Progress on Very/Ultra Low Frequency Mechanical Antennas

Mechanical antennas have attracted wide attention due to their outstanding properties of ultra small size and low power in existing long wave communications. Here, a review of progress on mechanical antennas used in very low frequency (VLF: 3 30 kHz) and ultra low frequency (ULF: 0.3 3 kHz) is presented. The topic of focus is on the performance analysis of permanent magnet-based and piezoelectric mechanical antennas, including both radiation mechanism and signal modulation. Moreover, basic mechanical antennas are generally classified in detail, and the radiation performance of various schemes is compared. It concludes the up-to-date progress on the mechanical antennas for providing a source of inspiration towards the future better outcome of designs and applications.