Showing papers on "Lamb waves published in 1988"
TL;DR: In this paper, a microsensor that uses ultrasonic Lamb waves propagating in a thin plate supported by a silicon die is presented, which can operate as a microphone, biosensor, chemical vapor or gas detector, scale, pressure sensor, densitometer, radiometer or thermometer.
Abstract: Initial experimental, analytical, and numerical evaluations of a microsensor that uses ultrasonic Lamb waves propagating in a thin plate supported by a silicon die are presented. Changes of oscillator frequency indicate magnitudes of the variables sensed. Because it is sensitive to many measurands, the device could operate as a microphone, biosensor, chemical vapor or gas detector, scale, pressure sensor, densitometer, radiometer, or thermometer. Because it is based on the use of Lamb waves, the sensor has selective response and sensitive operation in the low-megahertz frequency range in vacuum, in a gas, or while immersed in a liquid. >
264 citations
TL;DR: In this article, the authors show that reflection data mainly resolve high wavenumbers, while transmission data mainly resolves low-wavenumbers of the P-wave and S-wave velocity model.
Abstract: Elastic inversion of multioffset seismic data by wavefield fitting yields a maximum probability P-wave and S-wave velocity and density model of the Earth. Theoretically, the inversion accounts for all elastic waves including reflected and transmitted waves, mode conversions, shear waves, head waves, Rayleigh waves, etc. These different wave types tend to resolve different components of the Earth properties. By inverting two-component synthetic data, I show that reflection data mainly resolve high wavenumbers, while transmission data mainly resolve low wavenumbers of the P-wave and S-wave velocity model. The inversion of reflection data (shot gathers) yields a result that looks like a prestack elastic migration but the meaning of the inverted data is not simply reflectivity: it is the P-wave and S-wave velocity perturbation. The inversion of transmission data (VSPs) yields a solution that contains useful interval velocity information and is comparable to an elastic diffraction tomography result.
169 citations
TL;DR: In this article, the fluid loading of Lamb waves propagating in a 3 mm×9 mm composite membrane consisting of low-stress silicon nitride deposited by low-pressure chemical vapor deposition was described.
Abstract: We describe the fluid loading of Lamb waves propagating in a 3 mm×9 mm composite membrane consisting of low‐stress silicon nitride deposited by low‐pressure chemical vapor deposition (2.0 μm thick) supporting an aluminum ground plane (0.3 μm), a piezoelectric zinc oxide layer (0.7 μm), and a pair of 100‐μm‐period interdigital Al transducers (0.5 μm). When this device is operated in air, the phase velocity of the lowest antisymmetric mode is 474 m/s; it changes to 304 and 322 m/s, respectively, when the membrane is loaded on one side with de‐ionized water and with methanol. The large fluid‐loading effect, in excellent agreement with theory, and the stability of an oscillator made with this membrane (stability better than 1 part in 106) suggest the utility of the device as a sensitive densitometer and pressure sensor.
95 citations
TL;DR: In this article, a new and efficient absorbing boundary condition for two-dimensional and three-dimensional finite-difference calculations of elastic wave propagation is presented, where the elastic medium is assumed to be homogeneous in the region immediately adjacent to the boundary.
Abstract: Extant absorbing boundary conditions for the elastic wave equation are generally effective only for waves nearly normally incident upon the boundary. High reflectivity is exhibited for waves traveling obliquely to the boundary. In this paper, a new and efficient absorbing boundary condition for two‐dimensional and three‐dimensional finite‐difference calculations of elastic wave propagation is presented. Compressional and shear components of the incident vector displacement fields are separated by calculating intermediary scalar potentials, allowing the use of Lindman’s boundary condition for scalar fields, which is highly absorbing for waves incident at any angle. The elastic medium is assumed to be homogeneous in the region immediately adjacent to the boundary. The reflectivity matrix of the resulting absorbing boundary for elastic waves is calculated, including the effects of finite‐difference truncation error. For effectively all angles of incidence, reflectivities are much smaller than those of the co...
74 citations
TL;DR: In this article, wide-angle parabolic models were developed to describe the diffraction of linear water waves for bathymetry consisting of parallel bottom contours, and the first model, developed by operator correspondence, extended the validity of conventional forms of the parabolic model for wave angles up to 70" from the assumed wave direction.
