[QuadList] Alfecon II Video Heads (Was Quad Heads--When metal tips gave way to Ferrite... and what role Spin Physics played--)

Thu Sep 4 23:36:57 CDT 2014

Hello Gary,

This is it (or part of) what I was referring to (but still searching):

http://www.google.com/patents/US3479738

J. J. HANAK MAGNETIC HEADS Nov. 25, 1969 Filed May 23, 1967 II I I mvnvron JEJEPH Joy/v HAN/1K BY {ii/ M 9 E!- United States Patent 3,479,738 MAGNETIC HEADS Joseph John Hanak, Trenton, N.J., assignor to RCA Corporation, a corporation of Delaware Filed May 23, 1967, Ser. No. 641,443 Int. Cl. H01f 7/06; Gllb 5/42 US. Cl. 29-603 6 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a magnetic transducer and method of manufacturing the same for use in high frequency recording and reproducing apparatus. The transducer comprises at least two circuit parts of single crystal ferrite positioned to form a front gap, which is filled by a suitable technique with a non-magnetic spacing material. The back surfaces of the ferrite circuit parts are united by molecular transport which provides a relatively low reluctance path in the vicinity of the final assembled transducer which was formerly occupied by the back surfaces of the circuit parts or back gap. The molecular transport bond results in a ferrite molecular distribution which affords a reluctance of the same order of magnitude as the reluctance associated with a continuous body of ferrite, minimizing the drive current required for operation because of the virtual elimination of the back gap in the transducer.

BACKGROUND OF INVENTION A recording head is basically a miniature horse shoe electro-magnet in which the pole piece separation is a function of the frequency of operation. For use in high frequency recording and reproducing apparatus, there is needed a transducer which has a very small pole piece separation gap width in the order of magnitude of 1 to 3 microns. Furthermore, because of the techniques employed in video recording there is a contacting of the transducer with the recording medium resulting in increased wear of the transducer and a low life expectancy. Many high frequency heads normally employ some type of ferrite because of the characteristics ferrites possess such as low reluctances, good magnetic properties and excellent high frequency response. In spite of these characteristics such heads are still susceptible to cracking and chipping especially in the vicinity of the pole piece separation or gap. Hence as is taught in the prior art, the gap is usually filled with a material of equal hardness to that of the ferrite such as glass or a suitable metallic substance. However, due to the small pole separation or gap length of high frequency transducers the construction of such heads becomes diflicult in that the required tolerances cannot be easily obtained. Such transducers or heads have been made of two halves of ferrite held together by forcing the parts together either mechanically or by the application of a poting resin or some other suitable type of glues. The gap material is made from a non-magnetic material and also held in place by a compression technique or glue. From the above it is clear that in these particular transducers the gap material is usually not bonded to the ferrite parts and because of this such heads have very low life expectancy when operated in high speed devices.

Presently a great many recording heads are made of metal such as mu-metal which is rather soft and wears easily, or of an aluminum-silicon-iron alloy known as Sendust or Alfacon which is hard and brittle. Recently ferrite heads have been employed as transducers and as such are capable of longer life and better frequency response than the above types. But, as indicated, these transducers still suffer from erosion and loss as small 3,479,738 Patented Nov. 25, 1969 grains of the ferrite are shaken loose by the high speed moving tape or head assemblies used in modern transports. The prior art indicates some significant developmerits in ferrite head technology among which is the joining of the two ferrite circuit parts by flowing low melting point glass into the gap areas. In this manner the glass acts as both the bond and gap spacing material. However, in spite of the advancement in the technology such heads still exhibit relatively poor life"cha'rac'teristic because of the tendency of the glass gap to at a faster rate than the ferrite. Another problem is that glass is also utilized in an area designated by the prior art as the back gap. Glass or any other non-magnetic material in the back gap serves to increase the drive requirements for such heads and hence makes high frequency operation of such devices more difficult.

It is therefore an object of the present invention to provide an improved ferrite transducer capable .of high frequency operation and long life expectancy.

A further object is to provide an improved ferrite transducer in which a low reluctance path is provided throughout the body of the device, not including the front gap, whereby any back gap effect is virtually eliminated.

Still a further object is to provide a method for manufacturing an improved magnetic transducer where the reluctance due to the back gap is substantially eliminated.

According to one aspect of the invention, a transducer is provided which comprises at least two C-shaped circuit parts of single crystal ferrite. The circuit parts are positioned in a manner to form a front gap between two of their surfaces. The front gap is completely filled in with alumina which is bonded to the respective front gap forming surfaces. The head also is united at its back surfaces by a molecular transport of the ferrite grains from one circuit part to another. The bond formed by molecular transport provides a reluctance path in its vicinity which offer a reluctance equivalent to that of a continuous ferrite.

Also according to the invention 'a method of manufacturing such transducers is described in which at least the back surfaces of the circuit parts are joined together by molecular transport due to a glass film sputtered on the surfaces. The two treated back surfaces are now subjected to applied pressure and temperature preferably in the presence of a vacuum, which conditions cause the sputtered glass to flow in a manner causing it to behave as a flux. In this mode, the glass serves to transport ferrite molecules which form a chemical or a molecular transport bond between these back surfaces thereby uniting them in a low reluctance mode. In a second method according to the invention at least the front surface of the ferrite circuit parts are etched to a depth of one half the thickness of the final gap. The etched front surfaces are then coated by radio frequency sputtering of a thin film of glass thereof. A thin film of alumina is then sputtered onto one of the circuit parts. This film of alumina is again coated with another thin film of glass. The back gap area is also covered with a layer of glass whose-depth is closely controlled to enable the glass to behave as a transport flux. The treated circuit parts are then placed in a vacuum at a given temperature and by the useof pressure for a suitable time are united together and then cooled. The final assembly is a high frequency transducer with an alumina gap spacer in which there is virtually no reluctance contribution attributed to a back gap and in which the gap definition due to the alumina is unimpaired.

David Crosthwait
DC Video

On Sep 4, 2014, at 6:29 PM, Gary Adams via QuadList wrote:

> 
> 
> From: garyaadams at gmail.com
> Date: September 4, 2014 6:29:05 PM PDT
> To: "David Crosthwait" <david at dcvideo.com>, "Quad List" <quadlist at quadvideotapegroup.com>
> Subject: Re: [QuadList] Quad Heads--When metal tips gave way to Ferrite...	and what role Spin Physics played--
> Reply-To: garyaadams at gmail.com
> 
> 
> David. You are pretty good with this stuff too. Heard that term tossed about a few times. 
> 
> Regards. Gary

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