Application of Golay codes to improve the dynamic range in ultrasonic Lamb waves air-coupled systems

Air-coupled ultrasonic systems are usually limited by poor signal-to-noise ratios. The use of pulse compression techniques based on Golay codes can help to improve the ultrasound signal-to-noise ratio. This type of codes allows virtually side lobe free operation and causes the cancellation of self-induced noise. This paper proposes the use of Golay sequences to code Lamb waves excited in thin materials with a NDT system based on air-coupled piezoelectric arrays. Furthermore, a system for the generation of Lamb waves modulated by 16-bits Golay codes is also proposed. Successful results are presented in copper plates. An improvement in signal-to-noise ratio up to 21 dB is achieved when compared with conventional pulse transmission.