Abstract
The electromechanical impedance method has been seen as a promising tool for structural health monitoring regarding different types of structures and purposes. Most importantly, this method can be used in real-time applications. Frequently, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent electromechanical impedance functions and therefore infer about the presence, position and extent of an existing damage. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively, in order to increase the probability of successful detection of damage at an early phase. The literature describes many miniaturized systems that can monitor large structures, however, presenting serious restrictions on data acquisition capabilities. This paper presents a hardware that is not limited to any data acquisition restriction, exhibiting an innovative way to measure the electromechanical impedance of multiplexed bonded transducers. Each logical block of the proposed architecture is presented in detail. The proposed system not only avoids costly fast Fourier transform analyzers/ algorithms, but also evades high-speed data acquisition hardware. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure, and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer.
Highlights
Structural health monitoring (SHM) can be understood as a detection strategy, which aims at identifying and locating damage in several types of structures
The fast Fourier transform (FFT) algorithm can only generate precise results if the data points are acquired at a rate as large as two times the higher frequency presented in the acquired signal (Nyquist Theorem)
Experiments were conducted in two different structures to verify precision, stability, repeatability and capability of detecting structural modifications in the studied structures
Summary
Structural health monitoring (SHM) can be understood as a detection strategy, which aims at identifying and locating damage in several types of structures (civil, naval, mechanical, aerospace etc.). Peairs et al (2004), for example, studied hardware difficulties related to the EMI technique and proposed a low-cost approach that uses an operational-amplifier-based device (Fig. 3a) This method improves the accessibility of impedance-based structural health monitoring (SHM) and does not utilize cumbersome equipment. The FFT algorithm can only generate precise results if the data points are acquired at a rate as large as two times the higher frequency presented in the acquired signal (Nyquist Theorem) When this is not the case, the phase displacement calculated is higher than 90 degrees, and the real part of the PZT impedance becomes wrongly negative. The proposed measurement methodology overcomes these problems by allowing the proposed hardware to deal directly with the process of calculating the EMI parameters, without requiring complex instrumentation architectures (key point # III). The process is repeated within a pre-defined time delay to continuously monitor the structure
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call