A noninvasive AC current sensor with permanent-magnet biased PZT cantilever

Permanent magnet (PM) mounted piezoelectric cantilever current sensor with high sensitivity and no need of power supply attracted many attentions. This paper proposes an improved piezoelectric cantilever current sensor, of which the magnet mass is replaced by a ferromagnetic mass and a self-standing magnet bias. The PM-separated structure is of great advantage in resonance pre-setting adjustment and adapting to new application without sensitivity sacrifice. It also makes the sensor easy to be scaling down by MEMS technology because the process-incompatible magnet mass is not necessary in the vibration structure. Besides, the sensor has a slack requirement of installation. Experiment results of a built prototype show that the output voltage reaches 112mV when the AC current of a 45-turn coil is 10 mA, whose magnetic field equals to that of 10 mm apart from a straight wire with 1.8A current.