Performance of Electrically Small Conventional and Mechanical Antennas

Antennas that operate in the very low frequency (LF) band and below are useful for a number of applications, including long-distance and underwater communication. When constrained in size, the antennas are electrically small and very inefficient. This has motivated the need for novel approaches to LF antenna design. Here, we present concepts for antennas that generate electromagnetic signals from mechanical motion. We first review the generated fields and efficiency of conventional magnetic and electric dipole transmitters. This is then extended to their mechanical counterparts for comparison. Our results show that the motion of magnets or electrets (the electrical analog of a magnet) can efficiently radiate electromagnetic energy when coupled to a low-loss electromechanical suspension. Mechanical antennas, with spatial dimensions on the order of a meter, can theoretically exceed the performance of conventional short dipole and coil transmitters by more than eight orders of magnitude for frequencies of 1 kHz and below. This paper is intended to lay the foundation for future development involving the implementation of efficient, small form-factor, mechanically actuated antennas.