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JP2013055599

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DESCRIPTION JP2013055599
Abstract: The present invention provides an optical microphone capable of detecting the
propagation direction and the propagation direction of an acoustic wave. An optical microphone
according to the present invention is an optical microphone for detecting an acoustic wave
propagating an environmental fluid using a light wave, which is constituted by a solid
propagation medium, and the propagation medium through which the acoustic wave propagates
An acoustic wave receiving unit 2 including a supporting unit 9 supporting the propagation
medium unit 3, and the propagation medium unit 3 across the acoustic wave 1 propagating in
the propagation medium unit 3 A light source 4 for emitting a light wave 5 and a photoelectric
conversion unit 6 having a plurality of photoelectric conversion elements for receiving the light
wave transmitted through the propagation medium unit 3 and outputting an electric signal; The
propagation medium portion 3 has a pair of main surfaces on which the light wave enters and
exits, and at least one side surface located between the pair of main surfaces and on which an
acoustic wave is incident from the environmental fluid, The support portion is the at least one In
the region other than the opening and the opening 9a to expose at least a portion of the side
surface, and a sound insulation portion 9b that covers between said pair of main surfaces.
[Selected figure] Figure 1A
Optical microphone
[0001]
The present invention relates to an optical microphone that receives an acoustic wave that
propagates a gas such as air and converts the received acoustic wave into an electrical signal
using light.
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1
[0002]
A microphone is conventionally known as a device for receiving an acoustic wave and converting
it into an electrical signal.
Many microphones represented by dynamic microphones and condenser microphones include a
diaphragm. In these microphones, sound waves are received by vibrating the diaphragm, and the
vibrations are extracted as electric signals. Since this type of microphone has a mechanical
vibrating part such as a diaphragm, the characteristics of the mechanical vibrating part may
change by repeated use many times. Also, if a very strong sound wave is to be detected by a
microphone, the mechanical vibration part may be broken.
[0003]
In order to solve the problem of a microphone having such a conventional mechanical vibration
unit, for example, Patent Document 1 and Patent Document 2 do not have a mechanical vibration
unit and use acoustic waves by utilizing light waves. An optical microphone for detecting is
disclosed.
[0004]
Specifically, as shown in FIG. 22, Patent Document 1 discloses an optical microphone including a
light source 151, an emission system optical component 152, a light reception system optical
component 153, a detection unit 154, and a signal processing unit 155. There is.
According to Patent Document 1, after the light 5 emitted from the light source 151 is shaped by
the emission system optical component 152, the light 5 is caused to act on the acoustic wave 1
propagating in the air to generate diffracted light. At this time, two diffracted light components
whose phases are mutually inverted are generated. After the diffracted light is adjusted by the
light receiving system optical component 153, it is received by the detection unit 154 in which a
plurality of photoelectric conversion elements arranged on the circumference centered on the
optical axis of the laser light is converted into an electric signal. Acoustic wave 1 is detected. As a
result, it becomes possible to separately detect, separate and record the acoustic wave 1
according to the propagation direction.
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[0005]
Further, Patent Document 2 discloses a method of detecting an acoustic wave by propagating the
acoustic wave into the medium and detecting a change in optical characteristics of the medium.
As shown in FIG. 23, the acoustic wave 1 propagating in the air is taken in from the opening 201,
and travels in the acoustic waveguide 202 in which at least a part of the wall surface is formed of
the photoacoustic propagation medium 203. The sound waves traveling through the acoustic
waveguide 202 are taken into the photoacoustic propagation medium 203 and propagate
therein. In the photoacoustic propagation medium 203, a change in refractive index occurs as the
sound wave propagates. The acoustic wave 1 is detected by extracting this change in refractive
index as light modulation using a laser Doppler vibrometer 204. Patent Document 2 discloses
that by using silica dry gel as the photoacoustic propagation medium 203, acoustic waves in the
waveguide can be taken into the photoacoustic propagation medium 203 with high efficiency.
[0006]
JP, 2007-194677, A JP, 2009-085, 868.
[0007]
The optical microphone of Patent Document 1 can detect the propagation direction of an
acoustic wave, but can not identify the direction of propagation.
For this reason, there is a problem that it is impossible to distinguish two acoustic waves
different in the direction of propagation by 180 °.
[0008]
The method of Patent Document 2 uses a laser Doppler vibrometer. The laser Doppler vibrometer
is large in size because it requires a light frequency shifter such as an acousto-optic element, and
a complex optical system including a large number of mirrors, beam splitters, lenses, and the like.
For this reason, the subject that the whole measuring device indicated by patent documents 2
becomes large occurs. Further, in the optical microphone of Patent Document 2, the propagation
direction of the acoustic wave can not be separated and detected.
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[0009]
An object of the present invention is to solve at least one of such prior arts, and to provide an
optical microphone capable of detecting the propagation direction and the propagation direction
of an acoustic wave.
[0010]
The optical microphone according to the present invention is an optical microphone that detects
an acoustic wave that propagates an environmental fluid using a light wave, and is formed of a
solid propagation medium, and a propagation medium portion that the acoustic wave propagates,
An acoustic wave receiving unit including a support unit for supporting the propagation medium
unit; a light source for emitting a light wave passing through the propagation medium unit across
the acoustic wave propagating in the propagation medium unit; the propagation medium unit
And a photoelectric conversion unit having a plurality of photoelectric conversion elements for
receiving the light wave that has passed through and outputting an electric signal, and in the
acoustic wave receiving unit, the propagation medium unit is a pair that the light wave enters
and exits. And at least one side surface located between the pair of main surfaces and to which
an acoustic wave is incident from the environmental fluid, and the support portion exposes at
least a portion of the at least one side surface Opening In the region other than the opening, and
a sound insulation part that covers between said pair of main surfaces.
[0011]
The optical microphone according to the present invention is an optical microphone that detects
an acoustic wave that propagates an environmental fluid using a light wave, and is formed of a
solid propagation medium, and a propagation medium portion that the acoustic wave propagates,
An acoustic wave receiving unit including a support unit for supporting the propagation medium
unit; a light source for emitting a light wave passing through the propagation medium unit across
the acoustic wave propagating in the propagation medium unit; the propagation medium unit
And a photoelectric conversion unit having a light shielding portion that is rotatable about an
optical axis of the light wave and blocks a portion of the light wave. In the acoustic wave
receiving unit, the propagation medium unit is located between a pair of main surfaces on which
the light wave enters and exits and a pair of main surfaces, and at least one on which an acoustic
wave is incident from the environmental fluid Have two sides The support portion, in said at least
one region other than the opening and opening exposing at least a portion of the side surface,
and a sound insulation part that covers between said pair of main surfaces.
[0012]
The optical microphone according to the present invention is an optical microphone that detects
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an acoustic wave that propagates an environmental fluid using a light wave, and is formed of a
solid propagation medium, and a propagation medium portion that the acoustic wave propagates,
An acoustic wave receiving portion including a support portion for supporting the propagation
medium portion; a light source for emitting a light wave passing through the propagation
medium portion across the acoustic wave propagating in the propagation medium portion; A
photoelectric conversion unit that receives the lightwave transmitted through the propagation
medium unit at the light receiving surface and outputs an electrical signal, and the lightwave
does not receive a part of the lightwave transmitted through the propagation medium unit. A
center of the light receiving surface is shifted with respect to the optical axis of the light
receiving portion, and the light receiving surface is rotatable about the optical axis of the light
wave; Is the light wave incident and The support portion has a pair of main surfaces for emitting
light and at least one side located between the pair of main surfaces and on which an acoustic
wave is incident from the environmental fluid, and the support portion is at least one of the at
least one side. It includes an opening that exposes a portion and a sound insulation portion that
covers between the pair of main surfaces in a region other than the opening.
[0013]
In one preferred embodiment, the optical microphone further comprises a beam splitter and a
mirror, wherein the beam splitter is located between the light source and an acoustic receiver,
and the acoustic receiver is the beam splitter and the mirror. The light wave emitted from the
light source is transmitted through the beam splitter and the propagation medium portion and
reflected by the mirror, and the light wave reflected by the mirror is transmitted again through
the propagation medium portion, and the beam The light is reflected by the splitter and is
incident on the photoelectric conversion unit.
[0014]
In one preferred embodiment, the sound insulation part covers the light wave passing through
the propagation medium part at an angle of 90 ° or more.
[0015]
In one preferred embodiment, the sound insulation unit covers the light wave passing through
the propagation medium unit at an angle of 180 ° or more.
