Testing ourselves

TetngO rsle

Lovent Sevgi Do~uq University

Electronics and Communication Eng. Dept. Zeamet Sokak, No 21, Acibadem - Kadikoy Istanbul, Turkey Email: lsevgi~dogus.edu.tr, Ievent.sevgi~ieee.org http:/Awww3.dogus.edu.trllsevgi

I

_{elective undergraduate course in various universities in Istanbul}have given "Science, Technology, and Society" as a university for sometime. It sounds strange and quite uncorrelated because of my electromagnetic background, doesn't it? It sounds so to me, because I would never have imagined myself teaching a lecture like that. It all started back in 1998-99, when we began to receive calls from consumers, newspapers, radio and TV, industry, municipali-ties, even from ministries such as health, environmental, interior, etc. The sharp increase in the number of cell-phone users started in those years. People therefore began to worry about possible adverse health effects of base stations and cell phones. In order to reply to the requests, we started to gather information from various sites, such as the World Health Organization (WTHO, http://www.who.int), the International Non-Ionizing Radiation Protection Committee (ICNIRP, http://www.icnirp.de), Interna-tional Agency for Research on Cancer (IARC, http://www.iarc.fr), etc. Dr. James bin's "Telecommunications, Health and Safety" column in the Magazine has helped us a lot, since he has been periodically summarizing the current status based on prestigious research results.

I wrote many articles in daily newspapers and weekly maga-zines, gave several features, attended a few radio and TV pro-grams, and was invited to many regional meetings, etc. Our pri-mary aim was to give true information and to enlighten people. After a speech of an hour or so in a regional meeting, we saw that some thanked us for enlightening them and for being independent

and sensitive to this problem; a few others blamed us for defending

the interest of wireless and GSM companies. This astonished us a lot. We realized that whatever you say, everybody gets what he/she filters out from his/her perception window. Parallel to all those studies, we changed our track to scientific literacy and public understanding of science and technology studies and discussions, and ended up with this "Science, Technology and Society" course. We discuss many aspects. One of them is, of course, mobile phones, base stations, and public concern. I plan to go back to the scientific literacy topic in the future again, but I would like to see at least one tutorial in one of the Magazine issues in 2008.

I'm sure you all are aware of headlines like "A New 1 0-Year Statistical Study Indicates Positive/Negative Correlation Between Cell Phone Usage and Brain-Tumor Formation, ". .The Double-Blind Swedish Study Has Shown No Adverse Effects with a 5%

IEEE Antennas and Propagation Magazine, Vol. 50, No. 1, February 2008

Statistical Confidence Level," or "Recent Epidemniologic Study in Japan Has Pointed Out That There Might Be a Correlation," etc. What do these types of statements mean? As discusscd in the April 2007 tutorial [ 1], giving a number necessitates either a calculation or a measurement. From how and where do you think these state-ments are derived? What kind of a model is used? To what does a single-blind or double-blind study refer? What is epidemiology? How do you think epidemiologists report potential biological haz-ards of cell phones?

I'm looking for a quiz and a tutorial showing how statistics apply to electromagnetics for the assessment of relative risks in bioelectromagnietics. Rajeev (Dr. Bansal), Associate Editor of the Turnstile column, wrote me that he also would be happy to see such a tutorial. This is an open call for experts on this subject. Please keep it as simple as possible, so that I can understand: if I can, so can everybody!

The Quiz for this Issue

Based on the classical paper by Felsen and Kamel [2], we developed a MATLAB-based package for the ray-mode representa-tions and their interchange [3]. That paper is an excellent source for visualizing ray and mode contributions, which are local and global wave objects, respectively, and of a description of the pack-age does that. Because of their interchange, one can say that local (global) characteristics can be derived from global (local) behav-iors.

Ray-mode interchange is possible for wave-guiding struc-tures. Electromagnetic problems through waveguides can be divided into two types: The eigenvalue problem (i.e., the effects of the structure on to the propagating waves), and the Green's fuanc-tion problem (the effects of the excitafuanc-tion).

Here are the questions: Can you predict the eigenvalues of a wave-guiding structure by observing the waves propagating through it? Alternatively, can you predict the field from the eigen-values of the structure? How about preparing a short MATLAB package for this purpose? Don't you think it would be interesting to answer this question via a simple simulation package?

References

1. L. Sevgi, "Innumreracy: The Meaning of the Numbers We Use,"

IEEE Antennas and Propagation Magazine, 49, 2, April 2007, pp.

195-190.

2. L. B. Felsen and A. H. Kamel, "Hybrid Ray-Mode Formulation of Parallel Plate Waveguide Green's Functions," IEEE

Transac-tions on Antennas and Propagation, AP-29, 4, July 1981, pp.

637-649.

3. L. B. Felsen, F. Akieman, L. Sevgi, "Wave Propagation Inside a

Two-dimensional Perfectly Conducting Parallel Plate Waveguide: Hybrid Ray-Mode Techniques and Their Visualizations," IEEE

Antennas and Propagation Magazine, 46, 6, December 2004, pp.

69-89.

A Review of Discrete Solutions of Poisson,

Laplace, and Wave Equations

Levent Sevgi

Doou§ University, Electronics and Communication Engineering Department Zeamet Sokak, No 21, Acibadem - Kadik6y, Istanbul, Turkey

E-mail: lsevgi~dogus.edu.tr, levent~sevgi@ieee.org

Abstract

One- and two-dimensional discrete solutions of Poisson, Laplace, and wave equations are given in this tutorial. The terms wave propagation and numerical propagation are discussed. Simple MA TLA B scripts are also supplied.

Keywords: Poisson equations; Laplace equations; propagation; discretization; numerical analysis; FDTD methods; iterative methods; Taylor expansion; difference equations

1. Introduction

T

he wave equation is a second-order linear partial differential equation that describes the propagation of a variety of elec-tromagnetic, acoustic, and fluid waves. The Poisson/Laplace

equation, on the other hand, is a partial differential equation that

describes the behavior of electric, gravitational, and fluid

poten-tials. They describe some phenomena in electrodynamics and

elec-trostatics, respectively. What are the fundamental differences between wave and Poisson/Laplace equations? What do they repre-sent physically or numerically? What type of boundary conditions do they require? Both of them can be put into discrete and iterative forms, and can be solved numerically. People who simulate both the wave equation and Laplace equations use the term numerical propagation. To what does the termn numerical propagation refer

246

when waves or potentials are of interest? What do we mean when we say "wave propagation," "numerical wave propagation," or "numerical propagation?" This tutorial simply covers the answers to these questions, together with a few interesting MA TLAB scripts and examples.

2. Taylor's Expansion and

Finite

Difference Discretization

of the Differential Operator

Any continuous, infinitely differentiable function f (x) can

be represented as an infinite sum of terms, calculated from its derivatives at a single point, x0, as [1]