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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 2 • Date March 1994

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Displaying Results 1 - 18 of 18
  • Fiber optic ultrasonic sensor using Raman-Nath light diffraction

    Page(s): 166 - 171
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    A novel fiber optic ultrasonic sensor using the principle of Raman-Nath light diffraction has been developed. The sensor does not perturb the acoustic field and exhibits a wideband frequency response. In addition to the remote sensing of the field, it is suitable for measurements of both continuous and pulsed ultrasonic waves. The experimental results obtained with the sensor were compared to those measured using a calibrated PVDF needle hydrophone, showing excellent agreement. The sensor's frequency response in the range from 3 to 15 MHz, typical of that used in medical ultrasound imaging, was determined using the time delay spectrometry (TDS) technique. It appears that the fiber optic sensor provides a useful alternative to the widely used PVDF ultrasonic probes in specific applications where any perturbation between acoustic field and sensor is undesirable. Also, since the active element diameter of the sensor can be made comparable to the core diameter of an optical fiber, the fiber optic sensor minimizes the spatial averaging effects and offers significant improvement in comparison with the present state-of-the-art hydrophones which have a minimum diameter on the order of 300 /spl mu/m.<> View full abstract»

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  • A theoretical and experimental analysis of the received signal from disturbed blood flow

    Page(s): 172 - 184
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    A theoretical and experimental study of the received ultrasonic signal from calibrated stenotic flow phantoms is presented. A finite element analysis of the velocity profile for 30, 50, and 80% stenoses provides a basis for the study of the experimental results. High-resolution images of the returned signal obtained from a unique experimental system and a high volume concentration of scatterers are then presented. The authors show that in the presence of 30 and 50% stenoses, particularly for the low velocities which would be associated with diastole, the duration of the signal correlation increases in a region which is distal to the stenosis and near the vessel walls, rather than the expected decrease. This results from the decrease in the mean velocity and velocity spread within this region. In the presence of high velocities associated with systolic flow, the magnitude of the reverse flow component increases as does the peak velocity in the center of the vessel. These changes produce an increase in the radial velocity gradient, a shift in the gradient peak, and a decrease in the correlated signal interval in comparison with laminar flow. Thus, the spatial variation in the mean velocity and velocity gradient, and spatial variation in the signal correlation can be used to detect the change in the flow profile.<> View full abstract»

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  • A statistical analysis of the received signal from blood during laminar flow

    Page(s): 185 - 198
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    In order to determine the limiting velocity resolution that can be achieved using ultrasound, and to provide a model which can be generalized for the analysis of disturbed flow, a theoretical and experimental evaluation of the statistics of the received signal from laminar flow following the transmission of a train of short pulses is presented. The authors derive the autocorrelation function and determine the length of the correlated signal for various flow rates, comparing experimental measurements to theoretical predictions. High resolution experimental RF M-mode images are used to verify the theoretical model. Using a fluid with a density, viscosity, volume concentration, particle size, and speed of sound which is similar to that of blood, the authors show that the signal remains correlated for a long interval under many conditions of clinical interest. Including a comparison with experimental data, the effect of the lateral transit time through the sample volume and the axial velocity spread within the sample volume on the correlation of the received signal is evaluated. When a significant range of velocity components is present within the sample volume, this range is the limiting factor in the length of the correlated signal interval. Therefore, the use of a wideband signal, which reduces the sample volume size, produces a returned signal that may be correlated for a larger number of pulses, or for a longer time.<> View full abstract»

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  • Application of a beamforming technique to ultrasound imaging in nondestructive testing

    Page(s): 199 - 208
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    Many innovations in the modern testing of materials make use of ultrasound. As a result, ultrasound has become extremely important to nondestructive testing of complete engineered systems. However, despite the fact that ultrasound inspection techniques are based on well-established principles, a few key problems pertaining to their application still remain unresolved. One of these problems deals with materials having complex geometries, often making the scanning/data collection processes time consuming. Consequently, fast and accurate mechanisms for testing components with awkward configurations have been the focus of attention in modern nondestructive testing research. In this paper, the data independent beamformer is studied as a potential method to reduce ultrasonic data acquisition time. The finite element method (FEM) is used as a testbed to mimic the ultrasound measurements by simulating the action of a transducer array. Tests reveal that when the weights of the interpolating filters (beamformers) are adjusted properly, they can indeed be used to predict A-scan signals from a data set produced by a transducer moving in a line-scan direction at nonuniform increments; hence, reducing the data acquisition time. The same filter weights also predict accurately A-scan signals from another data set produced by the same transducer moving at nonuniform increments for a different material geometry.<> View full abstract»

