By Topic

Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 3 • Date May 1996

Filter Results

Displaying Results 1 - 22 of 22
  • Frequency dependence of backscatter coefficient versus scatterer volume fraction

    Page(s): 345 - 353
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (907 KB)  

    Various groups are using the frequency dependence of backscattering to characterize tissue. In most cases, sparse scatterer concentrations are assumed in relating scattering parameters to tissue properties. This study addresses the relationship between backscatter frequency dependence and scatterer volume fraction. Backscatter coefficients (BSC) in the 2.5 to 9.0 MHz frequency range were measured for agar-gel phantoms containing Sephadex scatterers (mean diameter 42 /spl mu/m) at volume fractions ranging from 5 to 50%. The BSC increased with scatterer volume fraction at low scatterer concentrations; at higher concentrations, the BSC reached a maximum with concentration and then decreased with yet increasing scatterer concentrations, as has been noted by previous authors. In addition, the volume fraction for the maximum backscatter coefficient varied with frequency, generally being greater at higher frequencies than lower frequencies, and the frequency dependence of the backscatter coefficient was greater for the higher scatterer concentrations than for the lower concentrations. These results are predicted by continuum models, where the spatial autocorrelation function depends on scatterer volume fraction. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Frequency synthesis chain for the atomic fountain primary frequency standard

    Page(s): 354 - 358
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (542 KB)  

    The frequency noise of the local oscillator may degrade the long-term stability of high-stability frequency standard; a simple evaluation of this effect is performed to optimize the design of a synthesizer to be used in Cs atomic primary frequency standard. A description of the microwave synthesis chain realized, which is suitable as a local oscillator for Cs atomic primary frequency standard, is reported. Phase noise spectra in the key points of the chain are also reported. The measured fractional frequency stability of the chain is better than 10/sup -17/ at one day. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vessel wall detection and blood noise reduction in intravascular ultrasound imaging

    Page(s): 359 - 369
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1507 KB)  

    Scattering from blood limits the contrast between the vessel wall and the lumen in intravascular ultrasound imaging. This makes it difficult to localize the vessel wall, especially on still images. This paper presents a method for automatic detection of vessel walls and reduction of blood noise based on correlation of the RF-signal between adjacent frames. The ultrasound RF-signal is quadrature demodulated, digitized, stored in memory, and transferred to a computer for processing and analysis. The absolute value of the cross-correlation coefficient between two adjacent frames is used to differentiate between stationary and fluctuating signals. Models and numerical calculations presented in this work indicate that the cross-correlation coefficient obtained from a radially dilating vessel wall will be larger than 0.8 under standard 20 MHz imaging conditions. The corresponding value from blood is less than 0.2 for blood velocities exceeding 0.5 cm s/sup -1/. The blood-noise filter is based on detecting this difference in correlation and displays vessel wall regions with no modifications, while regions detected as blood are rejected. A simplified vessel-wall detector that is suitable for real-time implementation is proposed. The performance of this detector and the blood noise filter are demonstrated by in vitro experiments. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A model for the theoretical characterization of thin piezoceramic rings

    Page(s): 370 - 375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (489 KB)  

    This work describes a matrix model of the radial mode of a thin piezoceramic ring capable of predicting the dynamic behavior when the two main surfaces are stress free, while the lateral, inner, and outer are loaded by an external medium. The ring is modeled as a three-port system with two mechanical ports and one electrical port. With this approach it is easy to compute the resonance frequency spectrum, the radial displacement, and the electric impedance of a thin ring. Good agreement between the computed and the measured electric impedance is found. The resonance frequency spectrum is computed as a function of the inner-to-outer radius ratio G: when the inner radius vanishes, the resonances of the ring coincide with those of a disk, while, increasing G up to one, the first-mode frequencies decrease approaching the value obtained with a lumped mode model. The frequencies of the higher-order modes, on the other hand, increase to infinity, justifying the lumped mode approximation. The spatial distribution of the displacement in the radial direction is also computed; it has a Bessel function shape which, as expected, becomes linear by increasing the inner radius. Finally, the behavior of the effective coupling factor k/sub eff/ with G is examined. It is shown that, when G/spl rarr/1, k/sub eff/ approaches the material coupling factor k/sub 31/, while when G/spl rarr/0, k/sub eff/ is proportional to the planar coupling factor k/sub p/. Further it is shown that for G>0.6, the approximation of the ring to a lumped mode system is quite acceptable. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultrasound three-dimensional velocity measurements by feature tracking

    Page(s): 376 - 384
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1081 KB)  

