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JP2003348681

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DESCRIPTION JP2003348681
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer and an ultrasonic flowmeter which measure the flow rate or flow rate of
gas or liquid by ultrasonic waves.
[0002]
2. Description of the Related Art Conventionally, as an ultrasonic transducer used in an ultrasonic
flow rate measuring apparatus of this type, for example, JP-A-11-322592 is known, and a
piezoelectric body is provided on the inner surface of the top of the case. An acoustic matching
layer is provided on the part.
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 11-325992
[0004]
However, in the conventional configuration, the acoustic matching layer is merely provided, and
no consideration has been made on an appropriate acoustic matching layer, piezoelectric
material, and case.
[0005]
In particular, no optimum combination of an acoustic matching layer, a piezoelectric body, and a
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case has been considered in terms of sensitivity of transmission and reception, and it has not
been described in terms of efficiency and reliability.
[0006]
And, in recent gas flowmeters, the type of gas used and the measurement accuracy (for example,
the accuracy required for the flow measurement device for city gas is 0.5 nsec or more, and the
ultrasonic transducer has more accuracy than this) From the point of demand), the functional
improvement of the ultrasonic transducer is desired, and the functional improvement of the
ultrasonic transducer is also desired from such industrial needs.
[0007]
In particular, the ultrasonic transducer performs its function by receiving an ultrasonic signal
transmitted from one ultrasonic transducer by the other ultrasonic transducer, but at that time
the sensitivity of transmission and reception Is a problem.
When the sensitivity is improved, the measurement accuracy is improved, and it is economical
because there is no need to supply power more than necessary to the piezoelectric body.
[0008]
An object of the present invention is to solve the above-mentioned problems, and to improve the
sensitivity of an ultrasonic transducer and to improve the measurement characteristics of an
ultrasonic flowmeter using it, and an ultrasonic flow rate using it Provide a measure.
[0009]
[Means for Solving the Problems] In order to achieve the above object, the present invention is
configured as follows.
[0010]
According to the first aspect of the present invention, a plate-like member, an acoustic matching
layer disposed on one surface of the plate-like member via an adhesive layer, and a face provided
with the acoustic matching layer of the plate-like member And the piezoelectric body disposed on
the opposite side to the surface via the bonding layer, and the installation area of the acoustic
matching layer is not less than the bonding area where the piezoelectric body is bonded to the
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plate-like member, or the piezoelectric body is the Provided is an ultrasonic transducer having an
area equal to or more than the area facing the acoustic matching layer via a plate-like member.
[0011]
Further, according to the second aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and the
acoustic matching layer of the plate-like member are provided. Surface of the plate-like member
facing the acoustic matching layer, the plate-like member and the acoustic matching layer form
the adhesive layer. Provided is an ultrasonic transducer having a bonding area or more which is
joined via an interface or a facing area or more in which the acoustic matching layer faces the
plate-like member.
[0012]
Further, according to the third aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and the
acoustic matching layer of the plate-like member are provided. Surface of the plate-like member
facing the piezoelectric body, the plate-like member and the piezoelectric body being joined via
the adhesive layer. An ultrasonic transducer having a bonding area or more, or an opposing area
or more in which the plate-like member and the piezoelectric body face each other is provided.
[0013]
Further, according to the fourth aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and the
acoustic matching layer of the plate-like member are provided. And the piezoelectric matching
the acoustic matching layer above the bonding area of the surface where the piezoelectric
member is bonded to the plate-like member, or the piezoelectric The area is equal to or greater
than the facing area in which the body faces the acoustic matching layer through the plate-like
member, and the facing area of the plate-like member is a bonding area in which the plate-like
member and the acoustic matching layer are joined via the adhesive layer. An ultrasonic
transducer, which has the above-mentioned or the above-mentioned acoustic matching layer
equal to or larger than the facing area facing the plate-like member, is provided.
[0014]
Further, according to the fifth aspect of the present invention, there is provided a plate-like
member, an acoustic matching layer disposed on one surface of the plate-like member via an
adhesive layer, and the acoustic matching layer of the plate-like member. And an opposite
surface of the piezoelectric body disposed via a bonding layer, the opposing area of the adhesive
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layer is greater than the bonding area of the bonding surface where the piezoelectric body is
bonded to the plate-like member, or the piezoelectric An ultrasonic transducer is provided, the
body of which is equal to or greater than an opposing area facing the adhesive layer.
[0015]
According to the sixth aspect of the present invention, a plate-like member, an acoustic matching
layer disposed on one surface of the plate-like member via an adhesive layer, and the acoustic
matching layer of the plate-like member are provided. And a piezoelectric material disposed via a
bonding layer on the surface opposite to the surface, and the opposing area of the adhesive layer
is not less than the bonding area of the acoustic matching layer to be bonded to the plate-like
member, or the acoustic matching layer An ultrasonic transducer is provided, which is equal to or
greater than an opposing area facing the adhesive layer.
[0016]
According to a seventh aspect of the present invention, there is provided the ultrasonic
transducer according to any one of the first to seventh aspects, wherein the area of the acoustic
matching layer is 100 to 110% of the area of the plate-like member. Do.
[0017]
According to an eighth aspect of the present invention, there is provided a flow rate measuring
unit through which a fluid to be measured flows, and a pair according to any one of the modes
according to any one of 1 to 7 provided in the flow rate measuring unit to transmit and receive
ultrasonic waves. There is provided an ultrasonic flowmeter comprising a sound wave transducer,
a measurement circuit for measuring a propagation time between the ultrasonic transducers, and
a flow rate calculating means for calculating a flow rate based on a signal from the measurement
circuit.
[0018]
According to the ninth aspect of the present invention, the pair of ultrasonic transducers have
substantially the same shape, and the frequency characteristic phase relationship of the
impedance of the pair of ultrasonic transducers in the working range of the frequency of 200
KHz to 750 KHz. The ultrasonic flowmeter according to the eighth aspect, wherein the number is
0.80 or more.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
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described in detail below with reference to the drawings.
[0020]
First, various forms of the present invention will be described before the ultrasonic transducer
according to various embodiments of the present invention and an ultrasonic flow meter using
the ultrasonic transducer are described in detail.
[0021]
According to the first aspect of the present invention, a plate-like member, an acoustic matching
layer disposed on one surface of the plate-like member via an adhesive layer, and a face provided
with the acoustic matching layer of the plate-like member And a piezoelectric body disposed on
the opposite surface via a bonding layer, the installation area of the acoustic matching layer is
equal to or larger than the bonding area where the piezoelectric body is bonded to the plate-like
member, or the piezoelectric body is the plate It is an ultrasonic transducer which is more than
the area which counters the above-mentioned acoustic matching layer via a loop member.
In the case of an ultrasonic transducer which also serves as transmission and reception, the
ultrasonic signal (or sound pressure) generated from the piezoelectric body is a plate when the
acoustic matching layer is larger than the piezoelectric body which is the drive source. The
propagated ultrasonic signal (or sound pressure) propagated to the acoustic matching layer
through the rod-like member hardly decreases.
[0022]
On the other hand, when the facing area of the acoustic matching layer is smaller than the
bonding area of the piezoelectric body and the plate member, only a part of the ultrasonic signal
(or sound pressure) generated by the piezoelectric can be transmitted to the acoustic matching
layer. The sensitivity is reduced.
Also, the reception sensitivity is not a problem if the acoustic matching layer is larger than the
piezoelectric body, but if the acoustic matching layer is smaller than the piezoelectric body, an
ultrasonic signal (or sound pressure) propagating to the piezoelectric body Lowers the energy
density of the receiver and lowers the reception sensitivity.
