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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 2 • Date March 1999

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Displaying Results 1 - 23 of 23
  • Interpolation methods for time-delay estimation using cross-correlation method for blood velocity measurement

    Publication Year: 1999 , Page(s): 277 - 290
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (454 KB)  

    The cross-correlation method (CCM) for blood flow velocity measurement using Doppler ultrasound is based on time delay estimation of echoes from pulse-to-pulse. The sampling frequency of the received signal is usually kept as low as possible in order to reduce computational complexity, and the peak in the correlation function is found by interpolating the correlation function. The parabolic-fit interpolation method introduces a bias at low sampling rate to the ultrasound center frequency ratio. In this study, four different methods are suggested to improve the estimation accuracy: (1) Parabolic interpolation with bias-compensation, derived from a theoretical signal model. (2) Parabolic interpolation combined with linear filter interpolation of the correlation function. (3) Parabolic interpolation to the complex correlation function envelope. (4) Matched filter interpolation applied to the correlation function. The new interpolation methods are analyzed both by computer simulated signals and RF-signals recorded from a patient with time delay larger than 1/f/sub 0/, where f/sub 0/ is the center frequency. The simulation results show that these methods are more accurate than the parabolic-fit method. From the simulation, the worst estimation accuracy is about 1.25% of 1/f/sub 0/ for the parabolic-fit interpolation, and it is improved by the above methods to less than 0.5% of 1/f/sub 0/ when the sampling rate is 10 MHz, the center frequency is 2.5 MHz and the bandwidth is 1 MHz. This improvement also can be observed in the experimental data. Furthermore, the matched filter interpolation gives the best performance when signal-to-noise ratio (SNR) is low. This is verified both by simulation and experimentation. View full abstract»

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  • Noise robust one-dimensional blind deconvolution of medical ultrasound images

    Publication Year: 1999 , Page(s): 291 - 299
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (343 KB)  

    Recently, several blind cepstral deconvolution methods for medical ultrasound images were compared experimentally. The results indicated that the generalized cepstrum or the complex cepstrum with phase unwrapping give the blind homomorphic deconvolution algorithms with the best performance. However, the frequency domain phase unwrapping for pulse estimation, which is an essential part of both methods, is sensitive to the sensor noise when the values of the spectrum are small due to the randomness of the tissue response. The noise introduces abrupt changes in the phase. The phase degradation due to the noise causes variable spatial and gray scale resolution in image sequences following deconvolution. This paper introduces a noise robust Bayesian phase unwrapping method using a noncausal Markov random chain model. The prior regularizing term accounts for the noise and smoothes the phase. The phase unwrapping is formulated as a least mean square optimization problem. The optimization is done noniteratively by solving a difference equation using the cosine transform. The resulting improvement in radial and lateral blind deconvolution is demonstrated on six short ultrasound image sequences recorded in vitro or in vivo. View full abstract»

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  • Analysis and classification of tissue with scatterer structure templates

    Publication Year: 1999 , Page(s): 300 - 310
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    Back-scattered ultrasonic signals provide scatterer structure information. Large-scale structures, such as tissue and tumor boundaries, typically create significant amplitude differences that reveal boundaries in conventional intensity images. Small-scale structures typically result in textures observed over regions of the intensity image. This paper describes the generalized spectrum (GS) for characterizing small-scale scatterer structures and applies it to analyze scatterer structures in a class of malignant and benign breast masses. Methods are presented for scaling and normalizing the GS to reduce effects from system response, overlaying tissue, and variability from noncritical structures. Results from a limited clinical study demonstrate an application of using the GS to discriminate between benign and malignant breast masses that contain internal echoes. Sections of rf A-scans in 41 breast mass regions were taken from 26 patients. A GS analysis was applied to determine critical structural properties between a class of fibroadenoma and carcinoma masses. Classifiers designed using significant structure differences identified by the GS analysis achieved approximately 82% true-positive and 10% false-positive rates. View full abstract»

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  • Ultrasonic arrays for monitoring cracks in an industrial plant at high temperatures

    Publication Year: 1999 , Page(s): 311 - 319
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB)  

