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DESCRIPTION JPWO2013183292

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DESCRIPTION JPWO2013183292
The ultrasonic transducer (5, 6, 30) is fixed to the metal plate (16, 31), the acoustic matching
member (15) fixed to one surface of the metal plate, and the other surface of the metal plate And
the insulating damping member (11, 20) covering the piezoelectric body (17) generating the
vibration and the surface of the piezoelectric body opposite to the fixing surface with the metal
plate The thickness dimension of the member is set to a length dimension of n / 2 of the
wavelength of the vibration propagating through the insulating damping member.
Ultrasonic transducer and ultrasonic flowmeter equipped with the same
[0001]
The present invention relates to an ultrasonic transducer that transmits and receives ultrasonic
pulses, and an ultrasonic flow meter equipped with the ultrasonic transducer.
[0002]
Conventionally, in an ultrasonic transducer that transmits and receives ultrasonic waves using a
piezoelectric element, it is known that unnecessary vibration in the piezoelectric element is
suppressed by a damping member.
For example, in the ultrasonic sensor 73 of Patent Document 1 shown in FIG. 7, the acoustic
matching layer 71 is fixed to one side of the piezoelectric element 70. A cylindrical case 72 is
fixed to the acoustic matching layer 71 so as to surround the piezoelectric element 70. An elastic
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resin 74 is filled in the cylindrical case 72 so as to fill the piezoelectric element 70.
[0003]
Japanese Patent Application Laid-Open No. 10-224895
[0004]
In the ultrasonic sensor 73, mechanical vibration generated in the piezoelectric element 70
propagates to the acoustic matching layer 71, and is irradiated from the acoustic matching layer
71 as ultrasonic waves.
However, this mechanical vibration is also transmitted from the piezoelectric element 70 to the
elastic resin 74 and propagates through the elastic resin 74. When the mechanical vibration is
reflected by the end face of the elastic resin 74 and amplified by interference, reverberation
noise and propagation noise occur. These noises make it impossible for the ultrasonic sensor 73
to radiate accurately.
[0005]
The prevention of the interference is realized by increasing the thickness dimension of the elastic
resin 74 to attenuate the reflected mechanical vibration. However, the size of the ultrasonic
sensor 73 is increased.
[0006]
The present invention has been made to solve these problems, and provides a small ultrasonic
transducer capable of accurately emitting ultrasonic pulses, and an ultrasonic flow meter
equipped with the same. The purpose is that.
[0007]
An ultrasonic transducer according to an aspect of the present invention includes a metal plate,
an acoustic matching member fixed to one surface of the metal plate, and a piezoelectric member
fixed to the other surface of the metal plate to generate vibration. And an insulating damping
member covering the back surface of the piezoelectric body opposite to the fixing surface with
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the metal plate, and the thickness dimension of the insulating damping member propagates the
insulating damping member Is set to a length dimension of n / 2 of the wavelength of the
vibration.
[0008]
According to the present invention, it is possible to provide a small ultrasonic transducer having
the configuration described above and capable of accurately emitting ultrasonic pulses, and an
ultrasonic flow meter equipped with the small ultrasonic transducer. Play.
[0009]
The above object, other objects, features and advantages of the present invention will be
apparent from the following detailed description of preferred embodiments with reference to the
attached drawings.
[0010]
BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the ultrasonic flow
meter which concerns on Embodiment 1 of this invention.
It is sectional drawing which shows the state which attached the ultrasonic transducer of the
ultrasonic flowmeter of FIG. 1 to the flow-path member.
It is the graph which represented typically the relationship between the thickness of the back
load part of the ultrasonic transducer of FIG. 2, and ultrasonic intensity.
It is sectional drawing which shows the state which attached the ultrasonic transducer which
concerns on Embodiment 2 of this invention to the flow-path member.
It is sectional drawing which shows the state which attached the ultrasonic transducer which
concerns on Embodiment 3 of this invention to the flow-path member. It is sectional drawing
which shows the state which attached the ultrasonic transducer concerning Embodiment 4 of this
invention to the flow-path member. It is a sectional view showing a conventional ultrasonic
sensor.
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[0011]
An ultrasonic transducer according to a first aspect of the present invention comprises a metal
plate, an acoustic matching member fixed to one surface of the metal plate, and a piezoelectric
member fixed to the other surface of the metal plate to generate vibration. And an insulating
damping member covering a back surface of the piezoelectric body opposite to a surface fixed to
the metal plate, wherein a thickness dimension of the insulating damping member propagates the
insulating damping member The length of n / 2 of the wavelength of the vibration is set.
[0012]
An ultrasonic transducer according to a second aspect of the present invention comprises a metal
plate, an acoustic matching member fixed to one surface of the metal plate, and a piezoelectric
member fixed to the other surface of the metal plate to generate vibration. An insulating damping
member covering a back surface of the piezoelectric body opposite to a surface fixed to the metal
plate, and a density higher than that of the piezoelectric body and the surface opposite to the
surface covering the piezoelectric body And a supporting portion in contact with the back surface
of the insulating damping member, wherein the thickness dimension of the insulating damping
member is (2n-1) / 4 of the wavelength of the vibration propagating through the insulating
damping member. It is set to the height dimension.
