Multilayer Absorber Research Articles

Boosting self-powered wearable thermoelectric generator with solar absorber and radiative cooler

The electrical output of wearable thermoelectric generators (wTEGs) has traditionally been constrained by small temperature differentials when powering microelectronics. In this study, we innovatively combine photothermal and radiative cooling mechanisms within a single wTEGs system, enabling substantial, uninterrupted power generation. Specifically, we designed a multilayer selective solar absorber (m-SSA) composed of flexible dielectric-metal stacks. This absorber demonstrates exceptional solar absorption efficiency of 93 % and significantly low thermal emissivity of 10 %. In practical outdoor conditions, it achieves a temperature increase of up to 108 °C under solar irradiation. Concurrently, we developed a flexible hierarchically porous radiative cooler (HP-RC), which reflects 96 % of solar energy and emits 97 % of thermal energy, achieving a cooling differential of up to 10 °C, even at ambient temperatures of 42 °C. Integration of the m-SSA and HP-RC with wTEGs allows for the simultaneous harvesting of heat from solar, cold space, and earth (robots or human body). This novel energy capture mechanism yielded a notable power density of 198 mW/m² for human body and 52 mW/m2 for steel robots in outdoor wearable applications. This significant advancement promotes the field toward high-performance, integrated green power technologies and holds promise for next-generation wearable self-powered devices.

Multi-layer nanoring array-based ultra-wideband solar absorber for photothermal conversion

In this work, based on the finite difference time domain method, we propose and investigate an efficient nanoscale solar absorber based on multilayer nanorings. The absorber is made up of a 4-layer TiO2-TiN nanoring array, a TiO2 insulating layer and a Ti substrate, all of which are high-melting materials. The absorber exhibits an absorption efficiency surpassing 95 % across a wavelength span of 280–4000 nm, thereby attaining a bandwidth of 3720 nm. Additionally, it maintains an average absorption efficiency of 98.8 % throughout the entire wavelength spectrum. Furthermore, calculations reveal that the absorber possesses a solar spectrum-weighted absorption of up to 99 %. The analysis of the electric field distribution indicates that the observed intense absorption is attributed to the plasmonic resonance phenomenon, along with the near-field coupling effects exhibited by the multi-turn nanorings. In addition, our calculations revealed a remarkably high thermal radiation efficiency for this absorber, specifically 99.2 % at 2000 K and 98.9 % at 1500 K, respectively. Therefore, we then calculated the photothermal conversion efficiency of the absorber. At the solar concentration factor C = 1000, the photothermal conversion efficiency surpasses 90 % across the entire temperature range. At C = 100, it is still greater than 80 % at 1000 K. At C = 10, it is still greater than 80 % at 700 K. And at C = 1, it is still greater than 80 % at 500 K. These results indicate that absorbers can be used in a variety of environments. Furthermore, the absorber sustains its superior absorption capabilities at wider solar radiation angles, demonstrating insensitive properties to polarization variations and robust tolerance to manufacturing inaccuracies. These exceptional attributes render it highly suited for diverse applications in solar energy harvesting and photothermal transformation.

Elasticity and modal effects on the optimal performance of micro-perforated multi-layered absorbers

Multi-layered wall-treatments with thin lightweight micro-perforated panels offer a potential solution to achieve broadband noise absorption while complying with mass saving and compactness. This study examines how vibrational effects, often neglected, may impede the wideband acoustical performance of such partitions, made up of a distribution of either periodic or graded micro-perforated membranes or panels. The impedance translation method and a scattering matrix analysis have been implemented. It is found that the elasticity behavior of thin micro-perforated membranes has a beneficial effect on the acoustical efficiency of the partitions. The contributions of the individual acoustical resonances tend to merge if the elasticity effects are accounted for. If the partition is optimized, near-constant high absorption and low transmission values are obtained over a wide frequency range. A more robust design involves partitions made up of micro-perforated panels. It was observed that the first volumetric volumetric mode of the panels modifies the absorption properties of the partition. It cross-couples with the acoustical resonances and redistributes their spectral locations. This structural resonance sets an upper frequency bound, below which the partition achieves a high broadband performance. It should be accounted for when setting the frequency limits of the total dissipation to be optimized.

