Interference of opposing longitudinal acoustic waves in an isotropic absorbing plate and a periodic structure with defects

Interference of longitudinal acoustic waves propagating in opposite directions in a homogeneous isotropic absorbing plate and a periodic structure with a defect is considered theoretically. The periodic structure consists of alternating absorbing solid and transparent liquid layers. The defect is modeled by replacing a solid layer by a liquid layer of the same thickness. The dependences of the transmission spectrum of the energy flux on the amplitude ratio and phase difference of the interacting waves are studied. It is shown that, by varying the parameters of the opposite pressure wave, it is possible to change the transmission spectrum of the direct wave in a wide frequency range. An expression is obtained to determine the extremums of the wave amplitude transmitted through an absorbing plate depending on the amplitude ratio of the interacting waves. The results of studying a one-dimensional periodic structure demonstrate the possibility to considerably change the transmission spectrum of the pressure wave leaving the structure and also to eliminate the invariance of this spectrum under the interchange of the k th and ( n − k +1)th layers (where n is the total number of layers in the structure).