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

Fig. 2. Amplitude-frequency and phase-frequency characteristics depending on the 
change in electrical capacitance of piezoceramic elements. 
As noted earlier, the operation of an ultrasonic vibrating system in gaseous media is 
accompanied by strong heating of its structural elements, which leads not only to a decrease in 
the resonant frequency, but also to an increase in the electrical capacity of piezoelectric elements 
by 1.5 times ... 2 times. With a high quality factor of the system, due to errors in the operation of 
the AFC system (caused by the influence of the capacitance of piezoceramic elements), the 
intensity of ultrasonic exposure and the efficiency of the processes being implemented decrease. 
To eliminate the influence of the electrical capacitance of the piezoelectric elements on the 
frequency matching of the electronic generator with the ultrasonic oscillatory system, a scheme 
for receiving the current of the mechanical branch was proposed and developed, the phase-
frequency characteristic of which repeats the phase-frequency characteristic of the emitter as a 
mechanical vibrational system does not depend on the electrical capacity of the piezoceramic 
elements of the emitter. The essence of this approach is explained below. 
In fig. 3 shows an equivalent electrical circuit of an ultrasonic emitter, describing its 
operation near the frequency of mechanical resonance. 

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Mechanical Engineering
221 
Fig. 3. Equivalent circuit of an ultrasonic emitter with a piezoelectric transducer 
 
In this circuit, inductance L
M
is equivalent to the oscillating mass of the system, 
capacitance C
M
is the elasticity of the system material; active resistance R
MП
- resistance to 
mechanical losses, C
K
- electrical capacitance of piezoceramic elements, R
Д
- dielectric losses. 
Elements L
M
, C
M
, R
MП
form the so called mechanical branch of the equivalent electrical circuit 
of a piezoelectric oscillatory system with a complex resistance Z
КЭ
. 
The current flowing through the L
M
, C
M
, R
MП
elements is the current of the mechanical 
branch, the frequency characteristic of which (amplitude and phase) completely repeats the 
frequency response of the ultrasonic emitter, if it is considered as a mechanical oscillatory 
system. Thus, a new criterion for tuning the electronic generator to the resonant frequency of the 
oscillatory system is the tendency to zero phase shift between the voltage on the piezoceramic 
elements of the emitter and the current of its mechanical branch. 
Under ultrasonic action on gaseous media, the parameters of the emitters, such as the Q-
factor, resonance frequency and vibration amplitude, do not change, in contrast, for example, to 
liquid media, the wave impedance of which changes by orders of magnitude. ... when ultrasonic 
fields of high intensity are applied, which leads to a dynamic change in the parameters of the 
emitters. The only factor that determines the change in the resonant frequency of a radiator 
operating in a gas environment is the heating of its structure. The rate of change of the resonant 
frequency of the emitter is approximately 5 Hz / s. In this case, the requirements for the speed of 
the AFC generator system can be significantly reduced (in this case, the level of frequency 
modulation is reduced). 
The proposed new technical solutions were implemented in the creation of electronic 
generators operating as part of ultrasonic installations designed to create powerful acoustic fields 
in gaseous media. 
With an ultrasonic generator power of 300 W and a radiating disk diameter of 350 mm, 
ultrasonic vibrations were obtained with an intensity of up to 165 dB. The level of amplitude 
modulation of the current in the power supply circuit of the emitter does not exceed 5%, while 
when operating existing AFC systems (when working with emitters, the Q factor of which 
reaches 1000), the level of amplitude modulation reaches 70%. 
Practical results on coagulation of fogs [15], solid particles in the air, fire-extinguishing 
foam in the process of beer filling [16], drying of products [17, 18] have confirmed the high 
efficiency of the developed electronic generators. 

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