Wireless energy transfer: Touch/proximity/hover sensing for large contoured displays and industrial applications

Abstract

This paper presents a new kind of touch sensor that utilizes the concept of wireless energy transfer (WET). A near-field sheet like a waveguide-based WET system was used for this purpose based on its geometric suitability. The approaching target object (human finger bioimpedance) disturbs the overall sheet reactance based on a complex power conservation equation at the resonant frequency. Thus, the drop in the efficiency of the power transfer can be utilized to carry out the task of sensing. The WET sensor was designed to operate at 29 MHZ, with a power transfer efficiency of -3.18 dB. An experimental demonstration was performed by feeding a 10 V peak-to-peak sine wave at the transmitter end and reading a dc output using a full-wave rectifier and multimeter at the receiver end. The system was designed to achieve a drop of 2.1 V when a touch was registered. The sensor was also designed to operate in the proximity mode. For operation in the proximity mode, the receiver had to be a wave trap cavity. This was achieved by designing the receiver to have a cylindrical wave cavity arrangement. The WET sensor had to be unaffected by the presence of an electric field, and this was demonstrated by carrying out sensing while the sensor was located under an LCD, which has a considerable electric field. It was experimentally demonstrated that the sensor had a linear output in proximity mode. Proposed sensor could be ideal candidate for: 1) touch screen panels; 2) human-robotics interactions; and 3) security applications.