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Enhancing the efficiency is an essential target of the wireless power transfer (WPT) technology. Enabling the WPT systems requires careful control to prevent power from being transferred to unintended areas. This is essential in improving the efficiency and minimizing the flux leakage that might otherwise occur. Selective field localization can effectively reduce the flux leakage from the WPT systems. In this work, we propose a method using a digital honeycomb metamaterial structure that has a property operation as a function of switching between 0 and 1 states. These cavities were created by strongly confining the field by using a hybridization bandgap that arose from wave interaction with a two-dimensional array of local resonators on the metasurface. A WPT efficiency of 64% at 13.56 MHz was achieved by using the metamaterial and improved to 60% compared to the system without the metamaterial with an area ratio of Rx:Tx~1:28. Rx is the receiver coil, and Tx is the transmitter one. [ABSTRACT FROM AUTHOR]

Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we propose a multilayer metamaterial-absorber (MA) structure comprising two resonant layers crafted with copper and FR-4 dielectric. The presented multilayer MA structure exhibited an absorption greater than 90% in a frequency range from 4.84 to 5.02 GHz, with two maximum absorption peaks at 4.89 and 4.97 GHz. The bandwidth of the multilayer MA surpassed that of the individual single-layer MAs, with extension fractions reaching 360% and 257%, respectively. Through the simulation and calculation, the field distribution and equivalent circuit model elucidated that both individual magnetic resonances and their interplay contribute significantly to the absorption behavior of the multilayer MA. The absorption of the proposed multilayer MA structure was also investigated for the oblique incidence in the transverse electric (TE) and transverse magnetic (TM) modes. In the TE mode, the absorption intensity of two maximum peaks was maintained at over 93% up to an incident angle of 40 degrees and dropped to below 80% at an incident angle of 60 degrees. In the TM mode, the absorption was more stable and not significantly affected by the incident angle, ranging from 0 to 60 degrees. An absorption greater than 97% was observed when the incident angle increased from 0 to 60 degrees in the TM mode. Additionally, the approach in our work was further demonstrated by adding more resonant layers, making 3- and 4-layer structures. The results indicated that the absorption bandwidths of the 3- and 4-layer structures increased by 16% and 33%, respectively, compared to the bilayer structure. Furthermore, we analyzed the thermal distribution within the MA to understand the dissipation of absorbed electromagnetic energy. This research offers valuable insight into the augmented MA through a multilayer structure, presenting the implications for microwave applications like electromagnetic shielding, as well as in the design of MAs for terahertz devices and technologies, including emission and thermal imaging. These findings contribute to the advancement of knowledge in enhancing the absorption capabilities across various frequency ranges, expanding the potential applications of metamaterials. [ABSTRACT FROM AUTHOR]

Metamaterial absorbers have garnered significant interest due to their unique electromagnetic properties, which facilitate the efficient absorption of electromagnetic radiation in a specific frequency range or multiple frequency ranges. The metamaterial absorbers are designed based on artificially engineered structures that enable tailored absorption properties. These structures might include multiple resonances or incorporate electrical resistive components to achieve broadband absorption. This review paper provides a comprehensive analysis of the progress made in the field of the bandwidth of metamaterial absorbers, encompassing the underlying design principles, key performance characteristics, diverse applications, and perspectives for further research. The paper draws to a conclusion by outlining the potential future directions for further advancements in this exciting area of research, and highlighting the challenges that need to be addressed for the widespread adoption of metamaterial absorbers. [ABSTRACT FROM AUTHOR]

This study presents a tri-layer broadband metamaterial absorber that operates in the GHz range. The absorber was composed of a polyhedral iron-cobalt alloy/graphite nanosheet material arranged in a flat sheet with two punched-in rings for the top layer, a continuous FR-4 layer at the middle, and a continuous copper layer at the bottom. For the normal incidence of the electromagnetic wave, the proposed absorber demonstrated an exceptional broadband absorption in a frequency range of 7.9–14.6 GHz, revealing an absorption exceeding 90%. The absorption magnitude remains to be above 90% in a frequency range of 8–11.1 GHz for transverse-electric-polarized waves at incident angles up to 55°. For both the transverse-magnetic- and electric-polarized waves, the absorption exceeds 90% in a frequency range of 9.5–14.6 GHz. The physical mechanism behind the absorption properties is analyzed thoroughly through the electric and magnetic field distributions. The obtained results could contribute potentially to the development of microwave applications based on metamaterial absorbers, such as radar-stealth technology, electromagnetic shielding for health safety, and reduced electromagnetic interferences for high-performance communications and electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a high-performance electromagnetic-wave metamaterial absorber which can be used directly for 5G technology. The absorber exhibits a high performance in a tailored frequency range of 28 ± 1 GHz. At both transverse-electric and transverse-magnetic polarization, the absorption exceeds 99% when the electromagnetic wave is incident normally, and the absorption keeps being over 97% as the incident angle increases even to 45 degrees. The absorber is flexible, and it is very suitable for mass production because the production process is simple. In addition, the minimum dimension of the meta-structure is only 0.2 mm, and the cost is relatively low. Similarly, another high-performance metamaterial absorber with a tailored bandwidth at the center frequency of 77 GHz, which is relevant to self-driving cars, was also prepared by a minimal adjustment to the original structure. [ABSTRACT FROM AUTHOR]

We demonstrated a multi-band plasmonic metamaterial absorber (MA), based on the near-field coupled resonators. In addition to the individual resonances of resonators in the proposed structure, which were split-ring resonator (SRR) and cross-shape structures, another resonance was also excited owing to the coupling of resonators, revealing a triple-band absorption. Furthermore, to control the absorption behavior, on the top of the SRRs, the identical SRRs made of graphene ink were pasted. By increasing the resistance of graphene ink, the coupling strength was weakened, changing the triple-band absorption to a dual-band one. Our work might be useful as the controllable devices, based on graphene-integrated plasmonic MA, such as filters, detectors and energy harvesters. [ABSTRACT FROM AUTHOR]

We demonstrate a dual-band, polarization-insensitive, ultrathin and flexible metamaterial absorber (MA), based on high-order magnetic resonance. By exploiting a flexible polyimide substrate, the thickness of MA came to be 1/148 of the working wavelength. The absorption performance of the proposed structure was investigated for both planar and bending models. In the case of the planar model, a single peak was achieved at a frequency of 4.3 GHz, with an absorption of 98%. Furthermore, additional high-order absorption peaks were obtained by the bending structure on a cylindrical surface, while the fundamental peak with a high absorption was maintained well. Our work might be useful for the realization and the development of future devices, such as emitters, detectors, sensors, and energy converters. [ABSTRACT FROM AUTHOR]

In this work, we proposed a flexible broadband metamaterial perfect absorber (FBMPA) by exploiting a pasted conductive-graphene ink on a polyimide substrate. For the flat FBMPA, an absorption over 90% was found to cover a wide frequency range (from 7.88 to 18.01 GHz). The high-absorption feature was polarization-insensitive and regarded as stable with respect to the oblique incidence up to 30 degrees of electromagnetic wave. The high absorption was maintained well even when the absorber was wrapped. That is, the FBMPA was attached to cylindrical surfaces (with the varying radius from 4 to 50 cm). For both flat and curved states, the absorption mechanism was explained by the perfect impedance matching and the dielectric loss of the proposed absorber. Our work provides the groundwork for the commercialization of future meta-devices such as sensors, optical filters/switchers, photodetectors, and energy converters. [ABSTRACT FROM AUTHOR]