Enhanced SWIR Absorption in PMMA‐Coated TiN‐Based Metamaterial

AbstractAchieving highly efficient absorption in the short wavelength infrared (SWIR) spectral region is crucial for advancing numerous technologies. SWIR absorption enhances energy harvesting in solar cells, improves the sensitivity of infrared sensors, and enables precise control of thermal radiative properties in thermal emission devices. These advancements are essential for applications such as thermal imaging, night vision, and thermophotovoltaic systems. The study presents a simple, cost‐effective design of a polymer‐coated multilayer perfect absorber (MPA) metamaterial optimized for the SWIR spectral region. The proposed MPA structure is composed of four distinct layers: a top layer made of polymethyl methacrylate (PMMA) polymer, a second layer featuring arrays of circular titanium nitride (TiN) disks, a dielectric middle layer consisting of a pure zinc oxide (ZnO) film, and a bottom metallic layer formed by a thin film of TiN. The results demonstrate that the MPA achieves near‐perfect absorption, with a remarkable 99% efficiency centered at a wavelength of 1.3 µm. The absorption properties are further investigated with respect to various structural parameters to ensure better performance of the absorber. These absorbers hold great promise for applications in energy absorption, infrared sensing, thermal emission, and related fields.

Compact multilayer selective absorbers based on amorphous carbon for solar-thermal conversion

In addressing the energy crisis and climate change, environmentally sustainable materials and structures with heightened absorption and enhanced photothermal conversion efficiency are urgently demanded. In this study, a series of ultrabroadband, omnidirectional, and near-perfect solar radiation absorbers based on amorphous carbon (a-C) were fabricated by magnetron sputtering. These absorbers, featuring 4, 6, and 8-layer compact multilayer thin film structures, exhibited measured absorption of 96.8 %, 96.5 %, and 96.6 % in the range of 300–2500 nm, respectively. The high absorption efficiency delves into the synergistic effects of intrinsic absorption of a-C and enhanced absorption through thin film interference. Through microstructure analysis, the reduced absorption compared to design originates from the optical thickness mismatch caused by the unstable growth rate of a-C. In addition, the absorbers show very slight variations in absorption within 40° and maintain a high absorption of more than 80 % in the incident angle of 60°. For samples with different air annealing temperatures from 100 to 250 °C, the microstructure, morphology, and optical properties were systematically investigated. The appearance of oxygen channels due to surface defects or voids leads to the oxidation reaction of the diffused Ti atoms at high temperature. Notably, the proposed absorber can be fabricated by a lithography-free method, paving a way for large-area application of a-C.

Tunable optically transparent graphene–ITO patterning-based millimeter-wave absorber

In this work, we demonstrated a multilayer millimeter-wave absorber capable of tuning the absorption frequency while simultaneously maintaining the optical transparency. It comprises indium tin oxide (ITO) as the bottom ground plane deposited over polyvinyl chloride (PVC) substrate over which a patterned ITO layer is formed. Above this ITO layer, a PVC spacer is put to isolate the upper graphene sandwich structure (GSS) comprising of two patterned graphene mediums separated by a diaphragm paper. The configuration shows the tunability of reflectance minima (which correspond to high absorptance of ≥ 98 %) in a frequency range of 92.5–97.5 GHz due to the adjustable bias voltage applied to GSS. Additionally, the designed absorber demonstrates adequate shielding effect, generally required for both commercial and military applications in the stated frequency range. This simultaneously configurable and optically transparent device has potential in multispectral and smart stealth technologies, particularly 6G applications.

Multilayer thin film mid-infrared broadband absorber with high visible light transmittance

Few reports on absorbers achieve both high transmittance of visible light and strong absorption of mid-infrared light. Here a multilayered absorber with high visible light transmittance and strong broadband absorption in the mid-infrared band is proposed. The absorber is four-layer films of ITO/SiO2/ITO/SiO2 successively deposited on single-sided conductive glass by electron beam evaporation technology. The experiment shows that the integral transmittance in the 400–800 nm range is 82.8 %, and the integral absorption in the 3–5 μm band is 88.2 %.

