Micro-Opto-Mechanical sensors for tactile width measurements of surface opening cracks in concrete

The fabrication and laboratory testing of Micro-Opto-Mechanical sensors for the measurements of width of surface opening cracks in concrete structures are presented. The sensors are designed to be operated on a fan-out connector containing 12 multimode optical fibers, using a microstructure that can be mounted on the connector with a self aligned procedure. Thanks to the optical alignment automatically provided by such mounting method, each fiber in the connector can be used to interrogate an individual pressure sensor within an array composed by 12 elements in total. Using a soft polymer layer between the microsensor and the crack opening, the width of the crack can be derived by means of a tactile measurement performed by interrogating the 12 elements of the array alternatively, with a space resolution of 0.25 mm. The device is designed to be operated on board of a Remotely Piloted Aerial Vehicle equipped with a vision system that will be able to locate surface cracks of the external surface of reinforced concrete bridges and perform contact measurements on cracks using a robotic arm operated from the vehicle.