A theoretical study of acoustically driven antennas

Acoustically driven antennas operating at resonant wavelengths up to 105 times smaller than electrical antennas offer great potential for portable, low power communication systems in the very low frequency and low frequency range. Acoustic antennas with real resonant impedances have been demonstrated to offer orders of magnitude better total efficiency compared to similar sized, subwavelength electrically small antennas exhibiting large reactances. While most acoustic antennas share favorable impedance characteristics offering significant matching efficiency advantages over electrically small antennas, radiation efficiency varies greatly based on the implementation of the acoustically driven antenna. This paper presents a theoretical analysis of the three primary methods for implementing acoustically driven radiating elements, investigating both radiation and matching efficiencies comprising the total antenna efficiency. Radiation from the linear movement of unipolar charge driven both piezoelectrically and capacitively, the piezoelectrically actuated rotation of fixed dipole charges, and from flipping dipoles inside strain driven piezoelectrics are all presented and analyzed in terms of their design parameters and fundamental challenges. The efficiency of each type of acoustic antenna is referenced to an equivalent electrical antenna to benchmark the performance to a more familiar framework. Of the analyzed antenna types, piezoelectric alternating dipole antennas exhibit the most promise, with efficiencies more than a million times greater than electrically small antennas expected as piezoelectric materials, and resonator designs are optimized for acoustic radiation.