This paper describes the development of the next generation of an extremely compact,
wireless impedance sensor node for use in structural health monitoring (SHM) and
piezoelectric active-sensor self-diagnostics. The sensor node uses a recently developed,
low-cost integrated circuit that can measure and record the electrical impedance of a
piezoelectric transducer. The sensor node also integrates several components, including a
microcontroller for local computing, telemetry for wirelessly transmitting data, multiplexers
for managing up to seven piezoelectric transducers per node, energy harvesting and storage
mediums, and a wireless triggering circuit into one package to truly realize a
comprehensive, self-contained wireless active-sensor node for various SHM applications. It
is estimated that the developed sensor node requires less than 60 mW of total power for
measurement, computation, and transmission. In addition, the sensor node is
equipped with active-sensor self-diagnostic capabilities that can monitor the condition
of piezoelectric transducers used in SHM applications. The performance of this
miniaturized device is compared to our previous results and its broader capabilities are
demonstrated.
This paper presents a piezoelectric sensor diagnostic and validation procedure that performs in-situ monitoring of the operational status of piezoelectric (PZT) sensor/actuator arrays used in structural health monitoring (SHM) applications. The validation of the proper function of a sensor/actuator array during operation, is a critical component to a complete and robust SHM system, especially with the large number of active sensors typically involved. The method of this technique used to obtain the health of the PZT transducers is to track their capacitive value, this value manifests in the imaginary part of measured electrical admittance. Degradation of the mechanical/electrical properties of a PZT sensor/actuator as well as bonding defects between a PZT patch and a host structure can be identified with the proposed procedure. However, it was found that temperature variations and changes in sensor boundary conditions manifest themselves in similar ways in the measured electrical admittances. Therefore, we examined the effects of temperature variation and sensor boundary conditions on the sensor diagnostic process. The objective of this study is to quantify and classify several key characteristics of temperature change and to develop efficient signal processing techniques to account for those variations in the sensor diagnosis process. In addition, we developed hardware capable of making the necessary measurements to perform the sensor diagnostics and to make impedance-based SHM measurements. The paper concludes with experimental results to demonstrate the effectiveness of the proposed technique.
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