Shape sensing has become an area of great interest for many medical applications, such as epidural administration, colonoscopy, biopsies, and cardiac procedures, where real-time data of a dynamic object is required and visual contact is absent. Fiber Optic Shape Sensors (FOSS) consist of optical multi-fiber cables or Multicore Fibers (MCF) with embedded strain sensors, which can reconstruct the sensor shape from its multidimensional bending. Regrettably, the accuracy of three-dimensional shape sensing is remarkably restricted because of twisting, which makes impossible to correctly detect the bending direction. This paper reports an experimental study aimed at investigating the accuracy of optical shape sensors based on spun multicore fibers in sensing twisting, employing one of the most used multicore fiber geometry for sensing applications, the seven-core fiber. Firstly, a theoretical approach to model the mechanical behavior of multicore fiber was developed. Secondly, a pre-twisted fiber optic shape sensor was fabricated in the Institute for Telecommunications and Multimedia Applications (iTEAM), by inscribing four Fiber Bragg Gratings (FBG) in a Spun Multicore Fiber (diameter of 125.1 μm) with a pre-twisting of 64.9 rotation/meter, manufactured and provided by FIBERCORE. To conclude, a series of experiments were performed to corroborate the theoretical approach and evaluate the sensor performance. The proposed Spun-MCF-based Shape Sensor was able to sense twisting with a sensitivity of 0.23 pm/° and accuracy of 4.81° within a wide dynamic range of ± 270°, maintaining a perfectly elastic behavior at high level of twisting deformation
A temperature-insensitive 2-D inclinometer by incorporating two fiber Bragg gratings (FBGs) with a homogeneous pendulum transducer is proposed and experimentally demonstrated. The two FBGs are located in two orthogonal planes of the pendulum and only half of each FBG is glued on the surface of the columnar rod. Due to the strain difference between glued- and non-glued part of each FBG, the reflection spectrum of each FBG splits into two peaks. The direction and magnitude of inclination can be readily determined by measuring the wavelength separations of the split peak in two FBGs, whilst the temperature-induced cross-sensitivity is eliminated. A sensitivity of 0.047 nm/° with an accuracy of 0.23° is achieved within the tilt angle range of -20°–+20°.
Fiber optic shape sensing is innovative technology, which enables distributed structural health monitoring, providing real-time feedback on shape and position, based on smart sensors arrays, which consists of optical fiber bundles or multicore fibers with embedded strain sensors. This paper describes a numerical analysis carried out to identify the effects of uncertainty in strain measurement and core position on the accuracy of fiber optic shape sensors, taking into consideration one of the most utilized geometry for fiber optic sensing applications, the seven-core Multicore Fiber, and distinct values of core spacings (distance between outer cores and sensor axis). The Monte Carlo Method was employed to simulate the real measurement process and one million of iterations were performed for each simulation with the aim of defining the laws of uncertainty propagation. The results of this study demonstrate the influence of core position uncertainty, strain measurement resolution and core spacing on optical shape sensors accuracy and can support the design of new sensors, predicting the achievable performance.