This book describes a new, extremely low frequency (ELF)/ very low frequency (VLF) miniaturized transmitter concept, based on the mechanical motion of permanent magnets or electrets. The authors explain how utilizing the very high energy density of modern ferromagnetic and ferroelectric materials, such “electromechanical transmitters’’ can provide much higher field generation efficiency than conventional antennas, thus enabling practical ELF/VLF wireless communications links. The text begins with the fundamental challenges of such links and provides an historical overview of the...