http://starc.stthomas.ac.in:8080/xmlui/xmlui/handle/123456789/135 2026-04-22T18:51:09Z http://starc.stthomas.ac.in:8080/xmlui/xmlui/handle/123456789/219 Measurement of dielectric constant of waxes at different temperatures using split ring resonator structure Chakyar, Sreedevi P; Shanto, TA; Aathira, Muralil; K, Sikha Simon; Paul, Nees; Andrews, Jolly; Joseph, VP Dielectric constant variation with temperature for different wax sampies is analysed with the help of split ring resonators (SRRs). The method employs a simple extraction procedure to obtain the unknown permittivity values from a calibration curve drawn between relative permittivity of standard sam pies and resonant frequency of SRR with each of the sampies placed above it. The wax sam pie is placed on the SRR surface and its transmission characteristics are analysed using a vector network analyser (VNA) with its transmitting and receiving probes placed on either side of the SRR - sam pie system. The temperature is gradually increased from room temperature to 60°C with the help of a hot metal plate placed near the SRR. The dielectric constant of wax sampie in contact with the SRR surface varies with the temperature, which in turn changes the capacitance of the SRR, resulting in a shirt in its resonant frequency. The method has its advantages like simple experimental setup, direct measurement and ease of sam pie preparation. 2016-12-01T00:00:00Z http://starc.stthomas.ac.in:8080/xmlui/xmlui/handle/123456789/206 Microwave absorption properties of flexible zinc oxide sheet Paul, Nees; Jimmy, Janet; Chakyar, Sreedevi P; Simon, Sikha K; Kizhakooden, Joe; Bindu, C; Sebastian, Anju; Umadevi, KS; Jose, Jovia; Andrews, Jolly; Joseph, VP This paper presents the fabrication and microwave absorption properties of low-cost flexible light-weight zinc oxide (ZnO) sheet. The elastomers, films and foams used as microwave absorbers are made of lossy materials impregnated on low density matrixes which are thicker, heavier and expensive in wide frequency ranges. The prepared ZnO sheet in polytetrafluoroethylene (PTFE) matrix and isopropyl alcohol (IPA) as binder is characterized using XRD which showed the crystalline structure of ZnO in the sample. The microwave characterization is done using waveguide method by placing the sheet samples of different thickness (1 mm and 2 mm) perpendicular to the direction of propagation of power inside the rectangular wave-guides with operating frequency ranges of 5 - 7 GHz and 7 - 9 GHz connected to a Vector Network Analyzer (VNA). Transmission (S21) and reflection (S11) coefficients are analyzed in the above frequency ranges. The reflection coefficients show no remarkable variation throughout the measured frequency range whereas the transmission coefficients exhibit noticeable drop in the transmitted power around 5 - 15 dB at certain frequencies. As the thickness of the sample increases, the absorption level also increases. The absorption of microwave power is observed to be maximum at 8 - 9 GHz frequency range. Absorption properties of conducting ZnO sheet may find applications in the design of novel type of microwave absorbers 2019-10-29T00:00:00Z http://starc.stthomas.ac.in:8080/xmlui/xmlui/handle/123456789/203 Scattering from artificial plasma cylinder using nonstandard FDTD Jose, Jovia; Simo, Sikha K; Sebastian, Anju; Chakyar, Sreedevi P; Kizhakooden, Joe; Paul, Nees; Bindu, C; Umadevi, KS; Andrews, Jolly; Joseph, VP This paper implements Nonstandard Finite Difference Time Domain (NS-FDTD) method to analyses the scattering effect of electromagnetic wave by an artificial plasma cylinder. This NS-FDTD which requires less iteration time for convergence has proved to be around 10,000 times more accurate than the standard FDTD. For a chosen problem, the ratio between wave length and grid space in NS-FDTD need to be only 8 whereas for the standard algorithm it has to be 1140 for the same qualitative result. In this paper, NS-FDTD algorithm which is already successfully implemented for lossless and low loss medium is extended to high loss medium. An artificial negative permittivity metamaterial medium of cylindrical profile is designed using periodic arrangement of thin conducting wires and NS-FDTD is used to study the scattering properties of the plasma structure. For simplicity, interacting field quantities are realized in terms of propagation equation. Converging points of stability function are carefully selected by choosing appropriate value of conductivity. Plane wave of frequency less than the plasma frequency of the artificial plasma cylinder is used for the study. The result obtained is compared with standard FDTD which proves the obvious advantage of using this novel algorithm. 2019-10-29T00:00:00Z http://starc.stthomas.ac.in:8080/xmlui/xmlui/handle/123456789/201 Enhancing the resolution in imaging using folded metamaterial split ring resonator structure at microwave frequencies Bindu, C; Chakyar, Sreedevi P; Sebastian, Anju; Simon, Sikha K; Jose, Jovia; Paul, Nees; Umadevi, KS; Kizhakooden, Joe; Andrews, Jolly; Joseph, VP A novel and better resolution topology for reducing the sensing area of conventional Split Ring Resonator (SRR) metamaterial structure is proposed. The conventional planar SRR structure is fabricated on a thin flexible film and is folded to raise its split region slightly up with respect to the plane of the SRR (Folded Split Ring Resonator-FSRR). The structure exhibits strong localization of electric field in the projected region of the sensor, by confining the evanescent waves in that region having dimension much smaller than the operating wavelength. The proposed sensor is placed between transmitting and receiving probes of a Vector Network Analyzer (VNA) to form the sensing probe. Two dielectric samples arranged at different distances of separation are scanned and the corresponding transmission characteristics S21 are drawn for analysing the image resolution. The resolution and sensitivity of the above proposed sensor is compared with conventional SRR and is found to be superior in performance. This novel FSRR provides a better resolution and thereby overcomes the diffraction limit in imaging up to λ/30, whereas for the conventional planar SRR it will be around λ /15. The design is simple, compact and inexpensive. The potential of proposed sensor can be extended to sub-wavelength imaging of dielectric materials, biological samples and can be used for non-destructive testing. 2019-10-29T00:00:00Z