[0016]
In a preferred embodiment, the at least one side surface is a curved surface, and the distance
from any portion exposed at the opening to the light wave transmitted through the propagation
medium portion is equal.
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[0017]
In one preferred embodiment, the propagation medium portion has a plurality of side surfaces on
which an acoustic wave is incident from the environmental fluid, and the plurality of side
surfaces are the lightwaves in a plane perpendicular to a lightwave transmitted through the
propagation medium portion. The plurality of side surfaces are flat, and the plurality of side
surfaces are exposed at the opening, and the distance from the plurality of side surfaces to the
light wave transmitted through the propagation medium portion is 5. An optical microphone as
claimed in any one of the preceding claims.
[0018]
In one preferred embodiment, the support portion is opaque to the light wave, and the support
portion has a hole that exposes a part of each of the pair of main surfaces of the propagation
medium portion, A light wave passes through the hole.
[0019]
In one preferred embodiment, the optical microphone further includes a plurality of horns
provided in the first opening, the plurality of horns around the light wave in a plane
perpendicular to the light wave transmitted through the propagation medium portion. They are
arranged at equal angles.
[0020]
In one preferred embodiment, the support portion has at least one section dividing the opening
into a plurality of opening sections, and the plurality of opening sections divided by the at least
one section transmit the propagation medium section. Are arranged equiangularly around the
lightwave in a plane perpendicular to the lightwave.
[0021]
In one preferable embodiment, in the photoelectric conversion element portion, the plurality of
photoelectric conversion elements are arranged at equal angles around the light wave.
[0022]
In a preferred embodiment, the orientation of each boundary of the plurality of side surfaces and
the orientation of each boundary of the plurality of photoelectric conversion elements are
coincident with each other around the optical axis of the light wave.
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[0023]
In one preferred embodiment, in the optical microphone, the propagation medium portion is
constituted of a silica nanoporous body.
[0024]
The optical microphone of the present invention comprises two of the optical microphones
defined in any of the above, and the light shielding portion of the acoustic wave receiving portion
of one optical microphone and the light shielding portion of the acoustic wave receiving portion
of the other optical microphone face each other Are arranged.
[0025]
According to the optical microphone of the present invention, in the region other than the
opening where the acoustic wave is incident, the sound insulation portion covers between the
principal surfaces of the propagation medium portion where the light wave of the propagation
medium portion is incident and emitted. The direction of propagation can be identified as well as
the direction of propagation of
Moreover, it becomes possible to separate for each propagation direction and to acquire a signal
corresponding to an acoustic wave.
[0026]
1 is a schematic perspective view of a first embodiment of an optical microphone according to
the present invention;
It is a figure which shows embodiment by which the side of a propagation medium part is curved
surface shape.
It is a figure explaining the angle in which the opening in a 1st embodiment is located, and a
detectable area.
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It is a figure showing the diffraction of the light wave by the acoustic wave in a propagation
medium part.
(A) And (b) is a figure which shows the overlap with a zero-order diffracted light wave and a +/first-order diffracted light wave.
(A) And (b) is a figure which shows the structure of an acoustic wave receiving part and the
photoelectric conversion part for description.
(A) to (f) is a figure which shows the position of the diffracted light wave in, when the acoustic
wave from which a propagation direction differs changes in the acoustic receiving part shown to
Fig.5 (a).
(A) And (b) is a figure which shows the electric signal obtained from a photoelectric conversion
part.
It is a figure which shows the structure of the experiment example of the optical microphone of
1st Embodiment.
It is a figure which shows the output waveform at the time of detecting the acoustic wave in an
experiment example.
It is a figure which shows the output waveform at the time of not detecting an acoustic wave.
It is a figure which shows another form of the optical microphone by 1st Embodiment.
FIG. 6 is a diagram showing how an acoustic wave 1 is refracted and propagated from air to a
propagation medium portion 3;
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It is a figure which shows the other form of an acoustic wave receiving part, Comprising: It is a
figure which shows the acoustic wave receiving part which has a horn.
It is a figure which shows the other form of an acoustic wave receiving part, Comprising: It is a
figure which shows an acoustic wave receiving part which has a horn which consists of a
propagation medium part.
It is a figure which shows the other form of an acoustic wave receiving part, Comprising: It is a
figure which shows the acoustic wave receiving part which has a division | segmentation in
opening. Fig. 2 shows a schematic perspective view of a second embodiment of the optical
microphone according to the invention; (A) to (c) is a figure which shows the positional
relationship of a light wave and a rotation light-shielding plate in 2nd Embodiment. (A) to (e) is a
figure which shows the positional relationship of the rotation light-shielding plate and a
diffracted light wave in, when the angle of a rotation light-shielding plate is changed in 2nd
Embodiment. It is a figure which shows the other example of 2nd Embodiment, Comprising: It is
a schematic diagram which shows the photoelectric conversion part rotatably supported. Fig. 3 is
a schematic view of a third embodiment of the optical microphone according to the invention;
Fig. 4 shows a schematic perspective view of a fourth embodiment of the optical microphone
according to the invention; It is a figure which shows the conventional optical microphone. It is a
figure which shows the other conventional optical microphone.
[0027]
First Embodiment The first embodiment of the optical microphone according to the present
invention will be described below. FIG. 1 is a perspective view schematically showing the
configuration of the optical microphone 101 according to the first embodiment. In the present
specification, “propagation direction” means an angle formed by a straight line with a
reference line or reference plane when propagating along a straight line such as an acoustic
wave, and “propagation direction” means the straight line In the above, it is referred to as to
whether the acoustic wave or the like is approaching or away from. When “propagation
direction” and “propagation direction” are specified, “propagation direction” is determined.
[0028]
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9
1. Configuration of Optical Microphone 101 The optical microphone 101 is surrounded by the
environmental fluid through which the acoustic wave 1 propagates. The environmental fluid is,
for example, air, but may be another gas or a liquid such as water. The optical microphone 101
includes an acoustic wave receiving unit 2, a light source 4, and a photoelectric conversion unit
6. The acoustic wave 1 propagating the environmental fluid is received by the acoustic wave
receiver 2 and propagates in the acoustic wave receiver 2. The light wave 5 emitted from the
light source 4 acts on the acoustic wave 1 propagating through the acoustic wave receiving unit
2 by passing through the acoustic wave receiving unit 2. The light wave 5 transmitted through
the acoustic wave receiving unit 2 is detected by the photoelectric conversion unit 6. In the
present embodiment, as will be described in detail below, in order to detect information of the
acoustic wave 1 including the propagation direction of the acoustic wave 1, the photoelectric
conversion unit 6 includes a plurality of photoelectric conversion elements 7-1 to 7-12. Have.
[0029]
(Light Source 4) The light source 4 emits the light wave 5 toward the acoustic wave receiver 2.
The light wave 5 transmitted through the acoustic wave receiving unit 2 enters the photoelectric
conversion unit 6. At this time, when the light path of the light wave 5 and the propagation
direction of the acoustic wave 1 coincide with each other, the signal of the acoustic wave 1 can
not be detected. Therefore, it is preferable that the propagation direction of the light wave 5 and
the propagation direction of the acoustic wave 1 at least intersect. More preferably, the optical
path of the light wave 5 and the propagation direction of the acoustic wave 1 are perpendicular
to each other.
[0030]
Since the light wave 5 needs to be transmitted through the acoustic wave receiving unit 2, it is
necessary to select the wavelength of the light wave 5 so that the propagation loss in the acoustic
wave receiving unit 2 does not increase. When silica dry gel is used as the propagation medium
portion 3 of the acoustic wave receiving portion 2 as described below, the wavelength of the light
source 4 is preferably 600 nm or more.
[0031]
The light wave 5 may be coherent light or incoherent light. However, interference of the
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10
diffracted light wave is more likely to occur when the coherent light such as the laser light is
generated, and the acoustic wave 1 is easily detected.
[0032]
The light source 4 is constituted by, for example, a laser light source. The light source 4 may be
configured by a laser light source and an optical fiber. In this case, the lightwave 5 is output from
the output end of the optical fiber.
[0033]
(Acoustic Reception Unit 2) The acoustic reception unit 2 includes the propagation medium unit
3 and the support unit 9.
[0034]
-Propagation medium portion 3 The propagation medium portion 3 is located between a pair of
main surfaces 3a and 3b on which the light wave 5 enters and exits and a pair of main surfaces
3a and 3b, and the acoustic wave 1 is incident from the environmental fluid It has at least one
side.