    A piezoelectric linear array structure has been designed to operate at temperatures up to 400/spl deg/C for nondestructive testing of steel components of a hot industrial plant. It is intended that these arrays be fixed permanently to the test subject so that known defects can be monitored by comparing measurements taken over a period of time without needing to shut down the plant. The arrays are used in pairs: the transmitter is a phased array producing a variable angle steered beam, and a second array is used for receiving. The defect can be identified from a series of scans collected from individual elements of the second array. A simple monolithic array structure was used, based on a single crystal of lithium niobate and operating in the frequency range 3 to 5 MHz. Prototype devices have 64 elements on a 0.5 mm pitch. Simulated defects in steel blocks have been scanned at high temperatures to illustrate the arrays' capability for nondestructive testing. The results suggest an accuracy better than 1 mm in finding the location of crack tips. View full abstract»

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  • Delta-sigma oversampled ultrasound beamformer with dynamic delays

    Publication Year: 1999 , Page(s): 320 - 332
    Cited by:  Papers (36)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (409 KB)  

    The principles of oversampling are exploited in a simple beamforming architecture using a single bit delta-sigma (/spl Delta/C) analog to digital converter (A/D) on every channel. The high sampling rate required for the single bit A/D provides adequate delay accuracy for high quality beamforming using elementary sample manipulations. Images produced with this beamformer exhibit significant artifacts directly related to dynamic focusing. However, a simple digital recording technique following delays permits dynamically focused beamforming without degrading image quality. The simplicity of this beamformer compared to conventional methods may facilitate very large channel count or low power beamformers suitable for 1.5-D arrays or portable scanners. View full abstract»

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  • Focusing of Rayleigh waves: simulation and experiments

    Publication Year: 1999 , Page(s): 333 - 340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A linear array of surface wave transducers has been developed to generate focused surface wave motion. A novel theoretical approach, whereby time-harmonic surface wave motion is represented by a carrier wave that satisfies a reduced wave equation on the surface of the body and supports the subsurface motion, is used to model the beam generated by a single element of the array. Comparison of theoretical and experimental results show that, for a single element, the opening angle of the beam is about 20/spl deg/ and its cross-section can be represented by a Gaussian distribution of the normal displacements. For an eight-element array, the focused beam is subsequently obtained by superposition considerations. For the focused beam comparisons of theoretical and experimental results, in which the latter have been obtained by the use of a laser interferometer, show excellent agreement both for the normal displacements along a radial line and across the width of the beam. The array can be used for self-focusing of surface waves on a surface defect. View full abstract»

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  • Line-focusing electromagnetic acoustic transducers for the detection of slit defects

    Publication Year: 1999 , Page(s): 341 - 346
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    This paper describes the design principles of a line-focusing electromagnetic acoustic transducer (LF-EMAT) and the results of a feasibility test for detecting slit-type defects in metals. The LF-EMAT excites shear vertical (SV) elastic waves and focuses them to a line in a metal body. It consists of a permanent magnet block and a meanderline coil, whose spacing is continuously varied so that the excited SV waves become coherent on a focal line after traveling oblique paths. The measured directivity of generation and reception show a sharp peak at the designed focal line. The LF-EMATs are then applied to detecting slit defects in the bottom surface of steel blocks, on which the focal lines are located. Portions of the scattered defect signals are received by the same EMAT. When operated at 4 MHz, the LF-EMATs are capable of detecting slits deeper than 0.05 mm. The sensitivity decreases with liftoff and the LF-EMATs are usable with liftoff up to 0.6 mm. View full abstract»

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  • Thinning and weighting of large planar arrays by simulated annealing

    Publication Year: 1999 , Page(s): 347 - 355
    Cited by:  Papers (56)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (397 KB)  

    Two-dimensional arrays offer the potential for producing three-dimensional acoustic imaging. The major problem is the complexity arising from the large number of elements in such arrays. In this paper, a synthesis method is proposed that is aimed at designing an aperiodic sparse two-dimensional array to be used with a conventional beam-former. The stochastic algorithm of simulated annealing has been utilized to minimize the number of elements necessary to produce a spatial response that meets given requirements. The proposed method is highly innovative, as it can design very large arrays, optimize both positions and weight coefficients, synthesize asymmetric arrays, and generate array configurations that are valid for every steering direction. Several results are presented, showing notable improvements in the array characteristics and performances over those reported in the literature. View full abstract»

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  • Analysis of noise in quartz crystal oscillators by using slowly varying functions method

