Scheduled System Maintenance:
Some services will be unavailable Sunday, March 29th through Monday, March 30th. We apologize for the inconvenience.
By Topic

Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 3 • Date May 1997

Filter Results

Displaying Results 1 - 24 of 24
  • Introduction To The Special Issue Element Applications

    Publication Year: 1997 , Page(s): 537
    Save to Project icon | Request Permissions | PDF file iconPDF (171 KB)  
    Freely Available from IEEE
  • Modeling of piezoelectric sensor fidelity

    Publication Year: 1997 , Page(s): 538 - 547
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    Ideal piezoelectric sensors should measure the response of a structure in a nonintrusive manner. The size of the sensor should be relatively small and its properties well matched to the structure. The voltage response of a piezoelectric sensor embedded in a fluid loaded plate structure is modeled using a hybrid finite element approach. The structure is excited by an obliquely incident acoustic signal. Finite element modeling is used for the structure and the fluid surrounding the transducer region, and a plane wave representation is invoked to match the displacement field on a mathematical boundary. On this boundary, continuity of field derivatives is enforced by using a penalty factor and to further achieve transparency at the mathematical boundary, drilling degrees of freedom (d.o.f.) are introduced in the finite element representation. Another novel feature in the FEM is the use of solid elements for the acoustic fluid augmented by an irrotational constraint to render the fluid inviscid. Numerical results are presented for the sensor response of an immersed plate structure. The voltage excited in the piezoelectric sensor is studied as a function of sensor and host material properties, size of sensor, and poling direction of the sensor with respect to the structure. The effect of multiple sensors on one another is also studied. It is found that piezoelectric sensors can be nonintrusive and sensitive to the characteristics of the structure. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Finite elements for piezoelectric vibrations with open electric boundaries

    Publication Year: 1997 , Page(s): 548 - 556
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    The problem of a piezoelectric body vibrating in the free space of infinite extent has been posed as a problem with open electric boundaries. A three-dimensional finite element analysis of piezoelectric vibrations has been complemented by the modeling of the external electrostatic field. The infinite exterior region that adheres to Laplace's equation is represented as a single "superelement" obtained by the ballooning of the outer boundary. The spectral transformation Lanczos method is used to find approximations to some solutions of the generalized eigenvalue problem arising from the finite element discretization of interior and exterior regions. The proposed approach was tested on simple vibrators with different mesh discretization and element order. The method produces numerically stable results, and was used to estimate the influence of the exterior leakage field on electromechanical properties of free piezoelectric vibrations. Numerical tests show that for some materials, vibrator geometries and modes, favorable to the coupling with the exterior field, the resonant frequency and electrical parameter shifts due to open electric boundaries may be as great as several percent. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Finite element simulation and visualization of leaky Rayleigh waves for ultrasonic NDE

    Publication Year: 1997 , Page(s): 557 - 564
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1194 KB)  

    The generation and propagation properties of transient leaky Rayleigh waves are characterized by a two-dimensional finite element model. The displacement vector is used as the primary variable for the solid medium and a potential scalar, which is a replacement for the pressure, is taken as the fundamental variable for the fluid medium. The coupled system of finite element equations are solved in the time domain by direct integration through the central difference scheme. Three configurations are considered: the conversion of a Rayleigh surface wave into a leaky Rayleigh wave, a focused beam probing a fluid/solid interface at the Rayleigh angle, and the interaction of a defocused wave with the interface. The wave velocity in the fluid (water) is lower than the Rayleigh wave velocity in the solid (aluminum). The wave propagation profile in each case is predicted by the model. The finite element model proves to be an effective tool for surface acoustic device design and ultrasonic NDE. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of 1-3 piezocomposite hydrophones using finite element analysis

    Publication Year: 1997 , Page(s): 565 - 574
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1081 KB)  

    The 1-3 piezocomposite material was originally developed because of its perceived good performance under hydrostatic operating conditions. Several constrained-dimensional models for piezocomposite hydrophones have been proposed but were found to lack accuracy when compared with experimental data. In addition, they could not be easily extended to include the effect of ancillary components such as cover plates, on the transducer behavior. In this work a finite element model is used for modelling of 1-3 piezocomposite hydrophones to help overcome these two shortfalls. A finite element model initially developed for modelling of thickness mode operation has been extended to include lateral pressures typical of the hydrostatic environment. The response of the new model has been compared with experiment with satisfactory results, allowing an extensive set of simulations to be presented for comprehensive evaluation of 1-3 piezocomposite design as an actuator or a hydrophone. The best hydrostatic performance was obtained by using a low volume fraction composite of PZT-5H and a soft, compressible polymer, with potential enhancements by the incorporation of stiff cover plates covering the ceramic pillars. It is shown that the aspect ratio of the ceramic pillars should be minimized to maximize stress transfer. Additionally, ceramic pillar shape and distribution do not exert a major influence on the hydrostatic behavior. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Deaberration of incoherent wavefront distortion: An approach toward inverse filtering