Design of a multilayer absorber for ultra‐wideband radar cross section reduction

AbstractThis study proposes an ultra‐wideband multilayer absorber by combining frequency selective surface (FSS) and absorbing material. The structure is composed by three layers which are FSS loaded with resistors, absorbing material at the bottom and each layer is separated by air. The FSS in bottom has good absorption performance at high frequency while the upper layer is used to achieve low‐band absorption. To extend the absorption band to the low frequency, it further add a layer of absorbing material at the bottom. Equivalent circuit is employed to analyze the principle of the designed absorber. The simulation results show that an ultra‐wide absorption band from 0.61 to 12.33 GHz with a fractional bandwidth of 181% is realized for both TE and TM waves under the normal incidence. Furthermore, the thickness of the structure is only 0.07λL, where λL represents the wavelength of the minimum operating frequency. The designed absorber is fabricated and measured, and the measurement is in good agreement with the simulation.

An ultra-broadband multi-layer dielectric gradient honeycomb microwave absorber enhanced by the double layer metasurface

A novel, 12 mm multilayer dielectric gradient honeycomb absorber (MGHA) was designed, fabricated and analyzed with a double layer metasurface consisting of a resistive film and an artificial magnetic conductor (AMC) checkerboard. Despite its thin profile, the MGHA demonstrates significantly enhanced absorption performance across a wide frequency range due to the impedance of the composite structure. Furthermore, two distinct metasurfaces are integrated into the dielectric gradient multilayer honeycomb absorber to further enhance its low-frequency properties without increasing thickness. This structure exhibits wideband absorption from 2.8 GHz to 18 GHz, featuring three absorption peaks at 3 GHz, 11 GHz and 16 GHz. The relative bandwidth can reach nearly 136.6 % of that achieved by a common honeycomb absorber with the same thickness, while maintaining an absorption peak reflection of about −22dB. The great attenuation of incident waves is attributed to Ohmic loss on the resistive film, electric resonance effect on the checkerboard, and magnetic resonance near 17 GHz on the checkerboard metasurface. The proposed MGHA structure holds significant potential for applications in aerospace and military.

Graphene-based Cr-GaAs-Ag multilayer absorber structure for solar heating applications

The optimization of the solar absorber is very important to develop the efficiency of the solar absorber. We have designed here one solar absorber which is optimized using variation in different physical parameters. The design of this absorber is based on Cr-GaAS-Ag materials which is also based on a thin film graphene material. The designed solar structure is used for heating applications which can be applied in industrial use. The highest absorption of more than 99 % is achieved for different wavelengths. The design also shows the 97.1 % absorption for the 1000 nm wavelength. The optimization section is also provided in this research at the end of results section. The conclusions are obtained using absorption for the different layer structures in this research. Layer by layer analysis for the absorption is provided in this manuscript. The research is aimed at renewable energy use in the industries by providing sustainable heating applications.

Design and analysis of a machine learning-optimized multi-layered absorber for renewable energy applications

Harvesting solar energy into other useful energy sources are essential now a days, hance there are many systems available for that, such as solar absorbers, solar PV, etc. In this study, we have investigated four different solar absorber designs. Out of that four, the Hash-Shaped Solar Absorber (HSSA) structure is more effective for absorbing solar radiation and converting it into heat energy. With the broad response range this structure absorb more than 90 % of the radiation in observed range (100–5000 nm). The HSSA structure demonstrates absorption > 99 % at specific wavelength peaks, including 170 nm, 550 nm, 1790 nm, 2750 nm, 3090 nm, and 3700 nm within the solar spectrum. With this the HSSA structure is having more than 93 % absorption in the 3000–4000 nm range, whereas more than 97 % absorption is achieved in the visible region. Further, the HSSA structure is treated with the Machine Learning model as the parameter optimization. The greatest R2 value for this structure is 0.999592with a test size of 0.25, and the mean squared error is 1.79801 × 10−4. The ML reduces time (takes ¼ of the traditional time) and other simulation requirements. Additionally, the structure is polarization insensitive and up to 60° incident angle insensitive. Due tothese characteristics, the HSSA structures find usage in variousapplications, including solar thermal energy harvesting systems, plasmonic sensors, and detectors.

