Keywords: Trapped Rainbow Storage, Metamaterials, Light
The graded acoustic artificial structures having a gradual variation of their geometric parameters play an important role in manipulating propagation of acoustic waves. By continuously changing either the lattice constant or the geometric size of the scatters, one can get phononic crystals or acoustic metamaterials with gradient index and realize many significant physical phenomena, such as acoustic focusing, wave bending, etc. Besides bulk acoustic waves, focusing of Lamb waves in the elastic plate has also been realized by introducing the graded structures.
Meanwhile, the periodically textured rigid plate has attracted much research interest for the quality to support a new kind of surface acoustic waves (SAWs)----spoof surface acoustic waves (SSAWs) in recent years. The SAWs on the periodically corrugated rigid surface originate from the coupling among the acoustic waves localized in the grooves. Therefore, the dispersion of SSAWs mainly depends on the geometrical parameters of the periodic structure rather than the material parameters.
Researchers from the Institute of Acoustics, Chinese Academy of Sciences and Nanjing University recently proposed a rigid surface decorated with an array of grooves with graded widths to get spatial separation of the SSAWs.
The properties of SSAWs on this graded structure are analyzed by the finite element method. The numerical results show that because of the intermodal coupling between forward and backward modes on the graded structure, the SSAWs with different frequencies stop propagating ahead and reflect back at different positions of the graded groove grating (see Fig. 1).
The intensity of acoustic field is effectively enhanced near the propagation-stop position due to the slow group velocity. Compared to the graded grating with varying groove depth, this planar system is easier to implant into the acoustic devices. It is believed that the proposed system has potential applications in acoustic wave coupling and absorption.
Fig. 1 Normalized acoustic amplitude distributions for five different frequencies within the cutoff frequency range. The frequency is indicated in each panel. Each distribution is normalized by the maximumpressure value above the textured surface (Image by JIA).
This research was supported by the National Natural Science Foundation of China (Grant Nos. 11304351 and 11174316) and the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No. XDA06020201).
References:
JIA Han, LU Minghui, NI Xu, BAO Ming, LI Xiaodong. Spatial Separation of Spoof Surface Acoustic Waves on the Graded Groove Grating. Journal of Applied Physics (vol. 116,no.12, September 2014). DOI: 10.1063/1.4895990
Contact:
JIA Han
Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China
Email: hjia@mail.ioa.ac.cn