|dc.description.abstract||The dissertation presents the design, development and realization of two novel structures of high-power composite ultrasonic transducers. The proposed composite transducers as a novelty contain a central metal mass, so instead of the classical structure of the Langevin’s transducer (back mass - active piezoceramic block - front mass) the following structure is obtained: back mass - active piezoceramic block - central mass - active piezoceramic block - front mass. Active blocks contain one or more pairs of piezoceramic rings, which are mechanically connected in series and have opposite polarized orientations. The difference between the proposed structures is that in the first structure, the central mass is connected to the metal endings with two central bolts, while in the second structure the prestressing is achieved with a single central bolt, which connects only metal endings and is not in contact with the central mass. With the proposed composite transducer without the direct contact between the central mass and the bolt, problems related to impedance adjustment with a mechanical load can be avoided. The proposed structures also increase the total output ultrasonic power of the transducers. If the mechanical load is connected via an acoustic transmission line, composite transducers can produce thickness, radial, flexion, edge, torsion and other vibration modes in the working environment.
In order to model the proposed composite transducers, one-dimensional models and approximate three-dimensional matrix models are developed. Firstly, general one-dimensional models, which include all the constituent parts of the transducers, have been developed. Also, a one-dimensional model, which does not include impact of the central bolt, has been developed. A one-dimensional model, which neglects the central bolt impact, is, according to its structure, suitable for simultaneous operation analysis of both proposed composite ultrasonic transducers. Due to the complexity of the proposed structures, the three-dimensional matrix electromechanical models of complete composite transducers were developed using modular solutions of the three-dimensional model of piezoceramic rings and the three-dimensional model of passive metal endings. The advantage of the newly developed three-dimensional models of the transducers is reflected in the possibility of predicting the thickness and radial oscillation modes, as well as their mutual couplings. With a minor modification of the three-dimensional models it is possible to determine any transfer function of the observed composite transducer. In the dissertation, in addition to the analysis of the basic thickness resonant mode, special emphasis is devoted to the shape and position of higher resonant modes, as well as
to the impact of various parameters on their characteristics. By comparing the experimental measurements of the input electrical impedance, of the realized novel composite transducers, and the corresponding Matlab/Simulink simulation results, the accuracy of the proposed three-dimensional models compared to the one-dimensional models was confirmed.||en