Patent GB-1415765-A (GB)
Title: Optical scanner
IPC: G11B5/00
Filed: 1973-08-06
Abstract: 1415765 Magnetic storage arrangements; controlling light E I DU PONT DE NEMOURS & CO 6 Aug 1973 37289/73 Headings H3B and H4F [Also in Divisions G1 and G5] A cylindrical domain in a transparent magnetic plate is propagated in a uniform and continuous manner along a track of constant width defined by a magnetic overlay, the progress of the domain being identified by passing a beam of polarized light through the whole of the plate to an analyser. Overlays.-One form of overlay defining a uniform propagation track in a magnetic plate 10 is shown in Fig. 2a, the overlay consisting of anisotropic permalloy initially magnetized with a north pole at a start end 11c and south poles at bifurcated ends 11a, 11b. When a domain 12 is positioned at the start end it initiates, in conjunction with a magnetic field in the plane of the sheet, the propagation of a moving domain wall 13a, 13b in the overlay to which the domain 12 magnetically locks, the propagation track for domain 12 being defined by the parallel arms of the overlay. An alternative form of overlay is shown in Fig. 5 and consists of a spiral 81 of permalloy having a domain start position 82 and an end position 83, domains being propagated by an in-phase rotating magnetic field along a uniform track defined by the spiral. Sequential line scanner.-A line scanner using the overlay arrangement of Fig. 2a is shown in Fig. 3, each line being formed by a respective overlay 21-25 on a magnetic plate 20 which may consist of Eu 0À09 Gd 2À32 Tb 0À59 Fe 5À0 O 12 . A permanent domain 42 is held by a permanent magnet 32, and a movable domain is split off by pulsing a conductor loop 33, the separated domain being held at a hard magnetic material overlay forming a holding station 26. This domain is itself split when a current loop 31 is pulsed, one divided domain passing to a holding station 27, and the other moving to the start position of overlay 21 and then propagating to its end where it is detected by a magnetoresistive strip 40 before locking to a permanent magnet overlay 34. The output signal from the magneto resistive strip triggers a pulse generator 51 which causes the domain at holding station 27 to divide by pulsing conductor 31, one divided domain passing to holding station 28 and the other commencing propagation along overlay 22. Sequential line scanning continues, each domain after completing propagation along a line being held by a respective permanent magnet 35-38, while the non-propagated domain divided from the final holding station 30 is held by a permanent magnet 39. At the completion of scanning, a signal from a magnetoresistive strip 41 causes a pulse generator 56 to reverse the direction of the in-plane magnetic field produced by a coil 52 so as to reset the anisotropic overlays 21-25 to their original magnetic states. Similtaneously a pulse to a pulse generator 58 causes a domain to be transferred to holding station 26, and the same pulse through a time delay 59 commences a new scanning cycle by energizing pulse generator 51. An optical scanner is shown in Fig. 4 which utilizes the domain propagating plate and overlay arrangement 73 of Fig. 3, the scanning domains being identified by an optical system comprising a light source 70, a polarizer 72 and an analyser 77, and collimating and field lenses 71, 78. Only light transmitted through a domain position is passed by the analyser to a photodiode or other light detector 79. In use an optical transparency 80 is located between the analyser and lens 78, and the detector responds to the modulated light received as the transparency is raster scanned. Spiral scanner.-In Fig. 5 the start position 82 constitutes a domain generating position, a mobile domain being detached from a permanent domain and locked to the rotating magnetic field in the permalloy spiral by momentarily reducing the bias field normal to the magnetic plate which is necessary to maintain the cylindrical domains. A fully circulated domain is held at the end position 23. An optical scanner is shown in Figs. 6a, 6b which utilizes the magnetic plate and spiral overlay arrangement 93, 94 of Fig. 5, an outwardly spiralling domain being identified by an optical system comprising a light source 90, a polarizer 92 and an analyser 95, and collimating and field lenses 91, 97. To record electrical signals such as audio signals, an unexposed photographic plate is positioned behind the analyser and a spiralling domain is propagated, the electrical signals either modulating the light source 90, which may be a light emitting diode, or modulating the bias field normal to the magnetic plate which causes corresponding variation in the area of the moving domain. After developing, the photographic plate is located in its former position and is interrogated by a spiralling domain of constant area, the resulting variation of light intensity due to the recorded modulation being identified by a detector 98. The rotating magnetic field propagating the spiralling domains is produced by A.C. energized orthogonal coils 100-103. The frequency of the rotating field may be varied so as to propagate the domains at a constant linear speed.