Development of CuS/C composite for microwave absorption using lignin biopolymer

In recent decades, electronic devices have become a crucial component of everyday life and an increasingly important aspect of national security. However, despite their convenience, the emission of electromagnetic (EM) radiation from these devices has created a pollution issue that demands urgent attention. In this study, the properties and performance of CuS/C composites as EM wave-absorbing materials were examined. The main technique employed involved modifying the surface structure and properties of a lignin biopolymer via a fiber laser to derive porous carbon as a microwave absorber in the X-band range. Flower-like CuS microspheres were integrated into the porous carbon to improve the electrical conductivity and promote internal reflections. In addition, multilayer microwave absorbers were developed using CuS/C/epoxy composites with varying weight percentages, which were fabricated through refluxing and annealing techniques. The return losses of the absorbers in single- and multi-layer modes were optimized by modified local particle swarm optimization (MLPSO). The minimum average return loss improved to −15 dB (96.8%) by optimization in the 4-layer mode with a thickness of 1.8 mm. The optimum absorption peak in the 3-layer structure was −54.52 dB at a frequency of 8.83 GHz. The shielding effectiveness assessments indicated that the CuS/C/epoxy composite significantly improved the shielding capabilities of porous C and CuS, resulting in an increase of the shielding effectiveness threshold (SET) from less than 2 dB in lignin to more than 10 dB in CuS/C/epoxy.

Efficient Design of Broadband and Low-Profile Multilayer Absorbing Materials on Cobalt-Iron Magnetic Alloy Doped with Rare Earth Element.

Magnetic metal absorbing materials have exhibited excellent absorptance performance. However, their applications are still limited in terms of light weight, low thickness and wide absorption bandwidth. To address this challenge, we design a broadband and low-profile multilayer absorber using cobalt-iron (CoFe) alloys doped with rare earth elements (REEs) lanthanum (La) and Neodymium (Nd). An improved estimation of distribution algorithm (IEDA) is employed in conjunction with a mathematical model of multilayer absorbing materials (MAMs) to optimize both the relative bandwidth with reflection loss (RL) below -10 dB and the thickness. Firstly, the absorption performance of CoFe alloys doped with La/Nd with different contents is analysed. Subsequently, IEDA is introduced based on a mathematical model to achieve an optimal MAM design that obtains a balance between absorption bandwidth and thickness. To validate the feasibility of our proposed method, a triple-layer MAM is designed and optimized to exhibit wide absorption bandwidth covering C, X, and Ku bands (6.16-12.82 GHz) and a total thickness of 2.39 mm. Then, the electromagnetic (EM) absorption mechanisms of the triple-layer MAMs are systematically investigated. Finally, the triple-layer sample is further fabricated and measured. The experimental result is in good agreement with the simulated result. This paper presents a rapid and efficient optimization method for designing MAMs, offering promising prospects in microwave applications, such as radar-stealth technology, EM shielding, and reduced EM pollution for electronic devices.

Miura-ori based reconfigurable multilayer absorber for high-efficiency wide-angle absorption.

Radar stealth structures that can achieve high-efficiency wide-angle absorption are key components of future military equipment. However, it is difficult for both planar and three-dimensional (3D) absorbers to achieve efficient absorption in a large incidence angle range. The multilayer reconfigurable absorber component based on Miura origami provides a unique solution. First, the multilayer origami absorber is parameterized in the simulation software. Each origami structure is covered with resistive films that fit the panels. Geometric constraints are satisfied among the multilayer structures. They support reconfigurability in the range of continuous states (as opposed to discrete states), which is conducive to finding the folded state with a more efficient absorption rate within the frequency band. Secondly, the designed structure does not require a specialized mechanically supported multilayer origami absorber. In addition, the equivalent analogue circuit method is used to analyze the efficient absorption of multilayer origami under oblique incidence. Finally, our proposed absorber satisfies the requirements of multiple absorption metrics: broadband, high efficiency, wide incidence angle, and polarization insensitivity. As the validation, we simulated and fabricated a double-layer origami absorber. Our proposed origami absorber can maintain an absorption rate of more than 90% for both transverse electric (TE) and transverse magnetic (TM) polarizations in the operating frequency band (5-20 GHz) over a wide range of incidence angles (0°-70°). When the incidence angle qinc = 40°, the double-layer origami absorber (q1 = 90°, α1 = 60°, and a2 = 75°) can achieve at least 10 dB reflection reduction of -18 dB and -20 dB in TE and TM modes, respectively. The proposed origami absorber provides a reference for the design of other absorbers.

