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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 1 • Date Jan. 2000

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Displaying Results 1 - 25 of 33
  • The history of ceramic filters

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (691 KB)  

    The history of ceramic filters is surveyed. Included is the history of piezoelectric ceramics. Ceramic filters were developed using technology similar to that of quartz crystal and electro-mechanical filters. However, the key to this development involved the theoretical analysis of vibration modes and material improvements of piezoelectric ceramics. The primary application of ceramic filters has been for consumer-market use. Accordingly, a major emphasis has involved mass production technology, leading to low-priced devices. A typical ceramic filter includes monolithic resonators and capacitors packaged in unique configurations. View full abstract»

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  • X-cut miniature tuning forks realized by ion track lithography

    Page(s): 8 - 15
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    With the recently developed ion track lithography based on the selective etching, widening, and merging of ion-induced defects collectively resembling a superimposed anisotropy in certain areas as defined by a stencil mask, 39-kHz x-cut miniature tuning forks with a tine size of 331/spl times/2, 500/spl times/42 /spl mu/m and a Q-value of up to 42 000 were fabricated from single crystalline quartz mostly to demonstrate this new technique's ability to structure difficult cuts, but also to benefit from the much simpler electrode configuration possible with this cut in comparison with ordinary z-cut watch tuning forks. View full abstract»

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  • Collinear guided wave to leaky wave acoustooptic interactions in proton-exchanged LiNbO/sub 3/ waveguides

    Page(s): 16 - 28
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    The results of a detailed theoretical study on collinear guided wave to leaky wave acoustooptic (AO) interactions in proton-exchanged LiNbO/sub 3/ (PE:LiNbO/sub 3/) planar waveguides are presented. The guided-to-leaky mode conversion for an input optical beam at the wavelength of 632.8 nm by the induced diffraction grating from a collinear surface acoustic wave (SAW) is analyzed using a generalized multimode formulation of the coupled mode theory. Mode conversion efficiency and AO bandwidth have been calculated as functions of acoustic frequency, interaction length, guiding layer thickness, and acoustic drive power density for three cuts of the LiNbO/sub 3/ substrate. High performance configurations that are desirable for application to demultiplexing and switching in optical communication systems are identified, and the corresponding channel capacity and frequency resolution are determined. For example, it was shown that the X-cut configuration features the highest mode conversion efficiency. However, a relatively small AO bandwidth is associated with this configuration. Both high mode conversion efficiency and large AO bandwidth can be accomplished at the guiding layer thickness of 1.0 /spl mu/m. A TM/sub o//spl rarr/TE/sub /spl nu// mode conversion efficiency as high as 42% together with an AO bandwidth of approximately 70 MHz can be achieved in the Z-cut waveguide at the guiding layer thickness of 1.0 /spl mu/m, acoustic drive power density of 50 mW/mm, interaction length of 40 mm, and acoustic frequency of 460 MHz. The corresponding channel capacity and frequency resolution are 745 and 0.09 MHz, respectively. Measured mode conversion efficiencies as high as 90 and 78% obtained at the acoustic frequencies of 107 and 367 MHz using the X-cut substrate and the Y-propagation SAW have verified the theoretical prediction on the mode conversion efficiencies. View full abstract»

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  • Small element array algorithm for correcting phase aberration using near-field signal redundancy. I. Principles

    Page(s): 29 - 48
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    A near-field, signal-redundancy algorithm for measuring phase-aberration profiles has been proposed previously. It is designed for arrays with a relatively large element size for which relatively narrow beams are transmitted and received. The algorithm measures the aberration profile by cross-correlating signals collected with the same midpoint position between transmitter and receiver, termed common midpoint signals, after a dynamic near-field delay correction. In this paper, a near-field signal-redundancy algorithm for small element arrays is proposed. In this algorithm, subarrays are formed of adjacent groups of elements to narrow the beams used to collect common midpoint signals and steer the beam direction, so that angle-dependent, phase-aberration profiles can be measured. There are several methods that could be used to implement the dynamic near-field delay correction on common midpoint signals collected with subarrays. In this paper, the similarity between common midpoint signals collected with these methods is also analyzed and compared using a so-called corresponding-signal concept. This analysis should be valid for general target distributions in the near field and wide-band signals. View full abstract»

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  • Small element array algorithm for correcting phase aberrations using near-field signal redundancy. Part II: Experimental results

