Investigation and Testing of Fiber Bragg Grating Sensors for Ultrasonic Applications

Broad band frequency response of Fiber Bragg Grating (FBG) sensors in comparison to piezo sensors is interesting for ultrasonic applications e.g. for detection of nonlinearity of ultrasonic waves. In order to increase the sensor sensitivity at higher ultrasonic frequency range (up to 7 MHz) -phase shifted FBG sensors are manufactured, investigated and tested. The ultrasonic sensor characteristics such as frequency response, directivity were identified. The sensitive shifted FBG sensors were then applied for detection of ultrasonic waves in solids (P-, S-, R-waves). The measurement results on a silicone sample show the feasibility of the shifted FBG sensors for thickness determination of multiple thin layers. In order to increase the sensor sensitivity at higher frequency the further investigations will be carried out in terms of grating lengths, variations of refraction indexes.