Microwave Absorption Research Articles

Miniaturized broadband absorber based on fractal structure metasurface

A broadband metasurface microwave absorber with a miniaturized size is presented under two mechanisms. A frequency selective surface based on the Minkowski (MSK) fractal structure is constructed to provide a lower resonance frequency with the similar size, and the Salisbury screen is designed to create high-frequency resonance. Then, a second-order MSK fractal ring is loaded to realize impedance matching over the entire bandwidth. The absorption performance of the metasurface absorber (MA) proposed is validated by the equivalent transmission line model, the Smith chart, and the surface current distribution. The simulation results demonstrate an absorption bandwidth of 125% with an absorption rate of >90% over 0.3–1.3 GHz. The thickness of the proposed absorber is 0.075λ, and the size of the unit cell is 0.1λ. The developed absorber exhibits stable absorption performance for both TE and TM polarizations within an incident angle of 40°. The experimental results agree with those of full-wave simulation.

Ultrawideband Lu chaotic surface-based microwave absorber design for stealth applications

Ultrawideband Lu chaotic surface-based microwave absorber design for stealth applications

High-Entropy (MnCoNiFeCu)-O@PPy Nanocomposites with Enhanced Corrosion Resistance for Microwave Absorption and Loss Control

High-Entropy (MnCoNiFeCu)-O@PPy Nanocomposites with Enhanced Corrosion Resistance for Microwave Absorption and Loss Control

Enhancing Signal Purity in Josephson Structure Measurements

Abstract Superconducting Josephson structures play a significant role in quantum‐state engineering. Achieving high‐fidelity quantum state measurements in superconducting Josephson structures requires ultra‐low noise environments and robust signal purification techniques. Here, the advanced low‐noise signal measurement system designed for dilution refrigerators is presented, integrating multi‐stage cryogenic filtering and electromagnetic shielding strategies to suppress noise sources across a broad frequency spectrum. The effectiveness of low‐pass RC filters is demonstrated, silver‐epoxy microwave absorbers, and optimized ground isolation to achieve an unprecedented noise reduction, enabling sub‐nanoampere switching current distribution measurements superior to commerical systems at mK temperatures. The system is optimized for precision studies of superconductor‐insulator‐superconductor, superconductor‐ferromagnet‐superconductor, and superconductor‐normal metal‐superconductor Josephson junctions with low critical currents. This approach establishes a reliable framework for next‐generation quantum electronic experiments, ensuring that observed switching phenomena are governed by intrinsic device physics rather than environmental perturbations.

Characterization of Mn1.3FeTi2Ow and Fe4Mn6V7Ow Nanocomposites by Ferromagnetic Resonance (FMR)

Nanocomposites based on multicomponent metal oxides, such as Mn1.3FeTi2Ow and Mn6Fe4V7Ow, present tunable structural and magnetic properties with high potential for technological applications. In this study, these nanomaterials were synthesized by urea and chalconcarboxylic acid assisted chemical routes, followed by heat treatments at different temperatures (400°C, 800°C and 1000°C). Magnetic characterization was performed by Ferromagnetic Resonance (FMR) spectroscopy, with analysis of the g factor and the line width at half height (ΔH). The results indicated that increasing the temperature favors the magnetic ordering and the formation of coherent crystalline phases, reflected in the progressive decrease of ΔH and stabilization of the g values. The Mn1.3FeTi2Ow structure showed optimized behavior at 1000°C, while Mn6Fe4V7Ow exhibited significant magnetic improvements already at 800°C. Thermal evolution allowed correlations between structure, magnetic ordering and local anisotropy, demonstrating the potential of these materials for applications in magnetoresistance devices, magnetic sensors, hyperthermia devices and microwave absorption.

Ionogel-based optically transparent multifunctional metasurface for tunable microwave absorption and vibrational energy harvesting

Ionogel-based optically transparent multifunctional metasurface for tunable microwave absorption and vibrational energy harvesting

Research on the Geometry Control and Microwave Absorption Performance of Auxetic Materials

