Abstract
Acoustic metamaterials are artificial structures which can manipulate sound waves through their unconventional effective properties. Different from the locally resonant elements proposed in earlier studies, we propose an alternate route to realize acoustic metamaterials with both low loss and large refractive indices. We describe a new kind of acoustic metamaterial element with the fractal geometry. Due to the self-similar properties of the proposed structure, broadband acoustic responses may arise within a broad frequency range, making it a good candidate for a number of applications, such as super-resolution imaging and acoustic tunneling. A flat acoustic lens is designed and experimentally verified using this approach, showing excellent focusing abilities from 2 kHz and 5 kHz in the measured results.
Highlights
Acoustic metamaterials are artificial structures which can manipulate sound waves through their unconventional effective properties
Different from the locally resonant elements proposed in earlier studies, we propose an alternate route to realize acoustic metamaterials with both low loss and large refractive indices
We describe a new kind of acoustic metamaterial element with the fractal geometry
Summary
Acoustic metamaterials are artificial structures which can manipulate sound waves through their unconventional effective properties. Acoustic metamaterials have focused on developing artificial structures that can manipulate and control sound waves in unconventional ways[2], made possible by the creation of unusual material properties such as double negativity (negative mass density and modulus)[3,4], zero – or even negative – refractive index[5,6,7,8], acoustic imaging[9,10], cloaking[11,12,13], transformation acoustics[14], active acoustic metamaterials[15], and acoustic metasurfaces[16,17]. The design of geometry-based non-locally resonant elements has been theoretically proposed and experimentally verified[20,21,22] These types of element can be designed to possess extreme parameters with low absorption and wide operating bandwidth. Our new strategy may offer an alternate route to the design of novel materials and devices in acoustic engineering in the future
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