US2468601A - Head for magnetic recording machines - Google Patents

Head for magnetic recording machines Download PDF

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US2468601A
US2468601A US637656A US63765645A US2468601A US 2468601 A US2468601 A US 2468601A US 637656 A US637656 A US 637656A US 63765645 A US63765645 A US 63765645A US 2468601 A US2468601 A US 2468601A
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gap
wire
head
magnetic
magnetic recording
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US637656A
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Thomas H Long
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CG Conn Ltd
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Conn Ltd C G
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/187—Structure or manufacture of the surface of the head in physical contact with, or immediately adjacent to the recording medium; Pole pieces; Gap features
    • G11B5/23—Gap features
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B15/00—Driving, starting or stopping record carriers of filamentary or web form; Driving both such record carriers and heads; Guiding such record carriers or containers therefor; Control thereof; Control of operating function
    • G11B15/60—Guiding record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/147—Structure or manufacture of heads, e.g. inductive with cores being composed of metal sheets, i.e. laminated cores with cores composed of isolated magnetic layers, e.g. sheets

Definitions

  • This invention relates to heads for magnetic recording machines and more particularly to the construction of magnetic heads for impressing a recording on a Wire, for playing back a recording from a wire or for erasing a recording from a wire. It will be understood that references to a recording machine or a recording head herein are intended to include playback or erasing machines or heads and that references to a wire are intended to include any elongated magnetic medium whether in the form of a conventional wire or a tape.
  • magnetic heads of this type have generally consisted of a magnetic core formed with a groove through which the wire runs and having a gap in th core traversed by the wire. It has been found in operation of these heads that magnetic mud accumulates on the core as a gummy residue and tends to shunt the working gap in the core. This mud also holds the wire slightly spaced from the core so that good magnetic contact is not obtained between the wire and the core material. These effects ar particularly objectionable at relatively high frequencies for example, above approximately 2500 cycles per second at wire speeds of about two feet per second and can be avoided only by frequent and careful cleaning and lubrication of the head.
  • the flux penetration is a function of the curvature of the surface to be penetrated so that penetration is less into a concave surface than into a plane surface.
  • a grooved head has certain inherent magnetic defects.
  • Still another object is to provide a head which is engaged by the wire at different positions along its working gap during operation.
  • This ar- 2 rangement which may be effected by a level-wind device, assists in keeping the head clean and in preventing channeling of the head by th wire.
  • Still another object is to provide a head in which the wire leaves the head in a position of minimum and/ or negligible magnetomotive force gradient. This arrangement reduces the stray field effect and minimizes demagnetization of the wire at the point where it leaves the head.
  • a further object is to provide a head in which the wire runs across a smooth cylindrical surface.
  • the gap in the magnetic core is filled with a relatively hard nonmagnetic material joining smoothly into the core material at opposite sides of the gap.
  • a still further object is to provide a head formed with a tapered gap across which the wir may trave1 at different positions to provide an easy means for varying the effective gap length.
  • Figure 2 is a top plan View of Figure 1;
  • Figure 3 is a partial top plan view of an alternative construction.
  • Figure 4 is an end elevation of a head illustrating a modified arrangement of the Winding thereon.
  • Figure 1 illustrates a portion of a more or less conventional magnetic recording machine on an enlarged scale.
  • the machine as shown, includes a windup spool l0 driven by a suitable power source, not shown, and geared through gears H to a level-wind device indicated generally at l2.
  • the level-wind device includes a screw 43 for driving a carriage I4 back and forth across the end of the spool.
  • the carriage l4 carries a guide or eyelet 15 through which a wire l6 may be threaded to be Wound evenly on the spool l0.
  • a magnetic head Adjacent the level-wind device and on the side thereof remote from the spool a magnetic head is mounted to engage the wire.
  • the head may be either for magnetizing the wire to impress a recording thereon. for playing back a recording from the wire or for erasing a previous recording from the wire.
  • the head construction will be substantially identical, it being noted that the same head may be used for any of these purposes except that the gap employed in an erasing head is generally somewhat greater than that in a, recording and playback head.
  • the body I! is cut away at its upper portion, as best seen in Figure 2 to expose the laminations adjacent the gap therein so that they may be en'- gaged by the wire I6, as shown.
  • the showing of the gap in the drawings is exaggerated for ease of illustration, the actual gap on a playback head for a wire speed of two feet per second being about .0015 inch.
  • the gap is preferably filled with a non-magnetic strip 59.
  • the strip [9 is formed of a hard material such, for example, as beryllium copper which is hardened to be as hard as, or harder than, the adjacent mag netic material to eliminate the tendency for the wire to drag metal across the gap from the pole pieces and to eliminate undercutting of the filler strip by the wire which might occur if a soft material were used for the filler strip.
  • the head may carry a winding of any desired type for recording, playback or erasing.