There is great potential for the development of microwave-absorbing materials (MAMs) for structural regulation. Auxetic structures have excellent mechanical properties, which can be applied to multifunctional MAMs in various fields. Here, the microwave absorption performances of the auxetic structures were simulated using the High-Frequency Structure Simulator (HFSS), by regulating the structure, dielectric constant, layer number, and pore size. The simulation results show that increasing the dielectric constant, layer number, or decreasing pore size will lead to a decrease in the frequency of minimum reflection loss (RLmin). The main purpose of this study is to elucidate the influence of structure, dielectric constant, layer number, and pore size on the absorption performance of auxetic structures and obtain practical auxetic MAMs with a performance of RLmin < −30 dB and effective absorption bandwidth (EAB) > 3 GHz. Finally, practical auxetic MAMs between 8 and 18 GHz and MAMs optimized in dielectric constant were obtained, which were proven to have the advantages of lightweight characteristics, high absorption, and wide bandwidth. The four structures exhibit great RLmin values of −51.09, −55.52, −47.09, and −54.98 dB with wide EAB values of 3.25, 3, 4.75, and 4.5 GHz, demonstrating the strong electromagnetic wave absorption performance of auxetic structures. This work provides theoretical guidance for the study of auxetic structures in the field of microwave absorption and provides an effective approach for multi-disciplinary research on MAMs.

Design and Optimization of Gradient Foam Core Sandwich Structures With Superior Microwave Absorption Performance

ABSTRACTWith the increasing demand for omnidirectional wideband radar stealth performance in fifth‐generation fighter jets, foam sandwich structures used in aerospace must possess excellent microwave absorption (MA) capabilities. In this study, 20 types of rigid closed‐cell microwave‐absorbing composite foams were prepared using a microsphere foaming method, with short carbon fibers (SCF), multi‐walled carbon nanotubes (MWCNT), and carbonyl iron powder (CIP) as absorbing agents and epoxy resin (EP) as the matrix. The effects of absorbing agents' types and contents on the microwave absorption performance of the foams in the 2–18 GHz range were analyzed. Based on the experimental data, a data enhancement method was employed to expand the material database of foams. Subsequently, a multi‐objective optimization of gradient foam sandwich structures (GFSS) was conducted using a genetic algorithm. The effective absorption bandwidth (EAB) of the sandwich structures ranged from 13.9 to 16.0 GHz, the minimum reflection loss (RLmin) reached −94.4 dB, and the ratio of EAB to density (η) was 34.8–50.2 GHz g−1 cm3. Additionally, the gradient foam with a thickness of 20 mm exhibited an EAB of 16.0 GHz and an η value of 60.1 GHz g−1 cm3. The effectiveness of the optimization results was validated through experimental measurements. A finite element analysis (FEA) model was established to investigate the broadband MA mechanisms of the GFSS. Finally, the bending performance of the GFSS was evaluated by conducting three‐point bending tests. This study provides an effective approach for the design and fabrication of lightweight GFSS with broadband microwave absorption functionality.

Development of an electron spin resonance spectroscopy code for measuring carbonate radicals in tooth enamel and verification of its practicality using irradiated Japanese macaque teeth

Purpose We developed a new computer program for the application of electron spin resonance (ESR) to dosimetry of wild animals related to the Fukushima Daiichi Nuclear Power Plant accident. Materials & Methods The ESR spectra of carbonate radicals and other inorganic radicals are calculated by the complete elliptic integral. A simulated annealing method is implemented for the parameter optimization. A cost function is designed to include the second derivative form of the microwave absorption spectrum to improve the fitting accuracy. As a testing ground for the developed code, we prepared tooth enamel samples from a Japanese macaque captured in a control area. Results The developed code well reproduced the measured ESR spectrum. With a test spectrum, we demonstrated that the cost function that includes the second derivative form of the microwave absorption spectrum is helpful for the precise analysis of the low-dose enamel samples. The smoothness of the ESR spectrum plays an important role in utilizing this feature. Conclusion The developed computer code can be used to analyze the ESR spectrum of tooth enamels of Japanese macaques. A precise analysis is essential to lower the detection limit and expand the applicability of ESR dosimetry. The code is independent of the computer operating system and is available publicly.

A Recyclable, Adhesive, and Self-Healing Ionogel Based on Zinc-Halogen Coordination Anion Crosslinked Poly(ionic Liquid)/Ionic Liquid Networks for High-Performance Microwave Absorption.

In the past, powder-like microwave absorbers have made notable breakthroughs in performance enhancements, but complicated processes and undesirable properties have limited their practical application. Herein, a novel poly(ionic liquid) (PIL)-based ionic gel with excellent microwave absorption properties was prepared via a facile UV-initiated polymerization method. By simply adjusting the mole ratio of the polymerizable ionic liquid (IL)monomer and the IL dispersion medium, the microwave absorption properties of the obtained ionic gels can be tuned. A maximum reflection loss (RLmax) of -45.7 dB and an effective absorption bandwidth (EAB) of 8.08 GHz were achieved, which was mainly ascribed to high ionic conduction loss induced by the high content of the dispersion medium. Furthermore, it displayed recyclable, adhesive, and self-healing properties, thus providing a new candidate for developing efficient microwave absorbers for practical applications.

