Radar Absorbing Research Articles

Non-iridescent magnetite photonic crystal films and pigments with enhanced magnetic coupling effect

Non-iridescent structural color films and pigments with novel enhanced microwave absorption characteristics are successfully fabricated at room temperature for the first time. The quasi-uniform magnetite nanoparticles (CV = 0.10 ∼ 0.20) with high refractive index (n = 2.42) and broad light absorption provide evident low-angle-independent property for the structural color pigments. More importantly, a universal technical protocol is developed for preparation of photonic crystals with inorganic nanoparticles, i.e., through designing of the binding strength between nanoparticles and mediated molecules, the slurry modulus is increased to 105 Pa, which effectively drives the nanoparticles to rapidly assemble into closely packed ordered arrays by our-designed powerful assembly technique. Additionally, the structural color materials are subjected as photonic crystal pigments (∼20 wt%) embedding in a transparent polymer matrix to form color coatings. Remarkably, the photonic crystal pigments exhibit strong magnetic coupling effect and enhanced microwave absorption performance due to the regular arrangement, with superior reflection loss (RLmin) values of −14.97 dB (increase by 65.8 % compared with randomized magnetic nanoparticles), and the effective absorption bandwidth (EAB) of 2.15 GHz. This new kind of photonic crystal pigment, combining visual color and radar wave absorption, provides a novel idea for developing of multi-wave-band high-performance stealth materials.

Design of multifunctional polymethacrylimide foam sandwich with excellent radar absorption capability and compressive performance

A composite multifunctional radar absorption polymethacrylimide (RAPMI) foam sandwich (MRAPS) was constructed. Analytical models for out-of-plane and in-plane compression of the MRAPS were established. Three-dimensional failure mechanism maps and specific strength cubic cloud maps were drawn. Finally, a multiobjective particle swarm optimization (MOPSO) algorithm was used to achieve an integrated design, and a specific calculation example was tested and verified through experiments. The resulting sandwich with a 43.0 mm thickness core and 0.13 g/cm3 density achieves 90% effective absorption above broadband (RL ≤ −10 dB) in the 2–18 GHz range. As a radar absorption absorber, the MRAPS increased the engineering value and strategic importance of PMI foam for structural components in the military and aerospace sectors.

Design and measurement of a tunable metasurface low-frequency radar absorber

At the turn of the millennium, developments on metasurfaces lead to a significant step forward in the design of radar absorbing structures, especially at lower frequencies, thanks to a reduced thickness. Still, as with other passive impedance matching systems, they remain constrained in their bandwidth-to-thickness ratio. Fortunately, the recent integration of active electronic components onto metasurfaces has multiplied their functionalities, unlocking new ways to overcome these limitations. For instance, using varactor diodes, which act as variable capacitors, an absorbing metasurface can be rendered tunable to cover a frequency range wider than would any passive system of similar thickness. This is a valuable feature when facing modern frequency-hopping radars. However, the bias-dependent resistance introduced by the varactor diodes can compromise the impedance matching throughout the tunable frequency range. This work, therefore, focuses on the design and measurement of a tunable radar absorbing metasurface using varactor diodes, highlighting the necessity for a joint tuning of capacitance and resistance to grant near-perfect absorption over a wide frequency range.

Fusedly Deposited Frequency-Selective Composites Fabricated by a Dual-Nozzle 3D Printing as Microwave Filter.

We report a fusedly deposited frequency-selective composite (FD-FSCs), fabricated with a dual-nozzle 3D printer using a conductive carbon black (CB) polylactic acid (PLA) composite filament and a pure PLA polymer filament. The square frequency-selective pattern was constructed by the conductive CB/PLA nanocomposite, and the apertures of the pattern were filled with the pure dielectric PLA material, which allows the FD-FSC to maintain one single plane, even under bending, and also affects the resonating frequency due to the characteristic impedance of PLA (εr' ≈ 2.0). The number of the deposition layer and the printing direction were observed to affect electrical conductivity, complex permittivity, and the frequency selectivity of the FD-FSCs. In addition, the FD-FSCs designed for an X-band showed partial transmission around the resonant frequency and was observed to, quite uniformly, transmit microwaves in the decibel level of -2.17~-2.83 dB in the whole X-band, unlike a metallic frequency selective surface with full transmission at the resonance frequency. FD-FSCs embedded radar absorbing structure (RAS) demonstrates an excellent microwave absorption and a wide effective bandwidth. At a thickness of 4.3 mm, the 10 dB bandwidth covered the entire X-band (8.2~12.4 GHz) range of 4.2 GHz. Therefore, the proposed FD-FSCs fabricated by dual-nozzle 3D printing can be an impedance modifier to expand the design space and the application of radar absorbing materials and structures.