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[0023]
Further, according to the second aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and an
acoustic matching layer of the plate-like member are provided. The surface opposite to the
surface is provided with a piezoelectric member disposed via a bonding layer, and the area of the
plate member facing the acoustic matching layer is determined by bonding the plate member and
the acoustic matching layer via an adhesive layer The ultrasonic transducer has a bonding area
or more, or an acoustic matching layer equal to or more than an opposing area facing the platelike member, and can suppress a decrease in the propagated ultrasonic signal.
[0024]
On the other hand, when the acoustic matching layer is larger than the plate-like member, the
rigidity of the region other than the bonding area is insufficient.
Therefore, the mechanical strength is also low, which is unreliable.
In addition, from the acoustic point of view, the area other than the bonding area causes
unnecessary vibration, and it is easy to generate a vibration mode different from the main
vibration mode propagated in the bonding area.
Therefore, the directivity and sensitivity of the ultrasonic signal are adversely affected.
[0025]
Further, according to the third aspect of the present invention, a plate-like member, an acoustic
matching layer provided on one surface of the plate-like member via an adhesive layer, and an
acoustic matching layer of the plate-like member are provided. The piezoelectric member is
provided on the surface opposite to the surface via a bonding layer, and the opposing area of the
plate member to the piezoelectric member is such that the plate member and the piezoelectric
member are bonded via an adhesive layer. It is an ultrasonic transducer which is more than the
bonding area of the above, or more than the opposing area where the above-mentioned plate-like
member and the above-mentioned piezoelectric body oppose, and can control the fall of the
ultrasonic wave signal propagated.
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[0026]
On the other hand, when the plate-like member is smaller than the piezoelectric body, the effect
as the plate-like member is obviously reduced or hardly achieved.
[0027]
Further, according to the fourth aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and an
acoustic matching layer of the plate-like member are provided. The piezoelectric member is
provided on the surface opposite to the surface via a bonding layer, and the opposing area of the
acoustic matching layer is equal to or larger than the bonding area of the surface where the
piezoelectric is bonded to the plate-like member, or the piezoelectric is plate-like More than the
opposing area facing the acoustic matching layer through the member, and the opposing area of
the plate member is the joining area over which the plate member and the acoustic matching
layer are joined via the adhesive layer, or the acoustic matching layer is a plate member It is an
ultrasonic transducer which is equal to or larger than the opposing area facing the surface of the
ultrasonic wave, and can almost suppress the reduction of the propagated ultrasonic wave signal.
[0028]
Further, according to the fifth aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and an
acoustic matching layer of the plate-like member are provided. The piezoelectric member is
provided on the surface opposite to the surface via a bonding layer, and the opposing area of the
adhesive layer is not less than the bonding area of the bonding surface at which the piezoelectric
member is bonded to the plate-like member, or the piezoelectric Is an ultrasonic transducer
which is equal to or larger than the facing area facing the adhesive layer, and it is possible to
almost suppress the reduction of the propagated ultrasonic signal.
[0029]
An adhesive layer for acoustically bonding and physically bonding the acoustic matching layer
and the plate member will be described.
When the adhesive layer is smaller than the bonding area or opposing area of the plate-like
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member and the acoustic matching layer, the ultrasonic signal transmitted from the piezoelectric
body to the plate-like member is propagated to the acoustic matching layer through the adhesive
layer. Propagation efficiency is reduced and transmission sensitivity is reduced.
On the other hand, also in the receiving sensitivity, the ultrasonic signal propagated to the
acoustic matching layer is propagated to the plate-like member via the adhesive layer.
Thus, if the adhesive layer is smaller than the acoustic matching layer, the ultrasound signal
received at the acoustic matching layer is reduced because it decreases as the area decreases.
Here, the facing area indicates an area where the plate-like member and the acoustic matching
layer face each other and overlap.
The adhesive strength between the acoustic matching layer and the plate-like member may be
mentioned as one index of the reliability, but the adhesive strength tends to depend on the area
when the film thickness of the adhesive layer is constant.
Therefore, by setting the adhesive layer to a bonding area or more of the plate-like member and
the acoustic matching layer, the adhesive strength can be enhanced and the reliability can be
improved.
[0030]
Further, according to the sixth aspect of the present invention, a plate-like member, an acoustic
matching layer disposed on one surface of the plate-like member via an adhesive layer, and the
acoustic matching layer of the plate-like member are provided. And a piezoelectric material
disposed via a bonding layer on the surface opposite to the surface, and the opposing area of the
adhesive layer is not less than the bonding area of the acoustic matching layer to be bonded to
the plate-like member, or the acoustic matching layer Is an ultrasonic transducer which is equal
to or larger than the facing area facing the adhesive layer, and it is possible to almost suppress
the reduction of the propagated ultrasonic signal.
[0031]
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On the other hand, an adhesive layer for acoustically bonding and physically bonding the
piezoelectric body and the plate-like member will be described.
When the adhesive layer is smaller than the facing area or bonding area of the piezoelectric body
and the plate-like member, the ultrasonic signal transmitted from the piezoelectric body to the
plate-like member is transmitted to the plate-like member via the adhesive layer. As the area of
the layer decreases, the propagation efficiency decreases and the transmission sensitivity
decreases.
On the other hand, also in the receiving sensitivity, the ultrasonic signal propagated to the
acoustic matching layer and propagated to the plate-like member via the adhesive layer is
propagated to the piezoelectric body via the adhesive layer.
Thus, if the adhesion layer is smaller than the piezoelectric body, the ultrasonic signal received
by the piezoelectric body is reduced depending on the reduction in area.
[0032]
Further, according to the seventh aspect of the present invention, ultrasonic vibration of any one
of the above-mentioned first to sixth forms provided in the flow rate measuring part and in which
the fluid to be measured flows. An ultrasonic flowmeter comprising a probe, a measuring circuit
for measuring the propagation time between the ultrasonic transducers, and a flow rate
calculating means for calculating the flow rate based on the signal from the measuring circuit
The flow rate can be accurately measured (for example, at least 3 liters / h or more for city gas).
[0033]
In the present specification, the facing area indicates an area where the piezoelectric body, the
plate-like member, and the acoustic matching layer directly or indirectly face each other and
overlap.
[0034]
Hereinafter, an ultrasonic transducer according to various embodiments of the present invention
and an ultrasonic flow meter using the same will be described with reference to FIGS. 1 to 16.
[0035]
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First Embodiment FIG. 1 is an external view of an ultrasonic transducer according to a first
embodiment of the present invention, FIG. 2 is a cross-sectional view of the embodiment, and
FIGS. 3 and 4 are ultrasonic flowmeters according to the embodiment. The cross section is
shown.
[0036]
In FIG. 1, 1 is an ultrasonic transducer, 6 is a piezoelectric body serving as a driving source, 4 is
an acoustic matching layer for transmitting an ultrasonic wave to a transmission medium such as
gas or liquid, 3 is one side (outer wall surface) It is a plate-like member in which the acoustic
matching layer 4 is provided on 3 a and the piezoelectric body 6 is provided on the opposite side
(inner wall surface) 3 b. A matching layer 4 and a piezoelectric body 6 are provided.
The plate-like member 3 is a vibration propagation member that transmits the vibration of the
piezoelectric body 6 to the acoustic matching layer 4, and acoustically connects the piezoelectric
body 6 and the acoustic matching layer 4.
[0037]
Reference numeral 2 denotes a support for supporting the plate-like member 3. Specifically, the
outer periphery of the plate-like member 3 is engaged with and joined to the cylindrical inner
periphery.
In the first embodiment, the plate-like member 3 and the support 2 constitute a bottomed case
32 having a top 32a, a side wall 32b, and an opening 32c.
