Meta-ring for enhancing emission efficiency of omnidirectional SH waves

The intensity of a wave emitted by a transducer affects its performance critically, especially when the emitted wave is omnidirectional. However, the development of omnidirectional transducers lags behind unidirectional ones, despite their practical usability in non-destructive testing. Here, we propose a metamaterial ring (meta-ring) enhancing the emission efficiency of omnidirectional SH elastic wave sources. Meta-ring is deliberately designed to follow the mechanical behavior of the discrete mass-spring model and is installed independently around the transducer. We interpret the involved physics for emission enhancement using homogenization and elucidate the two principles: a low impedance condition and a Fabry-Perot resonance. In addition, the two key design variables comprising the meta-ring are explored to modulate the practical adaptability. Experiments confirm that the meta-ring increased the emission efficiency of the transducer by over 250%. In that the intensity of an omnidirectional wave decreases inverse squarely in the two-dimensional space, the emission efficiency boosting by the proposed metamaterial concept can be critical in wide-area wave-based non-destructive evaluation.

Automated summary

In this study, a metamaterial ring (meta-ring) was proposed to enhance the emission efficiency of omnidirectional SH elastic wave sources. The meta-ring, designed based on the mechanical behavior of the discrete mass-spring model, was installed independently around the transducer. The physics behind the emission enhancement were interpreted using homogenization, and two principles, a low impedance condition and a Fabry-Perot resonance, were elucidated. Experiments confirmed that the meta-ring increased the emission efficiency of the transducer by over 250%, highlighting its critical importance in wide-area wave-based non-destructive evaluation.