Impedance analysis technique for frequency domain characterization of magnetoelastic sensor element by measuring steady-state vibration of element while undergoing constant sine-wave excitation

Abstract

Circuitry and program code adapted for carrying out an associated technique for characterizing the response of one or more magnetoelastic sensor elements during exposure to an excitation field generated by an interrogation coil: including: (a) measuring a total sensor signal from the coil with the sensor element positioned within the excitation field within a spacing created by a winding of the coil; and (b) automatically determining: (i) a total measured impedance spectrum from said total sensor signal so measured, and (ii) a plurality of magnitude values representing the real part of a reconstructed impedance spectrum for the sensor element. The reconstructed impedance spectrum for the sensor element, having been calculated by subtracting an impedance generally attributable to the coil during the time an AC excitation signal is provided, from the total measured impedance. Subtraction of coil impedance from total complex impedance is accomplished by separate subtraction of the real part and of the imaginary part, represented as follows(ω)]=(ω)]−(ω)]  Equation (12)and(ω)]=(ω)]−(ω)]  Equation (13)where subscript 't' indicates total complex impedance, 's' indicates sensor element impedance, and “c” indicates coil impedance.