(1). Fiber optic acoustic emission sensors

Acoustic Emission (AE) is a term used to describe the sound waves produced when a material undergoes stress (internal change) as a result of an external force. AE is a phenomenon that occurs, for instance, in mechanical loadings that generate sources of elastic waves. Acoustic emission technology, as a method of structural health monitoring, has been developed and applied. Our group focuses on:

(a) Novel fiber optic acoustic emission sensor based on fused-tapered fiber coupler has been invented.

(b) A fiber optic acoustic emission sensor based on a fused-tapered fiber coupler has been invented and embedded in composite materials for monitoring composite materials and structures damage. Linear damage location on an aluminum plate and a composite plate has been verified utilizing a pair of fused-tapered fiber couplers.

Fig.1 Schematic illustration of Fiber optic acoustic emission sensor

  Fig.2 Setup of acoustic emission technology with fiber optic sensors and PZT 

(2). Fiber Bragg grating sensors

A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core which generates a wavelength-specific dielectric mirror. A fiber Bragg grating can, therefore, be used as an inline optical filter to block certain wavelengths or as a wavelength-specific reflector.

As well as being sensitive to strain, the Bragg wavelength is also sensitive to temperature. This means that fiber Bragg gratings can be used as sensing elements in optical fiber sensors. In a FBG sensor, the measurand causes a shift in the Bragg wavelength. The relative shift in the Bragg wavelength due to an applied strain is given by: