Acoustic scattering and field enhancement through a single aperture

We study the acoustic field enhancement through a circular hole in a hard plate of finite thickness in this work. We derive the boundary-integral equations corresponding to the acoustic scattering to investigate the Fabry-Perot type resonant frequencies that induce the field enhancement. The asymptotic expansions of Fabry-Perot type resonances with respect to the size of the hole are derived, and the quantitative analysis of the field enhancement caused by the configuration at the resonant frequencies is presented with both the enhancement order and the shapes of resonant modes characterized. The transmission in the nonresonant quasi-static regime is also investigated.