Search Results (18)

This paper investigates the feasibility of CaZr₄(PO₄)₆ as a novel thermal barrier coating for SiO_2f/SiO₂, serving as a radome at 1200 °C. Initially, CaZr₄(PO₄)₆ powder undergoes TG-DSC testing across a temperature range from room temperature to 1200 °C, demonstrating excellent phase stability within this range. Subsequently, the coating’s properties and the thermal cycling performance are examined. The results indicate that the thermal conductivity of CaZr₄(PO₄)₆ falls within the range of 1.05 to 1.02 W·m⁻¹·K⁻¹ (RT ~ 1200 °C), with thermal expansion coefficients of the coating ranging from 2.07 to 5.55 × 10⁻⁶ K⁻¹. Moreover, the thermal cycling lifetime of the CaZr₄(PO₄)₆ coating is evaluated by performing 100 cycles (50 h) at 1200 °C. Mechanical properties are assessed through Vickers and Knoop hardness tests, revealing a fracture toughness of 1.4 Mpa·m^1/2. The primary cause of coating failure and peeling is the excessive internal stress between the coating and the expansion of transverse cracks. Fracture toughness serves as a key performance indicator reflecting the material’s resistance to unstable crack expansion, so the failure of the coating is attributed to the limited fracture toughness and the thermal mismatch stress between the coating and the substrate. Based on the aforementioned research findings, CaZr₄(PO₄)₆ might be the potential coating for SiO_2f/SiO₂ systems. Full article

Sapphire (α-Al₂O₃) has been widely used in high-power lasers, optical windows, semiconductor substrates, radomes, and other applications due to its exceptional optical properties, high hardness, excellent chemical stability, and thermal resistance. However, machining sapphire poses significant challenges because of the material’s high hardness and brittleness. Traditional mechanical and chemical–mechanical machine methods often fail to meet the processing requirements for micro and nanoscale structures. Recently, the use of femtosecond lasers—with ultra-short pulses and extremely high peak power—has allowed for the precise machining of sapphire with minimal thermal damage, a method akin to cold processing. Femtosecond laser processing offers significant advantages in fabricating three-dimensional micro- and nanoscale structures, surface and internal modification, optical waveguide writing, grating fabrication and dissimilar materials welding. Thus, this paper systematically reviewed the research progress in femtosecond laser processing of sapphire, covering technical approaches such as ablation, hybrid processing and direct writing micro- and nanoscale fabrication. The capability of femtosecond laser processing to modulate sapphire’s optical properties, wettability and mechanical and chemical characteristics were discussed in detail. The current challenges related to efficiency, cost, process standardization and outlines future development directions, including high-power lasers, parallel processing, AI optimization and multifunctional integration were also analyzed. Full article

This paper studies the progressive damage process and final damage form of composite laminate aircraft radome under high-speed hail impact A simulation method based on Peridynamic bond-based theory is proposed to study the progressive damage process and final damage form of composite laminate aircraft radome under high-speed hail impact. Using the Peridynamic theory, the dynamic damage behavior of hailstone impact on a composite laminate plate is analyzed, and an impact model of hailstone impact is established to study the damage initiation, expansion, and failure behavior of the composite laminate. The dynamic mechanical constitutive and failure criteria that characterize the macromechanical behavior of both hailstone and composite laminate during impact are established. Additionally, equations describing the interaction forces between these two materials are proposed to develop a numerical simulation method for the laminate failure process. The dynamic damage evolution and failure mechanisms are subsequently investigated to provide a theoretical foundation for the optimum design of composite structures, such as aircraft radomes, subjected to hail impact. To describe the interaction force equations between two materials, a new method based on Peridynamics (PD) is proposed to establish a numerical simulation method for the damage process of laminated plates. This method provides a theoretical basis for optimizing the design of composite structures (such as aircraft radome) after being impacted by hail. Full article

Radome stealth technology is a key research area in aircraft stealth design. Traditional aircraft stealth methods primarily focus on optimizing the shape to scatter radar waves and using absorbing materials to absorb radar waves. However, when these methods are applied to radomes, they can negatively impact antenna performance. By combining Frequency-Selective Surface (FSS) technology with radome design, it is possible to ensure good transmission performance for the antenna within its operating frequency range while simultaneously reducing the radar cross-section outside the operating frequency range, achieving an integrated design for both transmission and stealth. This paper outlines the technical approaches for radome stealth, reviews the research status of scattering stealth radomes and absorbing stealth radomes based on FSS both domestically and internationally, and provides an outlook on the future development of FSS radomes from the perspectives of omnidirectional broadband, conformal design, and intelligent control. Full article

