JPH05227596

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DESCRIPTION JPH05227596
[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. . The present invention has
been made in view of such circumstances, and completely solves or alleviates the abovementioned drawbacks of the existing microphones according to a new operation principle, and
further, the high-precision digital recording technology of recent years and the like. It is an object
of the present invention to provide a microphone that is truly suitable for the optical
transmission system and the optical circuit technology.
[0004]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
vibrates at a frequency corresponding to the frequency of an incoming sound wave and at a size
corresponding to the sound pressure of the sound wave, and emits radiation. Laser light
reflecting means for reflecting the laser light, and a light receiving device for capturing a change
in position or shape of the reflected laser light from the laser light reflecting means. The laser
beam reflection means may be an independent means connected in mechanical interlocking with
the diaphragm means directly receiving the sound wave, or the vibration means may double as
this. Furthermore, the laser light reflecting means is particularly in the form of a diaphragm, in
order to capture a change in shape of the reflected laser light rather than a change in the
position of the laser light at that moment. On the other hand, the light receiving device may be
any device as long as it can detect a change in the position or shape of the laser beam reflected
from time to time.
[0005]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a schematic
diagram of a first embodiment of a microphone constructed in accordance with the present
invention is shown. First, there is a vibrating means 1 capable of receiving the sound wave S to
be detected. The vibrating means 1 may generally be in the form of a plate and is therefore
referred to in the following as the diaphragm 1, which in this respect is similar to the
microphones previously proposed. In the absence of the input sound wave S, it is placed at a
predetermined stationary position, and is held by an elastic means 2 that is suitable so as to
vibrate at a movement distance according to the sound pressure (size) according to the frequency
of the input sound wave S It is done. The type and material of the elastic means 2 are arbitrary,
and springs, rubber, and other materials and parts that are desirable for existing microphones
may be used. By the way, if only the vibration system of the diaphragm 1 is considered without
considering distortion and non-linearity due to the conversion system to an electric signal, and
stray capacitance and inductance, even the existing mechanism has extremely low distortion,
wide band and wide dynamic range The vibration system of is obtained. In other words, the
present invention is to make the most of this excellent property of the vibration system without
losing it.
[0006]
In this embodiment, the diaphragm 1 is provided with laser light reflecting means 4 vibrating at
the same frequency and proportional magnitude as the diaphragm 1 through the appropriate
mechanical connection means 3. Generally, the laser beam reflection means 4 may also be in the
form of a plate, and hereinafter, it will be referred to as the laser beam reflection plate 4 or
simply as the reflection plate 4. It is supported by the shaft 5 and vibrates in the rotational
direction around the support shaft 5 according to the frequency and the magnitude of the input
sound wave S.
[0007]
On the other hand, the back surface of the laser light reflection plate 4 is irradiated with the laser
light Bi emitted from the laser light source 6, and the reflected laser light Bo reflected by the
laser light reflection plate 4 is input to the light receiving device 7. Do. The light receiving device
7 may be of any type obtained by the existing technology as long as it can detect the change of
the position of the reflected laser beam Bo inputted from time to time with an appropriate
resolution. Depending on the laser beam incident position, the corresponding binary code may be
output as an electrical digital signal, or an analog electrical signal or an optical signal may be
output, and further, it may be directly on the recording medium such as a photosensitive film.
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The position of the laser beam may be recorded. In addition, as for the laser light, for emitting
from the laser light source 6 so as to irradiate the laser light reflection plate 4, the code Bi is
used, and for the light reflected by the laser light reflection plate 4, the code Bo is used. If it is not
necessary to distinguish between the two, the subscripts i and o are omitted and simply referred
to as laser light B.
[0008]
According to such a microphone structure according to the present invention, when the
diaphragm 1 is vibrated by the incoming sound wave S and its movement is converted into
proportional rotational vibration about the support shaft 5 of the laser light reflection plate 4
The reflection direction of the laser light Bi incident on the back surface of the laser light
reflection plate 4 changes correspondingly. Therefore, by capturing the change in the incident
position of the reflected laser light Bo according to the frequency and the sound pressure of the
input sound wave S by the light receiving device 7, it is affected by the electrical stray
capacitance and inductance in the conversion system as in the prior art. It is possible to obtain a
low distortion, high dynamic range microphone without using a wide band.
