Low frequency mechanical antennas: Electrically short transmitters from mechanically-actuated dielectrics

Abstract

Antennas that operate in the low-frequency (LF) band and below are useful for a number of applications. However, the long wavelengths result in very low efficiency for antennas that could be made portable. This has motivated the need for novel approaches for electrically short antenna design. Here, we present the concept of an electromagnetic transmitter that operates by mechanically moving bound static charge. The resulting motion induces electromagnetic fields that are similar to a short dipole antenna. However, the voltage, current, and resistance of a conventional antenna are replaced by force, velocity, and damping in a mechanical system. The mechanical system offers very high efficiency at low frequencies where impedance matching naturally occurs and mechanical structures have very low losses. We present a basic proof-of-concept demonstration by rotating a charged electret material up to 167Hz and measuring the resulting time-varying magnetic field. This work is intended to lay the foundation for future tests involving the implementation of efficient, small form-factor, mechanically-actuated antennas.