[0013]
In the ultrasonic transducer according to the third aspect of the present invention, in the first or
second aspect, the metal plate may be formed in a flat plate shape.
[0014]
The ultrasonic transducer according to a fourth aspect of the present invention is the ultrasonic
transducer according to the first or second aspect, wherein the metal plate has a cylindrical side
wall portion, a top portion covering an opening at one end of the side wall portion, and the side
wall And the acoustic matching body is fixed to one surface of the top portion, and the other
surface of the top portion is fixed in the inner space of the side wall portion. The piezoelectric
body may be fixed to the surface, and the insulating damping member may cover the surface of
the piezoelectric body opposite to the surface fixed to the top portion.
[0015]
An ultrasonic transducer according to a fifth aspect of the present invention is the ultrasonic
transducer according to any one of the first to fourth aspects, wherein the insulating damping
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member is added to the back surface of the piezoelectric body, the side surface of the
piezoelectric body, The portion of the metal plate excluding the fixed portion with the acoustic
matching body and the fixed portion with the piezoelectric body may be integrally covered.
[0016]
In the ultrasonic flowmeter according to the sixth aspect of the present invention, any one of the
first to fifth pairs of ultrasonic transducers that transmit and receive ultrasonic pulses to each
other and the pair of ultrasonic transducers are mutually separated. And a propagation time
measuring unit for measuring a time during which the ultrasonic pulse propagates between the
pair of ultrasonic transducers, and a time measured by the propagation time measuring unit. And
a calculation unit that calculates the flow rate of the fluid to be measured.
[0017]
(Embodiment 1) (Configuration of Ultrasonic Flowmeter) FIG. 1 is a cross-sectional view
schematically showing an ultrasonic flowmeter 100 equipped with ultrasonic transducers 5 and
6.
As shown in FIG. 1, the ultrasonic flowmeter 100 is a device that measures the flow rate of the
fluid to be measured flowing in the flow path, and is attached to the flow path member 3.
The flow path member 3 is formed of, for example, a cylindrical tube, and has one opening 1 and
the other opening 2 at each of its ends.
An internal space of the flow path member 3 is used as a flow path, and the flow path
communicates with the one opening 1 and the other opening 2.
Further, the flow passage member 3 is provided with a first opening 4 and a second opening 4
penetrating through the pipe wall.
Each opening 4 protrudes, for example, to the outside of the flow path member 3 and has a
cylindrical internal space.
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The one opening 4 is provided on the one opening 1 side, and the other opening 4 is provided on
the other opening 2 side, and these are opposed to each other. Therefore, the central axes of the
openings 4 coincide with each other, and are inclined at an angle θ with respect to the central
axis of the flow path member 3.
[0018]
The pair of ultrasonic transducers 5 and 6 are fixed in contact with the flow path member 3 at
positions where they transmit and receive ultrasonic pulses to each other. That is, one ultrasonic
transducer 5 is attached to one opening 4, and the other ultrasonic transducer 6 is attached to
the other opening 4. The ultrasonic transducers 5 and 6 are arranged such that the acoustic
matching bodies 15 face each other, and the radiation planes of the acoustic matching bodies 15
are perpendicular to the central axis of the opening 4. Therefore, the ultrasonic transducers 5
and 6 emit ultrasonic pulses obliquely along the central axis of the opening 4, that is, at an angle
θ formed with respect to the central axis of the flow path member 3. Further, each of the
ultrasonic transducers 5 and 6 receives ultrasonic pulses obliquely incident at an angle θ
formed with respect to the flow path member 3 along the central axis of the opening 4.
[0019]
The ultrasonic wave propagation time measurement unit (hereinafter referred to as
“propagation time measurement unit”. ) 7 and operation unit 8 are configured by a control
device such as a microcomputer. The microcomputer includes a processing unit such as a CPU
and a storage unit such as a ROM and a RAM. The propagation time measurement unit 7 and the
calculation unit 8 may be configured by a single control device or may be configured by separate
control devices.
[0020]
The propagation time measurement unit 7 measures the time during which an ultrasonic pulse
propagates between the pair of ultrasonic transducers 5 and 6. The calculation unit 8 calculates
the flow rate of the fluid to be measured based on the time measured by the propagation time
measurement unit 7.
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[0021]
(Configuration of Ultrasonic Transducer) FIG. 2 is a cross-sectional view showing the ultrasonic
transducer 5 according to the first embodiment. In addition, since the structure of the ultrasonic
transducer 6 is the same as that of the ultrasonic transducer 5, the description is abbreviate |
omitted. As shown in FIG. 2, the ultrasonic transducer 5 includes a piezoelectric body 17, an
acoustic matching body 15, a metal plate 16, two lead wires 18, and an insulating damping
member 11. There is.
[0022]
The piezoelectric body 17 is an element that expands and contracts in the thickness direction by
application of a voltage, thereby converting electric vibration into mechanical vibration. The
piezoelectric body 17 is formed in a rectangular parallelepiped or cylindrical columnar shape, for
example, a short square columnar shape in this embodiment. The piezoelectric body 17 has a
pair of electrodes and a piezoelectric portion interposed therebetween in the thickness direction.