[0009]
As described above, although the light receiving device 7 is not essentially limited according to
the present invention, some preferable light receiving device configuration examples will be
listed here for reference. First, the light receiving device 7 shown in FIG. 2 will be described. In
this case, the laser light Bo is irradiated in the direction of travel (progressive direction like an
elongated rectangular shape schematically shown with a thin dot pattern) Optical system (shown
in FIG. 2) having a longitudinal dimension in a direction perpendicular to both of the abovementioned and the above-mentioned direction of change of position (the direction indicated by
the double arrow F in FIG. 2). (May be molded at the stage of incident light Bi)). On the other
hand, in the light receiving device 7, a one-dimensional photodiode array having at most m light
detection elements (for example, photodiodes) along the position change direction F of the
reflected laser light Bo is arranged in the laterally long direction of the reflected laser light Bo.
There are n rows arranged in parallel. In the illustrated case, if n is 4 and each photodiode array
is given a reference 81, 82, 84, 88 for each column, first, any photodiode array 81, 82, 84, 88 is
also It is configured to emit an electrical signal that can be regarded as an electrical logic "1" at
its output terminal if light is incident on any one of at least the maximum m light detection
elements in the row. ing.
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[0010]
However, in this embodiment, only the light detection elements indicated by the squares with
dark dot patterns in the respective photodiode arrays 81, 82, 84, 88 are shown for the light
incidence. The light detection element indicated by the white squares is configured not to show
the sensitivity by masking the light incident surface or cutting the converted electric output line.
Or the light detection element is provided only at the position of the grid with a dark dot pattern,
and when viewed in relation to each row, it is irradiated with the same horizontal laser light Bo
from time to time. When it does, it is different whether the light detection element which shows
sensitivity is in that position. That is, in the light receiving device 7 shown in FIG. 2, in the matrix
arrangement of the m × n light detection elements at the maximum, each output of the four
parallel photodiode arrays is formed according to the construction principle according to the socalled programmable logic array. The combination is designed to directly output a binary code as
a digital electrical signal according to the current position of the laser light. Therefore, in the case
of the illustrated arrangement, the output of the first photodiode array 81 located at the right
end in the figure is the LSB bit output D1 of weight 21 and the output of the second photodiode
array 82 is the second bit of weight 22 Output D2, the output of the third photodiode array 84
becomes the third bit output D4 with a weight of 24, and the output of the photodiode array 88
located at the left end is the MSB of the 28 most significant bits D8 as the so-called MSB. It
becomes. For example, when the laser beam Bo is at the position shown in FIG. 2, a photodiode
array is provided that has a photodetector that receives the laser beam Bo or that exhibits
sensitivity at the irradiation position. Is the leftmost array 88, the output logic according to the 12-4-8 code is "1000" from the MSB side.
[0011]
As is apparent, in the case of the light receiving device configuration example shown in FIG. 2, it
is recognized in the combination relation from the combination of the light detection elements
located at the bottom to the combination of the light detection elements located at the top. As
shown, an example is shown from the smallest binary value "0000" sequentially, in increments of
one by one, such as "0001", "0010", ... in normal binary notation, and an example up to the
maximum logical value "1111" is shown. However, the way of setting the logical value is
arbitrary, and the number of bits (number of arrays) can be arbitrarily changed depending on the
required resolution or dynamic range.
[0012]
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Similarly in FIG. 3, a digital binary code is output according to the change in position of the
reflected laser beam Bo and hence the instantaneous magnitude of the input sound wave, but the
configuration is different from that shown in FIG. A light receiving device 7 is shown.
