. >

Distortions of thickness shear mode shapes in plano-convex quartz resonators with mass perturbations

Abstract: A perturbation technique for calculating the change in mode shape in a plano-convex thickness shear resonator blank due to off-center mass perturbations is developed. The perturbed shape is built as a linear combination of the familiar unperturbed modes and their anharmonics. The change in the location of the average center of the mode is calculated for different contours and different mass perturbation shapes and thicknesses. The results are used to predict changes in the acceleration sensitivity of two-point mounted 10-MHz, third SC-cut resonators when patches of metal film are deposited on the major surfaces off-center. These theoretical results are compared with published experimental results. >

Analysis of leaky-surface-wave propagating under periodic metal grating

Abstract: A detailed field analysis is presented for a leaky surface wave propagating under a periodic metal grating, using a theory that neglects the effect of mass loading due to the grating. The approach is based on Floquet's theorem and the coupled equations of wave motion with unperturbed mechanical and perturbed (or periodic) electrical boundary conditions, yielding a general field solution applicable to any material and to arbitrary connections to the grating. As a key step, the periodic boundary equations are solved by combining them into a set of infinite homogeneous equations through algebraic treatment and performing orthogonal integration with respect to space harmonics. The advantage in using this method results from there being no need to use assumptions or complicated expressions anticipating an accurate solution if sufficient space harmonics are considered. It is shown that the theory proposed here can be directly extended to solve simpler SAW problems. An analysis is carried out for LiNbO/sub 3/ for both the leaky wave and Rayleigh wave, taking into account dispersion relations, propagation attenuation of the leaky wave, and other field distributions. Theoretical and experimental results for the width of the first stopband are discussed. >

High Q metal strip SSBW resonators using a SAW design

Abstract: An experimental study of metal strip surface skimming bulk wave (SSBW) resonators using a surface acoustic wave (SAW) design is presented. Characteristics of SSBW and SAW resonators fabricated with the same photolithographic mask are compared and discussed. High Q low-loss SSBW resonators are achieved using a conventional two-port SAW resonator design and taking special care of the distance L between both interdigital transducers, the metal thickness h/ lambda ( lambda =acoustic wavelength) and the finger-to-gap ratio. Best overall performance of the SSBW devices in this study is achieved at L=n lambda /2- lambda /4 (compared with L=n lambda /2- lambda /8 for SAW resonators), h/ lambda =1.6% (compared with 2% for SAW), and finger-to-gap ratio close to 1. The best device fabricated shows an unloaded Q of 5820 and an insertion loss of 7.8 dB at 766 MHz. The SSBW resonant frequency shows a stronger dependence on the metal thickness than the SAW one. This problem, however, is readily solved by frequency trimming using a CF/sub 4/ plasma etching technique. SSBW resonator can be trimmed by 0.2% down in frequency (compared with 0.05% for SAW) without affecting their performance. >

Phase noise performance of analog frequency dividers

Abstract: The phase noise performance obtainable using silicon and GaAs-based TTL (transistor-transistor logic) and ECL (emitter-coupled logic) logic level digital frequency dividers is discussed. Measurement of the spectral performance of two types of analog dividers is reported: a parametric divider using varactor diodes and a regenerative-type divider incorporating a double-balanced mixer in the oscillator feedback circuit. Both dividers were configured for divide-by-two operation at VHF. Evaluation indicates the regenerative divider is capable of providing much lower phase noise than conventional digital logic level devices. The regenerative divider can be successfully operated over bandwidths in excess of an octave, and the design lends itself to small (i.e. TO-8) modular package implementation. Operating frequencies are bounded only by the range of the mixer and RF amplifier utilized and, as such, should extend from HF through microwave. >

Computationally efficient algorithms for control of ultrasound phased-array hyperthermia applicators based on a pseudoinverse method

Abstract: Computationally efficient incremental algorithms for application of the pseudoinverse method for ultrasound phased-array field pattern synthesis are discussed and shown to significantly reduce computing effort when more control points should be added to existing subsets of points previously manipulated. These algorithms avoid calculation of inverse matrices, a time-consuming job for microcomputers when the dimensions of the matrices are large. This technique can be used to recursively modify the heating patterns of a phased-array hyperthermia applicator in the clinic. >

Bubble sizing with high spatial resolution

Abstract: The authors propose a technique that allows them to size bubbles with the same accuracy as with the double-frequency method and to locate them with the same range resolution as with the pulsed Doppler velocimeter. They demonstrate that the signal scattered by the bubble insonified by a high-frequency pulsed ultrasonic field and a low-frequency pumping field is a low-frequency signal sampled at the repetition frequency rate and in which the amplitude is maximum when the bubble resonates. However using a conventional Doppler flowmeter, the maximum amplitude is not detectable when the repetition frequency is a multiple of the pump frequency. The modifications of the signal processing needed to overcome this drawback are discussed and implemented in the conventional Doppler flowmeter. Using this modified setup the lateral and the longitudinal range resolution are the same as in conventional Doppler flowmeters. The resonance frequency thus obtained is also compared to the resonance frequency measured by the double Doppler frequency method. Some practical improvements are proposed to make the system easy to use. Using this latest version, the resonant requencies for ten different bubble sizes are measured and compared. The case in which the nonlinearity effect (due to a bubble at resonance) generates out-of-phase upper and lower sidebands is discussed, and it is demonstrated that this effect is so feeble that it is negligible. >

Shell theory for vibrations of piezoceramics under a bias

Abstract: A consistent derivation of the shell theory in invariant form for the dynamic fields superimposed on a static bias of piezoceramics is discussed. The fundamental equations of piezoelectric media under a static bias are expressed by the Euler-Lagrange equations of a unified variational principle. The variational principle is deduced from the principle of virtual work by augmenting it through Friedrich's transformation. A set of two-dimensional (2-D), approximate equations of thin elastic piezoceramics is systematically derived by means of the variational principle together with a linear representation of field variables in the thickness coordinate. The 2-D electroelastic equations accounting for the influence of mechanical biasing stress accommodate all the types of incremental motions of a polarized ceramic shell coated with very thin electrodes. Emphasis is placed on the special motions, geometry, and material of the piezoceramic shell. The uniqueness of the solutions to the linearized electroelastic equations of the piezoceramic shell is established by the sufficient boundary and initial conditions. >