Recently, sensors that can imitate human skin have received extensive attention. Capacitive sensors have a simple structure, low loss, no temperature drift, and other excellent properties, and can be applied in the fields of robotics, human-machine interactions, medical care, and health monitoring. Polymer matrices are commonly employed in flexible capacitive sensors because of their high flexibility. However, their volume is almost unchanged when pressure is applied, and they are inherently viscoelastic. These shortcomings severely lead to high hysteresis and limit the improvement in sensitivity. Therefore, considerable efforts have been applied to improve the sensing performance by designing different microstructures of materials. Herein, two types of sensors based on the applied forces are discussed, including pressure sensors and strain sensors. Currently, five types of microstructures are commonly used in pressure sensors, while four are used in strain sensors. The advantages, disadvantages, and practical values of the different structures are systematically elaborated. Finally, future perspectives of microstructures for capacitive sensors are discussed, with the aim of providing a guide for designing advanced flexible and stretchable capacitive sensors via ingenious human-made microstructures.

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Tungsten disulphide (WS), which exhibits excellent saturable absorption properties, has attracted much attention in the applications of photonic devices. In this paper, WS is applied for the preparation of a saturable absorber (SA). Using the pulsed laser deposition (PLD) method, WS is deposited on the side surface of the tapered fiber. In order to obtain larger non-linearity of the SAs with evanescent wave interaction, the tapered fiber had a smaller waist diameter and longer fused zone. Gold film was deposited on the fiber-taper WS SAs to improve their reliability and avoid oxidation and corrosion. Employing the balanced twin-detector method, the modulation depth of the fiber-taper WS SAs was measured to be 17.2%. With the fiber-taper WS SA, a generated pulse with 246 fs duration and a 57 nm bandwidth was obtained at 1561 nm. The electrical signal to noise ratio was better than 92 dB. To our knowledge, the pulse duration was the shortest among the reported all-fiber lasers with transition metal dichalcogenide (TMD) SAs. These results indicate that fiber-taper WS SAs with smaller waist diameter and longer fused zone are promising photonic devices for ultrashort pulse generation in all-fiber lasers.

Polymer nanocomposites are a promising substitute for energy-storage dielectric materials in pulsed power systems. A barium titanate/polyvinylidenefluoride (BT/PVDF) nanocomposite is one of the most widely studied composite systems due to its comprehensive excellent dielectric properties. As the dielectric response of nanocomposites depends strongly on the size of the fillers, in this study, BT/PVDF nanocomposites with 92.3 nm, 17.8 nm and 5.9 nm BT particle fillers are fabricated to reveal the particle size effect of the fillers on the energy storage performance of the polymer nanocomposites. Owing to the small particle size and good dispersibility of the nanofillers, the nanocomposites with smaller BT particles show more uniform and denser microstructures. Moreover, with the increase of the filler fraction, the dielectric results indicate a breakdown strength enhancement in the nanocomposites with sub-20 nm BT fillers, which is quite different from the nanocomposites with normal fillers, and therefore leads to superior energy storage performance. This study provides experimental evidence for the application of ultrafine nanofillers in the nanocomposite for future energy storage systems.

The search for efficient and cost‐effective catalysts for bifunctional oxygen reduction and evolution reaction (ORR and OER) is highly demanded because of the sluggish four‐electron transfer involved redox reactions in Zn–air batteries (ZABs). Herein, (N, P) codoped CoS2 nanoclusters embedded inside TiO2 nanoporous films (denoted as N, P/CoS2@TiO2 NPFs) are synthesized as novel bifunctional ORR/OER catalysts for ZABs. The catalytic activity and stability are promoted by the (N, P)‐dopants due to the enhanced conductivity, increased active surface area, and facilitated reaction kinetics. The N, P/CoS2@TiO2 NPFs exhibit exceptional onset potentials of 0.91 and 1.41 V for ORR and OER, respectively. When used as cathodes in ZABs, the N, P/CoS2@TiO2 NPFs exhibit a reduced charge–discharge gap of 0.8 V at 10 mA cm−2 and a stable cycling performance over 130 h, surpassing the conventional Pt/C+IrO2 catalysts. Moreover, the assembled ZABs delivering a specific capacity of 610 mAh g−1 can be used for flexible devices. This work provides a path for the rational design of bifunctional electrocatalyst for ZABs.

A novel metamaterial filter with stable passband performance based on frequency selective surface AIP Advances 4, 077114 (2014); 10.1063/1.4890108Self-biased planar millimeter wave notch filters based on magnetostatic wave excitation in barium hexagonal ferrite thin films Appl. Phys. Lett. 97, 173502 (2010); 10.1063/1.3504256Determination of magnetic properties of ultrathin iron films using microwave stripline technique

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region. Basically, all-dielectric metamaterials are composed of polymers, dielectrics, ferrites, or composite materials. [20-22] The unusual electromagnetic properties of all-dielectric metamaterials not only derive from their artificial structure, but also originate directly from the materials, revealing an approach to designing metamaterials with more freedom. [23] Since the initial proposal of all-dielectric metamaterials, various realization mechanisms have been studied and reported. [24-26] The most classical mechanism is based on the so-called Mie-resonance theory, and has been studied extensively. [27-29] In this strategy, dielectric particles with relatively high permittivity are used to generate strong magnetic or electric resonance through electromagnetic wave interaction. Therefore, a negative permeability or permittivity can be produced by the oscillation of the resulting magnetic or electric dipole. This mechanism is simple and versatile, and is generally adopted for the realization of all-dielectric metamaterials with low losses. [30] Ferromagnetic resonance (FMR) theory is another classical realization mechanism for all-dielectric metamaterials. [31,32] When the ferromagnetic resonance of the ferrite takes place, a negative permeability appears. Many factors can influence the FMR of the magnetic materials, including the bias magnetic field, magnetocrystalline anisotropy field, and demagnetization field. Hence, ferrite metamaterials with dual-band, multiband, or tunable properties can be obtained, providing a way to resolve the narrow band problem. Besides, mechanisms such as indefinite media or crystal lattice vibration have also been used to realize all-dielectric metamaterials. [33,34] When determining the realization mechanism for an all-dielectric metamaterial, one crucial factor must be considered: the choice of a fabrication method. Moreover, to achieve different performances, many types of materials with specific electromagnetic properties are used to prepare all-dielectric metamaterials. [35] Hence, researchers have developed various techniques for the fabrication of all-dielectric metamaterials derived from different materials. [36-40] In addition, the fabrication requirements are quite different for all-dielectric metamaterials operating at frequencies ranging from the microwave to optical regions. In particular, the size of the metamaterial unit cell is much smaller than the operational wavelength, making the fabrication technology for all-dielectric metamaterials become the key to their further application. Here, we present a comprehensive review of the various techniques used to produce all-dielectric metamaterials. We review the existing fabrication technologies for microwave, terahertz, and optical all-dielectric All-dielectric metamaterials with low loss are a rapidly developing research hotspot in the field of metamaterials, and offer additional design freedom for electromagnetic devices. Many types of fabrication techniques are used to prepare all-dielectric metamaterials, so as t...