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Isosurfaces for Near-Field Characterisation of Transmitter ICNIRP Boundaries

A description of how isosurfaces may be used to evaluate radiation hazard safety boundaries around transmitter structures against ICNIRP guidelines.

Introduction

Radiation hazard analysis is an essential component of modern communication engineering.  All radiating entities from mobile communication devices to fixed commercial land-based transmitters should comply with radiation safety guidelines.  The International Commission on Non-Ionizing Radiation Protection (ICNIRP) researches and publishes a commonly accepted guideline for radiation protection [1].  These guidelines are published in terms of basic restrictions (SAR-based) and reference levels (field-based).  FEKO is an ideal simulation tool for both these methods of estimation and this page focuses on how FEKO may be used to predict and visualize reference levels.

 

Physical Problem

In this example a large truss structure is used to support omnidirectional GSM antennas and Yagi-Uda antennas at FM frequencies.  These antennas transmit high energy levels and it is required to determine where the ICNIRP safety boundaries are to ensure the safety of personnel who work on the structure.  The simulation is done to determine the boundaries of the reference levels for public and occupational exposure guidelines.  The public reference level boundaries are plotted with a yellow isosurface and the occupational exposure boundaries are plotted with red isosurfaces.  These plots indicate that personnel without RF training should not cross the yellow boundaries and personnel that have RF-training should not cross the red boundaries.  The full truss structure is several wavelengths tall at GSM frequencies and  was simulated with the Multilevel Fast Multipole Method (MLFMM).

 

Simulation Results

The isosurfaces are plotted from a top and a front view to allow easy visualisation of where personnel can safely work on the truss.  Figure 1 presents an analysis of the omnidirectional GSM antenna boundaries and Figure 2 of the directional FM Yagis.  Click on the images to enlarge them.

Figure 1:  Omnidirectional GSM ICNIRP isosurfaces
(a) Front view
(b) Top view

OMNI topview (small)
Figure 2:  RF Yagi-Uda arrays ICNIRP isosurfaces
(a) Front view
(b) Top view
Yagi frontview (small)
Yagi topview (small)

 

References

[1] International Commission on Non-Ionizing Radiation Protection, "Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (Up to 300 GHz)," ICNIRP website.