The frequency response of the multilayered acoustic cloak made of isotropic materials is analyzed by the acoustic scattering theory. When concealing a rigid cylinder, the acoustic total scattering cross section (TSCS) monotonically increases with frequency. If concealing penetrable materials, the cloak-induced reverse-phase monopole and dipole resonances can increase the TSCS around the resonant frequencies, while the in-phase monopole resonance decreases the TSCS. The results are confirmed by numerical simulations of the finite element method. © 2008 American Institute of Physics.

We present theoretically a type of one-dimensional _1D_ structured ultrasonic metamaterial that exhibits a forbidden band where both the effective dynamic density and bulk modulus are simultaneously negative. The material consists of a 1D array of repeated unit cells with shunted Helmholtz resonators. The transmission coefficient, wave vector, negative dynamic density, and modulus are determined by means of the acoustic transmission line method (ATLM). The double negativity in the effective dynamic density and bulk modulus is an acoustic counterpart of negative permittivity and permeability in the electromagnetic metamaterials. The double negative band is ascribed to the localresonance. In order to confirm the ATLM results, we further calculate the field intensity, phase distribution, and transmission coefficient using the finite element method. In addition, the influences of some essential geometric acoustic parameters on the transmission properties, such as periodic constant L, are also discussed.

Thermal diffusivity has been investigated in ordered double perovskite Sr2FeMoO6 measn of transient surface grating technique in te temperatue rage of 300-450K. The thermal diffusivity showas an apprecialve decrese form 39mm/2s at 300K to 37mm/2 at 360K in the ferromagnetic phase, and then steeply drops to 10mm2/s with furtherincreasing temperature above the critical temperature Tc～380K. Such an abrupt decrease of the thermal diffusivity has been ascribed to the structural phase transition at Tc. We further investigate the lattice effect on the thermal diffusivity in A2FeMoO6 (A=Ca, Sr and Ba) by substitution of CA2+or Ba2+ ions for Sr2+ions at 300K. We find that the thermal difusivity increases form 35mm2/s for A=Ca to 41mm2/s for A=Ba. Considering the change of the Fe-O-Mo bond angle and hence the wider one-electrom bandwidth W.

An acoustic cloak with concentric alternating layered structure is designed with homogeneous isotropic materials on the basis of effective medium theory. The cloak possesses low-reflection and power-flow bending properties for different shapes of wavefront both in far-and near-fields, which could perfectly approximate the ideal cloak with inhomogeneous and anisotropic distribution of material parameters. © 2008 American Institute of Physics.