Ultrasound sensing Using Superimposed Fiber Bragg Grating

In this paper we report our investigation regarding specific design requirement of fiber Bragg grating (FBG) sensors in light of sensing dynamic stress waves which is immensely useful in the application of structural health monitoring using guided ultrasonic waves or the Lamb waves. For faithful signal detection gauge length of the FBG sensors needs to be much smaller than the wavelength of the stress waves as induced in the structure by the propagating ultrasonic waves. It has been shown that to satisfy this condition often other important issues like sensitivity, resolution and usable frequency band of operation is sacrificed. Experimental results shows that a set of suitably designed superimposed (co-located) Bragg gratings having different gauge length i.e. with different dynamic range and resolution can greatly enhance the domain of measurement. The single device contains a multi-resolution sensor in one hand and also allows wider usage of ultrasonic bandwidth by virtue co-located sensors of different gauge length.