Reference numeral 5 denotes a flange portion for joining the ultrasonic transducer 1 to a side
wall portion forming an attachment hole of the ultrasonic transducer 1 connected to the flow
path of the ultrasonic flow meter as described later.
[0038]
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In FIG. 2, 6 is a piezoelectric body disposed on the inner wall surface of the plate-like member 3,
7 is a terminal plate fixed to the flange portion 5, 8a and 8b are terminals provided on the
terminal plate 7, 9 is a terminal An insulator that insulates 8a and 8b, and 10 is a conductive
rubber for electrically connecting the piezoelectric body 6 and the terminal 8a.
The piezoelectric body 6 is closed by the bottomed case 32 and the terminal plate 7 and sealed
with an inert gas.
[0039]
FIG. 3 shows a cross-sectional view of an ultrasonic flowmeter 100 provided with the ultrasonic
transducer 1.
[0040]
A schematic configuration of the ultrasonic flowmeter 100 includes a flow rate measuring unit
11 for measuring the flow rate of the fluid to be measured introduced from an inlet passage
100a connected to a supply pipe to which the fluid to be measured such as gas is supplied. An
outlet path 100b communicating with the unit 11 and guiding the fluid to be measured to the
outside, and a pair of ultrasonic transducers 17 and 18 provided in the flow rate measuring unit
11 to transmit and receive ultrasonic waves (each to the ultrasonic transducer 1 It corresponds.
And a measurement circuit 101 that measures the propagation time between the ultrasonic
transducers 17 and 18, and a flow rate calculation unit 102 that calculates the flow rate based
on the signal from the measurement circuit 101.
Therefore, an ultrasonic wave is transmitted from one ultrasonic transducer 17 toward the other
ultrasonic transducer 18, and an ultrasonic wave that has passed through a fluid to be measured
such as gas is received by the other ultrasonic transducer 18. Thus, the measuring circuit 101
measures the propagation time between the ultrasonic transducers 17 and 18.
Then, conversely, ultrasonic waves are transmitted from the other ultrasonic transducer 17
toward the one ultrasonic transducer 18, and ultrasonic waves that have passed through the fluid
to be measured such as gas are the one ultrasonic transducer. By being received at 18, the
measuring circuit 101 measures the propagation time between the ultrasonic transducers 17, 18.
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Thus, the propagation time of the ultrasonic wave is measured between the pair of ultrasonic
transducers 17 and 18 a predetermined number of times, and the flow rate of the fluid to be
measured such as gas is calculated based on the average value by the flow rate computing means
102 I am trying to do it.
Therefore, the ultrasonic transducers 17 and 18 can transmit and receive.
Here, the measurement circuit 101 and the flow rate calculation means 102 constitute a flow
rate calculation system.
[0041]
As a practical example, in the flow rate measurement unit 11, a household gas meter for
measuring the flow rate of LP gas or natural gas as a material is assumed to be an aluminum
alloy die cast.
Then, as shown in FIG. 4, the upper plate portion 15 is screwed to the end faces of the side wall
portions 12 and 13 constituting the gas flow path via the sealing material 14 made of, for
example, a cork material, and the flow path cross section 16 is rectangular. Make up things.
Further, as shown in FIG. 3, the ultrasonic transducers 17 and 18 are provided obliquely on the
side wall portions 12 and 13 so that the transmission / reception wavefronts for transmitting and
receiving the ultrasonic waves face each other.
Specifically, it is fixed to the attachment holes 19 and 20 of the ultrasonic transducers 17 and 18
provided in the side wall portions 12 and 13 via the seal members 21 and 22 made of, for
example, an O-ring.
This is one example, and the present invention is not limited thereto.
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[0042]
On the other hand, the plate-like member 3 is sandwiched between the acoustic matching layer 4
and the piezoelectric body 6 and plays a role as a joint or fixing portion of the acoustic matching
layer 4 and the piezoelectric body 6 from the physical viewpoint. Also, from the acoustic point of
view, it is a connector for transmitting an ultrasonic signal (or sound pressure) from the acoustic
matching layer 4 to the piezoelectric body 6 to the piezoelectric body 6 from the acoustic
matching layer 4. Play. Therefore, the physical bonding area of the acoustic matching layer 4, the
plate member 3, and the piezoelectric body 6 is very important.
[0043]
Next, the operation of the ultrasonic transducer 1 will be described and the propagation
efficiency of transmission will be considered.
[0044]
The ultrasonic signal transmitted from the piezoelectric body 6 is propagated to the acoustic
matching layer 4 through the adhesive layer 31, the plate member (vibration propagation
member) 3, and the adhesive layer 30.
[0045]
(Consideration of propagation efficiency of transmission between the piezoelectric body and the
plate-like member) Propagation efficiency from the piezoelectric body 6 to the plate-like member
3 when an ultrasonic signal transmitted from the piezoelectric body 6 is propagated to the platelike member 3 Depends on the size of the coupling area in which the piezoelectric body 6 serving
as the driving source is acoustically coupled to the plate-like member 3.
The bonding area substantially matches the bonding area in which the plate-like member 3, the
piezoelectric body 6, and the bonding layer 31 overlap when the piezoelectric body 6 is bonded
to the plate-like member 3 using the bonding layer 31.
Therefore, in order to efficiently transmit an ultrasonic signal from the piezoelectric body 6 to
the plate-like member 3, the plate-like member 3 is not less than the bonding area of the plate-
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like member 3 and the piezoelectric body 6 (the plate-like member 3 and the piezoelectric body 6
or more) is desirable.
[0046]
Furthermore, the ultrasonic signal propagated to the plate member 3 is propagated to the
acoustic matching layer 4 via the adhesive layer 30 joining the plate member 3 and the acoustic
matching layer 4.
[0047]
(Consideration of propagation efficiency of transmission between the plate-like member and the
acoustic matching layer) The acoustic coupling area of the plate-like member 3 and the acoustic
matching layer 4 is the same as that of the plate-like member 3 and the acoustic matching layer
4. Match the overlapping area.
Therefore, in order to efficiently transmit the ultrasonic signal from the plate member 3 to the
acoustic matching layer 4, the plate member 3 is not less than the bonding area of the plate
member 3 and the acoustic matching layer 4 (the acoustic matching layer 4 More than the
opposing area facing the plate-like member 3 is desirable.
[0048]
From the above, the area where the acoustic coupling areas of the piezoelectric body 6, the platelike member 3 and the acoustic matching layer 4 overlap is the effective coupling area, which
substantially coincides with the joining area for joining each of them. Accordingly, the acoustic
matching layer 4 needs to have a bonding area or more of the piezoelectric body 6 and the plate
member 3 or a facing area or more in which the piezoelectric body 6 faces the acoustic matching
layer 4 and the area is smaller than the above condition. Since the ultrasonic signal generated by
the piezoelectric body 6 is propagated only in the proportion of the coupling area, the
propagation efficiency is lowered and the transmission sensitivity of the ultrasonic wave is also
lowered. Therefore, the area in which the coupling areas of the piezoelectric body 4, the plate
member 3, and the acoustic matching layer 6 overlap is an effective acoustic coupling area and is
a physical effective joining area.
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[0049]
Next, consider the case of receiving an ultrasound signal.
[0050]
In the case of reception, it is the opposite propagation step as in the case of transmission.
That is, the ultrasonic signal received from the acoustic matching layer 4 is propagated to the
piezoelectric body 6 through the adhesive layer 30, the plate member 3, and the adhesive layer
31.
