Nozdrachova K. Methods and means of excitation of ultrasonic pulses by capacitive method

In the dissertation work an actual scientific and practical problem is solved – the development of theoretical statements and means for excitation of high - frequency ultrasonic pulses by capacitive transducers in electrically conductive material samples with the increased sensitivity at the expense of increase of the ratio of amplitudes of a useful signal to noise. In the dissertation work the mathematical model of a capacitive transducer intended for excitation of ultrasonic oscillations in an electrically conductive product is developed for the first time by means of which two problems of electrostatics and the dynamic theory of elasticity for piecewise-homogeneous environment are solved. Diagrams of the acoustic field orientation are built experimentally and the main factors influencing the intensity of ultrasonic pulses excited by CT are determined. New designs of capacitive transducers designed for testing of electrically conductive products with different types of ultrasonic waves have been developed. The use of these converters increases the signal-to-noise ratio significantly. High-frequency excitation generators of high-voltage packets of unipolar and bipolar pulses for power supply of capacitive transducers were developed. The possibility of excitation of longitudinal and surface waves by capacitive transducers with ultrasonic field intensity sufficient for measurements, testing and diagnostics has been experimentally confirmed. The practical significance of the work lies in the technical feasibility of capacitive transducers usage for ultrasonic testing, measurement and diagnostics of electrically conductive samples. To implement the capacitive method, the following have been developed and manufactured: models of devices for studying the characteristics of CTs for various purposes; high- voltage pulse generators for power supply of CT; noise-resistant amplifier of ultrasonic signals; layout of the device for input pulses generation of supply units allowing to adjust the frequency, duration, sounding frequency, etc.; method of CT power generators output stages construction. The software solution for processing of device models for the research of characteristics of various function CT is created.