Improvement of FBG/PZT hybrid sensing system for composite materials

We have been developing a system for monitoring the health of aircraft structures made of composite materials. In this system, the Lamb waves that are generated by lead zirconium titanate (PZT) actuators travel through the composite material structures and are received by the embedded FBG sensors. To detect any Bragg wavelength change due to the reception of the Lamb wave, an arrayed waveguide grating (AWG) is used, which converts the Bragg wavelength change into an output power change. Since the conversion ratio is largely dependent on the initial Bragg wavelength, a temperture control was necessary for obtaining an optimum condition. However, we have developed a system that uses a denser AWG to eliminate the need for a temperature control. We suceeded in detecting 25 kHz to 1 MHz Lamb waves using our new system. We have also tried calculating the Bragg wavelength change of the obtained waveform, and confirmed that the Bragg wavelength change due to the reception of Lamb waves was less than I pico meter.