Microelectromechanical Systems-based Acoustic Metamaterials: Design Principles, Microfabrication Strategies, and Emerging Microacoustic Applications

Microelectromechanical Systems (MEMS)-based acoustic metamaterials (AMMs) enable precise manipulation of acoustic waves at the microscale through engineered compact, lightweight, subwavelength structures. Unlike most macroscale AMMs fabricated by additive manufacturing, MEMS-based AMMs are realized using microfabrication processes that ensure high precision, tight dimensional control, wafer-level integration, and compatibility with electronic microsystems. This review covers the main design types of MEMS-based AMMs: Helmholtz resonators (single and array), ultra-micro-perforated panels (UMPPs), membrane-cavity structures, phononic bandgap designs, and impedance-controlled systems. It focuses on how fabrication methods affect acoustic performance, especially thermo-viscous losses. Core MEMS fabrication techniques-such as photolithography, deep reactive-ion etching (DRIE), wafer bonding, soft lithography and polydimethylsiloxane (PDMS) casting, and Lithographie, Galvanoformung, Abformung (LIGA)-are examined for their structural fidelity, dimensional accuracy, and integration capability. UMPPs with sub-100 µm apertures suppress higher-order band narrowing and frequency shifting. Flexible UMPPs, fabricated by casting PDMS onto MEMS silicon molds, broaden the absorption bandwidth through structural flexibility, though with a slight reduction in peak absorption due to coupled structural-acoustic vibration effects. Applications include MEMS vibration isolation, phononic metaplates, implantable sensors, surface acoustic wave control, noise absorption, and RF filtering, covering kilohertz to gigahertz frequencies. This review links acoustic design with MEMS fabrication and system integration, providing a framework for developing microscale AMM devices.