Engineering
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Effective Analysis of Human Exposure Conditions with Body-worn Dosimeters in the 2.4 GHz Band
Chapters
Summary May 2nd, 2018
This study describes a protocol to measure exposure levels in the 2.4 GHz band, avoiding the uncertainties caused by the use of personal exposimeters as measuring devices. These alterations of the exposure levels should be taken into account, especially in compliance testing, where exposure limits are defined from non-perturbed data.
Transcript
The overall goal of this procedure is to measure exposure levels in the 2.4 gigahertz band while avoiding uncertainties caused by the use of personal dosimeters as measuring devices, body shadowing, limited sensitivity range, and nonidentification of the source. The main advantage of this technique is that it provides unperturbed measurement regarding E-field exposure conditions improving the use of exposimeters as measuring devices in compliance tests. Because uncertainties associated with the use of exposimeters are avoided, this method is appropriate in the regulatory field, providing reliable data that can be contrasted with the threshold defined for unperturbed exposure conditions.
Carry out the test in an indoor enclosure with a radiation source. This access point is on the ceiling and is turned off to prepare the dosimeters. A test subject will walk toward and away from the source along this path.
In some way mark a position 1.5 meters from horizontal position of the source. Have a test subject face the source at a distance of 12 meters. Use three dosimeters similar to this one and prepare them to sample every four seconds.
Place one dosimeter on the lumbar area of the person's back. Place a second on the person's front at waist height. For the third dosimeter, use a carton tube one meter in length.
Count the dosimeter in the tube's end so that it can be held away from the subject. With the radiation source on, turn on all the dosimeters as close to simultaneously as possible. Have the subject hold the tube at shoulder height with its dosimeter toward the radiation source.
Direct the subject to walk directly toward the radiation source at 10 centimeters per second while maintaining the tube with the dosimeter at shoulder height. It is important to maintain the slow pace during data collection. Have the person stop 1.5 meters from the source.
Mark the collected data as the first data set on the dosimeters before turning off the radiation source. With dosimeters in place, return the subject to the position 1.5 meters from the radiation source facing away. Turn on the source and the dosimeters before asking the subject to walk directly back to the starting point at 10 centimeters per second.
On arrival, collect date from the dosimeters and turn off the source. Prepare a new radiation source for the next measurement. Use an analog signal generator connected to a biconical antenna via a low-loss cable.
Turn on the signal generator to emit a common WiFi frequency continuously without modulation. Vertically orient the antenna in the center of the room to be in line with the subject's path. Start with the subject 12 meters away from the source facing it.
Center a dosimeter on the subject's back not in the line of sight of the source. Have a second dosimeter in a one-meter long carton tube. When ready, turn on the two dosimeters as close to simultaneously as possible.
Have the subject hold the dosimeter one meter in front at shoulder height. Direct the subject to walk at a constant 10 centimeters per second toward the antenna while maintaining the tube at shoulder height. Stop the subject 1.5 meters from the source.
Mark the collected data as the first data set on each of the dosimeters before turning off the signal generator. When done, return the dosimeters to the same positions and get ready to collect data, then start the signal generator and put the antenna in a horizontal orientation. Ask the subject to return to the start position and face the antenna.
After starting the dosimeters, have the subject repeat the walk toward the antenna in its new orientation. When done, remove the dosimeters and gather this set of data. These cumulative density functions are from data taken with dosimeters at three different positions for motion toward and away from the source.
When both are in the line of sight of the source, the body-fixed dosimeter registered field levels similar to but lower than the one located one meter away from the wearer. To study the Body Shadow Effect, plot the electric field intensity and the number of samples logged during the subject's walk toward the source. Dark blue is for measurements away from the body, light blue is for measurements in the body shadow.
In the case of a 63-cubic meter non-constant width enclosure with non-reflective walls, the data from the shadowed dosimeter is similar for both polarizations. Compare this with data from a 162-cubic meter constant-width enclosure with non-reflective walls, where there is a notable difference for the shadowed dosimeter in the two polarizations. This is a comparison of experimental data from the dosimeter located one meter away from the user in simulated results.
The user walked toward a vertically-polarized radiation source. The match is adequate for this enclosure and for the other enclosures in the study. There is no body influence in the logged data.
The implication of this technique extend to personal health due to widespread concerns regarding the possible health effects to exposure to RF energy emitted by wireless-enabled devices. While attempting this procedure, it's very important to remember to maintain the dosimeter one meter away from the user in order to avoid the Body Shadow Effect while walking at a low pace. Though this technique provides insight into indoor conditions and in the 2.4 gigahertz band, this method can also be applied to outdoor environments and to other frequency bands.
This technique helps for researcher in the field about the Body Shadow Effect through a specific measurement protocol that only requires one dosimeter and without the processing of data.
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