That is, although the light receiving device 7 also uses the photodiode array 8 as described
above, only one light receiving element may be provided, and m light detecting elements
provided in the moving direction F of the reflected laser light Bo All the squares) have
photosensitivity. In this case, the reflected laser light Bo does not have to be particularly long in
length, and may have a normal thin beam shape, and depending on the position of the laser light
reflecting plate 4 at that time, any one light detecting element Irradiate. The photodiode array 8
is configured to input the output of each light detection element to the combinational logic
circuit 9, and the combinational logic circuit 9 separates each light detection element according
to a predetermined relationship. Generate a logic value signal of magnitude. The resolution of
this output is also arbitrary, and in the case shown, as in the case described above, it is planned
that a logical value according to the 1-2-4-8 code (from the LSB side) of the output D1, D2, D4,
D8 is generated. But it is not limited to this.
[0013]
The light receiving device 7 shown in FIG. 4 is interposed in the middle of the optical path of the
reflected laser beam Bo, and the slits S10... Are made continuous at a predetermined pitch along
the position change direction F of the reflected laser beam Bo. It has a slit-like slit means 10.
Therefore, since the reflected laser light Bo is chopperd by the slit group according to the
magnitude of the sound wave at that time, the output light BS of the wedge-shaped slit means 10
is pulse width modulated according to the size of the sound wave It becomes an optical signal BS.
Therefore, this can be processed as it is by the optical circuit, but in order to convert it into an
electrical signal, the remaining configuration shown in FIG. 4 may be incorporated. That is, the
output light BS of the wedge-shaped slit means 10 is input to the light detection element 12
which is generally a photodiode by an appropriate lens system 11, and the converted electrical
signal is formed by the normal counter technology. If it is input to the pulse processing circuit 13
which can do, a digital code output can be obtained at the output.
[0014]
Of course, the digital code output according to the above-described three light receiving device
configurations can be converted into an analog electrical signal by digital-to-analog conversion,
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but rather, according to the light receiving device having the above-described configuration,
While the microphone can not directly generate a digital output according to the sound wave
input, it is characterized in that it can be generated. If it is preferable to obtain an analog
electrical output, there is also a light receiving device configuration example as follows.
[0015]
The light receiving device 7 shown in FIG. 5 has a variable density filter 14 in which the density
changes along the direction F of the positional change of the reflected laser light Bo. In the case
of the drawing, the variable density filter 14 having a triangular shape when viewed from the
side is shown as a result of having a structure in which the cross-sectional dimension in the
equivalent direction of the reflected laser light Bo changes along the moving direction F of the
reflected laser light. However, this may be one in which variable density characteristics are
obtained by changing the density distribution of the light absorbing medium inside the filter
along the direction F. In any case, according to the light receiving device having such a
configuration, it is possible to set the corresponding magnitude of the input sound wave to the
present light amount or attenuation amount of the laser beam Bo passing through the variable
density filter. By such amount of light, sound waves can be detected. When it is necessary to
convert this into an electrical signal, as shown in FIG. 5, the output light Bo 'of the variable
density filter 14 is converted to a light detection element 12 such as a photodiode by an
appropriate lens system 11. Input and then take out the analog electrical output.
[0016]
Similarly, there is also a method as shown in FIG. 6 for extracting the analog electrical output.
That is, the laser beam B is shown in the form of a thin rectangular pattern schematically shown
in FIG. 6 like an elongated rectangular shape, both in the irradiation direction (traveling
direction) and in the position change direction F described above. While forming through a
suitable optical system (not shown) so as to result in a transverse beam having longitudinal
dimensions in both orthogonal directions (in this respect as well as the embodiment shown in
FIG. 2 described above) ), A variable slit 15 in which the width of the aperture 16 for passing the
reflected laser light Bo is changed along the position change direction F of the laser light is
inserted in the middle of the optical path of the reflected laser light Bo having such a laterally
long shape. Do. In FIG. 6, the variable slit 15 is also shown as viewed from the front, which is
easy to understand. In this case, the slit or the opening 16 has a triangular shape in plan view.
