Inspection of CFRP components by ultrasonic imaging with air-coupling

This paper reports the investigations of air coupled ultrasonic imaging techniques which are part of the German research project MaTech. Project partners are Airbus, Bremen, Ingenieurburo Dr. Hillger, Braunschweig, and intelligeNDT, Erlangen, with DLR, Braunschweig, as subcontractor. One task is the development and the construction of a non-contact ultrasonic imaging system („Demonstrator III“) for basic researches. This system provides fast scanning with a single-shot data acquisition (without signal averaging). The dynamic range in one shot reaches up to 50 dB. The demonstrator allows the application of different types of air coupled transducers and therefore it allows the comparison of their performances. The modular design of the system provides further developments and adaptations to special inspection tasks. A power transmitter with burst-signals ( peak power of 1.2 kW) and a free programmable transmitter can be used for the excitation of the transducers. The user-friendly software records C-scans and full wave scans and provides C-scan evaluations. The development and construction of special transducers for air coupling and the development of a system for echo-technique are further research tasks of the MaTech project. Usually, the air coupled ultrasound is used in through-transmission technique with separate receiver and transmitter transducers on opposite sides of the component under test. In order to get a high acoustic power and a low noise in the receiver amplifier usually the bandwidth of the system is smaller than 10% of the centre (test) frequency. Therefore, the effects of (*/2)-resonances in the components are investigated. Also the application of broadband transducers will be investigated.