A novel Fe3O4/ZnO/PANI/rGO nanohybrid material for radar wave absorbing

In this study, a novel RAM utilizing Fe3O4, ZnO, polyaniline (PANI), and reduced graphene oxide (rGO) in the form of nanohybrid is invented, namely Fe3O4/ZnO/PANI/rGO nanohybrid. In this study, the effects of the rGO fraction in Fe3O4/ZnO/PANI/rGO composition on the radar absorbing performance were investigated. Meanwhile, exploring the quality of the nanohybrid sample, such as the crystal structure, functional groups, morphology, magnetic properties, and reflection loss was also examined carefully. It shows that two crystalline phases of Fe3O4 and ZnO, as well as amorphous structures of PANI and rGO are formed independently, indicating successful nanohybrid formation. In this case, PANI functioned as a binder for Fe3O4 and ZnO, and thus, it could infiltrate the pores of rGO. Fe3O4/ZnO/PANI/rGO nanohybrid possesses superparamagnetic properties with decreasing saturation magnetization as rGO composition increases. Nevertheless, rGO enhanced the radar absorption performance with a maximum reflection loss of −8.57 dB at 11.10 GHz. In this present research, the synergy of combination between the magnetic and dielectric losses in the Fe3O4/ZnO/PANI/rGO nanohybrid is discussed together with plausible strategies to obtain highly efficient RAM.

Performance of Electromagnetic Properties of Carbon Fiber Reinforced and AuNPs Functionalized MWCNTs Doped Hybride Composites

The purpose of this article is to compare the electromagnetic absorption properties of carbon fiber layer composite materials produced separately using Au particles doped MWCNT added epoxy with pure MWCNT added epoxy resin. This new material, produced using MWCNT doped with Au particles, increases its radar absorption capability. And therefore the as-prepared electromagnetic absorber demonstrates enormous potential in future military and aviation applications. Multilayer composite materials, consisting of Au/MWCNT doped epoxy, MWCNT doped epoxy and pure epoxy, were produced by vacuum infusion method. Electromagnetic absorbing properties of the produced materials were determined with the Agilent brand 2-Port PNA-L Network Analyzer device by conducting transmission/reflection measurements in the frequency range of 3–18 GHz. The electromagnetic absorbing properties of the produced composite materials were taken in two different measurements, both with and without metal plate. Measurements were made using two horn antennas. Show that the produced MWCNT doped and Au/MWCNT doped carbon fiber laminated composite material has good absorption behavior when used with metallic sheets and is good for RADOM applications at many points at 3–18 GHz.

Radar absorbing properties of different size carbon nanotube reinforced polymer composites

Carbon nanotubes (CNTs), which have a diameter on the nanometer scale, are tube-like materials composed of carbon and graphite sheets. Carbon nanotubes play an important role in many fields such as nanotechnology, electronics, optics and material science due to their superior properties such as high elasticity, high thermal conductivity, low density and being more chemically inert. In this study, the use of carbon nanotubes in radar absorbing materials (RAM) to reduce the reflection of electromagnetic waves was investigated. In this sense, by using a polymeric composite structure reinforced with carbon nanotubes, a material with unique properties such as solid absorption, low weight/thickness and cost-effectiveness has been produced, minimizing the reflection of electromagnetic waves. For this purpose, carbon nanotubes with different particle sizes of 8 nm, 30–50 nm and 48–78 nm were blended with polyester at the ratio of 1%. The resulting composites were characterized using a Network analyzer in the frequency range of 8–12 GHz. According to the results obtained, it was observed that radar absorption increased with increasing particle size. It has been determined that by changing the particle sizes of carbon nanotubes in composites, the absorption bands can be adjusted to suit different applications in different frequency bands.

Pneumatic Structural Deformation to Enhance Resonance Behavior for Broadband and Adaptive Radar Stealth.

