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.

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.

Three kinds of the periodical structures are designed as low-pass, high-pass, and band-pass filters for elastic wave. The theoretical simulations have proved that the periodical surface slots can act as a ow-pass filter for elastic wave. With increasing depth of the surface periodical structure in the sample,he cutoff frequency of the low-pass filter is decreased. Unlike the surface periodical structure, the eriodical subsurface structure can work as a high-pass filter for elastic wave. The cutoff frequency of the igh-pass filter is suppressed by the increase of the subsurface structure thickness. When the two eriodical structures are combined together, the band-pass filter is obtained, in which the pass band is etermined by the cutoff frequencies of the low-pass and high-pass filters. © 2009 American Institute of Physics. (DOI: 10.1063/1.3131043)

The authors demonstrate that a class of ultrasonic metamaterial, which is composed of subwavelength resonant units built up by parallel-coupledelmholtz resonators with identical resonant frequency, possesses broadocally resonant forbidden bands. The bandwidths are strongly dependent onhe number of resonators in each unit. The broadening of bands is ascribedo the change of effective acoustic impendence. The coupling effects onhe wave vector and negative dynamic modulus are discussed. Numericalimulations by finite element method further confirm the theoreticalesults. © 2008 American Institute of Physics.DOI: 10.1063/1.2839401

We have observed a photoinduced hphase transition (PIPT) in a spin-crossover Fe(II) complex Nafion-[Fe(Htrz)3] film (Nafion is an ion exchange polmer film, and Htrz-1, 2, 4-1H-triazole) from a low-spin (LS) state (S=0) to a high-spin (HS) state (S=2) below 150K. The phototransferred HS state relaxed to the initial LS state, exhibiting a nonexponeential time behavior, which has bee interpreted in terms of the ciical nucleation and subsequent growth of the LS clusters. We have also observed that the decay time Tc is approximately temperature independent inthe low temperature range of 4.2-20K, and then decreases exponentially with temperature.

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.

The second-harmonic sound beam nonlinearly generated by a conical source is analytically described It is shown that the radial second-hamonic beam is distributed as the Bessel function and independent of the porpagation distance. Anoher important feature is that the beamwidth of the second-harmonic component is just equal to 1/2 time that of the fundamental, not 1/√2 times in the general cases. A potential application of this beam in the acoustic noninearity parameter B/A imaging or measurement is also discussed.

The themal diffusivity has been ivestigatedin double perovskite Sr2MMoO6 (M=Fe, Mn and Co) by means of the mirage effect. We have found that the thermal diffusivity of metallic Sr2FeMoO6 is 0.39 cm2/s, wihich is larger than that (0.33cm2/s) of insulating Sr2MnMoO6 and Sr2CoMoO6. We further investigate the substitution effects of the La3+ions for the Sr2+ions in Sr2FeMoO6 and Sr2MnMoO6, and have found that the thermal diffusivities of both samples significantly increase with the La cncentration. Such an enhancement of the thermal diffusivities has been a scribed ot occupation of the extra itinerant electrons on te conducion Mo4d band.

Electronic structures of halogen bridged mixed-valence (MV) complexes Cs2Au2X6 (X=I, Br, and Cl)have been investigated by means of reflectivity measurements. We have observed five polarization-dependent opti-cal transitions in the energy range of 0.6-5.5eV. The lower-lying three bands below～3eV are due to the intermolecular transitions from AuX2 to Aux4 molecules, while the others are assigned to the intramolecular transitions. The optical ap Egap increases from 1.31 eV for X=I to 2.04 eV for X=Cl, due to enhancement of the nearest-neighboring Coulomb repulsion V and the Jahn-Teller distortion of AuX4 (S). We further investi-gated extemal pressure effects on the electronic state, and found pressure-induced disappearance of the Raman-active Au-Br stretching modes, which indicates an electronic phase transition from the MV state to a single-valence (SV) state.

Two kinds of cadmium sulfide (CdS) particulate films have been generated in situ by exposing stearic acid (SA) Langmuir monolayer at the air-aqueous CdCl2 interface to hydrogen sulficde(H2S) gas: particulate films composed of oriented rodlike nanocrystals (A-type particulate films), and those of dotlike nanocrystals which formed a stripelike domain with straight edges aligned with 6-fold symmetry(B-type particulate fims). The SA-coated CdS particulated films were transferred to a solid substrate and examined by transmission electron microscopy (TEM) and photoacoustic spectroscopy (PAS). The dark field image and the transmission particulte fims in detail. The PAS of the CdS particulate fims coposed of the oriented rodlike nanocrystals shows a new peak at 417.5nm. This peak implies some new physical phenomena corresponding to the oredred alignmert of the semiconductor nanocrystals. which exists in the ordered nanosystems. The novel synthesis method described here leads to the fabricaiton of the highly oriented semiconductor quantum wires and provides a new method to investigate the structure of the Langmuir monolayer at the air-water interface.