Investigating the Excitation of Elastic Waves in an Acoustic Waveguide

Abstract

As is known, much attention is aid to acoustic vibration propagating in plane layered structures behaving as acoustic waveguides. Stealth (from the viewpoint of communications intelligence) transmission of data, hidden interception, setting up communication with sufferers in carrying out rescue operations on sunken submarines or rock-falls are some examples of electroacoustic applications of such sort. The problem of exciting elastic waves in a rectangular acoustic waveguide is considered. The results from calculating acoustic fields using an approach based on superposition of propagating wave modes are presented. Since acoustic waves can be both transverse and longitudinal, solution of the elastic wave propagation problem is more complicated than solution of the same problems in the field of electromagnetics. Nonetheless, since the equations describing the physical phenomena in these areas have much in common, the solutions obtained in the field of electrodynamics can be applied for solving acoustic problems. An acoustic waveguide made in the form of an elastic plate is similar to an electrodynamic system in the form of a waveguide with metal walls. There is a similarity between the boundary conditions for an ideal conductor and the free surface of an elastic body. In both cases, waves do not escape from the waveguide boundaries. As a consequence, there is a characteristic dispersion law for waves the displacement or field strength vector of which is oriented along the interface surface. A mathematical model describing acoustic fields has been constructed, and numerical simulation has been carried out in the MultyPhys software package developed by the COMSOL company. For checking the results of numerical simulation and theoretical calculations, experimental studies were carried out using the developed computerized system. Acoustic field distributions on the waveguide surface are measured using an electroacoustic transducer, which is connected to the personal computer through a soundcard. Since the measurements are made at the sound range frequencies, the soundcard has sufficient capabilities for digitizing the signal, separating the useful parameters, and further processing them without any extra financial costs.