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

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, a long time for the ring-up/down process is resulted due to the narrowband characteristics of a high-Q_m ME antenna, which causes severe intersymbol interference (ISI) and greatly limits the transmitting data rate with conventional modulation schemes, e.g., Amplitude Shift Keying (ASK). 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 amplitude shift keying (modified BASK) modulation scheme is established. Experimental and simulation results show that modified BASK achieves a 5-fold 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.