Combating clothing counterfeiters with terahertz technology

Scientists from the UK’s National Physical Laboratory (NPL), in collaboration with Russia’s Institute of Monitoring of Climatic and Ecological Systems, have shown how a technique called terahertz time-domain spectroscopy (THz-TDS) can be used to identify counterfeit clothing and footwear - a practice said to costs designer brands and retailers around £3.5 billion each year.

“Counterfeit clothes can look and feel almost exactly like the real thing and so customs officials need technological assistance to spot them,” explained NPL researcher John Molloy.

THz-TDS requires the generation of a beam of terahertz radiation, which is a band of electromagnetic radiation that falls between microwaves and infrared light. A sample of fabric is then placed within this beam and the properties of the terahertz waves are detected after passing through the fabric.

The composition and structure of the different types of fabric give rise to different rates of beam scattering and absorption; thus, each type of fabric has a distinct transmission profile, or signature, associated with it. The detection of this signature could indicate whether or not the fabric in question is counterfeit.

The NPL examined fabrics made from wool, cotton, linen, silk and mixed fibres, all of which demonstrated distinct terahertz transmission properties. THz-TDS could clearly distinguish between fabrics that looked and felt similar but that had different compositions; it could, for example, tell the difference between plain wool and the more expensive merino wool, as well as between natural and synthetic silk.

The technique has been published in the journal Applied Optics and described by Molloy as “a fast, safe and reliable test” to identify different textiles and help prevent fraud.

The next stage will be to test batches of the same type of fabric from the same manufacturer in a potential collaboration. It is also necessary to create a database of the terahertz transmission properties of many different fabrics and to study further the relationship between these and the properties of the fabrics themselves.

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