Newsgroups: sci.physics.electromag From: jost@washpost.wdc.sri.com ("Randy J. Jost") Message-ID: Subject: FAQ pt 2/2 Reply-To: jost@washpost.wdc.sri.com Date: 26 Apr 1994 14:08:21 EST X-Received: by usenet.pa.dec.com; id AA12050; Tue, 26 Apr 94 11:33:23 -0700 X-Received: from sparkyfs.erg.sri.com by inet-gw-3.pa.dec.com (5.65/21Mar94) id AA02762; Tue, 26 Apr 94 11:23:06 -0700 X-Received: from washpost.wdc.sri.com by sparkyfs.erg.sri.com (5.65/2.7davy) id AA22606; Tue, 26 Apr 94 11:22:52 -0700 X-Received: From SRI_WDC_1/WORKQUEUE by washpost.wdc.sri.com via Charon 3.4 with IPX id 100.940426140838.1152; 26 Apr 94 14:22:17 -0500 X-To: sci.physics.electromag.usenet X-Priority: normal X-Mailer: Pegasus Mail/Mac v2.02 Lines: 513 Greetings to all! After much delay, here is the first offering of the FAQ for sci.physics.electromag. Please feel free to critique it, criticize, complain, suggest, add, subtract, praise, pan, whatever, just send us your input. Randy ************************* FAQ follows ********************************** sci.physics.electromag.FAQ part 2/2 Version: 0.1 Date: 26 April 1994 SCI.PHYSICS.ELECTROMAG Frequently Asked Questions Welcome to the sci.physics.electromag (SPE) Frequently Asked Question (FAQ) file. This is the initial version of the FAQ, hence it has some holes and areas where input is needed. Once this FAQ becomes stable, we will post it on a monthly basis. Until then, this list will be making more frequent appearances, as additional information is added. Because of limitations in certain mailers, and since this FAQ has already exceeded 32k, it has been split into multiple parts. That way, it should travel through all the Internet gateways, and be readable by almost any newsreader/email software without any trouble. If you have other topics that you think should receive FAQ status, want to submit a FAQ and answer, or have additional information on an existing FAQ, please contact either of the following individuals: Dr. Todd Hubing ( thubing@ee.umr.edu ) Dr. Randy J. Jost ( jost@washpost.wdc.sri.com ) We have intentionally left some topics unfinished, partly to get this out to the group, but also to encourage other people to contribute their ideas and thoughts. Please feel free to add more to this. It will only be as good as the input that goes into it. CONTRIBUTORS Several individuals submitted suggestions and contributions which went into the creation of this FAQ. Among these are: Raymond Anderson raymonda@uranium.ebay.sun.com Weston Beal weston.beal@sun.com Allen Davidson casr04@email.mot.com Jeff Haferman haferman@icaen.uiowa.edu Chuck Harrison 73770.1337@compuserve.com Todd Hubing thubing@ee.umr.edu Randy Jost jost@washpost.wdc.sri.com Gian Luigi Gragnani gragnani@dibe.unige.it Dave Michelson davem@ee.ubc.ca John Moulder jmoulder@post.its.mcw.edu Robert Perry perry@mimicad.colorado.edu Al Wong eunos@mercury.sfsu.edu --------------------------------------------------------------------------- CONTENTS Part 1/2 1. FAQ ADMINISTRATION 2. EM REFERENCES 3. EM THEORY ISSUES Part 2/2 4. COMPUTER MODELING 5. BIOLOGICAL EFFECTS 6. HISTORY OF ELECTROMAGNETICS --------------------------------------------------------------------------- COMPUTER MODELING [4.0] What commercial and/or non-commercial electromagnetic modeling codes are available? Non-commercial codes: Numerical Electromagnetics Code (NEC) - a moment method code that models wires and PEC surface patches using a surface integral technique. EFIE is employed for wire modeling and MFIE for surface patch modeling. NEC2 is available from ftp.netcom.com is the /pub/rander/NEC directory. Discrete-Dipole Approximation Code (DDA) - Written by Drain and Flatau, available by anonymous ftp at astro.princeton.edu in the directory /draine/scat/ddscat/ver4b/ddscat4b.tar.Z. Electromagnetic Surface Patch Code (ESPII) - a moment method code that models wires and PEC surface patches using a surface integral (EFIE) technique. Available from Dr. Edward H. Newman, ElectroScience Laboratory, Ohio State University, 1320 Kinnear Rd, columbus, OH 43212. Penn State FDTD code - a public domain FDTD code developed by R. Luebbers and K. Kunz that is described in their book "The Finite Difference Time Domain Method for Electromagnetics" CRC Press. Code is available from the emclab.ee.umr.edu ftp site in the directory /pub/aces/fdtd. ElectroMagnetic Analysis Program (EMAP2) - a 3D finite element modeling code available from the emclab.ee.umr.edu ftp site in the directory /pub/emap. Mie Scattering Code (MIEV) - a publically available code that computes many of the quantities involved in electromagnetic scattering from a homogeneous sphere. The code can be found at