Ideal radar absorbing materials (RAMs) require instantaneous, programmable, and spontaneous adaptability to cope with a complex electromagnetic (EM) environment across the full working frequency. Despite various material systems and adaptive mechanisms having been demonstrated, it remains a formidable challenge to integrate these benefits simultaneously. Here, we present a pneumatic matrix that couples morphable MXene/elastomer conductors with dielectric spacers, which leverages controllable airflow to reconfigure the spatial structure between a flat sheet and a hemispherical crown while maintaining resistance stability via wrinkle folding and unfolding. The interdimensional reconfigurations drastically induce multiple resonance behavior, enabling the matrix remarkable frequency tunability (144.5%), ultrawide bandwidth (15 GHz), weak angular dependence (45° incidence), ultrafast responsiveness (∼30 ms), and excellent reproducibility (1000 cycles). With multichannel fluidic and conceptual automated control systems, the final pneumatic device demonstrates a multiplexed, programmable, and autonomous transformable mode that builds a promising platform for smart radar cloaking.

Negative permittivity and permeability behaviour of SrFe12O19/rGO metacomposite for microwave absorption in 2–18 GHz range

Double-negative performance has played a significant role in electronic applications owing to its both permeability and permittivity negative values. Microwave absorption material has a substantial role in electromagnetic shielding, radar absorption, stealth applications, etc. Herein, a novel double-negative metacomposite, SrFe12O19/rGO, was designed by a simple one-pot hydrothermal method, and the microwave absorption properties of the material were studied in the microwave region from 2 to 18 GHz using VNA analysis. The structural and morphological studies were analysed using XRD, FT-IR, and SEM instrumentation techniques and the magnetic property of the material was studied using VSM analysis. Both studies confirmed the hard magnetic nature of the material. The particle sizes of SrFe12O19 and SrFe12O19/rGO measured from XRD are 55.60 nm and 41.55 nm, respectively. Hexagonal plate-like morphology were observed from FESEM images. The coercivity of SrFe12O19/rGO increased, and the magnetocrystalline anisotropy was changed due to the decrease in particle size. The magnetic saturation value decreases due to the presence of non-magnetic rGO. The resultant SrFe12O19/rGO metacomposite shows negative permittivity and permeability values. The minimum reflection loss values observed for pure and rGO-decorated strontium ferrites are −28.49 dB at 7.76 GHz and −23.78 at 11.04 GHz, respectively. In addition to experimental results, simulation studies were also performed to study the reflection loss with matching thickness using a quarter wavelength mechanism. The results show that this composite can be employed as a left-handed metamaterial that finds applications in absorption, antennas, sensors, wireless power transfer systems, etc. The left-handed metamaterial can shift the frequency region from a lower to a higher frequency region. The rGO decorated metacomposite is a promising material for microwave absorption at higher frequency regions.

Optimization Analysis and Design of Electromagnetic Matching Characteristics of Nano Radar Wave Absorbing Materials Based on Computational Intelligence

Nanometer radar wave absorbent is a new type of absorbent with great development prospect, which has important application demand in radar wave application. However, there are great differences in the practical application effects of different nano-radar wave absorbing materials, so it is necessary to optimize and analyze these differences, and the emergence of computational intelligence technology supplements this work. One of the great advantages of computational intelligence is that it does not rely on the correct model of the system when dealing with performance issues, and is affected by a variety of organisms and biota through algebraic methods. The high-level intelligent system with strong cognitive behavior awareness makes each algorithm have the characteristics of parallelism, social behavior, unit intelligence, openness and so on. Based on computational intelligence, this study analyzes the electromagnetic matching characteristics of nano-radar absorbing materials and concludes that: (1) An absorber cell structure with a tunable interface is designed using the tunable FSS bandpass to replace the previous fixed FSS bandpass. The results show that the transmission rate can be adjusted in a certain range and the input loss is low. Meets the design requirements of a customizable absorber. (2) In order to improve the impact force of nano-absorbing materials, it is necessary to analyze the similarities and differences with others, and process the life information after identification. The improved computational intelligence model can extract and analyze the information efficiently and quickly. (3) Under the same thickness of the design, the single-layer fabric has higher electric wave intensity, but the frequency band is narrower, while the double-layer fabric has higher electric wave input bandwidth. Electrical carbon black can be filled with magnetic nanomaterials to enhance radio wave performance. The composite material has very good electric wave mixing performance, and the polar grinding composite nano material is very suitable for improving the magnetic property and the uniformity of the carbon black particles. (4) For a particular secondary channel, consider using a fast numerical algorithm to optimize the path based on the curvature of the key channel. Proper planning in a robotic approach can not only perform the required tasks efficiently, but also improve performance, reduce workload, and extend the lifetime of the robot.

