| Abstract [eng] |
The purpose of this work is to design and investigate the control system of excitation circuits for capacitive micro-mounted ultrasonic transducers using standard microprocessor devices. This paper analyzes the scientific literature on capacitive micromountable ultrasonic transducers. An analysis of excitation solutions for ultrasonic transducers available on the market was performed. This research revealed, that the systems offered on the market are not flexible, lack control parameters and come at a high price. Traditional ultrasonic scanners use large arrays of transducers and FPGA-based electronic circuits, which are needed to generate transmissions and analyze received signals. CMUT can be used as sensors because of high sensitivity to mechanical load. Therefore, often a large number of channels is not required, so FPGA logic blocks in these cases are too complicated and expensive solutions. An option suitable for the realization of capacitive converter excitation has been selected. The system model consists of three elements: power supply, low voltage pulse generator, and voltage converter. The eight-channel, three-level Maxim Integrated Pulse IC (Integrated Circuit) MAX14808 was used for an experiment, which allowed to receive high voltage (up to 105 V), high 20 MHz frequency unipolar and bipolar pulses. An analysis of the research system and methodology of the low voltage pulse generator is also presented in this paper. A program was designed to evaluate the MAX14808 control capabilities with the Raspberry Pi 4B. A study of programming languages and their libraries for frequency management is included (with graphs). The programming has been done using the C language WiringPi library, which allowed access to the Raspberry Pi BCM2711 chip timer settings. The system is managed via Apache server with PHP programming language. The system management model has also been developed and it's management options are presented. A practical study of the experimental system design was performed – the change of the pulse shape from the load. The mathematical model of the system in MATLAB environment has been developed and experimental research of the system has been conducted. The complex study revealed that in order to obtain a signal of the required shape at a higher frequency power supply and the equivalent MAX14808 current limiting resistance must be as low as possible. It is recommended, if possible, to distribute the load between the individual channels. As the pulse repetition rate and amplitude increase, the MAX14808 temperature increases in direct proportion to the amplitude and frequency. Using marginal frequencies (20 MHz and higher) and pulse amplitudes close to 100 V would require additional cooling elements. |
