Gaurav Varshney

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• Doctor of Philosophy
• Professor (Assistant) at National Institute of Technology Patna

Dielectric resonator antennas (DRAs) operating in higher order modes provide wideband, enhanced gain, and circularly polarized performance. This paper presents a simple perturbation theory for predicting the resonant frequency of higher order modes in perturbed rectangular DRAs (RDRAs). The proposed theory has been validated for isolated RDRA, two‐...

This paper provides an idea for designing a highly efficient, second-order broadband fixed-IF subharmonic mixer. Attention is paid to the step-by-step design process with detailed fabrication methods. With the purpose to improve the accuracy of simulation, the diode model is separated into the passive (linear) and the active (nonlinear) model. HFSS...

Multi Broadband Absorber Device

A technique is introduced to precisely control the resonance behaviour of a metal-free graphene-based terahertz absorber by independently tuning the dual resonant peaks. The proposed ultrathin absorber features a multilayer configuration, with two isolated resonator layers of patterned graphene on dielectric (SiO2) substrates and a thin graphite sh...

A technique is implemented for obtaining tunable band notch/filtering features in terahertz (THz) monopole wideband antennas. A parasitic metal strip is engraved in the antenna radiator, which creates the band notch characteristics in the wideband response. The tunability of the created notched band can be obtained by engraving a non-resonant U-sha...

An absorber containing a vanadium dioxide (VO $_{2}$ ) resonator is designed and numerically studied to provide the thermally switchable response between the broad and narrow absorption spectrum. In the insulating phase, VO $_{2}$ resonator supports the dielectric resonance through the creation of standing waves to provide the narrow absorption s...

A technique is implemented for the generation and alteration of two independently tunable resonance peaks in a graphene based ultrathin absorber structure designed for the terahertz spectrum. The proposed structure is a multi-layered stacked arrangement of two resonator layers of graphene grown over the top of two isolated dielectric (SiO2) substra...

A plasmonic device is studied for the induction of 11 Fano resonances (FRs) in the transmittance spectrum. Initially, a circular ring resonator side coupled to metal–insulator–metal (MIM) waveguide with inclined slit yields 11 resonances in the spectrum. Out of these 11 resonances, seven are induced to the FRs and the rest four resonances remained...

Metal-insulator phase transitions in vanadium dioxide (VO $_{2})$ ring resonator can convert its resonance behavior to find the dual-band terahertz (THz) absorption. The surface charge distribution following the metallic boundaries in VO $_{2}$ establishes the dipolar and multipolar resonance in the lower and upper bands at frequencies 1.8 and 4....

A novel dual band tunable terahertz (THz) circularly polarized dielectric resonator antenna (CPDRA) is designed and numerically studied. Hybrid Silicon-Graphene materials are employed as radiator with cross-slot shaped aperture coupled feed, enabling tunable linearly and circularly polarized radiation. Silicon is a good material as dielectric reson...

A technique of slanting MIM plasmonic waveguide-based cavity is numerically studied and implemented. Initially, the proposed rectangular cavity is proficient for generating five Breit-Wigner and six Fano resonances. The polygonal cavity is designed out of rectangular cavity by slanting one of its edge that reshaped the Breit-Wigner resonances into...

A dual-band absorber is implemented for terahertz (THz) applications. The absorber provides the dual narrow bands which can be utilized for the refractive index sensing. The absorber provides the resonance peaks at 1.03 and 1.49 THz with the absorption of more than 95% at the peak frequency. The absorber provides the ultra-narrow Full-width-half-ma...

The coherent perfect absorption (CPA) occurring in the graphene sheet suspended in the air can be utilized to develop an ultrathin, ultra-broadband absorber working in the frequency range covering from the few hertz (Hz) to terahertz (THz) with perfect absorption. A graphene sheet is studied for inducing the CPA covering the radio, microwave and lo...

A thermally switchable ultrathin terahertz (THz) metal-free electromagnetic shield can be developed with the help of phase change material, vanadium oxide (VO2). The thermal alterations in the phase change material can modulate its conductivity hence the switchable absorptivity can be achieved. An ultrathin, (height ≈ / , is free space wavelength)...

