Advanced Power Control Scheme in Wireless Power Transmission for Human Protection From EM Field

The wireless power transmission (WPT) system must guarantee human protection from the electromagnetic (EM) field around the system in proportion to the increase of the transmit power. This paper presents an advanced power control scheme to reduce the EM field. The basic operation of the proposed scheme is the automatic control of the transmit power according to the proximity of the human body within a certain distance from the WPT system. For the initial design, the EM field simulation is carried out using the HFSS 3-D EM simulator. The initial regions around the system are set up according to the EM field simulation results and the human exposure guideline of the 1998 International Commission on Non-Ionizing Radiation Protection (ICNIRP). A WPT system is designed and implemented using the magnetic resonance in order to measure the EM field and confirm the final scheme. The system is operated at 1.8-MHz band to charge a 24-V 40-Ah lead-acid battery embedded in a docent robot. A laser sensor is also used to detect the proximity of the human body. Two communication schemes are used for automatic wireless charging and power control scheme. By the EM field measurement results of the WPT system, the power control scheme is finally confirmed. The performance measurement with a final scheme shows that the EM field is adaptively reduced to less than the guideline value depending on the proximity of the human body.