Millimeter-wave techniques for the detection of corneal water content

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2023-12-01
Degree programme
70 + app. 72
Aalto University publication series DOCTORAL THESES, 189/2023
This 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.
Supervising professor
Taylor, Zachary D., Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
Thesis advisor
Ala-Laurinaho, Juha, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland
Tamminen, Aleksi, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland
millimeter-wave, optical techniques
Other note
  • [Publication 1]: A. Tamminen, M. Baggio, I. Nefedova, Q. Sun, S. Presnyakov, J. Ala-Laurinaho, E. Brown, V.Wallace, E. Macpherson, T. Maloney, N. Kravchenko, M. Salkola, S. Deng and Z. D. Taylor. “Extraction of thickness and watercontent gradients in hydrogel-based water-backed corneal phantoms via submillimeter-Wave reflectometry”. IEEE Transactions on Terahertz Science and Technology, vol. 11, no. 6, pp. 647-659, Nov. 2021.
    Full text in Acris/Aaltodoc:
    DOI: 10.1109/TTHZ.2021.3099058 View at publisher
  • [Publication 2]: M. Baggio, A. Tamminen, J. Lamberg, R. Grigorev, S. Ville Palli, J. Ala-Laurinaho, I. Nefedova, J. Louis Bourges, S. X. Deng, E. R. Brown, V. P. Wallace, and Z. D. Taylor. “Submillimeter-wave cornea phantom sensing over an extended depth of field with an axicon-generated Bessel beam”. IEEE Transactions on Terahertz Science and Technology, Nov. 2022.
    DOI: 10.1109/TTHZ.2022.3221367 View at publisher
  • [Publication 3]: M. Baggio, Y. Hu, A. Tamminen, I. Nefedova, J. Ala-Laurinaho and Z. D. Taylor . “Submillimeter-wave imaging assisted alignment of millimeterwave spectroscopic system for quantification of corneal water content”. In Proceedings SPIE 11348, SPIE Photonics Europe, April 2020.
    Full text in Acris/Aaltodoc:
    DOI: 10.1117/12.2556309 View at publisher
  • [Publication 4]: Y. Hu, M. Baggio, S. Dabironezare, A. Tamminen, B. Toy, J. Ala-Laurinaho, E. Brown, N. Llombart, S. Deng, V. Wallace and Z. D. Taylor. “650 GHz Imaging as Alignment Verification for Millimeter Wave Corneal Reflectometry”. IEEE Transactions on Terahertz Science and Technology, vol. 12, no. 2, pp. 151-164, Mar. 2022.
    Full text in Acris/Aaltodoc:
    DOI: 10.1109/TTHZ.2021.3140199 View at publisher
  • [Publication 5]: M. Baggio, A. Tamminen, J. Ala-Laurinaho and Z. D. Taylor. “Design of double-reflector objective for corneal sensing in the 220-330 GHz band”. In Proceedings of the European Conference on Antennas and Propagation, 2022 16th European Conference on Antennas and Propagation, EuCAP, 2022.
    Full text in Acris/Aaltodoc:
    DOI: 10.23919/EuCAP53622.2022.9769685 View at publisher