Graphitization Optimization of Cobalt-Doped Porous Carbon Derived from Seaweed Sludge for Enhanced Microwave Absorption.

Utilizing biomass resources to develop carbon-based microwave-absorbing materials adheres to the principles of sustainable development. Nevertheless, the single loss mechanism of pure carbon materials is limited. Additionally, the carbonization of artificially synthesized polymers has poor environmental performance and involves complex processes. These issues restrict their performance and broader applicability. In this study, cobalt-doped seaweed sludge porous carbon (Co/SSPC) with different cobalt contents was synthesized via a simple grinding-carbonization treatment. The addition of cobalt can regulate the graphitization degree of porous carbon, achieving a suitable amorphous-to-crystalline carbon ratio of 2.05. This not only enhances magnetic loss but also modifies dielectric loss and optimizes impedance matching. The construction of synergistic magnetic and dielectric loss mechanisms enables Co/SSPC to exhibit excellent microwave absorption performance. Specifically, Co/SSPC achieved a minimum reflection loss (RLmin) of -66.91 dB at a thickness of 4.79 mm and an effective absorption bandwidth (EAB) of 5.09 GHz at a thickness of 1.6 mm. This study provides a practical approach for the functional application of natural polymer waste algal sludge and highlights its potential in the low-cost production of microwave absorbing materials.

Microwave Welding of Polypropylene Using SiC Nanowires as Susceptors: Effect of Silane Modification on Joint Performance

Abstract A reinforced silicon carbide nanowires/polypropylene (SiCNWs/PP) nanocomposite welded joint was successfully fabricated using microwave welding. To improve compatibility between hydrophilic SiCNWs and hydrophobic PP, silane coupling agents were employed for surface modification, leveraging their amphiphilic properties. Vinyltriethoxysilane (VTES) and γ-methacryloxypropyltrimethoxysilane (KH570) were selected as surface modifiers, with Fourier-transform infrared spectroscopy confirming the successful grafting of vinyl and methacryloxy groups onto SiCNWs. Incorporating 1 wt% VTES- and KH570-modified SiCNWs significantly enhanced the mechanical performance of the welded joints, improving tensile strength, flexural strength, and modulus of elasticity. The tensile strengths of joints with 1 wt% VTES- and KH570-modified SiCNWs reached 2.45 MPa and 2.83 MPa, respectively, surpassing the 2.21 MPa recorded for joints with unmodified SiCNWs. Flexural strength also improved substantially, increasing by 123.43% and 201.86% for 1 wt% VTES- and KH570-modified SiCNWs, respectively, compared to approximately 7 MPa for unmodified SiCNWs. Notably, joints with 1 wt% KH570-modified SiCNWs exhibited superior mechanical properties compared to VTES-modified joints, attributed to the higher hydrophobicity of the methacryloxy group. However, increasing the concentration of silane coupling agents to 3 wt% led to a decline in mechanical performance, likely due to insufficient microwave absorption and incomplete weld formation. The tensile strengths of joints with 3 wt% VTES- and KH570-modified SiCNWs decreased to 2.25 MPa and 2.69 MPa, respectively. This study highlights the potential of silane-modified SiCNWs for fabricating high-strength nanocomposite joints via microwave welding, providing valuable insights into the advancement of thermoplastic joining technologies. Graphical Abstract

A novel multiphysics-based microwave continuous flow reactor with rotating electromagnetic heating

Abstract Continuous-flow microwave heating is a sustainable thermal technology that is highly esteemed within both the chemical and food processing sectors owing to its short residence time, modest environmental impact and the highly responsive thermal effect characteristic of microwave energy. However, the low efficiency of converting microwave energy into thermal energy and uneven heating during microwave continuous flow heating processes have hindered its industrial application. To overcome these challenges, this study proposed an optimized microwave continuous-flow reactor integrating a rotating electromagnetic field and coupled multilayer flow components. In this study, A multiphysics simulation framework is developed to couple the electromagnetic field, laminar flow, and temperature field, solving the Maxwell equations, flow field equations, and heat transfer equations numerically. The impact of key structural parameters (microwave feeding mode, tube distribution, reactor material, and wall thickness) and process parameters (flow rate and power) on microwave heating performance was analyzed. The results demonstrate that compared with the traditional horizontal energy feeding method, vertical waveguide excitation improves electric field uniformity by 15%-20% and reduces temperature variation between regions by up to 22%. The use of copper and aluminum reactor materials enhances microwave absorption efficiency by 12%-15%, while an optimal chamber thickness of 4 mm maximizes energy conversion. This work uniquely evaluates the optimal fluid volume for maximizing microwave-to-heat conversion and further analyzes the impact of rotating electromagnetic heating on energy efficiency, verifying the feasibility and application potential of the proposed design in industrial continuous microwave heating.

