A Novel DC Current Sensor Using SMA Controlled Piezoelectric Bimorph Cantilever

A new approach to measure direct current (DC) using shape memory alloy (SMA) tuning piezo cantilever resonant frequency technique is proposed in this work. The proposed current sensor system is designed using an electrically insulated SMA wire surface mounted on the cantilever beam with piezoelectric actuator. The cantilever beam is maintained at resonance using a closed loop piezo resonator circuit and the current ‘I’ to be measured is given to the SMA wire. The current induced temperature change of the SMA wire produces a mechanical shape change and produces a stiffness change to the resonating cantilever beam. The shift in resonant frequency due to the stiffness change is measured, which is related to the input electrical current ‘I’ to the SMA wire. The key enabling concept of this proposed work is to alter the cantilever resonant frequency using the shape changing property of SMA wire with input unknown electric current. The analytical model of the current sensor system is derived and the results are compared with the experimental results. The SMA coupled with piezo actuator based resonant current sensing system is evaluated for the input current range of 0 to 0.5A. The proposed current sensing concept is simple and completely novel and it is found that it has very high sensitivity to current and result is piecewise linear.