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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 6 • Date Nov. 2001

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Displaying Results 1 - 25 of 29
  • Techniques for perfusion imaging with microbubble contrast agents

    Page(s): 1483 - 1494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    The acoustic properties of ultrasound contrast agents vary widely with agent composition and insonation conditions. For contrast imaging, methods are required to match RF and Doppler processing to each combination of transmission parameters and agent and tissue properties. We propose a method that uses the measured or modeled echoes from agent and tissue to specify directly the characteristics of RF and Doppler filters for contrast imaging. The proposed method is sufficiently general to cover most common imaging techniques including harmonic greyscale, Doppler, and pulse inversion imaging. Using this method, sample filters were designed to detect myocardial perfusion with the contrast agent Optison TM (Mallinckrodt Medical, St. Louis, MO) under selected imaging conditions. Simplified power Doppler filtering, using a weighted sum of the Doppler samples, matched the performance of more complicated matrix filters. By coordinating the selection of RF and Doppler filters rather than designing these filters sequentially, agent-to-tissue contrast was increased by up to 3.9 dB. Under some conditions, fundamental RF filtering outperformed harmonic filtering for intermittent Doppler imaging. View full abstract»

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  • Novel, wide bandwidth, micromachined ultrasonic transducers

    Page(s): 1495 - 1507
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    Surface micromachined, capacitive ultrasonic transducers have been fabricated using a low thermal budget, CMOS-compatible process. This process allows inherent control of parameters such as membrane size and thickness, cavity size and the intrinsic stress in the membrane to be achieved. Devices fabricated using this process exhibit interesting properties for transduction in air at frequencies in excess of 1 MHz when driven from a standard ultrasonic voltage source. Experiments have been performed with devices containing silicon nitride membranes of variable thicknesses over a 2 μm thick air cavity and with device dimensions of up to 5 mm square. This is much larger than has been reported for a device with a single membrane. Calibration measurements using 1/8 inch microphones in air, and miniature PVDF hyrdophones in water, have been performed. The dependence on d.c. bias voltage is examined, involving static membrane deflection measurements and received peak voltages. Pulse-echo and pitch-catch mode operation have been achieved. Interferometric measurements of membrane displacement have been performed in air to illustrate the membrane deflection characteristics. Operation in liquids is also discussed. View full abstract»

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  • A simple method for SC-cut resonator design

    Page(s): 1508 - 1512
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (182 KB) |  | HTML iconHTML  

    Presents a design method utilizing simple semi-empirical equations for round, plano-convex SC-cut resonators. These equations were developed on the basis of experimental results, collected over a long period, relating SC-cut resonator design and performance covering a wide range of frequencies, radii of curvature, and plate diameters. The equations make possible the design of fundamental, third overtone, and fifth overtone resonators. An example calculation of resonator parameters and comparison with experimental results are also presented. View full abstract»

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  • Implementation of the beam reversal technique on compact cesium clocks: towards an improvement in accuracy

    Page(s): 1513 - 1516
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Reports the evaluation of the residual phase difference /spl utri//spl phi/ in a short (18 cm) Ramsey cavity by implementing the beam reversal technique in an optically pumped cesium beam clock. /spl utri//spl phi/ is measured to be 21 /spl plusmn/1.5 /spl mu/rad, allowing a more accurate evaluation of the frequency performance of this small cesium clock. Finally, the clock accuracy is equal to 1.1/spl middot/10/sup -13/. View full abstract»

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  • Acoustic loss mechanisms in leaky SAW resonators on lithium tantalate

    Page(s): 1517 - 1526
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2354 KB) |  | HTML iconHTML  

    Discusses acoustic losses in synchronous leaky surface acoustic wave (LSAW) resonators on rotated Y-cut lithium tantalate (LiTaO/sub 3/) substrates. Laser probe measurements and theoretical models are employed to identify and characterize the radiation of leaky waves into the busbars of the resonator and the excitation of bulk acoustic waves. Escaping LSAWs lead to a significant increase in the conductance, typically occurring in the vicinity of the resonance and in the stopband, but they do not explain the experimentally observed deterioration of the electrical response at the antiresonance. At frequencies above the stopband, the generation of fast shear bulk acoustic waves is the dominant loss mechanism. View full abstract»

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  • Full electrical characterization of aperiodic acoustic gratings by an enhanced /spl delta/-function model: theory and experiment

