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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 5 • Date Sept. 1996

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Displaying Results 1 - 25 of 27
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  • A point-matching method for array pattern synthesis

    Page(s): 773 - 781
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    In this paper, a newly developed point-matching method is presented to obtain a set of excitation coefficients of a linear array that generates a desired radiation pattern with arbitrarily suppressed sidelobe levels. This method can be used for linear arrays with nonuniform spacing and nonisotropic elements. The design examples presented show that the point-matching method is both effective and efficient. View full abstract»

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  • Multiresonance design of a Tonpilz transducer using the finite element method

    Page(s): 782 - 790
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    The design and characterization of a wide bandwidth Tonpilz transducer is carried out using the finite element method. This wide bandwidth has been achieved by introducing a symmetric flexural resonance (sometimes called a "flapping" resonance) in the head-piece of the Tonpilz transducer. This flexural resonance is exploited by lip-mounting of the transducer as opposed to the more traditional nodal mount. Each transducer is characterized by high-power handling, high-electroacoustic efficiency, broad bandwidth (low-Q), and high-electromechanical coupling. These are characteristics which are usually associated with designs employing more complicated electrical or mechanical matching techniques. An array of these transducers was constructed and displays low-ripple (<3 dB) transmission of one-octave 20-40 kHz signals. A comparison with a recent broad-band design by Inoue et al. [1993] which uses a matching plate is also made to illustrate the inherent simplicity of the flexural resonance approach. View full abstract»

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  • Transcutaneous measurement and spectrum analysis of heart wall vibrations

    Page(s): 791 - 810
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    For the noninvasive diagnosis of heart disease based on the acoustic and elastic characteristics of the heart muscle, it is necessary to transcutaneously measure small vibration signals, including components with an amplitude of less than 100 /spl mu/m, from various parts of the heart wall continuously for periods of more than several heartbeats in a wide frequency range up to 1 kHz. Such measurement, however, has not been realized by any ultrasonic diagnostic methods or systems to date. By introducing the constraint least-square approach, this paper proposes a new method for accurately tracking the movement of the heart wall based on both the phase and magnitude of the demodulated signal to determine the instantaneous position of the object so that the vibration velocity of the moving object can be accurately estimated. By this method, small vibrations of the heart wall with small amplitudes less than 100 /spl mu/m on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected with sufficient reproducibility in the frequency range up to several hundred Hertz continuously for periods of about 10 heartbeats. The resultant small vibration is analyzed not only in the time domain, but also in the frequency domain. As confirmed by the preliminary experiments herein reported, the new method offers potential for research in acoustical diagnosis of heart disease. View full abstract»

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  • Two-dimensional analysis using one-dimensional FEM for straight-crested waves in arbitrary anisotropic crystal plates and axisymmetric piezoelectric vibrations in ceramic disks

    Page(s): 811 - 817
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    We have developed a hybrid method applicable to straight-crested waves in arbitrary anisotropic crystal plates and to axisymmetric piezoelectric vibrations in ceramic disks. The solutions to two-dimensional (2-D) equations of motion are described with a linear combination of eigenmodes guided by a pair of parallel edges. The guided eigenmodes and their amplitudes are determined by using one-dimensional (1-D) finite element method (FEM). The method developed here provides rapid convergence with small matrix size compared with 2-D FEM. Computer programs have been developed for three examples, SC- and AT-cut quartz plates and barium titanate (BaTiO/sub 3/) disks, for which the frequency spectra and the corresponding mode shapes were calculated. The frequency spectra of AT-cut quartz plates are compared with those obtained from Mindlin's plate equations, with the aim of examining the accuracy of the straight-crested wave solutions for Mindlin's plate equations. A convergence study is also presented for BaTiO/sub 3/ disks. View full abstract»

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  • Influence of a magnetic field on quartz crystal resonators

    Page(s): 818 - 831
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    The magnetic sensitivity of quartz crystal resonators is a consequence of the ferromagnetic properties of the metal used as support for the vibrating plate. Various magneto-mechanic interactions can contribute to the overall sensitivity, the most important of which is shown to be the change in Young's modulus of the spring material submitted to a magnetic field, which in turn modifies the stress in the quartz plate and then induces a change in the crystal resonant frequency. The experimental setup and procedure are described and a large number of experimental results obtained with resonators of different technologies are presented and discussed. A comparison between the magnetic behavior of identical resonators mounted with different materials definitely proves the responsibility of the supports in the magnetic sensitivity of resonators and gives interesting information on its reduction. View full abstract»

