Newsgroups: sci.physics.electromag From: jost@washpost.wdc.sri.com ("Randy J. Jost") Message-ID: Subject: FAQ pt 1/2 Reply-To: jost@washpost.wdc.sri.com Date: 26 Apr 1994 14:07:03 EST X-Received: by usenet.pa.dec.com; id AA12032; Tue, 26 Apr 94 11:32:06 -0700 X-Received: from sparkyfs.erg.sri.com by inet-gw-3.pa.dec.com (5.65/21Mar94) id AA02756; Tue, 26 Apr 94 11:22:56 -0700 X-Received: from washpost.wdc.sri.com by sparkyfs.erg.sri.com (5.65/2.7davy) id AA22594; Tue, 26 Apr 94 11:22:39 -0700 X-Received: From SRI_WDC_1/WORKQUEUE by washpost.wdc.sri.com via Charon 3.4 with IPX id 100.940426140717.544; 26 Apr 94 14:22:02 -0500 X-To: sci.physics.electromag.usenet X-Priority: normal X-Mailer: Pegasus Mail/Mac v2.02 Lines: 367 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 1/2 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 reached approximately 40k, 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 FAQ ADMINISTRATION [1.0] What is sci.physics.electromag all about? The sci.physics.electromag charter is given as: Sci.physics.electromag will be dedicated to the discussion of topics pertaining to electromagnetics. These include, but are not limited to: electromagnetic wave theory computational EM modeling microwave devices and circuits antenna design electromagnetic interference biological effects ELF and VLF fields EM measurements wave propagation shielding electrostatic discharge new RF devices and technology [1.1] How do I post and/or receive to sci.physics.electromag? There are two ways to post to sci.physics.electromag. One way is to use a newsreader program. The other way is to post e-mail to the group by sending articles to: sci.physics.electromag.usenet@decwrl.dec.com Everything else, such as title, and message text should be done as per a normal email message. To receive the posts from sci.physics.electromag, presently you must use some type of newsreader software that will allow you to subscribe to the newsgroup. We are currently investigating other ways to get the contents of sci.physics.electromag to those who do not have access to the USENET newsgroups. It is possible to read newsgroup articles by gopher server. This can be of benefit if a local newserver has died. There are several gopher sites that allow users to read newsgroups. One of them is, gopher commsun.its.csiro.au (gopher 152.83.8.2) When a menu shows up, chose the following options :- 5. USENET News - Internet Bulletin Board/ 48. sci / 73. physics / 3. electromag / (Presently accessable from anywhere/anytime) [1.2] Is there an ftp site dedicated to sci.physics.electromag? Work is in progress on setting up a site, but is as yet, not ready. Still in the category of "Coming soon to a computer near you!" EM REFERENCE [2.1] What organizations, groups, or societies are oriented towards electromagnetics? Applied Computational Electromagnetics Society (ACES) This organization is oriented toward the computational aspects of electromagnetics. For information on becoming a member of ACES, contact Dr. Richard W. Adler, ECE Department, Code EC/AB, Naval Postgraduate School, 833 Dyer Rd., Rm 437, Monterey, CA 93943-5121, USA; Telephone: (408) 646-1111; Fax: (408) 646-0300; E-mail: 5541304@mcimail.com. Bioelectromagnetics Society (BEMS) For information, contact the society at the following address: 120 West Church Street, Frederick, MD 21701, USA; Telephone: (301) 663-4252; Fax: (301) 663-0043. Computer Applications in Electromagnetic Education (CAEME) This is an organization of industries and universities who support the development of computational tools for EM education applications. For more information contact Dr. Magdy Iskander, CAEME Director, Electrical Engineering Department, University of Utah, Salt Lake City, UT 84112. Electromagnetics Society (EMS) European Bioelectromagnetics Association (EBEA) This organization groups together many European as well as noneuropean researchers involved in both low and high frequency interactions. For additional information, contact its president: Guglielmo D'Inzeo; Dept. of Electronic Engineering; "La Sapienza" University of Rome; Via Eudossiana 18; 00184 Roma, Italy; Telephone: + 39 6 44585853; Fax: + 39 6 4742647; E-mail: dinzeo@tce.ing.uniromal.it. Institute of Electrical and Electronics Engineers (IEEE) The largest profesional organization in the world, IEEE has several societies that are oriented towards electromagnetics. Chief among these are