Air-Coupled Ultrasonic Inspection of Fiber-Reinforced Plates Using an Optical Microphone
* Presenting author
In comparison to conventional ultrasound techniques, air-coupled ultrasound (ACU) offers an advantage in the automatization of the test process. ACU can also be conveniently applied to fragile or corrosive specimens. In ACU testing, the ultrasound (US) power losses due to impedance mismatches from air to the material necessitate a high power US source and a sensitive-enough detector on the receiver side. A novelty in our measurement setup is a laser-based optical microphone manufactured by XARION which we used together with the focusing US transducer manufactured by SONOTEC. Due to its broad frequency spectrum and small aperture, the optical microphone has a great potential for the C-scan inspection of plates. Firstly, we use it to characterize the US field of the US transducer. Secondly, we changed the setup configuration and performed a C-scan of plates (made of CFRP, wood, PMMA) with different defects (delaminations, cracks) in the through-transmission configuration. The results show a comparable sensitivity (signal-to-noise ratio) and a better spatial resolution compared to the ACU techniques which use piezoelectric receivers.