Design Of Absorber Research Articles

Spherical porous structures for axial compression

Porous structures have attracted much attention because of the advantages of lightweight and strong energy absorption efficiency. This work proposes a spherical porous structure (SPS) and a square porous structure (SQPS), and the SPS sample is manufactured by selective laser sintering (SLS) technique with the material nylon 11. Their axial compression results of experiment and simulation show that the compressive strength of hollow cylinders is greater than that of porous spheres, and porous spheres are always crushed during compression. SPS exhibits the rapid collapse characteristics of porous spheres layer by layer, and it shows four sharp valley forces and significant negative stiffness characteristic. In addition, the specific energy absorption (SEA) value of SPS is higher than that of SQPS 30.84%. The compression capacity of porous spheres is stronger than that of porous cubes. This study furtherly discuss the mechanical behavior of SPS with different structural parameters. The negative stiffness characteristic, energy absorption efficiency and deformation mode of SPS depends on the strength combination of porous spheres and hollow cylinders, and smaller overall cell size, more cell layers, and thicker cells contribute to improving the anti-compression properties of SPS. The SEA values of SPS- T1.6 and SPS- F7 are 12.52% and 12.16% higher than that of SPS. In summary, SPS shows novel mechanical properties, providing a reference for the design of new energy absorbers.

Deep learning empowering design for selective solar absorber

Abstract The selective broadband absorption of solar radiation plays a crucial role in applying solar energy. However, despite being a decade-old technology, the rapid and precise designs of selective absorbers spanning from the solar spectrum to the infrared region remain a significant challenge. This work develops a high-performance design paradigm that combines deep learning and multi-objective double annealing algorithms to optimize multilayer nanostructures for maximizing solar spectral absorption and minimum infrared radiation. Based on deep learning design, we experimentally fabricate the designed absorber and demonstrate its photothermal effect under sunlight. The absorber exhibits exceptional absorption in the solar spectrum (calculated/measured = 0.98/0.94) and low average emissivity in the infrared region (calculated/measured = 0.08/0.19). This absorber has the potential to result in annual energy savings of up to 1743 kW h/m2 in areas with abundant solar radiation resources. Our study opens a powerful design method to study solar-thermal energy harvesting and manipulation, which will facilitate for their broad applications in other engineering applications.

Inverse design of omnidirectional coherent absorbers for optical power beaming applications.

An efficient photovoltaic power converter is a critical element in laser power beaming systems for maximizing the end-to-end power transfer efficiency while minimizing beam reflections from the receiver for safety considerations. We designed a multilayer absorber that can efficiently trap monochromatic light from broad incident angles. The proposed design is built on the concept of a one-way coherent absorber with inverse-designed aperiodic multilayer front- and back-reflectors that enable maximal optical absorption in a thin-film photovoltaic material for broad angles. We argue that the broad bandwidth is achieved through an optimization search process that automatically engineers the modal content of the cavity to create multiple overlapping resonant modes at the desired angle or frequency range. A realistic design is provided based on GaAs thin films with inverse-designed multilayer binary AlAs/AlGaAs mirrors. The proposed device can pave the way for efficient optical power beaming systems.

Design of a multilayer wideband absorber based on frequency selective surface

Design of a multilayer wideband absorber based on frequency selective surface

Confined dissipation cage in dual-shell structured Ti3C2Tx@CNTs/Ni hollow spheres for lightweight and broadband electromagnetic wave absorption

Ti3C2Tx can dissipate energy well due to its high conductivity, but at the expense of severe electromagnetic (EM) wave reflection, which is exacerbated by self-stacking. Despite various attempts to tackle this problem, the excessive isolation of Ti3C2Tx and massive high-density inorganic components render these designs unfavorable for lightweight and broadband absorption. Meanwhile, improvements in absorption performance are related to active surface and polarization interface expansion, as well as conductive path reconstruction, but the main contributing factor remains unknown. In this work, the dual-shell structured Ti3C2Tx@CNTs/Ni-HS (hollow sphere) composites are fabricated. This structure creates a confined dissipation cage, where the CNTs/Ni shell confines the electron transfer among spheres and prevents self-restacking and the tightly contacted Ti3C2Tx shell forms an uninterrupted conductive path for effective dissipation. Therefore, Ti3C2Tx@CNTs/Ni-HS-1 exhibits a broad effective absorption band of 6.1 GHz and a minimum reflection loss of −64.6 dB at a mass ratio of only 15 wt%. Importantly, when hollow structure cracks, although large active surface and polarizable interface remain, the absorption capacity of fragmented Ti3C2Tx@CNTs/Ni-HS-1 deteriorates, indicating rational conductive path in confined dissipation cage is the main factor in achieving excellent performance. This work provides new insight for the rational design of high-performance absorbers.

