The object of research is thermal processes in Langevin-type piezoceramic electroacoustic transducers (PET), taking into account the housing. The piezoceramic electroacoustic transducers heat up during operation. Overheating of the converter leads to negative consequences, accompanied by a change in the parameters, characteristics of the device, as well as the failure of the converter. Or limitation on the duration and mode of operation, output power, current, amplitude and speed of oscillation of the converter. The paper investigates the effect of the housing on the temperature field of a Langevin-type PET by the finite element method, using modeling in SolidWorks. The results of temperature reduction of such cooling methods are shown: – filling the housing cavity with electrical insulating liquid, gas, a mixture of thermal paste; – use of holes in the housing; – changing the shape of the rear cover to have radiator side fins, vertical radiator fins, cylindrical radiator fins; – heat-resistant layer; – use of active air cooling at three different speeds. The most efficient 53 % and a uniform temperature field were found when filling with a mixture of thermal paste, but this solution is accompanied by additional experiments and a preparatory stage with the mixture. The cooling efficiency of 47 % was provided by active cooling – blowing with air, and this method requires additional equipment. Filling with insulating liquid gave a cooling efficiency of 27 % – an optimal result that does not require expensive investments. Slow blowing of the housing or adding only holes resulted in a decrease in the maximum heating temperature from 10 to 20 %, therefore, if the PET design allows the presence of holes, then it is necessary to rationally place them. Changing the shape of the back plate, heat-absorbing element, filling the housing with gas gave an efficiency decrease in the maximum temperature by 6–8 % compared to a closed housing with air. The research results make it possible to choose the optimal option for reducing the heating temperature of the Langevin-type PET to increase its efficiency and long-term trouble-free operation.
Radio and acoustic thermometry allow measuring the temperature of internal tissues at depths of several centimeters, which is of interest in early diagnosis of diseases, hearing diagnostics, identifying inflammatory processes, monitoring physiotherapy procedures, conducting surgical operations accompanied by patient cooling, long-term control of the engraftment process of transplanted organs, monitoring treatment of malignant neoplasms by hyperthermia and thermal ablation methods, as well as using synergistic effects in oncology.In the acoustothermometry research method, the internal temperature is measured by receiving and recording
Goal. Analysis of the effect of load inductance at the output of the class D amplifier for different values of the duration of «dead time» and assessment of the adequacy of existing mathematical models for calculating the THD at the output of the amplifier depending on the duration of «dead time». Methodology. The study of the effect of «dead time» on the THD was performed using a computer model of the half-bridge converter board EPC9035 from Efficient Power Conversion. This board contains GaN transistors EPC2022 eGaN®, the corresponding control driver and other necessary elements for operation. The use of GaN transistors has made it possible to investigate the operation in a wide range of frequent switching, both to control the motor and to amplify the audio signal. Results. It is established that the value of load inductance affects the level of nonlinear distortions caused by «dead time». At inductance values that provide a constant sign of the output current, a difference arises between the duration of the input and output pulses, which increases the THD. At inductance values, when the choke current changes sign during a pulse, there is no error between the duration of the input and output pulses. Changing the inductance changes the relationship between the error signal and the non-error signal. THD changes accordingly. At high conversion frequencies, the voltage spikes caused by the choke current through the built-in diodes during the dead time are partially compensated by overcharging the output capacitance of the transistors, which also reduces harmonic distortion. Originality. For the first time, the value of the THD at the outlets in the fallowness of the different indices of the inductance of the choke and the theoretical calculation of the value in the results of the computer model was obtained. Practical significance. The dependence of the THD values on the inductance of the choke for converters with a switching frequency range from 1 kHz to 400 kHz, which allows them to be used both to control the motor and to amplify the audio signal.
The object of research: the shift of resonant frequency of the piezoceramic electroacoustic transducer Langevin type depending on the shape of the back plate. Investigated problem: the relationship between changes in shape of back plate of the Langevin type transducer with the resonant frequency of the oscillating system. Search quantitative contribution to shift the resonant frequency of each of the modifications: shape, diameter, thickness, weight of back plate. The main scientific results: vibration modes of a transducer with a back plate with horizontal and vertical radiator ribs were obtained. The graphs of the shift resonant frequency depending on the change in the diameter and thickness of the back tail with vertical radiator ribs are presented. It is established, that the change in the thickness and diameter of the back plate of the transducer effects on resonance frequency much less than the change in mass. The area of practical use of the research results: designing piezoceramic electroacoustic transducer with passive cooling method. Innovative technological product: guidelines for choosing the shape changes back plates of the Langevin type transducer for decreasing heating temperature, with keeping resonant frequency. Scope of the innovative technological product: scope of application of the Langevin type transducer: underwater acoustics, ultrasonic technological equipment, ultrasonic engine, piezotransformer, medical equipment, rock drilling devices.
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