Articles written in Pramana – Journal of Physics

    • Metamagnetism in Ce(Ga,Al)2

      K G Suresh S Radha A K Nigam

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      Effect of Al substitution on the magnetic properties of Ce(Ga1−xAlx)2 (x=0, 0.1 and 0.5) system has been studied. The magnetic state of CeGa2 is found to be FM with a TC of 8 K, whereas the compounds with x=0.1 and 0.5 are AFM and possess TN of about 9 K. These two compounds undergo metamagnetic transition and the critical fields are about 1.2 T and 0.5 T. respectively at 2 K. These variations are explained on the basis of helical spin structure in these compounds.

    • Dynamic frequency analysis of stress–strain-dependent reversibly deformable broadband RF antenna over unevenly made elastomeric substrate


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      This paper presents the design and development of stretchable and deformable broadband antenna using low-cost silicone rubber-based dielectric substrate. A slot is introduced in the substrate to improve the stretchable behaviour. The dielectric properties of the substrate are measured using suspended ring resonator method. The proposed antenna uses silver elastomeric Lycra fabric as the conductive medium. The resistivity of the conducting Ag fabric is 1 $\Omega$ per sq. mm. The conducting patch and ground plane are attached with the substrate using silicone-based adhesive. The fabricated antenna is tested for its resonant characteristics using the vector network analyser.

    • Terahertz broadband metamaterial absorber enabled by SiO$_{2}$, polyimide and PET dielectric substrates


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      A broadband polarisation-insensitive terahertz (THz) metamaterial absorber (MMA) is presented in this paper. The MMA consists of a simple planar structure as a unit cell and an optically transparent indium tin oxide (ITO) ground plane, both are separated by a 50 $\mu$m dielectric substrate. We designed three combinations of MMA here, which are ITO–polyimide–ITO, ITO–polyethylene terephthalate (PET)–ITO and ITO–silicon dioxide (SiO$_{2}$)–ITO for the same planar structure. By changing the substrate of the structure, the resonant frequency and bandwidth of the absorber structure can be varied. The numerical simulation of the absorber shows that the absorptivity is $>$ 96% for all three substrates. Polyimide, PET and SiO$_{2}$ based absorbers demonstrated the bandwidth of 0.558 THz,0.603 THz and 0.658 THz with covered broadband frequency range of 0.4254–0.9829 THz, 0.457–1.16 THz and 0.511–1.169 THz respectively. ITO–PET–ITO absorber structure produced optical transparency. These bandwidths are compatible and convenient for electronic sources in the terahertz region. This study also provides applications in THz sensing and imaging, communication and detection systems.

    • Terahertz single dual multi-band metamaterial absorber


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      In this study, a new multifunctional terahertz (THz) metamaterial absorber (MMA) has been presented which is controlled by the thickness of the substrate used. The proposed structure consists of copper as the ground plane and polyimide dielectric layer is placed in between the ground panel and the top radiating patch. The resonant frequency and number of resonating modes of the proposed absorber can be changed by varying the thickness of thesubstrate from 10 to 100 μm for the same planar structure. Depending on the thickness of the substrate, this MMA gives a narrow (10 μm), double (20 μm), triple (30 μm), quad (50 μm) and hexa (100 μm) number of resonating modes. In order to analyse the physical mechanism of the proposed absorber, we took 10, 20 and 30 μm-based MMA and their electric and magnetic fielddistributions are demonstrated. We compared the resonant frequency ranges and the number of bands with the previously reported papers. The polarisation and angle insensitivity of the design have been validated by numerical simulation up to 90$^◦$ of oblique incidence. The effects of variationin geometrical parameters and sensing habits have been studied in the narrow band (10 μm) MMA structure. The designed multifunctional absorber has the advantage of using the same MMA to produce multiple (narrow, double,triple, quad and hexa) band absorbers.

    • A miniaturised FSS with band-stop response for shielding application in X-band frequency


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      A novel miniaturised single-layer square loop frequency-selective surface (FSS) designed and optimised for effective shielding in X-band is presented. The proposed FSS structure provides a wider bandwidth response of 4.0 GHz and it covers the X-band frequency (8–12 GHz) with a centre frequency of 10 GHz and attenuation of 39 dB. The proposed design compared the simulation results with equivalent circuit method results. Both achieved the same frequency response and bandwidth but the attenuation level is varied. Due to the symmetric structure,the proposed design achieves polarisation-independent characteristics and provides stable response at normal and oblique incidences for both TE and TM modes up to 60º. Both the measured and simulated results are in good agreement.

    • Polarisation-insensitive and broadband band-stop metamaterial filter for THz waves


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      This paper describes the design and analysis of the tri-band metamaterial band-stop filter for terahertz applications. The design consists of a structured gold metallic patch over a flexible polyimide substrate. The thicknesses of the substrate and the metallic patch are 125 and 1 μm, respectively. The simulation results reveal that the designed structure resonates at three frequencies: f$_1$ = 0.6 THz, f$_2$ = 1.4 THz and f$_3$ = 2.4 THz. The proposed structure has polarisation-insensitive and angle-resolved transmission characteristics. The structure has 200 GHz and 800 GHz bandwidths at f$_1$ and f$_2$. This proves that the proposed design will be useful for broadband terahertz applications. The multiband resonances have been confirmed and analysed using the field and surfacecurrent distributions.These multiband resonances were due to the combination of electric dipolar, quad polar and magnetic dipolar resonance behaviour of the patterned metallic structure.

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