We present a combined experimental and theoretical study of valley populations in the valence bands of trilayer ${\mathrm{WSe}}_2$. Shubnikov–de Haas oscillations show that trilayer holes populate two distinct subbands associated with the $K$ and $\mathrm{\Gamma }$ valleys, with effective masses $0.5m_e$ and $1.2m_e$, respectively; $m_e$ is the bare electron mass. At a fixed total hole density, an applied transverse electric field transfers holes from $\mathrm{\Gamma }$ orbitals to $K$ orbitals. We are able to explain this behavior in terms of the larger layer polarizability of the $K$ orbital subband.

In this study, we propose a broadband and wide-incidence angle optically transparent metamaterial absorber (MMA) using eight-resistive-arm cells. The MMA uses soda-lime glass as the substrate and indium tin oxide (ITO) as the conductive pattern. Leveraging these materials, the proposed MMA achieves optical transparency of over 78.06% at 550 nm. Simulation results indicate an absorption ratio exceeding 90% in the 7.49-10.01 GHz band for all polarizations under normal incidence. The proposed MMA is verified through fabrication and measurement. Under the oblique incidence of transverse electric and transverse magnetic modes, the absorption ratio is above 90% in the ranges of 8.0-9.01 GHz up to 50 ${}^{\circ }$ and 9.34-11.83 GHz up to 60 ${}^{\circ }$ .

A comprehensive review of 3-D/4-D-printed reconfigurable metasurfaces (RMSs) is presented in this article. A metasurface (MS) demonstrates exceptional abilities for electromagnetic (EM) wave molding beyond that offered by conventional planar interfaces, and RMS provides MS with more diverse EM wave-control capabilities. RMSs are categorized by the type of external stimulus used for reconfiguration, such as electrical RMS, fluidic RMS, mechanical RMS, and thermal RMS. To implement these RMSs, it is important to understand the design and fabrication requirements as well as the EM characteristic of each RMS, including its advantages and disadvantages. In particular, except for electrical RMS, RMSs require complex 3-D structures or special materials that are difficult to implement with conventional subtractive manufacturing methods such as printed-circuit-board manufacturing. Recently, advanced 3-D/4-D printing technology has achieved high fabrication freedom and meets the design and fabrication requirements of each type of RMS. In this article, we introduce representative RMSs with the development of 3-D/4-D printing technology and materials. Furthermore, current issues of RMSs based on 3-D/4-D printing technology and future directions are described.

Metamaterial absorbers (MMAs) are designed to achieve near-total absorption of electromagnetic radiation. In radio-frequency fields, MMAs exhibit absorption behavior that stems from RF resonance. Thus, MMAs are useful in fields such as stealth coatings. However, the use of MMA unit cells for stealth applications is limited due to their heavy weight. In this paper, we demonstrate that a weight reduction of up to 61.31% and a 66.22% decrease in PLA volume can be achieved in a Jerusalem Cross MMA unit cell, with minimal impact on key absorptive properties such as resonant frequency and absorptivity. This was accomplished by selectively removing material from the corners and near-edge regions of the dielectric layer within the unit cell. The simulation results were verified with an array consisting of $12\times 12$ MMA unit cells, where resonant behavior was observed at 10.33 GHz with an absorptivity of 99.84%. Polylactic acid was used as the dielectric material for 3D printing, and the conductive surfaces were fabricated using silver paste. The results of this study demonstrate the feasibility of lightweight MMA designs for real-life applications.

In this study, we propose a novel wideband aperture-coupled magneto-electric (ME) dipole antenna that achieves enhanced bandwidth by simultaneously leveraging ME resonance and aperture-coupled excitation. Building upon the conventional ME dipole architecture, the antenna integrates a pair of horizontal metal patches forming the electric dipole and a pair of vertical metal patches forming the magnetic dipole. A key innovation is the aperture-coupled feeding mechanism, where electromagnetic energy is transferred from a tapered microstrip line to the dipole structure through a slot etched in the ground plane. This design not only excites the characteristic ME resonances effectively but also significantly improves impedance matching, delivering a markedly broader impedance bandwidth. To validate the proposed concept, a prototype antenna was fabricated and experimentally characterized. Measurements show an impedance bandwidth of 84.48% (3.61–8.89 GHz) for $S_{11}$ ≤ −10 dB and a maximum in-band gain of 7.88 dBi. The antenna also maintains a stable, unidirectional radiation pattern across the operating band, confirming its potential for wideband applications such as 5G wireless communications.

In this study, we propose a novel approach to enhance upper stop-band attenuation in a split-ring resonator-based bandpass filter by partially inserting W-type hexaferrite films into a strategically placed mechanical hole. The hexaferrite exhibits a substantial increase in magnetic loss tangent in the desired band owing to ferromagnetic resonance, considerably improving attenuation in the upper stop-band while maintaining an acceptable insertion loss in the pass-band. The obtained results indicate that selectively placing the hexaferrite film enhances out-of-band rejection by up to 4 dB, with a slight degradation of 0.84 dB in pass-band insertion loss. Before inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.01 dB at 28 GHz and an attenuation of 20.04 dB at 32 GHz. By contrast, after inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.95 dB at 28 GHz and an attenuation of 24.45 dB at 32 GHz.