    Page(s): 49 - 57
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    For part I see ibid., vol.47, p.29 (2000). A small element array algorithm for phase-aberration correction using near-field signal redundancy was proposed in part I. Using this algorithm, subarrays are formed to narrow the transmitted and received beams when collecting common midpoint signals, so that angle-dependent aberration profiles across the array can be measured. In this paper, this algorithm is tested on data collected from a phantom with a non-isoplanatic aberrator attached to the front surface of a phased array. The aberrator is made from cast room temperature vulcanizing (RTV) silicone rubber, which has a sound velocity of about 1.02 mm/spl middot//spl mu/s/sup -1/. Results show that the subarray technique can be used to measure and correct angle-dependent, phase-aberration profiles. The theoretical results regarding the performance of several implementation methods for dynamic near-field delay correction on subarrays are also experimentally tested using data from a phantom. View full abstract»

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  • A demonstrator for a low-cost, cordless, multi-carrier spread-spectrum system

    Page(s): 58 - 64
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    Because of the need for spectrally efficient systems for wireless communication, many research activities have been carried out in the area of spread-spectrum techniques. Multi-carrier spread-spectrum (MC-SS) is a new modulation technique with better spectral properties than direct-sequence spread-spectrum (DS-SS). In this paper, a new MC-SS system is introduced. A customized surface acoustic wave (SAW) filter has been designed as a fast analog correlator. A demonstrator testbed has been developed for the 2.4-GHz industrial, scientific, and medical (ISM) band. Experimental measurements of the intermediate frequency (IF) and baseband correlation are presented. View full abstract»

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  • Fast, all-optical Rayleigh wave microscope: Imaging on isotropic and anisotropic materials

    Page(s): 65 - 74
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    A fast, non-contact Rayleigh wave scanning microscope is demonstrated, which is capable of scan rates of up to a maximum of 1000 measurements/s with typical speeds of up to 250 measurements/s on real samples. The system uses a mode-locked, Q-switched Nd:YAG laser operating at a mode-locked frequency of 82 MHz and a Q-switch frequency of 1 kHz. The Q-switch frequency determines the upper limit of the scanning rate. The generating laser illumination is delivered and controlled by a computer-generated hologram (CGH). The generating laser produces around 30 pulses at 82 MHz and additional harmonics at 164 and 246 MHz and above. The microscope can operate at these harmonics provided the spatial bandwidth of the optics and the temporal bandwidth of the electronics are suitable. The ultrasound is detected with a specialized knife-edge detector. The microscope has been developed for imaging on isotropic materials. Despite this, the system can be used on anisotropic materials, but imaging and interpreting images can be difficult. The anisotropy and grain structure of the material can distort the Rayleigh wavefront, leading to signal loss. A model has been developed to simulate polycrystalline-anisotropic materials; this is discussed along with possible solutions that would overcome the problems associated with anisotropy. Rayleigh wave amplitude images are demonstrated on silicon nitride at 82 and 164 MHz and on polycrystalline aluminium at 82 MHz. View full abstract»

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  • Experimental determination of phase velocity of perfluorocarbons: Applications to targeted contrast agents

    Page(s): 75 - 84
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    Targeted acoustic contrast agents are designed to enhance the sensitivity and specificity of ultrasonic diagnoses. We have previously developed a ligand targeted ultrasonic contrast system that is a lipid-encapsulated, liquid-perfluorocarbon emulsion. The emulsion particles are small (250 nm) and have inherently low echogenicity unless bound to a surface by a pretargeted ligand through avidin-biotin interactions. We have recently proposed a simple acoustic transmission line model that treats the emulsion particles as a thin layer over the targeted surface. In this model, the acoustic reflectivity of the sample increases for perfluorocarbons with smaller velocities of longitudinal sound or lower densities. In this study, we measure and report the velocity of longitudinal sound for 20 perfluorocarbons using a broadband phase spectroscopic approach for estimating phase velocities. Experimentally determined velocities ranged from 520/spl plusmn/2 m/sec (perfluorohexane) to 705/spl plusmn/5 m/s (perfluorodecalin). No measurable dispersion was observed over the useful bandwidth of 2 to 22 MHz. Increasing carbon backbone chain length and fluorine substitution with halogens of greater atomic weight increased the measured speed of sound. Our experimental data were consistent (R=0.87) with a published empirical model that predicts velocity as a function of molecular structure. These data provide a rational basis for optimizing targeted perfluorocarbon-based contrast agents and offer further insight into the physical mechanisms responsible for the observed enhancement of surface acoustic reflectivity. View full abstract»

