All-dielectric Absorber Research Articles

Sensitivity Analyses for All-Dielectric Absorber Structures Having Different Dielectric Resonator Geometries and Investigation of the Effect of Boundary Conditions on the Absorption Spectra

Sensitivity Analyses for All-Dielectric Absorber Structures Having Different Dielectric Resonator Geometries and Investigation of the Effect of Boundary Conditions on the Absorption Spectra

All-dielectric absorber based on nano-graphite sheets/ionogels with configurable absorbing band.

With the increasing complexity of the electromagnetic environment, there is a growing demand for the manipulation of electromagnetic waves, leading to the rapid development in configurable microwave absorbers. All-dielectric absorbers offer broadband and high-intensity absorption effects in microwave absorption and shielding. However, they face a significant challenge: their performance is not adjustable once the design is completed. In this study, we propose a solution to this problem by creating all-dielectric absorbers with flexibly configurable absorbing properties. We achieve this by designing a composite material of ionogels/nano-graphite sheets into compressible deformable absorbing units that can be molded into different shapes using 3D printing modes. The plasticity allows us to change the performance of the all-dielectric absorber, including the microwave absorption intensity, absorption peak, frequency bandwidths, and wide-angle absorption performance. With this approach, we can flexibly manipulate electromagnetic waves using all-dielectric absorbers through different plasticity models.

Stacked all-dielectric absorber based on degenerate critical coupling for visible to near-infrared light

We design a wideband all-dielectric perfect absorber of nanopillar Mie resonators based on degenerate critical coupling. In addition, the nanopillar perfect absorber is found to have a characteristic “degenerate critical length” beyond which the absorption peak is almost unaffected by increasing length. Based on the existence of the degenerate critical length, we develop a broadband dielectric quasi-perfect absorber by stacking nanopillar Mie resonators of different materials that selectively absorb incident light like photon sorters. The 1300 nm-thick absorber achieves an average absorptivity of above 94% from 300 to 1000 nm and has great potential for photodetection and photovoltaic applications.

Broadband all-dielectric absorber based on supercell cylindrical metamaterials

Based on the cylindrical array microstructure of doped silicon, we propose an all-dielectric terahertz-band broadband absorber. First, we design an absorber with a cylindrical structure in a unit cell. Due to the electromagnetic dipole resonance characteristics, the absorber has an absorption efficiency of over 99.97% at a single frequency of 1.24 THz. In order to obtain wide-bandwidth angular absorption characteristics, we propose a kind of superstructure absorber with a single unit cell containing multiple cylinders with different diameters. The results show that the optimally designed absorber has wide-bandwidth angular absorption characteristics under different polarization states and different incident angles of terahertz waves. In order to further improve the absorption bandwidth, we propose a superimposed superstructure absorber. After optimized design, the absorption efficiency reaches more than 90% in the broadband frequency range of 1.42 THz–4.5 THz. At the same time, different structural parameters have different effects on the peak absorption efficiency.

Broadband absorber coupled with anti-reflection inverted pyramid type all-dielectric microstructure

In order to improve the absorption efficiency and absorption bandwidth, we propose an inverted pyramid type all-dielectric absorber. Using the anti-reflection interface characteristics of the inverted pyramid microstructure, the designed absorber can achieve 100% perfect absorption in the range of 1.5THz to 1.7THz. Based on the structural diffraction analysis and electromagnetic field distribution characteristics, we have deeply explored the physical mechanism of wave absorption of the designed structure, and revealed the dual physical mechanism of electromagnetic wave diffraction conversion and resonance absorption. Based on the unique wet etching technology, we have experimentally prepared this inverted pyramid type all-dielectric absorber. Through experimental measurement, the consistency of the theoretical design and experimental test was confirmed.

An all-dielectric microwave absorber composed of a dielectric hollow cylinder filled by chemical liquids and its application on sensing

In this study, design, characterization and sensing application of an all-dielectric absorber are studied in microwave S-band. In the design, the unit-cell is composed of a cylindrical dielectric container (CDC), a cylindrical dielectric resonator (CDR) and a dielectric substrate as the support material. For an important part of the study, except the parametrical analyses, the CDR is formed by specially selected chemical liquids (CLs) separately. The study consists of three main stages. In the first stage, several analytical analyses take part for the determination of the CDR dimensions (i.e., height and the radius) regarding the microwave rectangular waveguide medium. In the second stage, some specific numerical analyses have been performed to reveal the dependence of the absorption spectra on relative permittivity and loss tangent of CDR and also to explain the resonance mechanism considering the electric and the magnetic field distributions inside the structure. This stage is important to demonstrate that electric and magnetic dipole resonances are merged at a common frequency which results in a stronger absorption peak. In the final stage, a sensing application is presented. On this aim, the CDC has been filled by three selected CLs (i.e., acetone, acetonitrile and ethyl methyl ketone) separately and the changes in the absorption spectra have been presented both in simulations and experiments. The numerical and the experimental results reveal that the location of the absorption peak decreases effectively with the increase of the relative permittivity of the CL and the absorption band gets broader as the loss tangent of the CL gets higher. These results reveal that obtaining a relatively narrow band of absorption and controlling the absorption spectrum is possible in microwave all-dielectric designs by an engineered choice of the CL as the CDR material. This approach may not only be used for concentration sensing of chemical solutions but also for tuning the absorption spectrum in magnitude or in frequency by controlling the CDR (i.e., CL inside the CDC).