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  • An alternative approach of acousto-ultrasonic technique for monitoring material anisotropy of fiber-reinforced composites

    Page(s): 209 - 214
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    An alternative acousto-ultrasonic (AU) technique has been developed for nondestructive evaluation (NDE) of fiber-reinforced composites. The technique measures the time of flight (TOF) of AU waves, instead of the stress wave factor, by two low-frequency (0.5 MHz) transducers and relates TOF to material properties and fiber orientation. As the transducer separation increases, the measured time-domain AU signals clearly separate into two groups, since the excitation is under the first critical frequency, which correspond to the first two fundamental modes of the Lamb waves. One is an antisymmetric mode with slower propagation velocity and is highly dispersive, while the other is a symmetric mode with faster propagation velocity, which is very close to that of the longitudinal bulk wave, and is nearly nondispersive. The phase velocity in the composites can be accurately determined from the slopes of the TOF curves, and depends strongly on the azimuthal angle, frequency, and plate thickness. If the wave propagates away from the fiber direction, a slower but more attenuated wave is observed. Phase-velocity curves in azimuthal angles were obtained for E-glass/polyester, S-2-glass/epoxy, and Kevlar 49 composites. The theoretical solutions, for the longitudinal bulk wave and Lamb wave, are obtained by solving an eigenproblem once the material mechanical properties are defined. Good agreement is obtained between the measurements and the theoretical calculations.<> View full abstract»

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  • Ultrasound speckle reduction using harmonic oscillator models

    Page(s): 215 - 224
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    A speckle reduction algorithm called the harmonic imaging (HI) algorithm is presented. It is based on a multicomponent scattering model for medical ultrasonics. The backscattered ultrasound quadrature signal is modeled as the sum of three components after demodulation. The first component represents nonresolvable diffuse scatterers, while the second component represents subresolvable quasi-periodic scatterers. The third component represents resolvable quasi-periodic scatterers and mirroring surfaces. Since the second component gives rise to the most long range destructive interference effects it is eliminated in the HI algorithm to reduce speckle. Due to its slow spatial variation, it can be almost completely eliminated simply by differentiating the backscattered demodulated quadrature signal. Lissajous-like figures are observed in complex plots of the signals from ultrasound beams going through tissues with quasi-periodic components and sometimes in areas with only diffuse scatterers. Therefore the sum of the complex signals from the resolvable and nonresolvable scatterers within a resolution cell is modeled by two orthogonal and independent harmonic oscillators. The estimated, total energy of these two oscillators determines the gray level value of the HI image within the resolution cell. The HI images produced using radio frequency data from a phantom and from tissues in vivo are more blurred than ordinary envelope images, but the signal to noise ratio and tissue contrast were higher for the HI images.<> View full abstract»

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  • Modeling and optimization of high-frequency ultrasound transducers

    Page(s): 225 - 230
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    Obtaining an accurate transducer model for a high-frequency transducer can be troublesome using traditional models, such as the KLM model, since it is often difficult to measure precisely the piezoelectric, dielectric, and mechanical properties of the transducer. This paper describes an alternative method of modeling transducers using network theory. The network theory model for a transducer is determined from a measurement of the transducer impedance in water and the pulse-echo response of the system for a given electrical source and load. A discussion of how this model can be used to optimize the design of an electrical matching circuit is given. This method is illustrated by designing a two-element transmission line matching circuit for a miniature 53 MHz transducer. Excellent agreement between the network model prediction and the experimental response is obtained.<> View full abstract»

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  • Fabrication of high frequency spherically shaped ceramic transducers

    Page(s): 231 - 235
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    Difficulty in obtaining well focused efficient ultrasound transducers has limited the development of new high frequency applications of B-mode imaging. This paper describes a method for fabricating high frequency (53 MHz) spherically focused lead zirconate titanate (PZT) transducers. A transducer is fabricated by bonding a malleable backing layer onto a thin plate of PZT and then pressing the plate into a spherically shaped well. The backing layer evenly distributes stresses across the material when it is pressed into the well. Local concentrations of stress which lead to fracture are avoided and the material can be deformed without macroscopic cracking. The characteristics of a 2 mm diameter 53 MHz PZT transducer with a 4 mm focal length are described. A lateral beam width of 68 /spl mu/m and a 12 dB depth of field of 1.5 mm were obtained. The minimum two-way insertion loss of the system was /spl minus/25 dB and the 6 dB bandwidth of the pulse echo response was 30%. An image of a resolution phantom and an in vivo skin image illustrate the excellent imaging characteristics of the transducer.<> View full abstract»

