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DESCRIPTION JP2004072461

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DESCRIPTION JP2004072461
An object of the present invention is to realize an ultrasonic transducer that efficiently
propagates the vibration of a piezoelectric body into a fluid to be measured. The directivity and
sensitivity distribution of sound waves output from an acoustic matching layer can be controlled
by partially changing the thickness of the acoustic matching layer through a case. As a result, the
flow rate distribution characteristic of the fluid to be measured in the flow rate measurement unit
can be covered, and stable flow rate measurement can be performed. [Selected figure] Figure 3
Ultrasonic transducer and ultrasonic flowmeter using the same
TECHNICAL FIELD [0001] The present invention relates to an ultrasonic flowmeter that
measures the flow rate or flow rate of a gas or liquid by ultrasonic waves. [0002] As an ultrasonic
transducer used for an ultrasonic flowmeter, for example, JP-A-11-118550 has been disclosed,
and an external view of the ultrasonic transducer is shown in FIG. As shown in FIG. 11, reference
numeral 26 is an ultrasonic transducer, 27 is a case, 28 is a top portion of the case 27, and 29 is
an acoustic matching layer fixed to the top portion 28. The acoustic matching layer 29 has a
uniform thickness and a disk shape having the same area as the top of the case 27. FIG. 12
shows a cross-sectional view of the ultrasonic transducer. Reference numeral 30 denotes a
piezoelectric body disposed on the inner wall surface of the top portion 28, and reference
numeral 31 denotes a support portion for fixing the case 27. Reference numeral 32 denotes a
conductor, 33 denotes a terminal plate fixed to the support portion 31, 34a and 34b denote
terminals fixed to the terminal plate 33, and 35 denotes an insulating portion for insulating the
terminal 34a from the terminal 34b. Reference numeral 36 denotes a groove provided in the
piezoelectric body 30. When a voltage is applied to the piezoelectric body 30 from the terminals
34 a and 34 b through the conductor 32. The piezoelectric body 30 vibrates by the piezoelectric
phenomenon. However, in the above-mentioned conventional acoustic matching layer, since the
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size of the acoustic matching layer is equal to the area of the case top and the thickness is
uniform, the vibration generated in the piezoelectric body is generated. When it is transmitted to
the acoustic matching layer through the case, unnecessary vibration may be converted to the
sound wave when performing the flow rate measurement. This is because, in the flow rate
measurement, only the sound wave of the portion where the vibration of the piezoelectric body is
large is generated from the ultrasonic transducer, so that it is possible to perform the flow rate
measurement without variation. However, in the conventional acoustic matching layer, the noise
component due to unnecessary sound waves and the sound waves in a portion where the
vibration is large are mixed, so that the flow rate measurement may become unstable. The
present invention solves the above-mentioned conventional problems, and by partially making
the thickness different in the thickness direction of the acoustic matching layer wall, the sound
wave of the portion where the vibration of the piezoelectric body through the case is large It is
an object of the present invention to provide an ultrasonic transducer that efficiently propagates
only the fluid to be measured and an ultrasonic flow meter using the ultrasonic transducer.
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to
the present invention, an acoustic matching layer constituting an ultrasonic transducer is
partially different in thickness in a thickness direction, A stable measurement with no variation is
performed by transmitting and receiving only the sound waves necessary for measurement
without transmitting and receiving unnecessary sound waves when measuring the fluid to be
measured.
