Radiation of surface Stoneley waves by distributed force sources acting at the solid earth-atmosphere interface

Using the Fourier transform, we find an integral solution describing the excitation of seismoacoustic waves in the solid Earth and the atmosphere by time-dependent forces arbitrarily distributed over the interface between the media. The solid Earth and the atmosphere are modeled by an isotropic solid half-space and a homogeneous gaseous half-space, respectively. Depending on the types of the excited surface and bulk waves, classification of the corresponding force distributions is performed. In the case of harmonic sources, an expression for the period-averaged radiated power of the Stoneley wave is obtained. For arbitrary time dependence of the forces, we find an expression describing the the Stoneley-wave energy radiated during the entire time of the source operation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 7, pp. 624–637, July 2007.     

分层半空间表面非线性瑞利波的激发*

针对非线性瑞利波在均匀分层半空间结构中的激发和传播规律进行研究。根据摄动理论和模态分解将分层半空间结构中瑞利波的二次谐波声场表示为二倍频瑞利波模式的线性组合,经由互易关系得到各模式的展开系数表达式。对不同分层半空间结构中瑞利波二次谐波的激发和传播特性进行讨论,结果表明相速度匹配的瑞利波模式其二次谐波分量随传播距离线性增长,非匹配模式的二次谐波分量则沿传播方向周期震荡传播。此外,文中定义非线性参数表征瑞利波模式产生的非线性程度,这有利于选择出具有明显非线性效应的匹配点,为后续检测工作提供理论依据,具有指导意义。     

Excitation of the acoustic and leaky waves in the atmosphere by a sub-surface seismic source

We study excitation of acoustic, leaky, and surface waves by a time-harmonic force source located in a homogeneous isotropic elastic half-space contacting a homogeneous gas. The force acts in the normal direction to the interface between the media. We consider the case where the sound velocity in the gas is less than the velocity of the Rayleigh wave propagating along the surface of the solid. An expression is derived for the period-averaged radiation power of the surface Stoneley wave. The total radiation power is calculated for the acoustic wave in the gas and for the leaky pseudo-Rayleigh wave. Variations in the radiation powers of the surface and leaky waves are analyzed as functions of the source depth. If the velocities of compressional and shear waves in the elastic medium significantly exceed the sound velocity in the gas, then the radiation power of the Stoneley wave turns out to be a factor of 10⁶–10⁸ smaller than the radiation powers of other waves. The radiation power of the Stoneley wave decreases monotonically with increasing source depth, and the decrease becomes more pronounced with the increase in the difference between the acoustic impedances of the contacting media. If the shear-wave velocity in the solid is close to the sound velocity in the gas, then the radiation power of the Stoneley wave is comparable with the radiation powers of other waves and exhibits maximum at a certain source depth. For some parameters of the gas and the solid, and for certain source depths, the Stoneley wave carries away more than a half of the total radiation power. It is shown that, for certain relations between the parameters of the media, the radiation power of the Stoneley wave increases due to redistribution of the radiated power from the pseudo-Rayleigh leaky wave. The total power of these waves remains approximatly constant and, with accuracy of the order of 10⁻³, is equal to the radiation power of the Rayleigh wave at the vacuum-solid interface. It is shown that the acoustic-wave power which can be transmitted to the upper layers of the atmosphere during an earthquake does not exceed 0.01% of the total power radiated at a given frequency. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 577–592, July 2006.     

Modeling of atmospheric propagation of acoustic gravity waves generated by different surface sources

A model of acoustic gravity wave propagation is developed and a numerical algorithm for solving the corresponding hydrodynamics equations is elaborated. Behavior of the waves in the upper atmospheric layers is studied in relation to the parameters of the ground-based sources.     

Excitation of acoustic waves in metals by electrons and protons

A study of the excitation of acoustic oscillations in metals by electrons and protons is described. For thin metal plates, the amplitude of the electric signal is independant of the energy of the electrons and is proportional to the ionization losses of the charged particles. The dependence of the amplitude of the acoustic signal on the energy of the incident electrons and protons is considered and a comparison between the Cherenkov radiation, thermoelastic, and dynamic models is made.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 72–76, October, 1973.The authors thank I. A. Grishaev, I. I. Zalyubovskii, V. V. Petrenko, M. F. Lomanov, L. L. Gol'din, and Ya. L. Kleinbok for constant help in carrying out this work and to V. T. Lazurik-Él'tsufin for useful discussions.     

Exciton transport by surface acoustic waves

Long-range acoustic transport of excitons in GaAs quantum wells (QWs) is demonstrated. The mobile strain field of a surface acoustic wave creates a dynamic lateral type I modulation of the conduction and valence bands in a double-quantum-well (DQW) structure. This mobile potential modulation transports long-living indirect excitons in the DQW over several hundreds of μm.     

