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DESCRIPTION JP2002152889

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DESCRIPTION JP2002152889
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor and an electronic device using the same, for example, an ultrasonic sensor for
measuring a gas flow rate by transmitting and receiving ultrasonic waves, and an electronic
device using the same.
[0002]
2. Description of the Related Art Generally, in a high frequency ultrasonic sensor, an ultrasonic
sensor that applies the vibration surface of a vibrator to one main surface of an acoustic
matching layer and transmits and receives ultrasonic waves from the other main surface of the
acoustic matching layer is Are known. In the ultrasonic sensor having such a configuration, the
acoustic impedance of the acoustic matching layer should be set to a value intermediate between
the acoustic impedance of the fluid to which the acoustic matching layer is exposed, such as air,
and the acoustic impedance of the transducer. Thus, ultrasonic waves can be efficiently
transmitted and received. That is, by reducing the density of the acoustic matching layer,
ultrasonic waves can be transmitted and received with high sensitivity. However, in the case
where the fluid is a flammable gas, if the density of the acoustic matching layer is lowered, the
gas intrudes from the gap of the acoustic matching layer into the periphery of the piezoelectric
body, and sparks generated from the piezoelectric body ignite the gas There is a fear. Therefore,
when the density of the acoustic matching layer is reduced, it is necessary to cover the acoustic
matching layer with a hermetic coating.
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[0003]
FIG. 6 shows a conventional ultrasonic sensor attached to fluid flow piping. In FIG. 6, the
conventional ultrasonic sensor 4 has a piezoelectric body 74 which is a vibrator, an acoustic
matching layer 71, a case 73, an airtight film 72, and a support member 70. The piezoelectric
body 74 and the case 73 are attached to one main surface of the acoustic matching layer 71. The
airtight film 72 covers the acoustic matching layer 71 without any gap and is fixed near the end
of the case 73. The one main surface side of the support member 70 to which the case 73 is fixed
is attached to the pipe 81.
[0004]
The ultrasonic sensor 4 is inserted into the inside of the pipe 81a, and the flow rate of the fluid
flowing through the pipe 81a is measured by the ultrasonic wave transmitted and received from
the other main surface of the acoustic matching layer 71.
[0005]
In the ultrasonic sensor 4 having such a configuration, by providing the airtight film 72, the
airtightness of the piezoelectric body 74 to the fluid is achieved.
Therefore, the ultrasonic sensor 4 can measure the flow rate of the flammable fluid.
[0006]
In addition, the conventional ultrasonic sensor is disclosed by Unexamined-Japanese-Patent No.
11-23332, for example.
[0007]
However, in the ultrasonic sensor 4, a case 73 is present between the acoustic matching layer 71
and the support member 70.
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Therefore, there is a problem that the height reduction of the case 73 is hindered by the height
of the case 73. In addition, the ultrasonic sensor 4 has a problem that the volume inserted into
the inside of the pipe 81a increases by the height of the height, and the fluid flowing through the
pipe 81a is affected, and accurate measurement of the flow rate can not be performed.
[0008]
Then, an object of this invention is to provide the ultrasonic sensor which can attain reduction in
height.
[0009]
Another object of the present invention is to provide an electronic device capable of accurately
measuring the flow rate without substantially affecting the fluid flowing through the piping.
[0010]
In order to achieve the above object, according to the ultrasonic sensor of the present invention,
a support member having a flat plate portion provided with a hole at a substantially central
portion, and one main surface of the support member An airtight film provided to cover the hole,
a vibrator attached to one principal surface side provided with a support member for the airtight
film at substantially the center of the hole, and the vibrator facing the vibrator, And an acoustic
matching layer attached to the other principal surface side of the hermetic membrane.
[0011]
In the ultrasonic sensor according to the present invention, the acoustic matching layer has a
diameter larger than that of the hole of the support member, and a central axis passes
substantially through the center of the hole of the support member.
[0012]
In the ultrasonic sensor according to the present invention, the acoustic matching layer has a
diameter smaller than that of the hole of the support member, and a central axis passes
substantially through the center of the hole of the support member.
[0013]
In the ultrasonic sensor according to the present invention, the support member is provided with
a notch along the edge of the hole, and the length from the approximate center of the hole to the
tip of the notch is the radius of the acoustic matching layer It is characterized by being larger
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than.
[0014]
Moreover, the ultrasonic sensor of the present invention is characterized in that the hermetic
membrane has conductivity.
[0015]
In the ultrasonic sensor of the present invention, the thickness of the hermetic membrane is 100
μm or less.
