There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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Computational Methods For Electromagnetics

Ultra-high sensitivity sensor has significant application for micro-nano optical devices in terahertz. Here, we propose a simple graphene metasurface, which can achieve obvious graphene plasmon-induced transparency (PIT) phenomenon. We can find that PIT, reflectivity, and absorbance can be effectively tuned by the Fermi level. Moreover, the finite-different time-domain (FDTD) numerical results are well agreement with the coupled mode theory (CMT) results. Interestingly, an ultra-high sensitivity sensor performance based on tunable PIT in terahertz bands can be realized in our proposed metasurface, the sensitivity and Figure of merit (FOM) can reach up to 1.7745 THz/RIU and 23.61, respectively. Hence, these results can provide theoretical guidance for terahertz dynamic integrated photonic devices.

Graphene-based metasurface sensing applications in terahertz band

In this work, we present an efficient polarization conversion device via using a hollow graphene metasurface. The platform can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear-to-circular polarization conversion (LTC-PC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range. For instance, the proposed device obtains an x-to-y CPC function with the bandwidth up to 1.83 THz (χPCR ≥98.8%). Moreover, the x-to-y CPC function can be switched to LTC-PC function via artificially tuning the Fermi energy of graphene. The maximal frequency shift sensitivity (S) of polarization conversion function reaches 23.09 THz/eV, suggesting a frequency shift of 2.309 THz for the LTC-PC function when the chemical potential is changed by 0.1 eV. Based on these superior performances, the polarization converter can hold potential applications in integrated and compact devices, such as polarization sensor, switches and other optical polarization control components.

Multi-functional polarization conversion manipulation via graphene-based metasurface reflectors.

Quad-Band Transmissive Metasurface with Linear to Dual-Circular Polarization Conversion Simultaneously

In this paper, a transmittive-type dual-band linear (LP)-to-circular Polarization (CP) converter has been reported. The structure can convert the incident LP wave into right-handed circularly polarized wave in two non-adjacent frequency ranges of C and Ku bands. It bears a tri- layer configuration of three concentric square shape split ring resonators having slits oriented along 45° with each other. The simulated results show that the axial ratio of the proposed converter is under 3-dB over the frequency ranges of 4.07-4.15 GHz and 14.19-14.51 GHz. The ellipticity of the structure is - 0.98 and -0.99 at 4.1 GHz and 14.3 GHz, respectively; thereby confirming the right-handed CP nature of the transmitted wave. This transmittive-type metasurface can be easily mountable to a simple dual-band LP antenna to obtain the desired dual-band CP wave for satellite communication system. The structure has the periodicity of λ/5 while maintaining thickness of λ/6.6 w.r.t. the center frequency of the first conversion band.

A Transmittive-type Metasurface for Dual-band Linear to Circular Polarization Conversion

In this paper, the authors has tried to bring in focus of the research community towards the presentation of UWB base antenna in terms of Single and Multi-Band where the profiles are countered for Notch operations. They are particularly obtained in the presence of Split Ring Resonator (SRR). The Overall Antenna size is 30 × 36 mm2 as standard where it is designed using FR-4 and is simulated by using Full Wave Simulator known as ANSYS-HFSS. The final designed prototype offers better VSWR, Omni-Directional Radiation Pattern, with the elongated form of Gain & Overall Efficiency resulting out in controllable Bandwidth. All of them are based on the simulation outcomes where they are being mathematically modeled out to support the advances or features from the fabrication point of view which is the last & concluding aim of the authors.

Modifications of an antenna from UWB to multi-band with acquired notch characteristics

We focus on rare-earth-free anti-perovskite Mn4− xNi xN epitaxial films, which can be used for ultrafast current-induced domain wall motion (CIDWM) in magnetic strips. The magneto-transport properties of these materials are very important for a deep understanding of CIDWM. In this study, we investigated the magneto-transport properties of Mn4− xNi xN epitaxial films grown on SrTiO3(001) and MgO(001) substrates through anisotropic magnetoresistance (AMR) measurements at temperatures between 2 and 300 K. In samples with a small Ni composition such as x = 0.05−0.1, the AMR ratio of Mn4− xNi xN drastically decreased with increasing temperature. We also analyzed the twofold and fourfold symmetries in the AMR curves. Fourfold symmetry is caused by tetragonal crystal fields and is unique to anti-perovskite 3 d-metal nitrides such as Mn4N and Fe4N. Only slight fourfold symmetry was observed in Mn4− xNi xN. We also performed first-principles calculations with the Vienna ab initio simulation package (VASP) to obtain the projected density of states (PDOS) of d orbitals in Mn4− xNi xN, which is responsible for the magnetism of these materials. We conclude that these results are due to the Ni atoms, which function as magnetic impurities and lead to a noticeable change in PDOS, as proved by VASP calculation.

Anisotropic magnetoresistance in Mn4−xNixN and the change in the crystalline field

Compact printed antennas are an essential need of modern wireless world. An UWB planar aperture antenna for various wireless applications is presented in the literature. This antenna covers a wide range of frequencies from 2.14 GHz to 6 GHz. In this whole range of frequencies S11 is under −10 dB. The designers designed a bowtie shaped aperture from the thin copper layer fed by CPW feed line aperture. The antenna structure is more compact as the CPW ground and the aperture radiator shares the same plane. The antenna has got a size of 40×52×1.57 mm3 which is compact. The antenna prototype is designed and simulated using HFSS. The antenna offers good impedance matching, good radiation characteristics, moderate gain and good efficiency.

An aperture antenna for bluetooth, WLAN, WiMax, ZigBee and LTE applications

The COVID-19 pandemic attributed to the SARs-Cov-2 virus has disrupted the lives of individuals in every corner of the world, causing millions of infections and numerous deaths worldwide. Identifying and isolating infected people is very crucial to slow down the spread of the disease. In this paper, we report a design of highly sensitive, graphene-metasurface based biosensor for detecting the S1 spike protein expressed on the surface of the SARSCoV-2 virus in the terahertz band. Our structure consists of a silicon dioxide substrate sandwiched between a complete gold layer at the bottom, and a graphene monolayer on top etched with a phi-shaped slot tilted at 45 degree, which performs a wideband reflective-type cross-polarization conversion of the incident electromagnetic (EM) wave. The optimized polarization conversion ratio (PCR) has been achieved at 0.75eV chemical potential value of the graphene layer. When samples of Sars-CoV-2 virus contained in a phosphate buffer saline (PBS) solvent is put on top of proposed design of the sensing surface, the spike proteins of the virus interact with the spike antibody grown on the sensing surface; and it changes the refractive index of the overall system (Biosensor + Analyte), which in turn changes the PCR and the corresponding frequency of the reflected wave. The biosensor response has been computed using the Finite Integration Technique (FIT) in the terahertz region. The sensitivity of the biosensor is found to be 354 GHz/RIU at the PCR of 0.9.

Sambit Kumar Ghosh

Papers

A Transmittive-type Metasurface for Dual-band Linear to Circular Polarization Conversion

Modifications of an antenna from UWB to multi-band with acquired notch characteristics

Anisotropic magnetoresistance in Mn4−xNixN and the change in the crystalline field

An aperture antenna for bluetooth, WLAN, WiMax, ZigBee and LTE applications

Graphene-metasurface-based biosensor for SARS-CoV-2 detection