    Publication Year: 1997 , Page(s): 575 - 589
    Cited by:  Papers (16)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1670 KB)  

    Techniques for the correction of ultrasonic wavefront distortion are compared using measured pulse transmission through human breast specimens. The measured data were obtained by recording the pulse signals on each element of a linear array that was moved in elevation to synthesize a two-dimensional aperture. The one-way point spread functions were reconstructed using matched filtering technique, phase conjugation, time-delay compensation, and backpropagation followed by phase conjugation, each with and without amplitude compression. Two measures of performance were compared, the mainlobe diffraction shape and the ratio of the energy outside the mainlobe to the energy inside the mainlobe. Matched filtering, which compensates the phase distortion but also increases the variation in the modulus, performs more poorly than other techniques with respect to both measures. Phase conjugation and time-delay compensation, which leave the magnitude of the wavefront unchanged, have similar beamwidths but phase conjugation is consistently superior with respect to energy ratio. The backpropagation method, which models wavefront distortion using a phase screen at a computed position between the source and aperture, is shown to perform better. The use of a novel amplitude compression that approaches inverse filtering improves the performance of the compensation techniques significantly. This is because inverse filtering optimizes image fidelity, in contrast, for example, to matched filtering, which optimizes SNR. With the amplitude compression method, the results of the one-way experiments show that the mainlobe shape can be recovered down to -30 dB. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • SAW ring filters with insertion loss of 1 dB

    Publication Year: 1997 , Page(s): 590 - 596
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (721 KB)  

    This paper presents low loss ring SAW filters on 49/spl deg/YX, 64/spl deg/YX, 128/spl deg/YX LiNbO/sub 3/ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per /spl lambda/ (/spl lambda/ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128/spl deg/YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at /spl plusmn/25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at /spl plusmn/25 MHz, offset from the center frequency. The chip size is 5/spl times/4/spl times/0.7 mm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Composite piezoelectric transducer with truncated conical endcaps "cymbal"

    Publication Year: 1997 , Page(s): 597 - 605
    Cited by:  Papers (98)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1077 KB)  

    This paper presents original results obtained in the development of the moonie-type transducers for actuator applications. The moonie-type actuators fill the gap between multilayer and bimorph actuators, but its position-dependent displacement and low generative force are unacceptable for certain applications. The moonie transducers were modified systematically by using finite element analysis combined with experimental techniques. A new transducer design, named "cymbal transducer", was developed with larger displacement, larger generative forces, and more cost-effective manufacturing. The cymbal transducers consist of a cylindrical ceramic element sandwiched between two truncated conical metal endcaps and can be used as both sensors and actuators. The cymbal actuator exhibits almost 40 times higher displacement than the same size of ceramic element. Effective piezoelectric charge coefficient, Eff. d/sub 33/, of cymbal is roughly 40 times higher than PZT itself. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A stochastic model of the time-of-flight noise in airborne sonar ranging systems

    Publication Year: 1997 , Page(s): 606 - 614
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (961 KB)  

    A stochastic model is developed for describing the statistical properties of the noise present in the time-of-flight (TOF) measurements made by in-air ultrasonic (US) transducers. The proposed method of analysis decomposes the TOF noise into three components with different physical origin and properties: a deterministic time-varying mean, a correlated random process and an uncorrelated random process. The physics of US waves propagating in air and the operating mode of typical sonar ranging systems are considered in orienting the choice of the model structure. The time-varying mean correlates with global thermal changes and drafts affecting the environment. The de-trended data are assumed to result from the sum of a correlated random component, due to inhomogeneities in the medium, such as temperature gradients and air turbulence, and an uncorrelated random component, mainly due to the wide band electronic noise superimposed on the echo signal. Autoregressive-moving average (ARMA) modelling techniques are used to capture the correlation structure with exponential decay of the piecewise stationary correlated random process. A method of adaptive segmentation allows to test for weak stationarity of this component. Kalman filtering techniques are used for its estimation. The adequacy of the representation in typical indoor environments is demonstrated by analyzing experimental data from Polaroid sensors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Statistical modeling for the optimal deposition of sputtered piezoelectric films

