Ultrasonic pulse transmission through an acoustic barrier using a metamaterial with input impedance matching

This study proposes an input impedance-matching metamaterial to enable the transmission of ultrasonic pulses by attaching to only one side of a barrier. The metamaterial facilitates ultrasonic pulse transmission through the barrier by mitigating the mismatch between the characteristic impedance of the incident medium and the input impedance at the incident boundary of the barrier. The problem of designing the metamaterial is divided into two sub-problems by introducing a virtual intermediate layer with artificial material properties. In these sub-problems, two meta-layers constituting the metamaterial are designed through topology optimization and simplified to ensure fabrication feasibility. Numerical simulations demonstrate that the simplified metamaterial exhibits high transmittance exceeding 0.5 within 21.2% bandwidth relative to the center frequency, whereas it remains below 0.06 without the metamaterial. In water tank experiments, the transmitted pulse energy is enhanced by 6.83-fold by attaching the metamaterial to the barrier.