Measurerment of Radiofrequency Radiation – Dosimetry

Radiofrequency radiation (RF) – is a part of the electromagnetic spectrum that is delimited by the range of frequencies 3 KHz-300 GHz, with wave lengths between 1 mm and 100 km respectively. For further reading see Introduction to Radiofrequency (RF) Radiation. 

The use of devices emitting radiofrequency radiation (RF) has increased dramatically over the past three decades.  Examples of equipment and devices that emit radiofrequency radiation include radio and television transmitters, microwave transmitters and ovens, industrial equipment, military and civilian radar systems, satellite communication transmitters, transmitters for military communication and especially mobile devices and base stations for cellular communication.

The very widespread deployment of sources emitting RF radiation has aroused concern regarding the safety of use of this type of radiation. Consequently the need for regulation and for the development of means of measuring and surveillance has increased. Hence, comprehensive ongoing research is being conducted in an effort to quantify the radiation emitted from various instruments and the amount of radiation absorbed by the human body. This information forms the basis for assessing the health hazards arising from exposure to radiofrequency radiation, and for establishing recommended safety thresholds by the international organizations working in this field:

•  ICNIRP – International Commission for Non Ionizing Radiation Protection
•  IARC – International Agency for Research on Cancer
•  IRPA – International Radiation Protection Agency

ICNIRP is the leading international organization engaged in active research and in reviewing research conducted in this field.  This organization formulates conclusions and publishes recommendations and guidelines to minimize the effect of non-ionizing radiation on the human body.  It recommends an upper threshold for the safety limits of exposure to radiofrequency by humans, depending on various factors, such as frequency, power density, duration of exposure, characteristics of the radiation signals, etc. For further reading see: Radiofrequency Radiation at Low and High Frequencies.

Radiofrequency radiation is absorbed by the human body, creating internal electromagnetic fields.  It therefore became necessary to measure (by dosimetry) the electromagnetic fields emitted by sources of radiofrequency radiation (RF) and the internal electromagnetic fields induced in the body of a person exposed to such radiation, as a baseline for empiric evaluation of the biological effect of exposure to RF radiation.

The power distribution of the internal electromagnetic field induced by radiofrequency radiation in the human body depends on the nature of the external electromagnetic field interacting with it (frequency, power density, field strength, polarization, modulation, etc.), as well as on the size and shape of the human body, on the electronic properties of the different body tissues, and on the location of the body relative to the source of radiation.  It should be noted that the dose of radiation is also affected by the individual's environment (for instance, the exposure of a person talking on a mobile phone inside an elevator will be greater than that of a person talking outside the elevator).

Dosimetry is the assessment of the effect of the electromagnetic field on the human body (or, in general, on any living component such as an organ, cells, etc.), as expressed by clear measurable effects, such as electrical currents, heating of tissues, etc.  Specifically, dosimetry provides a measure of the rise in temperature resulting from exposure to an electromagnetic field and therefore can provide an estimate of the health hazard per unit of exposure.

While the measurement of the surrounding electromagnetic field is relatively simple and may be performed by standard equipment, measurement of the electromagnetic field absorbed by the human body is complicated and cannot be performed directly.  In order to estimate the strength of the electromagnetic field in the human body in specific organs, such as the head, simulations and calculated estimates based on complex models are performed. 

Dosimetry may be performed on animal cells or on human cells harvested from various tissues (in vitro), on living organisms (in vivo), or by simulated physical measurements in the laboratory. Laboratory measurements are performed on 'phantom' - systems mimicking parts of the body (e.g. the head) and containing dielectric liquids (i.e. liquids with defined electrical and magnetic properties) resembling the properties of human tissues. In such simulations, the phantom is exposed to the selected source of radiofrequency radiation, the electrical fields are assessed by a measuring probe, and the values are entered into numerical models that calculate the rate of rising temperature in the phantom resulting from the exposure.  The increase of temperature of a unit of body mass (1 gram or 10 grams) as a result of exposure to radiofrequency radiation is known as the Specific Absorption Rate (SAR).   

References

• International Commission for Non Ionizing Radiation Protection. ICNIRP guidelines for limiting exposure to time‐varying electric, magnetic and electromagnetic fields (Up To 300 GHz). Health Physics. 1998; 74:494‐522.
• Rao NS,, Babu GR, Srinivas PV. Study of electromagnetic radiation and specific absorption rate of mobile phones with fractional human head models via green's functions Journal of Computer Science. 2011; 7:1275-1283.El Dein AZ. Interaction between the human body and the mobile phone: control of the parameters of a mobile communication facility over distribution of specific absorption rate in human body. 2010; LAP LAMBERT Academic Publishing.