Therefore, the output light Bo 'passing therethrough is proportional to the input sound wave in
the light intensity. Therefore, when it is desired to convert this into an electric signal, as in the
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embodiment shown in FIG. 5, if the output light Bo 'is converged to the appropriate light
detection element 12 by the appropriate lens system 11, this light detection element An analog
electrical output corresponding to the twelve outputs can be obtained.
[0017]
FIG. 7 shows yet another modification. First of all, although the diaphragm 1 and the laser beam
reflection plate 4 were separate members so far, they are also used as the laser beam reflection
plate 4 by mirror-finishing the back surface of the diaphragm 1 It is a point that This point is
equally applicable to the other embodiments. On the contrary, when the diaphragm 1 and the
laser beam reflection plate 4 are separate members and are linked to interlock by mechanical
means, the degree of positional change of the reflected laser beam Bo is too small. At times,
mechanical amplification can be achieved by using a lever as the mechanical connection means.
However, for the purposes of the present invention, there are as few mechanical moving parts as
possible. From that point of view, as shown in FIG. 7, the configuration example in which the
diaphragm 1 doubles as the laser beam reflector 4 is extremely advantageous.
[0018]
The second modification shown in FIG. 7 is that a so-called laser range finder 17 is used.
Naturally, in this case both the laser light source and the light receiver 7 are included in the
components of this laser rangefinder. Among laser rangefinders, a representative and highly
accurate one utilizes the interference principle of laser beam. Therefore, in the case of adopting
this, if one of the plurality of reflecting mirrors constituting the laser interferometer is the laser
light reflecting plate 4 as referred to in the present invention, the movement amount
(displacement of the laser light reflecting plate 4) As long as the quantity) is large relative to the
laser wavelength, it is possible to obtain a pulse-width-modulated laser light output according to
the current magnitude of the input sound wave, based on the light / darkness of the light
generated by the interference principle.
[0019]
On the other hand, when the movement distance of the laser beam reflection plate 4 is
insufficient, as shown in FIG. 8, the laser beam reflection plate 4 is used as the first reflection
mirror, and in the relationship facing this. A fixed reflecting mirror 18 may be provided as the
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second reflecting mirror, and the laser beam B may be reflected and reciprocated between the
first reflecting mirror 4 and the second reflecting mirror 18 an appropriate number of times.
Even in the case of constructing a microphone targeting up to the ultrasonic region, the speed of
light is faster than the speed of sound so as not to be a problem, and no problem occurs even if
such a repetitive reflection method is adopted. Of course, this is also applicable to the other
embodiments and can be replaced by the use of the mechanical "lever" mentioned above.
[0020]
On the other hand, in all of the embodiments described so far, the entrance of the irradiation
laser light Bi to the laser light reflection plate 4 and the exit of the emission laser light Bo from
the laser light reflection plate 4 to the light receiving device 7 are spatially If the optical switch
mechanism shown in FIG. 9 is used to separate the input and output laser beams Bi and Bo in
time, the inlet and the outlet can be at the same position. . That is, FIG. 9 allows the laser light
source 6 to irradiate the laser light Bi to the laser light reflecting means 4 in the first time width,
and in the second time width, the laser light reflection plate 4 to the light receiving device 7. An
optical switch 19 is provided to allow irradiation of the reflected laser light Bo. Furthermore, in
this embodiment, as described above, the function of amplifying the mechanical quantity of the
laser light reflecting plate 4 accompanying the input of the sound wave S is also incorporated.
[0021]
In the following description, following the operation, the laser light Bi initially emitted from the
laser light source 6 passes through the optical switch 19 for a first time width which may be
suitably short, as indicated by the arrow a of the phantom line. And the laser beam reflection
plate 4 is irradiated. When the first time width has elapsed, the light switch 19 is closed, and the
reflected laser light indicated by the arrow c reflected from the laser light reflection plate 4 is
reflected again to the laser light reflection plate 4. Therefore, while the light switch 19 is closed,
the laser light reciprocates between the light switch 19 and the laser light reflection plate 4, and
the displacement amount of the laser light reflection plate 4 by the input sound wave S is as
described above. If it is small, it performs the function of amplifying this. At this time, if
attenuation of the reciprocating laser light is a problem, an appropriate optical amplifier 20 may
be inserted in the laser light path as shown in FIG. Next, the optical switch 19 switches the
optical path as shown by the arrow b of the phantom line also for the second time width which is
also appropriately short, and the reflected laser light Bo from the laser light reflection plate 4 to
the light detector 21. Let me input. On the other hand, the original laser light Bi emitted from the
laser light source 6 is also guided to the light detector 21 by the semitransparent mirror 22.
