Browsing by Author "Taylor, Zachary D., Prof., Aalto University, Department of Electronics and Nanoengineering, Finland"
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- Millimeter-Wave Antennas on Flexible Substrates: Roll-to-Roll Reverse-Offset Printing and Probe Station-Based Characterization
School of Electrical Engineering | Doctoral dissertation (article-based)(2020) Zheng, JianfangUpcoming generations of millimeter-wave (mm-wave) communication systems present significant challenges on traditional fabrication paradigms, and the characterization of antennas in such systems. To meet the next generation mm-wave systems requirements, the antenna manufacturing must be low cost, high resolution, and suitable for mass production. Further, characterization method for these antennas must be developed that are compatible with a probe station environment. This dissertation studies roll-to-roll reverse-offset (R2R-RO) printing based fabrication of mm-wave antennas on flexible substrates and investigates the antenna radiation performance characterization methods for mm-wave probe-fed on-wafer antennas. The first part of the dissertation presents the R2R-RO printing technique and its application in the fabrication of mm-wave antennas. Printing technology offers a viable option for mass production. At mm-wave frequencies, the structure feature sizes are on the order of a few 10s of microns making fabrication with conventional printing methods unfeasible. R2R-RO printing enables the fabrication with the resolution of less than 10 µm making it sufficient for the future mm-wave electronics manufacturing. The principle of R2R-RO printing is presented, and a customized design structure is proposed to enable large-area printing. Coplanar waveguide (CPW) and microstrip patch antenna structures are designed and printed with the R2R-RO technique, and measured in a probe station environment. The results demonstrate print ink layer conductivity sufficient for mm-wave antennas. The second part of the dissertation is devoted to the systematic study of methods to quantify antenna radiation performance (gain and radiation pattern). Traditional antenna gain measurement methods require a second antenna to probe the antenna under test (AUT) which substantially increases measurement system complexity and can be impractical in a probe station measurement. The one-antenna gain measurement requires only the AUT and specular conductor plate (reflector). This reduced set of equipment enables characterization of probe-fed antennas in cluttered environments. The effect of reflector size on the measurement is studied with the physical optics (PO) method. A standard gain horn (SGH) and a microstrip patch antenna were measured by the one-antenna gain measurement method with the application of time-gating on frequency domain data. In addition, the antenna gain measurement method is extended to characterize the radiation pattern by adding a rotator to measure gain values at different angles. The radiation pattern and gain of several mm-wave antennas with different designed beam directions were measured by the proposed method in the probe station environment. Good agreement was observed between experiments and simulation. - Millimeter-wave techniques for the detection of corneal water content
School of Electrical Engineering | Doctoral dissertation (article-based)(2023) Baggio, MariangelaThis thesis concerns the study of millimeter-wave and THz reflectometry for corneal sensing. Human cornea is a lossy thin film at millimeter wave frequencies. It sits on top of a material of known properties: water and its physical thickness can be measured with ultrasound and optical techniques. Two key features render it a great match to millimeter wave imaging. First, the thickness ranges from 0.4 mm up to 0.7 mm falling right in the middle of the submillimeter range: 0.1 mm to 3 mm. Second the permittivity at millimeter-wave and THz frequencies is a strong function of water content. Therefore, the water content of the cornea and even the water gradient can be studied by illuminating cornea with millimeter waves and solving the inverse scattering problem.An effective medium theory and multilayer T-matrices is proposed as a model for the cornea reflection coefficient. A Montecarlo sensitivity analysis is also performed to investigate the possibility of solving the inverse scattering problem with presence of additive white Gaussian noise and to extract the water gradient and thickness of cornea with a particle swarm optimization algorithm. The analysis reveals that corneal parameter extraction might suffer from ambiguity and an additional thickness measurement might be needed. This technique has also been implemented in two experiments with two different millimeter-wave systems. First, a Gaussian beam telescope was used to perform corneal phantom reflectivity measurements in the WR 3.4 waveguide band (220-330 GHz). The Gaussian beam telescope was chosen because it allows to create a Gaussian beam with a certain beam waist and radius of curvature evolution. The phantoms were aligned to the optics, their reflectivity was measured, and their thickness and water gradient were also extracted. Another WR-3.4 quasioptical system was built, which used an axicon-hyperbolic lens as focusing objective. This system is less sensitive to distance deviation than the Gaussian beam telescope as the axicon has a long depth of field. The corneal phantom reflectometry experiment was repeated. The phantom thickness and water extraction results were performed. Other quasioptical systems are studied to integrate millimeter-wave reflectometry with an adjunct system to assist the corneal alignment in real-time. A first solution is to use a fast-scanning submillimeter wave adjunct imaging system that creates coupling coefficient maps. Anterior segment optical coherence tomography is also explored as a possible adjunct system by integrating it with dual reflector objectives.