Radar sensors are critical for obstacle detection and navigation, especially for automated driving. Using the use-case “printing of heating coils on the inside of the front housing (primary radome)” needed for de-icing in winter, it is demonstrated that additive manufacturing (AM) can provide economic and functional benefits for manufacturing of the sensors. AM will allow significant cost reduction by eliminating parts and simplifying the manufacturing process. Different AM technologies for the coils were investigated, first, by applying the conductive traces by fused deposition modeling (FDM), and, second, by printing copper particle-free inks and pastes. The metal layers were electrically and mechanically characterized using a profilometer to measure the trace dimension and a four-point probe to measure the resistance. It was revealed that low-cost conductive filaments with low resistivity and current carrying capacity are commercially still not available. The best option sourced was a copper–polyester-based filament with 6000 µΩcm after printing. Therefore, low-cost particle-free copper inks and commercial copper flake paste were selected to print the heating coil. The Cu particle-free inks were amine-based Cu (II) formate complexes, where the Cu exists in an ionic form. Using contactless printing processes such as ink-jet printing or pneumatic dispensing, the traces could be deposited onto the low-melting temperature (225 °C) polymeric radome structure. After printing, the material needed to be sintered to form the conductive copper traces. To avoid damaging the polymer radome during sintering, two different processes were investigated: low-temperature (<150 °C) sintering in an oven for 30 min or fast laser sintering. The sintered Cu layers achieved the following specific electric resistivities when slowly sintered in the oven: paste 4 µΩcm and ink 8.8 µΩcm. Using laser sintering, the ink achieved 3.2 µΩcm because the locally high temperature provides better sintering. Also, the adhesion was significantly increased to (5 B). Therefore, laser sintering is the preferred technology. In addition, it allows fast processing directly after printing. Commercial equipment is available where printing and laser sintering is integrated. The potential of low-cost copper material and the integration in additive manufacturing of electronic systems using radar sensors as an example are demonstrated in this paper. Full article

We present waveguide cavity measurements used to evaluate several thin materials for use in radomes. In addition to the data on the materials, we show how these measurements can be performed with common laboratory equipment and simple calculations. We sought an approach that allowed candidate materials to be readily evaluated to deal with formerly selected materials becoming unavailable or cost-prohibitive. We used lengths of standard waveguide (WR650 and WR137 here) with readily manufactured irises and a vector network analyzer (Keysight N5225B here). To select the iris size and determine the limits of the simplifications in the equations used, we employed a full-wave 3D electromagnetic simulator (CST Microwave Studio). The equations required to calculate the dielectric properties of samples and their contribution to the equivalent system noise temperature from unloaded and loaded resonant frequencies and Q factors are shown. While these formulations can be found elsewhere, we did not find these assembled as conveniently in other studies in the literature. We also show that orienting the sample down the length of the cavity allows for higher-order modes to be fully utilized. We did not find this straightforward adaptation of the common cross-guide orientation in other works. Overall, the results allowed us to recommend three fabrics for use at the frequencies tested (1.7 and 5.6 GHz). The complete process is outlined to assist others in performing these measurements themselves. Full article

Radar systems are a type of sensor that detects radio signals reflected from objects located a long distance from transmitters. For covering a longer range and a higher resolution in the operation of a radar, a high-frequency band and an array antenna are measures to take. Given a limited size to the antenna aperture in the front end of the radar, the choice of a millimeter-wave band leads to a denser layout for the array antenna and a higher antenna gain. Millimeter-wave signals tend to become attenuated faster by a larger loss of the covering material like the radome, implying this disadvantage offsets the advantage of high antenna directivity, compared to the C-band and X-band ones. As the radome is essential to the radar system to protect the array antenna from rain and dust, a metamaterial surface in the layer is suggested to meet multiple objectives. Firstly, the proposed electromagnetic structure is the protection layer for the source of radiation. Secondly, the metasurface does not disturb the millimeter-wave signal and makes its way through the cover layer to the air. This electromagnetically transparent surface transforms the phase distribution of the incident wave into the equal phase in the transmitted wave, resulting in an increased antenna gain. This is fabricated and assembled with the array antenna held in a 3D-printed jig with harnessing accessories. It is examined in view of S₂₁ as the transfer coefficient between two ports of the VNA, having the antenna alone and with the metasurface. Additionally, the far-field test comes next to check the validity of the suggested structure and design. The bench test shows around a 7 dB increase in the transfer coefficient, and the anechoic chamber field test gives about a 5 dB improvement in antenna gain for a 24-band GHz array antenna. Full article

Composite radomes are usually located in the nose of aircraft and are important structural components that protect radar antenna. The finite element model of a radome structure is developed and analyzed in this article. Single-objective deterministic and reliability optimization models based on the minimum total mass of the radome structure were established, and the layer thickness of each part of the honeycomb sandwich radome structure was considered a design variable. A multi-objective deterministic and reliability optimization model for a radome structure with a minimum total mass and maximum buckling critical load was established, and a particle swarm optimization algorithm was used to solve the problem. Our optimized results satisfied the constraints and utilization rate of materials, and structural safety was improved. Full article

