Resonance absorption mechanism-based metasurface absorbers can realize perfect optical absorption. Further, all-dielectric metasurface absorbers have more extensive applicability than metasurface absorbers that contain metal components. However, the absorption peaks of the all-dielectric metasurface absorbers reported to date are very sharp. In this work, we propose a broadband optical absorption all-dielectric metasurface, where a unit cell of this metasurface is composed of two coupled subwavelength semiconductor resonators arrayed in the direction of the wave vector and embedded in a low-index material. The results indicate that the peak absorption for more than 99% is achieved across a 60 nm bandwidth in the short-wavelength infrared region. This absorption bandwidth is three times that of a metasurface based on the conventional design scheme that consists of only a single layer of semiconductor resonators. Additionally, the coupled semiconductor resonator-based all-dielectric metasurface shows robust perfect absorption properties when the geometrical and material parameters—including the diameter, height, permittivity, and loss tangent of the resonator and the vertical and horizontal distances between the two centers of the coupled resonators—are varied over a wide range. With the convenience of use of existing semiconductor technologies in micro/nano-processing of the surface, this proposed broadband absorption all-dielectric metasurface offers a path toward realizing potential applications in numerous optical devices.

Wireless power transfer is a nonradiative type of transmission that is performed in the near-field region. In this region, the electromagnetic fields that are produced by both the transmitting and receiving coils are evanescent fields, which should not transmit energy. This then raises the question of how the energy can be transferred. Here we describe a theoretical study of the two evanescent field distributions at different terminal loads. It is shown that the essential principle of wireless energy transfer is the superposition of the two evanescent fields, and the resulting superimposed field is mediated through the terminal load. If the terminal load is either capacitive or inductive, then the superimposed field cannot transfer the energy because its Poynting vector is zero; in contrast, if the load is resistive, energy can then be conveyed from the transmitting coil to the receiving coil. The simulation results for the magnetic field distributions and the time-domain current waveforms agree very well with the results of the theoretical analysis. This work thus provides a comprehensive understanding of the energy transfer mechanism involved in the magnetic resonant coupling system.

Inspired by the classic hole-cavity blackbody model, we propose an open metasurface blackbody operating at microwave frequencies, whose unit cell is a dielectric resonator lying on an opaque metal plate. The resonator has a high temperature coefficient of dielectric constant, thus the blackbody can be thermally tunable. Furthermore, when the resonator is combined with ferrite, a magnetically tunable blackbody is also obtained. Absorption spectra of these two tunable blackbody unit cells are measured, and they agree very well with the simulated results. The proposed blackbodies offer a new opportunity for practical tunable microwave absorbers in applications.

Impedance matching is an important factor for the electromagnetic resonators used to construct metasurfaces with perfect absorption and transmission properties. However, these resonators usually exhibit narrowband characteristics, thus greatly restricting their potential for application to metasurfaces to obtain excellent absorption and transmission performances. Therefore, realization of impedance matching over a wider range is of major importance. In this work, we demonstrate broadband impedance matching both theoretically and experimentally through use of coupled inductor-capacitor (LC) resonant coils, which are typical electromagnetic resonators. By adding a third resonant coil into the conventional system composed of two completely mismatched resonant coils, the new system realizes broadband impedance matching when the reflected impedances of the first two coils with respect to the third resonant coil are equal. The results in this work can provide useful guidance for realization of metasurfaces with broadband perfect absorption and transmission constructed using any type of electromagnetic resonator.

An all-dielectric metasurface composed of orthogonal-slit silicon disks is proposed in this study. By modifying the unit structure of the metasurface with the bound states in the continuum (BICs), a sharp Fano resonance can be generated. The resonance properties of the metasurface are investigated by analyzing the effects of the structural parameters on the resonance using the eigenmode analysis method. The Q factor and the resonance wavelength can be adjusted by varying the slit width, the disk thickness, and the disk radius. The electromagnetic characteristics and mechanism of the toroidal dipole BICs (TD-BICs) are explored in depth through an analysis of the multipole expansion of the scattered power, along with the electromagnetic field and the current distribution at resonance. This research provides a novel approach for the excitation of strong TD-BIC resonance and proposes potential applications in optical switches, high-sensitivity optical sensors, and related areas.

An all-dielectric metasurface composed of orthogonal-slit silicon disks is proposed in this study. By modifying the unit structure of the metasurface with the bound states in the continuum (BIC) theory, a sharp Fano resonance can be generated. The resonance properties of the metasurface are investigated by analyzing the effects of the structural parameters on the resonance using the eigenmode analysis method. The Q factor and the resonance wavelength can be adjusted by varying the slit width, the disk thickness, and the disk radius. The electromagnetic characteristics and mechanism of the toroidal dipole-BIC (TD-BIC) are explored in depth through an analysis of the multipole expansion of the scattered power, along with the electromagnetic field and the current distribution at resonance. This research provides a novel approach for excitation of a strong TD-BIC resonance and proposes potential applications in optical switches, high-sensitivity optical sensors, and related areas.