JP2003348695

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DESCRIPTION JP2003348695
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
medium microphone, and more particularly to a medium microphone that can accurately detect
vibration and sound waves of a structure, underwater, and a wide band propagating in the
ground.
[0002]
2. Description of the Related Art Microphones are classified into electrodynamic type,
electrostatic type, piezoelectric type, etc. depending on the conversion method, but
electrodynamic microphones (dynamic microphones) collect sound propagating in the air
Because of their superiority, piezoelectric microphones are often used mainly for low frequency
noise level measurement. In a general microphone, the sound from the sound source is applied to
the microphone diaphragm as sound pressure through air or directly, and the vibration of the
diaphragm is transmitted to the vibrating electric element, and the AC voltage proportional to the
vibration is between the element electrodes Sound pressure is calculated by digitizing the voltage
in a circuit. For example, since the frequency characteristic of the piezoelectric microphone can
be flattened in a region lower than the resonance frequency of the piezoelectric element to be
used, the measurement lower limit frequency can be set low, and this is known as a measuring
means suitable for ultra low frequency sound measurement. For example, by measurement,
underwater type piezoelectric microphones are used for observation of submarine eruptions and
eruptions of Crater Lake, and dustproof type ultra low frequency piezoelectric microphones are
used for observation of air oscillations associated with land volcanoes and pyroclastic flows .
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Such a piezoelectric microphone is suitable for directly capturing an acoustic wave propagating
through a medium such as water or a structure material without intervening air unlike an
ordinary dynamic microphone. In this specification, a microphone that allows such sound waves
to directly travel through the medium is referred to as a "medium microphone", and the present
invention performs technical development on performance improvement as the medium
microphone.
[0003]
SUMMARY OF THE INVENTION By the way, the conventional medium microphone for the abovementioned application aims to operate effectively in the very low frequency band (about 1 to 10
kHz). For this reason, in addition to capturing the transmission of sound waves in a medium such
as underwater, when capturing low-frequency vibration etc. in which the structure etc. is
transmitted as a medium, directly measure the type of microphone suitable for the situation to
the structure etc. There is also. In this case, the impedance in the very low frequency band may
be reduced due to the mounting structure of the microphone, and accurate measurement may
not be possible.
[0004]
Therefore, the object of the present invention is to solve the problems of the above-mentioned
prior art and, when a structure or the like is used as a sound wave propagation medium, leak of
sound wave or vibration between the medium and the vibrating portion of the microphone, It is
an object of the present invention to provide a medium microphone that can be reliably
prevented.
[0005]
[Means for Solving the Problems] In order to achieve the above object, according to the present
invention, a diaphragm of a microphone element housed in a casing is formed so as to be
exposed to the outside, and a diaphragm opening of the diaphragm A rubber pressure-sensitive
layer is formed in the recess in between.
[0006]
At this time, the rubber pressure-sensitive layer is preferably formed by filling the recess with
silicone rubber.
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[0007]
Further, it is preferable that the silicone rubber of the rubber pressure sensitive layer is formed
by being raised from the surface of the casing by a predetermined thickness.
When the microphone body is attached to the medium to be measured, it is preferable that the
raised portion of the rubber pressure sensitive layer be in close contact with the medium and
fixed.
[0008]
It is preferable to use a piezoelectric microphone as the microphone element having the above
features.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a medium microphone
according to the present invention will be described below with reference to the attached
drawings.
FIG. 1 is a perspective view showing the external configuration of the medium microphone of the
present invention.
FIG. 2 is a cross-sectional view showing an internal configuration of the medium microphone 10
shown in FIG.