Polymer matrix wave transparent composites are used in a variety of high-speed communication applications. One of the applications of these involves making protective enclosures for antennas of microwave towers, air vehicles, weather radars, and underwater communication devices. Material performance, structural, thermal, and mechanical degradation are matters of concern as advanced wireless communication needs robust materials for radomes that can withstand mechanical and thermal stresses. These polymer composite radomes are installed externally on antennas and are exposed directly to ambient as well as severe conditions. In this research, epoxy resin was reinforced with a small amount of quartz fibers to yield an improved composite radome material compared to a pure epoxy composite with better thermal and mechanical properties. FTIR spectra, SEM morphology, dielectric constant (Ɛ_r) and dielectric loss (δ), thermal degradation (weight loss), and mechanical properties were determined. Compared to pure epoxy, the lowest values of Ɛ_r and δ were 3.26 and 0.021 with 30 wt.% quartz fibers in the composite, while 40% less weight loss was observed which shows its better thermal stability. The mechanical characteristics encompassing tensile and bending strength were improved by 42.8% and 48.3%. In high-speed communication applications, compared to a pure epoxy composite, adding only a small quantity of quartz fiber can improve the composite material’s dielectric performance, durability, and thermal and mechanical strength. Full article

In this article, an aperture antenna excited by a waveguide with a circular cross-section and covered with a dielectric plate was analyzed via simulation calculation and verified via measurements. The influence of the geometrical and electromagnetic parameters of the dielectric plate on the reflection coefficient S₁₁ of the antenna opening was systematically analyzed. The geometrical parameters taken in this analysis are the thickness d and the width/length h₁/h₂ of the dielectric plate. The electromagnetic parameters used in this analysis are the real and the imaginary part of permittivity (ε_r, tan δ) and the electrical conductivity of the dielectric plate (σ). The simulation calculation and analysis included other structural and electromagnetic parameters of the dielectric plate (density of the radome material, relative permeability, and magnetic loss tangent (ρ, µ_r, and tan δ_µ, respectively)), but the results show that in the range of real values of these parameters for the materials used for the dielectric plate, they had no significant influence on the reflection coefficient. The results show that impedance-matched antennas with very low values of the reflection coefficients S₁₁ at the resonant frequency can be realized by changing the geometrical and electromagnetic parameters of the dielectric plate material. The results are presented for a circular aperture antenna on a planar grounded plane with a dielectric plate on the opening, and the achieved lowest values of the S₁₁ parameter were −45.17 dB (simulated) and −43.93 dB (measured) at the frequencies of 1.7820 GHz and 1.7550 GHz, respectively. The estimated values of the dielectric plate parameters in this case are thickness d = 11.08 mm (0.67 λ); width × length of grounded plane and dielectric plate h₁ × h₂ = 423 × 450 mm² (2.51 × 2.67 λ); relative permittivity 2.5, tan δ = 0.09, μ_r = 1, tan δ_μ = 0.00, ρ = 1200 kg·m⁻³; and electrical conductivity σ = 0 S/m. The simulation calculation results were verified by measuring the reflection coefficient S₁₁ on the created laboratory model of the aperture antenna with the dielectric plate and showed a very good match. Full article

In this study, we use a phase-changing material vanadium dioxide (VO₂) to design a multilayer metasurface structure to achieve the transition from an electromagnetically induced transparency(EIT) device to an absorber. The structure consists of a gold layer, a polyimide spacer layer, a VO₂ layer, and a sapphire substrate. The top layer consists of one cut wire and two split-ring resonators with the same parameters. When the VO₂ layer is in its insulating phase at room temperature, the peak of the EIT device will appear near 1.138 THz. When the VO₂ layer is in the metallic state, two absorption peaks above 99.5% appear separately at 1.19 and 1.378 THz, respectively. To the best of our knowledge, this is the first time that a coupled mode equation is used to perform theoretical calculations for EIT devices and perfect absorbers simultaneously, and this is also the first time that coupled mode equations are used for the theoretical calculations of two absorption peaks in an absorber. The proposed metasurface combines the advantages of terahertz absorption, EIT and active device control, which will provide more ideas for the design of future terahertz devices and is also significant for the design and development of radomes for future stealth aircraft. Full article