[0051]
(Consideration of propagation efficiency of reception between the plate-like member and the
acoustic matching layer) The ultrasonic signal received by the acoustic matching layer 4 is
through the adhesive layer 30 joining the acoustic matching layer 4 and the plate-like member 3
As it is propagated to the plate member 3, the bonding area of the plate member 3 and the
acoustic matching layer 4 matches the overlapping area of the plate member 3, the acoustic
matching layer 4, and the adhesive layer 30 as in the case of transmission. . Therefore, in order
to efficiently transmit an ultrasonic signal from the acoustic matching layer 4 to the plate-like
member 3, the plate-like member 3 is not less than the bonding area of the plate-like member 3
and the acoustic matching layer 4 (the acoustic matching layer 4 is plate-like It is desirable that
the opposing area facing the member 3 be equal to or greater than the opposing area.
[0052]
Further, the ultrasonic signal transmitted to the plate member 3 is transmitted to the
piezoelectric body 6 through the adhesive layer 31 which joins the plate member 3 and the
piezoelectric body 6.
[0053]
(Consideration of propagation efficiency of reception between the plate-like member and the
piezoelectric body) The bonding area between the plate-like member 3 and the piezoelectric body
04-05-2019
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6 coincides with the overlapping area of the plate-like member 3 with the piezoelectric body 6
and the adhesive layer 31 .
Therefore, in order to efficiently transmit the ultrasonic signal from the plate member 3 to the
piezoelectric body 6, the plate member 3 is not less than the bonding area of the plate member 3
and the piezoelectric body 6 (the plate member 3 and the piezoelectric body 6 Is preferably equal
to or greater than the opposing area).
[0054]
From the above, as in the transmission, the overlapping area of the bonding areas of the
piezoelectric body 6, the plate member 3 and the acoustic matching layer 4 is an acoustically
effective bonding area or a physically effective bonding area.
[0055]
Therefore, at the time of reception as well as at the time of transmission, the acoustic matching
layer 4 needs to have a bonding area or more of the piezoelectric body 6 and the plate member 3
or a facing area or more where the piezoelectric body 6 faces the acoustic matching layer 4 If
smaller than the above condition, the ultrasonic signal generated by the piezoelectric body 6 is
propagated only in the proportion of the bonding area, so the propagation efficiency is lowered
and the ultrasonic wave reception sensitivity is also lowered.
[0056]
Next, the adhesive layer 31 will be considered.
[0057]
The adhesive layer 31 for bonding the piezoelectric body 6 and the plate member 3 has a role of
not only physically bonding the piezoelectric body 6 and the plate member 3 but also for
acoustically bonding.
The adhesive 31 is, for example, an epoxy-based thermosetting adhesive, and temporarily bonds
the piezoelectric body 6 and the plate member 3 in a viscous state, and is cured by heat or the
like to be permanently bonded.
04-05-2019
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Then, when the adhesive layer 31 has a smaller facing area facing the piezoelectric body 6 and
the plate-like member 3 after curing for bonding, the ultrasonic signal generated from the
piezoelectric body 6 is applied to the plate-like member 3 At the time of propagation, the
bonding area between the piezoelectric body 6 and the plate-like member 3 becomes small, and
the propagation efficiency is lowered.
Therefore, the transmission sensitivity of the ultrasonic wave is reduced.
[0058]
The adhesive of the adhesive layer 31 may be a urethane, cyano or silicone resin adhesive.
[0059]
On the other hand, in the reception in which the ultrasonic signal propagated from the acoustic
matching layer 4 is propagated to the plate-like member 3 and is propagated to the piezoelectric
body 6 via the adhesive layer 31, the facing area facing the plate-like member 3 is the
piezoelectric body If it is smaller than 6, when the ultrasonic signal propagated to the plate-like
member 3 is propagated to the piezoelectric body 6, the bonding area between the piezoelectric
body 6 and the plate-like member 3 becomes small, and the propagation efficiency decreases. ,
The ultrasonic wave reception sensitivity is reduced.
[0060]
Therefore, in the adhesive layer 31 for bonding the plate-like member 3 and the piezoelectric
body 6, the area after curing of the adhesive layer 31 is equal to or larger than the bonding area
of the piezoelectric body 6 and the plate-like member 3 (the piezoelectric 6 faces the adhesive
layer 31) It is possible to minimize the degradation of the propagation efficiency by
[0061]
Further, in terms of physical bonding, that is, in terms of adhesive strength, the area after curing
of the adhesive layer 31 is required to be equal to or more than the facing area where the
piezoelectric body 6 faces the plate member 3.
When the area of the adhesive layer 31 after curing is smaller than the area of the piezoelectric
04-05-2019
17
body 6 facing the plate-like member 3, the adhesive layer 31 does not wrap around the
piezoelectric body 6 so as to surround it, so substantial bonding As the area is reduced and the
anchor effect can hardly be expected, the adhesive strength is reduced.
Therefore, the area after curing of the adhesive layer 31 needs to be equal to or larger than the
joint area of the piezoelectric body 6 and the plate-like member 3 or to be equal to or larger than
the opposing area where the piezoelectric body 6 faces the adhesive layer 31. The adhesive
strength can be improved and the reliability can be improved.
[0062]
Similarly, the adhesive layer 30 for joining the acoustic matching layer 4 and the plate member 3
is also a thermosetting adhesive, and it is possible not only to physically join the acoustic
matching layer 4 and the plate member 3 but also for acoustically. It has a role of combining.
Therefore, when the bonding layer 30 after curing is cured and the opposing area facing the
acoustic matching layer 4 and the plate-like member 3 is smaller than that of the acoustic
matching layer 4, the ultrasonic signal generated from the piezoelectric body 6 is a plate-like
member 3. When propagating from the plate-like member 3 to the acoustic matching layer 4, the
bonding area of the plate-like member 3 and the acoustic matching layer 4 becomes small, the
propagation efficiency is lowered, and the transmission sensitivity of the ultrasonic wave is
lowered.
[0063]
On the other hand, when the ultrasonic signal is received from the acoustic matching layer 4 and
then propagated from the acoustic matching layer 4 to the plate-like member 3, the adhesive
layer 30 is transmitted to the plate-like member 3 via the adhesive layer 30. In the case where
the ultrasonic signal transmitted to the acoustic matching layer 4 is propagated to the plate
member 3 when the opposing area facing the plate member 3 and the acoustic matching layer 4
is smaller than the acoustic matching layer 4 after curing. Since the bonding area between the
matching layer 4 and the plate-like member 3 is reduced and the propagation efficiency is
reduced, the ultrasonic wave reception sensitivity is reduced.
[0064]
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Therefore, the area after curing of the adhesive layer 30 for bonding the acoustic matching layer
4 and the plate-like member 3 is not less than the bonding area of the acoustic matching layer 4
or more than the opposing area where the acoustic matching layer 4 faces the adhesive layer 30.
It is possible to minimize the degradation of the propagation efficiency.
Further, in terms of physical bonding, that is, in terms of adhesive strength, the area after curing
of the adhesive layer 30 is required to be equal to or more than the facing area where the
acoustic matching layer 4 faces the plate member 3. If the area of the adhesive layer 30 after
curing is smaller than the area of the acoustic matching layer 4 facing the plate member 3, the
adhesive layer 30 does not wrap around the acoustic matching layer 4 so that the adhesive layer
30 substantially does not wrap around. The bonding area is reduced, and almost no anchor effect
can be expected. Therefore, also from the viewpoint of physical bonding, the area after curing of
the adhesive layer 30 needs to be equal to or larger than the joint area of the acoustic matching
layer 4 or equal to or larger than the opposing area where the acoustic matching layer 4 faces
the adhesive layer 30. The adhesive strength can be improved, and the improvement of the
reliability can be ensured.