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Therefore, the phase difference between the laser light reflection plate 4 and so on You can know
the position. Therefore, if the above operation is repeated at a speed sufficiently higher than the
frequency of the sound wave S to be detected, the sound wave S can be detected substantially in
real time.
[0022]
Obviously, in the operation of FIG. 9, if it is not necessary to amplify the amount of displacement
of the laser light reflecting plate 4, the above-mentioned first time width and the second time
width may be between them. Closing the optical switch 19 interrupted between the first and
second time widths in order to reciprocate the laser light between the laser light reflection plate
4 and the optical switch 19. There is no need for a third time span. Further, the optical switch 19
for switching the optical path can be assembled very easily by those skilled in the art according
to the existing technology, for example, by combining the deflection element and the electrooptical effect. Of course, the method of temporal laser light input / output separation according
to the embodiment shown in FIG. 9 can be combined with the other embodiments described
above.
[0023]
The embodiment shown in FIG. 10 is replaced with a method of detecting the position of the
laser light reflecting plate 4 according to the sound pressure of the input sound wave S as in the
previous embodiments. An example is shown of capturing the current sound pressure of the
sound wave S by changing the shape of the laser light. That is, the diaphragm 1 receiving the
input sound wave S is made of, for example, an elastic thin film, and the rear surface thereof is
subjected to processing such as metal deposition, plating, etc. to be mirror-polished to serve as
the laser light reflection plate 4. Furthermore, as shown by the cross-sectional shape in the
figure, the diaphragm 1 to the laser beam reflection plate 4 in this embodiment have a
diaphragm shape, and therefore, depending on the magnitude of the input sound wave S, the
curvature is A variable convex mirror (which may be a concave mirror opposite the cross section
shown) is obtained. Therefore, the laser beam Bi irradiated to the laser beam reflecting plate 4
from the laser light source 6 through the semitransparent mirror 23 is converged or diffused by
the reflecting mirror whose shape changes in accordance with the sound pressure of the input
sound wave S at that time. Since the beam diameter changes correspondingly, when it passes
through the semi-transparent mirror 23 again and illuminates the aperture 24 with an
appropriate opening diameter, the amount of light transmitted therethrough changes. Therefore,
the amount of light transmitted through the aperture 24 is detected by the light detector 25,
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while the amount of deformation of the laser light reflection plate 4, that is, the timely input, is
compared with the original light amount by another light detector 26. The magnitude of the
sound wave S can be detected.
[0024]
Of course, also in this embodiment, the configuration disclosed in the other embodiments
described above can be appropriately adopted as a modified structure. For example, the
diaphragm 1 and the laser beam reflection plate 4 may be separate structures mechanically
connected to each other. In this case, the laser beam reflection plate 4 has a diaphragm shape.
However, when mechanical connection means is adopted including the previous embodiment,
linear vibration of the diaphragm 1 is not changed as it is, but conversion to the rotational
vibration system as shown in FIG. It may be a system for transmitting to the laser beam reflection
plate 4 in the form of Furthermore, in all of the previous embodiments, the surface receiving the
input sound wave S and the surface receiving the laser light were on the opposite side, but
depending on the spatial positional relationship of each component It is self-evident that both the
incident surface of the sound wave and the incident surface of the laser light can be on the same
surface side with respect to the plate 1 to the laser light reflecting plate 4.
[0025]
The present invention is a microphone that uses laser light to detect the position or shape of the
laser light reflecting plate, which changes in accordance with the sound pressure of the sound
wave from time to time. The distortion in the conversion system can be greatly reduced (in
principle, to 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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