Excitation of surface elasticity waves in piezoelectric media by ion beams∗

Kinetically it has been shown that by considering a semi-bounded piezoelectric medium with hexagonal symmetry with an ion beam flowing on its free surface, the surface elasticity waves can be excited on their surface-vacuum interface as a result of the piezoelectric effect.     

Scattering of decimetric acoustic waves from the sea’s surface

The influence of the sea’s surface slopes caused by wind waves whose wavelength exceeds that of the Bragg components on the backscattering of acoustic radiation is discussed. The analysis is performed for long waves whose wavelengths are greater than 1.5 m. The study is based on the data of full-scale measurements of the sea’s surface slopes. Expressions relating the backscattering coefficient to the statistical characteristics of the sea’s surface slopes caused by long waves are presented.     

Comparison characteristics of surface acoustic waves propagating on LGT and quartz substrates

For comprehending the propagation characteristics of surface acoustic waves (SAW) on novel piezoelectric crystal Langatate (LGT), the numerical analysis of the most important propagation characteristics of surface acoustic waves (SAW) on LGT are presented and compared with that of quartz. The results are that the phase velocity on LGT is generally about 1000 m/s slower than that on quartz; there are zero temperature cuts and pure mode directions on LGT; the electromechanical coupling coefficient (K^2) of LGT is larger than that of quartz. The results show that LGT has lower propagation velocity, higher electromechanical coupling coefficient, good temperature stability and other good characteristic. The results also show that there are somewhat deviations with different material constants, especially, the temperature coefficient of frequency.     

Precision analysis of non—conformal reconstruction for the surface acoustic field on axisymmetric structures

Reconstruction of the surface acoustic field of axisymmetric body with arbitrary boundary conditions using near-field acoustic data is studied.The method of numerical reconstruction based on orthonormalization function expansion(OFE) and boundary element integral(BEI) is presented which can overcome the singular integral problem in the boundary integral equations.By numerical examples,the precision of reconstruction for the non-conformal surface with the axisymmetric or non-axisymmetric vibrating on axisymmetric body is given.The results of the numerical simulation are shown that this kind of reconstruction method is available for engineering.     

Torsional waves excited by electromagnetic–acoustic transducers during guided-wave acoustic inspection of pipelines

A theory of propagation of torsional waves excited by an electromagnetic–acoustic transducer in a pipe is proposed. This theory takes into account the excitation parameters, geometry, viscosity, and the elastic characteristics of an object. The main testing parameters (the frequency and geometry of the transducer) that determine the possibilities of guided-wave testing of pipelines of various dimensions using torsional waves are theoretically substantiated.     

A prediction of the acoustic field of a vibrating box by FEM-BEM

I.Mathematicalmodelofacousticfie1dByapplyingtheSommerfeldradiationcondihonThus,anacousticfic1disdescribcdbyHelmholtzformula.Byconsideringaficldpointinthearea,Helmholtzformulaisgivenbythefollowingthreeintegra1equations:(1)Theexternalintcgra1fOrmu1a'(2)Thcintcrnalintegralformu1af(3)Thesurfaceintegralformu1afwhcreP.isthesoundpressureonthcSsurface;rthedistancefrompointqtothee1ementsurfacedSiqtheficldpoint,tuthefrcqucncyoftheacousticradiation;pthedensityofthesurroundingmedium,vsthenormalvibrati…     

Influence of acoustic leakage at fluid–solid interface on interferometric detection of surface acoustic wave

When using laser interferometer to detect surface acoustic wave at fluid–solid interface, there are two factors which will cause the optical path length variation of the probe laser beam: interface deformation, and refractive index changes in fluid induced by acoustic leakage. Influence of acoustic leakage on laser interferometric detection for surface acoustic wave is researched here. A metal plate immersed in an infinite fluid is used as a physical model. Interface deformation due to laser-induced acoustic wave and pressure in fluid due to acoustic leakage are computed for select cases by finite element method. The optical path length variation caused by the two factors are calculated respectively and compared. The results show that the influence of acoustic leakage increases with the increasing acoustic impedance matching of fluid and solid, the peak-to-peak of influence degree increases linearly with the increasing acoustic impedance of fluid, and that decreasing the distance between the interferometer and interface can effectively reduce the influence of acoustic leakage.     