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  • Torsional vibrations of quartz crystal beams

    Page(s): 832 - 837
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    An exact solution of a partial differential equation including elastic compliance constant s'/sub 56/, with respect to stress function /spl psi/ has been found for torsional modes of vibration of an arbitrary (singly, doubly, triply) rotated beam with a pair of parallel free edges. The solution is obtained by relaxing the condition that the edge planes are perpendicular to the main faces of the beam. That is, the edges are off perpendicular by the angle /spl Theta/=arctan(-s'/sub 56//8'/sub 55/). The exact solution can reduce the difference of the calculated and measured values for a thickness-to-width ratio which gives the first-order temperature coefficient /spl alpha/=0. Also, a comparatively large inclination of the edge cuts is required to reduce the unwanted complicated mode shapes to simple ones. View full abstract»

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  • Acceleration measurement using PVDF

    Page(s): 838 - 843
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    An acceleration measurement system using the piezoelectric polymer poly(vinylidene fluoride) (PVDF) is described; furthermore a compensation of the polymer's pyroelectric effects has been achieved. The main advantages of this sensor are its robustness and that it has a very low cost compared with other sensors. The measured sensitivity is 1.071 V m/sup -1/ s/sup 2/. View full abstract»

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  • Perturbation method for analyzing mass sensitivity of planar multilayer acoustic sensors

    Page(s): 844 - 851
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    A perturbation method is developed to analyze the mass loading sensitivity of planar composite acoustic gravimetric sensors. The sensitivity formulas are obtained in explicit forms for the two lowest sagittal (D/sub 1/ and D/sub 2/) modes, the lowest shear horizontal (SH/sub 0/) mode and high-order SH/sub m/ modes in a two-layer isotropic composite plate sensor. The composite plate consists of a plate of thickness b coated by a film of thickness h on which the mass loading layer of infinitesimal thickness is deposited. This coating can be a chemically selective film which is assumed to be acoustically thin (h/spl Lt//spl lambda/), where /spl lambda/ is the acoustic wavelength. For Love modes supported by a film coated on a semi-infinite substrate and for Rayleigh modes on a semi-infinite substrate, the sensitivity formulas are expressed in analytical form. These formulas specify the contribution of each material parameter in the substrate and film, and of the elasticity of the mass loading layer for each planar sensor, and provide a general guide for enhancing the sensor sensitivity. View full abstract»

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  • Mass sensitivity of thin rod acoustic wave sensors

    Page(s): 852 - 857
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    Theoretical and experimental investigations of mass sensitivities of thin rod acoustic wave sensor are presented. From the low-frequency approximation of the dispersion equations, explicit forms of the relation describing the mass sensitivity are derived with the consideration of the effects due to elasticity and inertia of the loading layer. The three lowest thin rod acoustic modes are presented. Mass sensing experiments are based on the electrodeposition of loading material on a thin metallic fiber (the thin rod). Copper has been used to load the propagation of acoustic waves in gold fibers. The mass of copper deposited and the phase shift of the acoustical thin rod delay line were monitored simultaneously by a computer. Mass response curves showing the variation in phase due to the mass deposited per unit surface area were then obtained in order to determine the mass sensitivity. Both flexural and extensional wave modes have been excited. Theoretical and experimental results were found to be consistent in both sign and magnitude. View full abstract»

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  • On the performance characterization of ultrasonic air transducers with radiating membranes

    Page(s): 858 - 863
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    An ultrasonic air transducer used for sensing essentially requires an efficient transduction into the surrounding medium. A transducer consisting of a metal membrane coupled with a resonating piezoelectric disk, the latter being driven in its radial mode of vibrations, has been found to be significantly applicable in this aspect. The present study reports the performance characterization at resonance and at higher frequencies of two such transducers with different dimensions of the housings. Vibrational amplitude characteristics are studied employing phase-locked laser interferometry technique that presents sufficiently high displacement amplitude of the membrane at resonance. A consequent high-acoustic pressure field is also obtained. The design aspects for such ultrasonic air transducers with efficient transduction capability and adjustable bandwidth are discussed. View full abstract»

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  • Estimation of the angle between ultrasound beam and blood velocity through correlation functions