For the piezoelectric portion of the piezoelectric body 17, a material exhibiting piezoelectricity,
for example, barium titanate, lead zirconate titanate, or the like is suitably used. One of the
electrodes is joined to the metal plate 16 by a conductive material such as an adhesive or a
conductive paste. The other electrode is joined to one lead wire 18 by a conductive material such
as a conductive paste or a solder.
[0023]
The acoustic matching body 15 is an element that matches the acoustic impedance of the
piezoelectric body 17 with the acoustic impedance of the fluid to be measured in order to radiate
the mechanical vibration generated by the piezoelectric body 17 to the fluid to be measured as
an ultrasonic pulse. The acoustic matching body 15 has, for example, a cylindrical shape, and its
thickness dimension is set to a length dimension of 1⁄4 of the wavelength λ of the mechanical
vibration propagating through the acoustic matching body 15. The acoustic matching body 15 is
formed by filling and curing a thermosetting resin in the gaps of hollow spherical glass, or by
providing an acoustic film on the sound emitting surface of the ceramic porous body.
[0024]
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The metal plate 16 is a flat plate that supports the acoustic matching body 15 and the
piezoelectric body 17 and has, for example, a disk shape. The metal plate 16 is formed of a
conductive material, for example, a metal such as iron, stainless steel, brass, copper, aluminum,
and a nickel-plated steel plate. The acoustic matching body 15 is fixed to the one main surface of
the metal plate 16 and the piezoelectric body 17 is fixed to the other main surface. The metal
plate 16 is larger than the acoustic matching body 15 and the piezoelectric body 17 in the
direction perpendicular to its thickness. For this reason, the outer peripheral part of the metal
plate 16 protrudes from the acoustic matching body 15 and the piezoelectric body 17 in the
direction perpendicular to the thickness thereof. The other lead wire 18 is connected to the other
main surface of the outer peripheral portion by solder or the like. The metal plate 16 is
electrically connected to one electrode of the piezoelectric body 17 by an ohmic contact by a
conductive material. Therefore, one electrode of the piezoelectric body 17 and the other lead
wire 18 are electrically connected through the metal plate 16.
[0025]
One of the two lead wires 18 connects the other electrode of the piezoelectric body 17 and the
propagation time measurement unit 7 (FIG. 1). Further, the other lead wire 18 connects one
electrode of the piezoelectric body 17 and the propagation time measuring unit 7 via the metal
plate 16. For these connections, conductive materials such as solder and conductive paste are
used.
[0026]
The insulating damping member 11 integrally covers the outer peripheral portion of the metal
plate 16, the outer surface of the piezoelectric body 17, and the two lead wires 18. Here,
"integrally" means that the insulating damping member 11 is one member made of a continuous
material. Further, specifically, the portion of the metal plate 16 excluding the fixed portion with
the acoustic matching body 15 and the fixed portion with the piezoelectric body 17 is configured
at the outer peripheral portion of the metal plate 16. Furthermore, the outer surface of the
piezoelectric body 17 is specifically composed of a surface (rear surface) opposite to the bonding
surface with the metal plate 16 and a side surface between the bonding surface and the rear
surface. . The thickness dimension M of the insulating damping member 11 (rear load portion
20) covering the back surface of the piezoelectric body 17 is set to a half dimension of the
wavelength λ of the mechanical vibration propagating through the insulating damping member
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11. It is done. The back surface loading unit 20 may cover the entire back surface of the
piezoelectric body 17 or may cover a part of the back surface.
[0027]
The insulating damping member 11 is formed of a thermoplastic resin having a low glass
transition temperature, such as a thermoplastic elastomer material or a crystalline polyester.
Examples of the thermoplastic elastomer material include styrene-based elastomers, olefin-based
elastomers, polyester-based elastomers and the like. The glass transition point of the
thermoplastic resin is, for example, preferably -30 ° C or lower, for example, -50 to -90 ° C,
which is the lowest temperature at which flow rate measurement is performed. Thereby, at the
time of flow measurement, the insulating damping member 11 has rubber elasticity and can
exhibit a damping function. The melting point of the thermoplastic resin is preferably 80 ° C. or
more, for example, 100 to 200 ° C., which is the maximum temperature of flow rate
measurement. Furthermore, the Young's modulus of the thermoplastic resin is, for example, 0.1
to 1.0 GPa in the range from the lowest temperature to the highest temperature of the flow rate
measurement. Thereby, the insulating damping member 11 can fully absorb the vibration of the
metal plate 16 or the piezoelectric body 17 at the time of flow rate measurement.
[0028]
(Mounting of Ultrasonic Transducer) As shown in FIG. 2, each ultrasonic transducer 5 is fixed to
the flow passage member 3 by an annular fixing member 12 so as to be pressed against the flow
passage member 3 side. There is. At this time, the surface on the acoustic matching body 15 side
in the outer peripheral portion of the metal plate 16 abuts on the contact surface 10 a of the flow
path member 3 via the insulating damping member 11. Further, the end face of the metal plate
16 abuts on the contact surface 10 b of the flow path member 3 via the insulating damping
member 11. Furthermore, the surface on the piezoelectric body 17 side in the outer peripheral
portion of the metal plate 16 abuts on the fixing member 12 via the insulating damping member
11. For this reason, each ultrasonic transducer 5 is fixed to the flow path member 3 via the
insulating damping member 11.
