Use of Evanescent Plane Waves for Low-Frequency Energy Transmission Across Material Interfaces
The transmission of sound across high-impedance difference interfaces, such as an air-water interface, is of significant interest for a number of applications. Sonic booms, for instance, may affect marine life, if incident on the ocean surface, or impact the integrity of existing structures, if incident on the ground surface. Reflection and refraction at the material interface, and the critical angle criteria, generally limit energy transmission into higher-impedance materials. However, in contrast with classical propagating waves, spatially decaying incident waves may transmit energy beyond the critical angle. The inclusion of a decaying component in the incident trace wavenumber yields a nonzero propagating component of the transmitted surface normal wavenumber, so energy propagates below the interface for all oblique incident angles. With the goal of investigating energy transmission using incident evanescent waves, a model for transmission across fluid-fluid and fluid-solid interfaces has been developed. Numerical results are shown for the air-water interface and for common air-solid interfaces. The effects of the incident wave parameters and interface material properties are also considered. For the air-solid interfaces, conditions can be found such that no reflected wave is generated, due to impedance matching among the incident and transmitted waves, which yields significant transmission increases over classical incident waves.
Evanescent waves, Inhomogeneous plane waves, Sound transmission
Acoustics and Noise Control
Date of this Version
Daniel C. Woods, J. Stuart Bolton, Jeffrey F. Rhoads, “Use of evanescent plane waves for low-frequency energy transmission across material interfaces,” 169th meeting of the Acoustical Society of America, Paper No. 1aPA6, Pittsburgh PA, May 2015. Abstract published in the Journal of the Acoustical Society of America, 137, 2199, 2015.