High-resolution, air-coupled ultrasonic imaging of thin materials

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 50; no. 11; pp. 1516 - 1524
• Main Authors: Gan, T.-H., Hutchins, D.A., Billson, D.R., Schindel, D.W.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-11-2003; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustical measurements and instrumentation; Acoustics; Bandwidth; Capacitance; Contact; Exact sciences and technology; Ferroelectric materials; Focusing; Fundamental areas of phenomenology (including applications); High-resolution imaging; Image resolution; Imaging; Mirrors; Paper products; Physics; Pulse compression; Pulse compression methods; Receivers; Transducers; Ultrasonic imaging; Ultrasonic transducers; Image resolution; Acoustic measurement; Image processing; Ultrasound imaging; Capacitive transducer; Paper; Transmission mode; Experimental study; Acoustic image; Pulse compression; Ultrasonic transducer
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2003.1251135

This paper describes the use of a focused air-coupled capacitance transducer combined with pulse compression techniques to form high-resolution images of thin materials in air. The focusing of the device is achieved by using an off-axis parabolic mirror. The lateral resolution of the focused transducer, operating over a bandwidth of 1.2 MHz, was found to be less than 0.5 mm. A combination of the focused transducer as a source and a planar receiver in through-transmission mode has been developed for the measurement of different features in paper products, with a lateral resolution in through-transmission imaging of /spl sim/0.4 mm. Images in air of thin samples such as bank notes, high-quality writing paper, stamps, and sealed joints were obtained without contact to the sample.