Research On One-dimension Acoustic Black Hole Structure Based On Laser Ultrasonic Technique

Recently,with the development of sound physical,the technology of manipulating wave makes it possible to develop a new method to damp sound and vibration.As a representative structure of manipulating wave,the ‘Acoustic Black Hole'(ABH)structure is paid attention to and researched widely.When flexural wave propagates in ideal ABH structures,it will focus at the sharp edge of the structure and never reflect back.However,the manufactured ABH structures often have a small truncation at the sharp edge,which destroys the ABH structure's ideal property of zero reflection.By depositing thin strips of absorbing layers on surface of the ABH structure,the situation can be improved and the unwanted sound and vibration can be dissipated.The existing research about ABH effect is mainly on its efficiency,where there is little research on its generation mechanism.What's more,research on influence of the small truncation and the damping layer has its limitation,which may be not good for optimizing ABH structures.In this paper,laser ultrasonic technology is applied to research the ABH effect,by which the structure is experimented and studied in time domain.Firstly,visualization of flexural wave field is realized,and the propagation of flexural wave on the ABH structure is shown in time domain.The laser ultrasonic experimental system is designed and built in this paper.More,a method which uses the theory of virtual transducer is proposed to improve traditional laser ultrasonic technology and simulate plane wave.Secondly,change of flexural wave's representative characteristics and the generation mechanism of ABH effect are researched.By the method of wavelet transform and virtual transducer,the change of flexural wave's velocity,amplitude and ABH structure's effect of energy focalization are researched.Finally,the reflection coefficient is chosen to be an evaluating criterion which evaluates some parameters' influence to one-dimension ABH effect.Based on separation of the incident and reflected wave,a new method calculating the reflection coefficient is proposed.By comparing reflection coefficient of one-dimension ABH structure on different situations,the influence of the small truncation and the damping layer is researched for optimizing the choice of these parameters to get the best result.