FPI-POFBG Angular Movement Sensor Inscribed in CYTOP Fibers with Dynamic Angle Compensator

We present the development and application of an angular movement sensor based on Fabry-Perot interferometer (FPI) in series with a fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) using a femtosecond laser. The FPI was fabricated with UV-curable resin between the CYTOP and a silica pigtail, which provides flexibility and the possibility in situ fabrication. In this case, the FPI is an edge-filter for the FBG response, which presents both wavelength shift and optical power attenuation as the bending angle increases. A dynamic compensator for the material's viscoelastic response resulted in a six-fold reduction in the sensor's transient response error. The FPI-POFBG angular movement sensor was validated in knee angle monitoring during gait cycles, where the sensor presented errors as low as 2.5°. This is a low-cost sensor with high flexibility on fabrication and with the capacity of following subtle angle variations, as the ones commonly occurred in gait cycles

Perrogator: A Portable Energy-Efficient Interrogator for Dynamic Monitoring of Wavelength-Based Sensors in Wearable Applications

In this paper, we report the development of a portable energy-efficient interrogator (Perrogator) for wavelength-based optical sensors. The interrogator is based on a compact solution encompassing a white light source and the spectral convolution between the sensor and a tunable filter, which is acquired by a photodetector, where a microcontroller has two functions: (i) To control the filter tuning and to (ii) acquire the photodetector signal. Then, the data is sent to a single-board computer for further signal processing. Furthermore, the employed single-board computer has a Wi-Fi module, which can be used to send the sensors data to the cloud. The proposed approach resulted in an interrogator with a resolution as high as 3.82 pm (for 15.64 nm sweeping range) and maximum acquisition frequency of about 210 Hz (with lower resolution ~15.30 pm). Perrogator was compared with a commercial fiber Bragg grating (FBG) interrogator for strain measurements and good agreement between both devices was found (1.226 pm/µε for the commercial interrogator and 1.201 pm/µε for the proposed approach with root mean square error of 0.0144 and 0.0153, respectively), where the Perrogator has the additional advantages of lower cost, higher portability and lower energy consumption. In order to demonstrate such advantages in conjunction with the high acquisition frequency allowed us to demonstrate two wearable applications using the proposed interrogation device over FBG and Fabry-Perot interferometer (FPI) sensors. In the first application, an FBG-embedded smart textile for knee angle assessment was used to analyze the gait of a healthy person. Due to the capability of reconstructing the FBG spectra, it was possible to employ a technique based on the FBG wavelength shift and reflectivity to decouple the effects of the bending angle and axial strain on the FBG response. The measurement of the knee angle as well as the estimation of the angular and axial displacements on the grating that can be correlated to the variations of the knee center of rotation were performed. In the second application, a FPI was embedded in a chest band for simultaneous measurement of breath and heart rates, where good agreement (error below 5%) was found with the reference sensors in all analyzed cases