  • a double winding 2! is mounted on the head on opposite sides of the gap leaving the upper part of the head open for easy insertion or removal of the wire and for cleaning.
  • the open construction gives results comparable to those obtained with conventional closed heads although, if desired, a closed head can be employed by utilizing a winding 22 extending around the gap so that the wire must pass through it, as shown in Figure
  • One reason for the results obtained with the present head is believed to be the fact that the wire travels substantially tangentially across the gap and leaves the head in a direction of minimum magnetomotive force gradient. Therefore, no demagnetization of the wire occurs except that which necessarily occurs immediately after passing the gap.
  • the level-wind device causes the wire to move along the gap in the head as it travels across the gap. This produces a selfcleaning eiiect, tending to prevent the accumulation of magnetic mud on the head so that the gap will not be shunted and so that good contact between the wire and the magnetic core is obtained at all times. Since the head construction is completely open and does not involve any relatively small grooves in which magnetic mud or other foreign material can accumulate, it can easily be cleaned, simply by wiping the exposed magnetic core material with a suitable cleaning agent or solvent. In this way, uniform results over a long period of time are obtained with a minimum of attention and with substantially increased wear life over a conventional grooved head. The advantages of the present construction are particularly pronounced in the high frequency range.
  • the head is substantially similar to that of Figures 1 and 2 except that the gap istapered along its length
  • a non-magnetic cylindrical frame 23 carries magnetic laminations 2a, the ends of which are cut at an angle to provide a tapered gap which may be filled with a tapered non-magnetic filler strip 25.
  • a guide 26 is provided which can be adjusted transversely of the head by a screw 27 controlled by a manual handle or crank 28. By adjusting the position of the guide 26 through the screw 2?, the point at which the wire crosses the gap can be controlled so that the effective gap length can easily be varied.
  • This construction may be highly desirable for certain types of work.
  • a head for a magnetic recording machine comprising a magnetic body having a substantially smooth convex portion formed with a gap across which a magnetic wire is adapted to travel, a winding associated with the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across different points in the gap length.
  • a head for a magnetic recording machine comprising a magnetic body having a substantially smooth convex portion formed with a gap across which a magnetic wire is adapted to travel, a filler of non-magnetic material in the gap to provide a smooth surface over which the wire can travel, a winding on the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across different points in the gap length.
  • a head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with a gap across which a magnetic wire is adapted to travel, a winding on the body, and a level-wind device adjacent the body to move the magnetic wire along the gap as it travels across the gap the gap length being at least as great as the movement of the wire along the gap by the level wind device.
  • a head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with a gap across which a magnetic wire is adapted to travel, a filler of non-magnetic material in the gap to provide a smooth surface over which the wire can travel, a
  • the body and a level-wind device adjacent the body to move the magnetic wire along the gap as it travels across the gap, the gap length being at least as great as the movement of the wire along the gap by the level wind device.
  • a head for a magnetic recording machine comprising a hollow cylindrical body of mag netic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a winding on the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across difierent points in the gap length.
  • a head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a non-magnetic filler in the gap to provide a smooth cylindrical surface over which the wire travels, a winding on the body,
  • a head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a level wind device adjacent the body to move the wire along the gap as it travels across the gap, and a winding on the body the gap length being at least as great as the movement of the wire along the gap by the level wind device.
  • a head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a non-magnetic filler in the gap to provide a smooth cylindrical surface over which the wire travels, a level wind device adjacent the body to move the wire along the gap as it travels across the gap, and a winding on the body the gap length being at least as great as the movement of the wire along the gap by the level wind device.
  • a head for a magnetic recording machine comprising a series of thin laminations formed in a substantially cylindrical shape with their ends separated to form an axially extending gap, the ends of the inner laminations being separated to a greater extent than the outer laminations, a level wind device adjacent the head to move a wire along the gap as it travels across the gap, and a winding on the laminations the gap length being at least as great as the movement of the Wire along the gap by the level wind device.
  • a head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with an axially extending gap across which a wire is adapted to travel, the gap tapering to provide different gap widths at diiferent points in the gap length, a winding on the body, and adjustable guide means for the wire to guide it across difierent points in the gap length.
  • a head for a magnetic recording machine comprising partially cylindrical pole pieces formed with an axially extending gap therebetween so that a magnetic wire can be moved perpendicular to the gap and can have a component of motion parallel to the gap, a winding magnetically associated with the pole pieces, and guide means engaging the wire and movable parallel to the gap to give the wire said component of motion parallel to the gap.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Magnetic Heads (AREA)

