Abstrict An ultrasonic Doppler flow-meter comprises a substrate with a piezoelectricity,
input- and output interdigital transducers formed on a first end
surface of the substrate, and a signal analyzing unit connected
between the input- and output interdigital transducers. A second
end surface of the substrate is in contact with a liquid. The finger
direction the output interdigital transducer is slanting to that
of the input interdigital transducer. When an input electric signal
with a carrier frequency f.sub.0 is applied to the input interdigital
transducer, a leaky Lamb wave is excited in the substrate. The leaky
Lamb wave is radiated into the liquid in the form of a longitudinal
wave, which is reflected back by a material in the liquid. The reflected
longitudinal wave is detected at the output interdigital transducer
as a delayed electric signal with a Doppler frequency f. A moving
speed of the material is sensed at the signal analyzing unit in
terms of a frequency difference .DELTA.f between the carrier frequency
f.sub.0 and the Doppler frequency f.
Claims What is claimed is:
1. An ultrasonic Doppler flow-meter comprising: a substrate with
a piezoelectricity and made of a triple-zone body consisting of
a first- and a second piezoelectric zone parts and a nonpiezoelectric
zone part between said first- and second piezoelectric zone parts,
each zone part having two end surfaces; an input interdigital transducer
formed on one end surface of said first piezoelectric zone part;
an output interdigital transducer having the same interdigital periodicity
as said input interdigital transducer, and formed on one end surface
of said second piezoelectric zone part not only such that said input-
and output interdigital transducers are situated to be symmetrical
to a line, but also such that a first intersecting line on each
finger-center of the finger overlap-zone of said input interdigital
transducer and a second intersecting line on each finger-center
of the finger overlap-zone of said output interdigital transducer
run against each other; and a signal analyzing unit, said input
interdigital transducer receiving an input electric signal with
a carrier frequency, exciting a leaky elastic wave in said substrate,
causing a mode conversion from said leaky elastic wave to a longitudinal
wave in a liquid in contact with the other end surface of each zone
part, and making a material in said liquid reflect, said longitudinal
waveback, said output interdigital transducer detecting a reflected
longitudinal wave as a delayed electric signal with a Doppler frequency,
said other end surface of said each zone part being perpendicular
to a line passing through a reflection point at said material and
a cross point of said first- and second intersecting lines, said
signal analyzing unit sensing a moving speed of said material in
terms of a frequency difference between said carrier frequency and
said Doppler frequency.
2. An ultrasonic Doppler flow-meter comprising: a nonpiezoelectric
plate, one end surface thereof being in contact with a liquid; a
first piezoelectric substrate; a second piezoelectric substrate,
said first- and second piezoelectric substrates being formed on
the other end surface of said nonpiezoelectric plate under an electrically
separated condition; an input interdigital transducer formed on
one end surface of said first piezoelectric substrate; an output
interdigital transducer having the same interdigital periodicity
as said input interdigital transducer, and formed on one end surface
of said second piezoelectric substrate not only such that said input-
and output interdigital transducers are situated to be symmetrical
to a line, but also such that a first intersecting line on each
finger-center of the finger overlap-zone of said input interdigital
transducer and a second intersecting line on each finger-center
of the finger overlap-zone of said output interdigital transducer
run against each other; and a signal analyzing unit, said input
interdigital transducer receiving an input electric signal with
a carrier frequency, exciting a leaky elastic wave in said first
piezoelectric substrate, causing a mode conversion from said leaky
elastic wave to a longitudinal wave in said liquid, and making a
rotor in said liquid reflect said longitudinal wave back, said output
interdigital transducer detecting a reflected longitudinal wave
as a delayed electric signal with a Doppler frequency, said one
end surface of said nonpiezoelectric plate being perpendicular to
a line passing through a cross point of said first- and second intersecting
lines and a reflection point at said rotor, said signal analyzing
unit sensing a rotating speed of said rotor in terms of a frequency
difference between said carrier frequency and said Doppler frequency.