Integrated MCDM techniques for the selection of hybrid MWCNT/Ni–Zn–Fe nanocomposites for X-band radar absorption applications

In the 21st century, microwave-absorbing materials are used in a wide range of applications, such as in anechoic chambers and as electromagnetic interference shielding materials in radar and wireless communications. The design and development of new microwave-absorbing materials require substantial resources such as time, raw materials, and energy, and need to be cost-effective. Judicious selection of radar-absorbing materials from available alternatives often becomes difficult because it involves conflicting and non-commensurate attributes, such as bandwidth, reduced reflection loss, and thickness. This study aims to design and select novel double-layered multi-walled carbon nanotubes (MWCNT)/ Ni–Zn–Fe (NZF) microwave-absorbing materials using multi-criteria decision-making (MCDM) techniques such as TOPSIS, VIKOR, and PROMETHEE-II. Single-layered microwave-absorbing materials with various compositions of MWCNT and NZF were prepared using a low-cost and facilein-situpolymerization process. The multi-layered radar-absorbing materials reflection loss was determined using transmission line theory. Subjective and objective criteria weights from the analytical hierarchy process, entropy methods, and their calculated combined weights were utilized to implement the MCDM techniques. The combination of MWCNT/NZF radar-absorbing materials was chosen using integrated MCDM methods as the preferred microwave-absorbing material with a reflection loss of −15 dB for a 2.6 GHz bandwidth and a maximum reflection loss of –22 dB at 9.6 GHz in the X-band.

Evaluation of electromagnetic characteristics of 3D-printed radar absorbing structures based on three-dimensional period pattern surface

This paper aims to assess the electromagnetic (EM) characteristics of 3D-printed radar absorbing structures (RASs) based on three-dimensional period pattern surface (3D PPS) within the X-band frequency range (8.2–12.4 GHz). The assessment is validated through HFSS software, a 3D printer (Markforged, X7), and a scanning free-space measurement (SFM) system. Firstly, the analysis indicates that the EM characteristics of RASs based on 3D PPS are impacted by impedance matching in the thickness direction and the scattering of EM waves at the edges. The utilization of Onyx (Chopped carbon fiber/Nylon) reveals variations in resonance frequencies and EM wave absorption performance contingent upon the surface shape. Furthermore, significant differences in the variations of EM characteristics are observed even for RASs with the same surface shape but different materials. Secondly, the measurement results of 3D-printed RAS specimens based on PPS using Onyx exhibit similar trends to the analysis results obtained with the SFM system. Ensuring precise measurement results requires specific measurement conditions tailored to each surface shape, along with an examination of the EM characteristic distribution across the entire specimen area. This is crucial due to variations in the size, number, and range of reflected EM waves in the time domain. The analysis and measurement techniques presented in this study hold applicability in designing 3D-printed RASs that demand high EM wave absorption performance, whether under normal or oblique incident EM waves.

A transparent broadband flexible metamaterial absorber for radar infrared-compatible stealth

The iterative upgrading of the means of warfare has promoted the development of detection technology, and military activities are increasingly demanding target stealth. In this paper, a multifunctional metamaterial absorber is recommended, which simultaneously realizes the integrated stealth functions of ultra-wideband radar wave absorption, low infrared emission, and optically transparent. The structure is composed of an infrared shield, a radar-absorbing layer, and a reflective layer. Simulation results indicate that the absorption bandwidth in the radar band (1.81–20.4 GHz) is more than 90%, and the infrared emissivity is as low as 0.271 in the IR band (3–14 μm). Moreover, it has the features of flexibility, angle stability (0–45°), polarization insensitivity (0–90°), and so on. Furthermore, the electric field current distribution and equivalent circuit model of the structure are analyzed, and a 180 mm*180 mm sample is built and tested; the results show that the simulated and actual measurements are in agreement, and it is expected that such absorbers will be used in areas such as aircraft.