[0065]
The relationship described above in the first embodiment always holds regardless of the shapes
and sizes of the acoustic matching layer 4, the plate member 3, and the piezoelectric body 6.
[0066]
Also, as shown in FIGS. 8 and 9, the plate-like member 3 and the support 2 are not separately
configured, but as shown in FIG. 8, the plate-like member and the support are integrally formed.
The same effects can be obtained in the second embodiment using the bottomed case 33 and the
third embodiment in which the adhesive layer is not present as shown in FIG.
[0067]
EXAMPLES The following is an experimental discussion of the first embodiment of the present
invention, based on specific examples.
[0068]
(Example 1) In order to confirm the effective area of the acoustic matching layer 4 with respect
to the piezoelectric body 6, the sound pressure generated from the piezoelectric body 6 using the
three-dimensional simulation by the finite element method (FEM) We examined how it affected
04-05-2019
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the situation.
[0069]
The structure is as shown in FIG. 2, and it is a piezoelectric body / adhesive / case / adhesive /
acoustic matching layer, and for the piezoelectric body, a piezoelectric constant d31 = −185.9 ×
10 −12 m / V, d31 = 366 .5 x 10-12 m / V, d15 = 578.5 x 10-12 m / V, elastic constant s11 =
15.8 x 10-12 m2 / N, s33 = 17.6 x 10-12 m2 / N, s12 , S13 are calculated from the frequency
constant and the electromechanical coupling coefficient (frequency constant n1 = 1960 Hz.m, n2
= 1430 Hz.m, n3 = 1410 Hz.m, n4 = 1980 Hz.m, n2 = 856 Hz.m, electromechanical coupling
coefficient kr = 0.65, k31 = 0.38, k33 = 0.71, kt = 0.50, k15 = 0.70).
Further, Poisson's ratio: 0.3, dielectric constant: ε 33 = 1950 × 0.9, ε = 2130 × 0.9, density:
7.70 g / cm 3, machine Q: 70 (attenuation ratio 0.0007114), support The plate-like member of
the case consisting of the plate and the plate-like member has a Young's modulus: 0.178 (1012 N
/ m2), a Poisson's ratio: 0.29, a density 7.93 g / cm3, an adhesive has a Young's modulus: 0.003,
Poisson's ratio 0.3, density 1.4 g / cm 3, damping ratio: 0.01, acoustic matching layer: Young's
modulus: 0.001906 N / m 2, Poisson's ratio: 0.3718, modulus of transverse elasticity: G =
0.0006946 N / m 2 Calculation was performed as shear wave velocity (2 MHz): 1167 m / s
(measured value), longitudinal wave velocity: 2494 m / s (computed from measured value of
shear wave), machine Q: 50 (damping ratio: 0.001).
[0070]
The results are shown in FIGS.
FIGS. 5A and 5B are obtained by measuring the frequency characteristics of the impedance and
the phase and by performing simulation analysis.
The left is an actual measurement value obtained by supplying an AC voltage to the ultrasonic
transducer and changing its frequency to measure the output impedance, and the right is an
analysis value.
04-05-2019
20
It can be seen that the measured values and the analyzed values fit very well. In particular, when
resonance frequencies A to D are compared, respective resonances can be seen at substantially
the same frequency. The respective resonance modes are analyzed as follows: A: main resonance
(longitudinal wave) f = 475 KHz, B: main resonance (transverse wave) f = 190 KHz, C: secondary
resonance 590 KHz, D: split resonance f = 430 KHz, E: anti-resonance f = 650 KHz. Among them,
the resonance modes that greatly contribute to the generation of the ultrasonic signal are A: main
resonance (longitudinal wave) and C: secondary resonance. Ultrasonic signals are generated in
these two resonance modes. The modal analysis results at each resonance frequency are
illustrated.
[0071]
FIG. 6A is a diagram showing the displacement of the piezoelectric body, the plate-like member,
and the acoustic matching layer at a main resonance (longitudinal wave) at f = 475 KHz as a
concentration distribution. As for the displacement, it can be seen that displacement is
particularly large at a bonding surface of the piezoelectric body and the plate-like member, or at
a bonding surface of the piezoelectric body to the plate-like member, centering on the central
portion of the acoustic matching layer.
[0072]
Further, FIG. 6B is a view showing the displacement of each of the piezoelectric body, the platelike member, and the acoustic matching layer at C: secondary resonance at 590 KHz as a
concentration distribution. The displacement is particularly large in the vicinity of the outer
periphery of the acoustic matching layer, particularly at the bonding surface between the
piezoelectric body and the plate-like member, or at the bonding face to the plate-like member of
the piezoelectric body, as in the main resonance of A. I understand.
[0073]
Then, the main resonance and the secondary resonance affect the vibration of the acoustic
matching layer, and the composite component thereof becomes a composition with FIGS. 6A and
6B, and as a result, the acoustic matching layer is substantially piezoelectric. A large
displacement occurs particularly at the bonding surface with the plate-like member or at the
bonding surface of the piezoelectric body to the plate-like member.
04-05-2019
21
[0074]
FIGS. 7A and 7B are diagrams showing the displacements of FIGS. 6A and 6B from just above the
acoustic matching layer.
[0075]
FIG. 7A shows the displacement of each of the piezoelectric body, the plate-like member, and the
acoustic matching layer at a main resonance (longitudinal wave) at f = 475 KHz as a
concentration distribution.
Further, FIG. 7B shows the displacement of each of the piezoelectric body, the plate-like member,
and the acoustic matching layer at C: secondary resonance at 590 KHz as a concentration
distribution.
In this model, the piezoelectric element is divided into four so that the side facing the plate
member is processed in a slit shape. Also, the case is composed of a cylindrical support and a
plate-like member (here, assuming that the plate-like member and the support are continuously
connected with the same material), the acoustic matching layer is slightly smaller than the platelike member It had a circular shape. In the main resonance, a large displacement is mainly
observed around the center two divided into four. The displacement area is slightly larger than
the bonding area where the piezoelectric body is bonded to the plate-like member.
[0076]
On the other hand, in the secondary resonance in FIG. 7B, large displacements are observed near
the center and the two outer sides of the piezoelectric body, and the bonding area or bonding
area of the piezoelectric body and the plate member is the main drive range. It is a range where
the main displacement can be detected. Since the plate-like member is circular, it is assumed that
the boundary between the support and the cylindrical portion is very high in rigidity. Therefore,
displacement distribution can be seen in the shape of the top surface portion (here, a plate-like
member) in the vibrating portion.
[0077]
From the above points, it is clear that the acoustic matching layer is required to be equal to or
04-05-2019
22
larger than the bonding area of the piezoelectric body and the plate-like member, or to be equal
to or larger than the facing area where the piezoelectric body faces the acoustic matching layer.
[0078]
Example 2 In order to confirm the results of the three-dimensional simulation analysis of
Example 1, the following study was conducted.
The size of the piezoelectric body was a rectangular parallelepiped having a height, a height, and
a height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit
structure is provided on the side facing the plate member of the piezoelectric body. The acoustic
matching layer mainly used two types of shapes. One is a circular one similar to the threedimensional analysis, and the other is a square one close to the shape of the piezoelectric in plan
view. The circular one has the smallest size that can wrap the piezoelectric body, that is, the
circular shape whose diameter is the diagonal length (10.46 mm), and the square one has the
same size (7.4 mm × 7.4 mm) as the piezoelectric body. As a standard, the area of each acoustic
matching layer was similarly reduced from 50% to enlarged to 150%, and the transmission /
reception sensitivity of the ultrasonic transducer was measured in each shape. The results are
shown in Table 1.
[0079]
The measurement was performed under the conditions of a measurement voltage of 30 V and a
measurement frequency of 500 KHz with an interval of 70 mm between ultrasonic transducers.