    This article describes a new angle-independent method suitable for three-dimensional (3-D) blood flow velocity measurement that tracks features of the ultrasonic speckle produced by a pulse echo system. In this method, a feature is identified and followed over time to detect motion. Other blood flow velocity measurement methods typically estimate velocity using one- (1-D) or two-dimensional (2-D) spatial and time information. Speckle decorrelation due to motion in the elevation dimension may hinder this estimate of the true 3-D blood flow velocity vector. Feature tracking is a 3-D method with the ability to measure the true blood velocity vector rather than a projection onto a line or plane. Off-line experiments using a tissue phantom and a real-time volumetric ultrasound imaging system have shown that the local maximum detected value of the speckle signal may be identified and tracked for measuring velocities typical of human blood flow. The limitations of feature tracking, including the uncertainty of the peak location and the duration of the local maxima are discussed. An analysis of the expected error using this method is given. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Flexible ultrasonic transducer arrays for nondestructive evaluation applications. I. The theoretical modeling approach

    Page(s): 385 - 392
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    This paper presents the development of a theoretical modeling strategy to be used in the design of flexible ultrasonic transducer arrays. These new types of array device are intended for those applications where surface conformity is desirable. Such array structures allow much more efficient and effective coupling of acoustic energy between the transducer and test specimen than would have been otherwise possible with an equivalent rigid device. The objective of this work is to provide the transducer designer with a set of design tools that will permit the analysis of different material configurations and various transmit-receive aperture designs. Linear systems modeling is used to evaluate, and consequently optimize, the transduction performance, while a surface scattering model has been developed to facilitate the analysis of different transmit-receive aperture configurations. A theoretical modeling approach for flexible arrays is developed and where necessary, the validity confirmed by experimental measurement. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Flexible ultrasonic transducer arrays for nondestructive evaluation applications. II. Performance assessment of different array configurations

    Page(s): 393 - 402
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1174 KB)  

    For pt. I see ibid., vol. 43, pp. 385-92 (1996). This work describes a fundamental investigation into a new series of transducer array structures intended for those applications where surface conformity is desirable. The first objective is to consider which material combinations will offer flexibility, while at the same time maximize the electromechanical efficiency for operating into solid load media. The theoretical approach of Part I is employed to compare and assess different array structures for nondestructive evaluation (NDE) imaging applications. The array structures under consideration include multielement piezocomposite and piezopolymer arrays, and hybrid devices comprising piezocomposite transmitters with piezopolymer receivers. Experimental data are provided for a novel array configuration, comprising a separate piezocomposite transmitter coupled to a piezopolymer receiver. Good agreement is demonstrated between experimental and theoretical results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cutoff frequencies and noise power law model of spectral density: adaptation of the multivariance method for irregularly spaced timing data using the lowest-mode estimator approach

    Page(s): 403 - 409
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The concept of structure functions, which is an extension of the variance approach, is useful to determine the variance (the structure function) which is optimized for a type of noise and for an order of drift. The multivariance method was developed to use different variances over the same signal. It is then possible to select a set of variances in which each variance is optimized to the determination of one parameter (of one noise level, drift, or cutoff frequency). Recently, we adapted this method to irregularly spaced timing data. In this connection, we replaced the structure functions by another method of spectral density estimation: the lowest-mode estimator, introduced by J.E. Deeter and P.E. Boynton (1982, 1984) for the analysis of pulsar timing data. Different lowest-mode estimators can be constructed according to two priorities: the order of drifts that must be removed and the type of noise for which the sensitivity must be maximum. Thus, a multivariance system is developed using a set of different estimators. The details of this method are described, and the results for different signals are discussed in this paper. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • CMOS RLC and crystal oscillators based on current conveyors

    Page(s): 410 - 416
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    Analysis and design of RLC and crystal oscillators based on current conveyors, in 1.5 /spl mu/m CMOS integrated technology, are described. Maximal operating frequencies are 350 and 50 MHz, respectively. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Proton-exchanged Z-cut LiNbO/sub 3/ waveguides for surface acoustic waves

    Page(s): 417 - 421
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (455 KB)  

    Proton-exchanged (PE) waveguides in Z-cut LiNbO/sub 3/ have been fabricated using benzoic acid. Secondary-ion mass spectrometry (SIMS) measurements show that the distribution of hydrogen in the PE Z-cut LiNbO/sub 3/ samples exhibits a step-like profile with the diffusion constant D/sub 0/ and the activation energy Q of about 2.82/spl times/10/sup 8/ /spl mu/m/sup 2//h and 87.76 kJ/mol, respectively. On the other hand, the important parameters for the design of surface acoustic wave (SAW) devices are measured and discussed. The results show that the phase velocity and electromechanical coupling coefficient decrease with the increase of kd, where k is the wavenumber and d is the waveguide depth. The variation of insertion loss becomes saturated at about kd=0.068 with a maximum increase of about 4/spl sim/5 dB. The temperature coefficient of delay calculated from the frequency change of the output of SAW delay line shows an evident increase in the PE layer. Moreover, the effects of postannealing can result in a restoration of the decreased velocity and an improvement of the insertion loss. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Evaluation of spatial resolution of spherical-planar-pair lenses for elasticity measurement with microscopic resolution

