A wireless electric field sensor for measuring an electrical potential treatment chair is proposed. Research on the treatment effects of the electric field generated by high-voltage (HV) electrodes at low frequencies, in this case, 50 or 60 Hz, has been conducted. However, most studies have only provided the value of the voltage applied to the HV electrodes, not the electric field generated by those. Therefore, it is necessary to provide the value of the electric field to verify the treatment effects. Because the electric field by the chair is too high to be measured by conventional sensors, it is necessary to develop a sensor that can adaptively measure the low and high electric field. The proposed sensor has an adaptive voltage gain that relies on digital potentiometers, which exert control for the proper gain depending on the field strength. Using a capacitive dipole probe, the electric field generated by the HV electrodes applied the voltage of 7.2 kV at 60 Hz was measured at diverse distances. It was found that the electric field was measured from 1.3 to 45.5 kV/m. For wireless notification, the sensor is equipped with a Wi-Fi module in a microcontroller unit.

This paper presents a curved-retrodirective beamforming system for improving microwave power transmission efficiency in the Fresnel region. Since microwave power transmission in the far-field region has very low efficiency, studies on the Fresnel region are being actively conducted. In these studies, a retrodirective beamforming (RDB) technique is popular. The RDB system with a sub-array structure was a realistic structure that reduced system complexity. However, the transmission efficiency is lowered because the beamwidth of the transmitter antenna element is narrow. To solve this problem, this paper proposes a curved-retrodirective beamforming system that can focus the microwave power on the receiver. The proposed system uses the peak gain of the transmitter antenna element by using tilted beams to improve transmission efficiency. The system design method that can maximize the transmission efficiency is also presented depending on the given conditions such as transmission distance, characteristics of the transmitter and receiver antenna. The simulation showed a reduction in power leakage compared to the conventional system. The fabrication and measurement validated the efficiency improvement of the proposed system for IoT devices in the Fresnel region.