Year
2016
Abstract
A robust, counterfeit-resistant, unique, and nonintrusive tag of a solid part is of interest to applications such as safeguards, arms control, and customs. A method able to obtain such a tag is ultrasonic imaging of material microstructure. A tag signature is obtained by (1) placement of an ultrasonic probe at a tag site on the part surface, (2) generation of an ultrasonic wave, and (3) imaging backscatter caused by the wave-microstructure interaction underneath the surface of the part. An initial signature is collected on an item and subsequent signature readings collected any time thereafter are then compared to the initial signature for validation. Because the material volume is from the part, the signature is intrinsic to the part like a fingerprint is to a person. Applicable materials include alloys, ceramics, and composites. Design of ultrasonic intrinsic tags (UIT) dates back to the 1980s when a mechanical scanner and focused ultrasonic probe (collectively called a reader) were used to acquire signatures. A limitation was the difficulty in holding the reader steady during signature acquisition. To address this, an ultrasonic phased-array (PA) transducer was evaluated. This was facilitated by advances in PA transducers for medical ultrasound and nondestructive evaluation of materials. As a proof-of-concept test, a commercially available PA transducer was used to acquire signatures from five stainless steel specimens and sort the specimens based solely on the UIT signatures. The PA configuration reduced signature acquisition to less than a second and enabled the reader to be a handheld device. Advantages of the PA reader over the mechanical reader include a 98% reduction of the signature acquisition time, an 88% reduction of the volume of the signature reader, and an 80% mass reduction of the signature reader. Furthermore, the PA contains no moving parts and is expected to essentially be maintenance-free as compared to the mechanical reader, which requires periodic adjustment. This paper will provide a description of the previous UIT design that used a mechanical reader, the new instrumentation used for the PA UIT system, specimens selected for signature evaluation, the PA UIT signature, performance test results, and anticipated PA development.