Microwave-absorbing Structure Research Articles

Asphalt mixture with nucleus-shell structural microwave enhanced aggregate: Structure design, preparation and performance

The natural aggregates in asphalt mixture with poor electromagnetic loss have poorer microwave absorption capacity and lower microwave energy utilization. The nucleus-shell structural microwave enhanced aggregate (NSSA) consisting with external microwave absorbing and heat collecting structure layer (ESL) and internal limestone was designed to enhance the microwave absorption capacity. The composition and thickness of the ESL were determined. The microwave heating efficiency, microwave energy utilization rate and water stability of asphalt mixture with NSSA and the influence of NSSA on the distribution of electromagnetic field intensity were studied by laboratory test and numerical simulation. The electromagnetic parameters test results show that the ESL had better impedance matching with air when the SiC: Fe3O4: cement: water = 1:2:15:6.3. The ESL thickness should not exceed 4.68 mm considering the penetration ability of 2.45 GHz electromagnetic wave. The microwave heating test results show that the heating rate and energy utilization rate of NSSA were 1.76 times and 5.93 times higher than those of limestone. Furthermore, the asphalt mixture with NSSA had higher heating rate, temperature uniformity and energy utilization rate. The overall water stability of asphalt mixture with NSSA remained the same or even better because the ESL wrapped the pores inside the limestone. The simulation results show that the asphalt mixture with NSSA had larger electromagnetic field intensity and better uniformity of electromagnetic field distribution during microwave heating. In conclusion, the NSSA and the asphalt mixture with NSSA has better microwave absorption capacity and microwave energy utilization rate.

Effective Medium Approximation Fused Optimization Strategy Derived New Kind of Honeycomb Microwave Absorbing Structure

The development of an efficient microwave absorbing structure (MAS) for the concealment of electromagnetic (EM) waves is a consistent puzzling errand. In this regard, a new kind of lightweight broadband multilayer honeycomb (HC)-MAS is developed, by coating aramid HC with Fe/SiC polymeric paint optimized using effective medium approximations. An environment-friendly, cost-effective, and easily accessible procedure is embraced for the preparation of microwave absorbing paint and diverse coatings at X-band. The multi-objective Jaya’s algorithm is envisioned for the optimum design of multilayered and hybrid HC-MASs. A multi-objective fitness function is integrated into the optimization algorithm to resolve the issue of the thickness-bandwidth (BW) tradeoff. As a result, optimized single layer HC-MAS with thickness 2.1 mm attains a reflection coefficient (RC) of −12.0 dB at 10.3 GHz with a BW of 3.2 GHz below the −10 dB threshold. The intriguing results are obtained by doing a dual-mode analysis, i.e., multilayer HC-MAS and multilayer hybrid HC-MAS. Hybrid HC-MAS achieves an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> of −31 dB at 9.8 GHz with a thickness of 2.8 mm exhibiting 100% BW. Besides, the response of the proposed structure is evaluated for distinct oblique angles of incidence. The findings offer a significant opportunity for the improvement of lightweight and broadband HC-MAS for stealth applications.

Space hypervelocity impact-shielding and microwave absorbing composite composed of cobalt-coated aramid fibers

This study explores the development of a space hypervelocity impact-shielding and microwave absorbing composite (SHIMAC) that can simultaneously function as both a microwave-absorbing structure and a shield against hypervelocity impacts of micrometeoroids and orbital debris (MMOD). The multifunctional SHIMAC was implemented using the electrically modified aramid fabric used in bulletproof materials fabricated from radio frequency (RF) magnetron sputtering to enhance the electromagnetic (EM) wave absorption performance. The SHIMAC composed of a cobalt-coated aramid fiber/epoxy-aramid fiber/epoxy-carbon fiber/epoxy composite exhibited excellent microwave absorption performance in the X-band (8.2–12.4 GHz) with an absorbent layer of a thickness of 2.545 mm. Moreover, electromagnetic wave scattering analysis was conducted with a cube satellite model; the analysis indicated that the proposed SHIMAC can effectively reduce the radar cross section. The hypervelocity impact-shielding performance of the SHIMAC was measured using a two-stage light-gas gun with projectile velocities of 3.1–3.6 km/s. Experimental results indicated that the average specific energy absorption characteristics of the SHIMAC were comparable to those of carbon fiber-reinforced polymer composites. The results indicated that the proposed SHIMAC can be employed in stealth satellite systems as a hypervelocity impact shield to simultaneously ensure the structural integrity and stealth performance with strong absorption, low weight, and less thickness.