the Antennas & Propagation, Electromagnetic Compatibility, Microwave Theory & Techniques, Magnetics, Nuclear Science & Plasma Science. For information contact the IEEE at: Customer Service, 445 Hoes Lane, PO Box 1331, Piscataway, New Jersey, 08855-1331, USA; Telephone: 908-981-0060; Fax 908-981-9667; E-mail: member.services@ieee.org. Any overseas groups that should be included here would be especially helpful. [2.2] What are good ftp/gopher/www sites to obtain EM related software, freeware or shareware? Are there other discussion lists for emag related topics? What are they? The following ftp sites are known to contain electromagnetics related files: Address Directory Contents ------- --------- -------- ftp.netcom.com /pub/rander/NEC NEC (Numerical Electromagnetics (IP Address ) Code) archive microwave.jpl.nasa.gov EMlib files (IP Address 128.149.76.31) emclab.ee.umr.edu /pub/aces ACES files, misc. (IP Address 131.151.8.246) /pub/ieee IEEE EMC Society Ed. Comm. files If you know of other sites, please send the site name, IP address, whre in the directory the files are located, and a brief description of contents. The following are other electromagnetics related mailing lists known to exist: NEClist is an internet mailing list devoted to the Numerical Electromagnetics Code and its various incarnations. Participants include developers and users of NEC-derived codes. If you would like to join, send a message with your name and e-mail address in the text to Dave Michelson: davem@ee.ubc.ca. If you want to post a message, just send it to: nec-list@ee.ubc.ca. There is a BITNET list, EMFLDS-L (Electromagnetics in Medicine, Science & Communications) which is devoted to the applications of electromagnetics in the indicated areas. To subscribe, send the message "SIGNON EMFLDS-L" to the address LISTSERV@UBVM.BITNET (or LISTSERV@UBVM.CC.BUFFALO.EDU). When posting messages to this list, just send mail to the address "EMFLDS-L@UBVM.CC.BUFFALO.EDU". Archive files are also available and information on how to obtain them is included in the welcome message you receive after signing on. [2.3] What are good text/reference books on EM at the beginning, intermediate, and advanced levels? What other books should be on the shelf of the practising electromagneticist? Asking people's opinions on selecting an electromagnetics textbook for study is somewhat akin to asking about religion. Everyone has an opinion, and they can get quite incensed about the situation if you don't see things their way. Notwithstanding the potential pitfalls of offering an opinion, the following texts all have something to offer. The separation between beginning, intermediate and advanced is somewhat arbitrary. All entries will be considered, and if you offer a candidate for the list, please include a couple of reasons why you think the book deserves to be included. Eventually, it would be nice to have these selections annotated with their strengths and weaknesses. Although these are mostly favorites of mine (Jost), they should serve almost anyone in good stead. I'm afraid my engineering background is probably showing through, but I trust the many physicists in the group will show me the light. Remember, your mileage may vary! Beginning Level Cheng, D.K. "Fundamentals of Engineering Electromagnetics, 2nd ed.," Addison-Wesley Publishing Company, 1993. Kraus, J.D., "Electromagnetics, 4th ed.," McGraw-Hill, 1992. Zahn, M., "Electromagnetic Field Theory: A Problem Solving Approach," Wiley & Sons, New York, 1979. Intermediate Level Balanis, C. "Advanced Engineering Electromagnetics," Wiley, 1989. Collin, R.E. "Field Theory of Guided Waves, 2nd Ed," IEEE Press, 1991. Harrington, R.F., "Time-Harmonic Electromagnetic Fields," McGraw-Hill, 1961. Jordan, E.C. and K.G. Balmain, "Electromagnetic Waves and Radiating Systems," 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1968. Advanced Level Jackson, J.D. "Classical Electrodynamics, 2nd ed.," Wiley, 1975. Jones, D.S. "The Theory of Electromagnetism," Pergamon Press, Oxford, 1964. Landau, L.D. and E.M. Lifshitz, "The Classical Theory of Fields," 3rd. revised English edition, Addison-Wesley, Reading, MA, 1971. __________, "Electrodynamics of Continuous Media," Addison-Wesley, Reading, MA, 1960. Smythe, W.R. Static and Dynamic Electricity, 3rd ed., revised printing" Hemisphere Publishing Corporation, 1989. Sommerfeld, A. "Electrodynamics," Academic Press, New York, 