In the present embodiment, side surfaces 3c1, 3c2, 3c3, 3c4, 3c5 and 3c6 on which the acoustic
wave 1 is incident are provided. Hereinafter, when these aspects are collectively referred to, they
are referred to as side surfaces 3c1 to 3c6. Each of the side surfaces 3c1 to 3c6 has a planar
shape, and preferably has the same shape and the same area. It is because the acoustic wave 1
which injected into the propagation medium part 3 from side 3c1-3c6 propagates as a plane
wave, and the propagation direction of the acoustic wave 1 becomes easy to identify. The
propagation medium portion 3 has side surfaces 3 d, 3 e, 3 f located between the pair of main
surfaces 3 a, 3 b, in addition to the side surfaces 3 c 1 to 3 c 6.
[0035]
The acoustic wave 1 enters the inside of the propagation medium portion 3 from any of the side
faces 3c1 to 3c6 according to the propagation direction, and the acoustic wave 1 propagates in
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the propagation medium portion 3 and is transmitted through the propagation medium portion 3
Cross the lightwave 5 It is preferable that the distances from the side surfaces 3c1 to 3c6 to the
light wave 5 transmitted through the propagation medium unit 3 be equal to one another. As
described below, the acoustic wave 1 does not enter from the side surfaces 3d, 3e, 3f. Further, in
the present embodiment, the propagation direction of the acoustic wave 1 can be detected at an
angle of 180 ° around the light wave 5 in a plane perpendicular to the light wave 5 transmitted
through the propagation medium portion 3.
[0036]
If the angle around the light wave 5 on which the side surface on which the acoustic wave 1 is
incident is provided is constant, the more the number of side surfaces, the propagation direction
and direction (traveling direction), that is, the propagation direction of the acoustic wave 1 It
becomes possible to identify correctly. From these facts, it is preferable that the side surfaces 3c1
to 3c6 be the side surfaces of a regular polygonal column whose central axis is the optical axis of
the light wave 5 transmitted through the acoustic medium portion 3.
[0037]
As shown to FIG. 1B, in the propagation medium part 3, the surface where the acoustic wave 1
injects may be one. In this case, it is preferable that the acoustic wave 1 have a curved side
surface 3c 'at an incident possible angle. More specifically, it is preferable that the side surface
3c 'be a part of a side surface of a cylinder whose central axis is the optical axis of the light wave
5 transmitted through the propagation medium portion 3. This is because the distance from an
arbitrary position of the side surface 3c 'to the optical axis of the light wave 5 can be equal.
[0038]
It is preferable that the acoustic impedance difference between the environmental fluid and the
acoustic medium unit 3 be small in order to efficiently cause the acoustic wave 1 to be incident
on the propagation medium unit 3. The acoustic impedance can be expressed by the product of
the density of the material through which the acoustic wave propagates and the speed of sound
of the material. In a normal solid material such as glass or acrylic, the difference in acoustic
impedance with air is large, so most of the acoustic wave is reflected at the input interface, and
the acoustic wave can not be efficiently taken inside.
05-05-2019
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[0039]
In the present embodiment, it is preferable to use a silica dry gel as the acoustic medium portion
3. The density of the silica dry gel is 70 kg / m <3> or more and 280 kg / m <3> or less, and the
speed of sound of the silica dry gel is smaller than the speed of sound in air and is about 50 m /
sec or more and 150 m / sec or less. For example, when using a silica dry gel having a density of
100 kg / m <3> and a sound velocity of 50 m / sec, the acoustic impedance is about 11.3 times
the acoustic impedance of air. Therefore, the reflection of the acoustic wave 1 at the interface is
only 70%, and about 30% of the energy of the acoustic wave 1 is taken into the inside of the
silica dry gel without being reflected at the interface. That is, acoustic waves in the air can be
efficiently taken into the inside of the silica dry gel. From these reasons, by using silica dry gel as
the propagation medium that constitutes the propagation medium portion 3, the acoustic wave 1
propagating in the air can be efficiently incident.
[0040]
In addition, as the propagation medium portion 3, it is preferable to use a material having a large
refractive index change amount Δn with respect to the input sound pressure when the acoustic
wave 1 is propagated. The silica dry gel is characterized in that the refractive index change
amount Δn of the light wave is also large. While the refractive index change amount Δn of air is
2.0 × 10 <−9> for the sound pressure change of 1 Pa, the refractive index change amount for
the 1 Pa sound pressure change of the silica dry gel The Δn is as large as about 1.0 × 10 <-7>,
so that sufficient sensitivity can be obtained without preparing a large propagation medium
exceeding 10 cm.
[0041]
Support Unit 9 The support unit 9 supports the propagation medium unit 3. For this purpose, the
support portion 9 has an inner space connected to the opening 9a for the acoustic wave and the
opening 9a, and the propagation medium portion 3 is disposed and supported in the inner space.
The side surfaces 3c1 to 3c6 of the propagation medium portion 3 are exposed at the opening 9a
and are in contact with the environmental fluid. The acoustic wave 1 propagating the
environmental fluid is taken into the propagation medium portion 3 from any of the side surfaces
3c1 to 3c6 in the opening 9a. Further, the support portion 9 has a sound insulation portion 9 b
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covering between the pair of main surfaces 3 a and 3 b of the propagation medium portion 3 in
the region other than the opening 9 a.
[0042]
FIGS. 2A to 2C show the positional relationship between the opening 9a and the sound insulation
portion 9b around the light wave 5 in a plane perpendicular to the light wave 5 transmitted
through the propagation medium portion 3. FIG. As shown in FIG. 2A, when the sound insulation
portion 9b is provided at an angle of 180 ° around the light wave 5, the opening 9a exposes the
propagation medium portion 3 at an angle of 180 ° around the light wave 5. . In this case, the
propagation direction and direction of the acoustic wave 1 can be detected over the entire angle
of 180 ° at which the opening 9a is located.
[0043]
Further, as shown in FIG. 2B, in the case where the sound insulation portion 9 b is provided at an
angle θ smaller than 180 ° and smaller than 360 ° around the light wave 5, the opening 9 a is
formed around the light wave 5. The propagation medium portion 3 is exposed at an angle of
(360-θ) °, and the propagation direction and direction of the acoustic wave 1 can be detected
over this angle.
[0044]
On the other hand, as shown in FIG. 2C, when the sound insulation portion 9 b is provided at an
angle θ larger than 0 ° and smaller than 180 ° around the light wave 5, the opening 9 a is
formed around the light wave 5. The propagation medium portion 3 is exposed at an angle of
(360-θ) °.
However, in this case, the propagation direction and direction of the acoustic wave 1 can be
detected in the range of θ narrower than the angle at which the opening 9a is provided, and in
the region of (180-θ) ° sandwiching the region of this angle Although the propagation
direction can be detected, the direction can not be detected. That is, the propagation direction
and direction of the acoustic wave 1 can not be detected at an angle equal to or more than the
angle at which the sound insulation portion 9 b is provided.
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[0045]
The size of the angle θ can be determined according to the specification according to the
application required for the optical microphone 101 of the present embodiment.
[0046]
As described above, when the sound insulation portion 9 b covers the light wave 5 in the plane
perpendicular to the light wave 5 by 180 ° or more, the propagation direction and direction of
the acoustic wave 1 can be detected.
On the other hand, when the sound insulation portion 9 b covers the light wave 5 at an angle θ
larger than 0 ° and smaller than 180 ° in a plane perpendicular to the light wave 5, the
acoustic wave 1 is Although the propagation direction and direction can not be detected, it is
possible to detect whether the acoustic wave is propagating in a wider range. For example, by
determining θ to satisfy 45 ° ≦ θ ≦ 90 °, the propagation of the acoustic wave 1 can be
detected in the range of 270 ° to 315 °, and in the range of 45 ° to 90 °, The propagation
direction and direction of the acoustic wave 1 can be detected.
[0047]
When the support portion 9 is configured integrally with the sound insulation portion 9 b, it is
preferable to configure the support portion 9 with a material that can isolate the acoustic wave 1.
Therefore, a normal solid material such as glass, acrylic or metal may be used instead of a
material such as a silica nanoporous body, which has an acoustic impedance close to that of the
environmental fluid. The support 9 is preferably transparent to the light wave 5 emitted from the
light source 4. Therefore, it is preferable to use a transparent material such as glass or acrylic. In
the case of using a non-translucent material such as metal, the light wave 5 is incident on the
light incident position and the light emission position so that a part of the pair of main surfaces
3a and 3b of the propagation medium portion 3 is exposed. A hole of a sufficiently large size may
be provided, and the light wave 5 may be made to enter and exit therefrom.