Material Plasma Exposure eXperiment High Heat Flux Microwave Absorber Design, Manufacture, and Articles Test

The Material Plasma Exposure eXperiment (MPEX) at Oak Ridge National Laboratory is in the final design phase. MPEX will be capable of exposing neutron-irradiated materials to plasmas for the study of plasma-material interaction. This facility will provide information about the complex effects of plasmas on materials and contribute to examining new materials that can withstand high heat fluxes and high ion fluences for future fusion devices. MPEX plasma is heated by 70-GHz or 105-GHz electron Bernstein wave/electron cyclotron heating (ECH), and the high-frequency microwaves are prone to scattering microwave power, which can have detrimental effects, especially on diagnostic components. A large portion of the injected ECH power is expected to be absorbed by plasma, but the remainder requires that microwave absorbers be placed immediately upstream and downstream of the ECH launcher to minimize stray microwaves leaving the ECH region. These microwaves can inadvertently heat components that cannot be shielded or otherwise protected. The microwave absorber design is based on an array of pyramid-shaped ceramic tiles brazed to a water-cooled explosion-bonded heat sink and a stainless steel plate to produce one tile module. Computational fluid dynamics and structural analyses were performed to optimize and validate the design. Multiple test coupons were produced to validate the process for brazing the two different tile materials to the Glidcop AL-15 baseplate. The articles were tested to evaluate the reliability and thermal performance through exposure to an electron beam with a heat flux of up to 1.5 MW/m2. Nondestructive testing was performed before and after testing to identify voids or separations that may have been introduced by the high heat flux. This paper discusses the details of high heat flux microwave absorber design, manufacturing details and associated challenges, and test results, demonstrating the effectiveness of the proposed design.

Confinement engineering to enhance broadband microwave absorption of hierarchically magnetic carbon tubular composite

The development of carbon materials remains challenging due to a single loss mechanism and an electromagnetic impedance mismatch. Confinement engineering has been shown to provide a chemical microenvironment for the formation of confined object materials in order to regulate the physical and chemical properties of nanomaterials. In this study, we choose lightweight one-dimensional biomass carbon microtubes as the base, for the first time cleverly using the transition metal nickel only on the inner surface of carbon microtubes with an ultra-small CNT array, and construct a composite with a hierarchically magnetic carbon tubular structure (HMCT-I) on the basis of the theoretical analysis of electromagnetic parameters. Thanks to enhanced magnetic loss and the synergy of multiple polarization losses, HMCT-I ultimately shows encouraging microwave-absorption performance, with an ultra-wide effective absorption bandwidth of 8.44 GHz and an ultra-low reflection loss of −77.7 dB. In addition, the reasonable design makes HMCT-I have superior environmental stability, broadening the way for developing practical broadband carbon-based composite absorbers. This work also provides theoretical guidance and innovative ideas for the design of broadband and efficient microwave absorbers.

Experimental and numerical methods for the performance analysis of a tubular three-pass solar air heater

A new absorber surface is designed for solar air heaters to make them compact and enhance heat transfer parameters. The current paper presents the novel absorber design using a tubular surface having three-pass in counter-flow. The absorber tubes are constructed from thin sheets of aluminium; 15 tubes are closely spaced in line with each other to establish three-pass, i.e. five tubes per pass. The research paper investigates numerically and experimentally the thermo-hydraulic performance of a Tubular Three-pass Solar Air Heater (TTPSAH). The numerical model was developed using MATLAB to predict the performance and outlet air temperature. The error in numerical and experimental evaluation is approximately 5%, showing promising results. It was found that the TTPSAH accelerates heat transfer in a compact surface area. The maximum thermal efficiency was evaluated as 60.04%, 41% and 33.3% for an airflow rate of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s respectively. Thermal enhancement with a maximum outlet air temperature of 110.6 °C, 91.4 °C and 80.2 °C was recorded at a mass flow rate of 0.002 kg/s, 0.004 kg/s and 0.006 kg/s in glazed conditions. Furthermore, the research includes an estimation of the energy cost per kilowatt-hour (kWh), which amounts to $0.017, $0.025, and $0.0311 for mass flow rates of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s, respectively.

