Innovation in non-contact ultrasonic analysis: applications for hidden objects detection

 This paper describes unusual applications of ultrasound that are based upon recent advances in transduction efficiency in air and gaseous media. Piezoelectric transducer devices – capable of generating extremely high intensity ultrasound in ambient air up to 5 MHz – have been successfully developed and tested. This is in addition to the obvious uses for gas analysis, remote sensing, liquid level, gap, and thickness measurement, and proximity analysis. These new generation transducers make it possible to analyze solids and liquids not only non-destructively, but also without physically contacting the test sample. Among various applications to the non-destructive characterization (NDC) of industrial materials, we also describe the feasibility of a forensic application. This concerns the detection of objects such as knives, guns, contraband drugs, dead bodies, etc., hidden inside false compartments or walls. Received: 15 October 1997 / Accepted: 24 October 1997