Estimating the Perception Threshold of Electrostimulation and Heating for Radiofrequency Contact Current

Radiofrequency contact current occurs when a human touches objects with different electrical potentials. For emerging wireless power transfer systems, this type of exposure is potentially more restrictive than direct exposure. The limits for contact current are prescribed in the international guidelines for human protection from electromagnetic fields, but its rationale is limited compared with that for direct field exposure. In this article, the perceptional threshold for electrostimulation and heating was evaluated based on computational dosimetry from 10 kHz to 10 MHz. First, the time course of the temperature rise was calculated until each subject perceived the contact current. Second, the perception of current was estimated considering the nerve activation modeling. The computationally estimated current threshold for nerve activation was consistent with the measured data at 100 kHz and increased linearly with increasing frequency, which was contrary to the measured threshold for perception above 300 kHz. By contrast, the estimated perceptual temperature increase was smaller at 100 kHz than at 300 kHz and above. These results indicate that the transient frequency of the threshold for stimulation and heating lies between 100 and 300 kHz, supporting the transition frequency of contact current in the international guidelines.