[0029]
(Operation of Ultrasonic Flowmeter) For example, in the case of transmitting an ultrasonic pulse
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from the ultrasonic transducer 5, as shown in FIG. 1 and FIG. Voltage) signal is applied to the
piezoelectric body 17 of the ultrasonic transducer 5. Since this electrical signal is formed of a
rectangular wave having a frequency close to the resonance frequency of the piezoelectric body
17, the piezoelectric body 17 converts the electrical signal into mechanical vibration and vibrates
in the thickness direction. Then, mechanical vibration is applied from the piezoelectric body 17
to the acoustic matching body 15 via the metal plate 16, and the acoustic matching body 15
resonates with the piezoelectric body 17. Thereby, the mechanical vibration of which the
amplitude is increased is emitted from the radiation surface of the acoustic matching body 15 as
an ultrasonic pulse.
[0030]
The ultrasonic pulse emitted from the ultrasonic transducer 5 propagates on the propagation
path L1 and reaches the acoustic matching body 15 of the ultrasonic transducer 6, as shown in
FIG. The ultrasonic pulse mechanically vibrates the piezoelectric body 17 through the acoustic
matching body 15. Then, the piezoelectric body 17 converts the mechanical vibration into an
electrical signal, and outputs the electrical signal to the propagation time measuring unit 7. For
this reason, the propagation time measurement unit 7 is the difference between the time when
the electrical signal is output to the piezoelectric body 17 of the ultrasonic transducer 5 and the
time when the electrical signal is input from the piezoelectric body 17 of the ultrasonic
transducer 6 Based on the above, the propagation time t1 of the ultrasonic pulse is determined.
[0031]
Next, an ultrasonic wave pulse is transmitted from the ultrasonic wave transmitter / receiver 6,
and the ultrasonic wave transmitter / receiver 5 receives the ultrasonic wave pulse propagated
through the propagation path L2. Then, the propagation time measurement unit 7 determines
the difference between the time when the electrical signal is output to the piezoelectric body 17
of the ultrasonic transducer 6 and the time when the electrical signal is input from the
piezoelectric body 17 of the ultrasonic transducer 5. Based on the above, the propagation time t2
of the ultrasonic pulse is determined. Also in this case, since it is the same as the case where an
ultrasonic pulse is transmitted from the above-mentioned ultrasonic transducer 5, the
explanation is omitted. The ultrasonic transducer 6 may transmit the ultrasonic pulse first, and
then the ultrasonic transducer 5 may transmit the ultrasonic pulse.
[0032]
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Then, the calculation unit 8 calculates the flow rate of the fluid to be measured based on the
propagation times t1 and t2 of the ultrasonic pulse determined by the propagation time
measurement unit 7. Specifically, in the flow path of the flow path member 3, the fluid to be
measured flows from the one opening 1 toward the other opening 2 at the flow velocity V. The
central axis of the opening 4 is inclined at an angle θ with respect to the central axis of the flow
path member 3. Therefore, the propagation time t1 of the ultrasonic pulse propagating at the
velocity C through the propagation path L1 is different from the propagation time t2 of the
ultrasonic pulse propagating at the velocity C through the propagation path L2. The distance
between the propagation paths L1 and L2 is the distance L between the ultrasonic transducer 5
and the ultrasonic transducer 6. Further, the angle θ is an angle between the flow direction of
the fluid to be measured (the central axis of the flow path member 3) and the propagation
direction of the ultrasonic pulse (the central axis of the opening 4).
[0033]
The propagation time t1 of the ultrasonic pulse that reaches the ultrasonic transducer 6 from the
ultrasonic transducer 5 along the propagation path L1 is represented by the following equation
(1).
[0034]
t1 = L / (C + V cos θ) (1) Further, the propagation time t2 of the ultrasonic pulse arriving from
the ultrasonic transducer 6 to the ultrasonic transducer 5 along the propagation path L2 is
represented by the following equation (2) Be
[0035]
t2 = L / (C−V cos θ) (2) From these equations (1) and (2), the flow velocity V of the fluid to be
measured is represented by the following equation (3).
[0036]
V = L / 2 cos θ (1 / t 1-1 / t 2) (3) The distance L between the propagation paths L1 and L2 of
the ultrasonic pulse, and the angle θ between the flow direction of the fluid to be measured and
the propagation direction of the ultrasonic pulse Is known.
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The propagation times t1 and t2 of the ultrasonic pulse are measured by the propagation time
measuring unit 7.
Thereby, the calculating part 8 can obtain | require the flow velocity V of a to-be-measured fluid
based on Formula (3).
Furthermore, the calculation unit 8 can obtain the flow rate Q by multiplying the flow velocity V
by the cross-sectional area S of the flow passage member 3 and the correction coefficient K.