In this work, an efficient slotted waveguide antenna (SWA) system is designed for S-band high power microwave (HPM) applications. The designed SWA comprises of 10-slot elements placed on the broad wall of SWA with a modified Gaussian distribution (MGD), integrated with two inside-grooves and a Gaussian dielectric radome of high-density polyethylene (HDPE) material. The inside-grooves are introduced to suppress the surface current on the waveguide, which results in high gain as well as sidelobe level (SLL) reduction in the E-plane. The MGD controls the SLLs, and the unique Gaussian profile shape radome offers constant radiation characteristics. The proposed antenna system, within existing size constraints, offers a high gain of 20.1 dBi in conjunction with a high-power handling capability of greater than 100 MW. The designed SWA system has compact dimensions of 8.46λ₀ × 1.38λ₀ × 1.50λ₀, with SLLs of −20 dB and −22 dB in the H- and E-plane, respectively. The HPM antenna system, radiating at 3 GHz, is fabricated on aluminium material using the milling process. The simulated SWA system has good agreement with measured results. Moreover, the proposed SWA system offers clear advantages in terms of its robustness, design simplicity, high power handling capability, and high gain. Full article

The multiplicity of targets of the 5G and further future technologies, set by the modern societies and industry, lacks the establishment of design methods for the highly multidisciplinary application of wireless platforms for small cells. Constraints are set by the overall energy concept, structural safety and sustainability. Various Smart poles and Light poles exist but it is challenging to define the design drivers especially for a composite load-carrying structure. In this study, the design drivers of a composite 5G smart pole are determined and the connecting design between finite element modelling (FEM), signal penetration and computational fluid dynamics (CFD) for thermal analysis are reported as an interdisciplinary process. The results emphasize the significant effects of thermal loading on the material selection. The physical architecture, including various cutouts, is manipulated by the needs of the mmW radios, structural safety and the societal preferences of sustainable city planning, i.e., heat management and aesthetic reasons. Finally, the paint thickness and paint type must be optimized due to radome-integrated radios. In the future, sustainability regulations and realized business models will define the cost-structure and the response by customers. Full article

In order to improve the mechanical and dielectric properties of radome cyanate, a synergistic reinforcement method is employed to develop a resin-based ternary-composite with high heat-resistance and preferable radar-band transmission, which is expected to be applied to fabricate radomes capable of resisting high temperature and strong electric field. According to copolymerization characteristics and self-curing mechanism, epoxy resin (EP) and bismaleimide (BMI) are employed as reinforcements mixed into a cyanate ester (CE) matrix to prepare CE/BMI/EP composites of a heat-resistant radome material by high-temperature viscous-flow blending methods under the catalysis of aluminum acetylpyruvate. The crystallization temperature, transition heat, and reaction rate of cured polymers were tested to analyze heat-resistance characteristics and evaluate material synthesis processes. Scanning electron microscopy was used to characterize the micro-morphology of tensile fracture, which was combined with the tensile strength test and dynamic thermomechanical analysis to investigate the composite modifications on tenacity and rigidity. Weibull statistics were performed to analyze the experimental results of the dielectric breakdown field, and the dielectric-polarization and wave-transmission performances were investigated according to alternative current dielectric spectra. Compared with the pure CE and the CE composites individually reinforced by EP or BMI, the CE/BMI/EP composite acquires the most significant amelioration in both the mechanical and electrical insulation performances as indicated by the breaking elongation and dielectric breakdown strength being simultaneously improved by 40%, which are consistently manifested by the obviously increased transverse lines uniformly distributed on the fracture cross-section. Furthermore, the glass-transition temperature of CE/BMI/EP composite reaches the highest values of nearly 300 °C, with the relative dielectric constant and dielectric loss being mostly reduced to less than 3.2 and 0.01, respectively. The experimental results demonstrate that the CE/BMI/EP composite is a highly-qualified wave-transmission material with preferences in mechanical, thermostability, and electrical insulation performances, suggesting its prospective applications in low-frequency transmittance radomes. Full article

The surface quality and profile accuracy of a radar fiberglass radome are determined by the manufacturing of the fiber-reinforced-plastic (FRP) complex curved mold. The surface quality, thickness uniformity, and shape accuracy of the mold seriously affect the temperature and deformation control during the manufacturing process of the radome, thus affecting the antenna’s serviceability, including its wave permeability and stability. Abrasive belt grinding is an effective method for processing FRP materials. However, issues regarding the profile fitting of the abrasive belt section line contact state and its influence on the precision of complex curved surfaces have not been solved, which seriously affects the processing quality. Here, an FRP complex curved surface mold surface based on the least-squares method was established. The local two-dimensional line contact and profile contour trajectory were obtained by the algorithm of optimal trajectory planning. Based on this, a grinding experiment was carried out. The experiments showed that the surface roughness based on this method was reduced from 0.503 to 0.289 μm, and the contour accuracy was improved by 16.9% compared with the conventional error. Through our analysis, the following conclusions can be drawn: the algorithm can effectively solve the problem of line contact surface fitting and significantly improve the precision of an FRP complex surface. Full article