Chirp-Rate Shift Keying Modulation for Mechanical Antenna Based on Rotating Dipoles

This article presents a novel signal modulation method to efficiently improve the data transmission capability of the mechanical antenna based on rotating dipoles. Such mechanical antennas were shown to be orders of magnitude more efficient than conventional antennas in the extremely low frequency (ELF, 3–3000 Hz) band. However, the signal modulation is constrained by inertia because this mechanical antenna relies on mechanical motion rather than on electromagnetic wave resonance. When using the existing signal modulation methods designed for circuit systems, the performance of the mechanical antenna is limited. Therefore, we presented an inertial compatible modulation method for the mechanical antenna called chirp-rate shift keying (CSK). In CSK modulation, the transmitted data are directly related to the driving torque, which can change instantly regardless of inertia. The orthogonal modulation methods of CSK were also established to achieve optimal detection. To demonstrate the feasibility of CSK modulation, we conducted a wireless communication experiment that used a rotary magnet-based mechanical antenna as the transmitter. The experimental results indicated that CSK modulation requires less torque and can achieve a higher reliable communication rate at the same bit error rate (BER) level compared to conventional frequency-shift keying (FSK) modulation.