Magnetron sputtering nichrome on fiber fabric to construct microwave-absorbing structure

Nichrome has a small resistance temperature coefficient, high resistance accuracy and resistivity, good thermal stability and chemical stability, which has great potential for high temperature stealth applications, yet not been mentioned in previous studies. In this paper, a microwave-absorbing structure based on Salisbury screen produced by nichrome coated quartz fiber fabric (NFF) and pristine quartz fiber fabric (PFF) is proposed. A direct current (DC) magnetron sputtering technique is used to form the nichrome coating onto the quartz fiber fabric. The morphology, element, and phase identification of nichrome coated quartz fiber fabrics were examined by SEM, EDS, and XRD, respectively. The reflectivity of the proposed structure of nichrome coated quartz fiber fabrics sputtered at one side or both sides is obviously different, and relative to the sputtering time and the number of pristine quartz fiber fabric tiers. The so-made microwave-absorbing structure is thin and lightweight, and exhibits good absorption performance in X and Ku frequency band, with wide bandwidth below − 10 dB from 8.5 to 15.5 GHz, and reached a lowest reflectivity of − 53 dB at 11.48 GHz.

Microwave absorbing structure using periodic pattern coated fabric

In this study, a microwave absorbing structure consisting of a periodic pattern coated glass fabric (PPCF) and a glass-fiber/epoxy composite as the spacer is presented using a practical approach for application in aircraft. To fabricate a PPCF, a carbon-based conducting material bar coating device was used. To test the performance of the PPCF, an X-band (8.2–12.4 GHz) microwave absorbing structure was fabricated using an autoclave and measured using a free-space measurement system. The return loss of the fabricated PPCF microwave absorbing structure was −27 dB at the resonance frequency, and the measurement result was well matched with the simulation result. Since the pattern was implemented on an uneven surface, the performance stability of the distribution of sheet resistance on the surface, pattern spreading phenomena, and waviness of patterns was verified using a simulation method. The simulation result showed good performance stability. To verify the mechanical properties, an interlaminar shear strength (ILSS) test was performed. Since the pattern on the glass fabric can act in a similar way to a defect, there is a high probability of mechanical property degradation. However, the ILSS test results of the PPCF specimen was comparable with a pure glass-fiber/epoxy composite.

Characteristics of silicon carbide fiber-reinforced composite for microwave absorbing structures

A microwave-absorbing structure is a multifunctional composite composed of lossy materials, to obtain optimal electromagnetic properties combined with structural load-bearing capability. Microwave energy-loss properties can be obtained by modifying the matrix with a lossy filler, or by using a reinforcing fiber with lossy characteristics. The silicon carbide fiber is a conventional semi-conductive fiber that can cause microwave-energy loss, and can comprise a composite material by using a general resin system without lossy additives. This study investigated the mechanical and electromagnetic properties of SiC/epoxy composites, and the performance of microwave-absorbing structures composed of the SiC/epoxy. The fiber volume fraction and tensile properties of a SiC/epoxy composite cured at 6.0 bar were measured. Electromagnetic properties of SiC/epoxy composites cured at different pressures from 7.0 bar to 3.5 bar were measured in addition. Single-slab and multi-slab absorbers were fabricated, and their performance was evaluated. The −10-dB bandwidth and the minimum return loss of the four-slab absorber were 3.4 GHz and −31.0 dB, respectively.An analysis of the SiC/epoxy-composite characteristics indicated that it had excellent workability and mechanical-property advantages, although the performance of the SiC/epoxy microwave absorber was ordinary.

Thin and lightweight radar-absorbing structure containing glass fabric coated with silver by sputtering

In this paper, a new radar-absorbing structure produced by electrical modification of glass fabric via the silver-sputtering coating technique is proposed. Although conventional radar absorbers are fabricated using a conductive carbon nanomaterial, such fabricated absorbers have many limitations in their electrical and mechanical performance. A thin and lightweight silver-coated glass-fabric microwave-absorbing structure (with a thickness of 1.82, 1.84 and 1.95mm, respectively) having good microwave-absorbing performance in the X-band (8.2–12.4GHz) was designed and fabricated without dispersing conductive carbon nanomaterials in the resin matrix. The morphology, element composition and phase identification of silver-coated glass fabrics were examined by SEM, EDS and XRD, respectively. In addition, interlaminar shear strength (ILSS) tests were conducted according to ASTM D 2344 to evaluate the mechanical performance of the proposed absorbers. Additionally, to design a thin broadband absorber using the silver-coated glass fabric, the absorbing performance of the proposed absorbers were analyzed from the C-band to the Ku-band (4–18GHz), and the proposed broadband absorber showed excellent performance in the target frequency range.

