Himangshu Bhusan Baskey

Investigation and performance evaluation of carbon black- and carbon fibers-based wideband dielectric absorbers for X-band stealth applications

This paper presents the design, preparation, and electromagnetic testing of wideband dielectric absorbers based on carbon fibers and carbon black powders for stealth applications. The specially prepared absorbers are characterized using the partially filled waveguide technique for the complex permittivity, and the return loss of the sample is measured using the free-space system in the X-band frequency region. A maximum return loss of 29 dB i.e. absorption of 99% at 10.3 GHz is achieved with minimum 97% absorption throughout the X-band frequency region. The fabricated absorber having density of 0.28 gm/cc and thickness of 2 mm makes it a potential candidate for stealth applications especially for the defense targets. A multilevel fast multipole method-based electromagnetic simulation is carried out on the artillery shell model, and on the leading edge model of the aircraft using the measured electromagnetic properties of designed absorber for the radar cross-section (RCS) reduction. The maximum RCS reduction of 27 and 20 dB has been observed for the artillery shell model, and for the leading edge of stealthy aircraft model, respectively, as compared to that of the PEC structure at 10.3 GHz frequency.

Design of Flexible Hybrid Nanocomposite Structure Based on Frequency Selective Surface for Wideband Radar Cross Section Reduction

This paper presents the design, synthesis, and testing of a novel flexible hybrid nanocomposite (FHN) structure for the wideband radar cross section (RCS) reduction of targets. The proposed FHN structure consists of a frequency selective surface (FSS) pattern printed on a thin flexible polyimide film backed by aluminum foil, which is then integrated with a customized flexible nanocomposite sheet. The nanocomposite sheet consists of graphite fillers combined with zinc oxide powders, which are embedded into the thermoplastic polyurethane matrix. The fabricated nanocomposite sheet is first characterized for the effective permittivity and the dielectric loss tangent using the free-space measurement technique, and the measured electromagnetic properties are then used for the design of an FHN structure. The proposed FHN structure having overall thickness of 1.335 mm shows minimum reflection coefficient (RC) of −28 dB at 10.2 GHz, along with −10 dB RC bandwidth in the entire

Metamaterial Structure Integrated With a Dielectric Absorber for Wideband Reduction of Antennas Radar Cross Section

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Design, synthesis, characterization and performance evaluation of multi-band perfect metamaterial absorber

-band. Finally, the fabricated FHN structure is applied on a cylindrical target, which provides minimum 10 dB RCS reduction under various polarizations. The proposed work provides an effective way to combine the strength of FSS with that of a customized nanocomposite sheet in order to design an efficient FHN structure for various strategic applications.

Investigation on the Dielectric Properties of Exfoliated Graphite-Silicon Carbide Nanocomposites and Their Absorbing Capability for the Microwave Radiation

This paper presents the design, synthesis, and testing of a novel wide band electromagnetic hybrid absorber (HA) for the radar cross section (RCS) reduction of antennas. The proposed HA is based on the design of a metamaterial structure coated with the synthesized dielectric absorber material. The dielectric filler based composite absorber is fabricated by optimizing weight percentage of graphite and glass microballoon powders mixed into an epoxy medium. The proposed HA shows minimum –10 dB reflection loss (RL) in the 6–12 GHz frequency region having maximum absorption of 99.56% (–20 dB RL) at 9.26 GHz. The proposed HA is ultimately loaded onto a wide band antenna in order to reduce the in-band RCS of the antenna. The simulated and the experimental results show remarkable RCS reduction of the antenna over the full operating frequency range. It is also observed that the antenna characteristics, e.g., the gain and the radiation pattern remain almost preserved after loading the antenna with HA. The significant RCS reduction capability of the proposed HA shows that it has the potential applications for RF stealth technology.

A dual band multiple narrow slits based metamaterial absorber over a flexible polyurethane substrate

This paper presents the design, synthesis, characterization, and performance evaluation of a metamaterial absorber having four distinct absorption peaks. The proposed absorber is based on the periodic array of the hexagonal closed rings and octa-star structure printed over the dielectric substrate. The dimensions of unit cell are optimized such that the absorption takes place at the distinct frequency near the Federal Communications Commission defined radar spectrum e.g. at 4.10, 6.15, 10.05, and 15.52 GHz with the absorptivity of 0.98, 0.99, 0.99, and 0.99, respectively. The proposed structure is fabricated and the experimental result shows high absorptivity under transverse electric and magnetic polarization for the wide angle of incidence angles, which is in concurrence with the simulated results. The equivalent circuit model of the absorber has been developed sequentially for each of the structure. Furthermore, the complex refractive index of the metamaterial structure has been retrieved in order to have a detailed analysis, which supports the absorption phenomena at all the corresponding frequencies. The proposed metamaterial structure appears to be a potential candidate for absorber applications in the radar cross-section reduction, thermal detectors, and thermal imaging.

An improved measurement technique for retrieval of effective constitutive properties of thin dielectric/magnetic and metamaterial samples

The dielectric properties of the exfoliated graphite (EG) and sillicon carbide (SiC) powder based epoxy nanocomposites are investigated in the microwave frequency region for radar absorbers and stealth applications. The resulting composites are found to possess high dielectric constant and loss tangent in the X band (8.2–12.4 GHz) frequency region. It is observed that both the dielectric constant and the loss tangent of the nanocomposites increase as the weight percentages of the EG and SiC powders are increased. SiC powder is mainly introduced to enhance the thermal stability of the nanocomposites with the improved microwave absorption properties. The filler percentages of SiC nanopowder and EG powders are optimized for the wide band electromagnetic absorption (EM). Maximum EM absorption of 99.99% along with the minimum absorption value of 90% is achieved throughout X band frequency region. The resulting nanocomposites possess a very good agreement between the light weight, ease of processing, and cost. Furthermore, the complete morphological and thermal stability analyses are carried out for the nanocomposite samples which provide an insight into various mechanical and thermal properties. The observed electromagnetic, mechanical, and thermal properties of the proposed nanocomposites make them potential candidates as efficient electromagnetic absorbers in the microwave frequency region for various strategic applications.

Design of metamaterial based structure for the radar cross section reduction of a microstrip antenna

In this paper we present a novel multiple narrow slits based polarization insensitive metamaterial structure possessing electromagnetic absorption characteristics in C and X band frequencies. The proposed structure have been designed using CST Microwave studio, which shows the metal backed reflection loss of 17 dB and 19.36 dB at 7.30 and 10.80 GHz having percentage absorption of 98% and 98.85% respectively. The proposed metamaterial structure have been fabricated over a flexible polyurethane substrate, measurement for reflection loss have been carried out in an anechoic chamber at the respective frequency bands. A close match between experimental and theoretical results for absorption is observed. The proposed structure has the potential such as multi band absorption and flexibility features makes it a potential candidate for absorber in surveillance and stealth applications.

A flexible, ultra thin, frequency-selective-surface based absorber film for the radar cross section reduction of a cubical object

An improved partially filled waveguide based technique for the simultaneous measurement of complex permittivity and permeability of thin dielectric-magnetic and metamaterial samples is presented. The proposed approach requires placing a test specimen longitudinally at the centre of a rectangular waveguide cross section for the measurement of scattering coefficient in the specified frequency band. The constitutive properties of the specimen are determined in terms of the measured scattering coefficients using the newly derived expressions, which are based on the solution of the corresponding transcendental equation. The proposed approach is validated by measuring the permittivity and permeability of few standard samples, and comparing the results with the data available in literature. The overall procedure is non-iterative, which makes it quite versatile, and envisages the possibility of even online monitoring of certain parameters.