According to the invention, in order to efficiently propagate the vibration of the piezoelectric
body, unnecessary acoustic waves are eliminated and the directivity of the acoustic waves is
controlled by partially changing the thickness of the acoustic matching layer to the optimum
dimension. Can stably measure the flow rate of the fluid to be measured. DETAILED
DESCRIPTION OF THE PREFERRED EMBODIMENTS The ultrasonic transducer according to the
first aspect of the present invention has a covered case having a top portion and a side wall
portion, and an acoustic matching member fixed to the outer wall surface of the top portion with
an adhesive. Since the layer and the acoustic matching layer have partially different thicknesses
in the thickness direction, it is possible to obtain an ultrasonic transducer capable of controlling
the directivity of sound waves. The ultrasonic transducer according to the second aspect of the
present invention is unnecessary in the ultrasonic transducer according to the first aspect, in
which the central portion of the acoustic matching layer is thicker than the other portions. It is
possible to obtain an ultrasonic transducer that eliminates the sound wave and controls the
directivity of the sound wave. In the ultrasonic transducer according to a third aspect of the
present invention, in the ultrasonic transducer according to the first aspect, the central portion of
the acoustic matching layer is thinner than the other portions. An ultrasonic transducer capable
of adjusting the directivity and sensitivity distribution of sound waves can be obtained. The
ultrasonic transducer according to a fourth aspect of the present invention is the ultrasonic
transducer according to the first aspect, wherein the acoustic matching layer has a convex shape,
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whereby directivity and sensitivity distribution of sound waves are obtained. An ultrasonic
transducer capable of adjusting The ultrasonic transducer according to a fifth aspect of the
present invention is the ultrasonic transducer according to the first aspect, in which the acoustic
matching layer has a concave configuration to adjust the direction in which the sound waves are
emitted. An ultrasonic transducer capable of In the ultrasonic transducer according to a sixth
aspect of the present invention, in the ultrasonic transducer according to the first aspect, the
acoustic matching layer has a plurality of stages to control the sensitivity distribution of the
sound wave. An ultrasonic transducer capable of In the ultrasonic transducer according to a
seventh aspect of the present invention, in the ultrasonic transducer according to the first aspect,
the acoustic matching layer is configured in a similar shape in each of the stages so that
directivity of the sound wave can be obtained. Thus, an ultrasonic transducer capable of
controlling the sensitivity distribution is obtained. The ultrasonic transducer according to an
eighth aspect of the present invention is the ultrasonic transducer according to the first aspect,
wherein the acoustic matching layer has a configuration different from that of each step, so that
unnecessary acoustic waves can be generated. An ultrasonic transducer capable of reducing and
adjusting the directivity and sensitivity distribution of sound waves can be obtained. The
ultrasonic transducer according to a ninth aspect of the present invention is the ultrasonic
transducer according to the first aspect, wherein the acoustic matching layer is located at the
center of the acoustic matching layer in each stage. An ultrasonic transducer capable of
controlling the directivity and sensitivity distribution of sound waves can be obtained.
The ultrasonic transducer according to a tenth aspect of the present invention is the ultrasonic
transducer according to the first aspect, wherein the acoustic matching layer is located at a
position other than the center of the acoustic matching layer in each stage. Thus, an ultrasonic
transducer capable of adjusting the directivity of the sound wave and the output state of the
sensitivity distribution can be obtained. The ultrasonic transducer according to an eleventh
aspect of the present invention is the ultrasonic transducer according to the first aspect,
comprising: a flow rate measuring unit through which the fluid to be measured flows; and an
ultrasonic wave provided in the flow rate measuring unit. A pair of ultrasonic transducers
according to any one of claims 1 to 10 for transmission and reception, a measurement circuit for
measuring a propagation time between the ultrasonic transducers, and a signal from the
measurement circuit. Since the flow rate calculating means for calculating the flow rate is
provided, it is possible to obtain an ultrasonic flowmeter with little measurement variation.
EXAMPLE 1 Hereinafter, an example of the present invention will be described using the
drawings. The same reference numerals in the drawings denote the same components, and the
detailed description will be omitted. FIG. 1 is a schematic configuration diagram of an ultrasonic
flowmeter using an ultrasonic transducer shown in each of the following embodiments of the
present invention. In FIG. 1, 1 is a flow rate measuring unit through which a fluid to be measured
flows, 2 and 3 are ultrasonic transducers disposed diagonally opposite to the flow direction of
the flow rate measuring unit 1, 4 is an ultrasonic transducer 2, an oscillator circuit for
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transmitting the used frequency, 5 is a drive circuit connected to the oscillator circuit 4 to drive
the ultrasonic transducers 2, 3, 6 is a switching circuit for switching the ultrasonic transducer to
be transmitted / received, 7 is Reception detection circuit to detect ultrasonic pulse, 8 is timer to
measure propagation time of ultrasonic pulse, 9 is operation unit to calculate flow rate from
output of timer 8, 10 is output control signal to drive circuit 5 and timer 8 Control unit. The
operation of the ultrasonic flowmeter configured as described above will be described. In this
embodiment, it is assumed that the fluid to be measured is a city gas, and a household gas meter
is used as an ultrasonic flow meter, and the material constituting the flow rate measuring unit 1
is an aluminum alloy die cast. Further, about 500 KHZ is selected as the use frequency of the
ultrasonic transducers 2 and 3. The oscillation circuit 4 is composed of, for example, a capacitor
and a resistor and transmits a square wave of about 500 KHZ, and the drive circuit 5 is a burst
signal of three square waves for driving the ultrasonic transducers 2 and 3 from the signal of the
oscillation circuit 4 Enable output of a drive signal consisting of Moreover, in order to improve
the resolution of the measurement flow rate, a single-around method is used as the measurement
means. The control unit 10 outputs a transmission start signal to the drive circuit 5 and at the
same time starts the time measurement of the timer 8.
