Table 3.3. Some Rules of Thumb

1. Wetter materials (muscle, high-water content tissues) are generally more lossy than drier materials (fat, bone) and hence absorb more energy from electromagnetic fields.
   
   
2. The SAR is higher when the incident E-field is more parallel to the body than perpendicular to it.
   
   
3. The SAR is higher when the cross section of the body perpendicular to the incident H-field is higher than when the section is smaller.
   
   
4. Sharp corners, points, and edges concentrate E-fields. When placed perpendicular to E-fields, conducting wires and plates cause minimum perturbation to the fields; when placed parallel to them, maximum perturbation.
   
   
5. A uniform incident field does not generally produce a uniform internal field.
   
   
6. Depth of penetration decreases as conductivity increases, also as frequency increases.
   
   
7. Objects small compared to a wavelength cause little perturbation and/or scattering of electromagnetic fields.
   
   
8. Below resonance, the SAR varies approximately as f ².
   
   
9. For E polarization, SAR increases faster than f ² just below resonance; just beyond resonance, SAR decreases approximately as 1/f and then levels off. Variation of SAR with frequency is most rapid near resonance.
   
   
10. Near resonance and below, SAR is greatest for E polarization, least for H polarization, and intermediate for K polarization.
    
    
11. For E polarization, the SAR increases as an object becomes longer and thinner, and decreases as an object gets shorter and fatter.