    Page(s): 864 - 869
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    Correlation functions, calculated on the ultrasonic echoes scattered by blood, provide a rich harvest of information concerning the local speed, which has often been underestimated; in particular, blood flow measurement usually yields only the longitudinal component of the velocity, even if significant information about the speed direction can be extracted. In this paper it is shown how correlation functions, calculated on the dependency of both time and space displacements, allow us to evaluate the angle /spl Theta/ between ultrasound beam and blood flow; when straight vessels are considered, this single parameter, combined with the longitudinal velocity profile, permits the complete hemodynamic characterization. The underlying theory is developed and preliminary experimental results are presented. View full abstract»

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  • Laser-generated ultrasonic guided waves in fiber-reinforced plates-theory and experiment

    Page(s): 870 - 880
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    A pulsed laser source and a capacitance transducer detector have been used to record the propagation of guided waves in carbon fiber-reinforced polymer composite laminates. Despite the multimode nature of the recorded data, it is shown that the phase velocity dispersion curve of the a/sub 0/ mode can be extracted readily from the waveforms. Experimental dispersion curves have been compared to phase velocity predictions from a global matrix theory. Reasonable correlation between theory and experiment is obtained, demonstrating the validity of the calculations and experimental method. View full abstract»

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  • Adaptive pattern correlation for two-dimensional blood flow measurements

    Page(s): 881 - 887
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    One of the major drawbacks of ultrasonic Doppler instruments in measuring blood flow is their inability to measure the velocity perpendicular to the beam. Time domain RF echo or speckle tracking has been studied as an alternative to overcome this problem. By acquiring two-dimensional (2-D) echo signals, both lateral (perpendicular to the beam) and axial (parallel to the beam) velocities can be calculated with 2-D pattern correlation algorithms. One of the disadvantages of the current 2-D pattern correlation algorithms is the extensive computation time involved in computing the 2-D cross-correlation function. In this paper, we present several time-efficient bit-pattern correlation algorithms to execute 2-D speckle tracking. The proposed algorithms first estimate the noise level from the acquired signals and use it as a priori knowledge to minimize computation time. The reduction of computation time may make it more feasible for real-time measurements of flow velocities in two dimensions. Radio frequency and video data collected from two commercial scanners are used to validate the feasibility of these proposed algorithms with porcine blood as the flowing medium in in vitro experiments. The results obtained by the proposed algorithms are in good agreement with those computed from the cross-correlation function. View full abstract»

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  • Accuracy of crystal plate theories for high-frequency vibrations in the range of the fundamental thickness shear mode

    Page(s): 888 - 892
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    The first-order plate theories with correction factors are generally assumed to predict accurately the plate modes which have half wavelengths greater than the plate thickness, and at frequencies up to 20% higher than the fundamental thickness shear frequency. This assumption is assessed by comparing the straight crested wave solutions of the plate theories with those of the three-dimensional elastic equations of motion. The frequency spectra for bandwidths of resonant frequencies versus the aspect ratio of length to thickness of plate are compared for three sets of plate equations: the first-order Mindlin plate equations, the third-order Mindlin plate equations, and the third-order Lee and Nikodem plate equations. The finite element results for a quartz SC-cut strip with free edges show that Mindlin's first-order plate equations, and Lee and Nikodem's third-order plate equations yield less accurate frequency spectra of the modes in the vicinity of the fundamental thickness shear mode than the third-order Mindlin plate equations without correction factors. The degree of inaccuracy increases with the ratio of plate length to thickness, and the slope of the modal branches in the frequency spectra. For a plate length to thickness ratio of 31 to 33, the first-order plate theory is found to yield accurate frequency spectra for normalized frequencies less than 0.3, which is lower than previously assumed. At normalized frequencies greater than 0.3, deviations are seen in the frequency spectra, starting with the modal branches which are more steeply inclined. View full abstract»

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  • Producing bowtie limited diffraction beams with synthetic array experiment

    Page(s): 893 - 900
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    Limited diffraction beams have a large depth of field and could have applications in medical ultrasound and other wave related areas such as electromagnetics and optics. However, these beams have higher sidelobes than conventional focused beams at their focuses. Recently, a new type of beam, called bowtie limited diffraction beams, was developed. These beams can achieve both low sidelobes and a large depth of field in medical imaging. In this paper, the production of bowtie beams in water with a synthetic array experiment is reported. A broad-band PZT ceramic/polymer composite transducer of about 1 mm diameter and 2.5 MHz central frequency was scanned in a raster format and placed at the centers of elements of an equivalent two-dimensional array of 50 mm diameter aperture. A polyvinylidene fluoride (PVDF) needle hydrophone of 0.5 mm diameter was used to receive the waves produced by the transducer. Proper weighting functions were applied to the received signals to produce various beams. Results show that the bowtie beams produced with the synthetic array experiment are in good agreement with those derived from theory and obtained by computer simulations. The depth of field of these beams is about 216 mm and sidelobes of a tenth derivative bowtie X wave in pulse-echo imaging are about 30 dB lower than those of rotary symmetric limited diffraction beams such as the zeroth-order X wave discovered previously. View full abstract»