Description

April 26, 1949.
T. H. LONG HEAD FOR MAGNETIC RECORDING MACHINES Filed Dec. 28, 1945 iziarze w.
Patented Apr. 26, 1949 HEAD FOR MAGgTETIC RECORDING MA HINES Thomas H. Long, Elkhart, Ind., assignor to C. G. Conn, Ltd., Elkhart, Ind., a corporation of Indiana Application December 28, 1945, Serial No. 637,656
11 Claims. 1
This invention relates to heads for magnetic recording machines and more particularly to the construction of magnetic heads for impressing a recording on a Wire, for playing back a recording from a wire or for erasing a recording from a wire. It will be understood that references to a recording machine or a recording head herein are intended to include playback or erasing machines or heads and that references to a wire are intended to include any elongated magnetic medium whether in the form of a conventional wire or a tape.
As heretofore constructed, magnetic heads of this type have generally consisted of a magnetic core formed with a groove through which the wire runs and having a gap in th core traversed by the wire. It has been found in operation of these heads that magnetic mud accumulates on the core as a gummy residue and tends to shunt the working gap in the core. This mud also holds the wire slightly spaced from the core so that good magnetic contact is not obtained between the wire and the core material. These effects ar particularly objectionable at relatively high frequencies for example, above approximately 2500 cycles per second at wire speeds of about two feet per second and can be avoided only by frequent and careful cleaning and lubrication of the head.
Another difficulty which has been encountered is that the wire tends to form in the head a slight channel due to the fact that the wire travels at all times across the same portion of the groove. If there should be a section of wire whose diameter is only slightly in excess of that previously running through the head, binding may occur which will cause breakage of the wire or which will cause cold working of one side of the wire resulting in objectionable kinkiness.
It has further been determined that the flux penetration is a function of the curvature of the surface to be penetrated so that penetration is less into a concave surface than into a plane surface. Thus a grooved head has certain inherent magnetic defects.
It is one of the objects of the present invention to provide a head in which the several defects in or objections to conventional grooved heads are removed.
It is another object to provide a head which is substantially self-cleaning and which in any case can easily be cleaned.
Still another object is to provide a head which is engaged by the wire at different positions along its working gap during operation. This ar- 2 rangement, which may be effected by a level-wind device, assists in keeping the head clean and in preventing channeling of the head by th wire.
Still another object is to provide a head in which the wire leaves the head in a position of minimum and/ or negligible magnetomotive force gradient. This arrangement reduces the stray field effect and minimizes demagnetization of the wire at the point where it leaves the head.
A further object is to provide a head in which the wire runs across a smooth cylindrical surface. In one desired construction, the gap in the magnetic core is filled with a relatively hard nonmagnetic material joining smoothly into the core material at opposite sides of the gap.
A still further object is to provide a head formed with a tapered gap across which the wir may trave1 at different positions to provide an easy means for varying the effective gap length.
The above and other objects and advantages of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing, in which- Figure 1 is a diagrammatic view illustrating a head embodying the invention in side elevation;
Figure 2 is a top plan View of Figure 1;
Figure 3 is a partial top plan view of an alternative construction; and
Figure 4 is an end elevation of a head illustrating a modified arrangement of the Winding thereon.
Figure 1 illustrates a portion of a more or less conventional magnetic recording machine on an enlarged scale. The machine, as shown, includes a windup spool l0 driven by a suitable power source, not shown, and geared through gears H to a level-wind device indicated generally at l2. The level-wind device includes a screw 43 for driving a carriage I4 back and forth across the end of the spool. The carriage l4 carries a guide or eyelet 15 through which a wire l6 may be threaded to be Wound evenly on the spool l0.
Adjacent the level-wind device and on the side thereof remote from the spool a magnetic head is mounted to engage the wire. The head may be either for magnetizing the wire to impress a recording thereon. for playing back a recording from the wire or for erasing a previous recording from the wire. In any case, the head construction will be substantially identical, it being noted that the same head may be used for any of these purposes except that the gap employed in an erasing head is generally somewhat greater than that in a, recording and playback head. As
tion to provide increased flux concentration at the point Where the wire crosses the gap. The body I! is cut away at its upper portion, as best seen in Figure 2 to expose the laminations adjacent the gap therein so that they may be en'- gaged by the wire I6, as shown. The showing of the gap in the drawings is exaggerated for ease of illustration, the actual gap on a playback head for a wire speed of two feet per second being about .0015 inch.
In order to provide a smooth surface over which the wire IB may travel, the gap is preferably filled with a non-magnetic strip 59. The strip [9 is formed of a hard material such, for example, as beryllium copper which is hardened to be as hard as, or harder than, the adjacent mag netic material to eliminate the tendency for the wire to drag metal across the gap from the pole pieces and to eliminate undercutting of the filler strip by the wire which might occur if a soft material were used for the filler strip.
The head may carry a winding of any desired type for recording, playback or erasing. As shown in Figure 1, a double winding 2! is mounted on the head on opposite sides of the gap leaving the upper part of the head open for easy insertion or removal of the wire and for cleaning. With the head of the present invention, I have found that the open construction, as illustrated in Figure 1, gives results comparable to those obtained with conventional closed heads although, if desired, a closed head can be employed by utilizing a winding 22 extending around the gap so that the wire must pass through it, as shown in Figure One reason for the results obtained with the present head is believed to be the fact that the wire travels substantially tangentially across the gap and leaves the head in a direction of minimum magnetomotive force gradient. Therefore, no demagnetization of the wire occurs except that which necessarily occurs immediately after passing the gap.