[0081]
From the above results, the installation area (facing area) of the acoustic matching layer is the
bonding area where the piezoelectric body is bonded to the plate-like member (reduction
magnification ratio of 100% or more) or the piezoelectric body is facing the plate-like member
facing If the area is smaller than the area, the transmission sensitivity and the reception
sensitivity decrease extremely, and conversely, the bonding area (reduction magnification ratio
100% or more) where the piezoelectric member bonds to the plate member or the piezoelectric
member faces the plate member By setting the area or more, there is almost no change in
transmission sensitivity and reception sensitivity, and the difference in sensitivity change is
small, so that it is possible to suppress the decrease in propagation efficiency and prevent the
decrease in transmission / reception sensitivity.
04-05-2019
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[0082]
Example 3 Next, a plate-like member and a piezoelectric body were examined.
The size of the piezoelectric body was a rectangular parallelepiped having a height, a height, and
a height of 7.4 mm × 7.4 mm × 2.65 mm.
Similar to the three-dimensional analysis, a slit structure is provided on the side facing the plate
member of the piezoelectric body. The plate member was made circular and square, and the area
of the plate member was changed to produce an ultrasonic transducer. The area of a circle whose
diameter is the minimum size that can enclose the piezoelectric body, that is, the diagonal length
(10.46 mm) and the bonding area of the piezoelectric body of 7.4 mm × 7.4 mm, respectively,
50% of the area is similar The reduced size was expanded to 150%, and the transmission and
reception sensitivity of the ultrasonic transducer was measured with the shape of each plate
member. Table 2 shows the results. The measurement conditions are the same as in Example 2.
[0084]
From the results shown in Table 2, in both the circular and square plate members, when the plate
member is reduced relative to the piezoelectric body (the area ratio of the top is 100% or less),
the transmission sensitivity In the case where the receiving sensitivity is extremely reduced and
the plate member is increased relative to the piezoelectric member, the transmission sensitivity
and the receiving sensitivity hardly change and the difference in the sensitivity change is small.
[0085]
Since the area in which the piezoelectric body is acoustically coupled or physically joined to the
acoustic matching layer through the plate-like member is thus reduced, the transmission /
reception sensitivity is lowered.
However, when the area of the plate-like member is larger than that of the piezoelectric body, the
effective area for acoustic coupling hardly changes even if the plate-like member becomes large,
and therefore the transmission / reception sensitivity is hardly affected.
04-05-2019
24
[0086]
From the above results, it is preferable that the plate-like member be equal to or larger than the
bonding area of the plate-like member and the piezoelectric body, or more than the opposing
area where the plate-like member and the piezoelectric body are opposed.
[0087]
Example 4 Next, a plate member and an acoustic matching layer were examined.
The size of the piezoelectric body was a rectangular parallelepiped having a height, a height, and
a height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit
structure is provided on the bonding surface side of the piezoelectric body with the plate
member. The plate member was made circular and square, and the area of the acoustic matching
layer was changed to produce an ultrasonic transducer. Based on the smallest area that can
enclose the piezoelectric body, ie, the circular area whose diameter is the diagonal length (10.46
mm) and the same area as the bonding area of the piezoelectric body, each area is similarly
reduced by 50% to 150 What was expanded to% was produced, and the transmission-andreception sensitivity of the ultrasonic transducer was measured by each shape. Table 3 shows the
results. The measurement conditions are the same as in Example 2.
[0089]
From the above results, when the area of the acoustic matching layer is increased relative to the
area of the plate-like member, the area to be acoustically coupled does not change, but the
bonding area does not increase with the plate-like member. The area of free oscillation increases,
and modes different from the main resonance and the secondary resonance occur. Therefore, the
phenomenon that the transmission and reception sensitivity was reduced was observed. Also the
noise level has increased. On the other hand, when the area of the acoustic matching layer
decreases, the area of the piezoelectric body has a greater effect than the area of the plate-like
member, and the relationship between the piezoelectric and the acoustic matching layer, that is,
the results of examination in Example 2 (Table 1 The same tendency was observed as in
Therefore, the plate-like member needs to be more than the bonding area of the plate-like
member and the acoustic matching layer, or more than the facing area where the acoustic
matching layer faces the plate-like member, and the acoustic matching layer is the bonding area
of the piezoelectric and the plate-like member Above, or more than the facing area where the
04-05-2019
25
piezoelectric body faces the acoustic matching layer is required.
[0090]
Example 5 Next, the piezoelectric body and the adhesive layer 31 for bonding the piezoelectric
body and the plate member were examined. The size of the piezoelectric body was a rectangular
parallelepiped having a height, a height, and a height of 7.4 mm × 7.4 mm × 2.65 mm. Similar
to the three-dimensional analysis, a slit structure is provided on the bonding surface side of the
piezoelectric body with the plate member. The acoustic matching layer had the smallest area
(diameter 10.46 mm) that could cover the piezoelectric body. Moreover, the plate-like member
was made circular, the area of the adhesive layer 31 was changed, and the ultrasonic transducer
| vibrator was produced. Based on the maximum bonding area (7.4 mm × 7.4 mm) of the
piezoelectric body, the area of the adhesive layer 31 is similarly reduced by 50% to 150% and
manufactured, and transmission and reception of the ultrasonic transducer The sensitivity was
measured. Furthermore, the result of the reliability test by a heat cycle at -40 ° C to 80 ° C is
shown in Table 4. The measurement conditions are the same as in Example 2.
[0091]
:: no change in sensitivity, △: 10% or less in sensitivity decrease rate, ×: 50% or more in
sensitivity decrease rate
[0092]
From the results of Table 4, when the area of the adhesive layer 31 was reduced, a decrease in
transmission / reception sensitivity was observed.
Further, also from the result of the reliability test, when the area ratio is 70% or less, the
sensitivity reduction rate is 50% or more, and the reliability as an ultrasonic transducer is
reduced. Therefore, the area after curing of the adhesive layer 31 needs to be equal to or more
than the bonding area of the piezoelectric body, or more than the opposing area where the
piezoelectric body faces the adhesive layer 31.
[0093]
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Example 6 Next, the acoustic matching layer, and the adhesive layer 30 for joining the acoustic
matching layer and the plate member were examined. The size of the piezoelectric body was a
rectangular parallelepiped having a height, a height, and a height of 7.4 mm × 7.4 mm × 2.65
mm. Similar to the three-dimensional analysis, a slit structure is provided on the bonding surface
side of the piezoelectric body with the plate member. The acoustic matching layer had the
smallest area (diameter 10.46 mm) that could cover the piezoelectric body. Moreover, the platelike member was circular and the area was 128.84 mm 2, and the area of the adhesive layer 30
was changed to manufacture an ultrasonic transducer. Based on the maximum bonding area
(85.89 mm 2) of the acoustic matching layer, the area of the adhesive layer 30 is similarly
reduced by 50% to 150%, and the transmission and reception sensitivity of the ultrasonic
transducer is measured. did. Furthermore, the result of the reliability test by a heat cycle at -40
° C to 80 ° C is shown in Table 5.
[0094]
:: no change in sensitivity, △: 10% or less in sensitivity decrease rate, ×: 50% or more in
sensitivity decrease rate
[0095]
From the results of Table 5, when the area of the adhesive layer 30 was reduced, a decrease in
transmission / reception sensitivity was observed.
