Developing a passive DC current sensor

This paper reports a novel method for passive DC current sensing without using a cord separator. In this method, a piezoelectric thin-film cantilever with a micro-magnet on its end is positioned near a power cord. The DC current in the power cord induces a magnetic field, which generates a magnetic force acting on the micro-magnet. Consequently, the piezoelectric cantilever is bent and induces an output voltage that is sensitive to any rapid change of the DC current. Compared to Hall effect based sensing, this method has the advantages of no need of driving voltage or cord separators even for two-wire appliance cords. The device has been successfully fabricated and experimentally studied. It was found that the initial peak amplitude of the piezoelectric output voltage increases linearly with the DC current value upon “ON-OFF” switching. This self-sensing, non-contact passive piezoelectric DC current sensing method is more convenient than Hall sensors in measuring and monitoring DC current particularly for consumer electronics.