Health Monitoring of Single-element Piezoelectric Transducer Using Its Electromechanical Admittance.

The transducer is an essential part of all ultrasonic systems used for applications such as medical diagnostics, therapy, non-destructive evaluation, cleaning…because its health condition is vital to their proper operation. Defects within the active element, backing or other constitutive elements, loss of adhesion between layers can significantly weaken the performance of a transducer. The objective of this work is to determine procedures to monitor the behavior of a single-element probe during its lifetime and detect degradations before they significantly affect the performance of the system. To achieve this, electromechanical admittance (EMA) based method is envisaged numerically and experimentally. A simplified single-element transducer consisting of a piezoceramic disc, a bonding layer, and a backing is studied and the influence of bonding delamination on EMA is investigated. This study considers three different types of delaminations, which are named respectively "center" (circular delamination from the center of the disc towards the peripheric zone), "peripheric" (annular delamination from the peripheric zone towards the center), and "wedge" (wedge-shaped delamination with a given angle). For each case, a numerical model based on the finite element method is developed: a two-dimensional (2D) finite element analysis is implemented for the first two types of delaminations, taking advantage of their axisymmetric structure, and "wedge" delamination is modelled in three dimensions (3D). Then, transducers with different shapes of 3D printed backings are mounted and experiments are conducted using an impedance analyzer. Finally, experimental results are found to be in good agreement with numerical solutions and it shows that changes in EMA can particularly reveal the occurrence and extent of delamination in an ultrasound probe.