In the master's thesis, an automated ultrasonic skin regeneration system based on the digital generation of an ultrasonic signal with a Sinc waveform was developed and investigated. The work is dedicated to solving the relevant scientific and technical task of creating compact, energy-efficient, and affordable medical equipment for dermatology and aesthetic medicine.
The relevance of the master's thesis topic is conditioned by the rapid development of non-invasive therapy methods, among which ultrasonic exposure occupies a leading position due to its safety and proven effectiveness in stimulating regenerative processes. Existing devices for ultrasonic therapy on the market are predominantly built on traditional analog circuitry, which leads to significant dimensions, high energy consumption due to the low efficiency of output stages, and high production costs. Furthermore, analog generators have limited capabilities regarding flexible control of the signal's shape and spectral composition, which reduces the selectivity of the therapeutic effect.
The approach proposed in the work is based on the concept of Software-Defined Ultrasound and the use of modern microcontrollers for direct digital synthesis of signals. The use of a stepped approximation of the ideal Sinc signal allows for forming radiation with a strictly limited rectangular spectrum, ensuring energy concentration exclusively within the therapeutic frequency range. This method allows for the elimination of bulky analog filters and complex cooling systems, replacing them with software algorithms and simple digital logic. This opens the way for creating portable devices capable of competing with stationary clinical equipment.
The object of the study is the process of formation and spectral transformation of complex ultrasonic signals in digital medical generators. The subject of the study is the methods of optimizing the parameters of the stepped approximation of the Sinc signal to ensure the necessary spectral purity under the conditions of microcontroller hardware limitations.
The aim of the work is the development and justification of the structure of an automated skin regeneration system that provides the generation of a therapeutic ultrasonic signal with specified spectral characteristics while minimizing hardware costs. To achieve this goal, tasks of mathematical modeling of signals, analysis of the impact of discretization on the spectrum, and development of circuit solutions and software are solved.
The research methods are based on the theory of digital signal processing, spectral analysis using the Fast Fourier Transform (FFT), and computer modeling in MATLAB environment. The work conducts a detailed study of the influence of time discretization and level quantization on the spectral characteristics of the output signal. In particular, the influence of the asymmetry of the output driver voltage levels and the time parameters of the pulses on the suppression of out-of-band harmonics is analyzed.
The scientific novelty of the obtained results lies in substantiating the possibility of using a stepped approximation of the Sinc signal with low bit depth to form high-quality therapeutic radiation. It is proven that when using a digital-to-analog converter update frequency that significantly exceeds the upper limit of the therapeutic band, the main signal energy is concentrated in the working area, and parasitic spectral components are shifted to the high-frequency region, where they are effectively suppressed by the natural properties of the output path and simple filters. Optimal parameters for a three-pulse sequence, taking into account the time discreteness limitations of modern microcontrollers, are proposed.
The practical value of the work lies in the creation of a layout and functional diagram of a device that can be implemented in serial production. The developed solution allows for reducing the cost of the component base, decreasing the weight and dimensions of the device, as well as providing high flexibility of settings due to software control of generation parameters. The research results can be used in the design of the latest samples of medical equipment for cosmetology and dermatology.
Research advisor: V.Bazhenov
