The use of broadband acoustic transducers and pulse-compression techniquesfor air-coupled ultrasonic imaging

A pulse-compression technique has been applied to air-coupled testing of so lid materials. Capacitance transducers were used to generate wide bandwidth swept-frequency (chirp) signals in air, which were then used to measure an d image solid samples in through transmission. The results demonstrate that such signal processing techniques lead to an improvement in the signal to noise ratio and timing accuracy for air-coupled testing. Measurements of th ickness and spectroscopic experiments are presented. Images of defects in a wide range of materials, including metals and carbon-fibre composites have also been obtained. This combination of capacitive transducers with pulse- compression techniques is shown to be a powerful tool for non-contact air-c oupled ultrasonic measurements. (C) 2001 Elsevier Science B.V. All rights r eserved.