As the sole dominator of the commercial thermoelectric (TE) market, Bi2Te3‐based alloys play an irreplaceable role in Peltier cooling and low‐grade waste heat recovery. Herein, to improve the relative low TE efficiency determined by the figure of merit ZT, an effective approach is reported for improving the TE performance of p‐type (Bi,Sb)2Te3 by incorporating Ag8GeTe6 and Se. Specifically, the diffused Ag and Ge atoms into the matrix conduce to optimized carrier concentration and enlarge the density‐of‐states effective mass while the Sb‐rich nanoprecipitates generate coherent interfaces with little loss of carrier mobility. The subsequent Se dopants introduce multiple phonon scattering sources and significantly suppress the lattice thermal conductivity while maintaining a decent power factor. Consequently, a high peak ZT of 1.53 at 350 K and a remarkable average ZT of 1.31 (300–500 K) are attained in the Bi0.4Sb1.6Te0.95Se0.05 + 0.10 wt% Ag8GeTe6 sample. Most noteworthily, the size and mass of the optimal sample are enlarged to Ø40 mm‐200 g and the constructed 17‐couple TE module exhibits an extraordinary conversion efficiency of 6.3% at ΔT = 245 K. This work demonstrates a facile method to develop high‐performance and industrial‐grade (Bi,Sb)2Te3‐based alloys, which paves a strong way for further practical applications.
composed of an elastic membrane and rigid disks, can absorb nearly the whole incident sound energy at certain frequencies and their thicknesses are even less than the peak absorption wavelength by two orders of magnitude. Nevertheless, it is susceptible to the mechanical damage because of the soft membrane. The coiled-up space metamaterials [9][10][11][12][13][14][15][16][17][18], which can achieve extreme acoustic absorption performance by increasing the sound path, are another significant type of the acoustic metamaterials. The structure presented by Li et al can absorb the sound with a thickness of 1/223 of the wavelength [9]. However, most of these metamaterials can only obtain good absorption performance within a narrow frequency band
AbstractWe present a theoretical and experimental realization of a thin multi-unit metasurface with multi-order sound absorption that exhibits a continuous near-perfect absorption spectrum in the broadband range of 450 Hz-1360 Hz. The metasurface unit is a perforated composite Helmholtz-resonator (PCHR) that is constructed by inserting one or more separating plates with a small hole into the interior of a Helmholtz resonator (HR). The multi-order sound absorption mechanism can be achieved so that with the original absorption peak and the structural size unchanged, multiple near-perfect peaks are obtained in higher frequencies by a PCHR unit. This extraordinary multi-peak performance is the result of the upgraded multi-degree-of-freedom system with the separating plates, which is explained well by the equivalent acoustic circuit. The specific absorption properties of the PCHR unit are investigated thoroughly with a theoretical approach similar to the plane wave expansion method, and verified via the finite element simulations. On this basis, by precisely balancing the parameters of each unit, the absorption bandwidth of the subwavelength 8-unit metasurface is dramatically broadened about 65% by the proposed mechanism. This work would offer a new guidance for the achievement of the wider absorption band and has great potential in engineering applications.
In this paper, we propose a bilayer plate-type lightweight double negative metasurface based on a new synergetic coupling design concept, by which the perfect absorption, double negative bands, free manipulation of phase shifts with a 2π span and acoustic cloak can be successively realized. Firstly, the synergetic behavior between resonant and anti-resonant plates is presented to construct a bilayer unit in which each component respectively provides a pre-defined function in realizing the perfect absorption. Based on this bilayer structure, a double negative band with simultaneously negative effective mass density and bulk modulus is obtained, which, as a metasurface, can obtain continuous phase shifts almost completely covering a 2π range, thus facilitating the design of a three-dimensional (3D) acoustic cloak. In addition, based on this strong sound absorption concept, a two-dimensional (2D) omnidirectional broadband acoustical dark skin, covering between 800 to 6000 Hz, is also demonstrated through the proposed bilayer plate-type structure form. The proposed design concepts and metasurfaces have widespread potential application values in strong sound attenuation, filtering, superlens, imaging, cloak, and extraordinary wave steering, in which the attributes of strong absorption, double negative parameters or continuous phase shifts with full 2π span are required to realize the expected extraordinary physical features.
A novel membrane-type acoustic metamaterial with a high sound transmission loss (STL) at low frequencies (⩽500Hz) was designed and the mechanisms were investigated by using negative mass density theory. This metamaterial’s structure is like a sandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within two layers of honeycomb cell plates. Negative mass density was demonstrated at frequencies below the first natural frequency, which results in the excellent low-frequency sound insulation. The effects of different structural parameters of the membrane on the sound-proofed performance at low frequencies were investigated by using finite element method (FEM). The numerical results show that, the STL can be modulated to higher value by changing the structural parameters, such as the membrane surface density, the unite cell film shape, and the membrane tension. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.
We propose a multi-order Helmholtz metamaterial with deep-subwavelength thickness in which perfect continuous acoustic absorption is achieved within 400 Hz ∼ 2800 Hz. The metamaterial is composed of multiple detuned cells, each of which is constructed by several perforated plates inserting into the cavity of a Helmholtz resonator (HR) and hence gains multiple individually-tuned high-order peaks besides the original HR peak. By precisely designing each peak of the cells, the extra-broadband perfect absorption can be obtained. This kind of metamaterials could possess broad applications in noise control engineering owing to the extraordinary absorption performance and high flexural stiffness.
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