Accelerating multilayer frequency selective surface absorber design by combining equivalent circuit models with machine learning

Designing high-performance electromagnetic functional materials and artificial structures is of great significance for electromagnetic wave modulation applications. Optimizing performance in the high-dimensional parameter space of electromagnetic functional materials has posed a challenging problem. This paper proposes the use of reinforcement and transfer learning methods to facilitate the quick and accurate design of wideband circuit analog absorbers (CAA). A trained reinforcement learning network is utilized to comprehend the relationship between reflectivity performance and changes in impedance parameter. Furthermore, the transfer learning method is applied to accelerate the training process, leading in a 20-fold reduction in the number of simulations. To validate the effectiveness of this approach, a double-layer absorber aiming for reflectivity less than −20 dB at 3–10 GHz is designed, requiring only 50 simulations. This demonstrates that the proposed method provides a flexible strategy for the interactive design of equivalent circuit and electromagnetic structural parameters. Moreover, it presents a novel and efficient solution for microwave absorber design, with potential applications across various microwave design fields.

Development and Fabrication of a Multi-Layer Planar Solar Light Absorber Achieving High Absorptivity and Ultra-Wideband Response from Visible Light to Infrared.

The objective of this study is to create a planar solar light absorber that exhibits exceptional absorption characteristics spanning from visible light to infrared across an ultra-wide spectral range. The eight layered structures of the absorber, from top to bottom, consisted of Al2O3, Ti, Al2O3, Ti, Al2O3, Ni, Al2O3, and Al. The COMSOL Multiphysics® simulation software (version 6.0) was utilized to construct the absorber model and perform simulation analyses. The first significant finding of this study is that as compared to absorbers featuring seven-layered structures (excluding the top Al2O3 layer) or using TiO2 or SiO2 layers as substituted for Al2O3 layer, the presence of the top Al2O3 layer demonstrated superior anti-reflection properties. Another noteworthy finding was that the top Al2O3 layer provided better impedance matching compared to scenarios where it was absent or replaced with TiO2 or SiO2 layers, enhancing the absorber's overall efficiency. Consequently, across the ultra-wideband spectrum spanning 350 to 1970 nm, the average absorptivity reached an impressive 96.76%. One significant novelty of this study was the utilization of various top-layer materials to assess the absorption and reflection spectra, along with the optical-impedance-matching properties of the designed absorber. Another notable contribution was the successful implementation of evaporation techniques for depositing and manufacturing this optimized absorber. A further innovation involved the use of transmission electron microscopy to observe the thickness of each deposition layer. Subsequently, the simulated and calculated absorption spectra of solar energy across the AM1.5 spectrum for both the designed and fabricated absorbers were compared, demonstrating a match between the measured and simulated results.

Design of an optically transparent and broadband absorber based on a multi-objective optimization algorithm.

In this Letter, an optically transparent and broadband absorber designed using a multi-objective genetic algorithm (MOGA) is proposed. The absorption of the multilayer lossy frequency selective surface-based absorber is calculated by multilayer absorption equations and equivalent circuit models. To solve the problem of the unbalanced structure absorption bandwidth and thickness, an algorithm is used for optimizing the geometric and sheet resistance parameters of the structure. A multilayer and optically transparent absorber with 90% absorption bandwidth covering a frequency range of 2-18 GHz (S-band to Ku-band) is developed based on the MOGA design method with optical transmittance of 60%. Its total thickness consists of a wavelength of only 0.095, and it has high oblique incidence stability, which makes it useful in the stealth technology and transparent electromagnetic shielding applications.