    Publication Year: 1999 , Page(s): 356 - 365
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    By using formal manipulation capability of commercially available symbolic calculation code, it is possible to automatically derive the characteristic polynomial describing the conditions for oscillation of a circuit. The analytical expression of the characteristic polynomial is obtained through an encapsulation process starting from the SPICE netlist description of the circuit: by using a limited number of simple transformations, the initial circuit is progressively transformed in a simplified standard form. In this method, the nonlinear component is described by its large signal admittance parameters obtained from a set of SPICE transient simulations of larger and larger amplitude. The encapsulation process involving linear and nonlinear components as well as noise sources leads to a perturbed characteristic polynomial. In the time domain, the perturbed characteristic polynomial becomes a nonlinear nonautonomous differential equation. By using an extension of the slowly varying functions method, this differential equation is transformed into a nonlinear differential system with perturbation terms as the right-hand side. Eventually, solving this system with classical algorithms allows one to obtain both amplitude and phase noise spectra of the oscillator. View full abstract»

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  • Frequency performances of a miniature optically pumped cesium beam frequency standard

    Publication Year: 1999 , Page(s): 366 - 371
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB)  

    The optically pumped cesium beam clock named Cs IV is operated with a new short Ramsey cavity satisfying strict requirements on the microwave leakage level. The most relevant characteristics of the device are presented. Cs IV is presently driven by standard electronics coming from a HP 5061 B clock that provides a sinusoidal modulation of the interrogation microwave signal and a microwave power stability of about 1% at a temperature of 20/spl plusmn/1/spl deg/C. The short- and medium-term frequency stability measurement gives /spl sigma//sub y/(1 day)=2/spl times/10/sup -14/: this value holds up to 3 days. The accuracy evaluation results in an uncertainty of 10/sup -12/, and the repeatability is evaluated to 3/spl times/10/sup -13/. It appears that the flicker floor is beginning at 2/spl times/10/sup -14/ and is mainly due to both the power fluctuations of the free running microwave interrogating signal and the fluctuations of the external static magnetic field. The accuracy is limited by the lack of knowledge of the end-to-end cavity phase shift. View full abstract»

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  • Pulse inversion Doppler: a new method for detecting nonlinear echoes from microbubble contrast agents

    Publication Year: 1999 , Page(s): 372 - 382
    Cited by:  Papers (93)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (390 KB)  

    A novel technique for the selective detection of ultrasound contrast agents, called pulse inversion Doppler, has been developed. In this technique, a conventional Doppler or color Doppler pulse sequence is modified by inverting every second transmit pulse. Either conventional or harmonic Doppler processing is then performed on the received echoes. In the resulting Doppler spectra, Doppler shifts from linear and nonlinear scattering are separated into two distinct regions that can be analyzed separately or combined to estimate the ratio of nonlinear to linear scattering from a region of tissue. The maximum Doppler shift that can be detected is 1/2 the normal Nyquist limit. This has the advantage over conventional harmonic Doppler that it can function over the entire bandwidth of the echo signal, thus achieving superior spatial resolution in the Doppler image. In vitro measurements comparing flowing agent and cellulose particles suggest that pulse inversion Doppler can provide 3 to 10 dB more agent to tissue contrast than harmonic imaging with similar pulses. Similar measurements suggest that broadband pulse inversion Doppler can provide up to 16 dB more contrast than broadband conventional Doppler. Nonlinear propagation effects limit the maximum contrast obtainable with both harmonic and pulse inversion Doppler techniques. View full abstract»

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  • Propagation of longitudinal leaky surface waves under periodic SiO/sub 2//Al structure on Li/sub 2/B/sub 4/O/sub 7/ substrate

    Publication Year: 1999 , Page(s): 383 - 391
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    The properties of longitudinal leaky surface waves (LLSW) under a periodic SiO/sub 2//Al structure on Li/sub 2/B/sub 4/O/sub 7/ (LBO) substrate, were investigated theoretically and experimentally, in order to improve the high propagation losses of LLSWs under a periodic Al grating with the normalized thickness over 2%. In the theoretical analysis, the previously presented method based on the boundary integral equations for the periodic metal grating structure on the substrate was extended to include the dielectric layer. In the experiments, devices with Al electrodes recessed into a SiO/sub 2/ groove on LBO were fabricated, and the propagation losses of them were estimated. As a result, it was shown that, when the surface of the structure was flattened, the propagation losses were sufficiently low and the first Bragg stopband width decreased. View full abstract»

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  • Time transfer using multi-channel GPS receivers

    Publication Year: 1999 , Page(s): 392 - 398
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB)  

