P3F-1 Lamb Wave Generation with an Air-Coupled Piezoelectric Array Using Different Square Chirp Modulation Schemes

This paper describes a new Lamb wave excitation technique using square chirp signals for air-coupled inspection of laminate materials in a non destructive testing system. The airborne ultrasonic waves are generated with an air-coupled ultrasonic plane array transducer with 15 active elements. Each array element is excited with a square chirp signal in order to apply pulse compression techniques. The advantages of using chirp signals are a greater SNR when using pulse compression (compared with burst or single pulse), a more precise time of flight calculation and a greater use of the transducer bandwidth. However, a decrease in the signal amplitude is expected due to the dispersion of the Lamb waves.