The multiple electromagnetic (EM) resonances created using vanadium dioxide (VO $_{2}$ ) resonators supported by graphene sheet can provide the metal-free, multifunctional terahertz (THz) absorber. Thermally modulated conductivity of VO $_{2}$ results in switchable near-perfect absorption over broad frequency band 2 to 14 THz to narrow with full-...

xD;-An ultrathin broadband absorber covering the frequency range of 0.1 to 10 terahertz is designed and numerically analysed. The absorber structure utilizes a partial reflecting surface and reflector of graphene separated by a thin dielectric spacer providing the metal-free structure. Multiple resonances are generated in the absorber structure who...

A technique of simultaneous detection of multiple analytes through Fano resonance based plasmonic waveguide is implemented. A rectangular cavity coupled through a narrow channel to the metal-insulator-metal waveguide and supported with two vertical stubs induce six Fano resonances. The rectangular cavity and vertical stubs induce the Fano resonance...

The excitation and tuning of multiple resonances with narrow spectral width based on the Brewster's effect is possible in an ultrathin dual-band terahertz absorber. The angular variation establishes a monotonic relation with the frequency of some generated resonances offering tunability. Moreover, burying a graphene ring resonator beneath the metal...

Nowadays, RF energy harvesting systems are good alternative for energizing low-power electronic devices. This chapter proposes such system consisting of RF to DC signal converter with a dual-band impedance matching network (DBIMN) and diamond slotted MIMO antenna. The proposed MIMO antenna captures unused ambient RF energy in GSM1800, Wi-Fi, ISM, s...

Thermally-electrically tunable ultrathin metal-free structure of a terahertz (THz) absorber is implemented. The switching capability in absorption response is affirmed by the thermal variations incorporated in the resonators made of phase change material Vanadium-dioxide. The frequency tunability is acquired by the variations in electronic properti...

This research work reports a technique using which the antenna response can be reformed either with or without band notch characteristics. A metallic antenna is implemented for attaining the wideband response in terahertz (THz) frequency covering 8.55-12.4 THz. The radiator is inscribed with the slots in it for attaining the band notch feature in a...

This article demonstrates asymmetric transmission in a chiral metamaterial across 7-11 GHz. When right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) waves impinge on this chiral metasurface, they exhibit different transmission characteristics. Non-reciprocity is observed when the RCP and LCP waves are incidents on the...

A terahertz (THz) rectangular dielectric resonator (DR) antenna (DRA) is designed and numerically studied. The analysis is reported with the selection of aspect ratio of DR such that antenna operates with four modes with triple band response. A two port multi-input-multi-output (MIMO) antenna is designed keeping the separation between radiating ele...

A technique is implemented for the generation of multiple Fano-resonances in a plasmonic waveguide based rectangular cavity. A rectangular cavity provides four Fano peaks which can further be increased to nine by inserting the metallic bars in it. The trapped surface plasmon polaritons by metallic bars cause the generation of multiple Fano peaks ov...

Here, a tunable graphene based thin absorber which can be applied for sensing different analytes, has been proposed. A graphene ring has been used to tune the absorption characteristics from 4.2 THz – 4.8 THz with varying chemical potential from 0–0.9 eV for both transverse electric (TE) and transverse magnetic (TM) incident waves. When no chemical...

A technique is implemented for the enhancement of isolation between the ports in terahertz multi-input-multi-output (MIMO) antenna. A rectangular metallic patch is utilized for developing the two-port dual-band THz antenna. The radiator is perturbed with six elliptical slots and a square slot at the center achieve the peak/average value of the isol...

A technique is developed for enhancing the isolation between the ports of a terahertz (THz) dielectric resonator (DR) antenna (DRA) with two ports and single radiator. A two-port DRA provides the isolation of 6.88 dB which is further enhanced to 16.78 dB by inserting a circular slot in the ground plane of this antenna structure. The sidewalls of th...