    This report is on time transfer experiments using a Global Positioning System (GPS) receiver constructed using a commercial GPS "engine" and a standard PC. The receiver measures the time difference between the local clock and a 1 pps signal synchronized to GPS time using data from up to 8 satellites. The receiver also reports the difference between GPS time as estimated using each of the satellites being tracked and the composite output pulses that have a rate of 1 Hz (1 pps signal). These data can be used to construct the standard 13-minute tracks as defined in the BIPM standard; the same data also can be averaged in other ways that make better use of the multi-channel capabilities of the hardware. The 13-minute averages can be directly compared with standard time-transfer receivers using common-view analysis. The results of the tests suggest that the methods currently used for national and international time and frequency coordination should be re-examined, and an alternative approach based on multi-channel receivers is suggested that should be more flexible, simpler, and easier to operate than the current system. View full abstract»

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  • PSpice modelling of ultrasound transducers: comparison of software models to experiment

    Publication Year: 1999 , Page(s): 399 - 406
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    This paper presents a complete PSpice model of an ultrasound single-element transducer, including electrical and mechanical matching as well as the focusing lens. By using this model, it is possible to obtain a relation between the electrical driving source and the acoustic velocity on the transducer surface. This boundary condition then allows the acoustic field to be calculated by numerical methods. Experimental data obtained with two different transducers are in good agreement with results predicted by the related models. View full abstract»

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  • Controlling the microwave amplitude in optically pumped cesium beam frequency standards

    Publication Year: 1999 , Page(s): 407 - 413
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    Assuming square wave frequency modulation, the response, versus the amplitude of the microwave field, of an optically pumped cesium beam tube is considered. The properties of the first maximum of this response are analyzed. The effect of the neighboring lines is taken into consideration, and a model of the profile of the microwave field in each interaction region is validated. A symmetry property of the response considered is pointed out. It enables us to implement a feedback control of the microwave amplitude with a large depth of the amplitude modulation. Residual frequency offsets that may occur as a consequence of a spurious amplitude modulation correlated with the frequency modulation are assessed. And, with a cavity designed such that /spl sigma/=/spl pi/ between the two oscillatory fields, it also is possible to measure the microwave amplitude at the first maximum of the sole contribution of the reference atomic line. View full abstract»

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  • A 3.7 MHz phased array probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/

    Publication Year: 1999 , Page(s): 414 - 421
    Cited by:  Papers (12)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A novel 128-channel phased array probe for echocardiography with a center frequency of 3.7 MHz using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ (PZN-9%PT) single crystal has been fabricated to realize greater sensitivity and broader bandwidth properties. The echo amplitude of the PZN-9%PT single-crystal probe is about 5 dB higher than that of the conventional lead airconate titanate (PZT) ceramic probe, and the fractional bandwidth is about 25 percentage points broader. The quality of B mode images obtained by the PZN-9%PT probe satisfies the performance of the two types of conventional PZT ceramic probes that have center frequencies of 2.5 and 3.75 MHz. At the reference frequency of 3 MHz, the Doppler sensitivity of the PZN-9%PT probe is about 5 dB higher than that of the 3.75 MHz PZT probe; the blood flow of a pulmonary vein in a hard-to-image patient is much more clearly imaged than in the case of using the PZT probe. These superior images are attributable to the use of sufficiently large PZN-9%PT single crystals obtained by the self-flux method. View full abstract»

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  • A new approach to calculate the field radiated from arbitrarily structured transducer arrays

    Publication Year: 1999 , Page(s): 422 - 440
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (886 KB)  

    A efficient time-domain algorithm, based on the spatial pulse response approach, is proposed for the determination of the acoustic fields radiated by means of acoustical sources. The computations are performed by the discrete representation array modelling (DREAM) procedure, specially adapted to study the planar and arbitrarily structured multielement transducer arrays. DREAM, based on the discrete representation computational concept, acts as the generator of the array velocity potential impulse response, and thus, does not require any analytical solutions prior to the computations. The computations are valid for all field regions and may be performed for any excitation form. Apart from the classic case of rigid baffle conditions, the free and soft planar baffle also can be considered. The use of the time-domain solution for causal Green's function for lossy media enables the wideband absorption effects to be modeled. The accuracy of computations depends on temporal and spatial discretization and can be obtained as required. The quantitative rules, which determine the required discretizations to be predicted, are proposed. The computational examples show that DREAM allows the different and various transducers to be modeled. Its possibilities are illustrated by computations for the multielement transducers, including the beam-steered, amplitude-weighted sonar array, the focusing annular transducer, and the diverging and converging cylindrical array. View full abstract»