[0037]
(Function, Effect) As shown in FIG. 2, the mechanical vibration generated by the piezoelectric
body 17 is transmitted to the acoustic matching body 15 through the metal plate 16 and emitted
as an ultrasonic pulse from the radiation surface of the acoustic matching body 15 Ru. At the
same time, the mechanical vibration generated in the piezoelectric body 17 is transmitted to the
rear load portion 20 and propagates, and travels to the surface opposite to the bonding surface
with the piezoelectric body 17 (the rear surface of the rear load portion 20). Then, the
mechanical vibration is reflected on the back surface of the back surface load unit 20 and returns
to the side of the surface to be bonded to the piezoelectric body 17.
[0038]
When the reflected mechanical vibration reaches the bonding surface with the piezoelectric body
17, a part of the mechanical vibration is propagated to the inside of the piezoelectric body 17. In
addition, the remaining mechanical vibration is reflected again by the bonding surface with the
piezoelectric body 17 and propagates in the back load direction on the back load portion 20.
Then, when the mechanical vibration propagating in the rear surface load unit 20 interferes with
the mechanical vibration transmitted from the piezoelectric body 17 to the rear surface load unit
20 and its amplitude increases, the ultrasonic flowmeter 100 accurately measures the fluid to be
measured. It becomes difficult to measure
[0039]
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That is, for example, when the piezoelectric transducer 17 or the like continues to vibrate by the
amplified mechanical vibration after the ultrasonic transducer 5 emits an ultrasonic pulse,
reverberation noise occurs. For this reason, next, when the ultrasonic transducer 5 emits an
ultrasonic pulse, reverberation noise affects mechanical vibration propagating through the
piezoelectric body 17 and / or the acoustic matching body 15. As a result, the ultrasonic
transducer 5 can not accurately emit the mechanical vibration as an ultrasonic pulse.
[0040]
Further, when the mechanical vibration amplified in the ultrasonic transducer 5 propagates to
the ultrasonic transducer 6 via the flow path member 3 or the like, it becomes propagation noise.
For this reason, when the ultrasonic transducer 6 emits an ultrasonic pulse, the propagation
noise affects the mechanical vibration propagating through the piezoelectric body 17 and / or
the acoustic matching body 15. As a result, the ultrasonic transducer 6 can not accurately emit
the mechanical vibration as an ultrasonic pulse.
[0041]
Here, the case where the ultrasonic transducer 5 transmits an ultrasonic pulse and the ultrasonic
pulse is received by the ultrasonic transducer 6 has been described. On the other hand, the same
applies to the case where the ultrasonic transducer 5 and the ultrasonic transducer 6 are
interchanged.
[0042]
On the other hand, since the thickness dimension M of the rear load portion 20 is set to λ / 2,
the influence of the reverberation noise and the propagation noise is suppressed. As a result, as
shown in FIG. 3, without increasing the size of the ultrasonic transducers 5, 6, the reduction of
the intensity of the ultrasonic pulse is prevented. FIG. 3 is a graph schematically showing the
relationship between the back load part (thickness) and the ultrasonic intensity. The rear load
portion (thickness) indicates the thickness dimension M of the rear load portion 20 of the
ultrasonic transducers 5 and 6. Further, the ultrasonic intensity indicates the magnitude of the
ultrasonic pulse emitted by the ultrasonic transducers 5 and 6.
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[0043]
Specifically, as shown in FIG. 2, one surface (the bonding surface with the piezoelectric body 17)
of the back surface load unit 20 is in contact with the piezoelectric body 17 and the other surface
(back surface) is in contact with the air. For this reason, the piezoelectric body 17, the back load
portion 20, and the air are arranged in this order, and their density decreases in this order.
Therefore, the acoustic impedance defined by the product of the density and the velocity of
sound also decreases in this order.
[0044]
In the case of such an acoustic impedance relationship, when the mechanical vibration
(propagation vibration) propagating through the rear load portion 20 is reflected by the bonding
surface with the piezoelectric body 17, the phase of the propagation vibration is shifted by half
wavelength. On the other hand, when this propagation vibration is reflected on the back surface
of the back surface addition part 20, the phase of the propagation vibration does not shift.
Therefore, as shown in the following (Equation 12), when the thickness dimension M of the back
side load portion 20 is an integral multiple of the half wavelength (λ / 2), the amplitude of the
propagation vibration is minimized by the interference. In equation (12), n represents an integer.
Also, λ represents the wavelength of mechanical vibration propagating through the rear load
unit 20.
[0045]
M = n · λ / 2 (Equation 12) As a result, when the thickness dimension M of the rear load portion
20 is an integral multiple of a half wavelength as shown in (Equation 12), the influence of the
propagation vibration (reverberation noise or propagation noise ) Is suppressed. For this reason,
as shown in FIG. 3, it is suppressed that the intensity of the ultrasonic pulse which ultrasonic
transducer 5 and 6 radiates is reduced by the influence of propagation vibration, and the
intensity of the ultrasonic pulse is secured large. can do.
