Communications: electrical – Audible indication – Diaphragm
Reexamination Certificate
2001-05-10
2003-07-15
Crosland, Donnie L. (Department: 2632)
Communications: electrical
Audible indication
Diaphragm
C340S388300, C340S396100, C336S232000
Reexamination Certificate
active
06593847
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-150058, filed May 22, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a planar acoustic converting apparatus.
FIG. 1
is a sectional view schematically showing a conventional planar acoustic converting apparatus. The planar acoustic converting apparatus shown in
FIG. 1
is disclosed in WO/099/03304 and has a flat yoke
10
formed from a ferromagnetic metal plate such as an iron plate, and permanent magnets
12
attached to one surface of the yoke
10
with their magnetic axes set perpendicular to the surface of the yoke
10
. The permanent magnets
12
are arrayed on one major surface of the yoke
10
while being spaced apart from each other by a predetermined gap, and attached to the yoke
10
such that adjacent permanent magnets have opposite polarities.
The planar acoustic converting apparatus shown in
FIG. 1
also has a diaphragm
14
. This diaphragm
14
is held while being apart from the pole-faces of the permanent magnets
12
by a predetermined distance. The diaphragm
14
has a structure in which spiral coils
18
are formed on both surfaces (or one surface) of an insulating base film
16
in correspondence with the permanent magnets
12
. The spiral coils
18
are formed such that each coil
18
surrounds a region being opposed to the magnetic pole of a corresponding permanent magnet
12
and such that, near the boundary between each two coils
18
adjacent to each other, a direction of current-flow through the conductor of one coil
18
is the same as that of another coil
18
.
FIG. 2
is a view schematically showing the wiring pattern of the spiral coils
18
shown in FIG.
1
. Referring to
FIG. 2
, reference numeral
18
n
1
denotes a coil formed on the upper surface of the base film
16
, and reference numeral
18
n
2
denotes a coil formed on the lower surface of the base film in correspondence with the coil
18
n
1
. The coil
18
n
1
on the upper surface spirals clockwise from the outer to the inner side. On the other hand, the coil
18
n
2
on the lower surface spirals clockwise from the inner to the outer side. The internal end of the coil
18
n
1
and that of the coil
18
n
2
corresponding to the coil
18
n
1
are electrically connected to each other via a through hole or through stud extending through the base film
16
. Hence, the coils
18
n
1
and
18
n
2
constitute one coil
18
which spirals clockwise.
Referring to
FIG. 2
, reference numeral
18
m
1
denotes a coil formed on the upper surface of the base film
16
to be adjacent to the coil
18
n
1
, and reference numeral
18
m
2
denotes a coil formed on the lower surface of the base film
16
to be adjacent to the coil
18
n
2
. The coil
18
m
2
on the lower surface has an outer end connected to that of the adjacent coil
18
n
2
and spirals counterclockwise from the outer to the inner side. On the other hand, the coil
18
m
1
on the upper surface spirals counterclockwise from the inner to the outer side. The internal end of the coil
18
m
1
and that of the coil
18
m
2
corresponding to the coil
18
m
1
are electrically connected to each other via a through hole or through stud extending through the base film
16
. Hence, the coils
18
m
1
and
18
m
2
constitute one coil
18
which spirals counterclockwise.
When the plurality of spiral coils
18
are formed in this way, near the boundary between adjacent coils
18
, a current flows through the wire of one coil
18
in the same direction as that of the current flowing through the wire of the other coil
18
. Each coil
18
is placed in a magnetic field formed by a corresponding permanent magnet
12
that has a polarity opposite to that of an adjacent permanent magnet
12
, as shown in FIG.
1
. For this reason, when a current flows in the above way, the diaphragm
14
receives an electromagnetic force by the Fleming's left-hand rule. That is, as shown in
FIG. 2
, when magnetic poles N and S of the permanent magnets
12
form magnetic fields H, and currents flow through the coils
18
in the directions of arrows, a force is generated in a direction F. With this principle, the diaphragm
14
vibrates in correspondence with the sound currents flowing through the coils
18
.
A planar acoustic converting apparatus of such type can be made as thin as about 5 to 15 mm and can be suitably used for a wall-type TV or notebook personal computer. Such a planar acoustic converting apparatus can also be built in a pillar or sun visor of a car.
However, in a planar acoustic converting apparatus of this type, each coil generates Joule heat. In addition, since the area occupied by the spiral coils
18
on the base film
16
is very large, the influence of heat on the base film
16
cannot be neglected. To prevent this, it has been proposed to use a polyimide film with high heat resistance as the base film
16
. However, tan &dgr;, which is an index of acoustic absorptivity, of a polyimide film is as low as 0.02, so noise, so-called chattering noise, is readily generated when the diaphragm
14
vibrates. In addition, since a polyimide film is hygroscopic, when a polyimide film is used as the base film
16
, the sound quality is expected to change due to a slight extension upon absorbing moisture.
Use of a PET (polyethylene terephthalate) film as the base film
16
has also been proposed. However, a PET film has also poor acoustic absorptivity tan &dgr;=0.014, and noise is readily generated when the diaphragm
14
vibrates.
In a planar acoustic converting apparatus of the above type, when the diaphragm
14
largely vibrates, it may hit the permanent magnet
12
to generate impact noise. This problem becomes more conspicuous when the diaphragm
14
slacks due to the above-described heat generation by the coils
18
. As a known means for preventing this problem, a flexible material such as polyurethane foam or glass wool is inserted between the diaphragm
14
and the permanent magnets
12
. However, such a flexible material hinders the free vibration of the diaphragm
14
to degrade the sound quality.
When the coils
18
receive an electromagnetic force, the diaphragm
14
vigorously vibrates in the direction of thickness. If the adhesive force between the base film
16
and the coils
18
m
1
,
18
m
2
,
18
n
1
, and
18
n
2
is not sufficiently strong, the coils
18
m
1
,
18
m
2
,
18
n
1
, and
18
n
2
may peel off from the base film
16
. The diaphragm
14
having the plurality of spiral coils
18
formed on one or both surfaces of the base film
16
can be manufactured by the normal flexible printed circuit board manufacturing technology. To effectively prevent the coils
18
m
1
,
18
m
2
,
18
n
1
, and
18
n
2
from peeling off in such a manufacturing technology, the surfaces of the base film
16
are roughened to increase the adhesive force per unit area, or the conductor width of the coils
18
m
1
,
18
m
2
,
18
n
1
, and
18
n
2
is increased. However, the former technique can hardly be applied when a thin base film
16
is used to improve the vibration characteristic, and the latter technique is not preferable because the planar acoustic converting apparatus becomes bulky.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a planar acoustic converting apparatus in which generation of noise is suppressed.
It is another object of the present invention to provide a planar acoustic converting apparatus in which impact noise generated by collision of the diaphragm to the permanent magnets can be suppressed without hindering free vibration of the diaphragm.
It is still another object of the present invention to provide a reliable planar acoustic converting apparatus in which the spiral coils of the diaphragm hardly peel off from the base film.
According to the first aspect of the present invention, there is provided a planar acoustic converting apparatus comprising a
Hori Masashi
Iizuka Kenji
Ishiwa Masayuki
Miyazaki Toshiiku
Nishimura Takeshi
Crosland Donnie L.
Knobbe Martens Olson & Bear LLP
The Furukawa Electric Co. Ltd.
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