Abstract: \For a bathymetry consisting of parallel bottom contours, wide-angle parabolic models are developed to describe the diffraction of linear water waves. The first model, developed by operator correspondence, extends the validity of conventional forms of the parabolic model for wave angles up to 70" from the assumed wave direction. Through the use of Fourier decomposition, wave models valid to 90" are developed for three different lateral boundary conditions. By application, it is shown that the diffraction of waves through gaps or around structures is governed by the initial wave condition at the structure, which can be expanded into progressive and evanescent wave modes. Away from the structure, the wave field consists of only the progressive wave modes, which disperse according to their direction of propagation, the water depth and Snell's Law. Examples are shown for oblique waves through a gap, directional seas past a breakwater, a plane wave with varying crest amplitude, and finally for the diffraction of waves into a channel.
71 citations
TL;DR: The geometrical theory of diffraction (GTD) has been extended to describe surface elastic wave (SEW) contributions to backscattering from spheres and cylinders in water at high frequencies as mentioned in this paper.
Abstract: The geometrical theory of diffraction (GTD) has been extended to describe surface elastic wave (SEW) contributions to backscattering from spheres and cylinders in water at high frequencies. The coupling (described by a coefficient Gl ) of the lth class of SEW with the acoustic field and the resulting contribution fl to the form function for solid spheres were previously derived [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 79, 1702–1708 (1986)] via a Sommerfeld–Watson transformation (SWT). That work gave a Fabry–Perot representation of fl . A similar representation was postulated by applying the principles of GTD to the Lamb wave contributions to backscattering from empty cylindrical shells [V. Borovikov and N. Veksler, Wave Motion 7, 143–152 (1985)]. In either case, ‖ fl ‖=‖Gl exp[−2βl ×(π−θl )]/[1+j exp(−2πβl +i2πkac/cl )]‖ ,where j=1 for spheres and j=−1 for cylinders, each of radius a. The SEW phase velocity and attenuation coefficient are cl and βl , sin θl =c/cl , and c and k are the veloc...
62 citations
TL;DR: In this article, the phase and group velocities of the S1 mode of Lamb waves were measured for the fd range of 2.0-2.3 MHz.
Abstract: The propagation characteristics of Lamb waves in a solid plate are typically represented by a set of dispersion curves, which describe the Lamb‐wave phase velocity as a function of the product fd, where f is the acoustic frequency and d is the plate thickness. For certain modes, within a range of phase velocity and fd, it has been theoretically predicted that the associated group velocity could be negative, i.e., the energy transport is in the opposite direction to the phase velocity. In the present study, Lamb waves are generated via mode conversion from a water‐borne sound beam incident onto a flat brass plate. Measurement of the phase and group velocities of the Lamb waves of the S1 mode is performed for the fd range of 2.0–2.3 MHz‐mm. Comparison of the measured and computed values of phase and group velocities shows good agreement and clearly demonstrates that S1‐mode Lamb waves have a negative group velocity for fd=2.08–2.24 MHz‐mm.
54 citations
TL;DR: In this article, the properties of circumferential waves on thin-walled elastic, air-filled cylindrical shells immersed in water are investigated, and a spectral decomposition of the multiple echo pulses using the Numrich-de Billy method, and subsequent analysis by the resonance scattering theory are presented.
Abstract: An experimental and theoretical study is presented of the properties of circumferential waves on thin‐walled elastic, air‐filled cylindrical shells immersed in water, and of their excitation by normally incident acoustic pulses of short duration. A spectral decomposition of the multiple echo pulses using the Numrich–de Billy method, and subsequent analysis by the resonance scattering theory (RST), reveal for an aluminum shell the presence of an l=2 wave that can be identified with the S0 Lamb wave on a plate, and of an l=0 wave that at low frequencies corresponds to a water‐borne circumferential wave, not given by the Lamb theory of free‐plate vibrations but by its extension to a plate with one‐sided fluid loading. Calculations of complex pole resonances on aluminum and steel shells, as well as of the corresponding circumferential wave speeds and attenuations, serve to clarify the physical situation.
