Design of Embedded Piezoelectric Transducers for Structural Health Monitoring in Concrete Structures

In the last decades the field of structural health monitoring and damage detection has been intensively explored. Active vibration technique allows to excite the structure at high frequency vibrations which are sensitive to small damage. Ideal candidates for the generation of high frequency (ultrasonic) signals are piezoelectric PZT transducers, due to their small size, low cost and large bandwidth. Current ultrasonic systems are based on external piezoelectric transducers which need to be placed on two faces of the concrete specimen. This arrangement is often impractical due to limited accessibility when in service. An alternative is to embed permanently low-cost transducers inside the structure. Such types of transducers have been applied successfully for the in-situ estimation of the P-wave velocity in fresh concrete, and for crack monitoring. Nevertheless, major issues concerning the efficiency of these embedded transducers have been raised in previous studies. In the present study, we explore the working principles of embedded piezoelectric transducers in comparison to external transducers which are found to be significantly different. A simple Finite Element model of a piezoelectric transducer embedded in an infinite media is developed. It is coupled with a multi-objective genetic algorithm which is used to design specific ultrasonic embedded transducers.