Practical issues in the implementation of electro-mechanical impedance technique for NDE

Abstract

The electro-mechanical impedance (EMI) technique, which utilizes 'smart' piezoceramic (PZT) patches as collocated actuator-sensors, has recently emerged as a powerful technique for diagnosing incipient damages in structures and machines. This technique utilizes the electro-mechanical admittance of a PZT patch surface bonded to the structure as the diagnostic signature of the structure. The operating frequency is typically maintained in the kHz range for optimum sensitivity in damage detection. However, there are many impediments to the practical application of the technique for NDE of real-life structures, such as aerospace systems, machine parts, and civil-infrastructures like buildings and bridges. The main challenge lies in achieving consistent behavior of the bonded PZT patch over sufficiently long periods, typically of the order of years, under 'harsh' environment. This necessitates protecting the PZT patch from environmental effects. This paper reports a dedicated investigation stretched over several months to ascertain the longterm consistency of the electro-mechanical admittance signatures of PZT patches. Possible protection of the patch by means of suitable covering layer as well as the effects of the layer on damage sensitivity of the patch are also investigated. It is found that a suitable cover is necessary to protect the PZT patch, especially against humidity and to ensure long life. It is also found that the patch exhibits a high sensitivity to damage even in the presence of the protection layer. The paper also includes a brief discussion on few recent applications of the EMI technique and possible use of multiplexing to optimize sensor interrogation time.

Development and Integration of Hardware and Software for Active-Sensors in Structural Monitoring

“…Once the measurement was performed, the data was sent wirelessly to an XBee modem that was Three different parts of an impedance measurement were recorded: real impedance, imaginary admittance and impedance magnitude. The real impedance is used in impedancebased SHM as the primary damage detection measurement, because it is more sensitive to damage or changes in the structure [9,14]. The imaginary admittance measurement is used for sensor diagnostics, because the slope of the imaginary admittance line varies with PZT sensor condition [10,6], which would include sensor debonding and sensor breakage.…”

“…The theory has been substantially developed by Park et al [6,7,8], Bhalla et al. [9,10], Giurgiutiu et al [11,12,13] and Sun et al [14].…”

Structure Health Monitoring Method based on Electrio-Mechanical Impedance (EMI) Technique

“…By affixing PZT sensor to critical section of the bridge. In 2002, Bhalla et al and Naidu et al monitored the initial damage of concrete structure by using the EMI technique, and meanwhile they have also monitored the strength increase of concrete during curing by using the EMI technique and obtained the correlation between concrete stiffness and the peaks value of the EMI signal [5][6][7]. In 2002-2005, Giurgiutiu et al performed the structural online health monitoring in conjunction with the EMI technique and Lamb wave sensor into the structure.…”

Investigation of the effects of structure-sensor interaction on piezoceramic transducers for structural health monitoring applications

“…air, gel, water)), ((Brunner et al, 2004), p10), ((Schubert and Herrmann, 2012), p3635), semi-permanent ( (Bhalla et al, 2002), p492), ((Chetwynd et al, 2006), p302), or permanent ( (Bhalla et al, 2002), p492), ((Paget et al, 2003), p367).…”

“…Semi-permanent attachment of transducers using double sided adhesive tape was investigated by Bhalla et al (2002), (p492) and found to produce poor coupling with the host structure. Chetwynd et al (2006), (p306) found that a thin viscoelastic layer in the form of double sided tape to be successful even though it is a softer material than conventional epoxy adhesive.…”