The coupling between the ports of a two-port device implemented based on a single dielectric resonator (DR) of silicon material can be controlled to develop the terahertz multi-input-multi-output (MIMO) antenna and a filter. The ground plane of device is modified by engraving a circular slot for obtaining the function of a two-port MIMO dielectric...

An ultrathin structure of graphene-based absorber is implemented and numerically analyzed. The absorber is designed with the usage of graphene ring resonators and graphene reflector in the lower terahertz (THz) frequency ranges. The geometry of the absorber can be implemented with the thickness as small as / ; (: free space wavelength). A number of...

An ultra-wideband (UWB) terahertz (THz) antenna is designed and numerically analyzed. A technique is implemented for obtaining the filtering characteristics in the antenna response. A graphene sheet is placed in antenna structure for achieving the filtering response. The variation in the surface conductivity of the covered area by graphene sheet pr...

A terahertz (THz) antenna with tunable filtering is designed and numerically studied. A slotted monopole radiator with defected ground structure is used for operating with wideband response with an impedance bandwidth in the range of 3.80–11.98 THz for ${S_{11}} \le - 10\;{\rm dB}$ . A slot is engraved in the radiator for obtaining the filtering ch...

A terahertz (THz) wideband antenna is implemented and numerically studied for achieving the controllable and tunable filtering characteristics. A rectangular-shaped metal-based monopole antenna is designed for obtaining the wideband response. A slot is engraved in the radiator to obtain the filtering characteristics. The slot in radiator is filled...

The response of terahertz (THz) microstrip antenna can be altered using a graphene sheet placed at the position of created null of the near field region. THz antenna with metallic radiator operates with the fundamental mode and single band resonance created due to the effect of fringing field. The placement of graphene sheet of appropriate size and...

An ultrathin metal-free terahertz (THz) absorber is implemented and numerically analyzed. The absorber structure with a rectangular graphite resonator is designed to operate with the fundamental magnetic resonance in the lower- and higher-order magnetic resonance in the upper band. Carving the slots in the graphite resonator converts the magnetic r...

A tunable terahertz slotted monopole antenna is implemented with self-diplexing capability. The radiating arms of the antenna are filled with the graphene strips. The variation of electrical parameters of graphene material alters the surface current distribution in the radiating arms which results in tuning the antenna response through individual i...

A terahertz (THz) antenna with the metallic radiator is designed to provide the monopole like radiation characteristics and ultra-wideband (UWB) response. A graphene disc is applied beneath to the substrate of antenna opposite to the metal radiator. The confinement of the electric field in the area of the graphene can be varied using the chemical p...

A tunable terahertz four-port multiple-input-multiple-output (MIMO) graphene-based microstrip patch antenna with self-multiplexing ability is designed and numerically studied. Insertion of cross-slot in the graphene patch improved the isolation level to the order of 50−70 dB in the four-port MIMO mode operation. Four separate biasing pads are used...

A terahertz (THz) antenna is implemented with a technique of achieving the multiband response by exciting the higher order modes without changing the antenna structure. A patterned triangular shaped THz microstrip patch radiator is designed and numerically analyzed for providing the dual-band response with and modes. A graphene strip is applied in...

The state of graphene loop applied in the slotted antenna radiator is converted from non-resonant to resonant to achieve the tunable band notch characteristics in an UWB antenna. In the non-resonant state, the graphene loop with value of chemical potential as acts as a parasitic element and does not contribute to radiation. Increasing the chemical...

The frequency ratio of higher to lower order mode can be electronically tuned in a terahertz (THz) antenna with metallic radiator using a graphene loop. Antenna is designed with slotted metallic radiator to obtain the dual-band response with fundamental and second order transverse magnetic mode providing the directional and bi-directional radiation...

A technique is implemented for achieving the multiband terahertz (THz) absorption with high-quality factor in an absorber containing an ultrathin silicon resonator. The symmetrical perturbation is done in the silicon layer for obtaining the multiple multi-order electric and magnetic resonances. The proposed absorber structure provides the polarizat...