the following sites: climate.gsfc.nasa.gov in subdirectory /pub/wiscombe or at sunsite.unc.edu in /pub/academic/physics/Electro-mag/miev.tar Commercial codes: Maxwell 2D & 3D - Finite element modeling codes available from AnSoft Corporation 412-261-3200. MSC EMAS - 3D finite element modeling software from MacNeal-Schwendler Corporation (414) 357-8723. EESoft - Moment method software for analyzing microstrip & MIMIC circuit configurations. (818) 991-7530 HFSS - Moment method software for analyzing microstrip & MIMIC circuit configurations. Available from Hewlett Packard (415) 964-2456. [4.1] What is the "best" (numerical, analytical) method to compute EM interactions with objects? The answer to this question depends to a great extent on the particular problem that is to be analyzed. Analytical methods are very good at analyzing certain problems with a high degree of symmetry and they can provide a great deal of insight into the behavior of many configurations. However, an accurate evaluation of most realistic electromagnetic configurations requires a numerical approach. Numerical techniques based on the method of weighted residuals are called moment methods. EM modelers have come to use the term "moment method" synonymously with "surface integral technique" even though the method of weighted residuals can be applied to differential equations as well as integral equations. In general, moment method techniques do an excellent job of analyzing unbounded radiation problems and they excel at analyzing PEC (perfect electric conductor) configurations and homogeneous dielectrics. They are not well-suited to the analysis of complex inhomogeneous geometries. Finite element techniques require the entire volume of the configuration to be meshed as opposed to surface integral techniques, which only require the surfaces to be meshed. However each mesh element may have completely different material properties from those of neighboring elements. In general, finite element techniques excel at modeling complex inhomogeneous configurations. However, they do not model unbounded radiation problems as effectively as moment method techniques. Finite difference time domain (FDTD) techniques also require the entire volume to be meshed. Normally, this mesh must be uniform, so that the mesh density is determined by the smallest detail of the configuration. Unlike most finite element and moment method techniques, FDTD techniques work in the time domain. This makes them very well-suited to transient analysis problems. Like the finite element method, FDTD methods are very good at modeling complex inhomogeneous configurations. Also, many FDTD implementations do a better job of modeling unbounded problems than finite element modeling codes. As a result, FDTD techniques are often the method of choice for modeling unbounded complex inhomogeneous geometries. BIOLOGICAL EFFECTS [5.0] Is there any truth to the statements that low level electric and magnetic fields are harmful to humans? Most of the concern about power-frequency fields and human health stems from epidemiological studies of people living near powerlines or working in "electrical occupations". Some of these studies appear to show a relationship between exposure to power-frequency magnetic fields and the incidence of cancer and birth defects. Laboratory studies have shown little evidence of a link between power-frequency fields and either cancer or birth defects. [5.1] How do the biological effects of power-frequency electromagnetic [EM] sources differ from those of other EM sources? The interaction of biological material with an EM source depends on the frequency of the source. At the very high frequencies characteristic of UV light and X-rays, EM particles (photons) have sufficient energy to break (ionize) chemical bonds. The well-known hazards of X-rays are associated with this ionization. At lower frequencies, such as those characteristic of visible light, RF, and MW, the photons do not carry enough energy to break chemical bonds; this is the non-ionizing portion of the EM spectrum. Because EM sources at non-ionizing frequencies cannot break chemical bonds, there is no analogy between the biological effects of ionizing and nonionizing EM energy. Non-ionizing EM sources can still produce biological effects. The electrical fields associated with the power-frequency fields have very little ability to penetrate buildings or even skin. However, exposure of people to power-frequency magnetic fields results in the induction of electrical currents in the body. If these currents are sufficiently intense, they can cause heating, nerve excitation and other effects. At power frequencies, the