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JPH04126489

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DESCRIPTION JPH04126489
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
submersible electro-acoustic transducer suitable for use in, for example, an underwater speaker
used in water.
[0002]
2. Description of the Related Art A typical example of this type of underwater electroacoustic
transducer, such as an underwater speaker, is a voice coil driven underwater speaker, as shown
in FIG. That is, the case 1 of the underwater speaker has a lower case 2 and an upper case 3
which functions as a diaphragm. In the case 1, a support plate 4 is disposed. A magnetic circuit 9
composed of the upper plate 5, the lower plate 6, the permanent magnet piece 7 interposed
between the upper and lower plates 5 and 6, and the center pole 8 is attached to the support
plate 4. A voice coil 11 is inserted into the magnetic gap 10 formed by the center pole 8 and the
upper plate 5, and the upper end of the voice coil 11 is fixed to the upper case 3. In addition, a
water injection hole 12 is formed in the lower case 2 and a shield member 13 is fixed to the
lower surface of the support plate 4 in order to prevent the voice coil 11 from being immersed in
water in relation to this. ing. Therefore, the inside of the upper case 3 is an air chamber.
[0003]
In an underwater speaker having such a structure, when a voice current is applied to the voice
coil 11 through the winding paper 14, a direct current magnetic flux passing through the
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magnetic gap 10 acts on the voice coil 11 in the vertical direction. The upper case 3 is driven to
emit a sound wave proportional to the audio current.
[0004]
SUMMARY OF THE INVENTION The above-described conventional underwater speaker has the
following problems.
Since the conventional underwater speaker is of a voice coil drive type and uses an external
magnet type magnetic circuit, it is necessary to form a relatively large magnetic gap 10 for
inserting the voice coil 11. However, by forming such a magnetic air gap 10, a leakage magnetic
flux is generated in the magnetic air gap 10, and the reliability of the electroacoustic conversion
is degraded due to this. Since the inside of the upper case 3 is an air chamber, water pressure
acts on the upper case 3 to suppress the vibration of the diaphragm. Therefore, the reliability of
the electroacoustic conversion is also degraded for these reasons. When used in deep water, the
underwater speaker itself is broken due to water pressure. Therefore, it can only be used at
relatively shallow water depths. Such problems as described above apply not only to underwater
speakers but also to other underwater electroacoustic transducers.
[0005]
An object of the present invention is to provide an underwater electro-acoustic transducer in
which the reliability of electro-acoustic conversion is improved in view of the above problems.
Another object of the present invention is to provide a submersible electroacoustic transducer
which can be used even in deep water.
[0006]
SUMMARY OF THE INVENTION In order to achieve the above object, the feature of the present
invention is to convert electrical energy into acoustic energy and output it into water by vibration
of a diaphragm. In addition, in the underwater electroacoustic transducer capable of converting
into the electric energy the acoustic energy propagating in the water by the vibration of the
diaphragm and taking it into electric energy, (A) a bottomed cylindrical first yoke (B) (1) A rodshaped magnetostrictive element disposed concentrically with the first yoke in one yoke, (C) a
voice coil wound around the outer peripheral surface of the magnetostrictive element and
through which an audio current flows, and (D) an upper end of the magnetostrictive element. A
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second yoke disposed movably in the axial direction of the magnetostrictive element, wherein
(d1) the outer peripheral surface abuts against the inner peripheral surface of the first yoke to
form a magnetic path with the first yoke or Extending to the vicinity, on the inner circumferential
surface of the first yoke (E) such a second yoke having a sliding base and (d2) a base connected
to the base and extending upward and connecting with the central part of the diaphragm; A third
yoke disposed at the lower end of the magnetostrictive element, and (F) a permanent magnet
piece interposed between the bottom of the first yoke and the third yoke and magnetized in the
thickness direction (G The inner peripheral edge is fixed to the outer peripheral surface of the
first yoke, and the outer peripheral edge is fixed to the outer peripheral edge of the diaphragm to
hold the outer peripheral edge of the diaphragm and seal the inner side space of the diaphragm
(H) a magnetic circuit is formed by the permanent magnet piece, the first yoke, the two yokes,
the magnetostrictive element, and the third yoke. .