Design and preparation of an epoxy resin matrix composite structure with broadband wave-absorbing properties

Aiming at the poor effect of broadband wave-absorbing, the structural wave-absorbing composites structure were designed and prepared by choosing FeNi alloy powder/epoxy nanocomposites as the wave-absorbing interlayer, and carbon fibers/epoxy composites as the structural materials. Firstly, “80 wt% Fe50Ni50 alloy powder/epoxy resin nanocomposites” were successfully prepared, with a density of about 2.4 g/cm3, which can be applied as wave-absorbing interlayer. Then, electromagnetic parameters and loss mechanisms of the wave-absorbing sandwich in the frequency band of 1–18 GHz were studied in detail. Finally, the radar wave absorption characteristics of the structural wave-absorbing composites were optimized. The study shows that the electromagnetic loss mechanism of wave-absorbing sandwich is dominated by conductive loss and eddy current loss in the frequency range of 1–6 GHz, and eddy current loss, resonant loss and relaxation polarization in the frequency range of 6–18 GHz. In the frequency band of 2.5–8 GHz, the angular tangent of the magnetic loss of the interlayer is tanδm ≥ 0.5, and, the attenuation constant is stabilized in the range of 160–180 in the frequency band of 5.2–13.2 GHz, which shows that the interlayer has a good capacity of electromagnetic wave absorption. Different wave-absorbing properties can be designed by changing the thickness of the wave-absorbing interlayer. And the “fiberglass/interlayer/carbon fiber” composite board with a thickness of 2.0 mm interlayer and 3.0 mm-thick “fiberglass/ epoxy” has excellent broadband wave-absorbing properties. The sandwich composites have wave-absorbing peaks of |RL|≥10 dB in the frequency bands of 4.93–8.79 GHz and 14.96–18.0 GHz, with the peak width of 6.90 GHz, and the absorption peak of |RL|≥54 dB.

Enhanced thermomechanical properties of epoxy-multiwalled CNT nano-composites.

Viscoelastic properties of thermo-set composites using an epoxy matrix reinforced with pristine CNT and silane-modified MWCNT at different concentrations (0%, 1%, 2% and 4%) were studied to observe the enhanced thermal and mechanical properties supplemented by the increased interfacial interaction due to CNT modification. The composite with pristine CNT was labeled as EPB-CNT, whereas that with silane-modified carbon nanotubes (CNTs) was referred to as ECB-CNT. The silanes used were glycidyloxypropyltrimethoxysilane (GPTS) and 3-aminopropyltriethoxysilane (APTES). Diglycidyl ether of bisphenol-A (DGEBA) was completely cured by Jeffamine D-400 to prepare EJ-0. The amine groups of the 3-aminopropyltriethoxysilane (APTS) partially cured the diglycidyl ether of bisphenol-A (DGEBA) in EAJ-0 by a sequential polymerization process, while the methoxy groups subsequently produced a silica network through the sol-gel method. Subsequently, Jeffamine D-400 was used as a curing agent at elevated temperatures for cross-linking and complete curing. EJ-0 and EAJ-0 were considered as neat films of EPB-CNT and ECB-CNT composites, respectively. Tensile and storage modulus tests, thermal property analysis using TGA, and microstructure characterization using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and TEM were all part of the study. Comparing composites with varying percentages and with neat films, the chemically bonded epoxy-silanized MWCNTs (ECB-CNTs) showed improved performance. ECB-CNT 4% had the highest tensile and storage modulus as well as improved thermal stability. Improved filler material distribution and fewer voids were found through microstructure analysis, strengthening the link between the reinforcement and matrix. The results underscore the potential applications of the CNT-enhanced nanocomposites in the engineering fields of automotive, aerospace, radar-absorbing materials and others. This marks a significant development in the field of composite technology to produce durable and effective materials.