In operation of the apparatus, as shown in Figures 1 and 2, the level-wind device causes the wire to move along the gap in the head as it travels across the gap. This produces a selfcleaning eiiect, tending to prevent the accumulation of magnetic mud on the head so that the gap will not be shunted and so that good contact between the wire and the magnetic core is obtained at all times. Since the head construction is completely open and does not involve any relatively small grooves in which magnetic mud or other foreign material can accumulate, it can easily be cleaned, simply by wiping the exposed magnetic core material with a suitable cleaning agent or solvent. In this way, uniform results over a long period of time are obtained with a minimum of attention and with substantially increased wear life over a conventional grooved head. The advantages of the present construction are particularly pronounced in the high frequency range.
In the construction of Figure 3, the head is substantially similar to that of Figures 1 and 2 except that the gap istapered along its length,
as shown. In this construction, a non-magnetic cylindrical frame 23 carries magnetic laminations 2a, the ends of which are cut at an angle to provide a tapered gap which may be filled with a tapered non-magnetic filler strip 25. To control the position at which the wire crosses the gap, a guide 26 is provided which can be adjusted transversely of the head by a screw 27 controlled by a manual handle or crank 28. By adjusting the position of the guide 26 through the screw 2?, the point at which the wire crosses the gap can be controlled so that the effective gap length can easily be varied. This construction may be highly desirable for certain types of work.
While several embodiments of the invention have been shown and described in detail, it will be understood that these are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.
What is claimed is:
1. A head for a magnetic recording machine comprising a magnetic body having a substantially smooth convex portion formed with a gap across which a magnetic wire is adapted to travel, a winding associated with the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across different points in the gap length.
2. A head for a magnetic recording machine comprising a magnetic body having a substantially smooth convex portion formed with a gap across which a magnetic wire is adapted to travel, a filler of non-magnetic material in the gap to provide a smooth surface over which the wire can travel, a winding on the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across different points in the gap length.
3. A head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with a gap across which a magnetic wire is adapted to travel, a winding on the body, and a level-wind device adjacent the body to move the magnetic wire along the gap as it travels across the gap the gap length being at least as great as the movement of the wire along the gap by the level wind device.
4. A head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with a gap across which a magnetic wire is adapted to travel, a filler of non-magnetic material in the gap to provide a smooth surface over which the wire can travel, a
winding on the body, and a level-wind device adjacent the body to move the magnetic wire along the gap as it travels across the gap, the gap length being at least as great as the movement of the wire along the gap by the level wind device.
5. A head for a magnetic recording machine comprising a hollow cylindrical body of mag netic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a winding on the body, and guide means engageable with the wire and movable parallel to the gap to guide the wire across difierent points in the gap length.
6. A head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a non-magnetic filler in the gap to provide a smooth cylindrical surface over which the wire travels, a winding on the body,
and guide means engageable with the wire and movable parallel to the gap to guide the wire across diiferent points in the gap length.
7. A head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a level wind device adjacent the body to move the wire along the gap as it travels across the gap, and a winding on the body the gap length being at least as great as the movement of the wire along the gap by the level wind device.
8. A head for a magnetic recording machine comprising a hollow cylindrical body of magnetic material formed with an axially extending gap in one side across which a magnetic wire is adapted to travel, a non-magnetic filler in the gap to provide a smooth cylindrical surface over which the wire travels, a level wind device adjacent the body to move the wire along the gap as it travels across the gap, and a winding on the body the gap length being at least as great as the movement of the wire along the gap by the level wind device.
9. A head for a magnetic recording machine comprising a series of thin laminations formed in a substantially cylindrical shape with their ends separated to form an axially extending gap, the ends of the inner laminations being separated to a greater extent than the outer laminations, a level wind device adjacent the head to move a wire along the gap as it travels across the gap, and a winding on the laminations the gap length being at least as great as the movement of the Wire along the gap by the level wind device.
10. A head for a magnetic recording machine comprising a magnetic body having a substantially cylindrical portion formed with an axially extending gap across which a wire is adapted to travel, the gap tapering to provide different gap widths at diiferent points in the gap length, a winding on the body, and adjustable guide means for the wire to guide it across difierent points in the gap length.
11. A head for a magnetic recording machine comprising partially cylindrical pole pieces formed with an axially extending gap therebetween so that a magnetic wire can be moved perpendicular to the gap and can have a component of motion parallel to the gap, a winding magnetically associated with the pole pieces, and guide means engaging the wire and movable parallel to the gap to give the wire said component of motion parallel to the gap.
THOMAS H. LONG.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,230,913 Schuller i Feb. 4, 1941 2,351,005 Camras June 13, 1944 FOREIGN PATENTS Number Country Date 143,240 Austria Oct. 25, 1935
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2628284A (en) * 1949-10-31 1953-02-10 Rca Corp Magnetic transducer
US2647167A (en) * 1950-03-21 1953-07-28 Rca Corp Magnetic transducer construction
US2655563A (en) * 1947-03-31 1953-10-13 Lawrence H Connell Magnetic reproducing service for automobiles
US2698875A (en) * 1950-03-24 1955-01-04 Magnecord Inc Plural track magnetic recording and/or reproducing apparatus
US2839613A (en) * 1952-07-07 1958-06-17 Marchant Res Inc Magnetic transducer head
DE1033439B (en) * 1953-03-14 1958-07-03 Zeiss Ikon Ag Magnetic head
DE1043655B (en) * 1953-03-14 1958-11-13 Zeiss Ikon Ag Magnetic head
DE1084933B (en) * 1957-03-20 1960-07-07 Telefonbau Rotatable electromagnetic transducer with several pairs of poles for sound reproduction devices
US3626344A (en) * 1969-07-28 1971-12-07 Viktor Egorovich Shaternikov Eddy currents transducer for electrical devices to control coating thickness and surface profile of metal articles

