One Way Effect In Acoustic Band-gap Material

Recently acoustic band-gap materials, including phononic crystal and acoustic metamaterial, have drawn much attention due to its inherent novel and unique properties and effects. Phononic crystals are a kind of artificial periodic composite material, which can produce the prohibition due to the Bragg scattering and Mie's scattering. While acoustic metamaterial could produce negative effective density and modulus due to local resonance. Acoustic band-gap materials have paved the way for the controlling of acoustic waves propagation. Therefore, this kind of specially-designed structure has demonstrated its potential in acoustic devices like ultrasonic filters, sensors and ultrasonic imaging systems.This thesis is mainly focused on studying, both in theory and experiment, the one way transmission and propagation in sonic crystals, lamb wave phononic crystals and 1D grating with single subwavelength apertures. Main work in this thesis is described as follows: 1. One way transmission of acoustic wave in asymmetric sonic crystal has been studied in theory and experiment. We utilized a sonic-crystal-based acoustic diode that had broken spatial inversion symmetry and experimentally realized sound unidirectional transmission in this acoustic diode. Based on EFS and band structure analysis, the spatial jump mechanism has been proposed and verified in experiment. In addition, we have discussed the contribution of high order diffraction wave. Different from non-reciprocity due to the nonlinear acoustic effect and broken time reversal symmetry, this new model leads to a one-way effect with higher efficiency, broader bandwidth, and much less power consumption, showing promising applications in various sound devices.2. A tunable sonic crystal has been constructed using square steel rods. One way phenomenon in this composite artificial material could be effectively by simply changing the rotation direction of all steel rods. Through the rotation, the band structure could be manipulated, which would cause the disappearance of one way effect in the second band-gap. Based on the controllable structure, one way transmission could be simply turned "on" or "off'.3. Time reversal symmetry and spatial inversion symmetry have been discussed in various models of one way or non-reciprocal effect. The one way transmission or reflection demands both the breaking of time reversal symmetry and spatial inversion symmetry. Including the time reversal of acoustic evanescent wave, several time reversal symmetry breaking mechanisms have been discussed in detail.4. With the help of Finite Element Method (FEM), Lamb wave propagating in phononic crystal has been analyzed. Both the Bragg scattering and local resonance could induce the band-gap. Various structures are discussed, including plate with periodic stubbed surface and holes. On a plate with periodic holes, band-gap exists inΓX direction. Combining diffraction structure with this directional band-gap, one way effect of Lamb waves is simulated. Besides, the experimental setup has been discussed, including Laser Ultrasonic Detection. In addition, the band structure of FCC hypersonic crystal is calculated.5. Sub-wavelength extraordinary acoustic transmission is studied both theoretically and experimentally. With Laser Ultrasonic Detection System, the acoustic waves propagating along the interface, which make great contribution to the extraordinary acoustic transmission, have been detected in both acoustic grating and single aperture structure. Most importantly, one way extraordinary transmission and beaming effect has been studied theoretically in single aperture with asymmetric grooves. A rigorous analytical model has been proposed to study this one way effect, which is attributed to groove resonance, slit resonance and acoustic surface wave.Above all, one way and non-reciprocal transmission in artificial acoustic band-gap materials have been studied experimentally and theoretically. Research in this field involves not only frontier physics, including PT (Parity-Time) symmetry, non-reciprocity, but also the preparation, measurements and investigation on high frequency acoustic devices. The study of artificial acoustic band-gap materials will become the trend of studying artificial periodic materials, showing great promise in both theoretical explorations and practical applications.