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  • Ultrasonic density sensor for liquids

    Page(s): 85 - 92
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    This paper presents an ultrasonic density sensor for liquids that unifies high accuracy with high durability and is suitable for on-line measurements in a wide range of tube diameters. The sensor consists of a transducer with a piezoceramic disk mounted between two reference rods of quartz glass. Additionally, a second transducer is used as a sound receiver. The density is obtained from the reflection coefficient of ultrasound at the interface between the quartz glass rod and the liquid and the transit time of sound between this interface and the second transducer. Parameters, such as high long-term stability and accuracy of /spl plusmn/0.1% of full scale, were obtained by an internal acoustic reference measurement. The reference signal is generated using the sound radiated from the rear side of the piezoceramic disk. Design aspects such as sensor materials and signal-to-noise ratio are discussed, and experimental results are given in this paper. Applications of the sensor include concentration measurement, and ultrasonic mass flow measurement. View full abstract»

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  • Sparse 2-D array design for real time rectilinear volumetric imaging

    Page(s): 93 - 110
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    Several sparse 2-D arrays for real time rectilinear volumetric imaging were investigated. All arrays consisted of 128/spl times/128=16384 elements with /spl lambda/ spacing operating at 5 MHz. Because of system limitations, not all of the elements could be used. From each array, 256 elements were used as transmitters, and 256 elements were used as receivers. These arrays were compared by computer simulation using Field II. For each array, beamplots for the on-axis case and an illustrative off-axis case were obtained. For the off-axis case, the effects of receive mode dynamic focusing were studied to maintain the beam perpendicular to the transducer face. Main lobe widths, side lobe heights, clutter floor levels, and pulse-echo sensitivities were quantified for each array. The sparse arrays, including a vernier periodic array, a random array, and a Mills cross array, were compared with a fully sampled array that served as the "gold standard". The Mills cross design showed the best overall performance under the current system constraints. View full abstract»

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  • Conductance measurements on a leaky SAW harmonic one-port resonator

    Page(s): 111 - 116
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    Conductance measurements are reported on a leaky SAW (LSAW) harmonic one-port resonator on a 64/spl deg/Y-X LiNbO/sub 3/ substrate. This employed a short three-finger IDT for fundamental and second harmonic operation together with long reflection gratings. Conductances were measured with and without the end gratings. From an analysis of the measurements, it was deduced that, for optimum second harmonic performance, the grating stop-band frequency should be higher than the IDT unperturbed center frequency. This result is in contrast to fundamental frequency resonator designs in which the end grating stop-band frequency is placed below the IDT center frequency for optimum performance. View full abstract»

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  • Evaluation of the radiation pattern of a split aperture linear phased array for high frequency imaging

    Page(s): 117 - 124
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    Developing transducer arrays for high frequency medical imaging is complicated because of the extremely small size and spacing of the array elements. For example, a 50 MHz linear phased array requires a center-to-center spacing of only 15 /spl mu/m (one-half wavelength in water) to avoid the formation of grating lobes in the radiation pattern of the array. Fabricating an array with these dimensions is difficult using conventional technology. A split aperture design that permits much larger element spacing (3 to 4 times) while avoiding the formation of grating lobes is described. The 3-D radiation pattern of a 1.9/spl times/1.4 mm, 50-MHz split aperture linear phased array with 33 transmit elements and 33 receive elements has been evaluated theoretically. The azimuthal beam width is 90 /spl mu/m at a distance of 4.0 mm. Grating lobes are suppressed by at least 60 dB at distances >4.0 mm (/spl sim/f/2). The elevation beam width is 220 /spl mu/m at 4.0 mm, and a useful depth of field over the axial range from 4 to 10 mm is obtained. View full abstract»

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  • A theoretical assessment of the relative performance of spherical phased arrays for ultrasound surgery

