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Dariush Mirshekar-Syahkal

Bio: Dariush Mirshekar-Syahkal is an academic researcher from University of Essex. The author has contributed to research in topics: Microstrip & Antenna (radio). The author has an hindex of 27, co-authored 191 publications receiving 2362 citations. Previous affiliations of Dariush Mirshekar-Syahkal include University of Tehran & University College London.


Papers
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Journal ArticleDOI
TL;DR: Short-term exposure to a typical GSM base station-like signal did not affect well-being or physiological functions in sensitive or control individuals, and this difference was likely to be due to the effect of order of exposure rather than the exposure itself.
Abstract: Radio frequency electromagnetic fields (rf-emf) do not fall within the ionizing spectrum. Nevertheless, high-intensity rf-emf can cause thermal effects with serious implications for human health (Conway 2001). In everyday life, however, most humans are not exposed to such high intensity rf-emf and do not possess sensory organs that can detect electric or magnetic fields. The question remains as to whether exposure to low-intensity rf-emf, even if undetected, can negatively affect human health. A subgroup of the population has claimed that they are sensitive to rf-emf and this condition, formerly known as electromagnetic hypersensitivity, has recently been relabeled in a World Health Organization workshop (Hansson Mild et al. 2006) as idiopathic environmental intolerance with attribution to electromagnetic fields (IEI-EMF). In a recent U.K. survey, it was reported that around 4% of people claim that they are sensitive to rf-emf to some degree (Eltiti et al. 2007). A variety of negative health effects (e.g., cold and flu-like symptoms) are attributed to exposure to rf-emf from objects such as computers and mobile phones. Previous research has indicated that IEI-EMF individuals report lower levels of well-being compared with healthy individuals (e.g., Eltiti et al. 2007; Regel et al. 2006; Rubin et al. 2005; Zwamborn et al. 2003) and that the symptoms they experience may greatly affect their quality of life (e.g., Bergqvist and Vogel 1997; Irvine 2005). However, evidence that IEI-EMF symptoms are indeed caused by rf-emf exposure is yet to be established. A systematic review of 31 blind and double-blind provocation studies yielded no evidence that IEI-EMF individuals could detect the presence of rf-emf, and only seven studies indicated that exposure to rf-emf did affect health indices (Rubin et al. 2005). In two of these studies, however, the authors failed to replicate their own findings. Another four studies involved inappropriate use of statistics, while one reported improved mood in the active exposure condition. One unpublished double-blind study that specifically examined base station signals did find that exposure to a universal mobile telecommunications system (UMTS) signal resulted in reduced subjective well-being for both sensitive and nonsensitive individuals, whereas a global system for mobile communication (GSM) base station signal had no effect (Zwamborn et al. 2003). However, a recent study conducted in Switzerland was unable to replicate this effect (Regel et al. 2006). Another double-blind study recently reported no negative health effects from exposure to a standard 900 MHz GSM handset signal for either sensitive or control participants (Rubin et al. 2006). The existing evidence therefore indicates that exposure to rf-emf signals from mobile phone base stations and handsets has little effect on health, even in those individuals with a perceived sensitivity to rf-emf. Nevertheless, only two double-blind studies have been conducted with base station signals, with contrary results. Given the increase in mobile phone base stations around the world and the level of public concern regarding possible negative health implications, further research is necessary to investigate the short-and long-term impact of exposure to rf-emf in both healthy and IEI-EMF groups. The current study tested whether short-term exposure to typical GSM and UMTS base station signals affected a variety of measures of well-being in sensitive and control individuals, using both open provocation and double-blind tests. It was hypothesized that sensitive participants would report more symptoms and lower levels of well-being during GSM and UMTS exposures compared with sham. In addition, sensitive participants should be able to identify above chance level whether the base station was turned “on” or “off.” For control participants no difference was expected in the number or severity of symptoms reported during exposures. Previous research has reported higher levels of heart rate, heart rate spectrum ratio, and electrodermal activity in sensitive compared with control individuals (e.g., Lyskov et al. 2001a, 2001b). Thus, physiological measurements were also conducted to determine whether exposure to GSM and UMTS base station signals affected objective measures of well-being in both sensitive and control individuals.