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  • Ultrasonic linear motor using surface acoustic waves

    Page(s): 901 - 906
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    The first success in the operation of an ultrasonic linear motor at HF band driving frequency using the Rayleigh wave is described. The substrate material is a 127.8/spl deg/ Y-cut LiNbO/sub 3/ wafer whose diameter is three inches. Four interdigital transducers (IDT's) are arranged to excite x- and y-propagation waves in both directions. The dimensions of the IDT are 25 mm aperture size, 400 /spl mu/m pitch, 100 /spl mu/m strip width, and 10 pairs. The operation area is about 25 mm square, The driving frequency is about 9.6 MHz in the x direction and about 9.1 MHz in the y direction. The most important point of the success is the shape of the contact surface and slider materials. For the contact materials, small balls about 1 mm in diameter are introduced to obtain sufficient contact pressure around 100 MPa. The use of ruby balls, steel balls, and tungsten carbide balls is investigated. Each slider has three balls to enable stable contact at three points. The maximum transfer speed is about 20 cm/s. The transfer speed is controllable by changing the driving voltage. View full abstract»

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  • An experimental study of frequency jumps during the aging of quartz oscillators

    Page(s): 907 - 910
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    The cause of abrupt frequency jumps observed during the aging of high-stability quartz oscillators is investigated. For this purpose a precise method of measuring the resonant frequency versus drive current is used, and this method is applied to AT-cut crystal resonators used in oven controlled crystal oscillators (OCXOs). Experimental results show that there are some cases where the resonance frequency jumps when crystal current is changed; this phenomenon originates with spurious resonances near the fundamental mode, and the current that causes coupling between the spurious and fundamental modes shifts according to crystal driving time. Furthermore, we show that the abrupt jumping in long-term frequency observation is caused by a "shift" of the current that causes the couplings. View full abstract»

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  • Isomorphism between pulsed-wave Doppler ultrasound and direction-of-arrival estimation. I. Basic principles

    Page(s): 911 - 922
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    Direction-of-arrival (DOA) estimation of signals is an important area of research in sonar and radar signal processing. Over the last few decades, numerous techniques have been developed for high-resolution DOA estimation. In this paper, we show that velocity measurement using pulsed-wave Doppler ultrasound and DOA estimation are isomorphic problems. We discuss a number of DOA methods and their potential application to flow velocity measurement using ultrasound. Wide-band DOA methods are of special interest because the pulses used for Doppler ultrasound are also wide band. These wide-band methods generally involve a preprocessing step to convert wideband signals to narrow band before applying high-resolution techniques. Application of DOA methods to Doppler ultrasound provides tools for high-resolution velocity measurement, identification of multiple velocity components within a sample volume, and clutter rejection. View full abstract»

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  • Isomorphism between pulsed-wave Doppler ultrasound and direction-of-arrival estimation. II. Experimental results

    Page(s): 923 - 935
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    For pt. I see ibid., vol. 43, no. 5, p. 911-22 (1996). Pt. I presented the basic principles for applying high-resolution wide-band direction-of-arrival estimation techniques to pulsed-wave Doppler ultrasound. Such techniques provide high-resolution velocity profiles and enable the identification of multiple velocity components inside a sample volume. Another important application is the identification and rejection of wall clutter signals. A first and essential step in applying these techniques is to convert the wide-band echoes to narrow band. The 2D DFT projection method is used for this conversion. Two different narrow-band high-resolution methods are then applied to estimate the velocity distributions; the minimum variance (MV) and the multiple signal classification (MUSIC). Experimental results are presented to illustrate the potentials and limitations of applying wide-band DOA methods to different applications in pulsed-wave Doppler ultrasound. View full abstract»

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  • An ultralow noise microwave oscillator based on a high-Q liquid nitrogen cooled sapphire resonator

