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JPH05227597

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH05227597
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone for capturing sound waves and converting them into optical or electrical signals.
[0002]
2. Description of the Related Art The history of microphones for converting sound waves into
electrical signals is long and characteristically progressive, but over the years there have been no
innovative improvements. Incidentally, when the conventional microphones are classified based
on the principle of operation, they are an electromagnetic induction type called a magnetic type
or a dynamic type, one using an electrostatic effect such as an electret condenser type, and a
crystal type or a ceramic type. Etc., which were limited to those utilizing the piezoelectric effect.
[0003]
The above-mentioned conventional microphones have advantages and disadvantages for each
operation principle, but the common drawback is that they can only extract analog electrical
signals, and their size is representative. It is very weak, about several millivolts. Therefore, it is
difficult to obtain a good S / N (signal-to-noise) ratio, and in order to obtain high conversion
performance for the entire microphone circuit, it is required that the subsequent amplifiers have
extremely low noise, up to the amplifiers. I had to pay great attention to the wiring. In addition, it
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is not possible to escape from the non-linear distortion associated with the non-uniformity of the
electric field or magnetic field, and even if the characteristics are considerably excellent, it is
impossible to avoid generation of distortion of several% order. This is three or four orders of
magnitude worse than the amplification distortion in the subsequent amplifier. Even a very
simple amplifier with distortion on the order of a few percent can be easily obtained, and in highgrade amplifiers, it is no longer on the order of%, it is necessary to measure distortion on the
order of ppm, so even low noise and distortion Given one thing, microphone distortion at the
input is the problem that must be greatly reduced. Furthermore, due to the influence of stray
capacitance and inductance, the frequency characteristics do not expand so much, and some
high-grade electret capacitor types have frequency characteristics that clear 20KHZ, which is
considered the upper limit of the audible band, with a margin. Most were forced to accept the
narrow frequency band. Therefore, as a matter of course, even if it is required to detect only the
audible band, such as the ultrasonic band can be detected beyond the conventional concept of
the microphone, there is hardly any one that can respond to this. . Furthermore, as a more
fundamental problem, all the microphones provided so far have required a mechanical vibrating
plate that vibrates by sound waves. Certainly, if only the vibration system of the diaphragm is
considered, it is necessary to obtain a vibration system having considerably good linearity with
respect to the input sound wave by optimizing the material and mass used for the diaphragm, the
molding accuracy and the elastic supporting method. You can. However, the distortion does not
necessarily become zero, and the mechanical resonance frequency of the vibration system also
limits the frequency characteristics, and the dynamic range also has limitations. It can not but be
complicated mechanically. The present invention has been made in view of such circumstances,
and completely eliminates or greatly alleviates the above-mentioned drawbacks of the existing
microphones by totally excluding the presence of the diaphragm in accordance with a completely
new operating principle. Furthermore, it is intended to provide a microphone that is truly suited
to the recent high-precision digital recording technology, optical transmission system, and optical
circuit technology.
[0004]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention first
provides a sound wave input portion in which air is present, which is a space open to an
incoming sound wave. The sound wave input unit is provided with means for irradiating a laser
beam and means for detecting a change in the laser light due to a change in density of air in the
sound wave input unit caused by the sound wave input to the sound wave input unit. . With
respect to the basic configuration of the present invention, as a lower aspect, the sound wave
input unit forms a part of the laser interferometer, and the input sound wave is detected by
detecting a change in laser optical path length accompanying a density change of air. A laser
light transmitting member having a refractive index different from that of air is provided in the
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2
sound wave input unit, and an angular change caused to laser light emitted from the laser light
transmitting member due to a change in refractive index of the air accompanying a density
change of air. We also propose a microphone that captures sound waves by detecting
[0005]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown
the general construction of a first embodiment of a microphone constructed in accordance with
the present invention. First, there is a sound wave input unit 1 to which a sound wave S to be
detected is input. The sound wave input unit 1 in this embodiment has a pair of semitransparent
mirrors 3 and 4 parallel to each other facing in a direction orthogonal to the traveling direction
of the sound wave, in other words, between the pair of semitransparent mirrors 3 and 4 The
space portion is the sound wave input unit 1 to which the sound wave S to be detected is input.
The sound wave input unit 1 forms an open space for the sound wave being input (that is, in a
space portion where the sound wave is directly input without passing through any vibrating
member, shielding member, etc. There is a need, and therefore, in a practical environment, of
course there is air here.
[0006]
The laser beam B emitted from the laser light source 2 is irradiated from one side of the pair of
semitransparent mirrors 3 and 4, for example, the semitransparent mirror 3 from the outside of
the semitransparent mirror 3, and this laser light B crosses the sound wave input unit 1 Between
the semitransparent mirrors 3 and 4 so as to reciprocate appropriately by reflection repeatedly.