41 citations
01 Jan 1988
TL;DR: In this paper, shear deformation and rotary inertia are included in plate theory to determine the dispersion curves for flexural waves propagating in laminated composite plates, and the results of a unidirectional laminate are compared with the elasticity solutions for flexurys traveling in transversely isotropic plates to determine shear correction factors in the low frequency, long wavelength range.
Abstract: Shear deformation and rotary inertia are included in plate theory to determine the dispersion curves for flexural waves propagating in laminated composite plates. The results of a unidirectional laminate are compared with the elasticity solutions for flexural waves traveling in transversely isotropic plates to determine the shear correction factors in the low frequency, long wavelength range. The values of the shear correction factors for the unidirectional composite laminate are in good agreement with the theoretical values calculated from static cylindrical bending. An acousto-ultrasonic technique using narrowband excitation frequencies is used to obtain experimental data for flexural waves. By measuring the phase velocities for different excitation frequencies, dispersion curves are generated. There is excellent agreement between the experimentally determined values and the theoretical results for aluminum and unidirectional composite plates. For symmetric cross-ply and quasi-isotropic laminates, the data definitely have the characteristic of a dispersion curve for flexural waves, although the agreement between analytic and experimental results is not quite as good. The results of the present work indicate that the inclusion of shear deformation and rotary inertia in plate theory improves the prediction of dispersion curves for flexural waves propagating in composite laminates and suggest that the acousto-ultrasonic technique can be used to characterize composite plates with and without damage since each material and stacking sequence gives distinct dispersion curves.
41 citations
TL;DR: In this article, the authors made ultrasonic and Brillouin scattering measurements at ambient temperature on small single crystals of monoclinic ZrO2 and established various features of the angular anisotropy in the acoustic longitudinal wave and shear wave velocities, and computed the elastic stiffness and compliance moduli.
Abstract: We have made ultrasonic and Brillouin scattering measurements at ambient temperature on small single crystals of monoclinic ZrO2. Using these data, we have established various features of the angular anisotropy in the acoustic longitudinal wave and shear wave velocities, and we have computed the elastic stiffness and compliance moduli. We observe shallow minima in the transverse shear wave velocity in directions parallel to the a and c crystallographic axes. We anticipate that acoustic shear wave softening will be observed in these directions when measurements are made at temperatures close to the monoclinic-tetragonal transformation.
38 citations
Journal Article•
TL;DR: Visualisation directe des modes de Lamb reflechis par le bond de la plaque au moyen d'une technique photoelastique dynamique as mentioned in this paper is a technique used for image-based visualization.
Abstract: Visualisation directe des modes de Lamb reflechis par le bond de la plaque au moyen d'une technique photoelastique dynamique
TL;DR: In this paper, the Lamb wave is launched into a thin-section metal plate (10) which extends generally vertically above the contents of a vessel, and the Lamb waves are reflected at the lower boundary to give a full amplitude return signal.
Abstract: Ultrasonic Lamb waves are launched into a thin-section metal plate (10) which extends generally vertically above the contents of a vessel. As long as the lower end (18) of the plate (10) is above the liquid level, the Lamb waves are reflected at the lower boundary to give a full amplitude return signal. If however the liquid level rises into contact with the plate, mode conversion occurs at the interface between the plate and the liquid resulting in a reduced amplitude return signal. The arrangement may be used as a limit switch or may be calibrated to enable the liquid level to be related to the strength of the return signal. In a more elaborate arrangement, the plate (10) is of stepped configuration so as to present a series of shoulders (20A, 20B) at different heights. Each shoulder gives rise to a respective return signal and analysis of the return signals allows the liquid level to be determined. The plate may be tens of meters in length and may be used as a level sensor in the primary vessel of a nuclear reactor. The transducer and associated electronics may therefore be located remotely from the liquid level (e.g. externally of the reactor vessel).
TL;DR: In this paper, the responses of two coated-oscillator chemical sensors, a ZnO/Si surface-acoustic-wave (SAW) oscillator and a plate-wave oscilaltor, were examined using computer simulation.
TL;DR: In this article, a detailed analysis of acoustic interface waves in symmetrically embedded layers is presented, and the dispersion curves and the spatial dependence of the displacement fields of these acoustic phonon modes are calculated and presented in graphical form.
TL;DR: In this paper, a solution of geometric type is proposed that eliminates these parasitic waves but causes others to appear, which, while less important, are still troublesome, and its good behavior is demonstrated with regard to reflection phenomena.
