Peculiarities of quasi-longitudinal elastic wave propagation through the interface between isotropic and anisotropic med
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ICAL PROPERTIES OF CRYSTALS
Peculiarities of QuasiLongitudinal Elastic Wave Propagation through the Interface between Isotropic and Anisotropic Media: Theoretical and Experimental Study A. N. Nikitina, R. N. Vasina, T. I. Ivankinaa, A. A. Kruglova, T. Lokajicekb, and L. T. N. Phanc a
Joint Institute for Nuclear Research, ul. JoliotCurie 6, Dubna, Moscow oblast, 141980 Russia email: [email protected] b Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojova 269, 165 00 Praha 6 – Lysolaje, Czech Republic c Tula State University, pr. Lenina 92, Tula, 300600 Russia Received May 26, 2011
Abstract—The peculiarities of elastic wave propagation in a bilayer medium are studied theoretically and experimentally. One (isotropic) layer was an acrylic glass plate, and the other (anisotropic) was a quartz sin gle crystal. In experiments, the elastic waves were generated by a piezoelectric transmitter and received by a piezoelectric transducer contacting the surface of the model medium. The propagation time of a quasilon gitudinal wave was determined using highorder statistics. In the general case, the incident elastic waves are split at the interface between the layers: beams undergo double reflection and triple refraction. The measured dependences of the propagation times of quasilongitudinal split waves on the angles of refraction are in sat isfactory agreement with the calculated ones. The calculation was performed by solving the Christoffel equa tion with allowance for the boundary conditions. DOI: 10.1134/S1063774512040098
INTRODUCTION The study of the anisotropy of the properties of crystals, rocks, and constructural materials is presently an important line of research in materials science and geophysics. The consideration of elastic properties of the Earth’s lithosphere is important, e.g., for seismol ogy. In [1–3], the peculiarities of the propagation of quasilongitudinal and quasitransverse elastic waves in samples of rocks with crystallographic textures were studied by neutron diffraction and acoustic methods. It was noted in [3] that the model values of the anisot ropy coefficient of quasilongitudinal wave velocities calculated for a textured rock are much lower than the values determined by direct ultrasonic measurements. Studies [3–5] were carried out to elucidate the rea sons for this discrepancy. An original method was applied to describe anisotropy. The socalled anisot ropy vector and anisotropy parameter were introduced instead of equations containing tensor quantities; as a result, the solution to the problem of elastic wave propagation in an anisotropic medium and the elastic wave reflection from a free surface was simplified. The analysis that was performed showed, e.g., that coupled waves with quasilongitudinal and quasitransverse polarizations coexist in an axially anisotropic medium; this finding is similar to the conclusions of [6, 7]. These waves propagate with different velocities. In general, their reflection from an interface is non
specular and is accompani
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