[0016]
The ultrasonic sensor according to the present invention is an ultrasonic sensor used to measure
a fluid flowing in a pipe, wherein the support member has fixing means for fixing the pipe to the
pipe.
[0017]
The electronic device according to the present invention is characterized by including the
ultrasonic sensor, a drive circuit for vibrating the vibrator, and a detection circuit for detecting an
output generated from the vibrator.
[0018]
By configuring in this manner, the ultrasonic sensor of the present invention can achieve a
reduction in height.
[0019]
Also, the ultrasonic sensor of the present invention can adjust the band to a desired value by
changing the size of the hole or notch.
[0020]
In addition, the electronic device of the present invention can measure flammable fluid because it
uses an airtight ultrasonic sensor.
[0021]
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In addition, since the electronic device of the present invention uses the low-profile ultrasonic
sensor, it can measure the flow rate accurately while hardly affecting the fluid flowing through
the pipe.
[0022]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an ultrasonic
sensor according to the present invention.
1 (a) is a perspective view thereof, FIG. 1 (b) is a plan view thereof, and FIG. 1 (c) is a 1x-1x
sectional view thereof.
[0023]
In FIG. 1, the ultrasonic sensor 1 has a support member 10 a having a flat plate portion, an
airtight film 20 made of metal, a piezoelectric body 30 which is a vibrator, and an acoustic
matching layer 40.
[0024]
The supporting member 10a is provided with a hole 50a smaller than the diameter of the
acoustic matching layer 40 at a substantially central portion, and an airtight film 20 is provided
to cover the hole 50a.
The airtight film 20 has a thickness of 100 μm or less and is airtight.
The piezoelectric body 30 is attached to one main surface side of the airtight film 20 on which
the support member 10a is provided substantially at the center of the hole 50a.
The acoustic matching layer 40 is attached to the other main surface side of the hermetic
membrane 20 so that the central axis of the acoustic matching layer 40 passes through the
approximate center of the hole 50 a and faces the piezoelectric body 30.
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As a result, the edge of the acoustic matching layer 40 is fixed and constrained on the support
member 10 a via the airtight film 20.
Electrodes (not shown) are formed on both main surfaces of the piezoelectric body 30, the
electrode on one main surface is directly connected to the lead wire 61, and the electrode on the
other main surface is a lead wire through the airtight film 20 having conductivity. Connected to
62.
In the vicinity of the hole 50a, two holes 51 penetrating the support member 10a and the airtight
film 20 are provided symmetrically with the hole 50a as a center.
The support member 10 a is fixed to the electronic device (not shown) by screwing using the
holes 51 which are fixing means.
[0025]
In the ultrasonic sensor 1 having such a configuration, the vibration of the piezoelectric body 30
causes the acoustic matching layer 40 to vibrate with the vicinity of the edge as a node.
[0026]
FIG. 2 shows frequency characteristics of the ultrasonic sensor 1 of the present invention and the
conventional ultrasonic sensor 4.
The characteristic indicated by the broken line in FIG. 2 is the frequency characteristic of the
ultrasonic sensor 4, and the characteristic indicated by the solid line is the frequency
characteristic of the ultrasonic sensor 1.
In addition, the characteristic shown with a dashed-dotted line is mentioned later.
In the ultrasonic sensor 1, the vicinity of the edge of the acoustic matching layer 40 is fixed on
the support member 10 a only via the thin airtight film 20.
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Therefore, the vicinity of the edge of the acoustic matching layer 40 is reliably fixed to the
support member 10a, and its vibration is reliably restrained, Q becomes high, and band
narrowing can be achieved.
Also, as shown in FIG. 2, the sensitivity can be increased only at a specific frequency.
[0027]
Further, in the ultrasonic sensor 1 of the present invention, since the acoustic matching layer 40
is fixed to the support member 10a only via the thin airtight film 20, the height can be reduced.
[0028]
Further, in the ultrasonic sensor 1 of the present invention, the airtightness of the piezoelectric
body 30 is realized by providing the airtight film 20.
Therefore, the ultrasonic sensor 1 can measure the flow rate of the flammable fluid.
[0029]
Further, in the ultrasonic sensor 1 of the present invention, the thickness of the hermetic film 20
is 100 μm or less, which is very thin, so that the vibration between the piezoelectric body 30
and the acoustic matching layer 40 is not inhibited.
[0030]
Further, in the ultrasonic sensor 1, since the hermetic film 20 is a conductive metal, the lead wire
62 can be connected to the piezoelectric body 30 via the hermetic film 20, and the lead-in
electrode is formed on the piezoelectric body 30. There is no need for additional processing for
installation, and manufacture is easy.
