Influence of Bonding Delaminations on The Electromechanical Admittance (EMA) of a Multi-element Piezoelectric Transducer

The transducer is an essential part of all ultrasonic systems used for applications such as medical diagnostics, therapy, nondestructive evaluation, cleaning or other purposes because its performance is crucial for that of the entire device. Its health condition is thus vital to ensure proper operation. Defects within constitutive elements or loss of adhesion between them can significantly reduce the transducer performance. The objective of this work is to determine procedures to monitor the behavior of a multi-element probe during its lifetime and detect degradations before they significantly affect the performance of the system. To achieve this, electromechanical admittance-based (EMA-based) method is investigated numerically and experimentally. A simplified multi-element transducer element consisting of a piezoceramic bar, a bonding layer and a backing is studied and the influence of bonding delamination on EMA is investigated. This study considers two different types of delamination, which are named respectively ”side” (from one side and expands towards the other) and ”center” (from the center and expands outwards). First, three dimensional numerical models based on the finite element method are developed. Secondly, transducers with and without defects are mounted using 3D-printed backings and matching layers, and finally measurements are conducted using an impedance analyzer. Experimental results are found to be in good agreement with numerical ones and it is shown that changes in EMA could allow early detection of delamination defects in an ultrasound probe