BACKGROUND OF THE INVENTION
Field of the invention
The present device relates to a magnetic head in, for example, a
tape recorder as a magnetic record playback apparatus, and more particularly to
a construction resistant to an external magnetic noise in an audio magnetic head.
Fig. 4 is a perspective view illustrating the construction of a conventional
magnetic head, and Fig. 5 a sectional view of the principal part thereof. As shown
in Fig. 1, a magnetic head 1 is provided with a shielding case 2 including head
cores 3 and shielding plates 4 fitted in the case and secured therein with filler
In order to increase the shielding effect, a known magnetic head
is constructed so that a shielding cover 5 is additionally fitted to the outer
face of a shielding case 2 afterward.
In this case, the shielding case 2 and the shielding cover 5 are
formed of Permalloy so as to seek shielding properties against a low-frequency
Since only Permalloy is used for shielding purposes in the conventional
magnetic head 1, however, the shielding properties against a high-frequency magnetic
noise and magnetic waves have been insufficient, though those against a low-frequency
magnetic noise have been prominent. Therefore, the shielding properties in question
still remain insufficient in such an environment that a high-frequency external
electromagnetic field frequently acts thereon, thus causing a problem to arise
from deteriorating the S/N ratio.
Moreover, the manday required to fit the shielding covers 5 to the
outer sides of the shielding cases 2 one after another results in not only increasing
the number of parts but also necessitating the production and management of individual
SUMMARY OF THE INVENTION
In view of the foregoing problems arising from a magnetic noise shielding
mechanism including a shielding case and a shielding cover for a magnetic head
as set forth above, an object of the present device is to provide a magnetic head
having shielding properties against an external magnetic noise without necessitating
such a shielding cover.
In order to accomplish the object above, a magnetic head embodying
the present device is provided with a shielding case of three-layer structure comprising
Permalloy layers with a non-magnetic layer held therebetween.
According to the present device, the magnetic head is provided with
the shielding case of three-layer structure comprising: a first Permalloy layer
as the outer layer of the case, a third Permalloy layer as the inner layer thereof,
and a second non-magnetic layer as an intermediate layer. As a result, the effect
of shielding a low-frequency magnetic noise is heightened by the Permalloy layers
and that of shielding a high-frequency magnetic noise is heightened by the non-magnetic
layer at the same time.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Fig. 1 is a perspective view of a magnetic head embodying the present device;
- Fig. 2 is a sectional view taken of line A - A' of Fig. 1 with the omission
of the internal construction of the magnetic head according to the present device;
- Fig. 3 is an enlarged sectional view of a plate material constituting the shielding
case of the magnetic head according to the present device;
- Fig. 4 is a perspective view of a conventional magnetic head;
- Fig. 5 is a sectional view taken on line B - B' of Fig. 4 with the omission
of the internal construction of the conventional magnetic head.
Referring to the drawings, an embodiment of the present device will
As shown in a perspective view of Fig. 1, a sectional view of the
principal part of Fig. 2 and a sectional view of a plate material of Fig. 3, a
magnetic head 10 embodying the present device structurally comprises head cores
12, and a shielding case 11 with shielding plates 13 internally secured with filler
Moreover, the shielding case 11 is of three-layer structure comprising:
a first Permalloy layer 11a as the outer layer of the case, a third Permalloy layer
11c as the inner layer thereof, and a second non-magnetic metal layer 11b of,
for example, copper or copper-nickel alloy as an intermediate layer.
The Permalloy layers 11a, 11c make available shielding properties
against a low-frequency magnetic noise, whereas the non-magnetic layer 11b make
available shielding properties against a high-frequency magnetic noise.
This embodiment of the present device features in that, as shown
in the sectional view of a plate material of Fig. 3 for use in processing the shielding
case 11, the plate material as a cladding material of three-layer structure comprising
a Permalloy layer 11a', a non-magnetic layer (of copper or copper-nickel alloy)
11b' and a Permalloy layer 11c' is processed by press-bonding into such a three-layer
shielding case in cross section of Fig. 2.
The present device is similar to the prior art in the respect that
press bonding is employed. In other words, it is unnecessary to alter the conventional
processing technique as long as the cladding plate material for use is produced
in three-layer structure.
Since the use of the three-layer cladding material formed with the
outer layers made of the same kind of metal and the inner layer made of a different
kind of metal prevents the material from cracking because of the difference in
malleability therebetween when it is press-bonded, thus allowing it to be pressed
into shapes satisfactorily in comparison with what is of two-layer structure.
Since the magnetic head 10 according to the present device has the
non-magnetic layer 11b formed over the whole the shielding case 11, moreover, the
obtainable surface area of the non-magnetic layer of the magnetic head 10 is greater
than what is obtainable from the conventional magnetic head 1, so that shielding
properties against an external magnetic noise is made improvable thereby.
The magnetic head according to the present device is equivalent in
construction to what is equipped with a shielding cover through the same process
step of press-bonding the shielding case as the step taken in the prior art. Thus
the number of parts can be decreased with the effect of shielding the external
Further, the use of the three-layer plate material including the
Permalloy layers and the non-magnetic layer held therebetween for what is intended
to process the shielding cover prevents the curved portion of the plate material
from cracking when it is press-bonded.