Security screening using ultrasound

This work will demonstrate that it is possible to produce images of hidden objects, using ultasound transmitted through air. For example, it can be shown that a knife can be imaged, when hidden behind a layer of clothing fabric. To achieve this, it is necessary to use coded waveforms and signal recovery techniques, in order to retrieve small signals in the presence of a much larger reflection from the outer fabric surface. In addition, ultrasound can be used in through-transmission to detect hidden objects within thin packages. This and other examples of the use of air-coupled ultrasound for security work will be demonstrated.