Examensarbeten för masterexamen // Master Theses
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- PostCharacterisation of recycled plastics for automotive radar applications at 77 GHz(2024) Ameerudeen, Mohamed Azad; Nourjoo, Mohammad; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Stake, Jan; Bevilacqua, Stella; Tell, Sara; Vakili, ImanThis work investigates the potential of various recycled plastic materials for use in bumper areas which are in closer proximity to automotive radar systems operating at 77 GHz. The study focuses on both experimental and analytical calculation approaches to assess the electromagnetic properties of these materials, specifically focusing on their complex permittivity and loss tangent characteristics at 77 GHz. For this purpose, a quasi-optical measurement setup which utilises metallic reflective mirrors to narrow and collimate the beam of waves produced by WR12 frequency extenders in the 65-90 GHz range is used. The S-parameters measured by the Vector Network Analyzer (VNA) of the samples are utilised to calculate the complex refractive index. This procedure allows for the determination of the permittivity and loss tangent for each specific sample material. To ensure the robustness of the calculation method, the known permittivity and loss tangent values at 77 GHz from a reference non-recycled material provided by the supplier are utilised to calculate theoretical S-parameters, which are then employed in the same method to re-evaluate the permittivity and loss tangent. This process enables a direct comparison with the initial VNA-derived results. This round-trip verification process confirms the reliability of the calculation method used in the analysis. From the analysis of all test materials, a particular recycled plastic material is chosen, suggesting its potential suitability for use in automotive bumper production. Overall, this research offers significant insights into the development of radar-compatible recycled plastics for bumper design and manufacturing.
- PostGroup Delay Variations in Microwave Filters and Equalization Methodologies(2013) Yu, Su; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceIn modern telecommunication systems, a constant group delay is necessary in order to avoid signal distortion. Unfortunately, a group delay variation is unavoidable. For example, a band-pass filter in microwave systems will create a group delay variation near the edge of pass band, i.e., in transition areas of the filter. According to simulations of ideal filter components (Q is infinite) in ADS, it shows a 5th-order Elliptic band-pass filter with stopband rejection of 20 dB and pass-band frequency from 7.5 GHz to 12.5 GHz would introduce a maximum group delay variation of 3.4 ns. System simulations in MATLAB show that it would cost extra power of 0.8 dB and 1.6 dB for 4QAM and 16QAM modulation respectively, to achieve the same performance (bit-error-rate) as the system without any group delay variation. Therefore, it is necessary to develop so-called group delay equalizers to compensate the variation of the group delay. Analog group delay equalizers are realized based on two methodologies: 1) allpass networks, which are used to generate a positive group delay with desired features; 2) a negative group delay circuit, which is used to compensate group delay variation originating from filters. Unfortunately, the existing negative group delay circuit suffers from a large attenuation in the frequency range where negative group delay occurs. In this thesis, a novel group delay equalizer circuit topology is proposed, to overcome the drawback of large attenuation. It is demonstrated that the proposed negative group delay circuit has a flat amplitude response with a variation less than 0.6 dB, keeping a feature of negative group delay. As example, the proposed equalizer is used to compensate the group delay variation originating from a low-pass filter with the pass-band from DC to 15 GHz. The simulation result exhibits that the group delay variation of the filter is reduced from 0.6 ns to 0.2 ns while the amplitude response is reduced less than 0.53 dB due to losses of the equalizer. For band-pass filters, one more stage of the proposed equalizer is needed in order to compensate the group delay variation in both sides of filters.
- PostInvestigation of Digitalization in Laser Rangefinder Receiver - How to Use Digital Signal Processing and Pulse Detection to Improve Performance in the Laser Rangefinder Receiver(2022) Åberg, Josefine; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Vassilev, Vessen; Horrdin, StefanDigitization provides many opportunities for a wide range of applications since it can generate more flexible and stable solutions compared to analog solutions. It also allows using other tools than the ones available for analog solutions. The purpose of this master’s thesis was therefore to investigate how the performance of an analog laser rangefinder receiver can be improved by digitalizing the receiver and using digital techniques on the laser rangefinder’s received echo signal. This included investigating the detection sensitivity, as well as, the possibility to separate false alarms and true optical echo pulses in the received signal. Separating the two would provide a possibility for increased bias voltage in the Avalanche Photodiode (APD), used for detection in the laser rangefinder. An increase in bias voltage would also improve the sensitivity of the laser rangefinder. The investigation was done by simulations in MATLAB. The simulations consisted of constructing a laser rangefinder’s received echo signal, applying digital signal processing to it and using digital pulse detection. It was also investigated if some other analog solutions in the laser rangefinder can be replaced by digital techniques in a digital solution. The Central Processing Unit (CPU) time for the investigated digital methods was also measured. The result demonstrated that a digital laser rangefinder receiver would be superior to an analog receiver under the circumstances of the thesis. The detection statistics were much improved and the detection sensitivity of the optical pulse amplitude was increased by 10.57 dB. The digital solution also managed to separate false alarms and true optical pulses to a certain extent. Thereby making it possible to increase the bias voltage in the APD.