This executive summary describes the final report for this project.
The goal of this project was to develop guidelines for measuring the electric and magnetic field distributions near specific field sources. Data from these measurements may help direct future biological effects research by better defining the complexity of magnetic and electric fields to which humans are exposed, and to provide the basis for rigorous field exposure analysis and risk assessment if a relationship between field exposure and human health effects is identified. The guidelines will also help researchers characterize EMF sources in a consistent manner with sufficient spatial and temporal detail to guide electric and magnetic field management if necessary.
The project is divided into three tasks: Task A - Selection of Field Parameters, Task B - Identification of Field Sources, and Task C - Development of Protocol.
The goal of Task A is to construct a set of characteristics for guiding and interpreting biological studies and for focusing any future effort at field management. This set would be quantified and reduced according to the availability (or possible development) of instrumentation to measure the desired characteristics. The report discusses many specific measures of sources. A specific measure is a method to perform spatial and temporal reductions of measurements in a consistent and defined matter. Specific measures fall into the general categories of intensity, frequency, intermittency, transients, spatial attenuation, and polarization. Examples include: ac-dc angle, ac rms, harmonic magnitude, maximum spatial phase, peak resultant, etc. A discussion and equation is given for each specific measure. A table is generated that shows the field attributes characterized by the specific measure and also the instrumentation that can support the specific measure. The waveform capture is the most efficient means to capture all electric and magnetic field attributes.
The goal of Task B is to develop a systematic method of identifying sources during surveys so that they can be correlated with measurements made in other surveys or in laboratory tests. The proposed classification system is restricted to a general quantification of the magnetic field attributes of a source. The classification system is based on identifying the source by its common name followed by alphanumeric descriptors for a total of 50 characters followed by a four digit code box. The first digit of the code box grades the range of magnetic field magnitudes that may be expected at a point 30 cm in front of the surface of the device. The second digit is a measure of the frequency of the most dominant magnitude. The third digit is a measure of how intermittent the point source may be. The fourth digit is a measure of two different attributes, spatial attenuation and polarization.
The goal of Task C is to develop guidelines for measurement of field sources. Guidelines are developed for in-situ measurements and for measurements at an appliance test center.
For the in-situ measurements, ideally three people should be present to conduct the protocol. The equipment required is: magnetic wave capture systems with a staff to hold four sensors; an electric field sensor with an ELF bandwidth if electric fields are to be characterized; a video camera and several cassettes of video tape; a staff for the magnetic sensor; measurement equipment including a non-metallic measuring tape; a data log with a supply of pens or pencils; a clamp-on current meter that may be used to measure source current; and a portable computer if the magnetic field recorder requires configuration or down-loading during or after the measurement process.
The following steps should be taken:
For measurements of appliances at a test center, a pilot study should first be conducted. The pilot study would produce the following findings to be used in developing the full characterization: the type of sensors, the expected maximum levels, the transient trigger levels, the location of dc sensors, the minimum frequencies for recording, the intervals for snapshots, and the LF-VLF recording requirements. The test center protocol utilizes structures with mounted sensors to allow maximum characterization in the minimum amount of time. The final protocol should include: creation of a sketch of the appliance; preparation of a set of photographs to document the details of the device; the size and construction of the wiring, voltage rating, current rating of the sources; collection of field data on spherical coordinates to completely surround the appliance; measurement of LF and VLF data; measurement of transient data; and analysis of data. Selection of the center of the location of an appliance for measurements in the spherical coordinate system is a complex issue. The physical center is an obvious choice, but the center of gravity of the appliance may actually be necessary. For the laboratory test fixture, the use of spherical coordinates and geometric ratios of distance provide an improvement in data reduction for the purposes of modeling. The attenuation coefficients can readily be calculated for essentially any direction from the appliance being tested. While spherical coordinates will generally produce the most information for modeling with the minimum of data, cylindrical coordinates are useful for some appliances. The use of Cartesian coordinates normally produces excessive data in the laboratory environment. It is recommended that for an appliance which has a `physical sphere' of about 30 cm radius, the measurements should be made at a fixed position with the first sensor located on the physical sphere. Recommended distances are 10 cm between the first and second sensor, 30 cm between the first and third sensor, and 100 cm between the first and fourth sensor.