[0046]
In particular, in equation (12), when n = 1, the thickness dimension M of the rear load portion 20
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can be minimized while reducing the magnitude of the mechanical vibration propagating through
the rear load portion 20. Therefore, when the thickness dimension M of the rear surface loading
unit 20 is λ / 2, the sizes of the ultrasonic transducers 5 and 6 can be minimized, and a large
ultrasonic pulse intensity can be secured.
[0047]
In addition, the thickness dimension M of the rear load portion 20 can be set to a length
dimension that satisfies (Expression 12) other than λ / 2. In this case, the thickness dimension
M is larger than when λ / 2. However, the thickness dimension M is smaller than the thickness
dimension by which the propagation vibration can be reduced. Therefore, the ultrasonic
transducers 5 and 6 can be miniaturized. In addition, with regard to the intensity of the
ultrasonic pulse, when the thickness dimension M of the back side load portion 20 is a length
dimension satisfying (Equation 12) other than λ / 2, the same function and effect as λ / 2 are
exhibited. be able to.
[0048]
In addition, when the thickness dimension M of the back surface load part 20 satisfy | fills the
relationship shown by the following (Equation 13), the mechanical vibration (propagation
vibration) which propagates the back surface load part 20 is amplified by interference. Therefore,
when the thickness dimension M satisfies the relationship shown in the following (Equation 13),
as shown in FIG. 3, the intensity of the ultrasonic pulse emitted by the ultrasonic transducers 5
and 6 is reduced by the influence of the propagation vibration Do. On the other hand, as the
thickness dimension M becomes larger, the propagation vibration is attenuated, so that the
strength of the ultrasonic pulse becomes larger as shown in FIG. However, as the thickness
dimension M increases, the size of the ultrasonic transducers 5 and 6 increases.
[0049]
M = (2 n −1) λ / 4 (Equation 13) In addition, when the back load portion 20 is excellent in the
function of attenuating the propagation vibration, even if the thickness dimension M of the back
load portion 20 is smaller than λ / 2, the back surface Propagation vibration in the load unit 20
can be reduced. In this case, since the back load portion 20 becomes thinner, the ultrasonic
transducers 5 and 6 can be further miniaturized.
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[0050]
Also, the insulating damping member 11 is integrally formed on the metal plate 16 and the
piezoelectric body 17 respectively. Therefore, it is not necessary to attach the insulating damping
member 11, and the mass productivity of the ultrasonic transducers 5 and 6 is excellent.
[0051]
Furthermore, the metal plate 16 has higher dimensional accuracy than the resin plate, and the
ultrasonic transducers 5 and 6 can be attached to the flow path 3 with high accuracy. For this
reason, since the transmission / reception loss of the ultrasonic pulse at the time of measurement
can be reduced, highly accurate flow measurement can be realized.
[0052]
Second Embodiment The flat metal plate 16 is used in the ultrasonic transducers 5 and 6
according to the first embodiment. However, in the ultrasonic transducer 30 according to the
second embodiment, brazing is performed. A container-shaped metal plate 31 is used as the
metal plate. FIG. 4 is a cross-sectional view showing an ultrasonic transducer 30 according to the
second embodiment.
[0053]
As shown in FIG. 4, the metal plate 31 is formed in the shape of a brazing container including the
side wall 33, the top 32 and the flange 34. The side wall portion 33 has a cylindrical shape, and
one end thereof is connected to the top portion 32 and the other end is connected to the flange
portion 34. The top portion 32 has a disk shape and covers one end opening of the side wall
portion 33. The collar 34 is annular and extends radially outward from the side wall 33.
[0054]
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In the metal plate 31, the acoustic matching body 15 is fixed to the top surface of the top portion
32, and the piezoelectric body 17 is fixed to the back surface of the top portion 32. Since the
inner diameter of the side wall 33 is larger than the length of the piezoelectric body 17, the
piezoelectric 17 is located in the internal space of the cylindrical side wall 33, and the gap 35 is
formed between the piezoelectric 17 and the inner surface of the side wall 33. Is formed.
[0055]
The metal plate 31 is formed by deep drawing using a conductive material, for example, a metal
such as iron, stainless steel, brass, copper, aluminum, or a nickel-plated steel plate. Therefore, the
top portion 32 of the metal plate 31 is electrically connected to the electrode of the piezoelectric
body 17 by an ohmic contact using a conductive material. Further, the flange portion 34 of the
metal plate 31 is connected to the lead wire 18 by a conductive material such as solder. Thereby,
the electrode of the piezoelectric body 17 and the lead wire 18 are electrically connected via the
metal plate 31.
[0056]
The insulating damping member 11 includes the outer surface of the side wall 33 of the metal
plate 31, the flange 34 of the metal plate 31, the gap 35 between the piezoelectric body 17 and
the inner surface of the side wall 33, the back of the piezoelectric body 17, and Integrally
covering the lead wire 18 of FIG. Further, the thickness dimension M of the insulating damping
member 11 (rear load portion 20) covering the rear surface of the piezoelectric body 17 is 1 of
the wavelength λ of mechanical vibration generated in the piezoelectric body 17 and
propagating through the insulating damping member 11 It is set to the length dimension of / 2.