This is because the area of junction with the plate-like member is reduced and the acoustic
coupling area is reduced, which causes a reduction in propagation efficiency, and a factor that
causes the non-joined portion to generate a mode vibration different from the main resonance
mode. The sensitivity drops from
[0096]
Further, also from the result of the reliability test, when the area ratio is 70% or less, the
sensitivity reduction rate is 50% or more, and the reliability as an ultrasonic transducer is
reduced. Therefore, the area after curing of the adhesive layer 30 needs to be equal to or larger
than the bonding area of the acoustic matching layer, or to be equal to or larger than the
opposing area where the acoustic matching layer faces the adhesive layer 30.
04-05-2019
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[0097]
Although each of the above embodiments is described in relation to the plate-like member, the
same effect can be obtained even if the plate-like member is an integral-type, bottomed case
shown in FIGS. However, in Examples 3 and 4, since the experimental results differ depending on
the storage relationship between the piezoelectric body and the case, Examples 7 and 8 have the
integral bottomed type shown in FIGS. A case will be described using the second and third
embodiments.
[0098]
EXAMPLE 7 A case and a piezoelectric body were examined. The size of the piezoelectric body
was a rectangular parallelepiped having a height, a height, and a height of 7.4 mm × 7.4 mm ×
2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the bonding
surface side of the piezoelectric body with the case. The case was made into a bottomed
cylindrical shape and a bottomed box shape, and the area of the top of the case was changed to
produce an ultrasonic transducer. Based on a circular shape with a diameter that is the smallest
size that can enclose the piezoelectric body, ie, the diagonal length (10.46 mm), the area is
similarly reduced by 50% to 150%. The transmission and reception sensitivity of the ultrasonic
transducer was measured in each shape. Table 6 shows the results.
[0100]
From the results shown in Table 6, it can not be manufactured as an ultrasonic transducer in
both the open top cylindrical and box-shaped cases because the piezoelectric body does not enter
the case when the case is reduced. It is. However, when the case is larger than that of the
piezoelectric body, no decrease in the transmission / reception sensitivity is observed. On the
other hand, when the case area facing the piezoelectric body is large, the effective area to be
acoustically coupled hardly changes even if the case is large, so that the sensitivity is hardly
affected. From the above results, it is preferable that the case is equal to or larger than the
bonding area of the case and the piezoelectric body, or more than the opposing area where the
case and the piezoelectric body are opposed.
04-05-2019
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[0101]
Example 8 A case and an acoustic matching layer were examined. The size of the piezoelectric
body was a rectangular parallelepiped having a height, a height, and a height of 7.4 mm × 7.4
mm × 2.65 mm. Similar to the three-dimensional analysis, the piezoelectric body has a slit
structure on the side of the joint surface with the case. The case was made into a cylindrical
shape with a top surface and a bottomed box, and the area of the acoustic matching layer was
changed to produce an ultrasonic transducer. Based on a circular shape with a diameter that is
the smallest size that can enclose the piezoelectric body, ie, the diagonal length (10.46 mm), the
area is similarly reduced by 50% to 150%. The ultrasonic transmission / reception sensitivity of
the ultrasonic transducer was measured in each shape. Table 7 shows the results.
[0103]
From the above results, when the area of the acoustic matching layer is increased relative to the
area of the top surface of the case, although there is no change in the acoustically coupled area,
the case and the joint area do not increase. The area oscillating freely increases, and a mode
different from the main resonance and the secondary resonance is generated. Therefore, the
phenomenon that the transmission and reception sensitivity of the ultrasonic wave was reduced
was observed. Also the noise level has increased. On the other hand, when the area of the
acoustic matching layer decreases, the area of the piezoelectric body has a greater effect than the
area of the case, and the relationship between the piezoelectric and the acoustic matching layer,
that is, the results of examination in Example 2 (Table 1) Similar trends were seen. Therefore, the
case needs to be more than the bonding area of the case and the acoustic matching layer, or
more than the opposing area where the acoustic matching layer faces the case. Furthermore, the
acoustic matching layer is more than the bonding area of the piezoelectric and the case, or the
piezoelectric is acoustic. It is necessary to have at least the facing area facing the matching layer.
[0104]
Next, the relationship between the case (plate-like member) 3 and the acoustic matching layer 4
in one ultrasonic transducer 1, 17, 18 will be described. Here, the case where the area ratio of
the piezoelectric body and the acoustic matching layer is 100% based on the piezoelectric body
will be described.
04-05-2019
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[0105]
The range of the area ratio between the case (plate-like member) 3 and the acoustic matching
layer 4 is a range in which no abnormal resonance mode is generated, and the area of the
acoustic matching layer 4 is 15% of the area of the case (plate-like member) 3 150% is
preferable. 150% of the area of the case (plate-like member) 3 means that it is the same area as
the case top surface. When the area of the acoustic matching layer 4 is larger than 150% of the
area of the case (plate-like member) 3, an abnormal resonance mode is generated in the
frequency characteristic of the impedance, which makes it unusable. In addition, when the area
of the acoustic matching layer 4 is less than 15%, the shape anisotropy of the acoustic matching
layer itself in the thickness direction becomes strong, and different resonance modes are
generated.
[0106]
On the other hand, according to the area of the acoustic matching layer 4 and the graph of the
sensitivity reduction rate (during transmission), when the piezoelectric body 6 and the acoustic
matching layer 4 have the same shape, the sensitivity reduction rate is in the range of 25% or
less. When the area of the acoustic matching layer 4 is 35% to 150% of the area of the
piezoelectric body 6 and the shapes of the piezoelectric body 6 and the acoustic matching layer 4
are different, the area of the acoustic matching layer 4 is 45% to 150% of the area of the
piezoelectric body 6 It is preferable to use% (see FIG. 10 and FIG. 11). The reason is that if the
area of the acoustic matching layer 4 is less than (35% to 45%) of the area of the piezoelectric
body 6, the measurement performance (accuracy) is lowered due to being close to the detection
limit in the flow rate calculation system. If it exceeds 150%, abnormal resonance occurs. That is,
according to FIG. 10, when the area of the case (plate-like member) 3 is 128.84 mm 2, the area
of the acoustic matching layer 4 of the square is 30 mm 2 or more, when the sensitivity
reduction rate at transmission is 25% or less. The area of the circular acoustic matching layer 4
may be 38 mm 2 or more. According to FIG. 11, when the area of the case (plate-like member) 3
is 128.84 mm 2, the area of the acoustic matching layer 4 of square is 38 mm 2 or more and
circular when the sensitivity reduction rate at transmission and reception is 25% or less. The area
of the acoustic matching layer 4 may be 45 mm 2 or more. If the sensitivity reduction rate
exceeds 25%, the detection performance approaches the detection limit on the flow rate
calculation system and the measurement performance (accuracy) decreases. Therefore, the
sensitivity reduction rate is preferably in the range of 25% or less.
[0107]
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30
Also, considering the directivity and sensitivity of the ultrasonic transducer, the area of the
acoustic matching layer 4 should be large, so the area of the acoustic matching layer 4 is 100%
to 150% of the area of the case (plate-like member) 3 Is preferred. This means that the sensitivity
reduction is allowed up to 20%, but the sensitivity reduction 25% is the limit value, so it is close
to the unstable area on the flow rate calculation system, and there is no margin of the guarantee
range. On the other hand, if it exceeds 150%, anomalous resonance occurs, so it is made 150% or
less. Moreover, if it is in the range of 100% to 150%, by improving the directivity of the
ultrasonic transducer, an unnecessary signal is not detected, so it becomes strong against
disturbance. Therefore, measurement accuracy can be improved. However, when the acoustic
matching layer 4 is larger than the adhesive layer 30, the directivity becomes narrow, and
conversely, when the acoustic matching layer 4 is smaller than the adhesive layer 30, the
directivity becomes wide. When the piezoelectric body 6 is larger than the adhesive layer 31, the
sensitivity is high. Conversely, when the piezoelectric body 6 is smaller than the adhesive layer
31, the sensitivity is low.
