Electromagnetic Fields


Electromagnetic fields (EMF) consist of electric (E) and magnetic (H) waves traveling together at the speed of light at a specific frequency, amplitude and wavelength. At frequencies as low as 50Hz, EM waves propagating in the air (ether) have very long wavelengths, with the electric and magnetic fields acting independently of one another and measured separately.

Electric fields arise from the difference in potential (voltage) between two or more points. They are measured in volts per meter (V/m) or kilovolts per meter (KV/m). When charges accumulate on an object, they create a tendency for like and opposite charges to be repelled and attracted, respectively. Any device connected to an electrical outlet, even if the device is not switched on, will have an associated electric field that is proportional to the voltage of the source which it is connected. Electric fields are strong closer to the device and diminish over distance.

Magnetic fields arise from the motion of electric charge in a conductor, that is, the current. They are measured in Amperes per meter (A/m) but are usually expressed in terms of the magnetic flux density in Tesla (T) or milliTesla (mT). In some countries, another unit called the Gauss (G), is commonly used for measuring magnetic induction (10,000 G = 1T). Any device connected to an electrical outlet and turned on has an associated magnetic field, the strength of which is directly proportional to the current drawn from the source (outlet). As electric fields, magnetic fields are strong closer to the device and diminish over distance.

There exists a wide range of instrumentation for measuring the strength of magnetic and electric fields. Field analyzers are used in order to obtain an accurate reading of the RMS (root mean square) values of the magnetic and electric fields at different pass bands and dynamic ranges. Such field meters are available with single and three axis coil probes with the capability of measuring alternating and static fields. T

he probes of magnetic field meters may be held by hand without affecting the accuracy of the measurement under normal conditions. In other words, there is no perturbation of the field due to human factor while measuring their intensity. The instrument used to measure these fields is the EFA-300 Isotropic Field Analyzer. This is an ideal analyzer for workplaces and public spaces and is capable of handling any measurement in the low frequency range. The EFA-300 is equipped with a built in isotropic magnetic field probe and is further enhanced using optional probes so as to obtain more accurate measurements. During our measurements an extra 100cm cross sectional area probe was used.

An isotropic cube shaped E-field measurement module, that contains both the sensor and the circuitry necessary for operating independently from the base units, is also used in the measurements. This module provides a great advantage in reducing the human error factor in the electric field measurements.