    Page(s): 125 - 139
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    Computer modeling of spherical-section phased arrays for ultrasound surgery (tissue ablation) is described. The influence on performance of the number of circular elements (68 to 1024), their diameter (2.5 to 10 mm), frequency (1 to 2 MHz), and degree of sparseness in the array is investigated for elements distributed randomly or in square, annular, and hexagonal patterns on a spherical shell (radius of curvature, 120 mm). Criteria for evaluating the quality of the intensity distributions obtained when focusing the arrays both on and away from their center of curvature, and in both single focus and simultaneous multiple foci modes, are proposed. Of the arrays studied, the most favorable performance, for both modes, is predicted for 256 5-mm diameter, randomly distributed elements. For the single focus mode, this performed better than regular arrays of 255 to 1024 elements and, for the case of nine simultaneous foci produced on a coplanar 3/spl times/3 grid with 4-mm spacing, better than square, hexagonal, or annular distributed arrays with a comparable number of elements. Randomization improved performance by suppressing grating lobes significantly. For single focus mode, a several-fold decrease in the number of elements could be made without degrading the quality of the intensity distribution. View full abstract»

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  • Automatic computer-aided design of SAW filters using slanted finger interdigital transducers

    Page(s): 140 - 147
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    This paper describes a design procedure for surface acoustic wave (SAW) filters using slanted finger interdigital transducers (SFIT) that are suitable for mid-band or wideband applications. The SFITs cannot represent the impulse response directly, in contrast to apodized IDTs. A design method for SFITs based on a building-block approach in the frequency domain is described. An automatic computer-aided design tool for SFIT filters has been achieved. The SFIT filters can be designed using a withdrawal weighting for stop-band responses, an aperture weighting for pass-band amplitude responses, and a distance weighting for pass-band phase responses. In addition, a SFIT pattern for photo mask can be automatically designed using this tool. Using this tool, an SFIT filter with a relative bandwidth of 15% was designed on an x-cut 112y-direction LiTaO/sub 3/ substrate. View full abstract»

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  • Single element high frequency (<50 MHz) PZT sol gel composite ultrasound transducers

    Page(s): 148 - 159
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    A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 /spl mu/m on aluminum substrates. The complex permittivity (/spl epsi//sub 33//sup S/), elastic stiffness (c/sub 33//sup D/), and the piezoelectric constant (h/sub 33/) of the coating and the complex elastic stiffness (c/sub 33//sup D/) of the substrate have been determined using impedance measurements and a commercially available software program [Piezoelectric Resonance Analysis Program PRAP 2.0, TASI Technical Software, Kingston, Ontario, Canada]. The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a dielectric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of a high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combining the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biological samples are shown. View full abstract»

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  • High frequency optoacoustic arrays using etalon detection

    Page(s): 160 - 169
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    Two-dimensional phased arrays for high frequency (>30 MHz) ultrasonic imaging are difficult to construct using conventional piezoelectric technology. A promising alternative involves optical detection of ultrasound, where the array element size is defined by the focal spot of a laser beam. Element size and spacing on the order of a few microns are easily achieved, suitable for imaging at frequencies exceeding 100 MHz. We have previously shown images made from a receive-only, two-dimensional optoacoustic array operating at 10 to 50 MHz. The main drawback of optical detection has been poor sensitivity when compared with piezoelectric detection. In this paper, we explore a different form of optical detection demonstrating improved sensitivity and offering a potentially simple method for constructing two-dimensional arrays. Results from a simple experiment using an etalon sensor confirm that the sensitivity of etalon detection is comparable with piezoelectric detection. This paper concludes with a proposal for a high frequency optoacoustic array system using an etalon. View full abstract»

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  • Axial control of thermal coagulation using a multi-element interstitial ultrasound applicator with internal cooling

    Page(s): 170 - 178
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    A multi-element, direct-coupled ultrasound (US) applicator with internal water cooling was investigated for axial control of interstitial thermal coagulation. A prototype implantable applicator was constructed with a linear array of three tubular PZT ultrasound transducers (each 2.5 mm OD, 10 mm length, 360/spl deg/ emittance). Acoustic beam distributions from each element were measured and found to be collimated within the transducer length. The internally cooled applicator could sustain high levels of applied power to each transducer (0 to 40 W) and maintain acceptable applicator surface temperatures (<100/spl deg/C). Thermal performance of the applicator was investigated through heating trials in vivo (porcine thigh muscle and liver) and in vitro (bovine liver). The radial depth of thermal lesions produced was dependent on the applied power and sonication time and was controlled independently with power levels to each transducer element. With 18 W per element (applied electrical power) for 3 min, cylindrical thermal lesions were produced with a diameter of /spl sim/3 cm and a length ranging from 1.2 cm (with one element) to 3.5 cm (three elements). Higher powers (24 to 30 W) for 3 to 5 min provided increased depths of coagulation (/spl sim/4 cm diameter lesions). Analysis of axial lesion shapes demonstrated that individual variation of power to each transducer element provided control of axial heating and depth of coagulation (for custom lesion shapes); lesion lengths corresponded to the number of active transducers. This ability to control the heating distribution dynamically along the length of the applicator has potential for improved target localization of thermal coagulation and necrosis in high temperature thermal therapy. View full abstract»

