Acoustic retroreflection characteristics of time-varying parameter modulated medium

A method of realizing acoustic retroreflection using time-varying parameter modulated medium is proposed. An acoustic propagation model for acoustic reflection of plane waves under both vertical and oblique incidence on time-varying parameter-modulated media is established, and analytical expressions for the complex pressure reflection coefficients are derived. This revealed the three-wave nonlinear coupling mechanism underlying the acoustic retroreflection effect. Numerical simulations are conducted using the finite-difference time-domain method to investigate the influence of the thickness, modulation depth, and modulation frequency of the medium on the propagation of the retroreflected wave. The simulation results align well with the theoretical predictions. An obvious retroreflection phenomenon occurs when the frequency of the sound speed modulation is twice that of the incident sound wave. There is obvious retroreflection phenomenon under the condition that the sound speed modulated frequency is twice the frequency of the incident sound wave. The proposed acoustic retroreflector has the characteristics of more channels, a simple structure and good tunability.