Gravitational waves from seismic sources

A fast moving mass radiates part of its energy through gravitational waves. It is possible to consider hurricanes and earthquakes as terrestrial sources of quadrupole gravitational waves. These phenomena have the necessary parameters for the generation of gravitational waves: large quadrupole moments m/r² and also energies and masses moving with large velocities. Estimates indicate a possibility of observing gravitons from the source of a strong earthquake. Local changes in the earth's gravistatic field and the generation of a gravidynamic field during earthquakes will cause variations in the trajectories of the moon and artificial satellites. A mathematical theory of trajectories, containing gravitons, will enable us to fix the graviton according to data from trajectory measurements.Published as a matter for discussion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 41–46, June, 1974.The author is grateful to Prof. A. A. Sokolov of the Moscow State University for discussing the material expounded here and for interesting remarks.     

Modeling Rayleigh and Stoneley waves and other interface and boundary effects with the parabolic equation

An improved approach for handling boundaries, interfaces, and continuous depth dependence with the elastic parabolic equation is derived and benchmarked. The approach is applied to model the propagation of Rayleigh and Stoneley waves. Depending on the choice of dependent variables, the operator in the elastic wave equation may not factor or the treatment of interfaces may be difficult. These problems are resolved by using a formulation in terms of the vertical displacement and the range derivative of the horizontal displacement. These quantities are continuous across horizontal interfaces, which permits the use of Galerkin's method to discretize in depth. This implementation extends the capability of the elastic parabolic equation to handle arbitrary depth dependence and should lead to improvements for range-dependent problems.     

Topological charge pump by surface acoustic waves

Quantized electron pumping by the surface acoustic wave across barriers created by a sequence of split metal gates is interpreted from the viewpoint of topology.The surface acoustic wave serves as a one-dimensional periodical potential whose energy spectrum possesses the Bloch band structure.The time-dependent phase plays the role of an adiabatic parameter of the Hamiltonian which induces a geometrical phase.The pumping currents are related to the Chern numbers of the filled bands below the Fermi energy.Based on this understanding,we predict a novel effect of quantized but nonmonotonous current plateaus simultaneously pumped by two homodromous surface acoustic waves.     

Rayleigh surface waves in a plate

In the article the analysis of a monochromatic elastic surface wave in an unlimited plate of limited thickness whose opposite surfaces are planar and mutually parallel, made of an elastic isotropic material of a constant density is described. Equations are calculated for the wave number calculation — speed of surface wave propagation, and an equation for the calculation of the vector components deformation (component trajectory) of the elastic medium.     

Transport of magnetic vortices by surface acoustic waves

In a thin film of superconducting Y Ba₂Cu₃O₇ the impact of surface acoustic waves (SAWs) traveling on the piezoelectric substrate is investigated. A pronounced interaction between the ultrasonic waves and the vortex system in the type II superconductor is observed. The occurrence of a SAW-induced dc voltage perpendicular to the sound path is interpreted as dragging of vortices by the piezoacoustic SAW, which acts as a conveyor for the flux quanta. The antisymmetry of this voltage with respect to the magnetic field directly evidences the induced, directed flux motion. This dynamic manipulation of vortices can be seen as an important step towards flux-based electronic devices.     

Imaging of surface acoustic waves

A new experimental method has been devised that directly determines the group velocities of surface acoustic waves. A point source and a point detector are employed to measure the ultrasonic transmission across a solid surface as a continuous function of the propagation direction. Results for single pulses give the times-of-flight for both Rayleigh surface waves (RSW's) and pseudo-surface-waves (PSW's). Calculations and measurements of the group velocities of the surface waves on silicon show some unanticipated behavior: fluid loading qualitiatively changes the group velocity curves for both RSW and PSW. In particular, the RSW branch gains an additional component which we denote here as an induced Rayleigh wave (IRW). If a wave train is employed in the experiment, the analog of phonon focusing is observed for the ultrasonic waves, modified by internal-diffraction effects. Systematic measurements of the wave intensities on silicon as a function of propagation distance are consistent with expected acoustic losses into the surrounding water: the attenuation length of a wave depends on the mode and frequency. A survey of surface-wave images on other crystals is included in this study.     

声表面波驱动的非接触式转动马达

在研究摩擦力驱动的接触式转动马达的基础上,本文研制了一种由声表面波驱动的非接触式转动马达。这种马达的定子选用128°YX-LiNbO₃晶体,在晶体表面光刻两对叉指换能器,由叉指换能器在定子表面激发两列平行而反向传播的声表面波。定子表面铺一层流体,转子就浮在流体表面。当定子表面有两列平行而反向的声表面波传播时,流体层中就会产生平行而反向的声流,这种黏性流体的声流运动就会驱动转子运动。实验上测定了马达的角速度随驱动电压、流体层厚度以及流体运动黏性系数变化的结果。同时,我们也发现,在相同工作频率下,非接触式转动马达的阈值电压远小于接触式。     

Excitation of cladding modes in photonic crystal fibers by flexural acoustic waves

We report the excitation by flexural acoustic waves of an individual cladding mode in a single-mode photonic crystal fiber. The propagation constant and the field distributions of the mode have been investigated by use of this technique. The results give the basis for developing a family of acousto-optic devices based on photonic crystal fibers.