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  • The experimental and theoretical characterization of the SAW propagation properties for zinc oxide films on silicon carbide

    Page(s): 179 - 187
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    The surface acoustic wave (SAW) propagation properties of zinc oxide (ZnO) films on silicon carbide (SiC) have been theoretically and experimentally characterized in the film thickness-to-acoustic wavelength ratio range up to 0.12. The experimental characterization of the SAW propagation properties was performed with a linear array of interdigital transducer (IDT) structures. The measurements characterized the velocity and propagation loss of two surface modes, a generalized SAW (GSAW) mode with velocities between 6000 and 7000 m/s, and a high velocity Pseudo-SAW (HVPSAW) mode with velocities between 8500 and 12 500 m/s. The experimentally determined characteristics of the two waves have been compared with the results of calculations based on published data for SiC and ZnO. Simulation of wave characteristics was performed with various values of the elastic constant C/sub 13/, which is absent in the published set of material constants for SiC, within the interval permitted by the requirement of positive elastic energy in a hexagonal crystal. The best agreement between the measured and calculated propagation losses of the HVPSAW has been obtained for C/sub 13/ near zero. Although for the GSAW mode the calculated velocity dispersion has been found nearly insensitive to the value of C/sub 13/ and consistent with the experimental data, for the HVPSAW, some disagreement between measured and calculated velocities, which increased with ZnO film thickness, has been observed for any C/sub 13/ value. Theoretical analysis of HVPSAW has revealed the existence of a previously unknown high velocity SAW (HVSAW). The displacement components of this wave have been analyzed as functions of depth and confirmed its pure surface, one-partial character. View full abstract»

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  • Doppler angle estimation using correlation

    Page(s): 188 - 196
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    Conventional Doppler techniques can only detect the axial component of blood flow. To obtain the transverse flow component, an approach based on the dependence of Doppler bandwidth on Doppler angle has been widely investigated. To compute the bandwidth, a full Doppler spectrum is often required. Therefore, this approach has not been applied to real-time, two-dimensional Doppler imaging because of the long data acquisition time. To overcome this problem, a correlation-based method is proposed. Specifically, variance of the Doppler spectrum is used to approximate the square of the Doppler bandwidth. Because variance is computed efficiently and routinely in correlation-based color Doppler imaging systems, implementation of this method is straightforward. In addition, the two-dimensional velocity vector can be calculated and mapped to different colors using the color mapping function of current systems. Simulations were performed, and experimental data were also collected using a string phantom with the Doppler angle varying from 23/spl deg/ to 82/spl deg/. Results indicate that the correlation-based method may produce significant errors if only a limited number of flow samples are available. With averaging, however, the Doppler angles estimated by the correlation-based method can achieve good agreement with the true angles by using only four flow samples with proper variance averaging. View full abstract»

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  • An experimental study for the compact hydrogen maser with a TE111 septum cavity

    Page(s): 197 - 200
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    We have made experiments on our compact active hydrogen maser with the cylindrical TE111-mode septum cavity, which is almost one-half the conventional TE011-mode cavity in size. An inductive radiation signal was observed, but the maser did not produce self-oscillation. The system supports oscillation when the cavity is placed in an external feedback loop. View full abstract»

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  • A finite element model for simulating acoustic streaming in cystic breast lesions with experimental validation

