Education of the republic of uzbekistan tashkent state technical university named after islam karimov

 
RESULTS AND DISCUSSIONS 
Ultrasonic vibrating systems work effectively only in resonance mode, i.e. at the resonant 
frequency of the disk radiator. In almost all systems of automatic frequency control (AFC) of 
electronic generators, the criterion for tuning to the resonant frequency is the desire for a zero 
phase shift between the current and voltage on the piezoceramic elements of the emitter. 
In fig. 3 shows the amplitude-frequency characteristic of the ultrasonic oscillatory system 
(curve 3) in the form of the frequency dependence of the mechanical branch current (the current 
consumed by the emitter, minus the current due to the static capacitance of the piezoceramic 
elements of the emitter). , the real phase-frequency characteristic of the oscillatory system as a 
mechanical oscillatory system (curve 1) and the phase-frequency characteristic obtained by 
measuring the phase shift between the current and voltage on the piezoceramic emitter elements, 
obtained at different values of the static capacitance of the piezoelectric transducer (curves 2). 
These curves were obtained using an equivalent electrical model of an ultrasonic 
transducer (Fig. 2) with a resonant frequency of 22 kHz. These dependences are given as an 
example to illustrate the influence of the electric capacitance of piezoceramic elements on the 
frequency dependence of the phase shift between current and voltage across the emitter 
piezoelectric elements (curves 2). 
From the presented dependences it follows that a change in the electrical capacity of 
piezoceramic elements due to their heating during operation of the emitter leads to the fact that 

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the AFC system of existing ultrasonic generators, directing the phase shift between the current 
and voltage on the piezoceramic elements of the emitter to zero, forces the ultrasonic electronic 
generator at a frequency , which does not correspond to the resonant frequency of the ultrasonic 
vibrating system, but is slightly higher (curves 2 in Fig. to the right relative to the point 
corresponding to the maximum on curve 3).