3. An ultrasonic Doppler flow-meter comprising: a nonpiezoelectric
plate, one end surface thereof being in contact with a liquid; a
first piezoelectric substrate; a second piezoelectric substrate,
said first- and second piezoelectric substrates being formed on
the other end surface of said nonpiezoelectric plate under an electrically
separated condition; an input interdigital transducer formed on
one end surface of said first piezoelectric substrate; an output
interdigital transducer having the same interdigital periodicity
as said input interdigital transducer, and formed on one end surface
of said second piezoelectric substrate not only such that said input-
and output interdigital transducers are situated to be symmetrical
to a line, but also such that a first intersecting line on each
finger-center of the finger overlap-zone of said input interdigital
transducer and a second intersecting line on each finger-center
of the finger overlap-zone of said output interdigital transducer
run against each other; and signal analyzing unit, said input interdigital
transducer receiving an input electric signal with a carrier frequency,
exciting a leaky elastic wave in said first piezoelectric substrate,
causing a mode conversion from said leaky elastic wave to a longitudinal
wave in said liquid, and making a material in said liquid reflect
said longitudinal wave back, said output interdigital transducer
detecting a reflected longitudinal wave as a delayed electric signal
with a Doppler frequency, said one end surface of said nonpiezoelectric
plate being perpendicular to a line passing through a cross point
of said first- and second intersecting lines and a reflection point
at said material, which is moved in accordance with a flowing speed
of said liquid, said signal analyzing unit sensing said flowing
speed of said material in terms of a frequency difference between
said carrier frequency and said Doppler frequency.
4. An ultrasonic Doppler flow-meter comprising: a nonpiezoelectric
plate, one end surface thereof being in contact with a liquid; a
first piezoelectric substrate; a second piezoelectric substrate
said first- and piezoelectric substrates being formed on the other
end surface of said nonpiezoelectric plate under an electrically
separated condition; an input interdigital transducer formed on
one end surface of said first piezoelectric substrate; an output
interdigital transducer having the same interdigital periodicity
as said input interdigital transducer, and formed on one end surface
of said second piezoelectric substrate not only such that said input-
and output interdigital transducers are situated to be symmetrical
to a line, but also such that a first intersecting line on each
finger-center of the finger overlap-zone of said input interdigital
transducer and a second intersecting line on each finger-center
of the finger overlap-zone of said output interdigital transducer
are vertical to each other; and a signal analyzing unit, said input
interdigital transducer receiving an input electric signal with
a carrier frequency, exciting a leaky elastic wave in said first
piezoelectric substrate, causing a mode conversion from said leaky
elastic wave to a longitudinal wave in said liquid, and making a
material in said liquid reflect said longitudinal wave back, said
output interdigital transducer detecting a reflected longitudinal
wave as a delayed electric signal with a Doppler frequency, said
one end surface of said nonpiezoelectric plate being perpendicular
to a line passing through a cross point of said first- and second
intersecting lines and a reflection point at said material, said
signal analyzing unit sensing a moving speed of said material in
terms of a frequency difference between said carrier frequency and
said Doppler frequency.
5. An ultrasonic Doppler flow-meter comprising: a nonpiezoelectric
plate, one end surface thereof being in contact with a liquid; a
first piezoelectric substrate; a second piezoelectric substrate,
said first- and second piezoelectric substrates being formed on
the other end surface of said nonpiezoelectric plate under an electrically
separated condition; an input interdigital transducer formed on
one end surface of said first piezoelectric substrate; an output
interdigital transducer having the same interdigital periodicity
as said input interdigital transducer, and formed on one end surface
of said second piezoelectric substrate not only such that said input-
and output interdigital transducers are situated to be symmetrical
to a line, but also such that a first intersecting line on each
finger-center of the finger overlap-zone of said input interdigital
transducer and a second intersecting line on each finger-center
of the finger overlap-zone of said output interdigital transducer
run against each other; and a signal analyzing unit, said input-
and output interdigital transducers having an arch-shaped electrode
pattern, respectively, and making a pair with a concentric center,
said input interdigital transducer receiving an input electric signal
with a carrier frequency, exciting a leaky elastic wave in said
first piezoelectric substrate, causing a mode conversion from said
leaky elastic wave to a longitudinal wave in said liquid, and making
a material in said liquid reflect said longitudinal wave back, said
output interdigital transducer detecting a reflected longitudinal
wave as a delayed electric signal with a Doppler frequency said
one end surface of said nonpiezoelectric plate being perpendicular
to a line passing through a cross point of said first- and second
intersecting lines and a reflection point at said material, said
signal analyzing unit sensing a moving speed of said material in
terms of a frequency difference between said carrier frequency and
said Doppler frequency.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic device for measuring
a flowing speed of a liquid or a material's moving speed in a liquid
by making use of the Doppler effect.
