We investigate a one-dimensional acoustic metamaterial with a refractive index of near zero(RINZ) using an array of very thin elastic membranes located along a narrow waveguide pipe. The characteristics of the effective density, refractive index, and phase velocity of the metamaterial indicate that, at the resonant frequency fm, the metamaterial has zero mass density and a phase transmission that is nearly uniform. We present a mechanism for dramatic acoustic energy squeezing and anomalous acoustic transmission by connecting the metamaterial to a normal waveguide with a larger cross-section. It is shown that at a specific frequency f_1, transmission enhancement and energy squeezing are achieved despite the strong geometrical mismatch between the metamaterial and the normal waveguide. Moreover, to confirm the energy transfer properties, the acoustic pressure distribution, acoustic wave reflection coefficient, and energy transmission coefficient are also calculated. These results prove that the RINZ metamaterial provides a new design method for acoustic energy squeezing,super coupling, wave front transformation, and acoustic wave filtering.
The conjunction of 'Chaotic Cavity Transducer(CCT)' focusing with Nonlinear Elastic Wave Spectroscopy(NEWS)methods has been discussed in the detection of the localization of micro-damage.CCT focusing is a combination process of CCT with the techniques of acoustic Time Reversal(TR)or Inverse Filter(IF),which can improve the ability of localization. In order to improve the quality of focalization,in the experimental process the chirped excitation source signal and inverse filtering techniques have been used.A focusing process in a non-reverberant composite plate sample and an image of a crack in a steel sample demonstrate the focalization ability and high efficiency of imaging of the combination of CCT with NEWS,and proves that CCT can efficiently overcome the problems of 'phantom' image and increasement of the strain at the boundary of medium.