As is apparent, such an apparatus mechanism constitutes a known Fabry-Perot laser
interferometer, so that the laser light B reciprocatingly reflecting between the pair of
semitransparent mirrors 3 and 4 interfere with each other, so that the other semitransparent
mirror If the interference light emitted from 4 is captured by the light receiving device 5, it
becomes a highly accurate detection system capable of detecting the change in the optical
distance between the pair of semitransparent mirrors 3 and 4 in the nanometer order.
[0007]
However, in the present invention, although the principle structure utilizes such an existing
Fabry-Perot interferometer, it is not used to detect a change in physical position between the pair
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of semitransparent mirrors 3 and 4, but They are both geometrically fixed and fixed, and use the
density change that the sound wave S exerts on the air between them. That is, since the sound
wave S is primarily the change in density of air, if such a change in density of air occurs in the
optical path of the laser light B, it is equivalent to the change in optical path length equivalent to
the laser light B Become. The density change of the air by the sound wave S itself is on the order
of microbars at most, but the input unit 1 to which the sound wave S is input is between the pair
of semitransparent mirrors 3 and 4 which form a part of the Fabry-Perot interferometer. In the
case of the space portion 1 of the above, even if the geometrical distance between the pair of
semitransparent mirrors 3 and 4 is made smaller than the wavelength at the upper limit
frequency of the sound wave to be detected, sufficient for the laser light B Optical path length
change can be generated.
[0008]
Therefore, if the light receiving device 5 can detect the degree of interference according to the
same principle as the light receiving mechanism in the existing Fabry-Perot interferometer, the
detection information is used as the detection information of a sound wave, an analog electric
signal, Because it is easy to convert it into an electrical signal as a digital binary code, a
microphone of extremely high precision (low distortion) and a wide band can be configured. Even
in the dynamic range, according to the configuration of the present invention, in principle there
is no limit to this, so it can be taken considerably wide in practice, and the design freedom is
enhanced. Of course, it is also possible to send an optical signal as it is to a subsequent optical
circuit by a laser amplifier (not shown) or the like without converting it into an electrical signal.
[0009]
In any of the embodiments described below, including this embodiment, the same reference
numerals as those in the other embodiments denote the same or corresponding reference
numerals in any of the embodiments. The matters described for each component are equally
applicable to the corresponding components in the other embodiments unless otherwise
specified.
[0010]
A second embodiment of the present invention is shown in FIG. 2 which utilizes a two-pass laser
interferometer.
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The laser beam B emitted from the laser light source 2 is split into two optical paths by the beam
splitter 6 and can be provided as required. After passing through appropriate reflecting mirrors
71 and 72, the same optical function is obtained. Are respectively arranged between the pair of
reflecting mirrors 31, 41 and 32, 42 and reciprocated between them a suitable number of times,
and then combined again into one optical path through the multiplexer 8 and received. The
device 5 is reached. Here, if the optical path lengths of the split laser beams B1 and B2 are
designed to be equal to each other, the laser beams B1 and B2 interfere with each other at the
time of multiplexing, and thus such a device configuration A known two-path laser interferometer
is constructed.
[0011]
However, in the present invention, while using the principle of the two-path laser interferometer
capable of precisely measuring the difference between two optical path lengths in this way, one
set of each pair of reflecting mirrors 31, 41: 32, 42 is used. Only the interval between 31 and 41
is opened to the input sound wave S, and the sound wave input unit 1 in which air exists is used,
and the sound wave S is not input to the other. For this purpose, as schematically shown in the
drawing, a sound insulation plate 9 for shielding the input sound wave S is provided in front of
the other pair of reflecting mirrors 32 and 42.
[0012]
Because of this arrangement, the input sound wave S causes a change in air density according to
the sound pressure only between one pair of reflecting mirrors 31 and 41. An optical path
difference also occurs between the light beams B1 and B2 in accordance with the current sound
pressure of the sound wave S. Therefore, if the light receiving device 5 detects this using the light
interference principle, the input sound wave S can be detected with extremely high accuracy.
Also in the case of this embodiment, even if the distance between each pair of reflecting mirrors
31, 41: 32, 42 is made considerably smaller than the wavelength of the input sound wave, as
shown in FIG. If the laser beams B1 and B2 are reflected a plurality of times as appropriate, it is
possible to obtain a sufficiently large equivalent optical path difference between them.
[0013]
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5
A third embodiment of the present invention is shown in FIG. 3. This embodiment does not use
the laser light interference principle as in the previous embodiments, but uses the sound
pressure of the sound wave S. A change in the refractive index of air is detected. That is, the laser
light B emitted from the laser light source 2 enters the prism 12 selected in this embodiment as a
laser light transmitting member, and then exits into the air again. The refractive angle at this time
is determined by the refractive index ratio of the material (for example, glass) constituting the
prism 12 to the air, while the refractive index of air changes depending on the density of the air
at that time. Therefore, assuming that the portion of the laser beam B coming out of the prism 12
into the air again is the sound wave S input unit 1, the current refraction angle of the laser beam
B when going out of the prism 12 into the air is Since it changes according to the sound pressure
of the sound wave S at that time, if this is captured by the light receiving device 5, the light
detection signal that detected the sound wave S by the change of the incident position to the light
receiving device 5 at that time Alternatively, a converted electrical signal can be obtained. As a
simple and representative configuration example, for the light receiving device 5, for example, a
light detecting element such as a photodiode can be used which is arranged in an array along the
direction of displacement of the incident position of the laser beam B.