A tunable terahertz circularly-polarized dielectric resonator antenna is implemented and numerically studied. An aperture coupled terahertz rectangular dielectric resonator antenna operating with the fundamental magnetic dipole is designed. The modal field distribution is perturbed using the material-perturbation technique and the electric field ve...

A tunable terahertz (THz) dielectric resonator (DR) antenna (DRA) with circular polarization operating with multiple higher order modes is numerically studied and implemented. A rectangular DRA (RDRA) is designed with a length to width aspect ratio of the DR allowing the operation with the higher order modes. The RDRA provides the triple band respo...

A circularly polarized (CP) multi-input multioutput (MIMO) dielectric resonator (DR) antenna (DRA) with compact size and four ports is implemented. CP radiation was achieved using the deformed DR geometry excited with aperture coupled feeding. A CPDRA with a single and two ports is investigated. The defected ground structure (DGS) was incorporated...

A modified Koch frontier, super wide band antenna is designed and analyzed in both frequency and time domain. A novel combination of partial ground structure with asymmetric polygon shape patch is proposed in this letter. Higher order TM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb...

A tunable terahertz four-port multiple-input-multiple-output (MIMO) graphene microstrip patch antenna with self-multiplexing ability is designed and numerically studied. The top layer of the four-port patch antenna, which is a symmetric cross-shaped graphene patch, is patterned using a cross-slot. Insertion of this cross-slot improved the level of...

In this article, a technique for gain enhancement of metallic radiator based dual-band THz antenna has been implemented. The antenna operates in fundamental and second order modes, thus providing conical and biconical radiation. The different reflective frequency selective surfaces (FSS) have been designed and integrated with antenna for its gain e...

A tree-shaped graphene-based microstrip multiple-input and multiple-output (MIMO) antenna for terahertz applications is proposed. The proposed MIMO antenna is designed on a 600 × 300 μm² polyimide substrate. The designed MIMO antenna provides a wide impedance bandwidth of 88.14% (0.276–0.711 THz) due to the suggested modifications in the antenna co...

A technique for controlling the bandwidth of the multi–input–multi–output (MIMO) dielectric resonator antenna (DRA) is implemented in this paper. Firstly, a simple two ports aperture coupled rectangular DRA for providing the triple-band response is designed. The rectangular slots of size around quarter wavelength are inserted in the ground plane an...

A tunable terahertz (THz) dual-band circularly polarized (CP) dielectric resonator (DR) antenna (DRA) is numerically analysed and implemented. Initially, an aperture coupled dual-band rectangular DRA is designed. This operates with the fundamental mode in the lower band and third order mode in the upper band and provides the linearly polarized resp...

A technique is implemented for obtaining the high absorption over super-wideband (SWB) in a metal-free THz absorber. The multiple resonant modes with wide spectra are generated in a graphite-based resonator placed on a dielectric cavity merging of which provides the SWB response. The low permittivity dielectric slab sandwiched between the graphite...

In this article, two different types of polarization-insensitive frequency selective surfaces (FSS) have been employed for integration with the tunable graphene loaded terahertz (THz) patch antennas. Two different types of graphene loaded antennas have been proposed and studied through numerical simulations. The proposed antennas provide the reconf...

This paper presents a tunable terahertz (THz) two-port graphene patch antenna having isolation between the ports of the order of 40 dB over the whole range of tunability. This antenna could either be used in self-diplexing mode or as a multi-input–multi-output (MIMO) antenna with pattern diversity that can support simultaneous-transmit-and-receive...

The perturbation approach is presented here for the first time for the analysis of an inhomogeneous circularly polarized rectangular dielectric resonator (DR) antenna (DRA). The inhomogeneous permittivity is created by perturbing a rectangle-shaped region of different material inside the rectangular dielectric resonator antenna (RDRA). The orthogon...

Surface plasmons generated at the graphene dielectric interface can be altered by trapping the electric charge. A technique is implemented for trapping the bipolar electric charge on the graphene surface and arranged in a desired way to enhance the performance of a monolayer graphene metamaterial based tunable, ultrathin, dual narrow band terahertz...