    Page(s): 936 - 941
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    Two liquid nitrogen-cooled sapphire loaded cavities (SLC's) operating at about 80 K have been successfully constructed, Both cavities were designed to operate on the whispering gallery (WG) E/sub 12, 1, /spl delta// mode at a resonant frequency of 8.95 GHz. The first SLC was used as the frequency-determining element in a loop oscillator, while the second was used as a frequency discriminator to measure oscillator phase noise. The single sideband phase noise of a free running loop oscillator incorporating the first SLC was measured as -133 dBc/Hz at an offset frequency of 1 kHz, and was limited by the SLC Q-factor and the amplifier flicker phase noise. By using specially designed feedback electronics the oscillator phase noise was reduced to -156 dBc/Hz and -162 dBc/Hz at 1 and 10 kHz offset, respectively. This measurement was shown to be limited by the electronic flicker noise imposed by the phase detector in the feedback electronics, To our knowledge the phase noise and resonator Q-factor of 6/spl times/10/sup 7/ represent the best results ever measured at liquid nitrogen temperatures or above. View full abstract»

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  • Contributions of amplitude measurement in QCM sensors

    Page(s): 942 - 947
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    The characteristics of the amplifier and the feedback loop of a quartz crystal series oscillating circuit are investigated. The fact that the change of the vibration amplitude of the quartz crystal is proportional to the change of its motional resistance is derived. The concept of a characteristic damping coefficient is introduced and the behavior of a quartz crystal vibrating in liquids is analyzed. The experiment shows that the effect of mass loading can be distinguished from that of the liquid damping of a quartz crystal microbalance (QCM) sensor in liquids by simultaneously measuring the amplitude and the frequency change. View full abstract»

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  • A study of the water sorption kinetic of Poly(HEMA) hydrogels by SLAM and FT-IR measurements

    Page(s): 948 - 955
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    The relative changes in the ultrasonic attenuation measured by scanning laser acoustic microscopy (SLAM) during water sorption in poly-hydroxy-ethil-methacrilate[Poly(HEMA)] are analyzed. Acoustical images performed at 10 and 30 MHz of Poly(HEMA) during water absorption show an ultrasonic attenuation increase followed by a decrease. This phenomenon is analyzed in terms of reflections, scattering, and absorption of the acoustic waves. However, the contribution of scattering and reflection may be neglected and the time dependence of acoustic attenuation is attributed to absorption of the acoustic waves occuring in accordance with the glass transition, although induced by a solvent and not by temperature. Fourier transform infrared spectrometry (FT-IR) measurements indicate that bound water is responsible for the glass-rubber transition. On the other hand, the longitudinal velocity changes are only affected by the variations of density and mechanical properties of the polymer during water sorption. The traditional weight gain data are compared with the attenuation changes observed by ultrasonic measurements. View full abstract»

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  • Ultrasonic imaging by local shape function method with CGFFT

    Page(s): 956 - 969
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    A numerical algorithm for the reconstruction of the density and the compressibility of a biological body from ultrasonic scattering data is presented. The reconstruction algorithm is based on the local shape function method (LSF) combined with the conjugate gradient method with fast Fourier transform (CGFFT). The nonlinearity due to the multiple scattering has been accounted for in an iterative minimization scheme. Numerical examples of simulation data and real experimental data are given showing the capability of this algorithm. View full abstract»

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  • Absolute backscatter coefficient over a wide range of frequencies in a tissue-mimicking phantom containing two populations of scatterers

    Page(s): 970 - 978
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    The acquisition and interpretation of in vivo ultrasonic measurements in tissue encounter problems associated with limited access to the region of interest, intermixed scattering structures with different characteristic dimensions, and system-dependent effects. This work addresses these problems by adapting and testing a technique for measuring the absolute attenuation and the absolute backscatter coefficient (effective backscatter cross section per unit volume of material), as a function of frequency, in a single-transducer backscatter configuration. The frequency-dependent attenuation and backscatter coefficients of a tissue-mimicking gelatin phantom containing a random distribution of two populations of scatterers were measured, Three transducers with different center frequencies and focusing characteristics were used in order to verify that system-dependent effects were removed by the technique and to investigate the change in the measured parameters across a broad range of frequencies (2 to 60 MHz). A spherical autocorrelation model was applied to measurements of the backscatter coefficient in order to estimate the size of scatterers. Measurements demonstrate that the backscatter and attenuation properties of a mixture of two distinct intermixed scatterer-size populations change as a function of the frequency range across which the model is applied. Comparison of both the magnitude and the frequency dependence of the experimental results with the theoretical prediction of the backscatter coefficient showed good agreement. 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