We designed a new acoustic diode model, based on a one-dimensional structure consisting of piezoelectric ceramic films placed periodically in an epoxy plate. Specifically, the model is designed to exhibit non-reciprocal wave propagation in the audible and ultrasonic range. Our model includes no artificial forces to generate the asymmetry in the system but utilizes a mode-conversion mechanisms of elastic-wave propagation at interfaces. We demonstrate numerically that the model can achieve non-reciprocity at a particular frequency range for both S-mode and A-mode incidence of the Lamb wave. We further attempt to develop an additional model that can suppress unwanted backward propagation due to a large mismatch at the heterojunction interface.