Stress demagnetization in videotapes

Experience with helical-scan videotape recorders has shown that the mechanical forces involved in handling the tape are sometimes sufficient to cause significant reductions in signal level due to stress demagnetization. A tape-loop recorder was used in an investigation of stress demagnetization in videotapes. Results are presented illustrating the magnitude of stress demagnetization and its dependence on the type of tape and the number of applications of stress. The bending stress resulting from the wrap of the tape around guides was studied in considerable detail. It is found that bending stress can greatly exceed other stresses involved in the normal handling of tape. Results are presented to show how bending-stress demagnetization depends on the depth of recording in the magnetic coating and on the radius of the guide. It is found that there is also a strong dependence on wrap angle around the guide. A new analysis is presented to explain the wrap-angle dependence and to permit calculation of bending-stress demagnetization.