  The low propagation loss of electromagnetic radiation below 1 MHz offers
significant opportunities for low power, long range communication systems to
meet growing demands for IoT applications. Especially in the very low frequency
(VLF: 3-30 kHz) range and lower, propagation through tens of meters of
seawater, hundreds of meters of earth, and hundreds of kilometers of air with
only 2-3 dB of loss is possible. However, the fundamental reduction in
efficiency as the size of electrical antennas decreases below a wavelength (30
m at 1 MHz) has made portable communication systems in the VLF and low
frequency (LF: 30-300 kHz) ranges impractical for decades. A paradigm shift
from electrical to piezoelectric antennas utilizing strain-driven currents at
resonant wavelengths up to five orders of magnitude smaller than electrical
antennas offers the promise for orders of magnitude efficiency improvement over
the electrical state-of-the-art. This work demonstrates a lead zirconate
titanate transmitter >6000 times more efficient than a comparably sized
electrical antenna and capable of bit rates up to 60 bit/s using
frequency-shift keying. Detailed analysis of design parameters offers a roadmap
for significant future improvement in both radiation efficiency and data rate
in the new field of acoustically driven antennas.
