The attenuation of low-frequency sound has been a challenging task because the intrinsic dissipation of materials is inherently weak in this regime. Here we present a thin-film acoustic metamaterial, comprising an elastic membrane decorated with asymmetric rigid platelets that aims to totally absorb low-frequency airborne sound at selective resonance frequencies ranging from 100-1,000 Hz. our samples can reach almost unity absorption at frequencies where the relevant sound wavelength in air is three orders of magnitude larger than the membrane thickness. At resonances, the flapping motion of the rigid platelets leads naturally to large elastic curvature energy density at their perimeter regions. As the flapping motions couple only minimally to the radiation modes, the overall energy density in the membrane can be two-to-three orders of magnitude larger than the incident wave energy density at low frequencies, forming in essence an open cavity.

Electrorheology (ER) denotes the control of a material's flow properties (rheology) through an electric field. We have fabricated electrorheological suspensions of coated nanoparticles that show electrically controllable liquid-solid transitions. The solid state can reach a yield strength of 130 kPa, breaking the theoretical upper bound on conventional ER static yield stress that is derived on the general assumption that the dielectric and conductive responses of the component materials are linear. In this giant electrorheological (GER) effect, the static yield stress displays near-linear dependence on the electric field, in contrast to the quadratic variation usually observed. Our GER suspensions show low current density over a wide temperature range of 10-120 degrees C, with a reversible response time of <10 ms. Finite-element simulations, based on the model of saturation surface polarization in the contact regions of neighbouring particles, yield predictions in excellent agreement with experiment.

BackgroundMicrofluidics is a science and technology that precisely manipulates and processes microscale fluids. It is commonly used to precisely control microfluidic (10 −9 to 10 −18 L) fluids using channels that range in size from tens to hundreds of microns and is known as a "lab-on-a-chip" [1][2][3][4]. The microchannel is small, but has a large surface area and high mass transfer, favoring its use in microfluidic technology applications including low regent usage, controllable volumes, fast mixing speeds, rapid responses, and precision control of physical and chemical properties [1,5,6]. Microfluidics integrate sample preparation, reactions, separation, detection, and basic operating units such as cell culture, sorting and cell lysis [7]. For these reasons, interest in OOAC has intensified [8]. OOAC combines a range of chemical, biological and material science disciplines [9] and was selected as one of the "Top Ten Emerging Technologies" in the World Economic Forum [10].OOAC is a biomimetic system that can mimic the environment of a physiological organ, with the ability to regulate key parameters including AbstractThe organ-on-a-chip (OOAC) is in the list of top 10 emerging technologies and refers to a physiological organ biomimetic system built on a microfluidic chip. Through a combination of cell biology, engineering, and biomaterial technology, the microenvironment of the chip simulates that of the organ in terms of tissue interfaces and mechanical stimulation. This reflects the structural and functional characteristics of human tissue and can predict response to an array of stimuli including drug responses and environmental effects. OOAC has broad applications in precision medicine and biological defense strategies. Here, we introduce the concepts of OOAC and review its application to the construction of physiological models, drug development, and toxicology from the perspective of different organs. We further discuss existing challenges and provide future perspectives for its application.

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The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. Based on this concept, researchers have predicted valley-Hall topological insulators that could support valley-polarized edge states at non-trivial domain walls. Recently, several kinds of photonic and sonic crystals have been proposed as classical counterparts of valley-Hall topological insulators. However, direct experimental observation of valley-polarized edge states in photonic crystals has remained difficult until now. Here, we demonstrate a designer surface plasmon crystal comprising metallic patterns deposited on a dielectric substrate, which can become a valley-Hall photonic topological insulator by exploiting the mirror-symmetry-breaking mechanism. Topological edge states with valley-dependent transport are directly visualized in the microwave regime. The observed edge states are confirmed to be fully valley-polarized through spatial Fourier transforms. Topological protection of the edge states at sharp corners is also experimentally demonstrated.