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  • The design of SAW RAC's using arrays of thin metal dots

    Page(s): 236 - 244
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    Many successful dot array SAW devices including RAC's, resonators and band-pass filters have been reported, but the wide range of dot parameters, including dot dimensions, spacing and pattern, which allows flexibility in design, has not previously been utilized. This paper reports on the design of an RAC (reflecting array compressor) with a TB product of 1000, the emphasis being to exploit some of this flexibility. The design has been implemented using YZ LiNbO/sub 3/ with thin metal dots as the reflectors. It makes use of the wide range of reflectivities available from electrical effects in a novel weighting scheme based on dot size. The dots have been designed so that the sensitivity to over-etch is minimal. The array, which is sparse and near-periodic, has been designed to reduce unwanted reflections. This is least successful in the case of SAW to bulk wave reflection and the consequent loss due to this cause is accounted for in the design. The design approach is quite general and should be of use for other devices.<> View full abstract»

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  • An analysis of major frequency shifts in the LPTF optically pumped primary frequency standard

    Page(s): 245 - 249
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    An analysis of the major frequency shifts of our optically pumped cesium beam primary frequency standard is presented, together with a description of the most relevant characteristics of the device. The short term frequency stability was measured against a hydrogen maser. The square root of the Allan variance (/spl sigma//sub y/(/spl tau/) is at present 5.8.10/sup /spl minus/13//spl tau//sup /spl minus/1/2/, with a flicker level at 3.3.10/sup /spl minus/15/. This extremely good frequency stability enables a highly precise analysis of the most important systematic frequency shifts to be performed in a short time. Our first accuracy evaluation results in an uncertainty (1/spl sigma/) of 1.1.10/sup /spl minus/13/.<> View full abstract»

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  • Low temperature limitation on the quality factor of quartz resonators

    Page(s): 250 - 255
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    The quality factor (Q) for different resonators driven at several overtones has been determined between 1.5 and 300 K. These measurements give an improved interpretation of the Q-factor limitation. A significant consequence is a better understanding of the relationship between Q and random frequency fluctuations. The curves of 1/Q=F(T) show the usual features between 20 and 300 K. These include the sodium ion peak at 55 K as well as a peak at 20 K. However, the region of principal interest lies between 1.5 and 20 K. At very low temperatures, a plateau is always observed. If for a given resonator, the 1/Q value of this plateau is subtracted from the experimental values, the residual 1/Q is almost a linear function of T/sup 4/. This variation obeys the Landau-Rumer theory of acoustic wave absorption caused by phonon-phonon interaction in the crystal. Thus the authors conclude that between 6 and 20 K the main limitation in Q is due to the crystal itself, but the plateau is not caused by intrinsic crystal properties. Data for different overtones enable the elimination, at least for the seventh overtone, of damping effects of the crystal supports. Measurements have also been carried out on crystals with crystal surfaces with different roughness characteristics. These roughness characteristics have been measured using optical interferometry. With a well polished, good crystal the authors measured, for the seventh overtone at 3 K a loaded Q of 25 million corresponding to an unloaded Q of 33 million. Better control of surface roughness and crystal quality could lead to a Q of about 100 million in the liquid helium region. This value would be for an 11 MHz, seventh overtone crystal having an diameter of 15 mm.<> View full abstract»

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  • Modeling of waveguide-coupled SAW resonators

    Page(s): 256 - 260
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    Coupling of modes in space (COMS) is applied to the analysis of waveguide coupled surface acoustic wave (SAW) resonators. Standard one-dimensional COMS equations are extended to model distributed coupling between adjacent SAW reflector arrays. Computed frequency responses are presented for two-pole and four-pole waveguide coupled resonators.<> View full abstract»

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  • A simple single model for quartz crystal resonator low level drive sensitivity and monolithic filter intermodulation

