Technical Field
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This invention relates in an optical microphone device which uses an
optical microphone element, and it is related to the optical microphone element
and the optical microphone device that have excellent noise decrease
characteristics.
Description of the Related Art
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A general microphone has a fault that a wind pressure causes a noise
and obstructs a call when used in a motorcycle or windy environment.
Japanese Patent Publication No. 58-36879 discloses a microphone device for
noise prevention.
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The microphone device disclosed here stores a microphone element in
the frame inside of the body. A compressed foaming body with a consecutive
bubble fills a back portion of the frame body and surroundings of the element.
The forming body with a consecutive bubble also fills the space between an
inside protection board with a hole provided in front of the microphone element
and an outside protection film with a hole provided in front of the frame body.
On the edge of the frame body, a taper that spread out toward the front is
formed. By covering the side and the back of the microphone element with
foaming body as stated above, sensitivity becomes single directivity.
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An electret microphone for decreasing noise shown in Figure 7 and a
dynamic microphone shown in Figure 8 are known. Figure 7 shows the
structure of the electret microphone. Figure 7A shows a front view, Figure 7B
shows a sectional side view, and Figure 7C shows a rear view. The electret
microphone stores in a body 10 a diaphragm 3 which oscillates by the sound
pressure, and an electrostatic element 4 which converts the oscillation of the
diaphragm 3 to an electric signal. In this structure, voice enters through an
opening 1 provided in the front face 10a of the body. A small opening 2 is also
provided in off site part of the back-plane 10b of the body 10.
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Figure 8 shows the structure of the dynamic microphone. Figure 8A
shows a sectional side view, and Figure 8B shows a rear view: A magnet 21
having an opening is stored in a body 20, and a coil 22 is twisted around the
magnet 21. A diaphragm 23 is set up in the front to confront the magnet 21. A
small hall 23 is provided in the off site part in the back-plane 22b of the body 20
so that a little larger hole 24 may be connected to a hole of the magnet 21. A
sound pressure gradation caused by an oscillation of a diaphragm 23 is
detected as a gradation of magnetic flux density by the magnet 21 on which a
coil 22 is twisted, and this is converted to an electric signal. In the conventional
microphone device shown in figure 7 and figure 8, if the sound which enters
through the front face and the sound which enters through the back-plane face
are equivalent against the diaphragm, these sounds are canceled by each other,
and the microphone doesn't take influence by the sound.
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In the microphone device disclosed in Japanese Patent Publication 58-36879,
and figure 7 and figure 8, there was a limit of noise decrease capability.
Sound from the front face direction and sound from the back-plane direction
did not reach in the diaphragm symmetrically. Therefore, a noise decrease
effect was 5-7 dB at most, and a microphone device with increased S/N ratio is
not realized. On the other hand, an optical microphone device has been noticed
as a microphone device that may follow the variation of the weak sound wave,
and that has the high sensitivity and wide-band characteristics which does not
depend on a use environment.
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Figure 6 shows the structure of the head part of the conventional optical
microphone device. A diaphragm 31 that oscillates by a sound wave is provided
inside of the microphone head 30, and a surface 31a at the side that a sound
wave hits is exposed in the outside. Therefore, a sound wave 37 that reached in
this surface 31a oscillates the diaphragm 31. The space inside of the head 30 is
divided to a portion facing a surface 31a and another portion facing an opposite
surface 31b. In the portion facing the surface 31b, a light source 32 such as an
LED irradiating a light beam in the surface 31b of the diaphragm 31 from a
slant, a lens 33 to make a light beam from this light source 32 a predetermined
beam diameter, a photodetector 35 which receives a reflection light reflected in
the surface 31b, and a lens 34 to zoom a displacement of an optical path of the
reflection light caused by the oscillation of the diaphragm 31 are provided.
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In this structure, when a sound wave hits the surface 31a of the
diaphragm 31, and a diaphragm 31 oscillates, a receiving position of the
receiving surface 35a of the reflection light changes. If a photodetector 35 is
composed as a position sensor, an electric signal that met the oscillation of the
diaphragm 31 from the irradiation location of the reflection light is taken out.
This is the basic structure of the optical microphone device. However, even
such optical microphone device is used, a noise decrease effect can't be expected
very much. This is because a diaphragm 31 oscillates by the noise which
reaches a diaphragm 31 and this is piled as a noise signal by oscillation by the
usual sound wave 37. Therefore, it is an object of this invention to provide an
optical microphone device with energizing the characteristics of the optical
microphone device, and to provide an optical microphone of high noise decrease
effect.
SUMMARY OF THE INVENTION
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The optical microphone element of this invention comprises:
- a diaphragm which oscillates by the sound pressure;
- a storage container which the diaphragm is stored in and which has a first
opening and a second opening provided in symmetrical positions to each other
and confront the diaphragm;
- a light source which irradiates a light beam in the diaphragm; and
- a photodetector that receives a reflection light of the light beam irradiated in
the diaphragm and which outputs a signal coping with the oscillation of the
diaphragm.
Furthermore, in the optical microphone element of this invention,
the diaphragm, the light source and the photodetector are arranged so that a
directivity response pattern on the first opening side and a directivity response
pattern on the second opening side may be symmetrical to each other. An
optical microphone device of this invention comprises:
- the optical microphone element;
- a substrate which the optical microphone element is carried on; and
- a cover that covers the first opening and the second opening symmetrically
toward the substrate so that the sound wave may go through;
- wherein the incidence of the sound wave through the cover via the first opening
and the second opening is made equally.
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BRIEF DESCRIPTION OF DRAWINGS
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- Figure 1 shows a structure of an optical microphone element of an
embodiment of this invention.