The back surface loading unit 20 may cover the entire back surface of the piezoelectric body 17
or may cover a part of the back surface.
[0057]
Such an ultrasonic transducer 30 is fixed to the flow path member 3 by the annular fixing
member 12 so that the acoustic matching body 15 is located on the opening 4 side and pressed
against the flow path member 3. At this time, the surface on the acoustic matching body 15 side
of the flange portion 34 of the metal plate 31 abuts on the contact surface 10 a of the flow path
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member 3 via the insulating damping member 11. Further, the end face of the flange portion 34
of the metal plate 31 abuts on the contact surface 10 b of the flow path member 3 via the
insulating damping member 11. Further, the surface of the flange 34 of the metal plate 31 on the
piezoelectric body 17 side is in contact with the fixing member 12 via the insulating damping
member 11. For this reason, each ultrasonic transducer 30 is fixed to the flow path member 3 via
the insulating damping member 11.
[0058]
According to the above configuration, the thickness dimension M of the rear load portion 20 is
set to 1/2 or n / 2 of the wavelength λ of the mechanical vibration propagating through the rear
load portion 20. Therefore, the same operation and effect as in the first embodiment are
provided.
[0059]
Third Embodiment In the ultrasonic transducers 5 and 6 according to the first embodiment, the
outer peripheral portion of the metal plate 16 is fixed by the annular fixing member 12. On the
other hand, in the ultrasonic transducers 5 and 6 according to the third embodiment, as shown in
FIG. 5, the outer peripheral portion of the metal plate 16 and the piezoelectric body 17 are fixed
by the fixing member 112 in the form of a brazed container. ing. FIG. 5 is a cross-sectional view
showing an ultrasonic transducer 5 according to the third embodiment. In addition, since the
structure of the ultrasonic transducer 6 is the same as that of the ultrasonic transducer 5, the
description is abbreviate | omitted.
[0060]
As shown in FIG. 5, the fixing member 112 is formed in the shape of a brazing container
including an outer peripheral portion, a support portion 112 a and an attachment portion. The
outer peripheral portion is a cylindrical shape having a square cross section with respect to the
short square columnar piezoelectric body 17. The support portion 112 a is a rectangular flat
plate shape with respect to the short square columnar piezoelectric body 17, and covers one end
opening of the outer peripheral portion. The attachment portion has an annular shape and
extends outward in the radial direction from the other end of the outer peripheral portion. The
fixing member 112 is formed of a metal such as aluminum.
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[0061]
The mounting portion is attached to the flow path member 3 such that the outer peripheral
portion of the metal plate 16 of the ultrasonic transducer 5 is pressed to the flow path member 3
side by the mounting portion of the fixing member 112. Thus, the ultrasonic transducer 5 is fixed
to the flow path member 3. Further, the inner surface of the support portion 112 a is in contact
with the back surface of the back load portion 20, and the support portion 112 a supports the
piezoelectric body 17 via the back load portion 20. For this reason, the piezoelectric body 17 is
protected by the support portion 112a.
[0062]
In this case, the piezoelectric body 17, the back load portion 20, and the support portion 112a of
the fixing member 112 are stacked in this order. Since the piezoelectric body 17 and the support
portion 112 a have a density higher than that of the rear load portion 20, the piezoelectric body
17 and the support portion 112 a have an acoustic impedance larger than that of the rear load
portion 20.
[0063]
In such a relationship of acoustic impedance, the mechanical vibration (propagation vibration)
propagating through the rear load unit 20 is reflected in any of the bonding surface with the
piezoelectric body 17 and the rear surface of the rear additional portion 20, The phase of the
propagation vibration is shifted by half that wavelength. Therefore, when the relationship shown
in the following (Equation 14) is satisfied, the amplitude of the propagation vibration is
minimized by the interference. In equation (14), n represents an integer. Also, λ represents the
wavelength of mechanical vibration propagating through the rear load unit 20.
[0064]
M = (2n-1) · λ / 4 (Equation 14) As a result, when the thickness dimension M of the rear load
portion 20 satisfies the relationship shown in (Equation 14), the influence of the propagation
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19
vibration (reversing noise and propagation noise) It is suppressed. For this reason, it is
suppressed that the intensity of the ultrasonic pulse which ultrasonic transducer 5 and 6 radiates
is reduced by the influence of propagation vibration, and the intensity of an ultrasonic pulse can
be secured large.
[0065]
In particular, in equation (14), in the case of n = 1, the thickness dimension M of the rear load
portion 20 can be minimized while reducing the magnitude of the mechanical vibration
propagating through the rear load portion 20. Therefore, when the thickness dimension M of the
back side load part 20 is λ / 4, the sizes of the ultrasonic transducers 5 and 6 can be minimized,
and the strength of the ultrasonic pulse can be secured large.
[0066]
In addition, the thickness dimension M of the rear load portion 20 can be set to a length
dimension satisfying (Expression 14) other than λ / 4. In this case, the thickness dimension M is
larger than that at λ / 4. However, the thickness dimension M is smaller than the thickness
dimension by which the propagation vibration can be reduced. Therefore, the ultrasonic
transducers 5 and 6 can be miniaturized. In addition, with regard to the intensity of the
ultrasonic pulse, when the thickness dimension M of the back load portion 20 is a length
dimension satisfying (Expression 14) other than λ / 4, the same function and effect as λ / 4 are
exhibited. be able to.