Fabrication and structural optimization of integrated gradient honeycombs with the conductive/absorbing coatings for ultra-wideband microwave absorption

With the advancement of complex radar reconnaissance and stealth technologies, research on microwave-absorbing materials (MAM) in a broad frequency range is in great demand, especially for lightweight honeycomb structures designed for aerospace applications. The challenge lies in achieving a balance between small thickness and wideband absorption in high-performance aramid honeycombs. This study proposes a novel approach known as the integrated gradient honeycomb structure (IGHS). The IGHS is designed based on the theory of impedance matching through electromagnetic parameter simulations of the graphene conductive/carbon black absorbing coatings and further optimized by tailoring the factors such as the height of the conductive/absorbing coatings, the square resistance of the conductive coatings, and the thickness of the absorbing coatings, all while maintaining an overall height of 15 mm. The optimized integrated gradient honeycomb is fabricated by employing an experimental anisotropic impregnation technique, achieving a reflection loss below –10 dB across the whole frequency range of 2.2–18 GHz, consistent with the simulated results, with the compressive strength of the structure reaching 4.76 MPa, along with shear strengths of 1.25 MPa and 1.72 MPa in the W-direction and L-direction, respectively. In the present work, a cyclical system integrating simulation and experimentation has been established, reducing the trial-and-error costs for researchers and offering valuable insights for the design of a gradient honeycomb structure (GHS) for wide-frequency microwave absorption.

Improving microwave absorbing properties of epoxy resin with silane surface-modified copper oxide nanoparticles integration

Improving microwave absorbing properties of epoxy resin with silane surface-modified copper oxide nanoparticles integration

Robust Single-Walled Carbon Nanotube-Coated Aramid Fibers with Tunable Conductivities for Broadband Radar Absorption in Honeycomb Structures.

Single-walled carbon nanotubes (SWNTs), renowned for their high strength and electromagnetic properties, provide a potential solution for next-generation honeycomb-structured radar-absorbing materials (HRAMs). However, the integration of SWNTs into HRAMs is hindered by challenges including poor dispersion, wash-off loss, and the absence of scalable, compatible fabrication methods. Herein, we address these challenges by synthesizing tunable conductive SWNT-coated aramid fibers (SWNT-AF) via a continuous dip-coating method and integrating them into aramid paper-based composites (APBC) to fabricate HRAMs. The SWNT-AF serve as both structural reinforcements and dielectric loss centers within APBC, avoiding direct dispersion of SWNTs into the pulp and thereby mitigating agglomeration and wash-off loss. The optimized APBC, reinforced with these tailored fibers, exhibit improved dielectric properties, resulting in enhanced microwave absorption performance. The fabricated HRAMs achieve an effective absorption bandwidth of 14.8 GHz (2.0-18.0 GHz) with an ultralow SWNT loading of 0.2 wt % and a thin thickness of only 30 mm, demonstrating a reflection loss of -47.78 dB. These results highlight the potential of SWNT-AF as lightweight, broadband radar-absorbing materials for stealth applications.

Microwave absorbent enhancement of multi-thermal field effect: Pyrolysis of waste printed circuit boards.

Microwave absorbent enhancement of multi-thermal field effect: Pyrolysis of waste printed circuit boards.

Multi-shell bowl-like carbon microspheres for lightweight and broadband microwave absorption

Multi-shell bowl-like carbon microspheres for lightweight and broadband microwave absorption

Recycling of solid waste fly ash and coal gangue for fabricating low-cost and high-efficiency FexSiy/SiC/C composites as microwave absorbents

Recycling of solid waste fly ash and coal gangue for fabricating low-cost and high-efficiency FexSiy/SiC/C composites as microwave absorbents

The new insight into the microscopic enhancement mechanism of microwave absorption based on the electromagnetic heterogeneous interface of carbon nanocavity.

The new insight into the microscopic enhancement mechanism of microwave absorption based on the electromagnetic heterogeneous interface of carbon nanocavity.