Fiber optic device for monitoring local and geometric contour curvature.

The Electrical Impedance Tomography(EIT)  is a non-invasive imaging method of biological tissue interior, through the impeditivty distribution estimation. One of the limiting factors in the image quality is the information about the imaged region contour geometry. If it were possible, through some device, to monitor the contour at the same time as the tomography is performed, this limitation could be mitigated. The main objective of the project was to build and make a proof of concept for a device capable of measuring the countour's local curvatures and thus estimate its geometry through these measurements. The device was constructed in a way that can be appended to the EIT equipment in the future. The device was built using optical fiber made of polymeric material, together with circuits for amplification, filtering and sampling of the signals that were processed and treated in the Raspberry Pi microprocessor. For the device construction, the optical fiber was abraded in specific and periodically separated regions, where the light sensors were attached so that when the fiber is bent, the light that escapes through these regions can be measured. The behavior of the light that escapes in the abraded regions was mathematically modeled as a function of the local curvatures and then calibration tests were carried out to estimate the model parameters. The tests consisted of placing the fiber on different cylindrical surfaces, with known curvature, and measuring the amount of light that escapes in the abraded region. Knowing the model and parameters it was possible to use the device to measure the local curvatures of the contour and then estimate its geometry. At the end, measurements were taken on objects that were not purely cylindrical and the geometries were reconstructed, making it possible to estimate the error of the device's measurements.