    Page(s): 261 - 268
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    The nature of the observed phenomenon of "starting resistance" is reviewed, along with the accompanying experimental evidence of high drive-level altering and sometime "curing" of the malady. A simple phenomenological model is proposed, and then it is shown that this model does indeed predict all of the observed properties of starting resistance with the exception of "high-drive curing". This same model is then shown to predict the low level intermodulation effects seen in monolithic crystal filters. The ability to predict both starting resistance and intermodulation phenomena with the same model is taken as an indication that both phenomena have a common cause. Explanations of high-drive-level curing of the phenomena are contemplated.<> View full abstract»

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  • Improved OCXO's oven using active thermal insulation

    Page(s): 269 - 274
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    This paper shows how it is possible to improve the performance of thermal enclosures by using a compensating system the principle of which has been described by F. Walls a few years ago (41st AFCS, 1987). It is shown that because of the thermal network between the outside temperature, the temperature sensor and the device to be regulated, the latter may undergo residual temperature variations which reduce the overall thermal efficiency of the oven. This paper shows how thermal transfer functions can be measured by using an experimental setup in which the node temperatures are measured by thermal sensors. By identifying the thermal response of the nodes with the theoretical transfer function under external temperature or heater excitation, the components of the equivalent R-C network can be determined. By knowing these thermal transfer functions, it is then possible to make use of a compensating system which can eliminate the parasitic static as well as dynamic thermal effects. Validating measurements and experimental results are presented which show the strong improvement achieved by this compensating system with respect to the conventional approach.<> View full abstract»

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  • Oscillator phase noise measurements by picosecond synchroscan streak camera

    Page(s): 275 - 278
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    A new method/spl minus/with picosecond resolution/spl minus/allowing the recording of the instantaneous time phase fluctuations of a crystal controlled oscillator is presented. The oscillator under test drives the acoustooptic modelocker of a CW Nd:YAG laser associated with a synchronously pumped dye laser. By means of a streak camera illuminated by the ps dye laser pulses and synchronized by the oscillator signal the statistics of its zero crossings is analyzed.<> View full abstract»

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  • Characteristics of ultrasonic Lamb waves in 128/spl deg/ rotated Y-cut lithium niobate

    Page(s): 279 - 283
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    The characteristics of ultrasonic Lamb waves propagating along the X-direction of a 128/spl deg/ rotated Y-cut lithium niobate plate are investigated. The first higher-order antisymmetric mode, the A/sub 1/ mode, is found to exhibit an anomalous behavior. The velocity of this mode remains nearly constant for all values of h//spl lambda/, where h is the plate thickness and /spl lambda/ is the acoustic wavelength. The particle displacement of the mode tends towards that of a pure shear horizontal (SH) wave as the ratio h//spl lambda/ tends to zero. The electromechanical coupling coefficient of the wave has a value of k/sup 2/=0.78/spl times/10/sup /spl minus/2/ at h//spl lambda//spl cong/0. The coupling decreases as h//spl lambda/ increases, becoming negligible for h//spl lambda/>1. The velocity and coupling coefficient of the mode have been measured for various values of h//spl lambda/, and are found to be in fair agreement with theoretical calculations.<> View full abstract»

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  • OCXO design using composite-heating of the crystal resonator

    Page(s): 284 - 287
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    The design of a composite-heated quartz crystal resonator for OCXO applications is described. A mathematical model of the transient processes in the device is presented and is used to identify the physical and electrical parameters of the resonator providing optimized warm-up time, frequency stability, and power consumption. A prototype resonator exhibiting a warm-up time of 15 s, frequency versus temperature stability better than 3/spl times/10/sup /spl minus/8/, and heating current of about 5 mA is described.<> View full abstract»

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  • Consideration of measurement of electrostriction in quartz using Bragg reflection of X-rays

    Page(s): 287 - 289
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    Calculation shows that the linear piezoelectric effect should be readily demonstrated in X-cut quartz by Bragg reflection of X-rays, equipment for which is available in every crystal finishing room. Electrostriction should also be observable and measurable in X-cut, Y-cut and Z-cut quartz, and in other cuts having their major surfaces parallel to X-ray diffracting planes of the crystal. Mechanical compression of the quartz due to the charge on the electrodes must be considered.<> View full abstract»

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Aims & Scope

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control focuses on the theory, design, and application on generation, transmission, and detection of bulk and surface mechanical waves.

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