Patent GB-1463120-A (GB)
Title: Magnetic head and method of making same
IPC: G11B5/21
Filed: 1974-03-20
Abstract: 1463120 Magnetic transducer heads MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 20 March 1974 [20 March 1973 (3) 6 July 1973 (2)] 12381/74 Heading G5R A scanning-type magnetic head, in which variation of the currents in scanning coils 11, 11<SP>1</SP> of E-shaped electromagnets 10, 10<SP>1</SP> scans the operative transducing point along a gap 4, has first magnetic polepieces 3, 3<SP>1</SP>, and second polepieces formed by thin films 1, 101 and 1<SP>1</SP>, 101<SP>1</SP> of magnetically soft material, the films having parts 1, 1<SP>1</SP> on planar faces of pieces 3, 3<SP>1</SP> and parts 101, 101<SP>1</SP> joined at respective edges at the gap 4 to parts 1, 1<SP>1</SP>, the parts 101, 101<SP>1</SP> extending at an acute angle to parts 1, 1<SP>1</SP> respectively and defining a triangular space between parts 101, 101<SP>1</SP> in which is located a central magnetic core 2 of a material having a permeability which is constant with variation of magnetic field, signal coils 7, 7<SP>1</SP> being located around film parts 101, 101<SP>1</SP> and polepieces 3, 3<SP>1</SP> and the E-shaped cores of magnets 10, 10<SP>1</SP> being located with their centre legs coupled with respective end faces of centre core 2 and their outer legs coupled with respective end faces of polepieces 3, 3<SP>1</SP>. The transducing point for recording or playback signals in series connected coils 7, 7<SP>1</SP> is caused to scan along the gap by applying sawtooth waveform currents to coils 11, 11<SP>1</SP>, whereby tracks transverse to the length of a magnetic tape may be scanned without moving the head. Alternatively, track selection, e.g. on a magnetic disc or drum, can be effected by supplying various preset currents to coils 11, 11<SP>1</SP>. The films 1, 101, 1<SP>1</SP>, 101<SP>1</SP> may be of permalloy or Fe-Al-Si alloy and are anisotropic with the directions of higher permeability perpendicular to gap 4. The films may be bonded or applied by vapour deposition in two stages, one stage forming film 1 or 1<SP>1</SP> on magnetically soft, high permeability core 3 or 3<SP>1</SP>, made of ferrite, and the second stage forming film 101 or 1011 on a ceramic substrate 15 or 15<SP>1</SP>, e.g. of hotpressed zinc ferrite, glass-bonded to core 3 or 3<SP>1</SP>. In an alternative construction, Fig. 6 (not shown), glass (23) is melted on to core 3 or 3<SP>1</SP> and the resultant element lapped to produce a planar top face to receive film 1 or 1<SP>1</SP> and a planar glass face oblique to the top face to receive film 101 or 101<SP>1</SP>, the glass parts replacing substrate 15 or 15<SP>1</SP> and also filling the void present between this substrate and core 3 or 3<SP>1</SP> in the first construction. A photo-etching process on the films 1, 101, 1<SP>1</SP>, 101<SP>1</SP> produces layers in the form of a fine stripe pattern, the stripes being perpendicular to gap 4 and the stripes of film 1 or 1<SP>1</SP> continuing as corresponding stripes of film 101 or 1011. The thin films may be 1 to 10, preferably 1 to 5, microns thick, the pitch of the stripes being 20 to 200 microns. The centre core 2 is of low permeability (e.g. 10 to 200) material, such as carbonyl iron or Fe-Al-Si alloy.