Reflection Of Acoustic Waves Research Articles

A new sensor principle based on the reflection of surface acoustic waves

We present a new method for surface acoustic wave (SAW) sensing which overcomes the main disadvantages of the well-known dual-delay-line oscillators, namely the insufficient sensitivity for atmospheric measurements and the strong temperature-dependent drift of the output frequency signal. Our method is based on the reflection of a SAW by a periodic array. SAW reflection occurs at discontinuities of the surface. If these discontinuities vary with the presence of the substance to be detected, the reflection coefficient of the array, and thus the amplitude of the reflected SAW, changes. With this method we have reached a sensitivity of 0.3 ppb for NO 2 with a 370 MHz device on a LiNbO 3 substrate.

Surface acoustic wave reflections from a proton exchanged dispersive dot array

Proton-exchanged (PE) regions in LiNbO3 create an invisible inhomogeneity that can be used as surface acoustic wave (SAW) reflectors similar to metallized overlays, implanted layers, or grooves. We report the detection of coherently reflected SAW, from a dispersive array of proton-exchanged dot rows, by utilizing a sensitive interferometric heterodyne laser probe.

Inversion of acoustic waves reflection rules in near critical pure fluids

The reflection of linear acoustic waves propagating in a very compressible, low heat diffusing, supercritical fluid (CO2) is studied by solving the nonlinear Navier–Stokes (NS) equations written for a near-critical van der Waals gas. It is shown that close enough to the critical point, the reflection rules of acoustic waves on thermostatted boundaries are inverted, compared to those usually observed in ideal gases. This phenomenon has been put in evidence by numerical simulations, and its mechanism is shown to be due to the strong contraction or expansion of a hypercompressible thermal adaptation boundary layer. The asymptotic analysis of the equations gives the order of magnitude of the distance to the critical point where the inversion occurs. This transition corresponds to the transition to the so-called Acoustically Saturated Regime, in which the characteristic time scale of heat transfer reaches its lower limit, which is the acoustic typical time.

Nonlinear bulk acoustic waves in anisotropic solids: Propagation, generation, and reflection

In this article, we address the nonlinear properties of bulk acoustic waves in anisotropic solids. While ordinary driving waves are obtained by means of the quasiwave mode concept in the discussion on propagation problems, we focus our analysis on the driving wave satisfying the resonant condition which exhibits the characteristics of three-dimensional spatial accumulation. Then a theory as the basis for solving nonlinear boundary value problems is developed. The novel analysis is presented for nonlinear reflection of bulk acoustic waves at a free surface of a generally anisotropic solid, which reveals that the surface may generate freely propagating second-harmonic waves, and that the reflective second-harmonic waves increase two dimensionally in the bulk. This technique can also be applied to wave reflection problems at other kinds of planar boundaries. Some numerical calculation is carried out for the case in an isotropic solid.

Iterative calculation of reflected and transmitted acoustic waves at a rough interface

A rigorous iterative technique is described for calculating the acoustic wave reflection and transmission at an irregular interface between two different media. The method is based upon a plane-wave expansion technique in which the acoustic field equations and the radiation condition are satisfied analytically, while the boundary conditions at the interface are satisfied numerically. The latter is accomplished by an iterative minimization of the integrated squared error in the boundary conditions by a conjugate gradient technique, leading to a converging and relatively simple scheme. The plane interface result can be used as starting value. Although in principle the method is rigorous, numerical examples show that in practice there is a lower bound on the error in the boundary conditions which can be achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Acoustic reflection calculation using transfer matrices

SUMMARY This paper is in homage to Robert Stoneley for his many contributions to the analysis of acoustic wave propagation and, in particular, for his introduction of anisotropy into the computation of elastic surface-wave characteristics. The latter has proved to be fundamental to the industry which has grown up around the signal processing devices using surface acoustic waves. The problem reviewed here is that of the reflection of incident acoustic waves from planar interfaces of quite general geometries. The interface may consist of substrate and superstrate welded together, of periodic or non-periodic intervening layers between superstrate and substrate, of free surfaces or of layered free surfaces. Surface waves and layer waves are also included. The materials involved may be of arbitrary crystalline symmetry and may be piezoelectric. The goal is to summarize this range of reflection and transmission problems in a common transfer matrix formalism which is convenient for programming. The same format is used for all the problems and the size of the matrices depends not on the complexity of the interface geometry but only on the crystalline symmetry. The reflection results are expressed as scattering matrices linking the amplitudes of the modes propagating in the substrate and the superstrate.