[0108]
Judging from the above, the area of the acoustic matching layer 4 is preferably 100 to 150% of
the area of the case (plate-like member) 3. However, in consideration of directivity, sensitivity,
and abnormal resonance, it is desirable to appropriately select the area range within the range of
100 to 150% according to which property is regarded as important when using an ultrasonic
transducer. . That is, by appropriately selecting the area range within the range of 100 to 150%,
the directivity is improved, the sensitivity reduction rate can be set to 25% or less, and the
occurrence of the abnormal resonance mode is prevented. be able to.
[0109]
Example 9 Next, the piezoelectric body and the acoustic matching layer were examined. The size
of the piezoelectric body was a rectangular parallelepiped having a height, a height, and a height
of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is
provided on the bonding surface side of the piezoelectric body with the case. The case was made
into a bottomed cylindrical shape and a bottomed box shape, and the area of the acoustic
matching layer having the same shape as the bottom surface of the case top surface was changed
to produce an ultrasonic transducer. The top surface of the bottomed cylindrical case is φ11
mm, and the top surface of the bottomed box-shaped case is 8 mm × 8 mm. The rate of decrease
04-05-2019
31
in sensitivity was examined by changing from a relative reduction of 50% to an increase in the
area of the top surface of the case based on the smallest area capable of covering the
piezoelectric body. The results are shown in Table 8.
[0111]
From the above results, it was found that the sensitivity decreases when the acoustic matching
layer is made smaller relative to the area of the piezoelectric material, and conversely, the
sensitivity hardly changes when the size of the case top surface is maximized. . Therefore, the
acoustic matching layer is required to be equal to or larger than the area of the piezoelectric
body and equal to or smaller than the top surface of the case.
[0112]
Next, the directivity and sensitivity of the ultrasonic transducer will be considered.
[0113]
(I) In the case of transmission: The ultrasonic transducer has directivity because of the following
reasons.
That is, if the transmission direction of the ultrasonic wave deviates from the central axis of the
plate member 3 of the ultrasonic transducer even at a long distance,
[0115]
In the integration, the phase difference becomes large, and the integrated velocity potential
becomes smaller than the central axis direction of the plate member 3 of the ultrasonic
transducer. Here, as shown in FIGS. 12A and 12B, when the plate member 3 of the ultrasonic
transducer is a circular piston, a point P at which the distance from the center in the direction of
γ from the center axis is r0 And the distance from ds to P on (x, y) on the plane of vibration as
shown in FIG.
04-05-2019
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[0116]
## EQU2 ## r = r0-ysinγ
[0117]
となる。
However, the denominator ignores the distance as r r r0, but this only affects the absolute value
of 、, so r a a is acceptable. The result of this integration is
[0118]
となる。 Where a is the radius of the plate-like member 3. Further, Z is Z = k × a × sin γ = (πd
/ λ) × sin γ = (πdf / c) × sin γ. Where a is the radius of the plate 3, c is the propagation
velocity of the ultrasonic wave, k is the wavelength constant of the ultrasonic wave, d is the
diameter of the plate 3, and J 1 (Z) is the Bessel function.
[0119]
From the above, in the ultrasonic transducer, when the frequency is constant, the directivity
becomes sharper as the diameter of the plate-like member 3 is larger. When the diameter of the
plate-like member 3 is constant, the directivity becomes sharper as the frequency is higher.
[0120]
(II) In the case of reception: the directional gain of the sound transmission gives the intensity of
the directional gain multiple in the axial direction compared with the non-directional sounder
even if the same sound output is output . However, the directivity gain has a completely different
meaning in reception. To receive plane waves coming from one direction, if you point the axis of
the directional receiver, it tends to be more sensitive than the omnidirectional receiver, but the
degree is not directly related to the directional gain. If the frequency is constant, a directional
receiver can make a receiver with high sensitivity because the sound receiving area is larger.
04-05-2019
33
Alternatively, if the efficiencies of both receivers are equal, the electric power can be increased as
much as the input power is proportional to the sound receiving area. If the same size receiver is
used at high frequency, the directional gain is larger than at low frequency, but if the sound
pressure is constant, the high frequency may have larger electrical output than the directional
gain. I can not get it. Therefore, in the case of sound reception, assuming that the target signal is
a plane wave coming from one direction, and the disturbing noise comes uniformly from all solid
angles, the signal-to-noise ratio is better than when using an omnidirectional receiver Only
directivity gain is improved.
[0121]
From the above, it is desirable that the size of the acoustic matching layer 4 be equal to the size
of the case (diaphragm) 3 as much as possible.
[0122]
On the other hand, features when using a pair of ultrasonic transducers 17 and 18 as an
ultrasonic flow meter are as follows.
[0123]
First, the correlation coefficient of the pair of ultrasonic transducers 17 and 18 is 0.80 or more,
preferably 0.960 or more, when the frequency of the impedance is 200 KHz to 750 KHz (more
preferably, 350 KHz to 750 KHz) Is preferred.
Here, with the correlation coefficient, after measuring the frequency characteristics (FIG. 13 and
FIG. 14) of the impedance of each of the ultrasonic transducers 17 and 18, it was determined
how closely the impedance for each frequency matched. It is.
The frequency range is calculated at each measurement point of 200 KHz to 750 KHz in the
operating frequency range.
[0124]
When a current type circuit is used, the impedances of the ultrasonic transducers 17 and 18
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34
need to be as similar as possible. The reason is that in the case of an ideal current type circuit as
shown in FIG. 15 and FIG. 16, the output current is received and transmitted regardless of the
flow path and the impedance of the ultrasonic transducer if it is a secondary short circuit. It is
the same even if it replaces. However, in order to measure the output current, it is impossible to
completely short the secondary side, and a certain degree of resistance is required. At this time,
since it is not an ideal current type circuit, impedances as similar as possible to the ultrasonic
transducers 17 and 18 are required. If the value of the correlation coefficient of the ultrasonic
transducers 17 and 18 is 0.80 or more, preferably 0.960 or more, the flow rate of the fluid to be
measured is corrected by correcting the correlation coefficient on the measurement circuit side.
The ultrasonic transducers 17 and 18 can be used as ultrasonic flowmeters that can be measured
well (for example, with an accuracy of at least 3 liters / h for city gas).
[0125]
Further, when used as an ultrasonic flow meter, the pair of opposing ultrasonic transducers 17
and 18 have substantially the same shape, and the centers of the pair should be as close as
possible, and the pair of opposing members The parallelism between the facing surfaces of the
ultrasonic transducers 17 and 18 (the facing surfaces of the facing acoustic matching layers) is
preferably matched as much as possible.
[0126]
In addition, the effect which each has can be exhibited by combining suitably the arbitrary
embodiment in said various embodiment.
[0127]
According to the present invention, by optimizing the size of the acoustic matching layer, the
plate-like member, the piezoelectric body, and the adhesive layer, an ultrasonic transducer having
both efficiency and reliability and ultrasonic flow rate Realize the
[0128]
When the area of the acoustic matching layer is 100 to 110% of the area of the plate-like
member, the directivity is improved, the sensitivity reduction rate can be 25% or less, and the
abnormal resonance mode Can be prevented.
[0129]
Furthermore, in an ultrasonic flow meter including a pair of ultrasonic transducers, the pair of
ultrasonic transducers have substantially the same shape, and when the frequency of the
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35
impedance is 200 KHz to 750 KHz, the phase relationship of the pair of ultrasonic transducers If
the number is 0.80 or more, the flow rate of the fluid to be measured can be measured accurately
(for example, in city gas, at least 3 liters / h or more).
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36
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