[0048]
(Photoelectric Conversion Unit 6) The photoelectric conversion unit 6 includes a plurality of
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photoelectric conversion elements. Preferably, the plurality of photoelectric conversion elements
are arranged circumferentially around one point. In the present embodiment, the photoelectric
conversion unit 6 includes photoelectric conversion elements 7-1 to 7-12. Each of the
photoelectric conversion elements 7-1 to 7-12 has the same fan shape, and the vertexes of the
fan shape are aligned in the circumferential direction. As shown in FIG. 1A, the photoelectric
conversion unit 6 is disposed relative to the light source 4 such that the apex of the sector is
located on the optical axis of the light wave 5. Therefore, the photoelectric conversion elements
7-1 to 7-12 are disposed at equal angles around the light wave 5 transmitted through the
acoustic wave receiving unit 2.
[0049]
Preferably, the orientation of each boundary of the photoelectric conversion elements 7-1 to 712 around the light wave 5 matches the orientation of each boundary of the side surfaces 3 c 1
to 3 c 6 of the propagation medium portion 3. For example, as shown in FIG. 1A, when the
boundary between the side surface 3c1 and the sound insulating portion 9b is oriented at 0 °
with the light wave 5 at the center, the boundary between the photoelectric conversion element
7-1 and the photoelectric conversion element 7-2 The boundaries between the side surface 3c1
and the side surface 3c2 are both located at an orientation of 30 °. The orientation of the
boundaries of the other photoelectric conversion elements also coincides with the orientation of
the boundaries of the corresponding side surfaces.
[0050]
As described below, the optical microphone 101 according to the present embodiment detects
any one of the + 1st-order diffracted lightwave and the -1st-order diffracted lightwave generated
in the propagation direction of the acoustic wave 1 by transmitting through the acoustic wave
receiver. Detect the propagation direction and direction of the acoustic wave. In the plane
perpendicular to the light wave 5, the + 1st order diffracted light wave and the −1st order
diffracted light wave are generated at symmetrical positions with respect to the light wave 5, that
is, at azimuths different from the light wave 5 by 180 °. Therefore, in order to detect the
propagation direction and direction of the acoustic wave, the photoelectric conversion unit 6 may
arrange the photoelectric conversion element in the range of 180 ° or less with respect to the
light wave 5.
[0051]
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When the openings 9a are provided around the light wave 5 at an angle smaller than 180 °, the
photoelectric conversion element may be disposed only within the range of the orientation in
which the openings 9a are provided. The photoelectric conversion element may be disposed only
within the range of the azimuth that is point-symmetrical with respect to the light wave 5. When
the sound insulation portion 9 b is provided around the light wave 5 at an angle smaller than
180 °, the photoelectric conversion element may be disposed only within the range of the
orientation in which the sound insulation portion 9 b is provided. The photoelectric conversion
element may be disposed only in the range of the azimuth that is point-symmetrical with respect
to the light wave 5 in the range of the azimuth.
[0052]
For example, in the case of the optical microphone 101 shown in FIG. 1A, among the
photoelectric conversion elements 7-1 to 7-12, the photoelectric conversion elements 7-1 to 7-6
or the photoelectric conversion elements 7-7 to 7-12 are provided. It does not have to be.
[0053]
When providing a photoelectric conversion element in the range of 360 ° around the light wave
5, electrical signals obtained from a pair of photoelectric conversion elements located at
symmetrical positions with respect to the light wave 5 may be added.
In this case, the phase of one of the two electrical signals is inverted. This makes it possible to
obtain a larger detection signal.
[0054]
In the present embodiment, the photoelectric conversion elements 7-1 to 7-12 have a fan-like
shape, but the shape does not have to be a circle. It may be shaped. The number of photoelectric
conversion elements is also not limited to the illustrated number. Further, the areas of the
photoelectric conversion elements 7-1 to 7-12 may not be equal. Further, each of the
photoelectric conversion elements 7-1 to 7-12 may be configured of a plurality of photoelectric
conversion elements. For example, by arranging smaller photoelectric conversion elements,
grouping them into the same shape as the photoelectric conversion elements described above,
05-05-2019
17
and adding and obtaining output signals of photoelectric conversion elements in a group, one
photoelectric conversion of these groups is performed. It may be operated as one of the elements
7-1 to 7-12.
[0055]
2. Operation of Optical Microphone 101 Next, the operation will be described. As shown in
FIG. 1, the acoustic wave 1 propagating in the air is taken in from the side surfaces 3 c 1 to 3 c 6
of the propagation medium unit 3 through the opening 9 a and propagates inside the
propagation medium unit 3. The light wave 5 output from the light source 4 is incident on the
propagation medium portion 3 and contacts the acoustic wave 1 in the propagation medium
portion 3.
[0056]
FIG. 3 shows how the acoustic wave 1 and the light wave 5 contact in the propagation medium
portion 3. The wavelength of the acoustic wave 1 in the propagation medium unit 3 is Λ, and the
frequency is f. Further, the wavelength of the light wave 5 emitted from the light source 4 is λ,
and the frequency is f0. The propagation of the acoustic wave 1 in the propagation medium
portion 3 changes the density of the propagation medium of the propagation medium portion 3
and the refractive index changes accordingly. That is, as the acoustic wave 1 propagates, a
refractive index distribution pattern in which the refractive index changes at a period
corresponding to the wavelength 伝 搬 propagates in the propagation direction of the acoustic
wave 1. When the light wave 5 contacts this, the refractive index distribution pattern by the
acoustic wave 1 behaves like a diffraction grating. For this reason, the diffracted light wave is
included in the light wave 5 emitted from the propagation medium portion 3 after coming into
contact with the acoustic wave 1. A light wave diffracted in the direction in which the acoustic
wave 1 propagates is referred to as a + 1st order diffracted light wave 5a, and a light wave
diffracted in the opposite direction to the direction in which the acoustic wave 1 propagates is
referred to as a 1st order diffracted light wave 5c. The resulting light wave is referred to as a
zero-order diffracted light wave 5b. When the sound pressure of the acoustic wave 1 is large,
second-order or higher order diffracted light waves are also output. The following description
will be made using three diffracted light waves shown in FIG. 3 in consideration of the case
where high-order diffracted light waves can be ignored.
[0057]
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18
Since the acoustic wave 1 propagates in the propagation medium portion 3 in the direction
indicated by the arrow in FIG. 3, the diffraction grating having the refractive index distribution
pattern also propagates in the propagation direction of the acoustic wave 1 with momentum.
Therefore, the diffracted light due to the refractive index distribution pattern is subject to
Doppler shift. Specifically, the frequency of the + 1st order diffracted light wave 5a is f0 + f, and
the frequency of the −1st order diffracted light wave 5c is f0−f. Since the zeroth-order
diffracted light wave 5b is not diffracted, the frequency of the zero-order diffracted light wave 5b
remains f0 as before entering the propagation medium portion 3. Further, the phases of the +
1st-order diffracted light wave 5a and the -1st-order diffracted light wave 5c are inverted to each
other, and are 180 ° out of phase.
[0058]
When the zero-order diffracted light wave 5b and the + first-order diffracted light wave 5a, or the
zero-order diffracted light wave 5b and the -first-order diffracted light wave 5c are interfered, a
difference frequency light component having a frequency f is generated. When this is
photoelectrically converted in the photoelectric conversion unit 6, an electric signal of frequency
f is obtained. This electrical signal is one obtained by converting the acoustic wave 1 into an
electrical signal. When the sound pressure of the acoustic wave 1 is large and a high-order
diffracted light wave is generated, harmonics are superimposed on the electrical signal output
from the photoelectric conversion unit 6.
[0059]
FIG. 4 shows the direction of the diffracted light of the lightwave 5 transmitted through the
propagation medium unit 3 from the photoelectric conversion unit 6 toward the acoustic wave
receiving unit 2 (in the direction of the lightwave 5 emission) on the plane perpendicular to the
propagation direction of the lightwave 5 In the opposite direction). When the diffraction angles
of the + 1st diffracted light wave 5a and the -1st diffracted light wave 5b are large or the
distance from the acoustic wave receiving portion 2 is large, as shown in FIG. 4B, the + 1st
diffracted light wave 5a and the -1st diffracted light The light waves 5c are separated from each
other without overlapping with each other. However, as shown in FIG. 4A, when the diffraction
angles of the + 1st-order diffracted lightwave 5a and the -1st-order diffracted lightwave 5b are
small or when the distance from the acoustic wave receiver 2 is short, the + 1st-order diffracted
lightwave 5a And the -1st-order diffracted light wave 5c partially overlap with each other.