Scanning electron microscopy observation of surface acoustic wave propagation in the LiNbO/sub 3/ crystals with regular domain structures

This paper reports a scanning electron microscopy investigation of surface acoustic wave propagation in the LiNbO/sub 3/ crystals with regular domain structures. The regular domain structures in the LiNbO/sub 3/ crystals were formed by the method of the thermo-electric treatment after growth. We investigated two modes of the interaction between the surface acoustic waves and regular domain structures in the LiNbO/sub 3/ crystals: excitation of the surface acoustic waves by the curved regular domain structure, and propagation of the surface acoustic waves along and across the regular domain structures. It is shown that the regular domain structure in the first case can be used as an interdigital transducer for excitation of the surface acoustic waves through the longitudinal piezoelectric effect. In the second mode of the interaction we observed that the regular domain structure can be used as an acoustic wave-guide in the process of the propagation of the traveling surface acoustic waves along the regular domain structure. Also, we demonstrate the reflection of the surface acoustic waves from the domain walls in the process of surface acoustic wave propagation across the regular domain structure. >

Parametric study and sensitivity analysis of plane-wave reflection from poroelastic seafloor

Acoustic wave reflection from seafloor is very sensitive to the sediment properties. Assuming a plane wave reflected from an homogeneous but anisotropic seafloor, a parametric study is conducted for seabed properties such as shear and bulk modulus, permeability, porosity, etc. It is demonstrated from the numerical solution by the propagator matrix method that the porosity is the most sensitive parameters that affects the reflection coefficient and bottom loss. The effect is most pronounced at low grazing angles. The numerical evidence is further supported by an asymptotic analysis of the analytical expressions of sediment wave velocity and the reflection coefficient at the water–sediment interface, for homogeneous, isotropic material. The numerical study is then extended to inhomogeneous sediment and the sensitivity to different layering patterns is examined. a)Present address: Office of Naval Res., Ocean Acoust. Prog. Code 324 OA, 800 N. Quincy St., Arlington, VA 22217.

Reflection of surface acoustic waves on domain walls in a LiNbO3 crystal

This letter reports on a scanning electron microscopy study of reflection of surface acoustic waves on the domain walls in a LiNbO3 crystal. The regular domain structure with ∼5-mm period was formed in a LiNbO3 crystal by the method of aftergrowth thermoelectrical treatment. It is shown that the regular domain structure reflects surface acoustic waves on the domain walls in a ferroelectric LiNbO3 crystal.

Resonant reflection of two-dimensional acoustic waves from shocks in solids

Le probleme d'emission spontanee des ondes sonores generees par chocs dans les solides est explore. Un modele auto-consistant du milieu est construit, qui permet le calcul des proprietes thermodynamiques comme l'energie interne, l'entropie, le parametre de Gruneisen et, en particulier, le nombre de Mach derriere le choc. Ce dernier est utilise pour calculer le critere de stabilite, representant la condition d'occurence d'emission acoustique spontanee derriere le choc. Les adiabatiques de choc experimentales sont reproduites par le modele. Une forme simple du critere de stabilite est obtenue, s'exprimant au moyen du parametre de Gruneisen du milieu non- perturbe et de la compression relative maximale

Acoustic wave reflector capable of working under deep submersion

In an acoustic wave reflector working in the sea, a sheet of air is set up between a reflecting plate and a perforated plate. This sheet of air forms a reflecting interface with the reflecting plate. A rubber bladder forms a container which, under the effect of the pressure of the water, feeds the sheet of air through the perforated plate. The thickness of this sheet of air is kept substantially constant up to the limit of submersion of the reflector. This makes it possible to increase the depth at which the acoustic reflectors are used.

Phonon scattering from ferroelectric domain walls: Phonon imaging in KDP.

The ferroelectric domain wall is an ideal interface for studies of the boundary scattering of high frequency acoustic phonons. These internal interfaces have no contamination and can be reversibly created and destroyed by application of an electric field at the phase transition---122 K in KDP. Images of phonons in single- and multiple-domain cases show remarkable differences in the ballistic heat flux. Theoretical modeling based on acoustic wave reflection reveals that the domain walls act as nearly perfect grain boundaries.

Interface reflection of spherical acoustic waves in the first- and second-order rational parabolic approximations and their artifacts

The accuracy of the first- and second-order rational parabolic approximations of the ‘‘vertical’’ slowness and the nature of the artifacts associated with them in the space-time solutions to the acoustic wave equations in a fluid medium are investigated. In particular, the reflection of an impulsive, point-source generated, spherical wave against the boundary with a medium with a higher wave speed is analyzed. From the space-time Green’s functions in the relevant two-media configuration, evaluated with the aid of the modified Cagniard method, it is found that, instead of generating the real, physical head wave, the approximations generate artificial head-wavelike arrivals. The analysis makes explicit in which regions of space and in which time interval the artifacts show up and of what nature they are. Numerical results are presented.

