Introduction to Measurements of Non-Ionizing Emissions

Today, there is growing concern among users of communication equipment, particularly cellular telephony users, and nongovernmental organizations and the community in general regarding the effects of non-ionizing emissions on human health, concern spurred by the growing numbers of wireless sources of non-ionizing emissions.

This results in different activities to gain information and protest.  Municipalities and different governmental levels are therefore particularly “active,” seeking initiatives, provisions, and solutions with a view to preventing future problems.  Often such initiatives are based only in part on the vast scientific and experimental efforts that have been made to study non-ionizing emissions, so that the political will to control and regulate is sometimes divorced from the way measures defined are implemented in practice.  There is also a risk of overlapping and inconsistent regulations, as numerous governmental players (national, provincial, and municipal) are issuing regulations in parallel.

This document will therefore provide a brief introduction to non-ionizing emissions measurements that may be useful to those with responsibility for analyzing, regulating, and controlling such emissions.

Non-ionizing emissions means electromagnetic spectrum emissions with insufficient energy to ionize matter.  Here, emission is the radiation produced by a single radio frequency source, while inmission is the combined radiation from all frequency sources whose fields are present at the location.

Public or uncontrolled exposure occurs in situations where the general public may be exposed to electric, magnetic, or electromagnetic fields or where persons exposed through their work may be unaware of such exposure or are unable to effect control thereof.

Commonly utilized regulatory procedures are:

• Predictive method:  based on theoretical calculations of non-ionizing emissions produced, as a step prior to making specific non-ionizing emissions measurements.

• Measurement method: based on practical implementation of a measurement protocol, with appropriate equipment and sounding devices yielding the precise non-ionizing emissions magnitudes produced.

Some propose, in simple cases, the use of both methods in order to avoid unnecessary measurements and cost (incurred by users) where, through the use of theoretical calculations, it may be determined that non-ionizing emissions is below levels predefined as safe.

Some also insist that, in view of the complexity of emissions and the growing number of radio frequency sources, the only possible method to ensure that predefined limits are not exceeded is to make measurements based on a specific protocol.

In our experience and view, whether one or the other method is used is a matter for special study and will depend on:

• The types of frequency sources;

• The density of intervening sources and their locations in the area to be measured;

• The power and frequency bands of intervening sources;

• The policy defined in the regulatory scheme.

In considering the problem in greater depth, the following concepts may be defined, based on “near field” and “far field” as shown in Figure 1:

• If far field is considered è non-ionizing emissions values calculated based on the predictive method.

• If maximum permissible exposure limits (MPE) are exceeded è the measurement method is used.

Figure 1

Translations:  o = or; el mayor de ambos:  the greater of the two; campo cercano reactivo:  reactive near field; campo cercano radiante:  radiating near field; campo lejano (Onda TEM plana):  far field (flat TEM wave)

Predictive method

The following is based on a single-antenna site where the equations are valid only for far field calculations, but may also be used to predict the worse case:

If the distance from the antenna to all points accessible by the general public is ≥ r, the site need not be checked via measurements.

Measurement method

The following steps must be taken to use this method:

• Determination and inspection of the site selected for measurement and determination of radio frequency sources, types of emission, emission characteristics, and surrounding environment;

• Determination of measurement procedure (near field, far field);

• Determination of measurement protocol to be used, and instruments and sounding devices to be used in the measurement process;

• Determination of points to be measured depending on the protocol selected and points of greatest risk (external and internal);

• Taking of measurements and preparation of reports.

The particular measurement procedure used in, for example, Argentine regulations, is:

• Near field è E, H, or both, are measured (MPD imposed limits must be observed);

• Far field è E or H are measured, to obtain S (MPD imposed limits must be observed);

• Sequence:  Inmission is measured. If the strictest MPD is exceeded, each station’s emission is measured;

• Inmission:  Use of broadband instruments (non-tunable electromagnetic emission detectors), with E and H isotropic measurement sounding devices;

• Emission:  Use of narrow band instruments (tunable field intensity meters, spectrum analyzers, etc.), with antennas appropriate for the frequency ranges to be measured;

• All instruments, antennas, and sounding devices must have calibration certificates (manufacturer’s or from a laboratory accredited in the country of origin);

• Recording of the value of the measurement made, plus specified uncertainties (manufacturer), and the error range of the method used.

Continuous monitoring

The methods evaluated are for specific or repetitive applications, but with long periods when measurements are not made.  Today, there are new measurement models based on continuous detection (24/7) of potential risk areas, with data published on the Internet that the public may access freely, which should be analyzed and evaluated for implementation by authorities with competence in the non-ionizing emissions area.

Use of this monitoring method has a series of advantages, such as:

• Population:  Objective data is available, 24 hours/day, to ensure that emission values are below regulatory limits.

• Municipalities:  Provides residents with peace based on the assumption that a comprehensive network is available to monitor electromagnetic emission.

• Service providers:  Reduction of the public’s perception of danger and/or alarm caused by service providers’ base stations.

Figure 2 shows a conceptualized continuous monitoring scheme.

Translations:  Cellular radio base station, monitoring station, central control node.

 Conclusions

From the above and the international state-of-the-art with regard to non-ionizing emissions, the following conclusions may be drawn:

1. There is no conclusive evidence to indicate that non-ionizing emissions, at the predefined levels, has negative impact on the population …

2.  … but neither does the evidence indicate that long exposure is without impact.

3. Therefore, the topic continues to be studied in the main international organizations (World Health Organization, ICNIRP, etc.)

4. Above all, the prevention principle must be respected as the basis for work carried out.

5. It is advisable to define and measure non-ionizing emissions exposure “hotspots.”

6. Methods for periodic and repetitive measurement must be established to generate a statistical base, defining emission maps and possibly generating protected areas.

7. In short, an attempt should be made to strike a balance between available technological resources and human health, which must be preserved (today’s comfort and society vis-à-vis prehistoric times).

Alfredo F. Debattista
Director
Consultora Federal de Comunicaciones (Argentina)