2. Description of the Prior Art
There are touch- and untouch-types of conventional devices for
detecting a vibration displacement. Devices, for example, as an
electric micrometer and a digital gauge for a small displacement,
a rotary encoder for a rotation displacement, and a linear scale
for a large displacement belong to the touch-type. These touch-type
devices have some problems on measurement accuracy, response time,
difficulty in use, durability and manufacturing. Devices, for example,
as a laser-type sensor and an electroacoustic-type sensor belong
to the untouch-type. The laser-type sensor has a defect that the
longer the length of the laser beam, the lower the measurement accuracy
because of flickering of the laser beam itself. In addition, the
use of the laser-type sensor is impossible for the measurement in
opaque media. The electroacoustic-type sensor has some problems
on measurement accuracy, resistance for a change of circumstances,
and so on. In addition, it is difficult to measure precisely and
conveniently a flowing speed of a liquid by conventional devices.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ultrasonic
Doppler flow-meter capable of measuring a flowing speed of a liquid
or a material's moving speed in a liquid with a high sensitivity.
Another object of the present invention is to provide an ultrasonic
Doppler flow-meter capable of operating at a high frequency.
Another object of the present invention is to provide an ultrasonic
Doppler flow-meter excellent in measurement accuracy, response time,
durability, and manufacturing.
A still other object of the present invention is to provide an
ultrasonic Doppler flow-meter easy in use and having a small size
which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided
an ultrasonic Doppler flow-meter comprising a substrate with a piezoelectricity,
an input- and output interdigital transducers formed on a first
end surface of the substrate, and signal analyzing unit. The finger
direction of the output interdigital transducer is slanting to that
of the input interdigital transducer. A second end surface of the
substrate is in contact with a liquid. When an input electric signal
with a carrier frequency is applied to the input interdigital transducers,
a leaky elastic wave if excited in the substrate. The leaky elastic
wave is radiated in the form of a longitudinal wave into the liquid,
and reflected by a material in the liquid. The reflected longitudinal
wave is detected at the output interdigital transducer as a delayed
electric signal with a Doppler frequency. The signal analyzing unit
senses a moving speed of the material in terms of a frequency difference
between the carrier frequency and the Doppler frequency.
According to another aspect of the present invention there is provided
a substrate made of a piezoelectric ceramic plate, of which the
polarization axis is parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided
a substrate made of a double-layer body consisting of a piezoelectric
layer part and a nonpiezoelectric layer part. Each layer part has
an inner- and an outer end surfaces. The input- and output interdigital
transducers are formed on one of the inner- and outer end surfaces
of the piezoelectric layer part. The liquid is in contact with the
outer end surface of the nonpiezoelectric layer part.
According to another aspect of the present invention there is provided
a substrate made of a triple-zone body consisting of a first- and
a second piezoelectric zone parts and a nonpiezoelectric zone part
between the first- and second piezoelectric zone parts. Each zone
part has two end surfaces. The input- and out put interdigital transducers
are formed on one end surface of the first piezoelectric zone part
and that of the second piezoelectric zone part, respectively. The
liquid is in contact with the other end surface of each zone part.
According to another aspect of the present invention there is provided
an ultrasonic Doppler flow-meter comprising a nonpiezoelectric plate,
a first- and a second piezoelectric substrates, an input- and output
interdigital transducers, and signal analyzing unit. One end surface
of the nonpiezoelectric plate is in contact with a liquid. The first-
and second piezoelectric substrates are formed on the other end
surface of the nonpiezoelectric plate under an electrically separated
condition. The input interdigital transducer is formed on one end
surface of the first piezoelectric substrate. The output interdigital
transducer is formed on one end surface of the second piezoelectric
substrate, the finger direction of the output interdigital transducer
being slanting to that of the input interdigital transducer.
According to another aspect of the present invention there is provided
a material rotating itself. In this case, the signal analyzing unit
senses a rotating speed of the material.
According to another aspect of the present invention there is provided
a material moving in accordance with a flowing speed of the liquid.
In this case the signal analyzing unit senses the flowing speed.
According to another aspect of the present invention there is provided
an output interdigital transducer, of which the finger direction
is vertical to that of an input interdigital transducer.
