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Browse Prior Art Database

Radiant Energy Mark Sensor

IP.com Disclosure Number: IPCOM000075312D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Holdaway, DO: AUTHOR

Abstract

Shown is a radiant energy sensor which detects the presence or absence of reflective marks on a background. The object being scanned comprises a transparent substrate or background material 1. This material has an index of refraction for the wavelength of radiant energy being used. Attached to this substrate 1 are reflective marks 2 which are formed by coating a highly reflective metal on the surface of substrate 1. The back of substrate 1 is coated with a light absorbent material 3.

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Radiant Energy Mark Sensor

Shown is a radiant energy sensor which detects the presence or absence of reflective marks on a background. The object being scanned comprises a transparent substrate or background material 1. This material has an index of refraction for the wavelength of radiant energy being used. Attached to this substrate 1 are reflective marks 2 which are formed by coating a highly reflective metal on the surface of substrate 1. The back of substrate 1 is coated with a light absorbent material 3.

When incident light 4 strikes substrate 1 (Fig. 1), a portion 8 of the light is refracted into substrate 1 and absorbed by material 3. The remaining light 7 is reflected from substrate 1 to polarizing screen 5. In this case, the reflected light 7 is blocked by screen 5 so that it does not reach photodetector 6. This is accomplished by having the incident beam of light 4 strike substrate 1 at or near the Brewster's angle and placing screen 5 to null out the polarized reflected light.

The Brewster's angle is given by the following expression: n2/n1 = tan theta where n2 is the index of refraction of substrate 1 and nl is the index of refraction of the incident medium and theta is the incidence angle of light beam 4.

In Fig. 2 the incident light 4 strikes reflective mark 2. The reflected light 9 is not polarized and passes through screen 5 to photodetector 6.

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