Input impedance-matching metamaterial to enhance ultrasonic pulse transmission through an acoustic barrier

Ultrasonic pulses lose energy when they hit an acoustic barrier because the barrier and the surrounding medium have different acoustic impedances. This limits ultrasound methods used for imaging, defect detection, and therapeutic ultrasound. The study designs an acoustic metamaterial to reduce this impedance mismatch. It uses a design strategy that introduces a “virtual intermediate layer,” turning the metamaterial design into mathematically equivalent subproblems to expand the design space. The metamaterial is fabricated using wire electrical discharge machining (WEDM). Experiments in a water tank compare pulse transmission with and without the metamaterial, showing a 7.78× increase in ultrasonic pulse energy and transmittance greater than 0.5 over about a 20% relative bandwidth.