    Page(s): 422 - 427
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    The spatial resolution of spherical-planar-pair (SPP) lenses used in an ultrasonic microspectrometer (UMSM) was evaluated by scanning the lenses over a sharp edge of a specimen. The variation of the output observed in experiments was in good agreement with the theory. In the direction perpendicular to the propagation of a leaky surface acoustic wave (SAW), the best spatial resolution was obtained. The distance a/sub 90-10/ over which the magnitude decreased from 90% to 10% was 5 /spl mu/m at the frequency of 260 MHz. In the direction parallel to the leaky SAW propagation, the spatial resolution was severely affected by the excitation of the leaky SAW. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Acoustic microscopy and dispersion of leaky Rayleigh waves on randomly rough surfaces: a theoretical study

    Page(s): 428 - 433
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (681 KB)  

    A theoretical investigation of the dispersion of leaky Rayleigh waves propagating along one-dimensional (1-D) rough fluid-solid interfaces was carried out by simulating the measurement process of a line-focus beam acoustic microscope. The interface profiles were described in terms of their rms, also known as the roughness of the profile, autocorrelation length, and autocorrelation function. The reflectivity of the interfaces was calculated by using a second-order perturbation approach in the profile roughness. Theoretical V(z) curves were generated and analyzed to yield values of the phase velocity of the Rayleigh waves. The dependence of the Rayleigh wave velocity on the profile and material parameters was examined. Significant variations of the phase velocity were found for values of the roughness which are small compared to the shortest of the wavelengths involved in the scattering. The dispersion relations also showed considerable sensitivity to changes in mechanical properties typical of materials of engineering interest. In the low-frequency range, simulations indicated the dispersion of Rayleigh waves to be rather insensitive to the spectral content of the profile. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The shear coefficient for quartz crystal of rectangular cross section in Timoshenko's beam theory

    Page(s): 434 - 440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (522 KB)  

    In this paper, we derive the shear coefficient K for quartz crystal of rectangular cross section in Timoshenko's beam theory of three-dimensional (3-D) elasticity. The theoretical result gives K as a function of the transformed elastic stiffness constants C/sub 22//sup '/, c/spl circ//sub 44/, C/sub 66/'. For an isotropic material it agrees completely with that derived by G.R. Cowper (1966). In addition, a value of K and its temperature coefficient versus cut angle is calculated so that K has a value of 0.796-0.867 and its temperature coefficient of the first order varies from -15.3/spl times/10/sup -6///spl deg/C to +13.2/spl times/10/sup -6///spl deg/C, when a Z-plate of quartz crystal is rotated with a cut angle /spl theta/ of 0-180/spl deg/ about the x axis. The values of K are then compared with those for isotropic materials obtained by other authors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A reflected-scanned ultrasound system for external simultaneous thermoradiotherapy

    Page(s): 441 - 449
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1052 KB)  

    The simultaneous delivery of hyperthermia and ionizing radiation has the potential to improve clinical outcome. To this purpose, a scanning ultrasound reflector-linear array system (SURLAS) with the ability both to conform power to superficial volumes and to operate concomitantly with medical linear accelerators is currently under development. In this purpose-specific design, the ultrasound waves generated by a linear array are directed toward a scanning reflector which in turn deflects the waves toward the target. In previous experiments, the technical feasibility of this design was demonstrated. Here, the authors are concerned with the minimization of a key design parameter, namely, the array element size, in order to minimize the amount of attenuating/scattering water-equivalent medium that a photon or a electron beam passes through before entering the target. First, the SURLAS design is described. Second, an acoustic model to compute power deposition patterns is presented. This model is coupled to a bioheat transfer model for computation of temperature fields. Third, an analysis is performed to determine the minimum array element size for three target categories. Finally, acoustic fields and temperature distributions induced by the SURLAS for the three target categories are presented. The analysis and simulations show that the SURLAS has the potential to induce uniform temperature distributions in large superficial volumes with small enough elements to allow simultaneous delivery with electron beam therapy. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transient modeling of ferroelectric capacitors for nonvolatile memories

    Page(s): 450 - 456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (787 KB)  