05-05-2019
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[0060]
When the interference light of the + 1st order diffracted light wave 5a and the 0th order
diffracted light wave 5b and the interference light of the -1 order diffracted light wave 5c and the
0 order diffracted light wave 5b are simultaneously received by the photoelectric conversion unit
6, two sets of interference lights Since the phases are 180 ° out of phase, it is not possible to
cancel each other and to detect the signal. Therefore, as shown in FIG. 4A, the interference light
can not be detected in the region 5f in which the + 1st order diffracted light wave 5a and the -1st
order diffracted light wave 5c overlap with each other and the 0th order diffracted light wave 5b.
In any case of FIG. 4A and FIG. 4B, in the regions 5d and 5e shown in the drawing, interference
light whose intensity changes according to the acoustic wave is obtained.
[0061]
The directions in which the + 1st-order diffracted light wave 5a and the -1st-order diffracted light
wave 5b occur coincide with the direction in which the acoustic wave 1 propagates. For this
reason, if interference light from the regions 5d and 5e is detected around the light wave 5
transmitted through the acoustic wave receiving unit 2 which is the zeroth-order diffracted light
wave 5b, + first-order diffracted light wave 5a and -first-order diffracted light wave 5b are
generated. The direction in which the acoustic wave 1 propagates can also be identified.
[0062]
Hereinafter, for ease of understanding, as shown in FIG. 5A, the shape of the propagation
medium portion 3 is a regular hexagonal column, and +1 occurs when the acoustic wave 1 is
incident on the regular hexagonal side surfaces 3c1 to 3c6. The interference light of the nextorder diffracted light wave 5a and the zero-order diffracted light wave 5b will be described. 6 (a)
to 6 (f) show that the acoustic wave 1 is input from the side surfaces 3c1 to 3c6 to the
propagation medium unit 3 and that the acoustic waves 11 to 16 and the light wave 5 are in
contact and + 1st order diffraction The positional relationship of the diffracted light wave at the
time of generating the light wave 5a and the -1st-order diffracted light wave 5c is shown.
[0063]
05-05-2019
20
As shown in FIGS. 6A to 6F, the + 1st order diffracted light wave 5a and the -1st order diffracted
light wave 5b occur at positions shifted in the propagation direction of the acoustic wave 1 with
respect to the 0th order diffracted light wave 5b, If the propagation direction of the acoustic
wave 1 changes, the directions in which the + 1st order diffracted light wave 5a and the -1st
order diffracted light wave 5b are generated also change. Therefore, as shown in FIG. 5 (b), in the
photoelectric conversion unit 6 in which the photoelectric conversion elements 7-1 to 7-6 are
provided in the direction corresponding to the direction of the side surfaces 3c1 to 3c6, the + 1st
order diffracted light wave 5a and- When the first-order diffracted light wave 5c is received, the
intensity of the electric signal obtained from the two specific photoelectric conversion elements
of the photoelectric conversion elements 7-1 to 7-6 is increased. Therefore, it can be seen that
the acoustic wave 1 propagates from the direction in which these photoelectric conversion
elements are located. For example, when the acoustic wave 1 is incident from the side surface
3c1, the largest electric signal is output from the photoelectric conversion elements 7-1 and 7-4.
In addition, when the acoustic wave 1 is incident from the side surface 3c2, the largest electric
signal is output from the photoelectric conversion elements 7-2 and 7-5. Thus, the photoelectric
conversion element at the position corresponding to the position of the side surface on which the
acoustic wave 1 is incident and the photoelectric conversion element arranged at the
symmetrical position with respect to the photoelectric conversion element and the light wave 5
have the largest intensity. An electrical signal is obtained.
[0064]
As can be seen from FIGS. 6A and 6D, when the propagation directions of the acoustic wave 1 are
opposite to each other (different 180 °), the positions of the + 1st order diffracted light wave 5a
and the -1st order diffracted light wave 5c. It turns out that it is the same arrangement only by
reversing. Therefore, when the acoustic wave 1 is incident from the side surface 3c1 and from
the side surface 3c4, a signal with the largest intensity is obtained from the photoelectric
conversion elements 7-1 and 7-4d. Therefore, it can not be determined from the signal strength
whether the acoustic wave 1 is incident from the side surface 3c1 or from the side surface 3c4.
For the same reason, two acoustic waves 1 propagating in opposite directions can not be
distinguished and detected.
[0065]
As described above, the interference light of the + 1st-order diffracted light wave 5a and the 0th-
05-05-2019
21
order diffracted light wave 5b and the interference light of the −1st-order diffracted light wave
5c and the 0th-order diffracted light wave 5b are mutually reversed in phase. Therefore, if the
phase of the signal of the acoustic wave 1 is known in advance, the phases of the output signals
of the photoelectric conversion element 7-1 and the photoelectric conversion element 7-4 are
compared with the phase of the acoustic wave 1, It is possible to specify the direction of
propagation, that is, the azimuth, by specifying. However, it is not common that the phase of the
acoustic wave 1 is known in advance. Therefore, it is difficult to identify the direction of
propagation of the acoustic wave 1 by this method.
[0066]
Taking this point into consideration, as described with reference to FIG. 2, the optical
microphone 101 of the present embodiment is provided with the sound insulation unit 9 b in the
acoustic reception unit 2 to limit the direction of the acoustic wave incident on the propagation
medium unit 3. Do. As described above, when the sound insulation portion 9 b is provided at an
angle of 180 ° or more around the light wave 5, the opening 9 a is 180 ° or less around the
light wave 5 as shown in FIGS. The propagation medium portion 3 is exposed at an angle, and the
propagation direction and direction of the acoustic wave 1 can be detected over the entire angle
of 180 ° or less where the opening 9 a is located. On the other hand, when the sound insulation
portion 9 b is provided at an angle of 180 ° or more around the light wave 5, the propagation
direction and direction of the acoustic wave 1 can be detected within the angle provided with the
sound insulation portion 9 b.
[0067]
As described above, the propagation direction and direction of the acoustic wave 1 can be
detected in the photoelectric conversion unit 6 shown in FIG. 1A by comparing the intensities of
the electrical signals obtained from any of the photoelectric conversion elements 7-1 to 7-6. . FIG.
7 schematically shows the waveform of the electrical signal obtained from the photoelectric
conversion element. As shown in FIG. 7A, when the acoustic wave 1 is not propagated or the
electrical signal obtained from the photoelectric conversion element 7 located in the direction
different from the propagation direction of the acoustic wave 1 is the acoustic wave 1 The
amplitude component of is not included. On the other hand, the acoustic wave 1 is propagated,
and the electric signal obtained from the photoelectric conversion element 7 positioned in the
propagation direction of the acoustic wave 1 includes the amplitude component of the acoustic
wave 1. Therefore, the propagation direction and direction of the acoustic wave 1 may be
specified by any method as long as the difference between the signal shown in FIG. 7A and the
05-05-2019
22
signal shown in FIG. 7B can be detected. For example, if a direct current (DC) component is cut
by passing an electrical signal obtained from the photoelectric conversion elements 7-1 to 7-6
through a high pass filter, the photoelectric conversion elements positioned in the direction and
direction in which the acoustic wave 1 propagates. An electrical signal is obtained only from 7.
Therefore, by making the photoelectric conversion elements 7-1 to 7-6 correspond to the
orientations of the side surfaces 3c1 to 3c6 of the propagation medium unit 3, the propagation
direction and direction of the acoustic wave 1 can be specified.
[0068]
As shown to FIG. 1A, the optical microphone 101 may be equipped with the propagation
direction determination part 51 which determines a propagation direction based on the output
from the photoelectric conversion part 6. FIG. The propagation direction determination unit 51
receives the electrical signals from the photoelectric conversion elements 7-1 to 7-6 of the
photoelectric conversion unit 6, and outputs a signal representing the propagation direction of
the acoustic wave 1 by an angle φ from the reference direction.
[0069]
For example, in FIG. 1A, with the boundary between the photoelectric conversion element 7-1
and the photoelectric conversion element 7-12 as a reference, the direction is clockwise. The
azimuth of the photoelectric conversion elements 7-1 to 7-6 is taken as the central value in the
circumferential direction of each element, and as shown in Table 1, it corresponds to the
azimuth. The propagation direction determination unit 515 has a memory in which data in which
such photoelectric conversion elements are associated with the direction is recorded.