1952. Stratton, J.A., "Electromagnetic Theory," McGraw-Hill, 1941. "Applied" Texts Balanis, C.A. "Antenna Theory," Wiley, 1982. Collin, R.E. "Field Theory of Guided Waves," 2nd ed., IEEE Press, 1991. Kraus, J.D. "Antennas, 2nd ed.," McGraw-Hill, 1988. Ramo, S., J.R. Whinnery, and T. Van Duzer, "Fields and Waves in Communication Electronics," 2nd ed., Wiley & Sons, New York, 1984. Stutzman, W.L. & G.A. Thiele, "Antenna Theory and Design," Wiley & Sons, 1981. Mathematical Texts Abromowitz, M. and I.A. Stegun, eds., "Handbook of Mathematical Functions," U.S. National Bureau of Standards, (1964), also Dover, New York 1965. Courant, R. and D. Hilbert, "Methods of Mathematical Physics," 2 vols., Wiley-Interscience, New York (1962). Gradshteyn, I.S. and I.M. Ryzhik, "Table of Integrals, Series, and Products," 4th ed., prepared by Yu. V. Geronimus and M. Yu. Tseytlin, corrected and enlarged edition, translated by Alan Jeffrey, 1980. Morse, P.M. and H. Feshbach, "Methods of Theoretical Physics," 2 vols., McGraw-Hill, New York, 1953. Sommerfeld, A. "Partial Differential Equations," Academic Press, New York, 1949. Miscellaneous Texts Maxwell, J.C. "Treatise on Electricity and Magnetism,"3rd ed. (1891), 2 vols., reprinted by Dover, New York, 1954. [2.4] What are the units of electromagnetics? Does anybody really use esu or emu units? When carrying out electromagnetic calculations, there are several systems of units that are available. To simplify matters greatly though, they can be broken into two groups: the MKSA (meter-kilogram-second-ampere) system and the CGS (centimeter-gram-second) system. Another factor to consider is whether the units have been "rationalized" or not. By "rationalized", we mean that the factor 4pi (where pi=3.14159265...) does not appear in what are commonly called "Maxwell's Equations". Rationalization does not eliminate the factor of 4pi, rather it changes where the factor will show up. These days, most engineering work is done with rationalized MKSA units. What is known as the Gaussian system, is an unrationalized CGS system, that is mixed in the sense that electric quantities are measured in "electrostatic" units, while magnetic quantities are measured in "electromagnetic" units. Finally, the Heaviside-Lorentz system is a rationalized Gaussian system. The various CGS systems are used mainly in the area of physics, where certain simplifications in formulas result with the use of CGS units. For additional information, see one of the following sources: Jackson, J.D. "Classical Electrodynamics," 2nd ed., Wiley, 1975. Wangsness, R.K. "Electromagnetic Fields," 2nd ed., Wiley, 1986. Smythe, W.R. Static and Dynamic Electricity, 3rd ed., revised printing" Hemisphere Publishing Corporation, 1989. [2.5] Is there a standard way of writing the various vectors operators for electromagnetics operations? I'd really like to hear people's thoughts on this issue. The next edition of the FAQ will be having equations in it, and it would be nice to incorporate them in a form with which the largest number of people are comfortable. Some questions to consider are, should vector operators be spelled out?, Should only E and H be used to describe Maxwell's equations? What form (units) would be most comfortable to most people. Being an engineer, you know what my vote will be. EM THEORY ISSUES [3.0] What are Maxwell's Equations? Maxwell's Equations can be thought of in many different ways. Mathematically, they represent a set of partial differential equations. Physically, they are a set of equations that describe the relationships between electric and magnetic fields. Historically, they may represent one of the major intellectual achievements in the area of physics. Just a few phrases to start someone off. Looking for a good exposition of what Maxwell's Equations are all about. If we don't get any takers, you'll have to deal with our "purple prose". [3.1] Are Maxwell's Equations good under all circumstances? Under what circumstances are they "invalid"? This is soneone's chance to wax poetic about linearity, high fields and relativity. end of sci.physics.electromag.FAQ part 1/2 -------------------------------------------------------------------- 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 -------------------------------------------------------------------- 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 --------------------------------------------------------------------