A Three Degrees of Freedom Structured Resonant Galvanometer for Noninvasive Passive High-Sensitivity Monitoring

This article mainly develops a kind of three degrees of freedom (DOF) structured resonant galvanometer (abbreviated as 3DS-RGM) with high sensitivity, as a new solution to the challenge of sensor nodes for ac current monitoring. The developed 3DS-RGM is typically comprised of three coupled magnetic cantilevers, given differentiated magnetic characteristics. When ac current is applied, the detecting cantilever, any of the side ones, subjected to the maximum magnetic force, passively outputs a large amplitude signal. A passive ac current sensing theory is proposed and demonstrated by fabricating a three-cantilever prototype. A high sensitivity, up to 0.624 V/A, is experimentally obtained with an increase to 1.5 times compared to that of single DOF structured resonant galvanometer. The observed output increase in the detecting cantilever is discussed and analyzed from the viewpoint of the energy transfer contributed by the other two sensing ones. The sensitivity of the developed 3DS-RGM can be further improved by combining with other known schemes for realizing both passive and non-invasive measurement of sensor nodes in wireless sensor networks (WSNs) applicable to industrial fields such as frequency conversion equipment and smart grid.