body is poorly coupled to external fields, and the induced currents are usually too small to produce obvious effects. Shocks, and other obvious effects usually require that the body actually touch a conductive objects, allowing current to pass directly into the body. [5.2] What sort of power-frequency fields are common in residences and workplaces? In the US magnetic fields are commonly measured in Gauss (G). In most of the rest of the world, they are measured in Tesla (T), were 10,000 G equals 1 T (1 G = 100 microT). Electrical fields are measured in volts/meter (v/m). Within the right-of-way (ROW) of a high-voltage (115-765 kV) transmission line, fields can approach 100 mG (10 microT) and 10,000 v/m. At the edge of a high-voltage transmission ROW, the field will be 1-10 mG (0.1-1.0 microT) and 100-1,000 v/m. Ten meters from a 12 kV distribution line fields will be 2-10 mG (0.2-1.0 microT) and 2-20 v/m. Actual fields depend on voltage, design and current. Fields within residences vary from over 1000 mG (100 microT) and 200 v/m a few inches (cm) from certain appliances to less than 0.2 mG (0.02 microT) and 2 v/m in the center of some rooms. Appliance fields decrease very rapidly with distance. Occupational exposures in excess of 1000 mG (100 microT) and 5000 v/m. have been reported. In "electrical" occupations typical mean fields range from 5 to 40 mG (0.5 to 4 microT) and 100-2000 v/m. [5.3] What is known about the relationship between powerline corridors and cancer rates? Some studies have shown that children living near certain types of powerlines have higher rates of cancer, particularly leukemia and brain cancers, but other studies have shown no such relationship. The correlation between exposure and cancer incidence is not strong, and none of the studies have shown dose-response relationships. When power-frequency fields are actually measured, no relationship is found. With one exception, all studies of correlations between adult cancer and residence near powerlines have been negative. The excess cancer found in epidemiological studies is quantified as relative risk (RR) -- the risk of an "exposed" person getting cancer divided by the risk of an "unexposed" person getting cancer. RRs are generally given with 95% confidence intervals. An overview of the epidemiology requires that studies be combined using a technique known as "meta-analysis". Meta-analysis indicates the following RRs for residence near powerlines (with 95% CIs): childhood leukemia: 1.5 (0.8-3.0) childhood brain cancer: 1.9 (0.9-3.0) childhood lymphoma: 2.5 (0.3-40) all childhood cancer: 1.5 (0.9-2.5) adult leukemia: 1.1 (0.8-1.6) adult brain cancer: 0.7 (0.4-1.3) all adult cancer: 1.1 (0.9-1.3) [5.4] What is known about the relationship between "electrical occupations" and cancer rates? Several studies have shown that people who work in electrical occupations have higher cancer rates, particularly for leukemia and brain cancer. Most of these studies are based on job titles, not on measured exposures. None of these studies show a dose-response relationship between exposure and cancer incidence. Meta-analysis indicates the following RR for occupational exposure for power-frequency fields (with 95% CIs): leukemia: 1.20 (1.0-1.4) brain: 1.10 (0.9-1.3) lymphoma: 1.15 (0.9-1.8) all cancer: 1.00 (0.9-1.1) [5.5] What do laboratory studies tell us about power-frequency fields and cancer? Carcinogens, agents that cause cancer, are generally of two types: genotoxins and promoters. Genotoxic agents (often called initiators) directly damage the genetic material of cells. Genotoxins usually effect all types of cells, cause many different types of cancer, and do not have thresholds for their effect. A promoter is something that increases the cancer risk in animals already exposed to a genotoxin. Promoters usually effect only certain types of cells, cause only certain types of cancer, and have thresholds for their effect. Power-frequency fields show none of the classic signs of being genotoxins - they do not cause DNA damage or chromosome breaks, and they are not mutagenic. No studies have shown that animals exposed to power-frequency fields have increased cancer rates. It has been suggested that power-frequency EMFs could promote cancer, but all but one study of promotion have shown no such effect. There are substances (called mitogens) that cause non-growing normal cells to start growing, and some mitogens appear to be carcinogens. There are no studies that indicate that power-frequency fields are mitogens, and with one possible exception no effects on cell growth have been reported for fields below 2000 mG (200 microT). Suppression of the