[0067]
Furthermore, when the back load portion 20 is excellent in the function of damping the
propagation vibration, the propagation vibration in the back load portion 20 can be reduced even
if the thickness dimension M of the back load portion 20 is smaller than λ / 4. In this case, since
the back load portion 20 becomes thinner, the ultrasonic transducers 5 and 6 can be further
miniaturized.
[0068]
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Fourth Embodiment In the ultrasonic transducer 30 according to the second embodiment, the
flange portion 34 of the metal plate 31 is fixed by the annular fixing member 12. On the other
hand, in the ultrasonic transducer 30 according to the fourth embodiment, as shown in FIG. 6,
the flange portion 34 and the piezoelectric body 17 are fixed by a flat fixing member 212. FIG. 6
is a cross-sectional view showing an ultrasonic transducer 30 according to the fourth
embodiment.
[0069]
The fixing member 212 is formed in a flat plate shape so as to cover the flange portion 34 of the
metal plate 31 and the piezoelectric body 17 as shown in FIG. When the piezoelectric body 17
protrudes to the back side from the flange 34, the support portion 212a of the solid member 212
is recessed from the outer peripheral portion according to the amount of the protrusion. The
fixing member 212 is formed of a metal such as aluminum.
[0070]
The outer peripheral portion of the fixing member 212 is attached to the flow path member 3 so
that the flange portion 34 of the metal plate 31 is pressed to the flow path member 3 side by the
outer peripheral portion of the fixing member 212. Thereby, the ultrasonic transducer 30 is fixed
to the flow path member 3. Further, the surface of the support portion 212 a of the fixing
member 212 is in contact with the back surface of the back load portion 20, and the support
portion 212 a supports the piezoelectric body 17 via the back load portion 20. For this reason,
the piezoelectric body 17 is protected by the support portion 212a.
[0071]
In this case, the piezoelectric body 17, the back load portion 20 and the fixing member 212 are
stacked in this order. Since the piezoelectric body 17 and the fixing member 212 have a density
higher than that of the rear load portion 20, the acoustic impedance of the piezoelectric body 17
and the fixing member 212 becomes larger than that of the rear load portion 20.
[0072]
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21
Therefore, as in the third embodiment, the propagation vibration is reflected while the phase
changes at the junction surface of the back load unit 20 with the piezoelectric body 17 and the
back surface of the back load unit 20. When the thickness dimension M of the rear load portion
20 satisfies the relationship of the above (Equation 14), the propagation vibration in the rear
load portion 20 is minimized, and reverberation noise and radio wave noise can be reduced. As a
result, the ultrasonic transducer 30 can accurately emit ultrasonic pulses while suppressing the
influence of noise while preventing upsizing.
[0073]
In addition, the thickness dimension M of the rear load portion 20 can be set to a length
dimension satisfying (Expression 14) other than λ / 4. In this case, the thickness dimension M is
larger than that at λ / 4. However, the thickness dimension M is smaller than the thickness
dimension by which the propagation vibration can be reduced. Therefore, the ultrasonic
transducers 5 and 6 can be miniaturized. In addition, with regard to the intensity of the
ultrasonic pulse, when the thickness dimension M of the back load portion 20 is a length
dimension satisfying (Expression 14) other than λ / 4, the same function and effect as λ / 4 are
exhibited. be able to.
[0074]
Furthermore, when the back load portion 20 is excellent in the function of damping the
propagation vibration, the propagation vibration in the back load portion 20 can be reduced even
if the thickness dimension M of the back load portion 20 is smaller than λ / 4. In this case, since
the back load portion 20 becomes thinner, the ultrasonic transducer 30 can be further
miniaturized.
[0075]
The above embodiments may be combined with each other as long as the other is not excluded.
[0076]
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From the above description, many modifications and other embodiments of the present invention
will be apparent to those skilled in the art.
Accordingly, the above description should be construed as illustrative only and is provided for
the purpose of teaching those skilled in the art the best mode of carrying out the present
invention. The structural and / or functional details may be substantially altered without
departing from the spirit of the present invention.
[0077]
The ultrasonic transducer according to the present invention and the ultrasonic meter equipped
with the ultrasonic transducer according to the present invention are a small ultrasonic
transducer capable of emitting ultrasonic pulses with high accuracy compared to the prior art,
and an ultrasonic flow meter equipped with the same Useful as.
[0078]
Reference Signs List 3 flow path member 5, 6, 30 ultrasonic transducer 7 ultrasonic wave
propagation time measuring unit (propagation time measuring unit) 8 arithmetic unit 11
insulating damping member 15 acoustic matching member 16 metal plate 17 metal plate 20
piezoelectric member 20 rear load unit (Insulating damping member) 31 metal plate 32 top
portion 33 side wall portion 34 ridge portion 100 ultrasonic flowmeter 112a support portion
212a support portion
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