    Page(s): 1527 - 1531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    We derive the admittance of an aperiodic one-dimensional acoustic grating with acoustically matched boundaries using an enhanced /spl delta/-function model combined with the Green's function approach. The expression obtained is compared with the classical /spl delta/-function model and with electric back reflection measurements on a linearly chirped bulk acoustic grating with matched boundaries formed in LiNbO/sub 3/ by domain inversion and excited in "crossed-field" scheme. The agreement between calculated and measured results is excellent. View full abstract»

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  • The use of harmonic analysis of the strain response in Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-based ceramics to calculate electrostrictive coefficients

    Page(s): 1532 - 1538
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (503 KB) |  | HTML iconHTML  

    The electromechanical response of ceramics has long been described with Landau Devonshire phenomenology, wherein the strain response is linked to a polynomial expansion in electric field or dielectric displacement. Consequently, the electromechanical response has been modeled with a variety of basis functions. However, these models have failed to accommodate hysteresis and the harmonic response that arises with saturation phenomena. In addition, no quantitative criterion has been used to truncate the expansion. By implementing a discrete Fourier transform in conjunction with Devonshire phenomenology, these three problems can be overcome as demonstrated with a dielectrically aged, lead magnesium niobate relaxor ferroelectric well above its T/sub max/, i.e., operating in the electrostrictive regime. View full abstract»

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  • Temperature processing of an ultra stable quartz oscillator

    Page(s): 1539 - 1546
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1171 KB) |  | HTML iconHTML  

    Commonly, the required short-term frequency stability of an ultra stable quartz crystal oscillator (USXO) is a few parts in 10/sup -13/ for averaging times of a few seconds. Moreover, the USXO must typically achieve a relative frequency variation of a few parts in 10/sup -10/ over a temperature range from -30 to +70/spl deg/C. Consequently, the USXO has to be ovenized. Basic data concerning the static and dynamic frequency versus temperature effects are first reviewed. These data allow one to evaluate how efficient the thermal regulator must be to achieve the aimed features in terms of temperature sensitivity. Usually the static thermal gain must reach at least 1000. A standard proportional-integral thermal controller, which can eliminate the static error, cannot afford doing this when fast thermal disturbances exist. Here, the thermal filtering must work in accordance with the cut-off frequency of the frequency-temperature transfer function of the quartz resonator. There exist various methods to control the oscillator temperature. The usual method consists of using more than one temperature-controlled-oven. This is often a volume-consuming process. An alternative approach, which is much simpler, is to add a slight compensation upon the feedback control system. Finally, a third way to improve the temperature regulation is based on a distribution of the monitored power. Obviously, a combination of those solutions is possible. Advantages and drawbacks of each of them are discussed in the paper. Practical results are shown and illustrated with 10-MHz USXOs. View full abstract»

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  • A model for phase noise generation in amplifiers

    Page(s): 1547 - 1554
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (405 KB) |  | HTML iconHTML  

    In this paper, a model is presented for predicting the phase modulation (PM) and amplitude modulation (AM) noise in bipolar junction transistor (BJT) amplifiers. The model correctly predicts the dependence of phase noise on the signal frequency (at a particular carrier offset frequency), explains the noise shaping of the phase noise about the signal frequency, and shows the functional dependence on the transistor parameters and the circuit parameters. Experimental studies on common emitter (CE) amplifiers have been used to validate the PM noise model at carrier frequencies between 10 and 100 MHz. View full abstract»

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  • Statistics of the integrated backscatter estimate from a blood-mimicking fluid

    Page(s): 1555 - 1567
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB) |  | HTML iconHTML  

