Body wave to surface wave conversion using tailored meta-structures

Elastic waves are important in many application areas. Their manipulation and coupling between different acoustic modes is important and presents a considerable challenge that offers to unlock the flexibility in wave transport required for efficient energy harvesting and vibration mitigation devices. In this paper, we present a new class of metamaterial conversion devices consisting of arrays of “acoustic pipes” that can arbitrarily convert between different acoustic wavemodes. These pipes are used to match the modal patterns and phases between the two different elastic waves. The technique is fairly general and can be used to match any acoustic mode to any other acoustic mode provided an appropriate geometry can be formed. Until recently the complexity of the geometries required has made the physical realisation of practical devices difficult because of the limitations of conventional fabrication processes but here we demonstrate practical devices made using additive manufacturing which can easily produce the complex topographies required for elastic waves around the MHz frequency region. • A new technique for easily transforming acoustic energy between different modes. • It uses an acoustic metastructure made of acoustic pipes to reshape wave patterns. • Demonstrated by converting longitudinal waves into various surface/plate modes. • Adaptable to a broad range of wave mode conversions. • Demonstrated using additive manufacturing to achieve the complex geometry.