130 citations

Journal ArticleDOI
TL;DR: In this article, a hybrid mode analysis for a multilayer dielectric within a rectangular conducting box is presented, where a set of conductors may be distributed along the lower surface of the top layer, so that single or coupled forms may be analyzed of slot line, microstrip or coplanar waveguide.
Abstract: A hybrid mode analysis is presented for a multilayer dielectric within a rectangular conducting box. An arbitrary set of conductors may be distributed along the lower surface of the top layer, so that single or coupled forms may be analyzed of slot line, microstrip, or coplanar waveguide. The analysis combines a transfer-matrix approach with the spectral domain method to give a versatile and efficient solution. CPU time on an IBM 360/65 is about 1 s per layer of substrate, for a single slot or strip, at one frequency.

91 citations

Journal ArticleDOI
TL;DR: In this paper, a spectral-domain approach is used for the analysis of coplanar and microstrip-type structures, where Legendre polynomials are used as the basis functions for fields having singularities near the edges, leading to fast convergence to the exact solution.
Abstract: For the analysis of coplanar- and microstrip-type structures, a higher order solution of the spectral-domain approach is introduced. Legendre polynomials are used as the basis functions for fields having singularities near the edges, leading to fast convergence to the exact solution. A perturbation technique is combined with the spectral-domain method to evaluate conductor and dielectric losses in microstrip, inverted microstrip, and coupled microstrip in the metallic enclosure. Computations of characteristic impedance and losses incurred in several structures are also presented. Central processing unit (CPU) time on an IBM 360/65 for the zeroth-order approximation ranges from 1 to about 5 s for the whole computation, and increases if higher order of solution is requested for better accuracy. The calculation of attenuation due to conductor losses is found to be particularly sensitive to order of approximation, so that the generally used "zeroth-order" solution is inadequate. A user-oriented program package has been written, including options on order of mode, order of solution (i.e., of approximation), impedance, attenuation, and number of substrates. Although written for single or coupled microstrip, the program can be adapted for arbitrary arrangements of thin coplanar conductors. The program is described separately.

90 citations

Journal ArticleDOI
TL;DR: In this article, a unique liquid crystal (LC) cell is proposed and using this, five different nematic LCs, including E7, K15, E44, E63, and MDA-00-3506, are measured and the values of their electrical and mechanical parameters are extracted.
Abstract: Due to their large birefringence and moderately low loss, liquid crystals (LCs) are a promising dielectric media for development of a variety of reconfigurable millimeter-wave devices. In order to optimize the design of tunable millimeter-wave devices, accurate values of the dielectric and elastic constants, as well as the loss tangents of LCs, are needed. However, characterization of LCs at millimeter-wave frequencies is a very challenging and demanding task. In this work, a transmission line method is used for the broadband characterization of nematic LCs in the frequency range of 30-60 GHz. For this purpose, a unique LC cell is proposed and using this, five different nematic LCs, including E7, K15, E44, E63, and MDA-00-3506, are measured and the values of their electrical and mechanical parameters are extracted. The extraction of these parameters from the measurements involves an optimization using two finite-element computer programs recently developed by the authors for the prediction of the local alignments of LC molecules and the wave propagation within the test cell. The highest values of the dielectric birefringence and the highest values of the loss tangents are recorded for E44 and MDA-00-3506. The loss tangent for all the LCs shows a general downward trend as the frequency increases, which is a useful characteristic in the development of reconfigurable millimeter-wave devices.

