Space-time modulation puts a new twist on controlling wave behaviors and opens the door for unprecedented wave manipulation capabilities. Here we propose a space-time modulated membrane system aiming to realize the unidirectional parametric amplification. Two different approaches, continuous model and transfer matrix method, are applied to analyze the acoustic response of the system under a monochromatic incidence. In the proposed space-time modulated membrane system, these two methods are in good agreement with each other. Results show that under a monochromatic incidence from one end of the system, a harmonic is generated, and both the incident wave and generated wave exponentially grow along with the system. Our work demonstrates a metamaterial realization of unidirectional acoustic parametric amplifier via space-time modulated membranes, which offers a design platform for a number of applications in sensing, imaging and communication.
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