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  • Electromechanical analysis of an asymmetric piezoelectric/elastic laminate structure: theory and experiment

    Publication Year: 1999 , Page(s): 441 - 451
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    The electromechanical characteristics of an asymmetric piezoelectric/elastic laminated actuator are investigated by electroelasticity and experiments. The axial expansion-bending coupled motion of the system is separated into quasi-axial expansion and quasi-bending by its physical significance of vibration modes. General formulation of calculations for the mechanical, electrical, and electromechanical characteristics of the structure are presented via parametric analysis. Finally, the displacement sensitivity and the frequency response of displacement and electrical current are experimentally measured for this piezoelectric/elastic laminated specimen. Close agreement between theoretical and experimental results confirms the validity of the theory. View full abstract»

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  • A nonuniform sampled coherent pulsed Doppler ultrasonic velocimeter with increased velocity range

    Publication Year: 1999 , Page(s): 452 - 456
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    Coherent pulsed Doppler ultrasonic velocimeters cannot measure large blood velocities in deep vessels. To overcome this limitation, a nonuniform sampling method is proposed. The method is based on adding a delayed sampling sequence interlaced to the conventional one. The time interval between two consecutive samples can be continuously adjusted to avoid undesirable sample volumes. Experimental results are shown, confirming theoretical expectations that the maximum measurable velocity and the maximum measurable velocity width are doubled. View full abstract»

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  • Ultrasonic inspection of studs (bolts) using dynamic predictive deconvolution and wave shaping

    Publication Year: 1999 , Page(s): 457 - 463
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    Bolt degradation has become a major issue in the nuclear industry since the 1980's. If small cracks in stud bolts are not detected early enough, they grow rapidly and cause catastrophic disasters. Their detection, despite its importance, is known to be a very difficult problem due to the complicated structures of the stud bolts. This paper presents a method of detecting and sizing a small crack in the root between two adjacent crests in threads. The key idea is from the fact that the mode-converted Rayleigh wave travels slowly down the face of the crack and turns from the intersection of the crack and the root of thread to the transducer. Thus, when a crack exists, a small delayed pulse due to the Rayleigh wave is detected between large regularly spaced pulses from the thread. The delay time is the same as the propagation delay time of the slow Rayleigh wave and is proportional to the site of the crack. To efficiently detect the slow Rayleigh wave, three methods based on digital signal processing are proposed: wave shaping, dynamic predictive deconvolution, and dynamic predictive deconvolution combined with wave shaping. View full abstract»

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  • Improved sidelobe performance of cosine series functions

    Publication Year: 1999 , Page(s): 464 - 466
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    The cosine series functions are used extensively for SAW filter design with noniterative techniques. This paper presents improved sidelobe levels of these functions by rigorous application of criteria for minimising the sidelobe peaks. An improvement of 2 dB in sidelobe levels is achieved with respect to the earlier results. A new approach is presented to determine the coefficients of these functions uniquely, which reduces the number of simultaneous equations to be solved to N-1 compared to N equations required to be solved in the earlier method. View full abstract»

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  • Avoiding diffraction grid effect in ultrasonic fields of 1-3 PZT polymer piezocomposite transducers

    Publication Year: 1999 , Page(s): 467 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB)  

    Improvement of sensitivity in ultrasonic fields of piezocomposite transducers is limited because of diffraction effects arising from the periodic structure. We present a theoretical and experimental study of ultrasonic fields of 1-3 PZT polymer piezocomposite transducers. The relation between the composite grid periodicity and the wavelength is critical in order to obtain a far field similar to that of homogeneous transducers. If diffraction grid effect is present, it results in an important energy loss in the higher diffraction orders. These higher orders perturb the central field of the transducer because of multipath contributions to the main lobe caused by reflections from the boundaries of the test sample. View full abstract»

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  • An ultrasound-based simple noninvasive procedure for abrasive slurries efficiency control

    Publication Year: 1999 , Page(s): 473 - 475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    Slurries are widely used in industry. Correct usage always requires granulometric measurements. Several methods are available, but the most attractive ones are on-line, noninvasive ultrasound based techniques. In this paper a simple procedure is proposed that refers to the use of abrasive slurries in sawing processes. The procedure uses ultrasound attenuation measurements to optimize the process efficiency by the on-line granulometric characterization of the abrasive slurry itself. 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