[0007]
At least one of the frame and the diaphragm is provided with a water injection hole for injecting
water into the space on the inner side of the diaphragm, and water in the first yoke is formed in
relation to the first yoke. In some cases, waterproofing means are provided to prevent the
infiltration of
[0008]
Further, the waterproof means includes a fourth yoke fixed to the upper end of the first yoke so
as to cover the opening of the first yoke, and a waterproof member, and the fourth yoke has a
central hole. The connecting portion of the second yoke is inserted through the central hole, and
a waterproof member may be interposed between the inner peripheral surface of the central hole
and the outer peripheral surface of the connecting portion.
Further, the space between the outer peripheral surface of the base of the second yoke and the
inner peripheral surface of the first yoke may be filled with magnetic fluid.
In addition, a guide portion extending in the vertical direction along the inner peripheral surface
of the first yoke may be formed at the base outer peripheral edge portion of the second yoke.
Furthermore, oil may be filled in the first yoke.
[0009]
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According to the present invention, a magnetic circuit is formed by the permanent magnet piece,
the first yoke, the second yoke, the magnetostrictive element, and the third yoke. Therefore, a
bias magnetic field is previously applied to the magnetostrictive element by the permanent
magnet piece, whereby the magnetostrictive element is displaced in advance in the axial
direction. Then, in this state, when a voice current flows in the voice coil, an alternating magnetic
field is applied to the magnetostrictive element, and the alternating magnetic field is
superimposed on the bias magnetic field. Therefore, the strength of the magnetic field applied to
the magnetostrictive element changes in accordance with the audio current. As a result, the
magnetostrictive element vibrates in the axial direction, and in conjunction with this, the second
yoke moves up and down, the diaphragm is driven, and a sound wave is radiated into the water.
In the case of converting acoustic energy into electrical energy, it is performed by the opposite
action to the above action. As described above, in the underwater electroacoustic transducer
according to the present invention, the diaphragm is driven by the displacement of the
magnetostrictive element, so that an internal magnetic circuit without a magnetic gap can be
formed.
[0010]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a half sectional view of an embodiment of the underwater speaker to which the present
invention is applied, FIG. 2 is a plan view thereof, and FIG. 3 is a bottom view thereof. A rodshaped magnetostrictive element 21 is disposed concentrically with the first yoke 20 in a
cylindrical first yoke 20 with a bottom. The magnetostrictive element 21 is made of, for example,
a single element or an alloy of a rare earth metal such as terbium or dysprosium, and has the
property of being extended and displaced in the direction of the applied magnetic field in
response to the increase of the magnetic field. The magnetostrictive element 21 is inserted with a
coil bobbin 22 made of a nonmagnetic material, and a voice coil 23 through which an audio
current flows is wound around the coil bobbin 22.
[0011]
A second yoke 24 is disposed at the upper end of the magnetostrictive element 21, and a
truncated cone third yoke 25 is disposed at the lower end of the magnetostrictive element 21. A
disc-shaped permanent magnet piece 26 is interposed between the third yoke 25 and the bottom
of the first yoke 20. The permanent magnet piece 26 is magnetized in the thickness direction.
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The permanent magnet piece 26 functions to apply a bias magnetic field to the magnetostrictive
element 21. The second yoke 24 is movable in the axial direction of the magnetostrictive element
21, and has a disk-shaped base 24A and a guide 24B which is suspended from the outer
peripheral edge of the base 24A along the inner peripheral surface of the first yoke 20. A
connecting portion 24C extends upward from the central portion of the base 24A and is
connected to the central portion of the diaphragm 27. The outer peripheral surface of the base
24 A extends to the vicinity of the inner peripheral surface of the first yoke 20. Further, the
magnetic fluid 28 is filled between the outer peripheral surface of the guide portion 24 B and the
inner peripheral surface of the first yoke 20. Therefore, the second yoke 24 can move smoothly.
[0012]
By the way, although the magnetostrictive element 21 is excellent in tensile resistance and
compression resistance, it has a property of being inferior in shear resistance. However, in the
present embodiment, by providing the guide portion 24B, the second yoke 24 can be moved
straight in the vertical direction while being guided by the guide portion 24B, and is twisted and
bent via the second yoke 24. There is no possibility that the shearing force caused by the like
acts on the magnetostrictive element 21. Accordingly, no crack or the like occurs in the
magnetostrictive element 21, and an underwater speaker having excellent durability can be
realized. A magnetic circuit is formed by the permanent magnet piece 26, the first yoke 20, the
two yokes 24, the magnetostrictive element 21, and the third yoke 25. This magnetic circuit is a
so-called internal magnet type magnetic circuit, in which no magnetic air gap is formed, and no
leakage flux is generated.
