Damage Detection Using Impedance Measurement With Magnetic Transducer

Impedance method has been explored for damage detection and identification. Typically, when the impedance sensor is integrated onto the mechanical structure to be monitored, its electrical impedance is directly related to the mechanical impedance of the host structure. Thus the change of impedance measurement before and after damage occurrence can be used as the damage indicator. Since the impedance information may be measured at relatively high frequency range, the impedance method could be sensitive to small-sized damage. Generally, piezoelectric transducers are employed in the impedance approach, which can serve as actuator and sensor simultaneously. In this research, a magnetic transducer approach is investigated for impedance based damage detection. To provide design guidelines, the analytical model of the resistive magnetic impedance measurement circuit is formulated. During the formulation, the two-way magneto-mechanical coupling between the transducer and the structure is systematically studied by using the Maxwell’s equations. The preliminary sensor enhancement is achieved by selecting the number of turns of wire in the electrical coil. Moreover, in order to reduce the negative effects of the high inherent inductance and large parasitic resistance of the coil with a large number of turns of wire, a new measurement circuitry is proposed, in which a negative resistive element and a capacitor are introduced to be serially connected with the original resistive circuit. Correlated numerical and experimental studies are carried out to validate the magnetic transducer in impedance based damage detection.