Further studies on thickness vibrations of piezoelectric plate excited by parallel field

I.IntroductionThcthickncssvibrationsofahomogeneous-anisotropicpiezoclectriccrystalplatewithanexcitingficldparallcltothemajorsurfacesofthep1ate,andalsototheplanewavefront(calledasthepara11e1fic1dcxcitatloninbricO,havebccnana1yzedI'1.Theprimarybehaviourofthick-nessvibrationshasbecnobtaincdasthepIatewitharbitraryorientationisexcitedbythepara11elfield.Inthispapcr,wcwillgofurthcrtogivcancwformu1aofthemechanicalresonantfrequen-cyequation.ILqformisthesameasthercsonantequationofthepuremodeandiseasyt…     

Selective enhancement of the hole photocurrent by surface plasmon–polaritons in layers of Ge/Si quantum dots

It is found that the integration of Ge/Si heterostructures containing layers of Ge quantum dots with twodimensional regular lattices of subwave holes in a gold film on the surface of a semiconductor leads to the multiple (to 20 times) enhancement of the hole photocurrent in narrow wavelength regions of the mid-infrared range. The results are explained by the light wave excitation of the surface plasmon–polaritons at the metal–semiconductor interface effectively interacting with intraband transitions of holes in quantum dots.     

A study of noise reduction by acoustic shock waves

I.IntroductionAcousticshockwavcs(ASW)isanimportantphcnomcnoninnonlinearacoustics.Experimentalrcsultshavcshownthatwhenanaircraftcngincinletopcratesneartheson-iccondition,vcrystrongnoisegcncratedbythcfanscanbcreduccdgreat1yowingtothcformationofASWatthcthroatofthcin1etll].ASWisadiscontinuityofacousticvaria-bles,whichisdifTcrcntfromthcshockwavesoccurringinhighspcedsteadyflowinducts.Theformer'sintensityismuch1cssthanthelattcr's.Furthcrmorc,thepositionandintensityofASWisalwayschangedwithtime.l…     

Optical surface polaritons of TM type at the nonlinear semiconductor–nanocomposite interface

TM-polarized optical surface polaritons in a nonlinear semiconductor–nanocomposite guiding structure have been considered. The nanocomposite consists of alternating layers of bismuth-containing garnet ferrite (BIG, Lu_{3 – x}Bi_xFe_{5 – y}Ga_yO₁₂) and gallium–gadolinium garnet (Gd₃Ga₅O₁₂), and the semiconductor (n-InSb) has a cubic nonlinearity and is characterized by two components of the nonlinear susceptibility tensor. With allowance for the anisotropy of the optical properties of the nanocomposite, caused by the magnetization of the BIG layers, the dispersion relation has been obtained and analyzed and its solutions are shown to split into two pairs of high- and low-frequency branches. The influence of the electric field at the interface on the wave characteristics and the existence domains of nonlinear surface TM polaritons has been studied. By solving the inverse problem of finding the profile of the longitudinal electric component of the surface polariton, it has been found that the nonlinearity gives rise to soliton-like wave fields.     

The effects of bonding conditions on the propagation of acoustic waves along a cased borehole

1 IntroductionIn geophysical logging, one must study the soUnd field in cased borehole to properly assessthe case bonding conditions. Geophysicists have studied the sound fields in cased boreholesquite thoroughly and drawn many useful c.nclusionsll--6]. Bat they usually assume that thebonding conditions of the illterfaces between the case and cemellt, or between the cemellt andformation, are either well or poorly bonded. In the latter case, the bonding condition is modeledby a fluid annulus. …     

The specific acoustic impedance of aperture on cylindrical surface

The acoustic impedance caused by sound radiation at the terminals ofthe aperturc on cylindrical surface is analyzed based upon rigorous soundtheory.In low frequency range,the approximate solution of the specific acousticresistance is derived.Special treatments are introduced in order to simplify the so-lution of the specific acoustic reactance.It is verified that the specific acousticreactancc of such an aperture is equal to that of a similar aperture on the infinitelylarge plane when the small quantities of high order are neglected.     

Reflection and transmission of acoustic waves on multilayered porous media

Based on the Boit theory of acoustic wave propagation in fluid-satu-rated porous medium we have studied in this paper the acoustic reflection andtransmission on multilayered porous media,in which the adequate boundaryconditions across the interfaces are taken into account.Numerical calculationsof the reflection and transmission coefficients at different incident angles andfrequencies of the fast compressional wave incident on porous media with threeor four layers are presented.The results indicate that the maximum or mini-mum reflection and transmission coefficients appear at certain ratios of thewavelength to the thickness.The acoustic incident angle and porous mediumproperties are shown to affect significantly these coefficients.As an example,the measured transmission coefficients in a water-saturated fused glass beadsample are in good agreement with theoretical prediction.     

