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Radiation Hazard Analysis with FEKO

ShipDeck.png
Determining radiation safety zones for ordinance, fuel,
personnel on the deck of a ship

Introduction

Radiation hazard regulations and guidelines are becoming commonplace all over the world. Designers of new communication equipment and system level integrators have to apply the appropriate standards in testing and validation processes for their devices and systems to ensure the safety of personnel and combustible stores in close proximity to sources of radiation.

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) publishes one of the globally accepted guidelines for radiation safety of humans, [1]. These guidelines provide reference levels for field strength and basic restrictions in terms of localised peak Specific energy Absorption Rate (SAR) and whole body average SAR, [2,3]. Millitary platforms typically have to conform to field strength regulations on the Hazard of Electromagnetic Radiation to Ordnance, Fuel and Personnel (HERO, HERF and HERP).

Numerical Techniques



Phantoms_SAR_cube_normal.png Phantoms_SAR_cube_jacket.png
(a) Normal use (b) Wearing a stab-proof jacket


Localized peak SAR positions for belt-worn TETRA radio

FEKO is ideally suited to radation hazard investigations in all of the above mentioned scenarios. Large platforms with several sources of radiation can be analyzed to evaluate designs relative to field strength regulations. FEKO provides full-wave solution methods for this task, i.e. the Method of Moments (MoM) and the Multilevel Fast Multipole Method (MLFMM). The Finite Element Method / MoM hybrid formulation (FEM / MoM) is applicable to the evaluation of designs with respect to SAR-based regulations. The following are examples of projects where these methods were applied.

High Power Transmitters


ICNIRP_transmitter_tower.png

ICNIRP occupational (red) and public (yellow)
radiation safety exclusion safety exclusion
zones around UHF TV transmitter.

High power transmitters are typically mounted on large structures, e.g. radio-mast truss structures, ships, buildings, etc. Although the positioning of these antennas mostly put them in hard to reach places, it is still important to characterize the radiation safety zones around the active antennas. In cases such as TV-transmitters or mobile phone base stations this information is important to servicemen who work on site, while the transmitter is active. Modelling of such structures are easily accomplished by drawing parametric models in FEKO, or by directly importing existing CAD data. Once the model is fully specified the large structures can be efficiently simulated by FEKO’s full-wave MLFMM formulation or high frequency Physical Optics (PO) and UTD (Uniform Theory of Diffraction) asymptotic approximation methods. Near-fields are typically computed to evaluate radiation levels. The best method to visualize the safety boundaries in near-fields are with iso-surfaces which are available as a visualisation option in FEKO’s postprocessing environment.

Personal Communication Devices


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Evaluation of safety zones near a high powered tactical radio
on a military vehicle

Terrestrial Trunked Radio (TETRA) [4] is a modern radio standard for use by anyone requiring a private wireless communication network. It presents several modes of operation, including communication via a base station backbone network, signal relaying via any TETRA mobile device, private device to device communication and communication with specified user groups. Multiple TETRA devices are often operated in close proximity to users and radiation safety must be assured for these users. FEKO was applied to investigate the radiation exposure of users of this system. The FEM/MoM hybrid formulation used the optimal FEM formulation to compute SAR levels inside human phantoms in a variety of typical TETRA operating scenarios inside cars or on a motorcycle, which was modelled with the MoM. Whole body average and localised peak SAR could be computed in all these scenarios for comparison with ICNIRP basic restriction guidelines.




Field_values_in_car.png
Phantom_SAR_onbike.png



Field values inside a vehicle from and active belt-worn TETRA radio     
Localized peak SAR position for
lapel-worn TETRA radio while seated
on a motorcycle

References

[1]
  ICNIRP, “Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz),” Health Physics 74 (4), pp 494-522, 1998



[2]   IEEE Std C95.3-2002, “IEEE Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields with Respect to Human Exposure to Such Fields, 100 kHz to 300 GHz,” 2003



[3]
  IEEE Standards Coordinating Committee 34, Subcommittee 2, “Draft Recommended Practice for Determining the Spatial-Peak Specific Absorption Rate (SAR) Associated with the use of Wireless Handsets - Computational Techniques,” IEEE SCC34/SC-2, Number IEEE P1529/D0.0, 2002



[4]
  TETRA Association, http://www.tetramou.com/.