Sviatnenkoa A. Cylindrical piezoceramic transducers with internal baffles

The dissertation is devoted to the development of theoretical principles of calculations and design of cylindrical piezoceramic emitters with internal screens, taking into account the interaction of electric, mechanical and acoustic fields of emitters and the practical implementation of these principles. The developed methods allow to take into account the influence of design features of radiators on the physical fields formed by radiators in the course of work. Methods of the decision of wave problems of this type which consider features of sound emission by the investigated converters are defined. These features include the interconnection of electric, mechanical and acoustic fields in energy conversion and the interaction of the acoustic fields of the piezoceramic shell and the screen in the formation of acoustic fields, due to the multiple reflection of emitted and scattered sound waves. Considerable attention is paid to the processes: conversion of electrical energy into mechanical and mechanical into acoustic; interactions through the acoustic field of the piezoceramic shell and the inner screen of the emitter; interaction of energy conversion processes and its radiation into the environment. The influence of the design characteristics of the radiator on its physical fields is investigated. It is established that at radially symmetrical electric excitation of a cylindrical piezoceramic cover of the radiator introduction to its structure of the internal acoustic screen causes emergence of a number of physical features of formation of mechanical fields of the radiator. The regularities of the behavior of frequency and angular dependences of the amplitudes and phases of the total oscillatory velocity and its modes depending on: the size of the screens at a constant distance between the surfaces of the shell and the screen; from the distance between the longitudinal axes of the shell and the screen at constant screen sizes; composition of applied piezoceramics; physical characteristics of the liquid in the inner cavity of the radiator; the size of the piezoceramic shell - its radius and thickness. It is established that at small screen sizes the newly generated natural resonances go far down into the low frequency range. With medium-sized screens, these new intrinsic resonances of the mechanical field are not formed in the low-frequency region, but are concentrated in the resonant and high-frequency regions. It is established that in the formation of patterns of behavior of acoustic fields of emitters with an internal screen, taking into account the above interactions, physical factors such as resonant properties of the piezoceramic shell and the internal volume of the emitter with a screen and the degree of asymmetry. The main laws of influence of these physical features on the acoustic fields of the shielded emitter are to enrich the spectrum of its natural frequencies and significantly spread them in the low frequency range compared to the natural frequency of the piezoceramic shell in vacuum without changing the size of the shielded emitter. Quantitative values ​​of these changes in the values ​​of new acoustic resonances and amplitudes of acoustic pressure are different depending on the characteristics of a design factor. It is established that in the areas of maximum sound radiation, due to the own resonances of the internal volume of the emitter, its non-directional properties do not change. At the same time, at the frequencies of the maximum radiation caused by the acoustic components newly generated due to the asymmetry of the construction of the emitter modes of oscillations, this radiation acquires a significant direction. The main part of the acoustic energy is formed in the direction opposite to the direction of placement of the internal screen. Qualitative and quantitative influences of the above design parameters of shielded emitters on such characteristics of their electric fields as frequency dependences of their currents and input electric resistances are established. It is shown that the total excitation current of the emitter has two components: capacitive and dynamic. In most cases, the patterns of changes in total current in a wide range of studied frequencies are determined by the patterns of frequency changes of the dynamic component of the electric current. Through the study of the input electrical resistances of the shielded emitter, the ability of its electric field to absorb electric energy from the generator exciting the emitter is established. The adequacy of the proposed calculation models and the obtained numerical results to real cylindrical piezoceramic emitters with internal screens have been experimentally confirmed. The results of the dissertation work were implemented at the State Enterprise "Kyiv Research Institute of Hydraulic Devices" when performing design calculations of a cylindrical radiator for China.