반도체 섬유 강화 복합재료를 이용한 전자파 흡수 구조

본 연구에서는 반도체 섬유 강화 복합재료를 이용하여 전자파 흡수 구조를 제작하였다. 두 종류의 반도체 섬유를 사용하여 복합재료를 제작하고, 자유공간 측정 장비를 이용하여 각각의 전자기적 물성을 측정하였다. 두께 최적화 방법으로 두 종류의 단층형 흡수 구조와 한 종류의 이층형 흡수 구조를 설계하였다. 설계한 전자파 흡수 구조를 반도체 섬유 강화 복합재료로 제작하고 그 흡수 성능을 측정하였다. 사용된 두 재료의 유전율은 Cole-Cole plot에 나타내었을 때 무반사 곡선에 가깝지 못하여 높은 흡수 성능을 기대하기 어려웠다. 두 종류의 재료로 제작한 단층형 흡수 구조는 10 GHz 근처에서 각각 -14.2 dB와 -8.8 dB의 흡수 성능을 보였다. 이러한 한계점을 보완할 수 있는 이층형 전자파 흡수 구조는 10 GHz 근처에서 -43.9 dB의 좋은 흡수 성능을 보였다. 반도체 섬유 강화 복합재료로 제작한 이층형 전자파 흡수 구조는 기존의 전자파 흡수 구조에 비해 간단한 제작 과정을 거쳐 좋은 흡수 성능을 갖는 흡수 구조를 얻을 수 있었으며, 상대적으로 더 적은 오차 요인을 갖고 있다. This paper deals with the fabrication and verification of the microwave absorbing structure using semiconductive fiber reinforced composite. Two kinds of fiber were used to fabricate composites. Electromagnetic properties of the composites were measured by freespace measurement system over X-band. Two single slab absorbers and a double slab absorber were designed by thickness optimization method. Single slab absorbers did not show good microwave absorption performance because the permittivity is away from non-reflection curve. Double slab absorber complemented the limitations on single slab absorber and it showed good microwave absorption performance. Double slab absorber showed -43.9 dB loss near 10 GHz.

Design, fabrication, and characterization of lightweight and broadband microwave absorbing structure reinforced by two dimensional composite lattice

Microwave absorbing structures (MASs) reinforced by two dimensional (2D) composite lattice elements have been designed and fabricated. The density of these MASs is lower than 0.5 g/cm3. Experimental measurements show that the sandwich structure with glass fiber reinforced composite (GFRC) lattice core can serve as a broadband MAS with its reflectivity below −10 dB over the frequency range of 4–18 GHz. The low permittivity GFRC is indicated to be the proper material for both the structural element of the core and the transparent face sheet. Calculations by the periodic moment method (PMM) demonstrate that the 2D Kagome lattice performs better for microwave absorbing than the square one at relatively low frequencies. The volume fraction and cell size of the structural element are also revealed to be key factors for microwave absorbing performance.

Effect of Ni concentration on electromagnetic wave absorption of (Ni,Mn,Zn)Fe2O4/resin particulate composites

This research aimed to investigate the effect of the Ni-concentration on the modulated crystallographic structure, constitutive electromagnetic properties, and microwave-absorbing behaviors of the MnZn ferrites. Substitution of Ni for Mn induced compressive strains in cubic spinel due to the smaller Ni than Mn. The activation energy of hopping carriers was determined from the plot of resistivity vs temperature. The conduction was considered to be small-polaron hopping among the spinel lattice which was distorted by Ni substitution. The ferrimagnetic properties of Ni0.5xMn0.5−0.5xZn0.5Fe2O4 ferrites were improved with the increasing Ni concentration. The ferrite with x=1 had the lowest intrinsic coercivity (Hc=7.4Oe) and the highest saturation magnetization (Ms=68.9emu/g). The increase of the saturation magnetization with the Ni substitution (x>0.24) is ascribed to the dense microstructure with less pores and the decrease of Fe2+/Fe3+ ratio. Additionally, a multilayer design of microwave-absorbing structure containing Ni0.5xMn0.5−0.5xZn0.5Fe2O4 granules distributing in a contiguous polymeric matrix was also investigated. The constitutive electromagnetic properties of the composite such as relative permeability and relative permittivity within the whole frequency range were characterized by a combined transmission/reflection method using a coaxial airline fixture. The frequency responses to the electromagnetic field of the ferrite–polymer composites are ascribed to macroscopic magnetic loss and dielectric loss in association with domain-wall oscillation, spin relaxation, and dipolar polarizations. In additions, the microwave-absorbing behaviors of the ferrite–polymer composites were determined using the constitutive electromagnetic properties. The maximum return loss was estimated as −32dB occurring at 2.3GHz for 6mm-thick composite for the composite with x=0.24. For composites with ferrites containing high Ni concentration, the broadening of absorption bandwidth reduced the products of matching thickness and frequency which consequently reduced the required thickness of the microwave absorber. The substitution of Ni for Mn in MnZn ferrites is beneficial in fabricating thin microwave absorbers in GHz frequency range due to the improved electromagnetic lossy characteristics.

Thin resonant structures for angle and polarization independent microwave absorption

We present a microwave absorbing structure comprised of an array of subwavelength radius copper disks, closely spaced from a ground plane by a low loss dielectric. Experiments and accompanying modeling demonstrate that this structure supports electromagnetic standing wave resonances associated with a cylindrical cavity formed by the volume immediately beneath each metal disk. Microwave absorption on resonance of these modes, at wavelengths much greater than the thickness of the structure, is dictated almost entirely by the radius of the disk and permittivity of the dielectric, being largely independent of the incident angle and polarization.