A wide-angle broadband dual-polarization electromagnetic absorbing structure based on the carbonyl iron powder/polydimethylsiloxane composites

Electromagnetic absorbing structure with wide-angle and broadband absorption plays a vital role in radar stealth. Hence, a novel gradient composite multilayer absorbing structure (GCMAS) is designed and fabricated by a simple and low-cost direct ink writing (DIW) 3D printing technology. The GCMAS consists of the CIP/PDMS composites composed of carbonyl iron powder (CIP) and polydimethylsiloxane (PDMS), which have outstanding flexibility, chemical and thermal stability. By metastructure design of gradient composites, a material-structure–function integrated absorbing structure with 50 wt% CIP/PDMS in the top layer, 60 wt% CIP/PDMS in the middle two layers, and 70 wt% CIP/PDMS in the bottom two layers is obtained. Simulations demonstrate that the designed GCMAS with the thickness of 13 mm can achieve the −10 dB absorbing bandwidth in the frequency range from 2.88 to 38.24 GHz, and the absorbing bandwidth corresponding to −15 dB in 2.97–36.17 GHz. The maximum reflection loss is −42.17 dB at 22.96 GHz. Experiments demonstrate that the GCMAS can achieve the −10 dB absorbing bandwidth in 3.6–40 GHz. Moreover, the GCMAS also can maintain the broadband and strong absorbing performance with incident angle from 0° to 50° for transverse electric (TE) polarization and 0° to 60° for transverse magnetic (TM) polarization. This work provides a promising strategy for the fabrication of functional gradient composites and flexible or bendable absorbing structure, which have great potential in satellite communications and radar stealth.

Controllable surface functionalization of rice husk-derived porous carbon by atomic layer deposition for highly-efficient microwave absorption

Multilayer absorbers, characterized by their distinctive structures and numerous heterogeneous interfaces, possess the potential to become exceptionally efficient and stable electromagnetic wave absorbers. Herein, we have ingeniously engineered multilayer ZnO/NiCo/C (ZNC) composite absorbers, utilizing a combination of an annealing procedure and atomic layer deposition (ALD) process. From the SEM images, the ZnO layers composed of ZnO nanoparticles (NPs) fabricated via ALD almost completely cover the surface of rice husk-derived carbon and the NiCo NPs residing on the surface. Benefiting from the specific multilayer structure, the well-designed ternary dielectric/magnetic components, and the synergistic interplay between dipole polarization relaxation and interfacial polarization relaxation, coupled with good impedance matching, the ZNC150 and ZNC200 composites exhibit best microwave absorption capacities. Through the precise control of the electromagnetic parameters by the deposition circle modifications, the minimum reflection loss reaches −52.5 dB and the effective bandwidth extends to 4.96 GHz with thin thickness of 1.52 mm.

Enhancing electromagnetic wave absorption performance through construction of three-dimensional multilayered SiCw/Y3Si2C2/Ni0.5Zn0.5Fe2O4 composites

In this study, three-dimensional (3D) multilayer electromagnetic wave absorbing (EMWA) materials SiCw/Y3Si2C2/Ni0.5Zn0.5Fe2O4 were fabricated for the first time. A two-dimensional (2D) Y3Si2C2 coating was synthesized onto the one-dimensional (1D) SiCw surface by the molten salt method. Subsequently, one layer of zero-dimensional (0D) Ni0.5Zn0.5Fe2O4 nanoparticles was deposited onto the Y3Si2C2 coating surface via hydrothermal reaction. The microstructure and electromagnetic wave absorption mechanism of SiCw/Y3Si2C2/Ni0.5Zn0.5Fe2O4 were systematically investigated. The introduction of 2D Y3Si2C2 and 0D Ni0.5Zn0.5Fe2O4 enhanced impedance matching and provided abundant heterogeneous interfaces, thus leading to interface polarization loss. Owing to the promoted impedance matching and superb attenuation capacity, 3D multilayered SiCw/Y3Si2C2/Ni0.5Zn0.5Fe2O4 composites exhibit superior EMWA performance in comparison with origin SiCw. For the SiCw/Y3Si2C2/Ni0.5Zn0.5Fe2O4 composites, their minimum reflection loss (RLmin) can be achieved −43.95 dB and the effective absorption bandwidth (EAB) is 4.08 GHz when the thickness is 2.12 mm. This study could pave a reference for the investigation of multi-dimensional hybrid structure EMWA material.