    This work evaluates the variance of the integrated backscatter (IBS) from moving blood [or blood-mimicking fluid (bmf)] as a way of determining the quality of the mean IBS estimate. The main motivation for this work comes from the fact that absolute IBS values from tissues adjacent to arterial blood can be found by normalizing the measured backscatter energy with the IBS of moving, deaggregated blood. The paper describes the parameters that control the statistics of the IBS estimate, which is calculated for the stochastic ultrasound backscatter signals from flowing blood. It further formulates how the measurement parameters should be specified so that an appropriately low blood IBS variance is ensured or, alternatively, a specified accuracy of the tissue IBS estimate is obtained. First, the paper provides an analytic formulation of the statistics of the IBS, based on a sequence of sampled echoes from a nonstationary Gaussian scattering medium. The analysis incorporates the correlation between the sample values as well as the correlation between the IBS of the individual echoes. The estimate of the mean IBS has been shown to be chi-squared distributed with a determinable order. With the degree of correlation between the samples and between the IBS of individual echoes specified, the number of measurements required to obtain an IBS estimate with a specified variance is readily calculated. Next, a sequence of synthetic echoes is produced and arranged as columns in a data matrix. The echoes are generated such that the second-order statistics along the rows and columns of the matrix match that of actually observed echoes. The actual variance of the mean IBS estimate for the synthetic echoes is calculated and compared with the variance determined from the analytic model, and a good agreement has been found. Finally, sequences of actual backscattered echoes from circulating blood-mimicking fluid are acquired and analyzed to determine the variance of their mean IBS estimate- - . Based on the measured second-order statistics of the rows and columns of the data matrix for the actual echoes, the observed variance of the mean IBS estimate was compared with the analytically determined variance and with good agreement. Thus, the paper has shown through modeling, simulations, and experiments how the variance of the IBS estimate of the blood backscatter signal can be quantified and reduced to a specified tolerable level. View full abstract»

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  • Phase-matched air ultrasonic transducers using corrugated PVDF film with half wavelength depth

    Page(s): 1568 - 1574
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (441 KB) |  | HTML iconHTML  

    A new type of large area PVDF film air transducer is proposed. The transducer features a high power output and a sharp beam angle. Conventionally known curved length mode resonators with two clamps at both ends have a resonance frequency determined by the curvature. In the present work, PVDF was formed into alternating concave and convex multiple curved sections, eliminating clamps, i.e., a periodic corrugation structure using a single PVDF film. Each convex and concave section has a common resonance frequency. A common excitation voltage induces vibration for each section, and the vibration direction is normal to the film surface. The vibration phase of convex section is shifted 180 degrees from the concave section. These waves add constructively to form a strong acoustic beam when corrugation height is approximately one-half of the wavelength. The corrugation height controls propagation path difference, canceling excitation phase difference. The design principle based on a uniform vibration mode is presented. Experimental investigations using 8.8/spl times/2.5-, 10/spl times/5-, and 20/spl times/20-cm/sup 2/ transducers are presented. Side lobes unique to this corrugation structure have been observed. A theoretical analysis of the side lobes is also presented. According to the theory, choosing the corrugation height appropriately will reduce side lobes to -15 dB with regard to the main lobe, and the observed side lobe height agreed with the theoretical result. View full abstract»

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  • Hydrophone spatial averaging corrections from 1 to 40 MHz

    Page(s): 1575 - 1580
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (461 KB) |  | HTML iconHTML  

    The purpose of this study was to develop and experimentally verify a practical spatial averaging model for frequencies up to 40 MHz. The model is applicable to focused sources of circular geometry, accounts for the effects of hydrophone probe finite aperture, and allows calibration by substitution to be performed when the active elements of reference and tested hydrophone probes differ significantly. Several broadband sources with focal numbers between 3 and 20 were used to produce ultrasound fields with frequencies up to 40 MHz. The effective diameters of the ultrasonic hydrophone probes calibrated in the focal plane of the sources ranged from 150 to 500 μm. Prior to application of the spatial averaging corrections, the hydrophones with diameters smaller than that of the reference hydrophone exhibited experimentally determined absolute sensitivities higher than the true ones. This discrepancy increased with decreasing focal numbers and increasing frequency. It was determined that the error was governed by the cross-section of the beam in the focal plane and the ratio of the effective diameters of the reference and tested hydrophone probes. In addition, the error was found to be reliant on the frequency-dependent effective hydrophone radius. After applying the spatial averaging correction, the overall uncertainty in the hydrophone calibration was on the order of ±1 dB. The model developed is being extended to be applicable to frequencies beyond 40 MHz, which are becoming increasingly important in diagnostic ultrasound imaging applications. View full abstract»

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  • Off-axis propagation of ultrasonic guided waves in thin orthotropic layers: theoretical analysis and dynamic holographic imaging measurement

    Page(s): 1581 - 1593
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2145 KB) |  | HTML iconHTML  

