A review of acoustic impedance matching methods to validate additive manufactured metamaterial for capacitive micromachined ultrasonic transducers

This review analyses methods for acoustic impedance matching that are used on ultrasonic transducers to increase acoustic energy transmission into the load medium. A capacitive micromachined ultrasonic transducer (CMUT) emits sound via electrostatic deflection of a membrane electrode. Especially air-coupled CMUTs exhibit a notable impedance mismatch. We propose a new approach to fabricate impedance matching metamaterials with extremely low load-side specific acoustic impedance values and an extraordinary level of control over gradient attributes, by employing a photolithographic additive manufacturing technology. It will enable gradient impedance matching, which has a beneficiary effect on acoustic bandwidth, efficiency and sensitivity of the CMUT.