Selectively thermal radiation control in long-wavelength infrared with broadband all-dielectric absorber.

Artificial control of the thermal radiation is of growing importance to fundamental science and technological applications, ranging from waste heat recovery to thermophotovoltaics. Nanophotonics has been proven to be an efficient approach to manipulate the radiation. In comparison with structures utilizing planar subwavelength scale lithography, in this paper, we propose a cascaded all-dielectric multilayer structure to selectively manipulate the thermal radiation characteristics in long-wavelength infrared (LWIR). The broadband emissivity in non-atmospheric windows (6.3-7.5 µm) can reach 0.95 and the average absorption rate is below 3% in atmospheric windows (8-14 µm). The multilayer structure is insensitive to the polarization of the incident waves and maintains a good rectangular absorptivity curve even with large oblique incidence angle at 45 degrees. The outstanding properties of the nanostructures promise various applications in infrared sensing and thermal imaging.

All-Dielectric Terahertz Plasmonic Metamaterial Absorbers and High-Sensitivity Sensing.

Two types of plasmonic metamaterial absorbers (PMAs) formed from patterned all-dielectric resonators are designed and demonstrated experimentally in the terahertz (THz) range. Both PMAs use a simple grating design on highly N-doped silicon. The first shows broadband absorption with near-perfect peak absorbance at 1.45 THz and a bandwidth of 1.05 THz for 90% absorbance, while the second is a dual-band absorber. Experiments show that the second absorber has two distinct absorption peaks at 0.96 and 1.92 THz with absorption rates of 99.7 and 99.9%, respectively. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the characteristics of both PMAs. Additionally, the optically tunable responses of these all-dielectric absorbers demonstrate that the absorption behavior can be modified. The quality factor (Q) values of the dual-band resonances are 4.6 and 7.8 times larger than those of the broadband PMAs, respectively, which leads to a better sensing performance. As an example, the two proposed PMAs act as high-sensitivity sensors and demonstrate considerable potential for chlorpyrifos detection. These results show that these PMAs can be used as sensors that can detect the presence of trace pesticides in adsorption analyses, among other practical applications.

Degenerate critical coupling in all-dielectric metasurface absorbers.

We develop the theory of all-dielectric absorbers based on temporal coupled mode theory (TCMT), with parameters extracted from eigenfrequency simulations. An infinite square array of cylindrical resonators embedded in air is investigated, and we find that it supports two eigenmodes of opposite symmetry that are each responsible for half of the total absorption. The even and odd eigenmodes are found to be the hybrid electric (EH111) and hybrid magnetic (HE111) waveguide modes of a dielectric wire of circular cross section, respectively. The geometry of the cylindrical array is shown to be useful for individual tuning of the radiative loss rates of the eigenmodes, thus permitting frequency degeneracy. Further, by specifying the resonators' loss tangent, the material loss rate can be made to equal the radiative loss rate, thus achieving a state of degenerate critical coupling and perfect absorption. Our results are supported by S-parameter simulations, and agree well with waveguide theory.

Polarization insensitive metamaterial absorber based on E-shaped all-dielectric structure

In this paper, we designed a metamaterial absorber performed in microwave frequency band. This absorber is composed of E-shaped dielectrics which are arranged along different directions. The E-shaped all-dielectric structure is made of microwave ceramics with high permittivity and low loss. Within about 1 GHz frequency band, more than 86% absorption efficiency was observed for this metamaterial absorber. This absorber is polarization insensitive and is stable for incident angles. It is figured out that the polarization insensitive absorption is caused by the nearly located varied resonant modes which are excited by the E-shaped all-dielectric resonators with the same size but in the different direction. The E-shaped dielectric absorber contains intensive resonant points. Our research work paves a way for designing all-dielectric absorber.

Compression of a pyramidal absorber using multiple discrete coordinate transformation.

The discrete coordinate transformation (DCT), as a unique technique to control the electromagnetic waves, has been applied for creating all-dielectric devices recently. To extend the applicability of this technique, we propose the concept of multiple discrete coordinate transformation, which serves to deal with more complicated geometries in the transformation domain. As an example, an all-dielectric absorber is created by compressing a pyramidal absorber to a third of its original thickness using the multiple DCT technique. The Finite-Difference Time-Domain (FDTD) method based numerical simulations demonstrate the broadband performance of the transformation absorber from 2 GHz to 20 GHz.