    The elastic properties of many materials in sheet or plate form can be approximated with orthotropic symmetry. In many sheet material manufacturing industries (e.g., the paper industry), manufacturers desire knowledge of certain anisotropic elastic properties in the sheet for handling and quality issues. Ultrasonic wave propagation in plate materials forms a method to determine the anisotropic elastic properties in a nondestructive manner. This work explores exact and approximate analysis methods of ultrasonic guided wave propagation in thin layers, explicitly dealing with orthotropic symmetry and propagation off-axis with respect to the manufacturing direction. Recent advances in full-field ultrasonic imaging methods, based on dynamic holography, allow simultaneous measurement of the plate wave motion in all planar directions within a single image. Results from this laser ultrasonic imaging approach are presented that record the lowest anti-symmetric (flexural) mode wavefront in a single image without scanning. Specific numerical predictions for flexural wave propagation in two distinctly different types of paper are presented and compared with direct imaging measurements. Very good agreement is obtained for the lowest anti-symmetric plate mode using paper properties independently determined by a third party. Complete determination of the elastic modulus tensor for orthotropic layers requires measurement of other modes in addition to the lowest anti-symmetric. Theoretical predictions are presented for other guided wave modes [extensional (S), flexural (A), and shear-horizontal (SH)] in orthotropic plates with emphasis on propagation in all planar directions. It is shown that there are significant changes in the dispersion characterization of these modes at certain frequencies (including off-axis mode coupling) that can be exploited to measure additional in-plane elastic moduli of thin layers. At present, the sensitivity of the imaging measurement approach limits e- perimental investigation to relatively large amplitudes easily produced by flexural wave motion (>0.1 nm). Extension of the measurement range and application to other plate wave modes are in progress and shall be reported in future work. View full abstract»

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  • A physically based, probabilistic model for ultrasonic images incorporating shape, microstructure, and system characteristics

    Page(s): 1594 - 1605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1574 KB) |  | HTML iconHTML  

    Describes a previous physical model for image formation that incorporates the imaging system characteristics, the surface shape, and the surface microstructure. That physical model was validated via a visual comparison of simulated and actual images of a cadaveric vertebra. In this work, a random phasor sum representation of the physical model provides the basis for a probabilistic form. In contrast to existing probabilistic models, we compute the amplitude mean and variance directly from the physical model. These statistics can be displayed as images to characterize the tissue, but, more importantly, they permit the subsequent assignment of a suitable density function to each pixel for the purposes of constructing a data likelihood. The order of these steps, i.e., first computing the statistics and then assigning a density function, permits the inclusion of the local surface shape, the surface microstructure, and the system characteristics at every image pixel without violating the physical model. Currently, the value of the SNR 0, the ratio of the mean to the standard deviation, is used to estimate whether a pixel is Rayleigh- or non-Rayleigh-distributed. This assessment forms the basis for a data likelihood constructed as a product of Rayleigh and Gaussian density functions describing the individual image pixels. View full abstract»

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  • Time-shift estimation and focusing through distributed aberration using multirow arrays

    Page(s): 1606 - 1624
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    The effects of element height on time-shift estimation and transmit focus compensation are demonstrated experimentally. Multirow ultrasonic transducer arrays were emulated by combining adjacent elements of a 3.0-MHz, 0.6-mm pitch, two-dimensional array to define larger virtual elements. Pulse-echo data were acquired through tissue-mimicking distributed aberrators, and time-shift maps estimated from those data were used for transmit focus compensation. Compensated beams formed by arrays with fine row pitches were similar, but focus restoration was significantly less effective for "1.75-D" arrays with a coarse row pitch. For example, when focus compensation was derived from strongly aberrated random scattering data [70-ns nominal rms arrival time fluctuation with 7 mm FWHM (full-width at half-maximum) correlation length], the mean -20 dB lateral beamwidths were 5.2 mm for f/2.0 arrays with 0.6- and 1.8-mm row pitches and 9.5 mm for an f /2.0 array with 5.4-mm pitch. Time-shift maps estimated from random scattering data acquired with 5.4-mm pitch arrays included large discontinuities caused by low correlation of signals received on vertically and diagonally adjacent emulated elements. The results indicate that multirow arrays designed for use with aberration correction should have element dimensions much less than 75% of the correlation length of the aberration and perhaps as small as 25 to 30% of the correlation length. View full abstract»

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  • Numerical analysis of the symmetric hybrid transducer ultrasonic motor

    Page(s): 1625 - 1631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (975 KB) |  | HTML iconHTML  

