IoT-powered remote sensing and handy real-time evaluation of strain imaging sheets installed on aged outdoor structures

Photonic crystal-based stress visualization film is promising for detecting age deterioration of large man-made structures and public infrastructures. However, as the number of the targets increases, it must be a big problem to prepare keeping a watch on all of them. Therefore, we propose two solutions: (1) solar battery-powered portable automated monitor stations to watch the color of the photonic coatings, and (2) an application of real-time image analysis on mobile phones for extracting the color change. The former assists us with efficient data collection and the latter helps non-expert collaborators to inspect them without using expensive spectroscopes. The portable monitor station consists of a micro computer connected with 3G mobile networks, a USB camera and a solar battery system installed in a water-proof box. Photographs of the stress visualization film are taken once every hour and, at all other times, the computer disconnects the camera in order to save the electricity. We placed four monitor stations in the shade of a bridge or a tree but they have run continuously for more than one year. The application displays a real-time image in which only stress-free area of the film is extracted. As a result, the region under stress and the background appear in white. This software runs on many mobile computers with built-in camera whose OS includes Android, iOS, Windows and Linux. This is possible due to the versatility of the computer vision library we used, OpenCV, which is popular in robotics and automatic car-driving.