Compact acoustic amplifiers based on non-adiabatic compression of sound in metamaterial waveguides.

• A compact acoustic wave amplifier based on non-adiabatic compression of sound in metamaterial waveguides is proposed. • It is found that the combined effects of structural discontinuity and thermal viscous dissipations in the metamaterial waveguides is the key to reduce the size of metamaterial device and optimize its sound amplification capability. • The idea of achieving miniaturized metamaterial devices based on non-adiabatic fast wave compression and amplification provides a novel technique to develop acoustic wave amplifiers, which could be practically used in many applications. Inspired by the optical non-adiabatic wave propagation effect in plasmonic waveguides, we explore the acoustic non-adiabatic wave compression effect in acoustic metamaterial waveguides, and demonstrate its potential for the development of compact metamaterial devices with significant sound amplification capability. In particular, our numerical and experimental results have shown that there exists combined effects of structure discontinuity and thermal viscous dissipations in the metamaterial waveguides, which is essential to reduce the size of metamaterial device and optimize its field enhancement capability. Our work provides a new way to design high-performance and compact metamaterial devices that could be practically used in automotive ultrasonic radars, robot sonar systems, structural health monitoring and medical instrumentation and imaging applications. [ABSTRACT FROM AUTHOR]