    Page(s): 201 - 214
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    Streaming detection is an ultrasonic technique that can be used to distinguish fluid-filled lesions, or cysts, from solid lesions. With this technique, high intensity ultrasound pulses are used to induce acoustic streaming in cyst fluid, and this motion is detected using Doppler flow estimation methods. Results from a pilot clinical study were recently published in which acoustic streaming was successfully induced and detected in 14 of 15 simple breast cysts and four of 14 sonographically indeterminate breast lesions in vivo. In the study, the detected velocities were found to vary considerably among cysts and for different pulsing regimes. A finite element model of streaming detection is presented. This model is utilized to investigate methods of increasing induced acoustic streaming velocity while minimizing patient exposure to high intensity ultrasound during streaming detection. Parameters studied include intensity, frequency, acoustic beam shape, cyst-diameter, cyst fluid protein concentration, and cyst fluid viscosity. The model, which provides both transient and steady-state solutions, is shown to predict trends in streaming velocity accurately. Experimental results from studies investigating the potential for nonlinear streaming enhancement in cysts are also provided. View full abstract»

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  • Improvement of the longitudinal vibration system for the hybrid transducer ultrasonic motor

    Page(s): 216 - 221
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    This paper presents a symmetric hybrid transducer ultrasonic motor designed to produce large longitudinal vibration stress in the rotor/stator contact interface for high-torque operation. The nodal plane of the longitudinal vibration mode was adjusted to match the rotor/stator contact interface, and the piezoelectric ceramic disks for the longitudinal vibration were installed at the nodal plane of the longitudinal vibration mode for effective excitation. An experimental motor, 20 mm in diameter, using the first torsional vibration mode and the second longitudinal vibration mode was manufactured. A maximum torque of 0.8 N/spl middot/m was achieved in the prototype, an improvement over previous versions. View full abstract»

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  • Design and characterization of a real-time angular scatter ultrasound imaging system

    Page(s): 222 - 232
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    A novel ultrasound imaging system has been implemented using two 32-element linear phased array transducers oriented at an angle of 40/spl deg/ to one another. The system simultaneously acquires and displays, in real time, a conventional backscatter image and an angular scatter image formed using side-scattered echoes from the same region. The design of the system is shaped by the influence of the scatter angle on the spatial resolution and receive signal processing requirements of the instrument. The subtended scatter angles are restricted to values >90/spl deg/ to ensure that the angular scatter receiver effectively tracks the transmitted pulse and that the spatial resolution in the two images is comparable. The system is sufficiently tolerant of small variations in the average acoustic velocity of the medium to guarantee reliable pulse tracking in biomedical applications. The angular scatter signal magnitude is significantly weighted by the directivity of the receive array. The imaging system will most effectively demonstrate angular variations in scattering at scatter angles between 125 and 145/spl deg/, where the angular response of the receiver is near its peak. View full abstract»

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  • New high performance SAW convolvers used in high bit rate and wideband spread spectrum CDMA communications system

    Page(s): 233 - 241
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    New surface acoustic wave (SAW) convolver structures with high conversion efficiency and self-temperature compensation characteristics have been developed. Strong piezoelectric substrates, regardless of temperature coefficients of delay (TCD), can be used in these convolvers. New demodulation techniques using the developed SAW convolver for high bit rate and wideband spread spectrum code division multiple access (CDMA) communications have also been developed. I- and Q-channel demodulation data can be derived directly from binary phase shift keying (BPSK) or quadri-phase shift keying (QPSK) CDMA signals. In an experiment using a 128/spl deg/ YX-LiNbO/sub 3/ substrate, CDMA signals of 9 Mbps (megabits per second) with 60 Mcps (megachips per second) spread by 13-chip Barker code and 11 Mbps with 140 Mcps spread by 25-chip Shiba's code were clearly demodulated, demonstrating the effectiveness of these techniques for use in future CDMA communications. View full abstract»

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  • Novel concepts for GaAs/LiNbO/sub 3/ layered systems and their device applications

    Page(s): 242 - 248
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    Thin semiconductor quantum well structures fused onto LiNbO/sub 3/ substrates using the epitaxial lift-off (ELO) technology offer the possibility of controlling the surface acoustic wave (SAW) velocity via field effect. The tunability of the conductivity in the InGaAs quantum well results in a great change in SAW velocity, in general, accompanied by an attenuation. We show that an additional lateral modulation of the sheet conductivity reduces the SAW attenuation significantly, enhancing device performance. At high SAW intensity the bunching of electrons in the SAW potential also leads to a strong reduction of attenuation. These effects open new possibilities for voltage-controlled SAW devices. We demonstrate a novel, wireless, passive voltage sensor, which can be read out from a remote location. 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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Meet Our Editors

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