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Electromagnetic Transducers

IP.com Disclosure Number: IPCOM000078812D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 65K

Publishing Venue

IBM

Related People

Hearn, BR: AUTHOR [+6]

Abstract

The electromagnetic transducers of Figs. 1 to 6 effect a write-wide read-narrow operation and have several common features of construction. Each includes a "single turn" copper strip element consisting of two spaced apart legs connected at their ends by a bridging strip. The bridging strip is sandwiched between two laminar magnetizable members made of a magnetic alloy, containing nickel and iron. These members form a magnetizable yoke and define a transducing gap adjacent one edge of the strip. The transducers are distinguished by having differently constructed yoke edge and center portions, as will be described.

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Electromagnetic Transducers

The electromagnetic transducers of Figs. 1 to 6 effect a write-wide read- narrow operation and have several common features of construction. Each includes a "single turn" copper strip element consisting of two spaced apart legs connected at their ends by a bridging strip. The bridging strip is sandwiched between two laminar magnetizable members made of a magnetic alloy, containing nickel and iron. These members form a magnetizable yoke and define a transducing gap adjacent one edge of the strip. The transducers are distinguished by having differently constructed yoke edge and center portions, as will be described.

The electromagnetic transducer of Figs. 1a, 1b and 1c includes a copper strip element 10, consisting of two spaced apart legs 11 connected at their ends by a bridging strip 12. The bridging strip is sandwiched between two laminar magnetizable members 13 and 14, which together form a magnetizable yoke 15. The members 13 and 14 define a transducing gap 16 adjacent one edge of the strip 12, and are magnetically joined to form a flux closure region 17 adjacent the opposite edge of the strip. The yoke 15 has edge portions 18 and a center portion 19 made of different magnetic materials. Both these magnetic materials have the low-hysteresis properties and linear magnetization curve generally desirable in a magnetic transducer. Center portion 19 is made of a nickel-iron alloy of relatively high permeability, whereas edge portions 18 are of a nickel- iron-cobalt alloy of substantially lower permeability.

Because the edge portions 18 of the yoke are of lower permeability than the center portion 19, the reluctance of the flux path around the strip from the gap edges is higher than that from the gap center. Consequently, a magnetic field incident on the gap edges is relatively less effective to produce a flux passing around strip 12, than is such a field incident on the gap center. The signal contribution from the edge portions can be attenuated to such an extent, that the transducer effectively reads only over the center portion of the gap.

By using a write current considerably in excess of that needed for the high- efficiency center portion, a strong write field can be produced at the edges to allow the transducer to write over the entire width of its yoke.

Several other alternative ways of varying the reluctance of the flux paths around the strip are possible. One of these, which allows the same magnetic material to be used for the edge and center portions, is to thicken the center portion of the overlying magnetizable member. Another way, as illustrated in Fig. 2, is to introduce diagonal slots 21 and 22 in edge portions 27 and 28 of the overlying magnetizable yoke member. These slots interrupt the path of flux around the bridging strip, thus increasing the edge path reluctance.

The transducer of Figs. 3a and 3b has a copper strip element 30 consisting of two legs 31, joined at their ends by a bridgin...