Slot antenna array synthesis using the infinitesimal dipole model technique: Theory and experiment

The present article proposes and validates a new general design methodology that can be used to automatically find proper positions and orientations of waveguide‐based radiating slots capable of realizing any given radiation beam profile. The new technique combines basic radiation theory and waveguide propagation theory in an analytical model that permits the prediction of the radiation characteristics of generic slots without the need to perform full‐wave numerical solution while completely avoiding using transmission‐line models or the slot impedance method. The analytical model is then used to implement a low‐cost objective function within a global optimization scheme and subsequently deployed to find optimum positions and orientations of clusters of radiating slots cut into the waveguide surface such that any desired beam pattern can be obtained, leading to very efficient and robust beamforming capability that can be applied to dynamic beamforming in real‐time scenarios like MIMO systems. The proposed design method is verified using both full‐wave numerical solution and experiment.     

Space‐time analysis of energy localization: A Poynting flow perspective with applications to pattern reconfigurable dipoles

In this paper, we explore the dynamics of electromagnetic energy, especially in the near‐field region of radiating antennas, from a fundamental perspective (ie, no limitations on antenna shape and nature of excitation signal) and identify some key future research directions. First, we provide a comprehensive critique of the frequency‐domain reactive energy and circuit‐theoretic Q‐factor based approach, which is predominantly adopted in literature. In this way, we emphasize on the importance of adopting a general time‐domain approach to characterize the near‐field electromagnetic energy of arbitrary antennas. Next, we revisit the inherent ambiguities associated with the Poynting power‐flux term in the context of electromagnetic energy, and point out the nonuniqueness of the reactive energy, conventionally obtained by subtracting the far‐field radiation density from the total electromagnetic energy density around antennas. Furthermore, we discuss the concept of Poynting localized energy and its potential integration with FDTD techniques, and investigate its space‐time behavior for a Yagi‐Uda principle based pattern reconfigurable dipole system.     

Thermoelectric behaviour of melt processed carbon nanotube/graphite/poly(lactic acid) conductive biopolymer nanocomposites (CPC)

The aim of the study was to examine the possible use of conductive polymer composites (CPC) as thermoelectrical material for energy harvesting from temperature gradient. Their ease of processing, low cost and environmental impact compared to typical thermoelectric semiconductor materials were found to be strong advantages for large scale production. Our results show that eGR-CNT hybrid fillers are the most effective to enhance the CPC electrical conductivity up to σ = 4123 S.m^− 1, but that eGR is more effective to improve both thermal conductivity (λ_c = 5.5 W.m^− 1.K^− 1) and seebeck coefficient (S = 17 μV.K^− 1), whereas finally CNT give the best compromise to reach the highest ZT = 7 × 10^− 5 at room temperature. This finding is attributed to the ability of CNT network to allow electron circulation by tunnelling, when junctions are separated by an insulating polymer film (even of some nm thick), whereas phonon scattering at nanointerfaces will prevent their effective transmission through the CPC. Although the intrinsic individual physical properties obtained (σ, λ_c, S) with the different kinds of carbon filler were good, it was not possible to completely uncouple them to maximise ZT. We believe that this value of ZT, too low for commercial application, can be enhanced by increasing the confinement of conducting fillers with exclusion volumes and by decreasing the thermal conductivity of the matrix with voids.     

Steady and transient numerical analysis of the performance of annular fins

This article presents a simple, straightforward and accurate numerical technique that can be used to predict the steady and transient temperature distributions in an annular fin with uniform cross‐section. Both convection and/or thermal radiation ambient conditions are considered in this study. The heat transfer rate and fin efficiency are also calculated. Results are compared with the exact solution for the steady case where excellent agreement was observed for an insulated tip fin and with approximate solutions for the transient case for a non‐insulated tip condition. Copyright © 2001 John Wiley & Sons, Ltd.     

A monolithic double-balanced direct conversion mixer with an integrated wideband passive balun

This paper presents the design and performance characteristics of a 20-40 GHz monolithic double-balanced direct conversion mixer implemented using InGaP/GaAs HBT process. The compact MMIC mixer makes use of a Gilbert-cell multiplier and utilizes a broadband monolithic passive balun that has been developed for MMIC applications. The new balun makes use of multidielectric layer structure to achieve a broadband performance in a simple coplanar configuration. A measured return loss better than 15 dB, with a maximum insertion loss of 4.5 dB including the 3-dB power splitting loss has been achieved over the band from 15 to 45 GHz. Operated as a downconverter mixer, the newly developed direct conversion mixer achieves a measured conversion gain of 16 dB given an RF signal at 30 GHz, LO drive of 5 dBm and a downconverted baseband signal at 10 MHz. The mixer IP3 occurs at an output power of 4 dBm while the IP2 occurs at an output power of 11 dBm.     

Ultra wideband monopole/dielectric resonator antenna

A hybrid antenna is presented, consisting of an annular dielectric resonator antenna combined with a quarter-wave monopole to simultaneously act as a radiator and a loading element, producing an ultra wideband response. A prototype antenna is designed and a 3:1 bandwidth is demonstrated.     

Evolution equations for nonlinear waves in a tapered elastic tube filled with a viscous fluid

In this work, employing the reductive perturbation method and treating the arteries as a tapered, thin walled, long and circularly conical prestressed elastic tube, the propagation of weakly nonlinear waves is investigated in such a fluid-filled elastic tube. By considering the blood as an incompressible viscous fluid, depending on the viscosity and perturbation parameters we obtained various evolution equations as the extended Korteweg-de Vries (KdV), extended KdV Burgers and extended perturbed KdV equations. Progressive wave solutions to these evolution equations are obtained and it is observed that the wave speeds increase with the distance for negative tapering while they decrease for positive tapering.     

New Half-Hemispherical Dielectric Resonator Antenna for Broadband Monopole-Type Radiation

A new half-hemispherical dielectric resonator antenna (h-HDRA) is proposed and a two-element h-HDRA configuration is employed to design a broadband monopole-type radiator. Two half sections of a hemispherical DRA are employed to enhance the impedance bandwidth by introducing an additional resonant mode. Since the new geometry of an h-HDRA is studied here for the first time, it is characterized using simulation and experimental studies. Two closely spaced resonant modes, which in a two-element h-HDRA generate monopole-type radiation are investigated. Results for both the single and two-element h-HDRAs are presented. As much as 35% impedance bandwidth (S₁₁<-10dB) with more than 5 dBi peak gain, 99.08% efficiency and monopole-type radiation pattern has been demonstrated using a prototype occupying a compact volume measuring 0.48lambda₀ by 0.2lambda₀ approximately, lambda₀ being the wave length corresponding to the center of the impedance bandwidth     

Compact dielectric loaded circularly polarised microstrip antenna

An investigation into the novel dielectric loading technique for reducing the size of low profile microstrip antennas is presented. Inserting or loading discrete dielectrics into the air substrate of a microstrip patch antenna can considerably reduce the antenna size while at the same time achieve good bandwidth and excellent axial ratio performance. Experimental and simulated results at L-band frequencies demonstrate the effectiveness of this approach