less than one decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) have rapidly been achieved to 22.7%, i.e., a level that is nearly on par with traditional silicon solar cells. [2] In addition, efficient, flexible, [3] color-tunable, and semitransparent PSCs [4] have also been demonstrated, showing the merit for application in portable devices and building-integrated photovoltaics (BIPV). Therefore, PSCs are considered to be the most promising candidate for next-generation high efficiency solar cell technology, and they hold great potential in photovoltaic market in the near future.Perovskite has a general ABX 3 structure. For newly emerged organic-inorganic halide perovskites for photovoltaic application, A represents methylammonium (namely, CH 3 NH 3 + , abbreviated as MA + ), formamidinium (namely, CH(NH 2 ) 2 + , abbreviated as FA + ), and Cs + (including its mixture with MA + and/or FA + ), B represents metal ions, including Pb 2+ and/or Sn 2+ , and X represents halide anions, such as I − , Br − , and Cl − (including the mixture of them). [1f,5] The basic structures of PSCs are shown in Figure 1a. Generally, there are two kinds of structures, namely, mesoporous structure and planar structure. A mesoporous-structured PSC consists of transport conductive oxide (TCO)/compact layer TiO 2 (cl-TiO 2 )/mesoporous layer (TiO 2 or Al 2 O 3 )/perovskite/ hole transport layer (HTL)/metal anode. The planar-structured PSC has an architecture: cathode/electron transport layer (ETL)/ perovskite/HTL/anode for conventional structure or anode/ HTL/perovskite/ETL/cathode for inverted structure. Both of the mesoporous and the planar PSCs are reported to yield high PCE. [6] As can be seen from Figure 1a, a PSC consists of several layers, including electrodes (cathode and anode), absorber layer, and carrier transport layers. The absorber layer is basically metal halide perovskite (such as MAPbI 3 and FAPbI 3 ), [7] mixed metal halide perovskite (such as FA 1−x MA x Pb(I 1−y Br y ) 3 ), [8] or inorganic perovskite (CsPbI 3 ). [9] For the ETL or HTL, it can be either inorganic (such as TiO 2 , SnO 2 , ZnO, CuI, NiO, etc.) [10] or organic material (such as phenyl-C61-butyric acid methyl ester (PCBM), fullerene (C 60 ), 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), poly(3,4ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), copper(I) thiocyanate (CuSCN), polytriarylamine (PTAA), poly(3-hexylthiophene) (P3HT), etc.). [11] Figure 1b simply shows a schematic representation of the interfaces and the energy levels in a PSC with planar structure (regardless of The rapid progress of organic-inorganic metal halide perovskite solar cells (PSCs) has attracted broad interest in photovoltaic community. A typical PSC consists of anode/cathode, a perovskite layer as absorber, and carrier transport layer(s) (electron/hole transport layer(s)), which are stacked together, resulting in multi-interfaces between these layers. Charge extraction and transport in these solar...

A review of microfabrication techniques and dielectrophoretic microdevices for A review of microfabrication techniques and dielectrophoretic microdevices for particle manipulation and separation particle manipulation and separation

We demonstrate that electromagnetic waves can transmit with unit transmittance through a slab of negative-permittivity media sandwiched between two identical slabs with high permittivity, although each single slab is nearly opaque. This type of transparency is accompanied by high magnetic fields, and is robust against incidence angles. Microwave experiments, in excellent agreement with finite-differencetime-domain simulations, are performed to successfully realize this idea. DOI: 10.1103/PhysRevLett.94.243905 PACS numbers: 42.25.Bs, 41.20.Jb, 78.20.2e Induced high transmittance of electromagnetic (EM) waves through opaque media has always been fascinating. Such a phenomenon is typically associated with the excitation of some kind of resonances. For example, the excitation of surface plasmons (SP's) [1], say using prism couplers, can induce high transmission through an opaque metallic film [2]. Excitation of SP's can also be enabled by the Bragg scattering of periodical surface structures, which explains Ebessen et al.'s experiment of high transmissions [3] through metal films with an array of subwavelength air holes [4][5][6][7][8]. High transmission through metallic films with thin slits can also be induced by Fabry-Perot (FP) resonance of propagating waves inside the slits [9][10][11]. We propose here another mechanism, different from the SPaided [2 -8] and FP ones [9][10][11], to make a classically opaque flat slab with a negative " (allowing evanescent waves only) perfectly transparent. We will discuss the conditions to realize this phenomenon and the associated unusual characteristics. Specifically, we show the perfect transparency to be accompanied by high magnetic fields at interfaces, and robust against varying incidence angles. We have performed microwave experiments and finitedifferent-time-domain (FDTD) simulations [12] to successfully realize this idea.While our idea is motivated by effective medium theory (EMT), the final conclusion is drawn from measurements of real samples and FDTD simulations. Let us consider a homogeneous layer B of thickness d 2 with " 2 < 0, which by itself is opaque. Consider first a double layer structure combining this layer with another homogeneous layer A with " 1 > 0 and thickness d 1 . Within the effective medium framework, the AB structure will become transparent when "For a circular frequency ! and fixed parallel k component k k , we obtain a 2 2 transfer matrix Q !; k k , by which both the transmission coefficient t Q 11 ÿ Q 12 Q 21 =Q 22 and reflection coefficient r ÿQ 21 =Q 22 can be calculated [13]. If there is no absorption, perfect transmission (T jtj 2 1) appears when Q 21 0. For this AB structure, the criterion of perfect transmission at normal incidence (k k 0) is