89 citations

Journal ArticleDOI
TL;DR: A low-profile twelve-beam printed patch antenna is presented for pattern reconfigurable applications and can steer its tilted beam in four different space quadrants in front of the antenna by exciting one feed at a time.
Abstract: A low-profile twelve-beam printed patch antenna is presented for pattern reconfigurable applications. The patch is fed at the four sides using coaxial feeds. Diagonal lines of vias are inserted on the patch surface to restrict currents to the edges. While majority of patch antennas have only axial beam pattern, the proposed antenna produces twelve different beams. When one of its four feeds on the sides is excited and the remaining feeds are open circuited, the antenna generates a linearly polarized tilted beam (6.1 dBi, $\theta _{\mathrm {max}}= 30^{\circ }$ ). This beam is directed away from feeding patch corner. Therefore, the antenna can steer its tilted beam in four different space quadrants in front of the antenna by exciting one feed at a time. The antenna is also capable of generating eight other beams using multiple feed excitations. They are four additional titled beams (6.1 dBi, $\theta _{\mathrm {{max}}}= 30^{\circ }$ ), two tilted-twin beam (5.8 dBi, $\theta _{\mathrm {{max}}}= \pm 36^{\circ }$ ), one semi-doughnut beam (5.8 dBi), and one axial beam (8.2 dBi). The antenna is designed to operate at the test frequency of 2.4 GHz and has a height = 1.5 mm ( $\lambda _{\mathrm {{0}}}$ /83). The impedance matching to $50~\Omega $ is achieved using right-angle slots etched on the patch antenna.

84 citations


Cited by
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Book
01 Jan 2001
TL;DR: In this paper, the authors describe the characteristics of conventional, Micromachined, and Superconducting Coplanar Waveguides, as well as their transitions in directional couplers, hybrid, and magic-Ts.
Abstract: Preface Introduction Conventional Coplanar Waveguide Conductor-Backed Coplanar Waveguide Coplanar Waveguide with Finite-Width Ground Planes Coplanar Waveguide Suspended Inside A Conducting Enclosure Coplanar Striplines Microshield Lines and Coupled Coplanar Waveguide Attenuation Characteristics of Conventional, Micromachined, and Superconducting Coplanar Waveguides Coplanar Waveguide Discontinuities and Circuit Elements Coplanar Waveguide Transitions Directional Couplers, Hybrids, and Magic-Ts Coplanar Waveguide Applications References Index

1,225 citations

Journal ArticleDOI
01 May 2001
TL;DR: In this review paper various high-speed interconnect effects are briefly discussed, recent advances in transmission line macromodeling techniques are presented, and simulation of high- speed interconnects using model-reduction-based algorithms is discussed in detail.
Abstract: With the rapid developments in very large-scale integration (VLSI) technology, design and computer-aided design (CAD) techniques, at both the chip and package level, the operating frequencies are fast reaching the vicinity of gigahertz and switching times are getting to the subnanosecond levels. The ever increasing quest for high-speed applications is placing higher demands on interconnect performance and highlighted the previously negligible effects of interconnects such as ringing, signal delay, distortion, reflections, and crosstalk. In this review paper various high-speed interconnect effects are briefly discussed. In addition, recent advances in transmission line macromodeling techniques are presented. Also, simulation of high-speed interconnects using model-reduction-based algorithms is discussed in detail.

645 citations

Journal ArticleDOI
TL;DR: In this paper, a simple method for formulating the dyadic Green's functions in the spectral domain is presented for generalized printed transmission Iines which contain several dielectric layers and conductors appearing at several Dielectric interfaces.
Abstract: A simple method for formulating the dyadic Green's functions in the spectral domain is presented for generalized printed transmission Iines which contain several dielectric layers and conductors appearing at several dielectric interfaces. The method is based on the transverse equivalent transmission line for a spectral wave and on a simple coordinate transformation. This formulation process is so simple that often it is accomplished almost by inspection of the physical cross-sectional structure of the transmission line. The method is applied to a new versatile transmission line, a microstrip-slot Iine, and some numerical results are presented.

567 citations

Journal ArticleDOI
TL;DR: In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined, in particular geometric and spectral properties of patch antennas are discussed.
Abstract: Dual-frequency patch antennas may provide an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is really needed for operating at two separate transmit-receive bands. When the two operating frequencies are far apart, a dual-frequency patch structure can be conceived to avoid the use of separate antennas. In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined. Geometries are discussed in particular.

467 citations