Design optimization of embedded ultrasonic transducers for concrete structures assessment

Abstract

In the last decades, the field of structural health monitoring and damage detection has been intensively explored. Active vibration techniques allow to excite structures at high frequency vibrations which are sensitive to small damage. Piezoelectric PZT transducers are perfect candidates for such testing 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. The limited accessibility of in-service structures makes such an arrangement often impractical. 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. Up to now, the design of such transducers was essentially based on trial and error, or in a few cases, on the limitation of the acoustic impedance mismatch between the PZT and concrete. In the present study, we explore the working principles of embedded piezoelectric transducers which are found to be significantly different from external transducers. One of the major challenges concerning embedded transducers is to produce very low cost transducers. We show that a practical way to achieve this imperative is to consider the radial mode of actuation of bulk PZT elements. This is done by developing a simple finite element model of a piezoelectric transducer embedded in an infinite medium. The model is coupled with a multi-objective genetic algorithm which is used to design specific ultrasonic embedded transducers both for hard and fresh concrete monitoring. The results show the efficiency of the approach and a few designs are proposed which are optimal for hard concrete, fresh concrete, or both, in a given frequency band of interest.

Ultrasonic Monitoring of Crack Propagation of Notched Concretes Using Embedded Piezo-electric Transducers

“…Piezoelectric disc, which has the advantages of low cost, small size, light weight, fast response and etc., is more suitable for being used as a sensing element of embedded piezoelectric transducer (Kee et al 2013;Dumoulin and Deraemaeker 2017a). However, the piezoelectric disc is extremely fragile and vulnerable to be damaged.…”

“…Hence there will be inevitable matching problems between concrete and transducers, which are caused by irregular concrete surface or man-made operational mistakes (Xu et al 2012;Kee et al 2013). For in-situ application of the ultrasonic transmission technique, it has limitations in applicability in hard-to-access areas of concrete structures using external probes (Kee et al 2013;Dumoulin et al 2017a).…”

Embedding ultrasonic transducers in concrete: A lifelong monitoring technology

“…The embedded transducers have been developed at ULB-BATir and are made of a thin Lead Zirconate Titanate (PZT) patch which is a piezoelectric material [31,32] and surrounded by several coating materials (Fig. 1).…”

Validation of Self‐Healing Properties of Construction Materials through Nondestructive and Minimal Invasive Testing

“…However, it is necessary to assure that no coupling changes between the transducer and cementitious matrix are caused through stress–strain effects. Based on this knowledge, further research was carried out to develop low‐cost and application‐oriented transducers …”