Identification of illicit drugs by using SOM neural networks

Absorption spectra of six illicit drugs were measured by using the terahertz time-domain spectroscopy technique in the range 0.2?2.6?THz and then clustered with self-organization feature map (SOM) artificial neural network. After the network training process, the spectra collected at another time were identified successfully by the well-trained SOM network. An effective distance was introduced as a quantitative criterion to decide which cluster the new spectra were affiliated with.