A conducting domain surface boundary applied to hybrid FEM-FDTD Electromagnetic Models

A modified boundary surface between the two domains in the hybrid FEM-FDTD technique is presented. This permits a heterogeneous surface to be imposed, allowing selected parts to be represented as being conducting or non-conducting. This enables a reduced surface size to be used in cases where an antenna is above a conducting plane, as well as facilitating a range of other practical scenarios. Examples presented show stable results and good agreement with published data

A Hybrid Computational Electromagnetics Formulation for Simulation of Antennas Coupled to Lossy and Dielectric Volumes

A heterogeneous hybrid computational electromagnetics method is presented, which enables different parts of an antenna simulation problem to be treated by different methods, thus enabling the most appropriate method to be used for each part. The method uses a standard frequency-domain moment-method program and a finite-difference time-domain program to compute the fields in two regions. The two regions are interfaced by surfaces on which effective sources are defined by application of the Equivalence Principle. An extension to this permits conduction currents to cross the boundary between the different computational domains. Several validation cases are examined and the results compared with available data. The method is particularly suitable for simulation of the behavior of an antenna that is partially buried, or closely coupled with lossy dielectric volumes such as soil, building structures or the human body

Computation of specific absorption rate in the human body due to base-station antennas using a hybrid formulation

A procedure for computational dosimetry to verify safety standards compliance of mobile communications base stations is presented. Compared with the traditional power density method, a procedure based on more rigorous physics was devised, requiring computation or measurement of the specific absorption rate (SAR) within the biological tissue of a person at an arbitrary distance. This uses a hybrid methd of moments/finite difference time domain(MoM/FDTD) numerical method in order to determine the field or SAR distribution in complex penetrable media, without the computational penalties that would result from a wholly FDTD simulation. It is shown that the transmitted power allowed by the more precise SAR method is, in many cases, between two and five times greater than that allowed by standards implementing the power flux density method

Currents induced on wired I.T. networks by randomly distributed mobile phones – a computational study

The probability density and exceedance probability functions of the induced currents in a screened cable connecting two enclosures, resulting from the close presence of single and multiple mobile phones working at 900 MHz, are investigated. The analysis of the problem is undertaken using the Method of Moments, but due to weak coupling, the impedance matrix was modified to reduce the memory and time requirements for the problem, to enable it to be executed multiple times. The empirical probability distribution functions (PDFs) and exceedance probabilities for the induced currents are presented. The form of the PDFs is seen to be quite well approximated by a log-normal distribution for a single source and by a Weibull distribution for multiple sources

Computation of Electromagnetic Fields in Assemblages of Biological Cells Using a Modified Finite-Difference Time-Domain Scheme

When modeling objects that are small compared with the wavelength, e.g., biological cells at radio frequencies, the standard finite-difference time-domain (FDTD) method requires extremely small time-step sizes, which may lead to excessive computation times. The problem can be overcome by implementing a quasi-static approximate version of FDTD based on transferring the working frequency to a higher frequency and scaling back to the frequency of interest after the field has been computed. An approach to modeling and analysis of biological cells, incorporating a generic lumped-element membrane model, is presented here. Since the external medium of the biological cell is lossy material, a modified Berenger absorbing boundary condition is used to truncate the computation grid. Linear assemblages of cells are investigated and then Floquet periodic boundary conditions are imposed to imitate the effect of periodic replication of the assemblages. Thus, the analysis of a large structure of cells is made more computationally efficient than the modeling of the entire structure. The total fields of the simulated structures are shown to give reasonable and stable results at 900,1800, and 2450 MHz. This method will facilitate deeper investigation of the phenomena in the interaction between electromagnetic fields and biological systems

Efficient Global Optimisation of Microwave Antennas Based on a Parallel Surrogate Model-assisted Evolutionary Algorithm

