Electromagnetic Field Modelling: Development and use of NORMAN

The public are concerned about the health effects of electromagnetic radiation. Scientific research is needed to find out exactly how electromagnetic fields interact with the human body. These measurements cannot be done on live people and so calculations must be used.

NORMAN

NORMAN is a computer model that allows calculations to be made inside the body. NORMAN is based on information from MRI scans of a real man, adjusted to make him the same height and weight as the average or 'reference' man. A 3D image of the body is divided into over 8 million 2 mm cubes (voxels). The tissue type (e.g. bone, brain, muscle, liver) of each cube is defined.

Using NORMAN to define the effects of high frequency electromagnetic radiation (including microwaves)

Heating is the main effect of exposure to electromagnetic radiation with frequencies greater than 100 kHz. NORMAN can be used to calculate how much power/heat is deposited in a body exposed to these frequencies, a quantity known as the specific energy absorption rate (SAR).

The picture below shows the power that would be absorbed in each voxel if the body were subject to an electromagnetic field of 120 MHz. The red shading indicates the areas that are heated the most. Purple areas are heated the least.

NORMAN can also be used to calculate the maximum SAR produced by mobile phone handsets. At these frequencies the power is absorbed mostly in the skin and muscles at the side of the head. There is little penetration (heating) inside the skull.

Using NORMAN to define the effects of low frequency electromagnetic radiation (including power frequencies)

If a body is exposed to electromagnetic radiation at frequencies below 100 KHz then the main effects are the production of electric currents within the body. Power transmission and domestic electricity work in this range (50 Hz).

NORMAN can be used to model the currents produced by being close to a 50 Hz field. The red areas show where the strongest currents are. The strength of the current depends on how the field is applied and tend to be higher in tissues that conduct electricity well. In the example below, high currents are seen in the intercostal muscles, neck, urine, cerebrospinal fluid and intestines.

New developments: reference woman

A female phantom, NAOMI, has now been developed for electromagmetic field calculations.

Kirstie Grainger, Peter Dimbylow and Jill Meara

First issued as an article in July 2002
(revised June 2005)

Last reviewed: 7 December 2007