    Publication Year: 1997 , Page(s): 615 - 623
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (859 KB)  

    The quality of sputtered-deposited piezoelectric films used for integrating bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices with semiconductor circuitry depends on several deposition parameters, including substrate temperature, background pressure, gas composition, gas flow rate, and deposition rate. It is desirable to establish the fabrication process based on a selection of the controllable parameter values that optimizes the film quality. It is common practice to perform a number of deposition experiments by varying the controllable parameters to determine the optimal film growth conditions. The films are grown under a number of different conditions within this space and a response parameter related to film performance is measured. Then a multiple linear regression model is fit to the data. By optimizing the fitted response, the best growth conditions can be obtained. This approach is illustrated with data from recent work on the development of very high quality magnetron sputtered aluminum nitride (AlN) films whose acoustic characteristics are like those of epitaxial films grown at considerably higher substrate temperatures. Because the resource cost involved can be high, depending upon the number of deposition runs made, it is desirable to minimize the number of experiments and maximize the amount of information gained from them. A discussion is given on how the statistical theory of experimental design can be used to obtain this goal. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fabrication of high sensitivity ZnO thin film ultrasonic devices by electrochemical etch techniques

    Publication Year: 1997 , Page(s): 624 - 628
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB)  

    In this experiment, high quality thin film acoustic devices were constructed utilizing zinc oxide (ZnO) thin film deposition, integrated circuit (IC), and electrochemical etch techniques. The bridge type ZnO thin film ultrasonic devices produced showed acute high frequency response sensitivity, with the high frequency response at 600 KHz attaining -124 dBV /spl mu/Bar. The highest response was near 8 MHz. Sensitivity increased in direct proportion to frequency, indicating that the bridge-type ZnO thin film acoustic devices were suitable for application as ultrasonic wave sensors at high operating frequencies. Further experimentation verified that the bridge-type ZnO thin film acoustic devices fabricated also had ultrasonic signal transmitting capability and signal bidirectional devices having both transmission and reception functions were successfully constructed. Therefore, bridge-type ZnO thin film acoustic devices will continue to be developed in the future due to the reliable control possible over the structural transformations involved; and, since IC fabrication techniques can be readily adopted in the process, the manufacturing of such devices will be greatly assisted. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Incorporating data from a primary frequency standard into a time scale

    Publication Year: 1997 , Page(s): 629 - 636
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1045 KB)  

    It is difficult to combine data from a primary frequency standard with the time-difference measurements that are usually used as input to most time scales because a primary standard usually operates only occasionally on an irregular schedule and because the fundamental output of a primary frequency standard is a frequency rather than a time, and there is often no natural way of inserting this kind of datum into the scale in a manner that is statistically robust. We will present a new time-scale algorithm that seeks to address these problems. We call this frequency-based algorithm AF1, by analogy with the time-based algorithm AT1 that has been used at NIST for many years. Unlike AT1 in which frequency is simply a parameter that specifies how the time of a clock evolves between measurements, however, the frequency of each clock is a fundamental parameter in AF1. This change in focus provides a natural way for incorporating data from a primary frequency standard into the ensemble. We will present the details of the algorithm and results using data from our primary frequency standard, NIST-7. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A regularization approach for the determination of the time of flight distribution in the cesium beam standards

    Publication Year: 1997 , Page(s): 637 - 642
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (641 KB)  

    In this paper, a new method is presented to directly determine from the shape of a Ramsey pattern the real microwave level present in the cavity of a beam frequency standard. Then a new method to evaluate the atomic time of flight distribution using a regularization approach is presented. In opposition to existing methods, this approach uses only one Ramsey measurement because it allows the incorporation of the a priori information about the time of flight distribution. The validity of this method is confirmed by experimental results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical and experimental investigations of lateral modes in 1-3 piezocomposites

    Publication Year: 1997 , Page(s): 643 - 651
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1629 KB)  