According to another aspect of the present invention there is provided
an input- and an output interdigital transducers having an arch-shaped
electrode pattern, respectively, and making a pair with a concentric
center.
According to another aspect of the present invention there is provided
a signal analyzing unit which comprises a signal generator generating
the input electric signal, an amplifier amplifying the delayed electric
signal, and a frequency counter detecting the frequency difference.
According to other aspect of the present invention there is provided
a signal analyzing unit which comprises a signal generator generating
the input electric signal, an amplifier amplifying the delayed electric
signal, and a frequency to voltage converter converting the Doppler
frequency to a voltage thereof. The frequency to voltage converter
detects the frequency difference in terms of the voltage converted
from the Doppler frequency.
According to a further aspect of the present invention there is
provided a signal analyzing unit which comprises a signal generator
generating the input electric signal, and a phase comparator comparing
a phase of the input electric signal with that of the delayed electric
signal. The phase comparator detects the frequency difference in
terms of a phase difference between the input- and delayed electric
signals.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the invention will be clarified
from the following description with reference to the attached drawings.
FIG. 1 shows a schematic illustration of an ultrasonic Doppler
flow-meter according to an embodiment of the present invention.
FIG. 2 shows a plan view of the detecting assembly composed of
substrate 1 input interdigital transducer 2 and output interdigital
transducer 3.
FIG. 3 shows a diagram of signal analyzing unit 4 according to
a first embodiment.
FIG. 4 shows a plan view illustrating a path of the longitudinal
wave in the liquid by an arrow.
FIG. 5 shows a side view illustrating a path of the longitudinal
wave in the liquid by an arrow.
FIG. 6 shows a relationship between the frequency and the calculated
phase velocity of a leaky Lamb wave for each mode in substrate 1.
FIG. 7 shows a relationship between the frequency and the calculated
transducer efficiency .eta. for a longitudinal wave radiation into
water.
FIG. 8 shows a spectrum relationship between the frequency observed
at frequency counter 10 and the amplitude thereof, when disk 6 is
rotating.
FIG. 9 shows a relationship between the rotating speed of motor
5 and the frequency difference .DELTA.f.
FIG. 10 shows a diagram of signal analyzing unit 4 according to
a second embodiment.
FIG. 11 shows a diagram of signal analyzing unit 4 according to
a third embodiment.
FIG. 12 shows a sectional view of another detecting assembly used
in place of the detecting assembly in FIG. 2.
FIG. 13 shows a sectional view of another detecting assembly used
in place of the detecting assembly in FIG. 2.
FIG. 14 shows a sectional view of other detecting assembly used
in place of the detecting assembly in FIG. 2.
FIG. 15 shows a plan view of a further detecting assembly used
in place of the detecting assembly in FIG. 2.
FIG. 16 shows an illustration in case of measuring a flowing speed
of a liquid in pipe 28 by using the ultrasonic Doppler flow-meter
in FIG. 1.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS
FIG. 1 shows a schematic illustration of an ultrasonic Doppler
flow-meter according to an embodiment of the present invention.
The ultrasonic Doppler flow-meter comprises substrate 1 input interdigital
transducer 2 having an input terminal, output interdigital transducer
3 having an output terminal, and signal analyzing unit 4. Piezoelectric
substrate 1 is made of a ceramic thin plate with a dimension of
150 .mu.m in thickness. It is possible to use a piezoelectric polymer
film as substrate 1. Input interdigital transducer 2 and output
interdigital transducer 3 made of an aluminum thin film, respectively,
are formed on a first end surface of substrate 1. Piezoelectric
substrate 1 input interdigital transducer 2 and output interdigital
transducer 3 form a detecting assembly. When sensing a rotating
speed of motor 5 having rotating disk 6 in a liquid, a second end
surface of substrate 1 is kept in contact with the liquid in liquid
bath 7. Thus, the ultrasonic Doppler flow-meter in FIG. 1 has a
small size which is very light in weight and has a simple structure.
The liquid is water in this embodiment.
FIG. 2 shows a plan view of the detecting assembly composed of
substrate 1 input interdigital transducer 2 and output interdigital
transducer 3. Input interdigital transducer 2 and output interdigital
transducer 3 have ten electrode-finger pairs, a finger-overlap length
of 4 mm and an interdigital periodicity of 340 .mu.m, respectively.
