| 摘要 |
A method and apparatus are disclosed for detecting the presence of a narrow band infrared absorptive material. Such materials are highly unusual and may be incorporated into inks or coatings for use in security printing applications. By illuminating an article bearing a coating with light alternately in the narrow band absorption region and outside that region, and by processing signals representative of the reflected intensity at the two different wavelengths, conclusions may be arrived at as to the presence or otherwise of the narrow band infrared absorptive material, even when broadband infrared absorptive material such as carbon black or other pigments is present in the coating, ink or the like. |
