Dragan Poljak

5G Italy 2019 / Dragan Poljak

Dragan Poljak

University of Split, Croatia


5G International PhD School 2019


Dragan Poljak received his PhD in el. Eng. in 1996 from the Univ. of Split, Croatia. He is the Full Prof. at Dept. of Electron. and Computing, Univ. of Split. His research interests are oriented to computational electromagnetics (electromagn. compatibility, bioelectromagnetics and plasma physics). To date Prof. Poljak has published more than 160 journ. and 250 conf. papers, and authored some books, e.g. two by Wiley, New Jersey and one by Elsevier, St Louis. He is a Senior member of IEEE, a member of Editorial Board of Eng. Anal. with Boundary Elements, Math. Problems in Eng. And IET Sci. Measur. & Techn. He was awarded by several prizes for his achievements, such as National Prize for Science (2004), Croatian sect. of IEEE annual Award (2016) and Technical Achievement Award of the IEEE EMC Society (2019). Since 2013 prof. Poljak has been a member of the board of the Croatian Science Foundation. He is currently involved in ITER physics EUROfusion collab. and in Croatian center for excellence in research for tech. sciences. He is active in few Working Groups of IEEE/Internat. Committee on Electromagnetic Safety (ICES) Tech. Comm. 95 SC6 EMF Dosimetry Modeling.

Tutorial: On Electromagnetic-Thermal Dosimetry

Abstract: This Tutorial, mostly based on the forthcoming book: Human Interaction with Electromagnetic Fields – Computational Models in Dosimetry, Elsevier 2019, by Poljak and Cvetković, aims to review various aspects of human interaction with non-ionizing part of electromagnetic (EM) spectrum including both the undesired exposure from artificial sources and the biomedical applications of EM fields. The tutorial covers basic aspects of environmental EM fields, coupling mechanisms between humans and static electric, static magnetic, and time-varying fields, established biological effects of EM fields from static to high-frequency range, international safety guidelines related to limiting human exposure to those fields, including relevant exposure limits and safety measures, electromagnetic-thermal dosimetry models and the related analytical/numerical solution methods.
First, some theoretical and experimental methods of incident field dosimetry for the assessment of external fields, due to low frequency (LF) and high frequency (HF) sources, are presented and accompanied with a number of realistic examples, dealing with power lines, transformer substations, PLC systems, RFID antennas and radio base stations.
Furthermore, some electromagnetic-thermal dosimetry methods for the assessment of human exposure to low frequency (LF), high frequency (HF) and transient electromagnetic radiation are given. In particular, the use of integral/differential equation formulations and related numerical solution procedures (primarily based on the use of Boundary Element Method – BEM, and Finite Element method – FEM) for the calculation of induced current densities, internal fields and specific absorption rate (SAR) are discussd in detail. For HF exposures the related temperature increase in tissues is dominant effect and is therefore carried out by numerically solving the bio-heat transfer equation. Computational examples pertaining to various realistic exposure scenarios, such as; pregnant woman/foetus exposed to low frequency (LF) fields, the human eye, the human brain and the human head exposed to HF EM fields will be given. Illustrative examples of thermal dosimetry stemming from the brain, eye and head exposed to HF fields are shown, as well.
The obtained numerical results for induced current densities, internal fields and SAR are compared against exposure limits proposed by ICNIRP (International Commission on Non Ionizing Radiation Protection).
This is followed by some examples of biomedical applications of electromagnetic fields, including the transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES), but also some electrotherapy and magnetotherapy techniques. Also, some illustrative numerical examples related to thermal modeling of various ophthalmological procedures will be given.
Finally, the last part of the Tutorial deals with an application of stochastic collocation (SC) for stochastic modeling (combined with deterministic approaches) of bioelectromagnetic phenomena.

Keynote: Some aspects of 5G dosimetry

Abstract: The fifth generation (5G) of mobile communication systems uses of mm-waves, i.e. the GHz frequency range which becomes of interest in a view of EM field (EMF) exposure guidelines. Thus, extensive study on human exposure to phased arrays radiating above 3GHz are of increasing interest. Frequencies at 3GHz in IEEEC95.1 standard, or 10GHz in ICNIRP guidelines represent transition frequencies for local exposure. Instead of specific absorption rate (SAR) averaged over tissue volume the incident power density (IPD) averaged over a specific area is used. Therefore, IPD as dosimetric quantity is used for localized exposure above 3 and 10GHz, respectively, in near field. Near field distribution is far more complex than the far field represented by the plane wave concept. The related surface temperature increase in the eye and skin are of interest as a relevant biological effect. Also, area-averaged transmitted power density (TPD) at skin surface as metric for the estimation of surface temperature elevation has been used. However, certain issues should be clarified regarding inconsistencies pertaining to transition frequencies. An important issue regarding exposure at frequencies above 3GHz is the choice of averaging area of the IPD. The second issue to be clarified is the biological rationale for transition frequency.
This lecture deals with the measurement and theoretical estimation of field levels generated by 5G base station antenna operating in the range between 3.4 GHz and 3.6 GHz. The electric field has been calculated by free space and Modified Image Theory (MIT) approximation, respectively. The exposure has been estimated according to ICNIRP guidelines, and by means of spectra integrals approach.
Furthermore, the lecture deals with the analysis of the averaged area for IPD calculation for a simple source geometry represented by Hertz dipole. A brief theoretical basis related to the Poyinting power flow and the most commonly used definition of IPD are given. What follows is the derivation of the analytical expression for IPD of Hertz dipole in the equatorial plane.
Furthermore, some illustrative results of IPD with respect to the averaging surface area and to the operating frequency, obtained using the analytical expression, are presented.

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