immune system in animals and humans is associated with increased rates of certain types of cancer (lymphomas, but not leukemia or brain cancer). Some studies have shown that power-frequency fields can affect cells of the immune system, but no studies have shown the type of immune suppression that is associated with increased cancer. It has also been speculated that power-frequency EM fields might suppress the production of the hormone melatonin, and that melatonin has "cancer-preventive" activity. Current laboratory studies do not provide much support for this idea. While the laboratory evidence does not suggest a link between power-frequency fields and cancer, numerous studies have reported that these fields do have "bioeffects", particularly at high field strength. Power-frequency fields intense enough to induce electrical currents in excess of those that occur naturally (above 5 G, 500 microT) have shown reproducible effects, including effects on humans. Below about 2 G (200 microT) there are few replicated reports of bioeffects. [5.6] How do scientists evaluate all the laboratory and epidemiological studies of power-frequency fields and cancer? There are certain widely accepted criteria, the "Hill criteria", that are weighed when assessing epidemiological and laboratory studies. Under these criteria one examines the strength and consistency of the association between exposure and risk, the evidence for a dose-response relationship, the laboratory evidence, and the biological plausibility. These criteria are viewed as a whole; no individual criterion is either necessary or sufficient for concluding that there is a causal relationship between an exposure and a disease. Overall, application of the Hill criteria shows that the current evidence for a connection between power-frequency fields and cancer is quite weak, because of the weakness and inconsistencies in the epidemiological studies, combined with the lack of a dose-response relationship in the human studies, and the negative laboratory studies. The current evidence for a connection between exposure to power-frequency other types of human health hazards (including birth defects) is even weaker. [5.7] Are there exposure guidelines for power-frequency fields? A number of governmental and professional organizations have developed exposure guidelines. These guidelines are based on keeping the body currents induced by power-frequency EM fields to a level below the naturally-occurring fields. The most generally relevant are: - National Radiation Protection Board (UK): 50/60 Hz electrical field: approx. 12,000 v/m and 1.5 mT (15 G) - American Conference of Governmental Industrial Hygienists: At 60 Hz: 1 mT (10 G); 0.1 mT (1 G) for pacemaker wearers - International Commission on Non-Ionizing Radiation Protection 24 hr general public: 0.1 mT (1 G) and 5,000 v/m Short-term general public: 1 mT (10 G) and 10,000 v/m Occupational continuous: 0.5 mT (5 G) and 10,000 v/m Occupational short-term: 5 mT (50 G) and 30,000 v/m [5.8] Where can I get more information about power-frequency fields and human health? This section for the FAQ sheet is drawn from a more extensive FAQ sheet called "FAQs on Power-Frequency Fields and Cancer". The latter FAQ sheet covers the following topics: - What is the difference between the EM energy associated with power lines and other forms of EM energy such as microwaves or x-rays? - What is difference between EM radiation and EM fields, and do power lines produce radiation? - How do EM sources produce biological effects, and why do different types of EM sources produce different biological effects?? - What sort of power-frequency fields are common in residences and workplaces, and can they be reduced? - What is known about the relationship between powerline corridors and cancer rates, and how close do you have to be to a powerline to be considered exposed? - What is known about the relationship between "electrical occupations" and cancer rates? - What do laboratory studies tell us about power-frequency fields and cancer? Are these fields genotoxic, do they enhance the effects of other genotoxic agents? How do studies on cell growth, immune function, and melatonin relate to the question of cancer risk? Do power-frequency fields show any effects at all in laboratory studies? - How do scientists evaluate all the laboratory and epidemiological studies of power-frequency magnetic fields and cancer? How strong and how consistent is the association between exposure and the risk of cancer, and is there a dose-response relationship? Is there laboratory evidence or a plausible biological mechanism for an association between exposure and the