Somak Bhattacharyya

Triple band polarization-independent metamaterial absorber with bandwidth enhancement at X-band

In this paper, we propose a triple band polarization-independent metamaterial absorber using square-shaped closed ring resonators over wide angle of incidence. The unit cell consisting of various square loops is designed by using the parametric analysis so that it exhibits a triple band absorption response with two bands lying in C-band and one in X-band for airborne and surveillance radar signal absorption applications. Furthermore, in X-band, the absorber exhibits a broadband response with full width at half maxima bandwidth of 940 MHz (9.43%). The structure exhibits bandwidth enhanced properties for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence up to 60°. The proposed structure is fabricated and experimental results show proper matching with the simulated responses.

Bandwidth-enhanced polarization-insensitive microwave metamaterial absorber and its equivalent circuit model

In this paper, a bandwidth-enhanced polarization-insensitive ultra-thin metamaterial absorber has been presented. A simple equivalent circuit model has been proposed describing the absorption phenomenon to estimate the frequency of absorption of the proposed microwave absorber. The basic structure consists of concentric rings embedded one inside another to enhance bandwidth by incorporating the scalability property of the metamaterials. Simulation results show that the structure has enhanced bandwidth response with full width at half maxima (FWHM) of 1.15 GHz (9.40–10.55 GHz) with two absorption peaks at 9.66 and 10.26 GHz (96% and 92.5% absorptivity, respectively). The structure is symmetric in design giving rise to polarization-insensitivity and can achieve high absorption for oblique incidence up to 40°. The proposed absorber has been fabricated and measured in anechoic chamber, showing that experimental results agree well with the simulated responses.

Triple band polarization-independent ultra-thin metamaterial absorber using electric field-driven LC resonator

In this paper, a triple band polarization-independent metamaterial absorber using electric field-driven LC resonators is proposed over wide angle of incidence. The unit cell is designed by parametric optimization in such a way that triple band absorption occurs in C-band. The proposed structure exhibits triple band absorption property for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence upto 60° for both TE and TM polarizations. The proposed structure is also fabricated and experimental results provide good agreement with the simulated responses. The constitutive electromagnetic parameters viz. effective permittivity and effective permeability are extracted from the simulated response, which support the absorption phenomena at all these three frequencies. The reflection from the structure is numerically computed and verified with simulated response, and it shows good agreement between them.

An Ultrawideband Ultrathin Metamaterial Absorber Based on Circular Split Rings

A simple design model for making ultrawideband ultrathin metamaterial absorber has been presented in microwave frequency regime. The proposed structure is composed of two concentric circular split rings imprinted on a metal-backed dielectric substrate. A 10-dB absorption bandwidth from 7.85 to 12.25 GHz covering the entire X-band has been observed in numerical simulation under normal incidence. The absorptivities of the proposed structure have been investigated under different polarization angles as well as oblique incidence. The electromagnetic field distributions and surface current plots have been illustrated to analyze the absorption mechanism of the proposed structure. The proposed absorber has been fabricated and its performance is experimentally verified at different angles of incidence and polarizations of incident electromagnetic wave. The designed absorber is compact, ultrathin (only λ0/15 thick corresponding to center frequency) and provides an alternative to construct broadband absorber for many potential applications.

Equivalent circuit model of an ultra-thin polarization-independent triple band metamaterial absorber

This paper presents equivalent circuit modeling of an ultra-thin polarization-independent metamaterial microwave absorber consisting of three concentric closed ring resonators (CRR). The unit cell size as well as the other geometrical dimensions like radii and widths of the rings are optimized so that absorptions take place at three distinct frequencies near to the middle of the FCC defined radar spectrum eg., at 5.50 GHz, 9.52 GHz and 13.80 GHz with peak absorptivities of 94.1%, 99.6% and 99.4% respectively. The equivalent circuit model of the triple band absorber has been developed sequentially considering the single band and double band absorber models. The circuit simulation of the final model agrees well with the full-wave simulation, thus validating the modeling technique. The structure is also fabricated and experimental absorption peaks are found close to the simulated values.

