A Study of SAR Values in Induction, High Frequency and Microwave Nearfields

Measurements of electric and electromagnetic field for safety controls are made by E field probes, typically with scaling in power flux density, indicating what would be true only for plane propagating waves. This presentation addresses the fact that such measurements at microwave frequencies have to be at a minimum distance from the nearest accessible part of the equipment emitting the field, and describes the different rationales for the validity of the 50 mm distance used since many years with e.g. microwave ovens and industrial equipment. - Since the emission of electric field energy dominates over that from the magnetic field in high frequency equipment, almost quasistatic E field emission conditions occur, resulting in a much weaker power absorption in human tissues than assumed in the existing safety standards. The phenomena are quantified, and a relaxation of the E field emission limits in industrial standards is proposed for such non-radiating conditions, as is a 150 mm minimum measurement distance in combination with barriers, etc., hindering access. - In induction equipment, the quasistatic magnetic fields instead dominate, and there is again a much weaker power absorption in human tissues than assumed in the existing safety standards. Some methods for safety assessments will be given in the oral presentation only, due to the limited space in this manuscript.