    In this paper, operation of a symmetric hybrid transducer ultrasonic motor with output produced by two rotors connected together via a drive shaft is numerically analyzed and compared with the traditional asymmetric hybrid transducer motor design that produces its output from only one rotor. A one-dimensional finite element model for torsional vibration in the stator and a Coulomb friction model for rotor/stator contact associated with the longitudinal vibration of the motor are introduced. The calculation results demonstrate that the symmetric design is capable of performance comparable with the traditional asymmetric design when an optimum static spring force in the rotor/stator contact interface is applied during operation. View full abstract»

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  • Design of advanced ultrasonic transducers for welding devices

    Page(s): 1632 - 1639
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2344 KB) |  | HTML iconHTML  

    A new high frequency ultrasonic transducer has been conceived, designed, prototyped, and tested. In the design phase, an advanced approach was used and established. The method is based on an initial design estimate obtained with finite element method (FEM) simulations. The simulated ultrasonic transducers and resonators are then built and characterized experimentally through laser interferometry and electrical resonance spectra. The comparison of simulation results with experimental data allows the parameters of the FEM models to be adjusted and optimized. The achieved FEM simulations exhibit a remarkably high predictive potential and allow full control of the vibration behavior of the transducer. The new transducer is mounted on a wire bonder with a flange whose special geometry was calculated by means of FEM simulations. This flange allows the transducer to be attached on the wire bonder, not only in longitudinal nodes, but also in radial nodes of the ultrasonic field excited in the horn. This leads to a total decoupling of the transducer to the wire bonder, which has not been achieved so far. The new approach to mount ultrasonic transducers on a welding device is of major importance, not only for wire bonding, but also for all high power ultrasound applications and has been patented. View full abstract»

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  • Application of on-wafer TRL calibration on the measurement of microwave properties of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ films

    Page(s): 1640 - 1647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (530 KB) |  | HTML iconHTML  

    A series of Al/Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST) /sapphire multi-layered coplanar waveguide (CPW) transmission lines of different geometries and thin-film configurations was fabricated. We employed an accurate on-wafer Through-Line-Reflect (TRL) calibration technique and quasi-TEM analysis to measure the dielectric constant, loss tangent, and tunability of BST thin films using this CPW structure. Experimental results show that the overall insertion loss is less than 3 dB/cm even at frequencies as high as 20 GHz, which is the lowest obtained to date for metal/BST CPW devices. This result indicates that, with optimized impedance matching, normal conductors are also possibly suitable for fabricating low-loss tunable phase-shifter devices. View full abstract»

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  • Tissue harmonic image analysis based on spatial covariance

    Page(s): 1648 - 1656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (955 KB) |  | HTML iconHTML  

    The van Cittert-Zernike theorem has been widely used to describe spatial covariance of the pressure field backscattered from a speckle object. Spatial covariance contains important information in the context of correlation-based correction of sound velocity inhomogeneities. Previous work was primarily based on spatial covariance analysis for linear imaging. In this paper, we extend the analysis to tissue harmonic imaging. Specifically, we investigate effects of the signal-to-noise ratio (SNR) and sound velocity inhomogeneities on spatial covariance. Results from tissue harmonic imaging are also compared with those from linear imaging. Both simulations and experiments are performed. At high SNRs, although both linear imaging and tissue harmonic imaging have spatial covariance functions close to theory, the spatial covariance of tissue harmonic imaging is consistently lower than that of linear imaging regardless of the presence of sound velocity inhomogeneities. At low SNRs, on the other hand, spatial covariance of tissue harmonic imaging is significantly affected. Because the tissue harmonic signal is much weaker than the linear counterpart, the low SNR reduces the accuracy of correlation-based estimation. It is concluded that the linear signal is more suitable for correlation-based correction of sound velocity inhomogeneities, despite the fact that tissue harmonic imaging generally has improved image quality over linear imaging. View full abstract»

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  • Light shift compensation in a Rb gas cell frequency standard with two-laser pumping

    Page(s): 1657 - 1661
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    One of the most important physical processes occurring in Rb frequency standards is the light shift, which depends strongly on the intensity and the optical frequency detuning of the pumping light. This paper presents a method to compensate the light shift by means of two-laser pumping. The two-laser pumping schemes will also improve the signal-to-noise ratio, because almost all atoms can be pumped to the desired state. View full abstract»

