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The penetration of microwave power inside a human head model is improved by employing a dielectric loaded rectangular waveguide as the transmission source. A multi-layer reflection model is investigated to evaluate the combined material characteristics of different lossy human head tissues at 2.45 GHz. A waveguide loaded with a calculated permittivity of 3.62 is shown to maximise the microwave power penetration at the desired frequency. A Quartz (SiO2) loaded rectangular waveguide fed by a microstrip antenna is designed to validate the power penetration improvement inside an inhomogeneous human head phantom. A measured 1.33 dB power penetration increment is observed for the dielectric loaded waveguide over a standard rectangular waveguide at 50 mm inside the head, with an 81.9% reduction in the size of the transmission source.

Orbital Angular Momentum (OAM), as a property of Electromagnetic (EM) fields has recently been proposed for Radio and Microwave communications. This paper investigates a new class of OAM radiation patterns for Radio and Microwave applications, namely, Quasi-OAM radiation patterns, induced by a proposed Quasi-Circular Array Antenna (QCA). Simulations and Experiments show that Quasi-OAM waves can be induced and preserved in the far-field using the proposed QCA apertures and configurations, demonstrating non-integer dominant OAM modes corresponding to l = +1 and l = −1 with a directional quasi intensity and rotational 2π phase profiles. The proposed method in this work significantly reduces aperture size and cost by using Quasi-Circular Arrays of N Q = 5 and N Q = 6 elements in lieu of conventional OAM circular aperture arrays with N = 8 elements.

Elastomeric, conductive composite yarns have recently received attention around the opportunity for them to offer special protective fields. A straightforward approach for fabricating tri-component elastic-conductive composite yarns (t-ECCYs) containing stainless steel wire (SSW) was proposed previously. This work mainly focuses on the electromagnetic shielding effectiveness (EMSE) of weft-stretchable woven fabric containing t-ECCY over the X-band under different testing conditions, e.g., single step-by-step elongation, cyclic stretch and lamination events. Results showed that a woven cotton fabric with weft yarn of t-ECCY not only exhibited superior weft stretch-ability to a higher elongation (&gt, 40%) compared with a pure cotton control but also had an acceptable 15-cyclic stability with 80% shape recovery retention. The t-ECCY weft fabric was effective in shielding electromagnetic radiation, and its EMSE was also enhanced at elevated elongations during stretch at parallel polarization of EM waves. There was also no decay in EMSE before and after the t-ECCY fabric was subject to 15 stretch cycles at extension of 20%. In addition, a 90&deg, by 90&deg, cross lamination of t-ECCY fabric remarkably improved the EMSE compared to a 0&deg, /90&deg, one. The scalable fabrication strategy and excellent EMSE seen in t-ECCY-incorporated fabrics represent a significant step forward in protective fields.

Graphene nanoplatelets (GNPs) were dispersed in poly lactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) via melt-mixing. Effect of GNP incorporation on electromagnetic properties and electromagnetic interference shielding effectiveness (SE) of PLA and PBAT was investigated and the two systems were systematically compared. Furthermore, applicability of Sihvola's mixing rule of complex electrical permittivity to these nanocomposites was studied. GNP addition significantly enhanced permittivity of both polymers. Dielectric constants of PLA and PBAT nanocomposites had comparable values. However, above 6 wt% GNPs, PLA nanocomposites showed significantly higher dielectric loss than PBAT nanocomposites, even though pure PLA had lower dielectric loss than pure PBAT. This was attributed to the dispersion state of GNPs in the two matrices, detected in morphological studies. SE of both polymers increased with GNP addition due to enhancement of their dielectric properties. The difference in dielectric loss of the two systems was revealed in their ability to attenuate the radiation by absorption. At 15 wt% GNPs, 1 mm-thick PLA/GNP nanocomposite had an effective absorbance of 70%. This value was only 43% for PBAT/GNP nanocomposite. Variations of polymers' permittivities with GNPs were successfully modelled by Sihvola's rule. While both systems returned close values for model's fitting parameters, it better fitted PBAT/GNP nanocomposites. Keywords: Electromagnetic interference shielding, Dielectric properties, Poly lactide, Poly (butylene adipate-co-terephthalate), Graphene nanoplatelet, Nanocomposite

A varactor-based tunable bandstop filter has been proposed in this article. The proposed filter is based on a dualmode circuit developed by introducing inductive and capacitive couplings into a notch filter. The frequency tunability is achieved by using varactor diodes instead of the lumped capacitors in the circuit. Next, the equivalent circuit model has been implemented in planar microstrip technology using thin inductive traces and varactor diodes. The fabricated filter prototype shows a continuous center frequency tuning range of 0.66 - 0.99 GHz with a compact size of 0.12lg*0:16lg, where lg is the guided wavelength at the middle frequency of the tuning range., 3 pages