As shown in FIG. 2, the medium microphone 10 includes a flat disk-like microphone element 11,
a resin casing 12 accommodating the microphone element 11, and a rubber pressure-sensitive
layer 20 covering the opening 13 of the resin casing 12. ing. Among these, as the microphone
element 11, a known piezoelectric microphone is used in the present embodiment. As described
above, the piezoelectric microphone is known to operate effectively in the very low frequency
band (about 1 to 10 kHz), and is suitable as a medium microphone. In the structure of the
medium microphone, as shown in FIG. 1, a stainless steel diaphragm (not shown) is attached to
the upper portion of the water resistant stainless steel housing 15, and the diaphragm (not
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shown) is provided inside. A piezoelectric element for converting the external force to be
transmitted and an amplifier circuit for amplifying and outputting the electromotive force are
accommodated. The electromotive force is connected via a signal cable 17 to a known sound
pressure measuring device (not shown). The specification of the microphone element 11 is
characterized in that the measurement range can be expected to be about 1 μV / 1 μPa, and the
frequency characteristic in this case exhibits a flat characteristic at 1 Hz to 10 KHz.
[0010]
Further, the microphone element 11 is accommodated in a vinyl chloride resin casing 12
composed of flat disk-shaped upper and lower two pieces 12A and 12B. As shown in FIG. 1, a
circular opening 13 is formed on the upper surface of the upper piece 12A of the casing 12 so
that the diaphragm on the upper surface of the microphone element 11 is exposed to the outside.
O-rings 16 are mounted at upper and lower positions around the periphery of the microphone
element in order to ensure water tightness in the casing. Further, a rubber pressure-sensitive
layer 20 is formed to cover the opening 13 of the upper piece 12A and the diaphragm (not
shown) on the upper surface of the microphone element 11. The medium microphone 10 is
attached to the measurement target structure 1 as a medium with a screw 15 (FIG. 3). For this
purpose, the casing 12 is provided with the three screw through holes 14 shown in FIGS. 1 and
2.
[0011]
In the present embodiment, the rubber pressure sensitive layer 20 completely and tightly covers
the upper surface of the housing 15 of the microphone element 11, the O ring 16, and the
opening 13 of the upper piece 12A as shown in FIG. It is filled. In the present embodiment, as
shown in FIG. 2, the upper surface 20 a of the rubber pressure sensitive layer 20 is shaped as a
smooth surface which protrudes about 1 to 2 mm from the upper surface of the casing 12. In
addition, it is preferable to appropriately set this raised thickness in consideration of the
hardness of the silicone rubber to be used, the roughness of the target surface, and the like.
[0012]
The silicone rubber used in the present embodiment exhibits sufficient compression set
characteristics over a wide temperature range and has good recovery characteristics, so it is
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excellent in sound wave and vibration propagation characteristics, and a high seal in this portion.
You can get the effect. In addition, since there is stability against oxygen, ozone, and ultraviolet
light, durability of the microphone attachment portion can be secured even when the medium
microphone 10 is attached to an outdoor structure.
[0013]
FIG. 3 is a cross-sectional view showing an example in which the medium microphone 10 shown
in FIGS. 1 and 2 is fixed to the surface of the structure 1. As shown in the figure, when the screw
15 is screwed sufficiently when attached to the surface of the structure 1 with the screw 15, the
silicone rubber that has been raised and shaped in advance adheres to the structure 1 in a
compressed state. . Thus, sound waves propagating through a concrete structure or the like as a
medium can be reliably collected by the medium microphone 10.
[0014]
Although it is preferable to use a piezoelectric microphone as the microphone element in order to
exhibit the features of the medium microphone described above, it is also possible to use an
electrodynamic microphone when used as a medium microphone. It's too late.
[0015]
EXAMPLES In the following experiments, the sound collection characteristics in the low
frequency band of the medium microphone 10 in which the conventional medium microphone
10 and the rubber pressure sensitive layer 20 of the present invention are interposed, and the
low frequency sound transmitted through the fixed structure Check the distribution of sound
pressure characteristics obtained by collecting sound.
[Experimental Environment] FIG. 4 is an explanatory view schematically showing an experimental
environment for measuring the sound collection characteristics of the medium microphone of the
present invention, taking train noise measurement as an example. As shown in the figure, the
medium microphone 10 is set on the concrete floor surface (structure) 1 in the interior of the
building 2 where the train (Shinkansen) 3 passes about 100 m away, and during nighttime
silence and train passing The low frequency sound at time is sampled, the sound pressure
characteristic in the target band is grasped from the obtained data, and the sound collection
characteristic of the microphone is confirmed. The microphone installation method was changed
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as a measurement case at this time, data collection was performed using the recording apparatus
4 classified by frequency in each measurement case, sound pressure characteristics were
determined, and differences in sound collection characteristics were confirmed. Case:
Conventional type-Fixed to the floor with medium microphone facing upward (see Fig. 1). Case:
Adhesion type-fixed to the floor by medium microphone floor adhesion (upside down direction in
Fig. 3).
