title: Coded waveforms for optimised air-coupled ultrasonic nondestructive evaluation.
abstract: This paper investigates various types of coded waveforms that could be used for air-coupled ultrasound, using a pulse compression approach to signal processing. These are needed because of the low signal-to-noise ratios that are found in many air-coupled ultrasonic nondestructive evaluation measurements, due to the large acoustic mismatch between air and many solid materials. The various waveforms, including both swept-frequency signals and those with binary modulation, are described, and their performance in the presence of noise is compared. It is shown that the optimum choice of modulation signal depends on the bandwidth available and the type of measurement being made.
authors.affiliation: School of Engineering, University of Warwick, Coventry CV4 7AL, UK. Electronic address: D.A.Hutchins@warwick.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Hutchins
authors.affiliation: Polo Scientifico Didattico di Terni, Università degli Studi di Perugia, 05100 Terni, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Burrascano
authors.affiliation: School of Engineering, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Davis
authors.affiliation: School of Engineering, University of Warwick, Coventry CV4 7AL, UK; Polo Scientifico Didattico di Terni, Università degli Studi di Perugia, 05100 Terni, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Laureti
authors.affiliation: Polo Scientifico Didattico di Terni, Università degli Studi di Perugia, 05100 Terni, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Ricci
keywords: Air-coupled; Coded waveforms; Cross-correlation; Non-destructive evaluation; Ultrasonic