    Materials with a periodic microstructure show resonances caused by the elastic wave Bragg diffraction. This paper presents a simple approach to describe these resonances (called lateral resonances) in 1-3 piezoelectric composite materials which have a 2-D periodicity. Our model is based on the analysis of the propagation of transverse waves in a 2-D periodic medium of infinite thickness and takes into account the periodic and interfacial boundary conditions. This model predicts the displacement field vectors and frequencies of lateral resonances from which the phase velocity of lateral waves is determined. The theoretical and experimental variations of this velocity versus the ceramic rod width to pitch ratio are compared. It is shown that the first lateral mode frequency is maximum when the ceramic volume fraction is around 0.65. Theoretical predictions of the mechanical displacement at the composite surface are compared with measurements obtained by an interferometric laser technique. A good agreement is observed, showing that lateral waves are mainly vertically polarized. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A coupling-of-modes approach to the analysis of STW devices

    Publication Year: 1997 , Page(s): 652 - 657
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB)  

    The dispersion characteristics of surface transverse waves (STW) on 36/spl deg/ rotated Y-cut quartz have been analyzed numerically. A closed form dispersion relation has been derived and introduced in the equations of the coupling-of-modes (COM) theory to account for the variation of energy trapping with frequency. The transmission and reflection coefficients at the finger edges have been determined from the stopband characteristics. Through the introduction of an electromechanical coupling which varies linearly with the electrode mass loading, quantitative agreement with experimental results on two different types of two-port STW resonators has been achieved, and characteristic features have been explained. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of step-like portions on the surface of ZnO/glass SAW filters on their frequency characteristics

    Publication Year: 1997 , Page(s): 658 - 665
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1531 KB)  

    The frequency amplitudes of surface acoustic wave (SAW) filters mass produced of zinc oxide (ZnO) films on glass were found to be different among the filters even when their center frequencies are the same. We attempted various experiments In order to reduce the deviation of amplitudes. We accidentally found that the frequency characteristics and the amplitude deviation could be improved by mirror-polishing the ZnO film surface. In a SAW filter with a ZnO/interdigital transducer (IDT)/glass substrate structure, periodic step-like portions due to the thickness of the finger electrode of IDT and fine roughness were present on the ZnO film surface. As a result of investigating the effect of surface structure on amplitude deviation, the step-like portions did not affect the electromechanical coupling factors but reduced the SAW phase velocities, experimentally and theoretically. In addition, it was clarified that the step-like portions due to the finger electrodes and fine roughness on the ZnO surface caused deviations in the SAW velocities and their reflections, causing the deviation in the amplitude characteristics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comparison of cepstrum-based methods for radial blind deconvolution of ultrasound images

    Publication Year: 1997 , Page(s): 666 - 674
    Cited by:  Papers (23)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1398 KB)  

    This paper compares the performance of seven different cepstrum-based methods for radial blind deconvolution of medical ultrasound images. The first is the generalized cepstrum method. The second is the spectral root cepstrum method. These methods have received little attention so far. The last five methods are all based on the complex cepstrum, but different computational techniques in the spatial and frequency domain are employed. Using in vivo radio frequency data from a clinical scanner, the generalized cepstrum method gave the best images closely followed by the complex cepstrum using phase unwrapping or polynomial rooting. The complex cepstrum method using higher-order statistics was ranked as low as number five. These results are an important guideline for selecting a specific cepstrum-based radial deconvolution method for implementation in ultrasound scanners. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RF sputtered PLZT thin film on Pt/Ti electrode

    Publication Year: 1997 , Page(s): 675 - 680
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (578 KB)  

    PLZT (7.5/65/35) thin films were deposited by rf magnetron sputtering on single crystal Si substrates using an oxide sintered target with excess PbO. The effects of postannealing and bottom Pt/Ti electrodes on the thin film crystal structures and ferroelectric properties were studied. Film deposited at 200/spl deg/C or below crystallizes to a perovskite phase after annealing treatment at 550/spl deg/C or above, and the crystal structure depends on the annealing treatment. The best crystal structures and electronic properties were obtained when the thin films were annealed at 600/spl deg/C to 650/spl deg/C for 1 h in O/sub 2/. For the Pt/Ti two-layer bottom electrode, the thickness of the Ti layer has a dominant effect. When the Ti layer was too thick or too thin, the PLZT thin film structures consist mainly of pyrochlore phases. However, using an appropriate Ti layer thickness, PLZT thin films having good crystal structures and ferroelectric properties can be obtained, with typical remanent polarization value of 220 mC/m/sup 2/ and coercive field strength of 6.5 MV/m. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Determination of elastic constants by time-resolved line-focus acoustic microscopy

