Modeling and Experimental Characterization of Bonding Delaminations in Single-Element Ultrasonic Transducer

Ultrasonic transducers performance can be seriously deteriorated by loss of adhesion between some constitutive elements such as the active element, the backing, or the matching layer. In the present work, the influence of bonding delaminations on the performance of a single-element ultrasonic transducer, which is composed of a piezoelectric disk, a backing, and a matching layer, is studied numerically and experimentally. Based on the positions between layers, two cases, i.e., delaminations between ceramic and backing or between ceramic and matching layer, are considered. Each case involves three different types of delaminations, which are marked as delamination type (DT)-I, II, and III. DT-I, a circular shape delamination, starts from the center and expands towards the peripheric zone; DT-II, an annular shape delamination, starts from the peripheric zone and expands towards the center; DT-III is a sector shape delamination with a given angle. The numerical simulations are performed by the finite element method and the influence of delaminations on the electromechanical admittance (EMA) of the transducer is investigated. 3D printed backings and matching layers are mounted on a PZT sample to assemble delaminated single-element transducers. An impedance analyzer is used for experimental measurements. Comparison between numerical and experimental results shows a reasonable agreement making changes in EMA an interesting indicator to inform about the occurrence and severity of delaminations in a single-element ultrasonic transducer.

On the bandwidth and beam profile characteristics of a simple low frequency collimated ultrasound beam source

We numerically investigate the bandwidth and collimation characteristics of ultrasound beams generated by a simple collimated ultrasound beam source that consists of a piezoelectric disk operated near its radial mode resonances. We simulate the ultrasound beam generated in a fluid medium as a function of the excitation frequency for two cases: 1) free piezoelectric disk that corresponds to zero-traction along the lateral edge, and 2) fixed piezoelectric disk that corresponds to zero-displacement along the lateral edge. We present and discuss the physical mechanism underpinning the frequency-dependent collimation and bandwidth properties of the ultrasound beams. We observe that the collimated beam generated by the free disk repeatedly lengthens/shortens and also extends/retracts sidelobes with increasing frequency. Alternatively, fixing the piezoelectric disk results in a consistent beam profile shape across a broad range of frequencies. This facilitates generating broadband signals such as a Gaussian pulse or chirp, which are common in ultrasound imaging. Thus, the fixed piezoelectric disk finds application as a collimated ultrasound beam source in a wide range of applications including medical ultrasound imaging, scanning acoustic microscopy, sonar detection, and other nondestructive ultrasound inspection techniques.

Static Electromechanical Characteristic of a Three-Layer Circular Piezoelectric Transducer

The paper presents research related to the functional features of a novel three-layer circular piezoelectric actuator/sensor. The outer layers of the transducer are made of non-piezoelectric material. The middle layer comprises two elements—a piezoelectric disk, and a ring made of non-piezoelectric material. The additional external passive layer has a very important function; it protects the transducer’s electrical components against damage caused by external factors. Also, if sparking on the transducer wires or electrodes occurs, this layer prevents fire. So far, there is no analytical model for such a transducer. Closed-form analytical equations are important tools for predicting and optimizing the operation of devices. Thus, using both the Plate Theory and constitutive equations of piezoelectric materials, an analytical formula describing transducer deflection as a function of electrical loads has been found (electromechanical characteristic of the transducer). In addition, it is worth noting that under certain assumptions, the developed analytical model can also be used for two-layer transducers. The tests carried out show satisfactory compliance of the results obtained through the developed solution with both literature data and numerical data. Moreover, based on the obtained analytical model, the effect of selected non-dimensional variables on the actuator performance has been examined. These parameters include dimensions and mechanical properties of both piezoelectric disk and passive plates and strongly influence the behavior of the transducer.