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Design and Fabrication of an Antenna and Transmitter for a Medical Microwave Imaging System

Masihi, Ahmad | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55388 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Shishegar, Amir Ahmad
  7. Abstract:
  8. In this thesis, a microwave imaging system has been designed and fabricated for medical applications. Compared to the conventional imaging methods such as X-ray and Magnetic Resonance Imaging (MRI), this technique is safer and more cost efficient, specifically for patients who need more frequent screenings over a short period of time, such as patients diagnosed with cancer. In electromagnetics, microwave imaging is referred to locating the heterogeneities or finding complex relative permittivity distribution in the imaging domain. In this project, in order to find the complex dielectric constant distribution of the imaged object, an array of 8 monopole antennas have been positioned on the circumference of a circle with a diameter of 15.5 centimeter. To reduce the reflection coefficients at the object boundary, as well as to minimize the effect of environmental interference and the multi-path signals, a mixture of glycerin and water (80% glycerin in volume) has been used as a lossy coupling liquid. The antennas have been placed inside a plexiglass container with the diameter of 29 centimeter and the container was filled with the mixture of glycerin and water. In each measurement, two antennas were selected to serve as transmitter and receiver respectively and the scattering parameters of these two-port network have been obtained. A total of 28 measurements were performed to extract 36 scattering parameters. The ratio of the corresponding scattering parameters was calculated for two states of object presence and object absence and this data was imported into an image reconstruction algorithm. In order to switch the antennas between transmitting and receiving modes, a 2 to 8 switching network was designed and fabricated using low-cost monolithic solid-state elements. A software defined radio with appropriate dynamic range of 70 dB was chosen as the transceiver for this imaging system at low cost. To evaluate the performance of the imaging system, a water-containing plexiglass cylinder, placed in a specific position with respect to the array of antennas, was imaged. In the results obtained from the reconstructed images, the position of the cylinder and its approximate size is well recognizable confirming that this microwave imaging system is able to successfully locate the target object within the imaging area.
  9. Keywords:
  10. Microwave Imaging ; Medical Imaging ; Software Defined Radio (SDR) ; Monopole Antenna Arrays ; 2x8 Switching Network ; Coupling Liquid

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