Ultrasonic, non-invasive classification/discrimination of liquid explosives (LEs) and threat liquids from non-threat liquids in sealed containers

This paper focuses on a set of laboratory measurements acquired with a Container Screening Device (CSD) that has been applied to several types of liquids in small commercially available plastic containers. The objective of this study was to further understand the critical acoustic measurement discrimination/sensitivity issues associated with quantifying the effectiveness of the approach for classifying and discriminating liquid threats from benign and commercially available liquids. A list of pertinent threat liquids was generated and measurements were conducted to demonstrate the CSD's ability to acquire accurate and repeatable acoustic information for effectively classifying and discriminating these liquids from non-threat liquids such as wine, whiskey, water, shampoo, etc. The device was used to measure the acoustic velocity, (the primary discriminator) and relative attenuation of 180 liquids at room temperature, while recording the key parameters that play a role in the accuracy and precision (repeatability) of the measurement. Density data were manually generated and evaluated to determine the effects of an additional acoustic signature on the discrimination algorithm. Results showed that by using a 3-parameter measurement approach (velocity, attenuation, and density), the methodology can be effectively employed for the rapid and accurate classification/discrimination of threat liquids versus non-threat liquids in small, carry-on, standard “stream-of-commerce” containers.