Air-coupled method to investigate the lowest-order antisymmetric Lamb mode in stubbed and air-drilled phononic plates

Dongbo Zhang,Jinfeng Zhao,Libing Li,Zheng Zhong,Yongdong Pan,Jianxin Wei,Bernard Bonello

doi:10.1063/1.4962222

Abstract

In this work, we applied a robust and fully air-coupled method to investigate the propagation of the lowest-order antisymmetric Lamb (A0) mode in both a stubbed and an air-drilled phononic-crystal (PC) plate. By measuring simply the radiative acoustic waves of A0 mode close to the plate surface, we observed the band gaps for the stubbed PC plate caused by either the local resonance or the Bragg scattering, in frequency ranges in good agreement with theoretical predictions. We measured then the complete band gap of A0 mode for the air-drilled PC plate, in good agreement with the band structures. Finally, we compared the measurements made using the air-coupled method with those obtained by the laser ultrasonic technique.

Highlights

As a result of their periodicity, phononic crystals (PC’s) exhibit absolute band gaps, i.e. frequency regions over which the propagation of elastic waves is forbidden whatever the incident direction
We further computed the transmission through the five unit cells of the PC shown in Fig. 1, when A0 mode propagates along the x-axis.[30,31]
The band structures of the designed PC plate that we show in Fig. 5(a) features a large complete band gap caused by the Bragg mechanism within the frequency range [197, 251] kHz

Summary

Introduction

As a result of their periodicity, phononic crystals (PC’s) exhibit absolute band gaps, i.e. frequency regions over which the propagation of elastic waves is forbidden whatever the incident direction These Bragg gaps, that open up at the Brillouin zone (BZ) boundaries when the wavelength is comparable to the period, originate from the destructive interferences that the waves undergo when they are multiply scattered by the periodic array of inclusions.[1,2,3,4,5] Another type of gap originating from a distinct physical process can appear in the dispersion curves when the scatters behave like local resonators. This coupling effect which occurs at oblique incidence, was generally not investigated in former studies where only the normal

Methods

Results

Conclusion