Project management: Gernot Schmid, Seibersdorf Labor GmbH
Start: 1 November 2021
End: 31 October 2024

Background

A central component of the internationally recommended protection concept against health effects of low-frequency electric and magnetic fields are the reference levels defined by ICNIRP ^[1] and IEEE^[2] and the associated basic restrictions. The latter are based on proven biological effects of intra-body electric field strengths and magnetic flux densities at frequencies below 10 MHz. Whilst the magnetic permeability for most tissue types does not differ from air and thus the internal magnetic flux density, which corresponds to the external value, the internal electric field strength is difficult to access and furthermore strongly dependent on the type and structure of the tissue. The dielectric properties of tissue types have been theoretically modelled ^{[3, 4, 5]} and partly measured in numerous studies (e.g. on pigs ^[6]). However, uncertainties – specifically in relation to the finer structures in human tissue – in hives remain. The IEEE therefore lists both the measurement of tissue conductances and the modelling of skin, muscle, and nerve tissue as the most urgent research gaps to be addressed (Chapters 2.1 and 2.2 ^[7]).

Objective

Based on the current state of data and simulation techniques, this research project aims to determine the dielectric properties of tissues of the peripheral nervous system using tissue samples. The focus is on skin and muscle tissue; these are especially exposed because of their location in the body. Based on the improved data basis, body part area models (induction models) which are currently used will be refined and used for the numerical simulation of field configurations. Of particular interest is the simultaneous effect of electric and magnetic fields such as those found in the vicinity of overhead power lines. Statements on the conservatism of the reference values (in air) derived from the baseline values (in the body) are expected.

Implementation

The research project is based on researching the current data on electrical conductivity, permittivity, mass density, specific heat, and thermal conductivity of human and mammalian tissues and their measurement methods. On the other hand, currently used numerical calculation methods for dosimetric modelling in the low-frequency range are reviewed and their advantages and disadvantages evaluated, especially with regard to numerical artefacts.

Based on these findings, the electrical conductivity and permittivity of skin, muscle, and fat tissue are determined in the frequency range up to 1 MHz using optimised measurement methods. In the case of skin tissue, its fine structure in epidermis, dermis, and subcutis is considered in separate measurements. In the case of muscle tissue, particular attention is paid to the anisotropy of conductivity and permittivity. In parallel to measurements on human tissue samples, measurements of electrical conductivity in vivo based on impedance measurements and MRI scans on volunteers are carried out. This new approach should provide further insight into the question of possible discrepancies between in vitro measurement data on tissue samples and the in vivo properties of the tissues.

Based on the original data obtained, available body part area models will finally be improved so that the correlation between externally acting field strengths and the field magnitudes induced in the body tissues can be determined with considerably less uncertainty than before. Special attention is paid to the analysis of artefacts caused by the discretisation of the computational space and by anatomical inaccuracies of the tissue models. In addition, the effect of tissue anisotropy on model accuracy is taken into account as well as “critical” tissue structures such as boundary layers or thin layers. With the optimised models and methods obtained in this way, extensive numerical calculations will be carried out in order to check the conservativeness of the reference values. In particular, exposure situations with simultaneous exposure to electric and magnetic fields are also considered.

References

1) International Commission on Non-Ionizing Radiation Protection, 2010. Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz). Health physics, 99(6), pp.818-836.

2) Laakso, I. and Hirata, A., IEEE Standard for Safety Levels with Respect to Human Exposure to Electromagnetic Fields, 0-3 kHz, C95. 6-2002 IEEE Standard for Safety Levels with Respect to Human Exposure to Electromagnetic Fields, 0-3 kHz, C95. 6-2002, 2002.

3) Foster KR, Schwan HP. Dielectric properties of tissues and biological materials: a critical review. Crit Rev Biomed Eng. 1989;17(1):25-104. PMID: 2651001.

4) Gabriel, S., Lau, R.W. and Gabriel, C., 1996. The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues. Physics in medicine & biology, 41(11), p.2271.

5) IT'IS Foundation, Dielectric properties

6) Gabriel, C., Peyman, A. and Grant, E.H., 2009. Electrical conductivity of tissue at frequencies below 1 MHz. Physics in medicine & biology, 54(16), p.4863.

7) Reilly, J.P. and Hirata, A., 2016. Low-frequency electrical dosimetry: research agenda of the IEEE International Committee on Electromagnetic Safety. Physics in Medicine & Biology, 61(12), p.R138.

