The doctoral dissertation presents the optimization of a frequency-modulated terahertz system for use in extreme conditions. The first part of the dissertation presents the basic operation of terahertz systems and their use. The biggest emphasis is on the explanation of the use of frequency modulation as a way of using the terahertz system in the radar configuration to detect the distance of the observed object.
The main part of the doctoral dissertation presents the design and construction of a terahertz system that measures the distance to the observed object in extreme conditions such as: high temperature, considerable amount of dust and smoke, and continuous vibrations around the system. Most often such conditions are found in heavy industry. In our case, the system is designed for use in the heavy industry to detect the amount of powder applied to lubricate a liquid metal mold.
In designing the terahertz system, the task was divided into two subsystems. The first subsystem that represents the transmitter is the terahertz wave source. The source of terahertz waves consists of a frequency synthesizer, frequency multipliers and a waveguide feed horn antenna. This subsystem also includes lenses for focusing terahertz waves. The second subsystem is responsible for receiving and processing the terahertz signal of which it consists, a signal detector, an analog-to-digital voltage converter, and a microcontroller that sends measurement data to a computer for further signal processing and display. The choice of the terahertz sensor is conditioned by the chosen method of terahertz frequency generation. In our case, we used a microbolometer for the signal detector. An important part of the system is also its housing. Due to the extreme environmental conditions in which the system is located, the housing is made of metal. Cooling of the entire system is provided at the industrial level using a "vortex" system.
The development and production of the microbolometer has been done in the laboratory for many years. In addition, lenses and a feed horn antenna were designed for the system, but only lenses could be made in the laboratory, and the horn antenna was outsourced. Other parts of the source and hardware were purchased, and all printed circuit boards and connections between the subsystems intended for proper system operation were designed in the laboratory.
At each stage of development, test measurements were performed to observe system improvements. A laboratory system was used for testing. There were many measurements, so only the final measurements with the laboratory system are shown in the doctoral dissertation, where the software and hardware were improved. After optimizing the test system, the final system for use in real extreme conditions was developed. This system was firstly tested in a laboratory approximation of real conditions, mainly for final adjustments that could not be observed in the test system. After optimization in simulated extreme conditions, the system was tested in real industrial conditions. The system worked smoothly in extreme conditions, and the performance testing was successful.
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