[0070]
[0071]
The propagation direction determination unit 51 receives an output from the photoelectric
conversion unit 6 and refers to the memory, and among the photoelectric conversion elements 71 to 7-6, a photoelectric conversion element to which an electric signal of a predetermined
intensity or more is output. The corresponding azimuth φ 'is output.
05-05-2019
23
Thereby, the propagation direction of the acoustic wave is detected.
[0072]
When the electrical signal is greater than or equal to a predetermined intensity in two or more
photoelectric conversion elements, the direction may be determined by averaging based on the
magnitude of the intensity of the electrical signal.
[0073]
Further, as shown in FIG. 7B, the electric signal obtained from the photoelectric conversion
element includes the amplitude component of the acoustic wave 1, so that the acoustic wave 1
can also be detected by the photoelectric conversion unit 6.
In addition, since the outputs of the photoelectric conversion elements 7-1 to 7-6 of the
photoelectric conversion unit 6 are independent, in the case where the acoustic wave propagates
from a plurality of directions in the environmental fluid, the acoustic wave of a specific direction
Can be detected separately. In this case, two photoelectric conversion elements, such as the
photoelectric conversion element 7-1 and the photoelectric conversion element 7-7, located at
symmetrical positions with respect to the light wave 5, obtain an electrical signal by interference
light whose phase is inverted. Therefore, when these two electrical signals are added, the signal
component of the acoustic wave 1 is canceled out by the phase difference.
[0074]
As described above, according to the optical microphone of the present embodiment, the acoustic
wave receiving unit is provided with the sound insulation unit, and the photoelectric conversion
including the plurality of photoelectric conversion elements is performed to restrict the direction
in which the acoustic wave is incident on the acoustic wave receiving unit. The part can be used
to identify the propagation direction and direction (orientation) of the acoustic wave. Further, an
acoustic wave is made incident on a solid propagation medium, and the light wave and the
acoustic wave are caused to act to detect the acoustic wave, so that the influence of air
convection and the like can be suppressed. Further, since the propagation medium is a solid, the
change in refractive index caused by the propagation of the acoustic wave in the propagation
05-05-2019
24
medium portion becomes large, and the acoustic wave can be detected with high sensitivity.
Further, since the modulation component due to the acoustic wave is detected as an interference
component between the 0th order diffracted light wave and the + 1st order diffracted light wave
or the -1st order diffracted light wave, the light quantity change of the interference component
corresponds to the acoustic wave to be detected. Therefore, even if it does not use a large-scale
optical system like a laser Doppler vibrometer, it becomes possible to detect an interference
component if a simple photoelectric conversion element is used. Therefore, the configuration of
the optical microphone can be made compact and simple.
[0075]
(Experimental Results of Optical Microphone) The inventor of the present application has
experimentally manufactured the optical microphone of the present embodiment. FIG. 8 shows
the prototyped optical microphone.
[0076]
As the propagation medium portion 3, a silica dry gel having a density of 108 kg / m <3> and a
sound velocity of 51 m / sec was used. Silica dried gel was prepared by sol-gel method.
Specifically, catalyst water is added to a sol liquid in which tetramethoxysilane (TMOS) is mixed
with a solvent such as ethanol, and a wet gel is formed by hydrolysis and polycondensation
reaction, and the obtained wet gel is subjected to a hydrophobization treatment gave. The wet gel
was filled in a mold having a 20 mm × 20 mm × 5 mm rectangular internal space and dried by
supercritical drying to obtain a 20 mm × 20 mm × 5 mm rectangular parallelepiped
propagating medium portion 3. The square surface is used as the input / output surface of the
light wave 5, and two adjacent surfaces in the 5 mm × 20 mm surface are used as the side
surfaces 3c1 and 3c2 to which the acoustic wave 1 is input.
[0077]
The support portion 9 was formed of a transparent acrylic plate with a thickness of 3 mm. The
support portion 9 has a rectangular solid internal space of 20 mm × 20 mm × 5 mm, and an
opening 9 a having a size of 5 mm × 20 mm is provided on two adjacent side surfaces to expose
the side surfaces 3 c 1 and 3 c 2.
05-05-2019
25
[0078]
As the light source 4, a He̶Ne laser having a wavelength of 633 nm was used. The light wave 5
was emitted from the light source 4 and was perpendicularly incident on the square surface of
the support 9. The light wave transmitted through the acoustic wave receiving unit 2 was
detected by the photoelectric conversion unit 6. The distance between the light source 4 and the
acoustic wave receiver 2 was about 15 cm. The spot diameter of the light wave 5 was about 0.6
mm.
[0079]
As the photoelectric conversion unit 6, for the sake of simplicity, one including two photoelectric
conversion elements 71 and 72 was used. The distance between the acoustic wave receiving unit
2 and the photoelectric conversion unit 6 was 25 cm. As the photoelectric conversion elements
71 and 72, photodetectors of silicon diodes were used. The photoelectric conversion elements 71
and 72 were disposed in the y direction so as to be symmetrical with respect to the optical axis
(central axis) of the light wave 5.
[0080]
The output of the photoelectric conversion unit 6 was input to an oscilloscope, and the acoustic
wave 1a propagating in the negative direction of the y-axis was made incident on the acoustic
reception unit 2, and the waveform was observed. A burst signal consisting of 15 sine waves
having a frequency of 40 kHz was input to the tweeter, and the acoustic wave was emitted to the
air as the environmental fluid. The waveform observed by the oscilloscope is shown in FIG. From
this, it could be confirmed that a waveform corresponding to the input acoustic wave 1a was
obtained. This is because the photoelectric conversion elements 71 and 72 are arranged shifted
with respect to the zero-order diffracted light wave 5b in the direction in which the plus firstorder diffracted light wave 5a and the minus first-order diffracted light wave 5b are generated. It
was also confirmed that the signals of the photoelectric conversion elements 71 and 72 are in
reverse phase.
[0081]
05-05-2019
26
Next, the acoustic wave 1 b propagating in the direction perpendicular to the acoustic wave 1 a
was input, and the output waveform of the photoelectric conversion element 71 was observed.
The waveform observed by the oscilloscope is shown in FIG. In this case, the signal
corresponding to the acoustic wave 1 b was not confirmed. This is because the photoelectric
conversion element 71 is not arranged shifted with respect to the zeroth-order diffracted
lightwave 5b in the direction in which the + first-order diffracted lightwave 5a and the -firstorder diffracted lightwave 5b occur.
[0082]
From FIGS. 9 and 10, it was confirmed that the propagation direction of the acoustic wave 1 can
be identified by observing the waveform using the optical microphone according to this
experiment.
[0083]
In this experiment, although the photoelectric conversion part 6 was comprised from the two
photoelectric conversion elements 71 and 72 for simplicity, as shown in FIG. 11, four
photoelectric conversion elements 71 are made so that the vertex which has an angle of 90
degrees may be united. , 72, 73 and 74 are arranged, in addition to the acoustic wave 1a
propagating in the negative direction of the y axis, the acoustic wave 1b propagating in the
negative direction of the x axis is detected. Can.
[0084]
(Other Configurations of Acoustic Reception Unit) When the shape of the propagation medium
unit 3 constituting the acoustic reception unit 2 has a polygonal columnar shape as shown in FIG.
1A, the acoustic wave 1 is on any of the side surfaces 3c1 to 3c6. At the time of incidence, it is
conceivable that the acoustic wave 1 is also incident on the adjacent side surface, for example, by
generating a diffracted wave at the end of the side surface.
In particular, when the density nn and the speed of sound Cn of the material constituting the
propagation medium portion 3 satisfy the following equation (1) with respect to the density aa of
the air and the speed of sound Ca, the acoustic wave 1 is not accompanied by reflection and the
propagation medium portion 3 It may be refracted and propagated inside.
05-05-2019
27
<img class = "EMIRef" id = "409774200-00004" />
[0085]
FIG. 12 shows how the acoustic wave 1 propagates on the interface between the air and the
propagation medium portion 3. The acoustic wave 1 refracts and propagates inside the
propagation medium portion 3 without reflection when the incident angle θa of the acoustic
wave 1 satisfies the equation (2). <img class = "EMIRef" id = "409774200-000005" />
[0086]
For example, when the density of the propagation medium portion 3 is 100 kg / m <3> and the
speed of sound is 50 m / sec, the propagation medium at the refraction angle θn = 8.4 ° when
the incident angle θa = 85.4 ° of the acoustic wave 1 It refracts and propagates to the inside of
the part 3.
