Enhanced SLF radiation efficiency in a piezoelectrically driven magnetic pendulum transmitter

Long-wave radio station based on an electrically small antenna and mechanical transmitter based on a rotating permanent antenna are commonly used for super low frequency (SLF, 30–300 Hz) communication. The current challenge is the difficulty in developing both an efficient and a miniaturized SLF transmitter. Enlightened by the advantages of piezoelectric motor over conventional electromagnetic motor in terms of efficiency and the output torque in low frequency band, we propose a piezoelectrically driven magnetic pendulum transmitter by combining a magneto-mechano-electric (MME) cantilever and a swinging magnet in this work. The magnetic force coupling between the MME cantilever and the swinging magnet is optimized by changing the thickness and the attached position of the used Metglas laminates. The experimental results show that the piezoelectrically driven magnetic pendulum transmitter has a working frequency of 57 Hz, and a flux density of 149 f Tpk at 100 m distance could be expected with a low power consumption of 40.64 mW. When driving the same magnet with an electromagnetic motor, however, the required power consumption reaches 4.2 W for 57 Hz magnetic field radiation. By dividing the induced magnetic moment over the consumed power, the effective radiation efficiency of our proposed piezoelectrically driven SLF magnetic pendulum transmitter significantly increased from 0.55 to 17.4. This proof-of-concept work is believed to open a dimension for the design and the application of efficient SLF mechanical transmitter in the future.