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT143240B (en) * 1934-12-14 1935-10-25 Aeg Magnetizing head for sound recording and playback.
US2230913A (en) * 1936-03-03 1941-02-04 Licentia Gmbh Magnetic sound recorder
US2351005A (en) * 1942-07-27 1944-06-13 Armour Res Found Magnetic recorder

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT143240B (en) * 1934-12-14 1935-10-25 Aeg Magnetizing head for sound recording and playback.
US2230913A (en) * 1936-03-03 1941-02-04 Licentia Gmbh Magnetic sound recorder
US2351005A (en) * 1942-07-27 1944-06-13 Armour Res Found Magnetic recorder

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2655563A (en) * 1947-03-31 1953-10-13 Lawrence H Connell Magnetic reproducing service for automobiles
US2628284A (en) * 1949-10-31 1953-02-10 Rca Corp Magnetic transducer
US2647167A (en) * 1950-03-21 1953-07-28 Rca Corp Magnetic transducer construction
US2698875A (en) * 1950-03-24 1955-01-04 Magnecord Inc Plural track magnetic recording and/or reproducing apparatus
US2839613A (en) * 1952-07-07 1958-06-17 Marchant Res Inc Magnetic transducer head
DE1033439B (en) * 1953-03-14 1958-07-03 Zeiss Ikon Ag Magnetic head
DE1043655B (en) * 1953-03-14 1958-11-13 Zeiss Ikon Ag Magnetic head
DE1084933B (en) * 1957-03-20 1960-07-07 Telefonbau Rotatable electromagnetic transducer with several pairs of poles for sound reproduction devices
US3626344A (en) * 1969-07-28 1971-12-07 Viktor Egorovich Shaternikov Eddy currents transducer for electrical devices to control coating thickness and surface profile of metal articles

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