Generation and Bragg reflection of surface acoustic waves in nearly periodic system of elastic metal strips on piezoelectric half-space

Propagation of surface acoustic waves (SAW) in a periodic system of metal strips on an anisotropic piezoelectric substrate is analyzed using Green’s function for both the substrate and the system of strips. Appropriate approximations to these functions in spectral domain result not only in a uniform theory of SAW generation and Bragg scattering by strips that accounts for both the electric and elastic properties of the strips, but also in analytical solutions for dispersion relations and a scattering matrix for interdigital transducers. A new, comprehensive model for such transducers is proposed.

Nonlinear reflection of bulk acoustic waves at an interface

A theory as the basis for solving nonlinear boundary value problems is described. A new analysis is presented for nonlinear reflection, which reveals that there is a two-dimensional spatial increase of the second-harmonic wave. The accretion along the propagation direction is the result of the self-interaction of the primary wave; the one in the wave front is due to the boundary restriction.

Stochastic analysis of acoustic plane wave reflection from inhomogeneous porous media : Badiey, M; Cheng, A; Jaya, I; Schulkin, M Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P11–16. Publ Japan: Coastal Development Institute of Technology, 1991

Stochastic analysis of acoustic plane wave reflection from inhomogeneous porous media : Badiey, M; Cheng, A; Jaya, I; Schulkin, M Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P11–16. Publ Japan: Coastal Development Institute of Technology, 1991

Effect of randomly inhomogeneous seafloor on the reflection and scattering of plane acoustic waves in shallow waters.

The bottom of the ocean is composed of randomly inhomogeneous, anisotropic layers of sediments. A geoacoustic data set is constructed from previously measured geological experiments in shallow-water regions of the New Jersey Continental Shelf. This data set is used as input for a stochastic reflection model based on the Monte Carlo technique in order to study the effect of the random variations of the seafloor properties on the scattering and reflection of acoustic plane waves in a shallow ocean. It is found that the random inhomogeneities as well as the anisotropy of the subsurface are major causes of volume scattering and certain anomalies in the reflection coefficient.

A comprehensive analysis of surface acoustic wave reflections. III. Oblique incidence grooved and metallic gratings

First- and second-order reflection effects in oblique incidence surface acoustic wave gratings are examined. A general formulation usable for both metallic and same material grooved overlays is provided. The existence of several important effects, particularly a reflection effect at the second harmonic of the grating and a velocity shift at the first harmonic for grooved gratings, are demonstrated, and the behavior of these effects as a function of incidence angle is examined. For angles of incidence of interest in the production of reflective array compressors, these effects are analyzed as a function of metallization ratio.

Acoustic End Effects in Magnetohydrodynamic Submerged Vehicular Propulsors

This paper treats the effects near the ends of the channel on the transmission and reflection of periodic acoustic waves generated at some cross section inside a magnetohydrodynamic (MHD) seawater propulsion system. A region of high uniform magnetic field inside the MHD submerged vehicular propulsor is separated from the essentially zero magnetic field outside the channel by a nonuniform, fringing magnetic field at each end of the channel. The channel configuration chosen here is that of a straight, rectangular duct with electrically insulating top and bottom walls perpendicular to the magnetic field and highly conducting sidewalls parallel to the field. In particular, the mathematical analysis focuses on determining the percentage of the incident wave which is reflected by the fringing-field region back into the uniform-field region and the percentage which is transmitted through the fringing-field region into the zero-field region. The key parameter is the acoustic interaction parameter N, which is the characteristic ratio of the electromagnetic body force opposing motions across magnetic field lines to the inertial "force" in the acoustic wave. Solutions are presented for the fundamental, plane acoustic mode for arbitrary values of Ν and for all acoustic modes for Ν &amp;lt; 1. The amplitudes of the reflected and transmitted waves depend on the wave frequency, the length of the fringing-field region, N, and the type of wave mode. The magnetic field introduces a strong anisotropy with strong damping of modes involving transverse motions across magnetic field lines and with weak damping of modes involving transverse motions along field lines. This is the third in a series of articles on MHD marine propulsion from the David Taylor Research Center MHD propulsion program [Brown et al (1990), Tempelmeyer (1990)].

Anomalous reflection and transmission of acoustic beam on the interface between two 180°-ferroelectric domains

Abstract The specific features of reflection and transmission of acoustic wave on the 180°-domain interface in ferroelectric crystal are investigated. It is shown that under certain conditions the coupling with leaky wave branch provides the effect of resonant transformation from almost total transmission to almost total reflection at small variation of incidence angle or orientation of incidence plane.