Electromagnetic Field Detection and Measurement



Electric Fields and Magnetic Fields are perpendicular to each other and to the conductor generating them. When you try to detect them or measure them you need to visualize what you are dealing with or, depending on your measuring equipment, you may not detect the field or your measurement may be in error.

If you're dealing with a straight wire, measuring nearby low frequencies, picture the wire as the axle of a wheel.
  • Electric fields extend straight outward (like spokes around an axle) down the entire length of wire
  • Magnetic fields rotate around the entire length of wire, like the rim of the wheel.
If you are dealing with a distant point source (radio/TV antenna or cellphone tower) both electric and magnetic fields will be polarized in one of three ways:
  • They may be horizontally polarized
  • They may be vertically polarized like radio, television, and cellphone signals
  • They may have circular polarization, like a satellite signal
To accurately detect and measure them your external receiving antenna, or internal antenna, needs to match the source. And you need to have your meter set up to either select an X, Y, or Z axis, depending on the polarization of the signal. The math to find the "resultant field" from three readings is: "the square root of (X squared + Y squared + Z squared)". Or, if you use a multi-axis meter, you can hope that the internal processor calculates an accurate signal level.

If you are checking electric fields, your meter (and you) must be grounded. This gives the meter a proper reference to allow accurate comparisons between the field and the ground potential in your area. Usually this involves a ground wire connected to the meter, a grounding point on the meter that makes contact with a finger (if the meter is hand-held) and a grounding clip or strap that must be connected to a ground rod, grounded water/gas pipe, or (in the U.S., at least) the center screw attaching the cover-plate to any properly grounded, 120-volt electrical outlet.

Your meter needs to operate within the bandwidth of the signal you are attempting to measure. Meters have full sensitivity within a certain frequency range. Sensitivity falls off on either side of that range. And even within their advertised range, if the meter is inexpensive or simply uncalibrated, the readings may not be completely accurate. For instance, a meter that has full sensitivity in a 50 MHz to 3 GHz range will either not pick up a 5.8 Ghz WiFi router or the reading will be greatly undervalued. But for detection purposes only, a meter that detects the frequency range of interest will suffice.

Your meter must also have enough sensitivity to detect the signal you wish to measure. Sensitivity ranges are advertised but are influenced by whether or not the meter can be switched to a single polarization axis, and by whether or not a more sensitive, frequency optimized, external antenna can be utilized. for instance, if you are simply trying to detect close-range microwave oven emissions, an inexpensive meter with an internal antenna and analog metering that works in the 2.4 GHz range will suffice. But if you are trying to accurately measure a distant cellphone tower to gauge your exposure you may need to spend more for a digital output including peak, maximum, average, and hold functions, along with selectable polarization axis, all calibrated for your target frequency.

In my actual work as a consultant I use a Gigahertz Solutions Digital Electrostress Analyzer, model ME3851A, low-frequency meter that cost roughly $650, but they make another model without frequency switching that costs around $140 (also found at LessEMF). Another meter that can be very educational is the "Zap Checker", model 270, also from LessEMF. This meter ranges from 10MHz. (10 megaHertz, or 10,000,000 Hz.) to 6.4 GHz. (6.4 gigaHertz, or 6,400,000,000 Hz., just above the frequency of many new cordless phones). It shows you where cellular phones and towers, radio and TV stations, microwave relay towers (and ovens), and all of the other myriad high-frequency sources are beaming from. In my actual consulting work, where I need a more exact, calibrated readout of high-frequency power levels, I use the TES-92 Electrosmog Meter. If you wish to pin-point both the frequency and the intensity level you will need to spend a great deal more for what amounts to a portable spectrum analyzer.

And you may have noticed, while shopping for an EMF meter, or while attempting to compare the measuring units on your meter to published materials regarding EMF exposure, that the mathematics can be daunting. For several years we have offered both a spreadsheet with most of the commonly used measuring units and the formulas used to make conversions between them as simple as possible.



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The U.S. Food and Drug Administration has not evaluated any of the information contained herein (nor is it likely to!), and said information is not intended to replace the advice of a physician, nor is it intended to diagnose, treat, cure, or prevent any disease.