    Present ferroelectric (FE) capacitor models mostly rely on continuous hysteresis loop characteristics of FE materials. Our experimental results show that this approach overestimates the remanent and saturation polarizations available for nonvolatile semiconductor memories by more than 50%. A behavioral transient model based on pulse measurement results is proposed and implemented as an HSPICE macro-model. The model mainly consists of two nonlinear capacitors, corresponding to the two different polarization states of an FE capacitor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A model for the hydrostatic pressure response of a 1-3 composite

    Page(s): 457 - 466
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    An analytical model has been developed for predicting the mechanical response of a composite cylinder that is composed of a solid right circular cylinder of one material surrounded by a cylindrical tube composed of some other material. It is assumed that there is no slippage at the boundary between the two phases. The model employs, throughout, the exact equations of linear elasticity and, thus, provides a solution that is exact for the specific boundary conditions that are imposed, In this paper, the specific case of hydrostatic pressure applied to the surface of the composite cylinder is discussed, The model yields the displacement and stress fields throughout the entire structure. The model was verified by comparing the results with a finite element model at several surfaces and interfaces in the structure, The model can be readily applied to the analysis of passive composite structures as well as to some of the recent active materials such as 1-3 piezocomposites. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Equivalent circuits for unidirectional SAW-IDTs based on the coupling-of-modes theory

    Page(s): 467 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A three-port distributed-parameter equivalent circuit representing the whole structure of a unidirectional interdigital transducer (IDT) is derived from generalized coupling-of-modes (COM) equations with complex parameters. The circuit has a simple form similar to that of a bidirectional IDT, but involves two additional impedance elements of opposite signs. It is shown that the two additional elements express well the behaviors of unidirectional IDTs and the directivity can easily be derived from the equivalent circuit. Some examples of calculations of device characteristics using the circuit are also presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two bit correlation-an adaptive time delay estimation

    Page(s): 473 - 481
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (991 KB)  

    Time delay estimation is a very important operation in ultrasound time-domain flow mapping and correction of phase aberration of an array transducer. As the interest increases in the application of one and a half-dimensional (1.5-D) and two-dimensional (2-D) array transducers to improving image quality and three-dimensional (3-D) imaging, the need of simple, fast, and sufficiently accurate algorithms for real-time time delay estimation becomes exceedingly crucial. In this paper, we present an adaptive time-delay estimation algorithm which minimizes the problem of noise sensitivity associated with the one bit correlation while retaining simplicity in implementation. This algorithm converts each sample datum into a two bit representation including the sign of the sample and an adaptively selected threshold. A bit pattern correlation operation is applied to find the time delay between two engaged signals. By using the criterion of misregistration as an indicator, we are able to show that the proposed algorithm is better than one bit correlation in susceptibility to noise level. Analytical results show that the improvement in reducing misregistration of the two bit correlation over its counterpart is consistent over a wide range of noise level. This is achieved by an adaptive adjustment of the threshold to accommodate signal corruption due to noise. The analytical results are corroborated by results from simulating the blood as a random distribution of red blood cells. Finally, we also present a memory-based architecture to implement the two bit correlation algorithm whose computation time does not depend upon the time delay of the signals to be correlated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rigorous treatment of leaky SAWs and new equivalent circuit representation for interdigital transducers

    Page(s): 482 - 490
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Leaky surface acoustic wave (SAW) interdigital transducers (LDTs) formed on 36/spl deg/ YX-LiTaO/sub 3/ and 41/spl deg/ and 64/spl deg/ YX-LiNbO/sub 3/ are theoretically analyzed, and a new equivalent circuit representation is proposed. The influence of the attenuation constant due to leakage as well as conductance caused by bulk wave radiation are taken into account. A new treatment based on an integral equation approach provides all circuit parameters. Fundamental experiments show fairly good agreement between theoretical and experimental results, confirming that this treatment provides very accurate tools for designing leaky-SAW devices. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Propagation of a quasi-shear horizontal acoustic wave in Z-X lithium niobate plates [and conductivity sensor application]

    Page(s): 491 - 494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB)  

    It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio h//spl lambda/, where h=plate thickness and /spl lambda/=acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: (1) phase velocity nearly constant for all values of h//spl lambda/; (2) ability to propagate in contact with a liquid medium; and (3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCI concentration from 0 to 0.15%. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multi-order sampling for digital beamforming of wide-band signals

    Page(s): 495 - 499
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    After proving that the second-order sampling method introduces too much error for beamforming of the wide-band signal generally used in ultrasound imaging systems, we suggest a new multi-order sampling method that significantly reduces sampling error but maintains advantages of the second-order sampling method with relatively simple hardware. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Full text access may be available. Click article title to sign in or learn about subscription options.

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.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Steven Freear
s.freear@leeds.ac.uk