When receiving the transmission start signal, the drive circuit 5 drives the ultrasonic transducer
2 to transmit ultrasonic pulses. The transmitted ultrasonic pulse propagates in the flow rate
measuring unit 1 and is received by the ultrasonic transducer 3. The received ultrasonic pulse is
converted into an electric signal by the ultrasonic transducer 3 and output to the reception
detection circuit 7. The reception detection circuit 7 determines the reception timing of the
reception signal, and outputs a reception detection signal to the control unit 10. When receiving
the reception detection signal, the control unit 10 outputs the transmission start signal to the
drive circuit 5 again after the lapse of the preset delay time td, and performs the second
measurement. After repeating this operation N times, the timer 8 is stopped. The arithmetic unit
9 divides the time measured by the timer 8 by N of the number of times of measurement and
subtracts the delay time td to calculate the propagation time t1. Subsequently, the ultrasonic
transducer connected to the drive circuit 5 and the reception detection circuit 7 is switched by
the switching circuit 6, and the control unit 10 outputs the transmission start signal to the drive
circuit 5 again, and at the same time measures the time of the timer 8. Start it. Contrary to the
measurement of the propagation time t1, ultrasonic pulses are transmitted by the ultrasonic
transducer 3 and the measurement received by the ultrasonic transducer 2 is repeated N times,
and the propagation time t2 is calculated by the calculation unit 9. Here, the distance connecting
the centers of the ultrasonic transducer 2 and the ultrasonic transducer 3 is L, the speed of
sound in the absence of air is C, and the flow velocity in the flow rate measuring unit 1 is V, nonmeasurement Assuming that the angle between the direction of fluid flow and the line connecting
the centers of the ultrasonic transducer 2 and the ultrasonic transducer 3 is θ, the propagation
times t1 and t2 are t1 = L / (C + V cos θ) (1) t2 = L / (C-Vcosθ) (2) When the sound velocity C is
eliminated from the equation (1) (2) and the flow velocity V is obtained, the following equation is
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obtained. V = L / 2 cos θ (1 / t1-1 / t2) (3) Since L and θ are known, the flow velocity V can be
obtained by measuring t1 and t2. Assuming that the flow velocity V and the area of the flow rate
measurement unit 1 are S, and the correction coefficient is K, the flow rate Q can be calculated by
Q = KSV (4). An embodiment of an ultrasonic transducer used in an ultrasonic flowmeter that
performs flow measurement according to the operation principle as described above will be
described with reference to FIG. FIG. 2 is a cross-sectional view of the ultrasonic transducers 2
and 3 of the present invention. In FIG. 2, 11 is a case. The acoustic matching layer 12 is provided
with a low layer portion 12a and a high portion 12b. The acoustic matching layer 12 and the
case top outer wall 13 and the case top inner wall 14 and the piezoelectric member 15 are
connected by adhesion. 16 is a case support portion, and 17 is a terminal plate fixed to the case
support portion.
Reference numerals 18a and 18b denote terminals provided on the terminal plate 17, 19 denotes
an insulating portion for insulating the terminals 18a and 18b, and 20 denotes lead wires for
electrically connecting the terminals 18a and the piezoelectric body 15. The ultrasonic
transducers 2 and 3 configured as described above will be described with reference to FIG. The
acoustic matching layer 12 uses a material not shown, which is a mixture of an epoxy resin and
hollow glass spheres. The case 11 is made of stainless steel, and the acoustic matching layer 12
and the case 11 and the piezoelectric body 15 are connected using a thermosetting epoxy resin.
In the acoustic matching layer 12, for example, the thickness of the lower layer portion 12 a is
set to a value lower than that corresponding to a quarter wavelength of the resonance frequency,
and the upper layer 12 b has a thickness equivalent to a quarter wavelength of the resonance
frequency. Sound waves are output only from the surface of the part 12b. The vibration of the
piezoelectric body 15 through the case 11 tends to be large in the vicinity of the center of the
case 11. Therefore, when the high-rise portion 12b is provided in the vicinity of the center of the
case 11, a sound wave having a wavelength near the resonance frequency component is
transmitted Ru. The upper portion diameter 21 is based on 20% to 90% of the lower portion
diameter 22, and may be 35% to 65% and 45% to 55%. The upper layer thickness 23 is 8% to
85% based on the total thickness 24 of the acoustic matching layer, and may be 35% to 70% or
about 43%. By reducing the area in the circumferential direction of the high-rise portion 12b, the
plane wave region of the sound wave output from the high-rise portion 12b becomes short and
diffuses and propagates as a spherical wave, so the sensitivity distribution of the sound wave is
controlled. It will be. Although FIG. 3 shows an example in which the shape of the high-rise part
12 b is circular and the low-rise part 12 a has a similar shape, the high-rise part 12 b has a
quadrangle or a polygon not shown as shown in FIG. I don't care. FIG. 5 shows the lower layer
12a of the acoustic matching layer 12 of the first embodiment as a central part, the high layer
12b is provided in the outer peripheral direction of the lower layer 12a, and the lower layer 12a
It is put to the same thickness as the part 12b. The matching material 25 is, for example, an
inorganic material and has a density lower than that of the acoustic matching layer 12, so that
the sensitivity distribution of the sound waves output from the ultrasonic transmitters / receivers
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2 and 3 can be controlled by having different density structures. It is also good. Second
Embodiment FIG. 6 is a perspective view of an ultrasonic transducer according to a second
embodiment of the present invention. The output of the sound wave can be obtained by setting
the thickness of the acoustic matching layer 12 to a thickness equivalent to 1⁄4 wavelength of
the resonance frequency of the piezoelectric body 15. For example, the high-rise portion 12b of
the acoustic matching layer 12 has By setting the thickness of the high-rise part 12b to a
considerable thickness and removing the position of the high-rise part 12b from the center of the
acoustic matching layer 12, it becomes possible to set the directivity and sensitivity distribution
of the sound wave to some extent freely.