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  • Application of finite element method and SPICE simulation for design optimization of oven-controlled crystal oscillators

    Page(s): 1662 - 1668
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1876 KB) |  | HTML iconHTML  

    Thermal finite element method (FEM) calculations and SPICE-based dynamic thermal models are used to simulate and optimize the static and dynamic performance of miniaturized oven-controlled crystal oscillators (OCXOs). FEM can be used to generate the values of the SPICE circuit elements. Good agreement is achieved between simulation and measurement. Several application examples, including directly heated OCXOs, are discussed. View full abstract»

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  • Efficient laser-ultrasound generation by using heavily absorbing films as targets

    Page(s): 1669 - 1680
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1509 KB) |  | HTML iconHTML  

    An efficient all-fiber optic source is presented; it adopts absorbing films, deposed directly over the fiber tip, as targets. It is demonstrated that the use of absorbing films made of pure graphite, or graphite powder mixed with epoxy resin, has produced a conversion efficiency increase of two orders of magnitude with respect to metallic materials. It is observed that the conversion efficiency increases monotonically as thickness is reduced down to the material optical penetration depth. Moreover, the conversion efficiency rises with the concentration of graphite powder. Principal advantages of this kind of source are the ease of production and miniaturization, the excellent electromagnetic compatibility, wide ultrasonic bandwidth and, consequently, high spatial resolution. The ultrasonic bandwidth can be controlled by varying the laser pulse duration. The possibility of generating ultrasonic signals with high frequency and flat spectral distribution makes the proposed device suitable for biological tissue spectral characterization. View full abstract»

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  • Doubly rotated quartz resonators with a low amplitude-frequency effect: the LD-cut

    Page(s): 1681 - 1685
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (771 KB) |  | HTML iconHTML  

    This article deals with a crystal quartz cut with virtually no amplitude-frequency effect (also called "isochronism defect" or "anisochronism"). The cut, called LD-cut (Low isochronism Defect), is set in a BVA-type structure for later use in an Ultra-Stable Oscillator (USO). Various design parameters are presented, along with the properties of the resonator. The resonance frequencies of various modes, the temperature dependence, the motional parameters and the phase noise in relation to the power supplied to the resonator are mainly studied. These properties are compared to those of the SC-cut resonators. View full abstract»

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  • Optical phase contrast measurement of ultrasonic fields

    Page(s): 1686 - 1694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1297 KB) |  | HTML iconHTML  

    This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (/spl lambda//sub l/ = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180/spl deg/ about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields). View full abstract»

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  • Superthreshold behavior and threshold estimates of ultrasound-induced lung hemorrhage in adult rats: role of beamwidth

    Page(s): 1695 - 1705
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (507 KB) |  | HTML iconHTML  

    It is well documented that ultrasound-induced lung hemorrhage can occur in mice, rats, rabbits, pigs, and monkeys. The objective of this study was to assess the role of the ultrasound beamwidth (beam diameter incident on the lung surface) on lesion threshold and size. A total of 144 rats were randomly exposed to pulsed ultrasound at three exposure levels and four beamwidths (12 rats per group). The three in situ peak rarefactional pressures were about 5, 7.5, and 10 MPa. The four 19-mm-diameter focused transducers had measured pulse-echo -6-dB focal beamwidths of 470 μm (2.8 MHz; f/1), 930 μm (2.8 MHz; f/2), 310 μm (5.6 MHz; f/1), and 510 μm (5.6 MHz; f/2). Exposure durations were 10 s, pulse repetition frequencies were 1 kHz, and pulse durations were 1.3 μs (2.8 MHz; f/1), 1.2 μs (2.8 MHz; f/2), 0.8 μs (5.6 MHz; f/1) and 1.1 μs (5.6 MHz; f/2). The lesion surface area and depth were measured for each rat as well as the percentage of rats with lesions per group. Logistic regression analysis and Gaussian-Tobit analysis methods were used to analyze the data. The effects of in situ peak rarefactional pressure and beamwidth were highly significant, but ultrasonic frequency was not significant. In addition, the estimated interaction between in situ peak rarefactional pressure and beamwidth was positive and highly significant. The ultrasound beamwidth incident on the lung surface was shown to strongly affect the percentage and size of ultrasound-induced lung hemorrhage lesions. Even though ultrasonic frequency was an experimental variable, it was not shown to affect the lesion percentage or size. 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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Steven Freear
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