[0087]
When the acoustic wave 1 is perpendicularly incident on any of the side faces 3c1 to 3c6 and
propagates inside the propagation medium portion 3, diffracted waves generated at the end of
the side face are adjacent at an angle close to the above incident angle When incident on the side
surface, the acoustic wave 1 enters the propagation medium portion 3 from any of the side
surfaces of the side surfaces 3c1 to 3c6 and the side surface adjacent thereto.
Therefore, it may be considered that identification of the propagation direction of the acoustic
wave 1 becomes difficult.
[0088]
If the incidence of the acoustic wave 1 from such an adjacent side face is a problem, the acoustic
wave receiver 2 may be provided with a structure in which the diffracted wave of the acoustic
wave 1 does not enter the adjacent side face.
[0089]
05-05-2019
28
For example, as shown in FIG. 13, horns 16 corresponding to the side surfaces 3c1 to 3c6 may
be provided at the openings 9a of the support portion 9 so that the diffracted waves of the
acoustic wave 1 do not enter adjacent sides.
Moreover, as shown in FIG. 14, it is also possible to configure the horn 16 with the propagation
medium portion 3.
[0090]
Furthermore, as shown in FIG. 15, a break 17 may be provided in the opening 9 a of the support
portion 9 to suppress the propagation of the diffraction wave of the acoustic wave 1. The
partition 17 divides the opening 9a into a plurality of openings, and covers the side surfaces of
the propagation medium portion 3 exposed from the opening 9a of the support portion 9 and the
side surfaces adjacent thereto and the boundary 3h. . The height h of the partition 17 preferably
satisfies h17D · tan θa with respect to the width D of the side surface. Moreover, it is preferable
that the partition 17 is in contact with the side surfaces 3c1 to 3c6. The break 17 may be
provided on the curved side surface 3c 'as shown in FIG. 1B, as well as in the case where the
propagation medium portion 3 has a plurality of side surfaces constituted by flat surfaces.
[0091]
Thus, the acoustic wave 1 is accurately propagated through the propagation medium portion 3
while suppressing the unnecessary wave by providing the horn 16 and the break 17 so that the
diffracted wave of the acoustic wave 1 does not enter the adjacent side face. It is possible to
detect the propagation direction of the acoustic wave 1 more accurately.
[0092]
Second Embodiment Hereinafter, a second embodiment of the optical microphone according to
the present invention will be described.
FIG. 16 is a perspective view schematically showing the configuration of the optical microphone
102 of the second embodiment. The optical microphone 102 includes an acoustic wave receiving
unit 2, a light source 4, a rotary light shielding plate 11, and a photoelectric conversion unit 12.
05-05-2019
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The optical microphone 102 is different from that of the first embodiment in that the
photoelectric conversion unit 12 includes one photoelectric conversion element and includes the
rotary light shielding plate 11.
[0093]
The optical microphone 102 shields part of the light wave 5 using the rotary light shielding plate
11 while changing the direction, and the photoelectric conversion unit 12 detects the light wave
5.
[0094]
Hereinafter, the rotary light shielding plate 11 and the photoelectric conversion unit 12 will be
described in detail.
[0095]
(Rotating Light-Shielding Plate 11) The rotary light-shielding plate 11 is disposed at a position
where the light wave 5 transmitted through the acoustic wave receiving portion 2 is partially
shielded.
The rotary light shielding plate 11 is made of a material that does not transmit the light wave 5
and includes a rotation mechanism that rotates around the optical axis (central axis) of the light
wave 5.
[0096]
The light wave 5 is partially blocked at one edge of the rotary light blocking plate 11 and is
propagated without being blocked by the remaining portion.
This ridge line will be referred to as a light shielding rod 13. It is preferable that the shading rod
13 be a straight line. This is because identification of the propagation direction of the acoustic
wave 1 is easy. As shown in FIG. 17 (b), when the light blocking weir 13 is disposed so as to pass
through the optical axis of the light wave 5, the electric signal obtained from the photoelectric
conversion unit 13 contains the component of the acoustic wave 1 most. For this reason, it is
05-05-2019
30
preferable that the light shielding wedge 13 passes (crosses) the optical axis of the light wave 5.
However, as shown in FIGS. 17 (a) and 17 (c), even if the light blocking wedge 13 is disposed
offset from the optical axis of the light wave 5, the acoustic wave 1 can be detected although the
amplitude is reduced. It is. The rotary light shielding plate 11 includes a mechanism that rotates
around the optical axis of the light wave 5. The electrical signal may be acquired from the
photoelectric conversion unit 12 while rotating the rotary light shielding plate 11, or the
electrical signal may be acquired by adjusting and stopping at an arbitrary angle.
[0097]
(Photoelectric Conversion Unit 12) The photoelectric conversion unit 12 includes a photoelectric
conversion element having a light receiving surface sufficiently larger than the light wave 5, and
receives the light wave 5 propagated without being blocked by the rotary light shielding plate
11. In addition, the photoelectric conversion unit 12 acquires information on the rotation angle
of the light shielding wedge 13 of the rotary light shielding plate 11 in real time. The output
signal of the photoelectric conversion unit 12 is detected and recorded in association with the
information of the rotation angle of the light shielding rod 13.
[0098]
Next, the operation of the optical microphone 102 will be described with reference to FIG.
[0099]
18 (a) to 18 (e) are produced by the light wave passing through the rotary light shielding plate
11 at various rotation angles and the acoustic wave receiving portion 2 in which the acoustic
wave 1 is transmitted through the propagation medium portion 3; The relationship between the +
1st order diffracted light wave 5a, the -1st order diffracted light wave 5c, and the position of the
0th order diffracted light wave 5b is schematically shown.
The acoustic wave 1 propagates in the negative direction in the y-axis in the figure. At this time,
the angle of the light shielding wedge 13 of the rotary light shielding plate 11 is taken as φ in
the clockwise direction with respect to the x axis. The light shielding wedge 13 of the rotary light
shielding plate 11 passes through the optical axis of the zero-order diffracted light wave 5b.
05-05-2019
31
[0100]
As shown in FIGS. 18 (a) to 18 (e), the + 1st-order diffracted light wave 5a and the -1st-order
diffracted light wave 5c are on the opposite side of the propagation direction of the acoustic
wave 1 with respect to the 0th-order diffracted light wave 5b. Generate
[0101]
As shown in FIG. 18A, in the case of φ = 0 °, the rotary light shielding plate 11 shields a region
where the + 1st order diffracted light wave 5a and the 0th order diffracted light wave 5b
intersect, and the 0th order diffracted light wave 5b and A region 5 e overlapping with the −1st
order diffracted light wave 5 c is detected by the photoelectric conversion unit 6.
Therefore, only the interference light from the area 5 e modulated by the acoustic wave 1 is
detected.
[0102]
As shown in FIGS. 18 (b), (c) and (d), when the rotation angle φ of the rotary light shielding plate
11 becomes large, a part of the region 5e is blocked by the rotary light shielding plate 11, and
the zeroth order diffracted light wave 5b and The interference light from the area 5 d
overlapping with the + 1st order diffracted light wave 5 a is detected. As the rotation angle φ
increases, the area of the region 5e decreases, and the light amount of interference light obtained
from the region 5e also decreases. On the other hand, the area of the region 5d is increased, and
the light amount of the interference light obtained from the region 5d is increased.
[0103]
As described with reference to FIG. 4, since the interference obtained from the region 5e and the
interference light obtained from the region 5d are opposite in phase to each other, when these
are simultaneously detected by the photoelectric conversion unit 12, an acoustic wave is
obtained. Some of the signal components of 1 are canceled out and not detected.
[0104]
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32
Therefore, as the rotation angle φ increases, the amplitude of the component of the acoustic
wave 1 in the electric signal obtained from the photoelectric conversion unit 12 decreases.
As shown in FIG. 18E, when φ = 90 °, the areas of the regions 5e and 5d become equal, so the
component of the acoustic wave 1 in the electrical signal obtained from the photoelectric
conversion unit 12 becomes zero. At this time, the light shielding weir 13 is parallel to the
propagation direction of the acoustic wave 1.
[0105]
As described above, when the rotation angle φ of the rotary light shielding plate 11 is 0 °, the
amplitude of the electric signal obtained from the photoelectric conversion unit 12 is maximum,
and when it is 90 °, the electric signal is minimum. That is, when the amplitude of the electrical
signal is maximum, the light blocking wedge 13 is positioned perpendicular to the propagation
direction of the acoustic wave 1 and when the amplitude of the electrical signal is minimum, the
light blocking wedge 13 is of the acoustic wave 1. It is parallel to the propagation direction. The
acoustic wave 1 does not enter the acoustic wave receiver 2 from the direction corresponding to
the rotation angle φ of 180 ° or more and 360 ° or less by the sound insulation unit 9 b.