The optimum values of directivity and sensitivity distribution of sound waves covering the entire
velocity distribution of the fluid to be measured may be derived from the positions of the
ultrasonic transducers 2 and 3 installed in the flow rate measuring unit 1 of FIG. . FIG. 6 shows
an embodiment in which the high-rise portion 12 b of the acoustic matching layer 12 having a
thickness equivalent to 1⁄4 wavelength of the resonance frequency has a similar shape to the
low-layer portion 12 a. The high-rise portion 12b may be elliptical. In the elliptical shape, the
sound wave output depends on the dimensional relationship between the major axis and the
minor axis, but a plane wave is output from the major axis side and a spherical wave is output
from the minor axis side. Third Embodiment FIG. 8 is a perspective view of an ultrasonic
transducer according to a third embodiment of the present invention. When there are a plurality
of resonance frequency points in the piezoelectric body 15, the first resonance frequency
acoustic matching layer portion 12c and the second resonance frequency acoustic matching
layer portion 12d of the acoustic matching layer 12 each have a thickness equivalent to 1/4
wavelength of the resonance frequency. The sound waves of a plurality of types of resonance
frequency components may be output by setting For example, in the case of the piezoelectric
body 15 in which two types of resonance frequencies of about 500 kHz and about 200 kHz
coexist and the one of about 500 kHz is designed as a resonance point, the portion of the first
resonance frequency acoustic matching layer portion 12c is about The portion of the second
resonance frequency acoustic matching layer portion 12d is provided in a portion other than the
first resonance frequency thickness 12c. By changing the area ratio of the first resonant
frequency acoustic matching layer portion 12c and the second resonant frequency acoustic
matching layer portion 12d, the output is from the first resonant frequency acoustic matching
layer portion 12c and the second resonant frequency acoustic matching layer portion 12d.
Adjustment of the sensitivity distribution of sound waves. In FIG. 8, the first resonance frequency
acoustic matching layer 12 c is at the center of the acoustic matching layer 12 and the second
resonance frequency acoustic matching layer 12 d is at a portion other than the first resonance
frequency acoustic matching layer 12 c. However, these may be reversed. 9 and 10 are crosssectional views of a modification of the second embodiment. As is apparent from the above
description, according to the ultrasonic transducer of the present invention and the flow meter
using the ultrasonic transducer of the present invention, it is possible to control the directivity
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and sensitivity distribution of sound waves. An acoustic transducer can be obtained. BRIEF
DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram including a partial crosssectional view of an ultrasonic flowmeter used for an ultrasonic transducer according to the
present invention. FIG. 2 an ultrasonic transducer according to a first embodiment of the present
invention. Fig. 3 is a perspective view of the ultrasonic transducer in the first embodiment of the
present invention. Fig. 4 is a perspective view of the ultrasonic transducer in the first
embodiment of the present invention. Fig. 5 is an embodiment of the present invention. 6 is a
perspective view of the ultrasonic transducer according to the second embodiment of the present
invention. FIG. 7 is a perspective view of the ultrasonic transducer according to the second
embodiment of the present invention. 8 is a perspective view of an ultrasonic transducer
according to a third embodiment of the present invention. FIG. 9 is a cross-sectional view of an
ultrasonic transducer according to a third embodiment of the present invention. 11 is a
perspective view of a conventional ultrasonic transducer. FIG. 12 is a sectional view of a
conventional ultrasonic transducer. [Explanation of the code] 1 flow rate measurement unit 2, 3
ultrasonic transducer 4 transmission circuit 5 drive circuit 6 switching circuit 7 reception
detection circuit 8 timer 9 operation unit 10 control unit 11 case 12 acoustic matching layer 12a
acoustic matching layer lower layer 12b acoustic matching layer upper part 12c first resonant
frequency acoustic matching layer 12d second resonant frequency acoustic matching layer 15
piezoelectric body 25 matching material
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