Underground Communications Using Capacitive Data Transfer Devices

This paper explores the feasibility of applying the capacitive power transfer (CPT) technology in underground data transmission applications. Based on the electrical properties of soils, the paper extends the existing CPT air coupler model into a more generalized model. The autonomous push-pull inverter is selected to power the CPT system and modified to further the data transmission range. With a designed load shift keying (LSK) circuitry, this self-oscillating inverter regards the data as a sequence of impedance changes, resulting in operation frequency drifts. A Frequency Shift Keying (FSK) demodulator is applied to capture the frequency variations and recover back to data. The proposed design has been simulated, verified, and implemented on a complete prototype. Various testings have been carried out, and the results are satisfactory.