Enlarged Modulation Rate for Narrowband Magnetoelectric Mechanical Antennas Through Predistortion Waveform Design

Abstract

High mechanical quality factor ( ${Q}_{m}$ ) for a magnetoelectric (ME) mechanical transmitter is normally desired to decrease the mechanical damping and thus to improve the coupling efficiency. However, the ring-up/down process requires a prolonged duration due to the narrowband characteristics of a high-Qm ME antenna, which causes severe intersymbol interference (ISI) and significantly limits the data transmission rate when conventional modulation schemes [e.g., amplitude shift keying (ASK)] are adopted. In this work, we propose a predistortion waveform design to suppress the ISI when transmitting a bitstream with high symbol rate for a narrowband ME antenna. Different from the arbitrary waveform design without any constraints, we limit the peak voltage of the predistortion waveform three times the level of the stable value after considering an economic power amplifier design. Accordingly, a modified binary ASK (modified BASK) modulation scheme is established. Experimental and simulation results show that modified BASK achieves a fivefold bandwidth improvement with only a 20% reduction in efficiency. Experimental results show that reliable communication rate based on the proposed waveform design can reach 1000 bps at a 15 m communication distance, while the counterpart for conventional BASK method is only 500 bps with 10 m distance. The proposed predistortion waveform and the established modulation method circumvent the mutual limitation between the information bandwidth and the physical bandwidth for a very-low frequency (VLF) mechanical antenna and are believed to speed up the communication application for ME antennas in VLF band.