[0031]
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Further, in the ultrasonic sensor 1, only the acoustic matching layer 40 is formed on the hermetic
membrane 20, so the part inserted into the electronic device is only the acoustic matching layer.
Therefore, it is difficult to disturb the state of the object to be measured, and high measurement
accuracy can be obtained.
[0032]
In addition, since the support member 10a and the airtight film 20 of the ultrasonic sensor 1
have a planar shape, they can be easily manufactured, and the manufacturing cost can be
suppressed.
Further, the work of providing the holes 50 a and the holes 51 and the work of adjusting the
sizes of the holes 50 a and the holes 51 can be facilitated.
[0033]
Next, FIG. 3 shows another embodiment of the ultrasonic sensor of the present invention.
Fig.3 (a) is the top view, FIG.3 (b) is the 2x-2x sectional drawing.
In FIG. 3, the same or equivalent parts as in the ultrasonic sensor 1 shown in FIG.
[0034]
The ultrasonic sensor 2 differs from the ultrasonic sensor 1 in that the ultrasonic sensor 2 has a
support member 10 b instead of the support member 10 a.
The supporting member 10 b of the ultrasonic sensor 2 is provided with a hole 50 b larger than
the diameter of the acoustic matching layer 40 at a substantially central portion.
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[0035]
The edge of the acoustic matching layer 40 of the ultrasonic sensor 2 is fixed on the hole 50b of
the support member 10b via the hermetic membrane 20, and not directly on the support
member 10b. Therefore, in the ultrasonic sensor 2, the restraint in the vicinity of the edge of the
acoustic matching layer 40 is weakened compared to the ultrasonic sensor 1. Therefore, the
bandwidth is broadened compared to the ultrasonic sensor 1. The frequency characteristic of the
ultrasonic sensor 2 is similar to the frequency characteristic of the ultrasonic sensor 4 shown by
the broken line in FIG.
[0036]
Further, the ultrasonic sensor 2 can be reduced in height because the acoustic matching layer 40
is fixed to the support member 10 b only via the thin airtight film 20.
[0037]
Next, FIG. 4 shows still another embodiment of the ultrasonic sensor of the present invention.
FIG. 4 (a) is a plan view thereof, and FIG. 4 (b) is a bottom view thereof. In FIG. 4, the same or
equivalent parts as in the ultrasonic sensor 1 shown in FIG. Further, in FIG. 4, the illustration of
the piezoelectric body 30 is omitted.
[0038]
The ultrasonic sensor 3 differs from the ultrasonic sensor 1 in that the ultrasonic sensor 3 has a
support member 10 c instead of the support member 10 a. The supporting member 10 c of the
ultrasonic sensor 3 is provided with a hole 50 c smaller than the diameter of the acoustic
matching layer 40 at a substantially central portion. The hole 50c is provided with a notch 52
along its edge. The length r1 from the approximate center of the hole 50c to the tip of the notch
52 is set to be larger than the radius of the acoustic matching layer 40.
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[0039]
A part of the edge of the acoustic matching layer 40 of the ultrasonic sensor 3 is fixed on the
support member 10c, and the remaining part is fixed on the hole 50c. Therefore, the ultrasonic
sensor 3 can achieve a wider band as compared to the ultrasonic sensor 1, and the sensitivity at a
specific frequency becomes higher than that of the ultrasonic sensor 2.
[0040]
The frequency characteristic of the ultrasonic sensor 3 configured in this way is the frequency
characteristic of the dashed-dotted line in FIG.
[0041]
In addition, the ultrasonic sensor 3 can adjust a zone etc. to a desired value by changing the
magnitude | size of the hole 50c or the notch 52, without the fall of a significant sensitivity.
[0042]
Also, the number of notches 52 may be one, two or more.
Further, the shape of the notch 52 is not limited to the shape shown in FIG.
[0043]
In each embodiment, the support members 10a, 10b and 10c can be made of spcc material (iron)
or the like, and the support members 10a, 10b and 10c and the airtight film 20 are adhesive or
laser welded. It can paste together using etc.
[0044]
Next, FIG. 5 shows an embodiment of an electronic device using the ultrasonic sensor of the
present invention.
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FIG. 5 is a block diagram showing an embodiment of a flow meter which is an electronic device
of the present invention.
