Title :
Variability in EMF permittivity values: implications for SAR calculations
Author :
Hurt, William D. ; Ziriax, John M. ; Mason, Patrick A.
Author_Institution :
Directed Energy Bioeffects Div., Air Force Res. Lab., Brooks AFB, TX, USA
fDate :
3/1/2000 12:00:00 AM
Abstract :
Digital anatomical models of man and animals are available for use in numerical calculations to predict electromagnetic field (EMF)-induced specific absorption rate (SAR) values. To use these models, permittivity values are assigned to the various tissues for the EMF frequencies of interest. There is, as yet, no consensus on what are the best permittivity data. This study analyzed the variability In published permittivity data and investigated the effects of permittivity values that are proportional on SAR calculations. Whole-sphere averaged and localized SAR values along the diameter of a 4-cm sphere are calculated for EMF exposures in the radio frequency range of 1 MHz to 1 GHz. When the dimensions of a sphere are small compared to the wavelength (i.e., wavelength inside the material is greater than ten times the dimensions of the object), the whole-sphere averaged SAR is inversely proportional to the permittivity of the material composing the sphere. However, the localized SAR values generally do not have the same relation and, as a matter of fact, vary greatly depending on the location within the sphere. These results indicate that care must be taken In choosing the permittivity values used in calculating SAR values and some estimate of the dependence of the calculated SAR values on variability in permittivity should be determined.
Keywords :
bioelectric phenomena; biological effects of fields; finite difference time-domain analysis; permittivity; physiological models; 1 MHz to 1 GHz; 4 cm; 4-cm sphere; EMF permittivity values variability; SAR calculations; animals; digital anatomical models; electromagnetic field-induced specific absorption rate values prediction; man; numerical calculations; Animals; Biological tissues; Data analysis; Dosimetry; Electromagnetic fields; Electromagnetic modeling; Permittivity; Predictive models; Radio frequency; Specific absorption rate; Animals; Anisotropy; Bone Marrow; Brain; Breast; Connective Tissue; Electric Conductivity; Electromagnetic Fields; Female; Humans; Models, Biological; Muscle, Skeletal; Radio Waves; Skin; Skin Physiology;
Journal_Title :
Biomedical Engineering, IEEE Transactions on