Abstract: The first-order absorbing boundary conditions for elastic waves are transparent for P and S waves at normal incidence, but give rise to parasitic reflections of Rayleigh waves. To treat these phenomena, a solution of geometric type is proposed that eliminates these parasitic waves but causes others to appear, which, while less important, are still troublesome. A second solution is proposed by constructing a new condition of second-order type, transparent for P and S waves at normal incidence as well as for Rayleigh waves. This condition is analyzed mathematically and its good behavior is demonstrated with regard to reflection phenomena.
TL;DR: In this paper, a discretized form of boundary integral equations and a plane-wave decomposition of seismic wave fields were used to investigate the effect of small-scale irregularities of a reflecting boundary on elastic wave reflections.
Abstract: Numerical modeling is used to investigate the effect of small-scale irregularities of a reflecting boundary on elastic wave reflections. The scattered wave field is computed by using a discretized form of boundary integral equations and a plane-wave decomposition of seismic wave fields. For various values of incidence angle of the P wave, we compute the distribution of diffracted energy for both P waves and S waves as a function of reflection angle. We show that corrugations with mean wavelength of the order of, or smaller than, the seismic wavelength have little effect on the reflected P wave. However, the pattern of P-to-S conversion is very different from that with a plane boundary. Scattered S waves appear at postcritical angles for any angle of incidence of the P wave. The amplitude of these nongeometrical shear waves decreases rapidly with decreasing amplitude of the corrugations, or when the mean wavelength of the corrugations becomes larger than the dominant seismic wavelength. The local geometry of the irregularities has a negligible effect on the scattered S waves. By analogy with perturbation theory, we propose interpreting the postcritically scattered S waves as the contribution to the shear wave field of converted inhomogeneous P waves diffracted along the boundary.
TL;DR: In this article, a theory describing the propagation of nonlinear hyperbolic waves of any strength is developed for small values of the wavelength, i.e. of the typical scale length of variation in the direction of propagation.
Abstract: A theory describing the propagation of nonlinear hyperbolic waves of any strength is developed. It is valid for small values of the wavelength, i. e. of the typical scale length of variation in the direction of propagation. At first the wave propagates along wave normals according to one-dimensional theory. It quickly splits up into a set of distinct waves, each of which soon becomes weak. The weak waves then propagate along rays according to weakly nonlinear geometrical optics.
TL;DR: In this article, the fractional volume dependence of stopbands in piezoelectric periodical composite plates has been studied experimentally by exciting the band-edge resonances, and the frequency and symmetry of such modes below the thickness resonance of the plate are successfully interpreted in terms of a theoretical model which provides approximate dispersion curves of the lowest Lamb waves propagating in the composite plate.
Abstract: The fractional volume dependence of stopbands in piezoelectric periodical composite plates has been studied experimentally by exciting the band‐edge resonances. The frequency and symmetry of such modes below the thickness resonance of the plate are successfully interpreted in terms of a theoretical model which provides approximate dispersion curves of the lowest Lamb waves propagating in the composite plate.
02 Oct 1988
TL;DR: In this paper, integrated circuit fabrication techniques were used to make a versatile silicon-based sensor that uses elastic wave propagation in a plate that is thin compared with the wavelength, which can operate as a microphone, biosensor, chemical vapor or gas detector, scale, manometer, densitometer, viscometer, radiometer or thermometer.
Abstract: Integrated-circuit fabrication techniques were used to make a versatile silicon-based sensor that uses elastic wave propagation in a plate that is thin compared with the wavelength. In-plane tension raises the velocity of the lowest antisymmetric flexural wave (474 m/s) above that predicted for a pure Lamb wave (422 m/s). Because of the low velocity, when in contact with a fluid the device excites an evanescent disturbance that extends just tens of micrometers from the membrane. The device is quite sensitive to loading: contact with a 6- mu l droplet of water shifts the oscillation frequency downward 36%, in excellent agreement with theory. The device could operate as a microphone, biosensor, chemical vapor or gas detector, scale, manometer, densitometer, viscometer, radiometer, or thermometer. It is concluded that the sensor offers unique means for separating out the influences of multiple measurands. >
TL;DR: In this paper, a unified explanation of the reflection of compact wave groups (e.g., pulses and bounded beams) from plane interfaces with application to signal propagation in waveguides is presented.