A tree-shaped graphene based microstrip MIMO antenna for terahertz applications is proposed. The proposed MIMO antenna is designed on a 600×300 µm ² polyimide substrate. The designed MIMO antenna exhibits a wide impedance bandwidth of 88.14% (0.276–0.711 THz) due to the suggested modifications in the antenna configuration. The MIMO design parameter...

A technique is implemented for altering the multimodal resonance generated in an ultrathin silicon ring resonator-based terahertz (THz) absorber. The absorber provides the dual-band resonance with the excitation of magnetic and electric dipole in the lower and upper band, respectively. The field of magnetic and electric dipoles is altered using a n...

An annular dielectric resonator (DR) antenna (DRA) is implemented for THz applications. A silicon made DR is loaded with graphene disk for obtaining the tunability in the frequency response. The physical parameters of silicon annular DR can be set to obtain the resonance at any frequency in the lower THz band and can be tuned by changing the chemic...

A wide band circularly polarized (CP) aperture coupled staircase shaped wideband dielectric resonator antenna (SSCPDRA) array is implemented. The proposed array is composed of identical four SSCPDRA elements. The wideband CP and gain of the single element is enhanced by using 2 × 2 array with sequential phase feeding network. The measured results o...

A compact tunable notch band ultra-wideband (UWB) antenna is implemented. The band notch characteristics have been obtained by placing a square-shaped metallic loop in the upper ground plane connected via PIN diode. The obtained notched frequency bandwidth can be altered by changing the states of the PIN diode. UWB response with narrow-band notch o...

A circularly polarized (CP) dielectric resonator (DR) antenna (DRA) is implemented and numerically analyzed for terahertz (THz) applications. A composite of different deformed geometries silicon based DRs is utilized for obtaining the orthogonal modes required for achieving the CP response in THz frequency range. A rectangular slab of silicon is ke...

A technique is implemented for multiband generation and absorption enhancement in a graphite-based absorber. The aspect ratio of the graphite sheet is selected to support the generation of multiple absorption bands. Later on, the notches and slots are inserted in the graphite sheet for absorption enhancement. The generated multiple absorption bands...

A wideband terahertz metal-free absorber is designed and numerically analyzed. The graphite/graphene disks supported by low permittivity dielectric disks are stacked. The stacked graphite disks are placed above a dielectric substrate acting as resonant cavity. The resonance of dielectric cavity is merged with the resonance of a graphite and graphen...

A graphite/dielectric cavity resonator-based absorber is numerically analyzed and implemented with wideband absorption. A graphite disk resonator is inserted in the low permittivity dielectric THz cavity resonator for the generation of multiple modes. The modes generated in dielectric cavity are merged with the resonating mode of graphite disk reso...

In the present paper, a multilayer stack of Yb doped ZnO (YZO) and p-Si has been designed in which the total internal reflection of optical light is combined to form constructive interference. The mechanism behind light propagation in a stack is revealed, and factors affecting the reflectivity of the stacked reflector are analytically investigated....

A technique is proposed for the enhancement of gain and circularly polarized (CP) bandwidth of a singly-fed CP dielectric resonator (DR) antenna. The specific geometry of DR is used to generate the orthogonal modes required for obtaining the CP response. The incremental harmonics of the fundamental and third order modes, TE_(11δ+1) and TE_(31δ+1) a...

A graphite disk resonator antenna is numerically analyzed and ultra-wideband response is obtained by exciting the higher order transverse magnetic modes. The physical parameters of antenna can be set to obtain either ultra-wideband or wide dual-band response. The antenna provides the 100% impedance bandwidth which can further be extended by changin...

A dual‐band rectangular dielectric resonator (DR) antenna is implemented with a multi‐frequency circularly polarised (CP) response. The wide dual‐band response is achieved by inserting the slots in the DR. The insertion of slots in the DR in a specific manner generates the orthogonal degenerate modes. Consequently, the multi‐frequency CP response i...