[0045]
In FIG. 5, a flow meter 8 of the present invention includes a pipe 81, an ultrasonic sensor 1, 1 ′
of the present invention, a switching circuit 82, a transmitting circuit 83, a receiving circuit 84,
and a propagation time measuring circuit 85. And a flow rate calculation circuit 86.
A flammable fluid such as a gas is flowing through the pipe 81 of the flow meter 8. The
ultrasonic sensor 1 is disposed on the upstream side of the pipe 81 so that the ultrasonic sensor
1 and the ultrasonic sensor 1 'are opposed to each other, and the ultrasonic sensor 1' is disposed
on the downstream side of the pipe 81. It is fixed by a screw 53 so that the formed side of the
layer 40 is disposed in the flow path. The ultrasonic sensor 1 and the ultrasonic sensor 1 ′ are
connected to the switching circuit 82, and the switching circuit 82 is connected to the
transmission circuit 83 and the reception circuit 84. The reception circuit 84 is connected to the
propagation time measurement circuit 85, and the propagation time measurement circuit 85 is
connected to the flow rate calculation circuit 86.
[0046]
Then, in the flow meter 8 configured as described above, the switching circuit 82 connects the
ultrasonic sensor 1 to the transmitting circuit 83 and connects the ultrasonic sensor 1 ′ to the
receiving circuit 84, and receives the ultrasonic sensor 1. The state of connection to the circuit
84 and connection of the ultrasonic sensor 1 'to the transmission circuit 83 is switched at
predetermined time intervals. The signal output from the transmission circuit 83 is output from
one of the ultrasonic sensors 1 and 1 ′, is input to the other through the fluid, and is input to
the reception circuit 84. The propagation time measurement circuit 85 processes the signal input
from the reception circuit 84, measures the propagation time required for the signal to
propagate in the fluid, and outputs the result to the flow rate operation circuit 86. Then, the flow
rate calculation circuit 86 determines the flow velocity of the fluid from the difference between
the propagation time when the signal is output from the ultrasonic sensor 1 and the propagation
time when the signal is output from the ultrasonic sensor 1 ′. To calculate the flow rate value
externally.
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[0047]
Since the flowmeter 8 of the present invention uses the airtight ultrasonic sensor 1 or 1 ', it can
measure the flow rate of the flammable fluid.
[0048]
Further, in the flow meter 8 according to the present invention, only the acoustic matching layer
40 is inserted into the inside of the pipe 81 and hardly affects the fluid flowing through the pipe
81.
Therefore, the flow meter 8 can measure the flow rate accurately.
[0049]
Moreover, since the flowmeter 8 of the present invention has high sensitivity and uses the
ultrasonic sensors 1 and 1 'which can facilitate the work process, high precision and cost
reduction can be achieved.
[0050]
As mentioned above, although the electronic device using the ultrasonic sensor of this invention
was demonstrated using the flow meter 8, the electronic device of this invention is not restricted
to the flow meter of this structure.
[0051]
According to the ultrasonic sensor of the present invention, since the acoustic matching layer is
directly fixed to the support member, the height can be reduced.
[0052]
Further, in the ultrasonic sensor of the present invention, the vicinity of the edge of the acoustic
matching layer is fixed on the support member only via the thin airtight film.
Therefore, the vibration of the node of the acoustic matching layer is surely restrained, Q
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becomes high, and band narrowing can be achieved.
[0053]
Further, in the ultrasonic sensor of the present invention, the lead wire can be connected to the
piezoelectric body via the conductive airtight film, and the manufacture becomes easy.
[0054]
Further, in the ultrasonic sensor according to the present invention, the thickness of the airtight
film is 100 μm or less, which is very thin, so that the vibration between the piezoelectric body
and the acoustic matching layer is not inhibited.
[0055]
Moreover, since the support member of the ultrasonic sensor of this invention is planar shape, it
can manufacture easily and can hold down manufacturing cost.
In addition, the work of providing the hole and the work of adjusting the size of the hole can be
facilitated.
[0056]
Also, the ultrasonic sensor of the present invention can adjust the band to a desired value by
changing the size of the hole or notch.
[0057]
In addition, the electronic device of the present invention can measure flammable fluid because it
uses an airtight ultrasonic sensor.
[0058]
In addition, since the electronic device of the present invention uses a low-profile ultrasonic
sensor, only the acoustic matching layer is disposed in the flow path, and it is possible to
accurately measure the flow rate while hardly affecting the fluid flowing through the piping. .
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[0059]
Further, since the electronic device of the present invention uses an ultrasonic sensor which has
high sensitivity and can facilitate the work process, high precision and low cost can be achieved.
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