Abstract: This article presents a unified explanation of the reflection of compact wave groups (e.g., pulses and bounded beams) from plane interfaces with application to signal propagation in waveguides. Expressions are developed for the spatial, temporal, and phase shifts that are experienced by such wave groups but not by plane waves.
TL;DR: In this paper, nonlinear waves for a model of viscoelastic materials are constructed and analyzed and the stress in the model depends on the present strain as well as its past history.
Patent•
15 Mar 1988
TL;DR: In this paper, a system and method for detecting defects in composite laminate material are described which comprise a first trtansducer for directing an ultrasonic beam of preselected frequency and tone burst excitation along a transmission axis through a sonic coupling bath onto a surface of the material at a preselected angle to generate Lamb waves in the material and leaky Lamb waves reflected therefrom.
Abstract: A system and method for detecting defects in composite laminate material are described which comprise a first trtansducer for directing an ultrasonic beam of preselected frequency and tone burst excitation along a transmission axis through a sonic coupling bath onto a surface of the material at a preselected angle to generate Lamb waves in the material and leaky Lamb waves reflected therefrom, a frequency modulator for selectively modulating the frequency of the incident beam, and a second transducer for receiving the reflected sonic field including leaky Lamb waves reflected from the material and for providing a recovered and envelope-detected output signal corresponding to the amplitude of the reflected waves.
01 Jan 1988
TL;DR: In this article, an EMAT is a coil of wire and a magnet, and an RF signal applied to the coil induces surface currents in the metal, which are acted upon by a Lorentz force due to the presence of the static magnetic field.
Abstract: Electromagnetic Acoustic Transducers (EMATs) provide a noncontact method of generating ultrasound in metals. In its simplest form, an EMAT is a coil of wire and a magnet. An RF signal applied to the coil induces surface currents in the metal. These surface currents are acted upon by a Lorentz force due to the presence of the static magnetic field. This disturbance is transferred to the lattice of the solid by collisions resulting in body forces which drive the elastic wave. EMATs can be used to produce all of the wave modes produced by conventional piezoelectric and magnetostrictive transducers.
TL;DR: In this paper, the resonances of the Lamb s0 mode in parallelepiped piezoelectric plates excited by surface electrodes have been measured and it was shown that the resonance of the first thickness mode can reproduce the dispersion of s0 in an infinite plate even for plates of small length.
Abstract: The resonances of the first Lamb s0 mode in parallelepiped piezoelectric plates excited by surface electrodes have been measured. Below the first thickness mode, the resonances are found to reproduce the dispersion of s0 in an infinite plate even for plates of small length. Moreover, a significant difference is observed between the behavior of the fundamental and its harmonics, reflecting the different effect of metallization in the two cases.
06 Jun 1988
TL;DR: In this paper, a microsensor that uses ultrasonic Lamb wave propagating in a thin plate supported by a silicon die is described, which can operate as a microphone, biosensor, chemical vapor or gas detector, scale, pressure sensor, densitometer, radiometer, or thermometer.
Abstract: Initial experimental, analytical, and numerical evaluations are described of a microsensor that uses ultrasonic Lamb wave propagating in a thin plate supported by a silicon die. Because it is sensitive to many measurands, the device could operate as a microphone, biosensor, chemical vapor or gas detector, scale, pressure sensor, densitometer, radiometer, or thermometer. Lamb waves offer unique means for obtaining selective response, and permit sensitive operation in the low MHz frequency range in vacuum, in a gas, or while immersed in a liquid. >
Journal Article•
TL;DR: In this article, the authors show that a TM wave can propagate along the interface between a linear and a nonlinear dielectric medium, provided that a high-power TE-polarized wave is also present.
Abstract: We show that a TM‐polarized wave can propagate along the interface between a linear and a nonlinear dielectric medium, provided that a high‐power TE‐polarized wave is also present. On the basis of the threshold powers for the two waves, we predict that 100% modulation of the TM wave by the strong beam is possible.
TL;DR: Weertman and Follansbee as discussed by the authors treated the steady-state finite-amplitude elastic-plastic wave as a summed infinitesimal elastic plastic wave, which is not the case in this paper.