North Carolina State University Researchers have demonstrated a self-repairing strain sensor waveguide created by self-writing in a photopolymerizable resin system. The self-repairing sensor is fabricated between two multi-mode optical fibers via lightwaves in the ultraviolet (UV) wavelength range and operates as a sensor through interrogation of the power transmitted through the waveguide in the infrared (IR) wavelength range. After failure of the sensor occurs due to loading, the waveguide re-bridges the gap between the two optical fibers through the UV resin. The response of the original sensor and the self-repaired sensor to strain are measured and show similar behaviors.

Optical-based strain sensor networks have been developed for condition monitoring of a wide variety of structural systems. One challenge when designing appropriate sensors for structural applications is that the sensor network must survive the same lifetime as the structure to be monitored, while often operating under extreme conditions. One solution to achieve this goal is to repair or replace damaged sensors. However, such sensors are not always easily accessible and may require considerable operational downtime of the structure to perform the repair.

Additionally, in the case of sensors embedded into structural components, replacement or repair may not be possible. The most common solution to this problem is through sensor redundancy. However, the sensors located closest to the point of impact (or any other extreme event) are, by default, those most likely to fail.

To compensate this difficulty is typically alleviated by intelligent processing, such as neural networks being applied, through which the information from faulty sensors can be filtered out of the structural response information. The accuracy of this approach can be increased by including a measure of the confidence of each sensor through sensor self-testing.

North Carolina State University Researchers developed the new self-repairing optical strain sensor. The self-repair is based on a self-writing polymer waveguide which acts as a strain sensor. The sensor repair is activated in the UV wavelength range and the sensor interrogation is performed in the IR wavelength range. Therefore, these two types of lightwaves can be propagated simultaneously through the sensor network without interference. Furthermore, no external inputs are required to initiate the self-writing process.

Source: IOP Science.