Mimicking the human nervous system with a triboluminescence sensory receptor for the structural health monitoring of composite structures

The human nervous system (HNS) provides one of the most advanced examples of how to monitor the structural state of a complex system. In attempts to mimic the HNS, a key component has been the development of the sensory receptor. This paper reports on the development of a triboluminescence (TL)-based sensory receptor that converts mechanical energy from fatigue or impact loads and cracks propagation, into optical signals. This sensor system has potential for wireless, in-situ and distributed sensing (WID). The approach differs from existing fiber optic methods in that it does not require any external light source to function. The optical signal is generated through mechanical excitation of the highly triboluminescent ZnS:Mn. It is then transmitted through optical fibers to photomultiplier tubes (PMT) for detecting, quantifying and locating (with further analysis), intrinsic damage in critical engineering structures like concrete bridges. The TL sensory receptor consists of a sensitized portion of a polymer optical fiber (POF) coated with epoxy containing ZnS:Mn crystals. The sensory receptors were then incorporated into cementitious and polymer samples. Results from preliminary investigation showed that the TL sensory receptor gives repeatable responses under multiple impact loads. The triboluminescent intensity of the signal is directly related to the magnitude of the impact load. Results from dynamic mechanical analysis show a reduction in the Tg of the ITOF coating (TSR) with higher concentration of the triboluminescent (ZnS:Mn) crystals for the epoxy system used. There was however significant enhancement of the modulus with increase in the TL crystals. High-performance epoxy system with the principles of particulate composites would be applied in subsequent work to optimize the properties and performance of the TL sensor system. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)