Double Layer Pixelate Checkerboard Optimization for Ultrawideband Radar Absorber With Light Weight and Optical Transparency

Double Layer Pixelate Checkerboard Optimization for Ultrawideband Radar Absorber With Light Weight and Optical Transparency

Development and Measurement of a 3D Printable Radar Absorber

Development and Measurement of a 3D Printable Radar Absorber

Development of barium hexaferrite core–shell composites as high-performance microwave absorption by optimizing hydrothermal synthesis

In conjunction with the enhancement of societal living standards and the rapid development of information technology, an extensive variety of high-capacity electronic devices are being introduced to the market. The heightened demands result in the generation of electromagnetic wave radiation, which poses a potential risk to human well-being. Barium hexaferrite (BHF) is one of the radar-absorbing materials (RAMs) that can absorb electromagnetic waves because it has a high anisotropic field. However, its drawbacks are narrow absorption and less stability. Molybdenum disulfide (MoS2), is the best candidate for the reinforcement of BHF. The study investigated the impact of increasing the thiourea, temperature, hydrothermal holding time, and sample thickness on reflection loss. This study used a two-step molten salt and hydrothermal synthesis to make a BaFe12O19@MoS2 core-cell composite. Two-step molten salt and hydrothermal synthesis methods created single-phase BaFe12O19@MoS2 core-cell composites that worked well. The results showed that adding MoS2 to BHF changed BHF's magnetic properties from hard to soft. Increasing the hydrothermal temperature up to 220 °C effectively reduced the reflection loss of BaFe12O19@MoS2. On a 2 mm thick sample containing 100 mmol thiourea, the study achieved an electromagnetic wave absorption of 99.97 % with a reflection loss of –35.41 dB (17.37 GHz). The results of this research can be applied to protect electronic devices vulnerable to signal interference from satellite radar systems at frequencies of 12–18 GHz

Tailoring Microwave Absorption Performance Using Tunable Core–Shell CoNi Alloy Nanospheres

In contemporary research endeavors, we have successfully synthesized a composite material endowed with extraordinary microwave absorption properties through a meticulously designed process involving the encapsulation of transition metal nanoparticles with a phenolic resin layer. This innovative material, centered around a core–shell architecture, boasts the incorporation of transition metals Co and Ni, presenting a systematic exploration of their compositional influence on the material’s wave absorption characteristics. Our investigation unravels a sophisticated interplay between alloy composition and microwave absorption performance. Noteworthy observations reveal a non-linear correlation between nickel content and absorption efficiency, where an initial decline precedes a subsequent augmentation. Intriguingly, this dynamic behavior is accompanied by a gradual shift in the absorption peak towards lower frequencies, elucidating the tunable nature of the material’s performance. Crucially, the pinnacle of absorption efficiency is attained at a precisely tuned Co:Ni ratio of 2:1, underscoring the significance of alloy composition in tailoring the material’s electromagnetic response. At an absorber thickness of 2.1 mm, our engineered material achieves a remarkable minimum reflection loss (RL) of −46.1 dB at a frequency of 13.5 GHz. This achievement is coupled with an impressive effective absorption bandwidth spanning 5.5 GHz, indicative of the material’s versatility and applicability across a wide frequency range. The results not only highlight the efficacy of the core–shell CoNi alloy composites but also emphasize the importance of meticulous composition control in achieving optimal microwave absorption performance. The work reported here presents a notable advancement in the synthesis of tunable microwave-absorbing materials, showcasing the potential for tailored electromagnetic responses. The intricate relationship between alloy composition and absorption characteristics elucidated in this study opens avenues for the development of radar-absorbing materials that meet the evolving demands of reduced thickness, light weight, and enhanced absorption performance across diverse frequency ranges.

Fabrication of multi-layer radar absorbing structures based on continuous fiber 3D printing and thickness correction method

Three-dimensional (3D) printing technology has revolutionized the fabrication of complex geometries, including electromagnetic wave absorbers. In this study, the multilayer radar absorbing structure (RAS) was designed and fabricated using a continuous fiber 3D printing process based on material extrusion (ME). However, a large thickness error occurred during the 3D printing process. The thickness error in the multilayer RAS, which is a resonant electromagnetic wave absorber, causes a large error in the electromagnetic wave absorption performance. To address this issue, the thickness correction method based on unit thickness was proposed. The unit thickness, which is the basic thickness of the multilayer RAS, was calculated to account for the thickness increase during printing. The redesigned RAS based on the calculated unit thickness effectively corrected the thickness error. The total thickness and thickness of each layer of the corrected RAS were measured and found to be similar to the design value. The measured electromagnetic wave absorption performance closely matched the analyzed value, confirming the effectiveness of the unit thickness-based correction method in improving the ME-based 3D printing process for fabricating RAS.