[0016]
[Results of Measurement] FIGS. 5 and 6 show the temporal change of the sound pressure level of
the measurement results in the case described above. In both figures, the vertical axis is the
sound pressure level (μPa), and the horizontal axis is the measurement elapsed time (9 minutes
and 20 seconds in the illustrated range). In particular, the temporal change of sound pressure
level in the low frequency band (1, 10, 100, 1 kHz, and all bands (ALL)) is plotted. As shown in
the figure, the bullet train passed several times within the measurement time. As a result, in
addition to the temporal change of the sound pressure level at the time of normal silence, a sharp
sound pressure peak indicating the passage of the Shinkansen was recorded, and the sound
collection characteristics in the range where the sound pressure level was largely different could
be confirmed. It was confirmed that the microphone sensitivity in the case of close contact with
the floor (FIG. 6) was sensitized approximately twice in both the silent and peak periods with
respect to the microphone upward in the case of close contact with the floor (FIG. 6).
[0017]
(Example 2) FIG. 7 is a sound pressure characteristic distribution chart showing the result of an
experiment of collecting low frequency sound generated during the working hours and midnight
during a certain office. When a conventional piezoelectric microphone is directly attached to a
structure 24 hours after the start of measurement (conventional type), the average sound
pressure obtained in the low frequency band (1, 10, 100, 1000 Hz) extracted is 5 μPa or less
Then, according to the measurement by the medium microphone of the present invention in
which the rubber pressure-sensitive layer 20 is interposed, the sound pressure level is sensitized
to an average of about 1.5 to 2 times in the frequency band of 10 Hz and 100 Hz. It was
sounded.
[0018]
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[Application Example] FIGS. 8 and 9 are schematic views showing an application example in
which the medium microphone 10 of the present invention is used to measure the structure
sound propagating in the structure. FIG. 8 shows a measurement example in which the medium
microphone 10 is embedded in part of the concrete bed 2 and the revetment 3 of the river. By
collecting the sound of the riverbed, it is possible to monitor the movement of sediment on the
riverbed, and observe or estimate the particle size distribution and the amount of sediment
flowing through the riverbed from the difference in the frequency of the obtained data. be able
to.
[0019]
In FIG. 9, a plurality of medium microphones 10 are embedded in the bridge pier 4 in the height
direction of the bridge pier, and the lower foundation 6 and vibration generated in the
superstructure 5 through which vehicles such as railways and automobiles pass. This is an
example of measuring the sound pressure distribution characteristic of the frequency that
propagates through the bridge pier to the surrounding ground 7. From the data obtained by this
measurement, it is possible to detect an extremely low frequency vibration region of about 1 Hz
due to the shaking of the bridge under traffic load action, wind load action and the like.
[0020]
As another application example, it is possible to measure in-hole underwater sound by immersing
and installing the medium microphone in a predetermined water level of the groundwater level
measurement well. In this case, although the rubber pressure-sensitive layer is not used in
pressure contact with the medium, sound waves propagating in water through the rubber
pressure-sensitive layer can be reliably captured by the microphone. In order to directly detect
the sound pressure in water from the data obtained by this measurement, it is possible to detect
a broad band sound wave at audio frequency from the pressure vibration in the very low
frequency region due to the water pressure fluctuation. As another application example,
monitoring of underwater sound in a natural environment in a clean flow state in a river or the
like can be used in various ways for investigation of sound, vibration, etc. in a zone where aquatic
organisms such as fish react.
[0021]
As described above, since the microphone can be closely fixed to the medium via the rubber
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pressure sensitive layer, the vibrations and sound waves of the ultra low frequency band of the
medium microphone can be surely and precisely It has the effect of being able to measure.
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