Computational efficiency is a major challenge for evolutionary algorithm (EA)-based antenna optimisation methods due to the computationally expensive electromagnetic simulations. Surrogate model-assisted EAs considerably improve the optimisation efficiency, but most of them are sequential methods, which cannot benefit from parallel simulation of multiple candidate designs for further speed improvement. To address this problem, a new method, called parallel surrogate model-assisted hybrid differential evolution for antenna optimisation (PSADEA), is proposed. The performance of PSADEA is demonstrated by a dielectric resonator antenna, a Yagi-Uda antenna, and three mathematical benchmark problems. Experimental results show high operational performance in a few hours using a normal desktop 4-core workstation. Comparisons show that PSADEA possesses significant advantages in efficiency compared to a state-of-the-art surrogate model-assisted EA for antenna optimisation, the standard parallel differential evolution algorithm, and parallel particle swarm optimisation. In addition, PSADEA also shows stronger optimisation ability compared to the above reference methods for challenging design cases

High gain CPW‐fed UWB planar monopole antenna‐based compact uniplanar frequency selective surface for microwave imaging

YesIn this article, a novel uniplanar ultra‐wideband (UWB) stop frequency selective surface (FSS) was miniaturized to maximize the gain of a compact UWB monopole antenna for microwave imaging applications. The single‐plane FSS unit cell size was only 0.095λ × 0.095λ for a lower‐operating frequency had been introduced, which was miniaturized by combining a square‐loop with a cross‐dipole on FR4 substrate. The proposed hexagonal antenna was printed on FR4 substrate with coplanar waveguide feed, which was further backed at 21.6 mm by 3 × 3 FSS array. The unit cell was modeled with an equivalent circuit, while the measured characteristics of fabricated FSS array and the antenna prototypes were validated with the simulation outcomes. The FSS displayed transmission magnitude below −10 dB and linear reflection phase over the bandwidth of 2.6 to 11.1 GHz. The proposed antenna prototype achieved excellent gain improvement about 3.5 dBi, unidirectional radiation, and bandwidth of 3.8 to 10.6 GHz. Exceptional agreements were observed between the simulation and the measured outcomes. Hence, a new UWB baggage scanner system was developed to assess the short distance imaging of simulated small metallic objects in handbag model. The system based on the proposed antenna displayed a higher resolution image than the antenna without FSS

Analysis of Improved µ-Law Companding Technique for OFDM Systems

YesHigh Peak-to-Average-Power Ratio (PAPR) of transmitted signals is a common problem in broadband telecommunication systems using an orthogonal frequency division multiplexing (OFDM) modulation scheme, as it increases transmitter power consumption. In consumer applications where it impacts mobile terminal battery life and infrastructure running costs, this is a major factor in customer satisfaction. Companding techniques have been recently used to alleviate this high PAPR. In this paper, a companding scheme with an offset, amidst two nonlinear companding levels, is proposed to achieve better PAPR reduction while maintaining an acceptable bit error rate (BER) level, resulting in electronic products of higher power efficiency. Study cases have included the effect of companding on the OFDM signal with and without an offset. A novel closed-form approximation for the BER of the proposed companding scheme is also presented, and its accuracy is compared against simulation results. A method for choosing best companding parameters is presented based on contour plots. Practical emulation of a real time OFDM-based system has been implemented and evaluated using a Field Programmable Gate Array (FPGA)

Investigations of polarization purity and specific absorption rate for two dual-band antennas for satellite-mobile handsets

A study of the effects of human proximity on the polarization purity of two types of circularly-polarized handset antennas for personal satellite communications was investigated using the hybrid method of moments (MoM)/finite-difference time-domain technique. Associated with this, assessments of specific absorption rate in the head were made. The method gave stable results, in accordance with physical expectations; good agreement with the pureMethod of Moments was shown in simplified cases omitting the head. The quadrifilar spiral antenna (QSA) was shown to be a propitious design for personal satellite communications

A conducting domain surface boundary applied to hybrid FEM-FDTD Electromagnetic models

A modified boundary surface between the two domains in the hybrid FEM-FDTD technique is presented. This permits a heterogeneous surface to be imposed, allowing selected parts to be represented as being conducting or non-conducting. This enables a reduced surface size to be used in cases where an antenna is above a conducting plane, as well as facilitating a range of other practical scenarios. Examples presented show stable results and good agreement with published data