    Publication Year: 1997 , Page(s): 681 - 687
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    The determination of elastic constants by using time-resolved line-focus acoustic microscopy (TRL-FAM) is discussed. Waveforms have been measured with a time-resolved line-focus acoustic microscopy system. A measurement model which simulates the measurements is also introduced for parametric studies of the waveforms. The determination of elastic constants is achieved by systematically comparing the relative wave-mode time-delays obtained from the measurement model and the experiments. The method has been applied to determine elastic constants of both isotropic and anisotropic materials. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Shear-horizontal acoustic wave storage in polycrystalline ferrite

    Publication Year: 1997 , Page(s): 688 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (542 KB)  

    Shear-horizontal acoustic wave storage in Ni-Co magnetostrictive polycrystalline ferrite was studied. The results show that the observed storage effect is acceptably efficient for applications. The use of shear-horizontal waves also decreases the level of the required electrical signals. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impact of new clock technologies on the stability and accuracy of the International Atomic Time TAI

    Publication Year: 1997 , Page(s): 693 - 700
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    The BIPM Time Section is in charge of the generation of the reference time scales TAI (International Atomic Time) and UTC (Coordinated Universal Time). Both time scales are obtained in deferred-time by combining the data front a number of atomic clocks spread worldwide. Since the end of 1992, the quality of the timing data received at the BIPM has evolved rapidly thanks to the extensive replacement of older designs of commercial cesium clocks by the new HP 5071A units and to the use of active auto-tuned hydrogen masers. Consequently, the stability and the predictability of the reference time scales has improved significantly: these are characterized by an Allan standard deviation /spl sigma//sub y/(/spl tau/) of 2.6/spl times/10/sup -15/ for averaging times /spl tau/=40 d. The accuracy of TAI is estimated by the departure between the duration of the TAI scale interval and the SI second as produced on the rotating geoid by primary frequency standards. It is now possible to estimate TAI accuracy through the combination of results obtained from six different primary standards: LPTF-FO1, PTB CS1, PTB CS2, PTB CS3, NIST-7, and SU MCsR 102, all corrected for the black-body radiation shift. This led to a mean departure of the TAI scale interval of +2.0/spl times/10/sup -14/ s over 1995, known with a relative uncertainty of 0.5/spl times/10/sup -14/ (1 /spl sigma/). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved estimation of phase aberration profiles

    Publication Year: 1997 , Page(s): 701 - 713
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1764 KB)  

    Two previous approaches to estimate phase aberration profiles with a single transmit pulse from speckle are examined. The first employs cross-correlation between signals on all pairs of neighboring elements. In the other, cross-correlation between signals on all elements and the beamsum is used. Here, the two methods are studied in detail, and the advantages and disadvantages of each are discussed. It is shown that cross-correlations between neighboring elements result in a bias in the estimated phase profile, while correlations to the beamsum result in higher error variance. A new approach combining the two is introduced. Experimental results demonstrate that this new method provides a superior phase aberration profile. Furthermore, it is shown that this improved phase profile enhances image quality when used to correct both transmitter and receiver. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Synthetic phased arrays for intraluminal imaging of coronary arteries

    Publication Year: 1997 , Page(s): 714 - 721
    Cited by:  Papers (56)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2150 KB)  

    A 64-element, high efficiency, ceramic piezoelectric array transducer operating at 20 MHz has been constructed for ultrasonic intraluminal imaging. The array is mounted on the surface of a 1.2 mm diameter catheter appropriate for coronary artery applications. Integrated into the catheter tip is a custom analog chip set permitting complete data capture from the array. That is, on each firing any combination of array elements can be selected independently as transmitter or receiver. Using data acquired in this way, a complete phased array aperture (i.e., independent transmit and receive apertures) can be synthesized. Reconstruction hardware based on a custom application specific integrated circuit (ASIC) has been designed and built to produce real-time images. Beam forming coefficients are derived using an optimal filtering approach accounting for the circular geometry of the array. Simulated and measured beam patterns for this system are compared. In addition, images of coronary anatomy acquired with the real-time system are displayed demonstrating the marked image quality improvement compared to previous synthetic aperture intraluminal systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Observation of ferrobielastic twinning in GaPO/sub 4/ under uniaxial stress

    Publication Year: 1997 , Page(s): 722 - 724
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (403 KB)  

    The phenomenon of ferrobielastic twinning stimulated by uniaxial pressure is optically observed in quartz-like material GaPO/sub 4/. For X-cut samples interdomain boundaries were detected at the pressure level 350 MPa applied at the angle 45/spl deg/ with respect to Z axis. In similar experiments with AlPO/sub 4/ domain boundaries were not observed. View full abstract»

    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