Metamaterial as perfect absorber for high sensitivity refractive index based biosensing applications at infrared frequencies

In this paper, we introduce a novel design of a metamaterial unit cell absorber, which is based on a metal/insulator/metal sandwich structure. The design is subjected to comprehensive finite element method computational analysis to ensure accurate and reliable results. The proposed metamaterial sandwich structure demonstrates exceptional absorption performance, achieving a nearly perfect absorption rate of 99.996% at the resonance infrared frequency of 39.8 THz. To provide a detailed theoretical explanation of nearly perfect absorption, we employ the effective medium theory, impedance matching, and field distribution analysis. Additionally, we have optimized the structural parameters of the sensor to maximize its absorption peak. This includes optimizing the thickness of the gold (Au) layer (from 0.03 to 0.28 μm), the distance between the L shape corners (from 0.60 to 0.90 μm), and the thickness of SiC dielectric spacer (from 0.20 to 0.45 μm). Furthermore, we showcase the remarkable sensitivity of the proposed metamaterial unit cell in detecting subtle changes in the refractive index through the implementation of a sensing medium setup in our model. Remarkably, we achieve a frequency shift sensitivity of 3.74 THz/RIU, along with a quality factor of 10.33, for a wide range of refractive indices (1.0–2.0). Moreover, for cancer detection, we attain a sensitivity of 3.5 THz/RIU. These findings highlight the exceptional performance of our approach in accurately detecting changes in refractive index, making it a promising candidate for various sensing applications. The novelty of our work lies in the design of a metamaterial unit cell structure. This configuration exhibits several noteworthy features, including wide incident angle () coverage up to 60°, polarization insensitivity, exceptional frequency shift sensitivity, high absorption peaks across a wide range of refractive indices, and the ability to distinguish cancer cells from healthy ones.

Dataset Shrinking for Accelerated Deep Learning-Based Metamaterial Absorber Design

The design of metamaterial absorbers (MMAs) using deep learning (DL) models typically involves the construction of a large dataset through time-consuming full-wave simulations (FSs). In this letter, an efficient dataset shrinking method is proposed that employs both electromagnetic (EM) theory and DL theory to enhance design efficiency. The impact of each MMA on training the DL model is estimated through the equivalent circuit model (ECM) of the MMA by analyzing the gradients of the MMA parameters with respect to DL model training. Impact sampling is then used to construct a smaller dataset while still maintaining DL model performance and reducing time on FS. The proposed approach is validated through the design of single-and multilayer absorbers using the inverse-DL algorithm and DL integrated into the genetic algorithm (GA). Numeric results demonstrate that the proposed method achieves a much faster design than those without optimized dataset construction processes.

Machine learning in design of broadband terahertz absorbers based on composite structures

Metasurface absorbers have gained increasing attention in the field of electromagnetic (EM) absorption in recent years. The conventional design method often involves designing various structures and comparing absorption bandwidth and intensity to determine the absorber's structural parameters. The absorption of EM waves by absorbers involves a complicated process of electric field excitation and impedance matching. Although design experience can reduce the number of design iterations, the selection of artificial parameters is often imprecise and can result in design bias. Fortunately, machine learning (ML) algorithms offer the possibility of automating the design of critical parameters for metasurfaces, which can effectively reduce the laborious design process and the high cost of trial and error. In this study, a pyramid-based metasurface absorber (PMA) and an inverted pyramid-based metasurface absorber (IPMA) were designed and optimized using the random forest (RF) algorithm. The results show that the absorption bandwidths of the two absorber models are 2.68 THz and 2.42 THz, respectively, and the mean absolute percentage error (MAPE) is only 0.60%, which is significantly better than other classical ML and deep learning (DL) algorithms. This study offers a new approach for designing complex systems related to EM wave absorption, reflection, and transmission propagation.

Design of near-ideal and omnidirectional selective solar absorber for high-temperature applications

Efficient absorption of solar radiation with minimal thermal losses is required for efficient solar-to-thermal energy conversion. For this purpose, spectrally selective and omnidirectional surfaces are required that have strong, ideally unity, absorption in the solar spectral window for all incident angles and low, ideally zero, emissivity in the spectral range of blackbody radiation at operating temperature. In this article, we propose theoretically and experimentally lithographic free broadband and omnidirectional solar absorber for high-temperature applications made in a dielectric-metal-dielectric-metal fashion. We have used chromium (Cr), titanium (Ti), and tungsten (W) as a metal layer in the designed absorber due to their high thermal stability at high temperatures and compared their performance. The power balance equation is used to calculate the steady-state temperature considering free and forced convection conditions. W-based absorber shows >90% absorption in the solar window below cutoff wavelength for blackbody working at 600 K with <10% emissivity in the thermal window. Finally, we fabricate the W-based sample and experimentally measure the temperature rise of 100 K under one sun condition. The designed absorber can be used for several solar-thermal applications including solar-steam to electricity generation, water purification, space heating, and solar-thermal energy storage.

