Development of Induced and Contact Current (ICC) Limits in the HF and VHF Regions

Radio frequency (RF) exposure limits have existed in one form or another since the early 1950’s. These limits were initially given in terms of either electric field strength in volts per meter (V/m), magnetic field strength in amperes per meter (A/m), or equivalent plane wave power density in watts per square meter (W/m2). These field parameters are relatively easy to measure or calculate using commercially available broadband instrumentation. However, from 100 kHz to 10 GHz, the basic RF dosimetric quantity is specific absorption rate (SAR) in watts per kilogram (W/kg). Hurt [1], has published an excellent overview of SAR based RF dosimetry. SAR is a difficult parameter to measure outside of the laboratory, and the purposes of field exposure limits are to insure that SAR limits will never be exceeded, thus preventing either whole body or localized heating in tissue. Another consequence of exposure to RF fields is that currents can be induced in the body, which can also cause localized heating, particularly in areas with a small cross-sectional area, such as the wrist or ankles. It is therefore necessary to limit the magnitude of these currents induced in the body. This paper will review the historical development of these induced and contact current (ICC) limits, their current status, and the need for future refinement and development of these limits, as well as techniques to measure them accurately.