The finger direction of output interdigital transducer 8 is vertical
to that of input interdigital transducer 2.
FIG. 8 shows a diagram of signal analyzing unit 4 according to
a first embodiment. Signal analyzing unit 4 comprises signal generator
8 amplifier 9 and frequency counter 10.
In the ultrasonic Doppler flow-meter in FIG. 1 having signal analyzing
unit 4 in FIG. 3 if an input electric signal with a carrier frequency
f.sub.0 approximately corresponding to the interdigital periodicity
of input interdigital transducer 2 is applied from signal generator
8 to input interdigital transducer 2 a leaky Lamb wave is excited
in substrate 1. Because substrate 1 is made of a piezoelectric ceramic
plate, and in addition, the polarization axis thereof is parallel
to the thickness direction thereof, the leaky Lamb wave is excited
in substrate 1 effectively. The leaky Lamb wave having the wavelength
approximately equivalent to the interdigital periodicity is radiated
effectively in the form of a longitudinal wave into the liquid,
in other words, a mode conversion from the leaky Lamb wave to the
longitudinal wave in the liquid occurs. Then, disk 6 reflects the
longitudinal wave in the liquid. The reflected longitudinal wave
is detected at output interdigital transducer 3 as a delayed electric
signal with a Doppler frequency f. The delayed electric signal is
amplified via amplifier 9. The amplified electric signal is transmitted
to frequency counter 10 counting the Doppler frequency f , which
is changed according to a rotation of disk 6. Thus, a rotating speed
of motor 5 is detected from a frequency difference .DELTA.f between
the carrier frequency f.sub.0 and the Doppler frequency f.
FIG. 4 shows a plan view illustrating a path of the longitudinal
wave in the liquid by an arrow. Disk 6 reflects the longitudinal
wave by 45.degree. on a horizontal section.
FIG. 5 shows a side view illustrating a path of the longitudinal
wave in the liquid by an arrow. Input interdigital transducer 2
radiates the longitudinal wave into water by 28.8.degree., because
that (1) substrate 1 has a dimension of 150 .mu.m in thickness,
(2) input interdigital transducer 2 have the interdigital periodicity
of 340 .mu.m, and (3) the liquid is water. In other words, a radiation
angle of the longitudinal wave is calculated by means of the leaky
Lamb wave velocity in substrate 1 and the longitudinal wave velocity
in water. As a result, disk 6 reflects the longitudinal wave by
28.8.degree. on a vertical section.
FIG. 6 shows a relationship between the frequency and the calculated
phase velocity of a leaky Lamb wave for each mode in substrate 1.
Piezoelectric substrate 1 has a shear wave velocity of 2450 m/s
and a longitudinal wave velocity of 4390 m/s. Each mode has an
effective radiation condition of the longitudinal wave into the
liquid.
FIG. 7 shows a relationship between the frequency and the calculated
transducer efficiency .eta. for a longitudinal wave radiation into
water. It should be noted that the S.sub.0 mode curve has the highest
peak at around 9.53 MHz, that is the most appropriate operation
frequency.
It is clear from FIGS. 6 and 7 that (1) the S.sub.0 mode Lamb wave
is most effectively converted to the longitudinal wave in water,
(2) the most appropriate operation frequency for the S.sub.0 mode
Lamb wave is approximately 9.53 MHz, which corresponds to the carrier
frequency f.sub.0 and (3) the phase velocity at around 9.53 MHz
in substrate 1 is approximately 3090 km/s.
FIG. 8 shows a spectrum relationship between the frequency observed
at frequency counter 10 and the amplitude thereof, when disk 6 is
rotating. The Doppler spectrum in FIG. 8 has two energy peak frequencies
at around 9.5285 MHz and 9.6345 MHz, corresponding to the Doppler
frequency f and the carrier frequency f.sub.0. Thus, the frequency
difference .DELTA.f is obtained. On the other hand, the Doppler
frequency f is calculated from the following equation, ##EQU1##
where V is the longitudinal wave velocity in water, v is the rotating
speed of motor 5 .alpha. is an incident angle of the longitudinal
wave to disk 6 and .beta. is a radiation angle of the longitudinal
wave into water from substrate 1. The Doppler frequency f calculated
from the equation is approximately coincident with that observed
at frequency counter 10.