Therefore, the angle φ at which the amplitude of the electrical signal of the photoelectric
conversion unit 12 becomes minimum coincides with the propagation direction of the acoustic
wave 1.
[0106]
In the present embodiment, a part of the light wave incident on the photoelectric conversion unit
12 is restricted using the rotary light shielding plate 11, and the light shielding region is rotated.
However, instead of using the rotary light shielding plate 11, the same operation can be
performed even if the photoelectric conversion unit 12 is provided with a rotation mechanism. In
this case, as shown in FIG. 19, the photoelectric conversion unit 12 can be disposed at a position
for receiving part of the light wave 5, and the same effect can be obtained by rotating the light
wave 5 about its optical axis. In this case, the light receiving surface of the photoelectric
conversion unit 12 is defined, and the side 12 e close to the optical axis of the light wave
functions as a light shielding wedge.
[0107]
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As described above, according to the optical microphone of the present embodiment, the electric
signal intensity obtained from the photoelectric conversion unit changes according to the angle
of the rotary light shielding plate or the rotation angle of the photoelectric conversion unit, and
the change in signal intensity is The light shielding region corresponds to the position of the
diffracted light wave, that is, the propagation direction of the acoustic wave. Therefore, the
propagation direction of the acoustic wave 1 can be specified from the angle of the rotary light
shielding plate or the rotation angle of the photoelectric conversion unit 12.
[0108]
Third Embodiment The third embodiment of the optical microphone according to the present
invention will be described below. FIG. 20 is a perspective view schematically showing the
configuration of the optical microphone 103 of the third embodiment. The optical microphone
103 includes an acoustic wave receiving unit 2, a light source 4, a photoelectric conversion unit
6, a beam splitter 15, and a mirror 14. The optical microphone 103 differs from that of the first
embodiment in that the light wave 5 is transmitted twice through the acoustic wave receiver 2 by
the mirror 14.
[0109]
The beam splitter 15 is provided between the light source 4 and the acoustic wave receiver 2,
and the mirror 14 is provided on the opposite side of the acoustic wave receiver 2 to the light
source 4. For this reason, the acoustic receiver 2 is located between the beam splitter 15 and the
mirror 14. The mirror 14 is preferably provided in close contact with the surface of the acoustic
wave receiver 2 opposite to the light source 4.
[0110]
In the optical microphone 103, as in the first embodiment, the acoustic wave 1 propagating in
the air is taken into the propagation medium unit 3 from the side surfaces 3c1 to 3c6. The light
wave 5 emitted from the light source 4 passes through the beam splitter 15 and enters the
propagation medium portion 3 of the acoustic wave receiving portion 2. In the propagation
medium portion 3, the light wave 5 is emitted from the sound receiving portion 2 while acting on
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the acoustic wave 1 and reaches the mirror 14.
[0111]
The light wave 5 is reflected by the mirror 14 and passes through the propagation medium
portion 3 of the acoustic wave receiving portion 2 again. For this reason, the light wave 5 is an
acoustic wave integrally in the forward path until reaching the mirror 14 and the return path due
to the reflection from the mirror 14 so as to transmit the propagation medium portion 3 whose
action length is twice. Acts with 1. As a result, when emitting from the propagation medium
portion 3 toward the beam splitter 15, the 0th-order diffracted light wave, the + 1st-order
diffracted light wave, and the 1st-order diffracted light wave are generated by the same
diffraction effect as transmitting through the propagation medium portion of double length. A 1st order diffracted light wave is generated. The lightwave 5 containing these lightwaves is
incident on the beam splitter 15, and is reflected toward the photoelectric conversion unit 6 by
the half mirror of the beam splitter.
[0112]
Similar to the first embodiment, the lightwave 5 reaching the photoelectric conversion unit 6
includes three lightwaves of + 1st order diffracted lightwave 5a, 0th order diffracted lightwave
5b, and -1st order diffracted lightwave 5c. However, the intensities of the + 1st-order diffracted
lightwave 5a and the -1st-order diffracted lightwave 5c are twice the intensity of the diffracted
lightwave obtained when transmitting the propagation medium portion 3 once.
[0113]
The method of specifying the propagation direction and direction (orientation) of the acoustic
wave 1 using the photoelectric conversion unit 6 is the same as that of the first embodiment. The
propagation direction and direction (orientation) of the acoustic wave 1 may be specified by
using the photoelectric conversion unit 112 and the rotary light shielding plate 11 of the second
embodiment instead of the photoelectric conversion unit 6.
[0114]
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According to the optical microphone of the present embodiment, the light wave 5 is reflected by
the mirror 14 and propagates back and forth in the propagation medium portion 3, so that a
larger diffraction effect can be obtained. For this reason, when the thickness of the propagation
medium portion 3 is the same, an optical microphone having higher sensitivity than that of the
first embodiment can be provided.
[0115]
Fourth Embodiment The fourth embodiment of the optical microphone according to the present
invention will be described below. FIG. 21 is a perspective view schematically showing the
configuration of the optical microphone 104 of the fourth embodiment. The optical microphone
104 includes two sets of optical microphones 101 ′ and 101 ′ ′ in which the sound
insulation unit 9 b of the acoustic wave receiving unit 2 is provided and in which the directions
are different.
[0116]
The optical microphone 101 ′ includes a light source 4, an acoustic wave receiving unit 2, a
photoelectric conversion unit 6, and a beam splitter 15. Further, the optical microphone 101 ′
′ includes an acoustic wave receiving unit 2, a photoelectric conversion unit 6, and a mirror 14.
[0117]
The beam splitter 15 is provided between the light source 4 of the optical microphone 101 'and
the acoustic wave receiving unit 2, and emits a part of the light wave 5 emitted from the light
source toward the mirror 14. The optical microphone 101 ′ ′ causes the light wave 5 reflected
by the mirror to be incident on the acoustic wave receiver 2 ′.
[0118]
The opening 9a of the acoustic wave receiving portion 2 of the optical microphone 101 'and the
opening 9a "of the acoustic wave receiving portion 2" of the optical microphone 101 "are
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36
disposed so as not to face each other. Specifically, the opening 9a of the acoustic wave receiving
portion 2 of the optical microphone 101 'is provided at an angle of 180 ° around the light wave
5, and in the range where the sound insulating portion 9b of the acoustic wave receiving portion
2 is provided, An opening 9a ′ ′ of an acoustic receiver 2 ′ ′ of the optical microphone 101
′ ′ is provided.
[0119]
By arranging the two optical microphones in this manner, the propagation direction and
direction of the acoustic wave 1 can be specified in the range of 360 ° around the light wave 5.
[0120]
In the present embodiment, the optical microphone 101 ′ ′ does not include the light source 4,
but instead of the beam splitter 15 and the mirror 14, the optical microphone 101 ′ ′ may
include another light source 4.
Also, the optical microphones 102 and 13 of the second and third embodiments may be used as
the optical microphones 101 ′ and 101 ′ ′, and the optical microphones 101 ′ and 101 ′
′ may have the same form. It may be in a form different from each other.
[0121]
According to the optical microphone of the present embodiment, it is possible to specify the
propagation direction and direction of the acoustic wave 1 at an azimuth of 360 °, and is
particularly suitable for detecting an acoustic wave whose propagation direction is unknown and
identifying the propagation direction. Used for
[0122]
The optical microphone of the present invention is useful as a small ultrasonic sensor or the like
or an audible sound microphone or the like.
In addition, it can be applied as an ultrasonic wave reception sensor or the like used in a
surrounding environment measurement system using ultrasonic waves.
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[0123]
DESCRIPTION OF SYMBOLS 1 acoustic wave 1a, 1b acoustic wave 2 acoustic wave receiving part
3 propagation medium part 4 light source 5 light wave 5a + 1st order diffracted light wave 5b
zero order diffracted light wave 5c -1 order diffracted light wave 5d, 5e detection area 6
photoelectric conversion part 7 photoelectric conversion element 7-1 to 7-12, 71 to 74
photoelectric conversion element 9 support portion 11 rotation light shielding portion 12
photoelectric conversion portion 13 light shielding frame 14 mirror 15 beam splitter 16 horn
101 emission system optical component 102 light receiving system optical component 201
opening 202 Acoustic Waveguide 203 Photoacoustic Propagation Medium 204 Laser Doppler
Vibrometer
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