[0014]
Of course, although the change in the one refraction angle of the laser beam B is small as
described above, the laser beam B passes through the prism 12 repeatedly using an appropriate
reflecting mirror means 10,... With such a configuration, integrated refraction angle change can
be obtained, which is sufficient for detection. The initial laser beam B from the laser light source
2 is irradiated from a slightly oblique upper side, for example, on the near side in the direction
perpendicular to the drawing sheet, and is incident on the prism 12 so as not to be caught on the
first reflecting mirror 10 After that, the laser beam B thus incident reciprocates between the
plurality of reflecting mirrors 10 a predetermined number of times, so that the portion of the
first reflecting mirror 10 is not touched. If the light escapes in the back side direction
perpendicular to the paper surface and reaches the light receiving device 5, the device
configuration is simplified, and in particular, the semi-transmissive mirror configuration and the
like become unnecessary.
[0015]
However, in each of the above-mentioned embodiments, the inlet and the outlet of the laser beam
B are spatially separated with respect to the sound wave input unit 1. However, if the input and
output of the laser light B are temporally separated, the inlet and the outlet can be spatially the
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same. FIG. 4 shows such an apparatus configuration as a modification of the embodiment using
the laser light interferometer principle. That is, at first, the laser light B emitted from the laser
light source 2 first passes through the optical switch 13 for a first time width which may be
suitably short, as indicated by an arrow a of a virtual line. The laser beam B emitted from the
light switch 13 passes through the sound wave input unit 1 and enters the reflecting mirror 4
and is totally reflected. In this embodiment, the sound wave input unit 1 transmits the sound
wave S in the traveling direction. The sound-insulation board 9 directly opposite to the soundinsulation board 9 is inserted. Therefore, the substantial sound wave input unit 1 is a space
above the sound-insulation board 9 and the area below the sound-insulation board 9 is not
affected by the sound wave S. Although this point is only schematically shown in FIG. 4, in any
case, the laser beam B which has passed through the sound wave input unit 1 which is the space
part above the sound insulation plate 9 is also the sound wave below the sound insulation plate 9
The laser beam B which has passed through the space portion which is not affected by the light
is also reflected by the reflecting mirror 4 and returns to the optical switch 13.
[0016]
However, the optical switch 13 closes the light path for the next predetermined time after the
above first time width passes, and functions as a kind of total reflection mirror. Therefore, the
laser beam B reciprocates between the reflecting mirror 4 and the optical switch 13 for the
predetermined time. This is because, as described in the previous embodiments, the laser in the
optical path passing through the sound wave input unit 1 with respect to the magnitude of the
density change of air according to the influence of the sound wave S in the sound wave input unit
1 This is to amplify the change in the optical path length of the light B. If the attenuation of the
laser beam B during this time is a problem, an appropriate optical amplifier 14 may be inserted
as shown in the figure.
[0017]
After the required time has elapsed, subsequently, the optical switch 13 switches the optical path
as shown by the arrow b of the virtual line for the second time width which is also appropriately
short, and the reflected laser light B from the reflecting mirror 4 Is input to the light receiving
device 5. If such an operation is repeated at a speed sufficiently higher than the speed of the
sound wave S, the sound pressure of the input sound wave S at that time is substantially almost
based on the phase difference information of the upper and lower laser light components
sandwiching the sound insulation plate It can be detected in real time.
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[0018]
The optical switch 13 for switching the optical path can be assembled very easily by a person
skilled in the art according to the existing technology, for example, by combining the deflection
element and the electro-optical effect. Of course, it is obvious that the method of temporal laser
light input / output separation according to the embodiment shown in FIG. 4 can also be applied
to the embodiment using refractive index change shown in FIG. It is. The material of the prism or
the laser light transmitting member shown in FIG. 3 is not limited to glass, but may be a material
having a refractive index different from that of air (however, it is desirable that the laser light is
not easily attenuated). ), The one with a large degree of difference is advantageous.
[0019]
According to the present invention, the microphone provided by the present invention does not
have any part such as the diaphragm for converting the vibration of the sound wave to the
mechanical vibration, so the structure itself is extremely convenient and the maintainability is
also improved. Of course, distortion in the conversion system that has been a problem in the
prior art can be dramatically reduced (in principle, zero). Furthermore, since there is no influence
of surrounding electric and magnetic fields and no influence of stray capacitance and inductance,
it is possible to provide a microphone having extremely wide frequency characteristics, a
sufficiently wide dynamic range, and a high degree of freedom in design. . In addition, since it is
possible to transmit as it is or to directly encode sound pressure information, it is truly suitable
for the future digital transmission technology and digital recording technology.
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