http://www.paper.edu.cn
-1-
Point-by-Point Scanning Piezoelectric Phased Array for
detecting damage for SHM
Xingang Li
1
，Zhenqing Wang
1
，Zhanwen Huang
2
1 College of Civil Engineering, Harbin Engineering University, Harbin, PRC, (150001)
2 Department of Mathematics and Statistics, University of Minnesota Duluth, 1117 University
Drive, Duluth, U.S., MN 55812-3000
E-mail：jackwinlxg@gmail.com
Abstract
The aim of the present work is to develop a system of smart devices that could be permanently attached
on the surface of the structure for monitoring cracks in most aerospace structures in isolated
environments. It is shown that temporal and spatial focusing can be achieved through synthetic
time-reversal array method for a linear phase array of sensors and actuators. A Piezoelectric phased
array system performs a point-by-point scan in which focusing allow the inspection of large areas.
Damage to the structure can be inferred if there is a significant change in the transient response of the
structure using the analysis of the amplitude of the received signal. The location of this damaged area
can be determined using the analysis of the time it reaches the transducer. By the method of synthesis
of received signal time delay from multiple sensors, we can considerably enhance the signal strength,
thus reducing the negative effects of noises to solve the tough problem of processing the echo signal.
The results suggest an accuracy better than 1 mm in finding the location of crack tips.
Keywords: monitoring cracks; piezoelectric phased array; point-by-point scan; received signal
1 Introduction
Active Structural health monitoring techniques are being developed to reduce operations and
support costs, increase availability, and maintain safety of current and future air vehicle systems
[1]
.
Among the available options for online structural health monitoring systems, piezoelectric sensors offer
special opportunities for developing sensor arrays for SHM system, because they are quick in response,
with high linearity, small, inexpensive and elastic wave generators/receptors that can be easily affixed
to a structure
[2, 3]
. They can be wired into sensor arrays and connected to data concentrators and
wireless communicators. Piezoelectric actuator/sensor system is used to generate or sense
high-frequency elastic wave propagation in the structure under inspection
[4-6]
and a reverse wave
technique is developed to locate the damage's position, shape and dimension using the obtained sensor
signals. When the outgoing wave reaches the surface of existing damages, the scattering and reflecting
wave propagation will be generated, which is recorded as sensor signals
[7]
.
Elastic waves in structures, which are sensitive to the change of the geometry and physical
properties of materials, can propagate over long distances and have been considered as a principal
candidate of potential signals in the active SHM system
[8, 9]
. Elastic wave based testing can potentially
detect varies of damages such as corrosion, delamination and cracks not only on the surface but also
inside the structures
[10]
. However, the difficulties of applying ultrasonic elastic wave based monitoring
lie on that the signals are not instinctually interpretable due to their dispersive characteristics and
complicated mode conversion phenomena due to wave reflection. This difficulty is further augmented
due to the interaction between host structures and incorporated piezoelectric actuators/sensors and
complicated electromechanical behavior in a smart SHM. Many investigations have been conducted to
develop robust diagnosis algorithm to extract health status information from the received sensor
signals.
In this thesis, efforts are focused on two critical problems: (1) the convergence of elastic wave
beams generated by the piezoelectric phased array; (2) the process of received signal generated by
reflecting wave propagation. We design a system which controls the piezoelectric phased array to
conduct point-by-point scanning, and model the control of wave beams in the process of phased
emission and phased reception
[11]
. By applying time-lapse algorithm to elements of the phased array,
control of wave beams is achieved. Meanwhile, finite element simulation of the control of wave beams
is conducted.
2 Models and Principles of active SHM systems
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