The photoacoustic effect in a periodically modulated structure

If an absorbing medium is constructed so that its sound speed varies periodically in space, the photoacoustic effect takes on a different character than when it is generated in a homogeneous medium. The case considered here is where either the density or the compressibility of the medium varies sinusoidally in space. The wave equation for pressure is shown to reduce to an inhomogeneous Mathieu equation. The properties of the waves generated by heat deposition in such a structure are investigated. Theoretical results are shown for a finite layer excited by a sinusoidal heating source that is a delta function in space.