Medicine and biology / Gyógyászat és biológia
Electromagnetic dosimetry and thermal modelling of mobile phones
József Bakos, György Thuróczy
Natl. Res. Inst. For Radiobiology and Radiohygiene, Dept. For Non-ionizing Radiation

The use of mobile telecommunication has increased very rapidly in the world: nowadays most widespread in Europe, in some Scandinavian countries more than 70 % of public use mobile phones. In Hungary: already more than 30 % of public use mobile phones, the number of users was doubled during last year.
Problems in radiation hygiene: the high number of users in the public can cause serious effect on public health even if the risk is low. Because of the quick application of new technologies and rapid development, there are gaps in knowledge in the field of biological and health effects and in RF dosimetry of mobile phone radiations. It is known that 30-70% of emitted power is absorbed in human head during use of mobile handsets. The absorption is depend on type of phones and way of use.
The dosimetry of mobile phone radiation in human head can be studied only on models. In case of physical models measurements are performed in phantoms.
The measurable quantities are the electric (magnetic) field or the temperature rise of the absorber material. For RF dosimetric purposes the specific absorption rate(SAR) is used in units of W/kg.
Difficulties of SAR measurement: The SAR distribution is very inhomogenous and depend on frequency and orientation of radiation and on size, shape and dielectric properties of exposed object.
Temperature rise measurements can be used only in case of high intensity, short pulses of RF radiation(eg. radar), because of errors caused by termoregulation and conduction of biological tissues. For temperature rise measurements a miniature, fast response, inplantable, high sensitivity temperature probe is needed, which is not unperturbing for RF fields. The advantages and disadvantages of used probes are the followings:.

	In case of numerical modelling computations are performed on the base of known physical properties of RF radiation and human tissues. The first step is the establishment of exact anatomical model on the base of NMR data (resolution = 1 mm3). Second step is the computation of SAR spatial distribution i.e. by finite difference time domain (FDTD) method. Finally the thermal modelling of heat conduction and heat transfer related to blood flow by Pennes bioheat transfer equation.
E-field dosimetry in head phantoms	Picture of head by thermocam