risk of cancer? - If exposure to power-frequency magnetic fields does not explain studies which show increased cancer incidence, what other factors could? Are there dose-assessment problems? Are there other cancer risk factors that could be causing a false association? Could the studies be biased by the methods used to select control groups or by publication bias? - What is the strongest evidence for and against a connection between power-frequency fields and cancer, and what studies are needed to resolve the cancer-EMF issue? - Is there any evidence that power-frequency fields could cause birth defects or any other human health problems - Are there exposure guidelines for power-frequency fields? - What effect do powerlines have on property values? - How are power-frequency magnetic fields measured? "FAQs on Power-Frequency Fields and Cancer" also contain an annotated bibliography covering: recent reviews of the biological and health effects of power-frequency fields, epidemiology of residential and occupational exposure to power-frequency fields, biophysics and dosimetry of power-frequency fields, laboratory studies of power-frequency fields that are directly or indirectly related to cancer or reproductive toxicity, regulations and standards for ionizing and non-ionizing electromagnetic sources. [5.9] Where can I get "FAQs on Power-Frequency Fields and Cancer"? The powerlines-cancer-FAQ sheet is posted monthly to: sci.med.physics, sci.answers and news.answers, and irregularly to sci.physics.electromag. The powerlines-cancer-FAQ is also available by anonymous FTP from: "rtfm.mit.edu", in directory: /pub/usenet-by-group/news.answers/powerlines-cancer-FAQ Files: part1, part2, part3, etc. . . . and by e-mail from: mailserver@rtfm.mit.edu -to get you the directory indicating the names and number of parts and when there were last updated, send the following message send /pub/usenet-by-group/news.answers/powerlines-cancer-FAQ -To get the current FAQ you would send the following message send /pub/usenet-by-group/news.answers/powerlines-cancer-FAQ/part1 . . . send /pub/usenet-by-group/news.answers/powerlines-cancer-FAQ/partn Maintainer of powerlines-cancer-FAQ John Moulder (jmoulder@its.mcw.edu) Voice: 414-266-4670 Radiation Biology Group FAX: 414-257-2466 Medical College of Wisconsin, Milwaukee HISTORY OF ELECTROMAGNETICS [6.0] The greatest contributor to the theory of electromagnetics was (Maxwell, Heaviside, Tesla, ....) because .... Undoubtably, one of the greatest contributors to the science of electromagnetics was James Clerk Maxwell (1831-1879). In his classic work, "Treatise on Electricity and Magnetism", (1873), he published the first unified theory of electricity and magnetism, postulated that light was electromagnetic in nature, that radiation should be possible at other wavelengths, and basically founded the science of electromagnetics. However, there were many other key players in the history of electromagnetics, both before and after Maxwell. It would be nice if other individuals would contribute 1-2 paragraph descriptions of some of these individuals. It would be especially interesting if some little known facts about these individuals could be included, making them that much more real. Ideally, individual who live in the countries where these people were from would contribute, giving all a perspective on who these giants were. Some individuals to start with would include: Name Dates ------ ------- William Gilbert 1540-1603 Benjamin Franklin 1706-1790 Charles A. De Coulomb 1736-1806 Alessandro Volta 1745-1827 Andre Ampere 1775-1836 Karl F. Gauss 1777-1855 Hans C. Oersted 1777-1851 Georg S. Ohm 1787-1854 Michael Faraday 1791-1867 Joseph Henry 1797-1878 James P. Joule 1818-1889 James C. Maxwell 1831-1879 Thomas A. Edison 1847-1931 Nikola Tesla 1856-1943 Heinrich Hertz 1857-1894 Guglielmo Marconi 1874-1937 Albert Einstein 1879-1955 It would also be nice to establish an electromagnetics "timeline" outlining when certain key events took place. Date Event ------ ------- 1873 Publication of Treatise on Electricity and Magnetism by James Clerk Maxwell, documenting the essential unity between electricity and magnetism. This is just a start on names, dates, and events. Are there any other students of the history of science out there? If so, this is a good place to provide some input. end of sci.physics.electromag.FAQ part 2/2 -------------------------------------------------------------------- Dr. Randy J. Jost Internet: jost@washpost.wdc.sri.com SRI International Phone: 703-247-8415 1611 N. Kent St. FAX: 703-247-8537 Arlington, VA 22209-2111 --------------------------------------------------------------------