A survey of mechanical antennas applied for low-frequency transmitting

The mechanical antenna (MA) is a new type of low-frequency (LF) transmitting antenna that generates an alternating electromagnetic (EM) signal through the mechanical movement of electric charges or magnetic dipoles, which is an interdisciplinary field including not only antennas but also electromagnetics, materials science, and dynamics. This principle of signaling makes it possible to break the constraints on physical dimensions decided by the wavelength of the traditional antenna so as to achieve LF communications with a smaller size and to provide a novel solution for long-range, underwater, and underground communications, navigation over the horizon, and geological exploring. Therefore, MA has become a research hotspot in the field of LF communications in recent 5 years, and this work proposed a survey on this topic of MA applied for LF transmitting. Firstly, we briefly review traditional low-frequency transmitting antennas and summarize the defect; then we introduce research progress of different implementation schemes for MA, comparing the signaling performance, advantages, and disadvantages of each scheme. Furthermore, we discuss the experiment setup, results, and related technology for MA including signal modulation methods. Finally, we explore prospects for future research about MA. This work presents a comprehensive and critical survey of small LF transmitters based on MA to help the readers to understand and identify the background, status, and challenges of research in this field.