Ph.D Thesis

Ph.D StudentMarkish Ofer
SubjectAnalysis of Heating and Absorption Mechanisms in Antennas
for Bolometers
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Yehuda Leviatan
Full Thesis textFull thesis text - English Version


   Bolometers are devices for measuring the power of incident electromagnetic (EM) radiation. Their operation is based on a sensor with a temperature dependent electrical resistance. When EM radiation impinges upon the sensor, its temperature rises and the change in its resistance can be translated to the power of the incident radiation.  Bolometers can operate from microwave up to optical frequencies in a variety of application areas such as imaging and astronomy. At optical frequencies, resistive sheets can be efficiently integrated to increase the amount of absorbed power. However, at lower frequencies, connecting an antenna is attractive since the antenna can improve the absorption of the incoming waves even when the wavelength becomes greater than the sensor size.

   Most of the recent studies of antenna-coupled-bolometers, separate between the EM analysis of the antenna and the thermal analysis of the rest of the system. Furthermore, often the antenna EM analysis carried out, does not give enough attention to the power dissipated in the antenna material, which can contribute to the detected signal. In this work, we introduce a systematic approach to the analysis and design of bolometer antennas. The presented analysis provides a better understanding of antenna-coupled bolometers, along with guidelines as to improve their performance.

    We first propose a gain-bandwidth product subject to heating rate and antenna size constraints. This metric serves as a constrained objective in a genetic algorithm that yields state-of-the-art antennas with fast heating rate and excellent EM performance. We next extend our analysis to include the antenna structural losses and present an approximate analytical expression for the optimal load impedance that maximizes the total absorbed power by a stand-alone and finitely-conductive dipole. Evidently, this load is different from the conjugate-matched load, which is required to maximize the load power alone. The optimal load for absorption is then investigated in the context of array of lossy dipoles above a ground plane. It is shown that with this load, perfect absorption can be attained but, in contrast to the known case of array of lossless dipoles, not for all heights of the array above the ground. To validate the perfect absorption phenomenon, an array of dipoles made of conductive ink was designed and fabricated, and good agreement between the absorption measurements and the simulations is presented. Finally, we define a new quality factor for absorption along with formulating a generalized absorption resonance condition. We show that the quality factor can be used to calculate the absorption bandwidth of antennas, based on the fields at the resonance frequency only.