Whispering gallery mode-based micro-optical sensors for structural health monitoring of composite materials

• Published in: Journal of materials science Vol. 44; no. 6; pp. 1560 - 1571
• Main Authors: Nguyen, Nguyen Quang, Gupta, Nikhil, Ioppolo, Tindaro, Ötügen, M. Volkan
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.03.2009; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Composite materials; Crystallography and Scattering Methods; Detection; Embedded sensors; Feasibility studies; Materials Science; Materials selection; Morphology; Optical measuring instruments; Particulate composites; Polymer Sciences; Refractivity; Semiconductor lasers; Sensors; Smart materials; Solid Mechanics; Stress concentration; Structural health monitoring; Syntactic and Composite Foams; Tunable lasers; Whispering gallery modes; Structural Health Monitoring; Finite Element Analysis; Transverse Electric; PMMA; Fiber Bragg Grating
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-008-3163-3

Development of smart materials with inherent damage sensing capabilities is of great interest to aerospace and other structural applications. Most of the existing smart materials are based on using embedded sensors for structural health monitoring. However, embedded sensors can lead to undesirable effects such as stress concentration and can cause premature failure. Therefore, using microstructural components for additional function of sensing of the structural health is the only option. Such possibilities exist only in selected few materials. The present study investigates the feasibility of developing fiber- and particle-reinforced composites into smart materials. The sensing approach considered is based on the morphology-dependent shifts of optical modes, referred to as the whispering gallery modes (WGMs), of spherical dielectric micro-particles. The WGMs are excited by coupling light from a tunable diode laser using single mode fibers. The WGMs of the micro-particles can be observed as sharp dips in the transmission spectrum through the fiber and are highly sensitive to the morphology of the particle. A minute change in the size, shape, or refractive index causes a shift of the optical modes, which can be interpreted quantitatively in terms of the parameter that caused the change. A theoretical framework is developed for such sensor systems that provides quantitative relations between the stress applied on the micro-particles and corresponding shift in WGMs. These relations are validated against the available experimental results.