title: Through-transmission imaging of solids in air using ultrasonic gas-jet waveguides.
abstract: An ultrasonic waveguide has been produced in air by using a gas jet. This uses the fact that a lower acoustic velocity can be produced within the jet, relative to the air surrounding it. The lower velocity is achieved by mixing carbon dioxide with air within the jet at a concentration that is a compromise between lower acoustic velocity and increasing attenuation. Using a capacitance transducer placed within the flowing gas, it is shown that improvements in the beam width can result when the gas jet is used. Air-coupled images of solid samples have been produced in through transmission, which demonstrate that an improved lateral resolution can result when a comparison is made to images from conventional air-coupled testing.
authors.affiliation: School of Engineering, University of Warwick, Coventry, CV4 7AL, UK. esrig@eng.warwick.ac.uk
authors.forename: David A
authors.initials: DA
authors.lastname: Hutchins
authors.forename: Doowon
authors.initials: D
authors.lastname: Choi
authors.forename: Lee A J
authors.initials: LA
authors.lastname: Davis
authors.forename: Tat-Hean
authors.initials: TH
authors.lastname: Gan
authors.forename: Duncan R
authors.initials: DR
authors.lastname: Billson