Electro-Mechanical Characteristics of Shape Memory Spring for Simulataneous Sensing And Actuation

Electric impedance is widely used in imaging and detection techniques. The applications range from nondestructive testing, structural health monitoring, and geophysical imaging to medical imaging. The frequency of the signal used for the measurement ranges from less than 1 Hz to about 1 GHz. This paper addresses the measurement and evaluation of the phase-dependent electrical resistance, inductance, capacitance and impedance of a shape memory alloy (SMA) spring (BMX 150, Toki Corporation). The material characteristics can be obtained by means of their electromechanical impedance. Experimental procedures are implemented and the electrical characteristics are obtained for a wide range of frequency. The electrical resistance, inductance and impedance of the Bio Metal at the austenite and martensite phases are determined to be (9.465 - 9.95) Ω and (10.358 - 10.8) Ω, (0.458 - 0.38) μH and (0.458 - 0.36) μH and, (9.47 - 10.24) Ω and (10.36 - 11.11) Ω respectively for the frequency range of 100 kHz - 1 MHz. The quality factor of the Bio Metal ranges between 0.03 and 0.2 during heating and, between 0.028 and 0.022 during the cooling phase. The experimental results herein show that an equivalent circuit of the SMA spring is a series combination of resistor and inductor with a parasitic capacitance effect.