Measurement of weak light emitted from mechanoluminescence materials using Si photodiode and light concentrator

Mechanoluminescence (ML) is light emission induced by mechanical deformation. Strain/stress monitoring using ML materials has been developed as a non-destructive method for diagnosis of deterioration in structures; this method is promising and is expected to find broad application in the field of structural health monitoring (SHM). This paper proposes a light measurement system for the weak and diffusive light emitted from ML materials considering applications for crack detection. Si photodiode (PD) is used as the light detector with respect to the cost when dealing with practical applications. In addition, light concentrators are developed in order to (1) increase light beams arriving at the PD surface and (2) enlarge the detecting area of a single PD. In this study, light concentrators are designed using flat reflective surfaces, and the size of concentrators is investigated. In the experiments, increase of PD's output current was achieved with a light concentrator.