Project management: Federal Office for Radiation Protection (BfS)
Start: 1 April 2018
End: 31 December 2022

Background

When constructing and substantially modifying installations for the supply of electrical energy, care shall be taken to ensure that the exposure of the general public is not significantly increased by the operation of the installations. The knowledge about the exposure of the population in Germany to anthropogenic magnetic fields is largely derived from studies carried out by the BfS in 1996 and 1997 on behalf of the Bavarian State Ministry for Regional Development and Environmental Affairs. At that time, a test collective was formed from 2000 Bavarian citizens. Each subject was equipped for one day with a compact, body-worn measuring device ("personal dosimeter"), which automatically recorded the temporal course of magnetic field exposure. The participants in the study were also asked to record their activities in bullet points on the day of the measurement. The study was designed to assess the contributions of different magnetic field sources (e.g. contributions from low and high voltage power lines, electrical appliances, and power and feeder lines for electrically operated means of transport (mainly railways)). The sample was selected in such a way that residents from municipalities of different sizes were represented according to their respective population numbers.

The BfS has also commissioned studies to compare exposures caused by overhead lines and underground cables. These investigations were carried out primarily without direct reference to individuals.

The data collected for the Bavarian State Ministry are over 20 years old. They were collected in one federal state only. At that time, only low-frequency magnetic fields with the power grid frequency (50 Hertz) and the frequency of the traction power grid (16.7 Hertz) were recorded. No data were collected for magnetic fields with frequencies that occur in today’s common switched-mode power supplies, induction cookers, or individual electric mobility solutions. The recording of anthropogenic static magnetic fields was also not part of the investigation at that time.

Objectives

In the present project, current data on the exposure of the general population in Germany are to be obtained. The aim is to update and expand the existing data basis (e.g. with regard to the frequency range covered and the federal states taken into account). If possible, the data should be collected in regions where pipeline construction measures are planned. Where possible within the project duration, before and after situations should be compared. Exposures from sources not covered by the Ordinance on Electromagnetic Fields (26th BImSchV) (electrical appliances, low-voltage installations) are to be included.

Implementation

In the first phase of the project, the state of the art in science and technology relevant to the project will be reviewed. This includes the evaluation of relevant technical literature with regard to the technical procedures used in comparable investigations (measuring devices, frequency ranges, measuring duration). Details of the study protocol (selection of measurement sites, contacting possible subjects, development of an activity diary) will also be worked out, taking into account the findings from previous studies. Also part of the first project phase is the testing of portable measuring devices ("personal dosimeters") available on the market. Based on the results of the first project phase, the actual data collection will begin in 2022.

The occurrence of contact currents in daily life, especially in the vicinity of power supply facilities, is to be investigated. On account of the expected higher ground field strengths, HVDC installations are to be included into the analysis as far as possible. Moreover, dosimetric models for various scenarios and population groups are to be developed which can be used for specifying the electric field strengths for the various tissues within the body when spark discharges and contact currents occur.

Project management: Danube University Krems, Department for Integrated Sensor Systems, Vienna
Start: 1 April 2020
End: 31 March 2022

Background

The high-voltage direct current transmission lines (HVDC) planned in Germany will emit static magnetic fields and, when designed as overhead lines, also static electric fields and possibly space charge clouds, which result in slowly varying quasi-static fields. In order to determine the exposure of the population, these fields must be measured. The progress in detecting exposure through static electric and magnetic fields in the vicinity of high-voltage direct current (HVDC) transmission lines and hybrid HVDC and high-voltage alternating current (HVAC) transmission lines largely depends on how reliable, low-maintenance, and mobile the measurement technology used is. In particular, difficulties in detecting static electric fields prevent fast, meaningful measurements.

The detection of the static electric field is associated with difficulties compared with the measurement of the low-frequency electric fields of high-voltage alternating current (HVAC) transmission lines. Because the measurement results strongly depend on the temperature and on the space charge or ion flow, the data output drifts slowly. As a result, the measuring systems often have to be recalibrated. The measurement is often subject to errors, especially at low field strengths. In addition, a strong distortion of the electric field results from the measuring system itself. In the presence of ions, an accumulation of space charges occurs near the sensor because the directional ion flow along the field lines. These space charges generate an additional electric field in the vicinity of the sensor; this superimposes the field to be measured on the line and can falsify the measurement result. This is particularly relevant in the vicinity of HVDC transmission lines, which are surrounded by higher ion concentrations.

Objective

Measurement technology must be developed for the reliable, cost-effective, and accurate detection of static electric fields in the vicinity of HVDC transmission lines. The primary objective of the project is the identification of field distortion-free, ion flux and potential-independent miniaturised measurement methods for the measurement of static and low-frequency electric fields in the typical environment of HVDC transmission lines and HVDC-HVAC hybrid lines as well as the testing, adaptation, and validation of these methods.

Implementation

In the first phase of the project, the researcher will review the state of the art in science and technology relevant to the project. This includes the evaluation of relevant technical literature with regard to suitable technologies, sensor designs, and readout procedures as well as the conditions that occur in the effective range of the lines. Based on this data, a catalogue of requirements for the measurement system will be drawn up, and the concept for the measurement system is developed with reference to this. The first phase of the project also includes a preliminary study based on computer simulations in order to be able to estimate the expected characteristics of the system in advance.

Based on the results of the first project phase, the construction, adaptation, and calibration of the measurement and calibration system will begin in 2020.