Few-mode fiber based saturable absorber for ultra-fast fiber laser at 2 μm

The saturable absorption of the single mode-few-mode-single mode fiber (SMF-FMF-SMF) structure with respect to its passive mode-locking performance is still largely unexploited, although it is more conducive to the design and performance of the saturable absorber (SA) based on the nonlinear multimode interference effect. A series of FMF-based saturable absorbers with different FMF lengths are employed in passively mode-locked Tm fiber lasers for ultrafast pulse generations at 2 μm. The mode-locking performances using different FMF-based saturable absorbers were demonstrated. By comparing the saturable absorption characteristics and the respective mode-locking performances, we can conclude that it is easier to obtain the stable mode-locking output using saturable absorbers with the FMF lengths of 15.12 cm and 30.2 cm. The FMF saturable absorber with a 15.12 cm FMF has a large modulation depth of 40% and a saturation fluence of 108.23 μJ /cm2 which delivers ultrafast pulses with pulse width of 1.96 ps at 1878 nm. In addition, the harmonic mode-locking with stable and well-organized pulse trains could also be instantaneously achieved by increasing the pump power within the same cavity. Our results indicate that the SMF-FMF-SMF structure could operate as a SA while tuning its saturable absorption properties by changing the FMF length making it advantageous for mode locking fiber lasers.

Optimized Design of Plasma Metamaterial Absorber Based on Machine Learning

Metamaterial absorbers have become a popular research direction due to their broad application prospects, such as in radar, infrared imaging, and solar cell fields. Usually, nanostructured metamaterials are associated with a large number of geometric parameters, and traditional simulation designs are time consuming. In this paper, we propose a framework for designing plasma metamaterial absorbers in both a forward prediction and inverse design composed of a primary prediction network (PPN) and an auxiliary prediction network (APN). The framework can build the relationship between the geometric parameters of metamaterials and their optical response (reflection spectra, absorption spectra) from a large number of training samples, thus solving the problem of time-consuming and case-by-case numerical simulations in traditional metamaterial design. This framework can not only improve forward prediction more accurately and efficiently but also inverse design metamaterial absorbers from a given required optical response. It was verified that it is also applicable to absorbers of different structures and materials. Our results show that it can be used in metamaterial absorbers, chiral metamaterials, metamaterial filters, and other fields.

A switchable terahertz metamaterial absorber between ultra-broadband and dual bands

Based on the phase change properties of vanadium dioxide (VO2), we propose a terahertz metamaterial absorber that can be switched flexibly between ultra-broadband and dual bands. The absorber consists of a resonator array above a conductive ground layer separated with a dielectric spacer, which includes four square-loop VO2 resonators and a crossed gold resonator in each unit cell. By changing the conductivity of VO2 through thermal control, the absorber can achieve the switching between ultra-broadband absorption and dual-band absorption. Simulation results show that at high temperature, the absorber realizes more than 90% absorption bandwidth in the range of 3.98 to 9.06 THz, which can be elucidated by the wave-interference theory and impedance matching theory. At low temperature, up to 95% of the dual-band absorption occurs at 5.95 and 6.95 THz, which originates the dipole mode and nonlocal surface-Bloch mode of metal resonators. In addition, the absorber has the advantages of polarization-independence and wide-angle absorption. Compared with previous studies, our design can switch between two absorption modes and its absorption performance is greatly improved. The proposed absorber design scheme is expected to expand terahertz devices and enable a variety of applications in the terahertz range, such as modulation, sensing, stealth, and switching devices.