- Figure 2 shows an appearance figure of an optical microphone device of this
invention.
- Figure 3 shows a decomposition figure that shows the internal structure of the
optical microphone device of this invention.
- Figure 4 shows a directivity response pattern figure of the sensitivity of the
optical microphone element of this invention.
- Figure 5 shows a figure to explain the sound intensity of the microphone
element put on the short distance field and the far range field.
- Figure 6 shows a structure of the conventional optical microphone device.
- Figure 7 shows a structure of the conventional electret microphone device.
- Figure 8 shows a structure of the conventional dynamic microphone device.
In these figures, 100 is optical microphone element, 40 is storage container, 31
is diaphragm, 32 is light source, 35 is photodetector, 38 is the first opening, 39
is the 2nd opening, 54 is cover and 50 is substrate. -
DESCRIPTION OF THE PREFERED EMBODIMENTS
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Figure 1 shows a point part configuration of an optical microphone
element 100 that relates for an embodiment of this invention. The same code is
put to the same part with the conventional element shown in figure 6, and the
detailed explanation is omitted.
In the optical microphone element of the invention, a diaphragm 31 which
oscillates by the sound wave 37 is provided in the central part of a storage
container 40. Then, on both sides of the storage container, a 1st opening 38 and
a 2nd opening 39 are set up to become symmetrical location to each other
against a diaphragm 31. In this structure, a sound wave may enter from both
openings into the storage container 40 to oscillate the diaphragm 31.
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As stated above, in the optical microphone shown in figure 1, When a
sound pressure of a sound wave from the 1st opening 38 and that from the 2nd
opening 39 are equal, these two sound waves never oscillate a diaphragm 31 as
they interfere each other on both sides 31a and 31b of the diaphragm 31. When
two microphones that have equal sensitivities are arranged close and they
receive sound wave which occurred in a far range, the two microphones detect
the sound wave equally.
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Figure 5 shows a characteristic curve of the distance vs sound intensity
from the sound source. Generally, as shown in the figure, a sound wave occurs
from the mouth of the person in a short distance from microphone element. In
other words, most voice occurs at the short distance from this microphone
element.
The voice of the person of this short distance has globular field characteristics
so that it may be shown by a circular curve. On the other hand, the sound wave
that occurs in the far range such as the sound wave by the noise has the
characteristics of the plane field. Although the sound intensity of the globular
wave is about the same along the spherical surface or the envelope and changes
along the radius of that glob, the sound intensity of the plane wave almost
becomes the same at all the points.
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Optical microphone shown in figure 1 can be thought to associate two
microphones. Therefore, when this was put on the far range field, the sound
waves which have almost the same intensity and phase characteristics from
the 1st opening 38 and the 2nd opening 39 comes in the diaphragm 31, to
interfere with each other, and those influences are decreased. On the other
hand, as a sound wave from the short distance field enters from the 1st opening
38 and the 2nd opening 39 non-uniformly, a sound wave from the short
distance field oscillates a diaphragm 31, and it is taken out as a signal by the
photodetector 35.
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Figure 4 shows the directivity response pattern of the sensitivity of the
optical microphone shown in figure 1. The optical microphone shown in Figure
1 has almost "8" shaped symmetrical directivity comprising a pattern in the
front face direction to go to the 1st opening 38 and a pattern in the back-plane
direction to go to the 2nd opening 39. When the optical microphone shown in
figure 1 is used, noise such as surroundings noise is imputed as sound from the
far range field as shown in figure 5. In this case, as the sound wave enters
equally from the 1st opening 38 and the 2nd opening 39 and interferes on the
diaphragm 31 to extinct, a diaphragm 31 is never oscillated.
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On the other hand, voice from the speaking person is inputted as sound
from the short distance field. Therefore, reception sensitivities in two
microphone elements M1, M2 are different to each other as shown in figure 5.
Id est, the sound which enters from the 1st opening 38 and the sound from the
2nd opening 39 are different in intensity, and a diaphragm 31 is oscillated.
Thus an optical microphone which decreased the influences of the noise can be
realized.
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Figure 2 is an appearance figure which shows the point part
configuration of the optical microphone device which the optical microphone
200 in figure 1 was carried on. Figure 2A shows a front view, Figure 2B shows a
side elevation view, and Figure 2C shows a rear view. Figure 3 is the
decomposition figure that shows internal structure. Referring to figure 2 and
figure 3, the configuration of the optical microphone device using an optical
microphone is explained. The optical microphone 200 shown in Figure 1 is put
almost on the center of the printed board 50. The optical microphone 200 is put
on the printed board 50 so that the 1st opening 38 may face upward and the
2nd opening 39 may face downward. In this structure, the optical microphone
200 achieve the directivity response pattern of the equal sensitivity in top and
bottom as shown in figure 4.
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An off site circuit 51 to drive this optical microphone 200 is arranged on
both surface of the printed board 50 to surround the optical microphone 200. To
the substrate 50, cable 52 for microphone output and powering is connected.
The printed board 50 with sponges 53a, 53b on top and bottom is covered by a
net-shaped cover 54a, 54b. By fixing this, the optical microphone device is
made. When the optical microphone device is put in the far range field, a sound
wave reaches a diaphragm equally through the net cover 54a, 54b. When the
optical microphone device is put in the short distance field, a sound wave
enters un-equally to oscillate the diaphragm and achieve amplification output.
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As explained above, the optical microphone device and the optical
microphone element of this invention have the structure that a sound wave
comes from the openings set up in symmetrical location against the diaphragm.
In this structure, a sound wave such as noise from the far range field is
cancelled and a sound wave from the short distance field is amplified and
outputted. Therefore, an audio device that remarkably decreased the
influences of the noise can be realized.