In this Letter, a new frequency-selective absorber (FSA) is presented that has wide-band transmission/absorption/reflection reduction responses. The presented absorber is completed by lossy cross-dog bone and lossless second-order frequency-selective surfaces (FSSs). The modal interaction pole generated by the lossy array is employed to achieve a wide-band transmission. Three absorption bands are combined to realize a continuous stop-band with high absorptivity. Furthermore, the improved absorber structure is investigated to reduce the strong reflection between the absorption and transmission bands. The 10 dB reflection reduction is obtained with a fractional bandwidth of 126.4%. Meanwhile, the - 3 dB fractional pass-band width is 41.3% with minimum insertion loss (IL) of 0.37 dB. The absorption bandwidth of 91.5% is provided with at least 90% absorptivity. The distance between the lossy and lossless layers is only 0.08 $\lambda_L$ L at the lowest operating frequency. Finally, the proposed design is validated by a good agreement between the numerical simulations and experimental measurements.

Electrospinning has revolutionized the field of semiconductor metal oxide (SMO) gas sensors, which are pivotal for gas detection. SMOs are known for their high sensitivity, rapid responsiveness, and exceptional selectivity towards various types of gases. When synthesized via electrospinning, they gain unmatched advantages. These include high porosity, large specific surface areas, adjustable morphologies and compositions, and diverse structural designs, improving gas-sensing performance. This review explores the application of variously structured and composed SMOs prepared by electrospinning in gas sensors. It highlights strategies to augment gas-sensing performance, such as noble metal modification and doping with transition metals, rare earth elements, and metal cations, all contributing to heightened sensitivity and selectivity. We also look at the fabrication of composite SMOs with polymers or carbon nanofibers, which addresses the challenge of high operating temperatures. Furthermore, this review discusses the advantages of hierarchical and core-shell structures. The use of spinel and perovskite structures is also explored for their unique chemical compositions and crystal structure. These structures are useful for high sensitivity and selectivity towards specific gases. These methodologies emphasize the critical role of innovative material integration and structural design in achieving high-performance gas sensors, pointing toward future research directions in this rapidly evolving field.

The miniaturization and low power consumption characteristics of RF MEMS (Radio Frequency Microelectromechanical System) switches provide new possibilities for the development of microsatellites and nanosatellites, which will play an increasingly important role in future space missions. This paper provides a comprehensive review of RF MEMS switches in satellite communication, detailing their working mechanisms, performance optimization strategies, and applications in reconfigurable antennas. It explores various driving mechanisms (electrostatic, piezoelectric, electromagnetic, thermoelectric) and contact mechanisms (capacitive, ohmic), highlighting their advantages, challenges, and advancements. The paper emphasizes strategies to enhance switch reliability and RF performance, including minimizing the impact of shocks, reducing driving voltage, improving contacts, and appropriate packaging. Finally, it discusses the enormous potential of RF MEMS switches in future satellite communications, addressing their technical advantages, challenges, and the necessity for further research to optimize design and manufacturing for broader applications and increased efficiency in space missions. The research findings of this review can serve as a reference for further design and improvement of RF MEMS switches, which are expected to play a more important role in future aerospace communication systems.

In recent years, advancements in the Internet of Things (IoT), manufacturing processes, and material synthesis technologies have positioned flexible sensors as critical components in wearable devices. These developments are propelling wearable technologies based on flexible sensors towards higher intelligence, convenience, superior performance, and biocompatibility. Recently, two-dimensional nanomaterials known as MXenes have garnered extensive attention due to their excellent mechanical properties, outstanding electrical conductivity, large specific surface area, and abundant surface functional groups. These notable attributes confer significant potential on MXenes for applications in strain sensing, pressure measurement, gas detection, etc. Furthermore, polymer substrates such as polydimethylsiloxane (PDMS), polyurethane (PU), and thermoplastic polyurethane (TPU) are extensively utilized as support materials for MXene and its composites due to their light weight, flexibility, and ease of processing, thereby enhancing the overall performance and wearability of the sensors. This paper reviews the latest advancements in MXene and its composites within the domains of strain sensors, pressure sensors, and gas sensors. We present numerous recent case studies of MXene composite material-based wearable sensors and discuss the optimization of materials and structures for MXene composite material-based wearable sensors, offering strategies and methods to enhance the development of MXene composite material-based wearable sensors. Finally, we summarize the current progress of MXene wearable sensors and project future trends and analyses.

In this Letter, an active second-order frequency-selective surface (AFSS) that features a switchable wide pass-band is proposed. Compared to other multi-layer feeding structures, only one layer of FSS is elaborately reconfigured in this design, whose full planar symmetry structure is not destroyed, to achieve the desired all-polarized controlled behavior. The presented design provides good responses under different incident angles and polarizations. The fulfilled structure is composed of three FSS layers and is controlled by semiconductor switches. When the switches are in OFF-state, the proposed design acts as a high-transmittance second-order filter with a low ripple level, whose -0.5 dB passband width is over 24.4% and minimum insertion loss is only 0.1 dB. By switching the semiconductors to ON-state, the unit cells of the top FSS layer are short-connected, which leads to an ultra-wideband shielding behavior from 0 to 10 GHz. Moreover, the proposed structure presents consistent responses under 0°-90° rotation polarizations. Both filter and shielding responses can be obtained up to the 60° incidence. Finally, a prototype is fabricated and measured, and the desired wideband, high-efficiency, wide-angle, and polarization-insensitive switchable performances are obtained through equivalent-circuit calculations, numerical simulations, and experimental measurements.