[0013]
A ring-shaped fourth yoke 30 is fixed to the upper surface of the first yoke 20 by a screw 31 so
as to cover the opening of the first yoke 20. A ring-shaped damper 32 is interposed between the
fourth yoke 30 and the base 24 A of the second yoke 24. The connecting portion 24C of the
second yoke 24 is inserted through the central hole 33 of the damper 32 and the central hole 34
of the fourth yoke 30, and the upper end thereof is in contact with the central portion of the
diaphragm 27.
[0014]
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The vibrating plate 27 is a cone-shaped vibrating plate whose central portion protrudes upward.
The central portion of the diaphragm 27 is coupled to the coupling portion 24C by a screw 41
screwed into a screw hole 40 formed in the coupling portion 24C, and the outer peripheral edge
portion of the diaphragm 27 is outside the frame 42. It is fixed to the peripheral portion by a
screw 43. The inner peripheral edge portion of the frame 42 is fixed to the outer peripheral
surface of the first yoke 20. Accordingly, in conjunction with the movement of the second yoke
24 due to the displacement of the magnetostrictive element 21 in the axial direction, the
diaphragm 27 is driven with the outer peripheral edge held.
[0015]
Also, a plurality of water injection holes 44 are formed in the frame 42. Therefore, water enters
the diaphragm 27 from the water injection hole 44, so the water pressure acting on the outer
surface and the inner surface of the diaphragm 27 becomes the same, thereby suppressing the
vibration of the diaphragm 27 due to the water pressure. The reliability can be improved.
Furthermore, by forming the water injection hole 44 in this way, the underwater speaker will not
be damaged even when used at a deep water depth. In this embodiment, although the inner space
50 of the first yoke 20 is an air chamber, the inner space 50 may be filled with oil. By so doing,
the water pressure resistance is further improved, and an underwater speaker that can be used in
deeper places can be realized.
[0016]
On the other hand, when water entering the water injection hole 44 touches the voice coil 23, a
short circuit of the voice coil 23 occurs. Therefore, in the present embodiment, the outer
peripheral surface of the connecting portion 24C of the second yoke 24 and the inside of the
fourth yoke 30. Between the peripheral surfaces, an O-ring 51 as a waterproof member is
interposed, which can prevent the entry of water from the arrow X1 direction. A recessed groove
52 is formed on the upper surface of the first yoke 20 along the circumferential direction, and an
O-ring 53 as a waterproof member is inserted into the recessed groove 52. Therefore, it is
possible to prevent the entry of water from the arrow X2 direction.
[0017]
FIG. 4 is a diagram for explaining the operation principle of the magnetostrictive element 21. FIG.
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5 is a graph showing the magnetostrictive characteristics of the magnetostrictive element 21. As
shown in FIG. As described above, the magnetostrictive element 21 has the property of being
extended and displaced in the direction of the applied magnetic field in response to the increase
of the magnetic field. Here, as shown in FIG. 4A, assuming that the length of the magnetostrictive
element 21 is L, the strength of the applied magnetic field is H (oersted), and the elongation of
the magnetostrictive element 21 is ΔL, the magnetostrictive characteristic of the
magnetostrictive element 21 is , M1 in FIG. The horizontal axis in FIG. 5 is the strength H of the
applied magnetic field, and the vertical axis is the magnetostriction (ΔL / L). Therefore, when the
bias magnetic field H0 is applied to the magnetostrictive element 21 in advance,
magnetostriction indicated by reference numeral M3 occurs in the magnetostrictive element 21
with respect to the alternating magnetic field indicated by reference numeral M2 in FIG. That is,
as shown in FIG. 4 (2), the magnetostrictive element 21 vibrates in the lateral direction with the
position of the extension ΔL0 generated by the bias magnetic field H0 as the origin.
[0018]
The diaphragm 27 is driven in the underwater speaker according to the present invention by
utilizing the characteristics of the magnetostrictive element 21 as described above. In the
underwater speaker according to the present invention, the magnetic flux Φ (see FIG. 1) of the
bias magnetic field HO due to the permanent magnet piece 26 It flows with the base 24 A of the
two yokes → the magnetostrictive element 21 → the third yoke 25 → the N pole of the
permanent magnet piece 26. Thereby, the magnetostrictive element 21 is stretched and
displaced in advance from the original length L by ΔL0. In such a state, when a voice current
flows in the voice coil 23, an alternating magnetic field is applied to the magnetostrictive element
21, and an alternating magnetic field is superimposed on the bias magnetic field HO. Thereby,
the magnetostrictive element 21 vibrates in the axial direction with ΔL0 as the origin in
response to the change of the audio current. During the movement of the second yoke 24, the
magnetic fluid 28 is maintained in a state of being filled between the guide portion 24B and the
inner peripheral surface of the first yoke 20 by the magnetic attraction force. In this way, the
magnetostrictive element 21 vibrates in response to the audio current, and the second yoke 24
also moves up and down in conjunction with it, the diaphragm 27 is driven, and a sound wave is
radiated into the water.
