Characterisation of coating material by comparing specularly reflected and scattered terahertz or infrared radiation

摘要

The present invention provides a method of analysing an object, comprising the steps of: (a) irradiating the object 29 with a pulse of electromagnetic radiation, from a THz source 23 said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz, such that a portion of the irradiating radiation couples to the object as a surface wave; (b) detecting radiation reflected and/or scattered from the object with detector 21 to obtain a time domain waveform; (c) extracting the parts of the radiation detected in step (b) relating to the surface wave on the object and (d) analysing the radiation identified in step (c) in order to derive information relating to a physical characteristic of the object. The phase or amplitude of the specularly reflected wave is compared to that of the radiation relating to the surface wave. The object comprises a central portion 35 and a coating 37, and may be a drug eluting stent.