Tech Briefs

LC Circuits for Diagnosing Embedded Piezoelectric Devices

Failures are readily identified through changes in resonance frequencies.

A recently invented method of nonintrusively detecting faults in piezoelectric devices involves measurement of the resonance frequencies of inductor-capacitor (LC) resonant circuits. The method is intended especially to enable diagnosis of piezoelectric sensors, actuators, and sensor/actuators that are embedded in structures and/or are components of multilayer composite-material structures.

In this method, a small induction coil is connected to each piezoelectric component that is embedded in the affected structure, composite material, or component by way of the electrical leads used for the basic sensor/actuator function. This connection is made manually or remotely during diagnosis of the piezoelectric component. Thus, what is formed, in addition to the basic sensor/actuator circuit, is an LC resonant circuit, in which the piezoelectric component acts as the capacitor. The inductance of the coil does not vary appreciably under most conditions, but the capacitance (and, hence, the resonance frequency) changes significantly if the piezoelectric device fails. Hence, a significant change in the resonance frequency can be taken as an indication of a failure of the piezoelectric device.

The resonance frequency can be measured in a conventional manner, either by induction or by direct connection via electrical leads. If a structure contains multiple embedded piezoelectric devices and the LC circuit of each piezoelectric device has a unique assigned resonance frequency, then one can rapidly and easily interrogate all the devices in a spectral scan over the range of assigned resonance frequencies. In the resulting spectral plot, a significant deviation of any of the resonance peaks from its assigned frequency indicates the failure of the corresponding piezoelectric device.

This work was done by Richard L. Chattin, Robert Lee Fox, Robert W. Moses, and Qamar A. Shams of Langley Research Center. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Semiconductors & ICs category.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Langley Research Center, at (757) 864-3521. Refer to LAR-16549-1

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LC Circuits for Diagnosing Embedded Piezoelectric Devices (reference LAR-16549-1) is currently available for download from the TSP library.

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