Dependence of the intensities of ultrasonic sidebands in the Mössbauer spectrum on the statistics of the acoustic field

The acoustic modulation of quanta is analyzed with regard for dissipation of the energy of the excited mode through resonance (having the acoustic frequency) modes. Given definite assumptions, the Rayleigh-Rice distribution function previously introduced phenomenologically is obtained for the oscillation amplitudes. It is proposed that the intensities of the ultrasonic sidebands be expressed in terms of the parameters m and , which are valid for any degree of sound coherence. The results of numerical computations are given.Translated from Izvestiya Vysshikh Uchebrnykh Zavedenii, Fizika, No. 7, pp. 54–57, July, 1979.In conclusion, the authors express their gratitude to Prof. Sh. Sh. Bashkirov for valuable comments.     

Effect of the free surface and the rigid plane on structural vibration and acoustic radiation

The coupled fluid-structure interaction equation is estabhshed for bodies in the half-space fluid domain, especially sitting on the infinite plane, based on the BEM (Boundary Element Method) theory. Then, the natural frequencies, vibration responses and the acoustic radiation for a box are calculated, and the effect of the free surface and the rigid plane is discussed. Finally, several relative factors including the plate thickness, the structure damping and the distance between the body and the infinite plane are studied. The results show that the effect of the free surface and the rigid plane on the structural natural frequencies, vibration responses and the acoustic radiation cannot be ignored.     

Controlling the transmission of ultrahigh frequency bulk acoustic waves in silicon by 45° mirrors

In this paper, we present a feasible microsystem in which the direction of localized ultrahigh frequency (∼1 GHz) bulk acoustic wave can be controlled in a silicon wafer. Deep etching technology on the silicon wafer makes it possible to achieve high aspect ratio etching patterns which can be used to control bulk acoustic wave to transmit in the directions parallel to the surface of the silicon wafer. Passive 45° mirror planes obtained by wet chemical etching were employed to reflect the bulk acoustic wave. Zinc oxide (ZnO) thin film transducers were deposited by radio frequency sputtering with a thickness of about 1 μm on the other side of the wafer, which act as emitter/receptor after aligned with the mirrors. Two opponent vertical mirrors were inserted between the 45° mirrors to guide the transmission of the acoustic waves. The propagation of the bulk acoustic wave was studied with simulations and the characterization of S₂₁ scattering parameters, indicating that the mirrors were efficient to guide bulk acoustic waves in the silicon wafer.     

Effect of the spatial structure of an acoustic field on Bragg’s acoustooptic diffraction under strong acoustic anisotropy conditions

Bragg’s acoustooptic diffraction in an acoustically anisotropic medium is considered taking into account the two-dimensional spatial diffraction structure of the acoustic beam. The conditions are determined under which reverse transfer of optical power from the diffracted to the transmitted beam in the regime of 100% efficiency of diffraction is considerably suppressed. It is shown that this effect is due to diffraction bending of wave fronts of the acoustic beam in the acoustooptic diffraction plane. The problem of optimization of the piezoelectric transducer size and the spatial position of the input light beam is solved using the criterion of the minimal required power of the acoustic field. The results of simulation in a wide range of the acoustooptic interaction parameters for a Gaussian light beam are reported. The correctness of the model is confirmed experimentally. Recommendations for designers of acoustooptic devices are formulated.     

Effect of Bohm quantum potential in the propagation of ion–acoustic waves in degenerate plasmas

A theoretical investigation has been carried out on the propagation of the ion–acoustic(IA) waves in a relativistic degenerate plasma containing relativistic degenerate electron and positron fluids in the presence of inertial non-relativistic light ion fluid. The Korteweg-de Vries(K-dV), modified K-dV(m K-dV), and mixed m K-dV(mm K-dV) equations are derived by adopting the reductive perturbation method. In order to analyze the basic features(phase speed, amplitude, width,etc.) of the IA solitary waves(SWs), the SWs solutions of the K-dV, m K-dV, and mm K-d V are numerically analyzed. It is found that the degenerate pressure, inclusion of the new phenomena like the Fermi temperatures and quantum mechanical effects(arising due to the quantum diffraction) of both electrons and positrons, number densities, etc., of the plasma species remarkably change the basic characteristics of the IA SWs which are found to be formed either with positive or negative potential. The implication of our results in explaining different nonlinear phenomena in astrophysical compact objects, e.g.,white dwarfs, neutron stars, etc., and laboratory plasmas like intense laser–solid matter interaction experiments, etc., are mentioned.