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Browse Prior Art Database

Measuring the Stress Distribution in a Flexible Medium Under Tension

IP.com Disclosure Number: IPCOM000085772D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Grimm, MA: AUTHOR [+2]

Abstract

The device shown schematically depicts an apparatus for measuring stress distribution in flexible media, be it in tape or disk.

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Measuring the Stress Distribution in a Flexible Medium Under Tension

The device shown schematically depicts an apparatus for measuring stress distribution in flexible media, be it in tape or disk.

Light emitted from laser 10 is redirected by a mirror M through a polarizer (POL) and a 1/2 wave retarder R onto a prism P1. After total internal reflection (TIR) at prism P1, the narrow light beam is directed toward the media (tape or disk) at some distance from the apparatus. After refraction and reflection from the media, the beam is redirected by a second prism P2 toward a detection system
12.

Prisms P1 and P2 are mounted on a rigid support S in such a way that a small air space 14 is created between the prisms and support S, thus allowing total reflection.

The purpose of the prisms arrangement P1, P2, S is twofold. First to deflect the light beam into the direction of the media and detector system 12 and secondly to act as a phase shifter in order to create circular polarized light. A relative phase shift of pi/2 between the p and s components of polarization is required in order to obtain circular polarized light. This is obtained in the following way. The retarder R is oriented in such a way as to turn the plane of rotation of the electric vector at an angle of 45 degrees with respect to the plane of incidence at the surface of TIR of P1. A second reflection at prism P2 will give an additional phase shift for a total of 90 degrees.

Incidently, the angle of incidence can be determined by well-established mathematical formulas which yield two angles of incidence, theta 1 and theta 2. Circular polarized light can be realized using either angle of incidence theta. The media is located at a distance d from the prism that is given by d = s/2 cot (2theta - 90 degrees), where s is the separation between prisms P1 and P2. Since the incident angle at the tape surface is much smalle...