[0019]
Although the magnetic fluid 28 is filled between the outer peripheral surface of the guide portion
24B and the inner peripheral surface of the first yoke 20 in the above embodiment, the outer
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peripheral surface of the guide portion 24B and the first yoke 20 are described. The magnetic
fluid 28 may be omitted if the inner peripheral surface of the is processed with high precision to
make it a flat surface with almost no frictional resistance. Even in this case, the movement of the
second yoke 24 will not be disturbed at all, and there will be no magnetic gap and no occurrence
of leakage flux. Although the water injection hole 44 is formed in the frame 42 in the abovementioned embodiment, it may be formed in the diaphragm 27 or may be formed in both the
frame 42 and the diaphragm 27. Also, in the case of the type used at a shallow water depth, the
water injection hole 44 is not particularly required. In the above embodiment, although the
magnetostrictive element 21 has the characteristic of elongation and displacement, it may have
the characteristic of contraction and displacement, and the diaphragm 27 may be used according
to the same principle as the operation principle described above. It can be driven. Furthermore,
although the above embodiments have been described for the underwater speaker, the present
invention is not limited to this, and can be suitably applied to, for example, a wide range of
underwater electroacoustic transducers such as microphones.
[0020]
As described above, according to the present invention, the following effects can be obtained.
According to the invention of the first aspect, it is possible to configure an internal magnetic type
magnetic circuit without a magnetic air gap, and to improve the reliability of electroacoustic
conversion significantly. According to the second aspect of the invention, since the water
injection hole is formed in at least one of the frame and the diaphragm, the water pressure of the
same magnitude acts on the outer surface and the inner surface of the diaphragm. Therefore, the
diaphragm can vibrate without being affected by water pressure, and the deterioration of the
reliability of electroacoustic conversion can be prevented. Furthermore, the water pressure is
prevented from damaging the underwater electro-acoustic transducer, and the underwater
electro-acoustic transducer can be realized that can be used in deep water.
[0021]
According to the third aspect of the present invention, it is possible to realize an underwater
electroacoustic transducer having a simple structure and excellent waterproofness. According to
the invention of claim 4, the second yoke can be moved smoothly, and the waterproofness can be
further improved.
[0022]
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According to the invention of claim 5, since the guide portion is formed on the base outer
peripheral edge portion of the second yoke, the first yoke is guided by the guide portion and
moves up and down substantially linearly. . Therefore, a shear force caused by twisting or
bending does not act on the magnetostrictive element through the first yoke, so that it is
excellent in elongation resistance and compression resistance, but magnetostriction having a
property inferior to shear resistance. In the element, a crack or the like does not occur, and an
underwater electroacoustic transducer having excellent durability can be realized. According to
the invention of claim 6, since the third yoke is filled with the oil, the water pressure resistance is
improved as compared with the case where the third yoke is filled with the air.
[0023]
Brief description of the drawings
[0024]
1 is a half sectional view of an embodiment of the underwater speaker to which the present
invention is applied.
[0025]
2 is a plan view of an embodiment of the underwater speaker to which the present invention is
applied.
[0026]
3 is a bottom view of an embodiment of the underwater speaker to which the present invention
is applied.
[0027]
4 is a diagram for explaining the operating principle of the magnetostrictive element used in the
present invention.
[0028]
5 is a graph showing the magnetostrictive characteristics of the magnetostrictive element used in
the present invention.
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[0029]
6 is a half sectional view of the conventional example.
[0030]
Explanation of sign
[0031]
20: first yoke, 21: magnetostrictive element, 23: voice coil, 24: second yoke, 24A: base, 24B:
guide portion, 24C: connecting portion, 25: third yoke, 26: permanent magnet piece, 27:
Diaphragm, 28: magnetic fluid, 30: fourth yoke, 34: central hole of fourth yoke, 42: frame, 44:
water injection hole, 50: inner space of first yoke, 51: O ring.
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