An ultra thin metamaterial absorber using electric field driven LC resonator with meander lines

This paper describes the electric field driven LC (ELC) resonator structure using Meander lines in C-band. The proposed ELC driven metamaterial structure is simulated using Ansoft HFSS which shows an absorption peak at 6.26 GHz with absorbance of 99.1% and S11 of -20.55 dB. The reduction of frequency at which absorption occurs can be explained from the equivalent LC circuit combination of the proposed structure. The incorporation of Meander lines enhances the net inductance, and thus frequency is reduced. The absorbance is supported by the real and imaginary parts of the impedance value extracted from S-parameters. The absorption frequencies can be shifted by varying the gap as well as length-segment of the Meander Line structure.

Study on ultra-thin dual frequency metamaterial absorber with retrieval of electromagnetic parameters

This paper describes the construction of ultra-thin dual frequency absorbers using metamaterials in microwave frequency (C-band). The geometrical dimensions of an electric field driven LC (ELC) structure are optimized using parametric analysis to achieve absorptions at two distinct frequencies, both in the C-band. The simulation of the proposed structure using HFSS shows that absorption occurs at two different frequencies, viz., 5.64 GHz and 6.22 GHz with absorptivities of 99.4% and 94.8% respectively. The absorption is explained by using the electric and magnetic excitations. The structure is also studied with different polarization and incidence angles. The structure is thereafter fabricated and experimental absorptivity response has been measured showing good agreement with the simulated one. After this, the backside of the structure is slightly modified by applying small cuts so that the transmission properties are little enhanced, and hence the effective constitutive parameters are retrieved. The retrieved effective permittivity and permeability are nearly equal to validate absorption.

An ultra-thin polarization independent metamaterial absorber for triple band applications

This paper presents an ultra-thin polarization independent metamaterial microwave absorber comprising of three concentric closed ring resonators (CRR). The unit cell sizes as well as the other geometrical dimensions like radii and widths of the rings are optimized so that absorptions take place at three distinct frequencies near to the middle of the FCC radar frequency spectrum. The proposed structure shows absorptivities of 94.1%, 99.6% and 99.4% at 5.5 GHz, 9.52 GHz and 13.8 GHz respectively. The proposed structure has been studied under oblique incidence, both for TE and TM polarization where it behaves as absorber upto 60 ° incident angles in both the cases. Due to the geometrical symmetry, the structure is found to be polarization independent absorber.

RADIO ASTRONOMY AND SUPER-SYNTHESIS: A SURVEY

Radio astronomy has a wide electromagnetic spectrum. It is based on antennas, electronics, software etc., and thus highly technical. The radio data obtained from distant objects like stars, galaxies, pulsars etc. are useful for studying the Universe. Many of the radio emissions, especially from the Sun have been studied over decades for understanding the ionosphere and its efiects on radio communication. Until now, this subject of radio astronomy has found its existence among those who are associated with astronomy and possessing at least some knowledge of RF engineering. A requirement of a review literature on this subject with technical details is felt by many working engineers and scientists. It is thus proposed to write a series of articles covering the subject from both engineering and

A Wideband Cross Polarization Conversion using Metasurface

A cross polarization conversion (CPC) structure using metasurface over wide bandwidth has been presented for practical applications in this article. The unit cell of the proposed metasurface is made of metallic patch of single circular split-ring imprinted on top surface of a metal-backed single layer dielectric substrate. Full width half maxima bandwidth of polarization conversion ratio (PCR) of 11.12 GHz is realized along with wide bandwidth of 9.92 GHz extending from 6.06 GHz to 15.98 GHz with more than 0.8 PCR magnitude is realized using suitable optimization of the geometrical dimensions. Four distinct PCR peaks are observed at 6.56 GHz, 10.38 GHz, 15.12 GHz and 16.68 GHz. The polarization conversion phenomena at these four frequencies have been analyzed in the light of electromagnetic resonances. The roles of several geometrical parameters of the design are simultaneously investigated. The proposed structure has been studied under oblique incidence, both for TE and TM polarizations. Wideband polarization conversion characteristics upto 45° incident angles have been observed for both cases. A prototype of the proposed metasurface is fabricated and experimental results are in good agreement with the simulated responses. The proposed structure is ultra-thin; ~ λ/11.8 with respect to the centre frequency of the CPC bandwidth.