Design of sound absorbers based on open-cell foams via microstructure-based modeling

Design of sound absorbers based on open-cell foams via microstructure-based modeling

Design and optimization of broadband metamaterial absorber based on manganese for visible applications

Metamaterial absorbers have been extensively researched due to their potential applications in photonics. This paper presents a highly efficient Broadband Metamaterial Absorber (BMA) based on a Manganese–Silica–Manganese three layer structure with a shaped pattern at the top layer. For maximum absorption efficiency, the geometrical parameters of the proposed absorber have been optimized based on Particle Swarm Optimization (PSO). The optimal structure with a thickness of 190 nm, can achieve more than 94% absorption spanning visible band (400–800) nm with 98.72% average absorption, and more than 90% absorption over the range from 365 to 888 nm. In the range from 447 to 717 nm, the design presented above 99% absorptivity, providing an ultra-wide bandwidth of 270 nm. The physical mechanism of absorption is illustrated through the exploration of the electric and magnetic field distributions. Additionally, the proposed structure maintains 85% absorption stability for wide incident angles up to 70° for both the TE and TM polarizations under oblique incidence. Further, the optimized absorber structure with excellent absorption capabilities makes it suitable for various applications, including optical sensors, thermal emitters, and color imaging applications.

Design and Manufacturing of a Hexapattern Frequency Selective Surface Absorber for Aerospace Stealth Application.

Integrated frequency selective surface (IFSS) absorbers with larger bandwidth, effective reflection loss, polarization-insensitive characteristics, angular stability with compact/thin design, and ease of fabrication have captivated significant importance in stealth technology. Herein, we report on an IFSS absorber that has been designed, simulated, and implemented for manufacturing to achieve effective stealth properties. Initially, frequency selective surface (FSS) layers have been designed that comprise a closed centroid honeycomb structure surrounded with four annular hexagonal rings, splitted, alternatively, and enveloped with four L-shaped elements. The simulated pattern has been optimized on glass fabric for reflection loss (RC, dB) at a thickness of ∼0.1 mm by choosing sheet resistance of pattern 110 Ω/□. A FSS layer combined with interlayer lossy dielectric laminates (1.8 mm) and a carbon-fabric-reinforced-plastic ground has been simulated as an IFSS absorber. The performance of RC, in normal and angular configuration (0-60°), under transvers an electric/magnetic mode of polarization, including analysis of the displacement current, volume power loss distribution, and complex admittance has been carried on IFSS. Subsequently, the proposed absorber has been fabricated using customized carbon-based resistive ink imprinted on glass fabric by mask lithography compounded with laminates (a carbon black powder/epoxy composite) and ground. Their manufacturing details, including free space and anechoic chamber RC measurements, have been presented. The simulated and experimental RC performances of the absorber are found to be in good agreement, possessing minimal 10 dB reflection loss (90% absorption) with a sample thickness of 1.9 mm (0.05λL, where λL corresponds to a lower operating frequency), covering 76% fractional bandwidth in X and Ku bands. The proposed design architecture of the IFSS is ideally suitable for aerospace stealth platforms.

Effect of alcohols on CO2 absorption, phase splitting, and desorption behaviors of biphasic anhydrous system: The primary amine-tertiary amine of DGA-PMDETA

Chemical absorption with organic amine solution is the most mature technology for CO2 capture. Some biphasic anhydrous absorbents show potential in reducing regeneration energy consumption, but high viscosity of the CO2 rich phase hinders its practical application. Alcohols are commonly employed as dilutes to reduce viscosity reducers, while its effect on CO2 absorption and phase splitting behaviors are still unclear. In this study, the effects of alcohols on CO2 absorption and phase-splitting of biphasic anhydrous 2-(2-Aminoethoxy)ethanol (DGA) -N,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) -alcohol systems are investigates. Adding alcohol reduces the viscosity of the CO2-rich phase, enhances desorption rate, and decreases the phase splitting time. The rich phase entrainment stage and the rich phase thickening stage, can be distinguished along with during CO2 absorption. The majority DGA reacts with CO2 in the rich phase since the phase splitting begins. This work may provide some basis for further biphasic absorbent design and regulation.

Broadband metamaterial absorber for stealth applications at K-band

This paper focuses on the design and analysis of a polarization-insensitive wide-angle broadband metamaterial absorber for stealth applications at the K band. The unit cell of the metamaterial absorber is comprised of a symmetrically arranged ladder shape geometry made of copper metal, which is imprinted on a metal-backed FR-4 substrate. The structure shows more than 91% absorptivity ranging from 21.2 to 28.2 GHz for both transverse electric (TE) and transverse magnetic (TM) polarized waves under normal incidence. The topology is four-fold symmetric and yields polarization-insensitive responses for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80% absorptivity holds up to 45° incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonances in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. The novelty of the proposed absorber lies in its unique metallic pattern on a λ0/8 thin FR-4 substrate while showing the wide absorption bandwidth to normal and oblique incidence. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction applications at the K band.