FIG. 9 shows a relationship between the rotating speed of motor
5 and the frequency difference .DELTA.f. It is clear that the rotating
speed is linearly correlated with the frequency difference .DELTA.f.
Thus, the rotating speed is obtained from the frequency difference
.DELTA.f. Some minus signs in FIG. 9 mean the reverse rotation.
FIG. 10 shows a diagram of signal analyzing unit 4 according to
a second embodiment. Signal analyzing unit 4 comprises signal generator
11 amplifier 12 and frequency to voltage (F/V) converter 13.
In the ultrasonic Doppler flow-meter in FIG. 1 having signal analyzing
unit 4 in FIG. 10 if an input electric signal with a carrier frequency
f.sub.0 is applied from signal generator 11 to input interdigital
transducer 2 a leaky Labm wave is excited in substrate 1. The leaky
Lamb wave is radiated in the form of a longitudinal wave into the
liquid. Then, disk 6 reflects the longitudinal wave in the liquid.
The reflected longitudinal wave is detected at output interdigital
transducer 3 as a delayed electric signal with a Doppler frequency
f. The delayed electric signal is amplified via amplifier 12. The
amplified electric signal is transmitted to F/V converter 13 which
converts the Doppler frequency f to a voltage thereof and detects
the frequency difference .DELTA.f in terms of the voltage converted
from the Doppler frequency f.
FIG. 11 shows a diagram of signal analyzing unit 4 according to
a third embodiment. Signal analyzing unit 4 comprises signal generator
14 attenuator 15 phase shifter 16 and phase comparator 17.
In the ultrasonic Doppler flow-meter in FIG. 1 having signal analyzing
unit 4 in FIG. 11 if an input electric signal with a carrier frequency
f.sub.0 is applied from signal generator 14 to input interdigital
transducer 2 a leaky Lamb wave is excited in substrate 1. The leaky
Lamb wave is radiated in the form of a longitudinal wave into the
liquid. Then, disk 6 reflects the longitudinal wave in the liquid.
The reflected longitudinal wave is detected at output interdigital
transducer 3 as a delayed electric signal with a Doppler frequency
f. A phase of the delayed electric signal is compared with that
of the input electric signal at phase comparator 17. In this time,
the phase of the input electric signal attenuated via attenuator
15 in case of no rotation of disk 6 is controlled to be coincident
with that of the delayed electric signal by phase shifter 16. Therefore,
the phase of the input electric signal is different from that of
the delayed electric signal, only when disk 6 is rotating. Thus,
phase comparator 17 detects the frequency difference .DELTA.f in
terms of a phase difference between the input- and delayed electric
signals.
FIG. 12 shows a sectional view of another detecting assembly used
in place of the detecting assembly in FIG. 2. The detecting assembly
in FIG. 12 has the same construction as FIG. 2 except for using
a double-layer body in place of substrate 1. The double-layer body
consists of piezoelectric layer part 18 and nonpiezoelectric layer
part 19. Each part has an inner- and an outer end surfaces. Input
interdigital transducer 2 and output interdigital transducer 3 can
be formed on either end surface of piezoelectric layer part 18.
In this embodiment, they are formed on the outer end surface of
piezoelectric layer part 18. The outer end surface of nonpiezoelectric
layer part 19 is in contact with the liquid in FIG. 1. In this time,
for example, an acryl plate is favorable as nonpiezoelectric layer
part 19 in view of the acoustic impedance matching. The detecting
assembly in FIG. 12 is superior to that in FIG. 2 in mechanical
intensity of the body.
FIG. 13 shows a sectional view of another detecting assembly used
in place of the detecting assembly in FIG. 2. The detecting assembly
in FIG. 13 has the same construction as FIG. 2 except for using
a triple-zone body in place of substrate 1. The triple-zone body
consists of first piezoelectric zone part 20 second piezoelectric
zone part 21 and nonpiezoelectric zone part 22 between first piezoelectric
zone part 20 and second piezoelectric zone part 21. Each zone part
has two end surfaces. Input interdigital transducer 2 and output
interdigital transducer 3 are formed on one end surface of first
piezoelectric zone part 20 and that of second piezoelectric zone
part 21 respectively. The other end surface of each zone part being
in contact with the liquid in FIG. 1. The detecting assembly in
FIG. 13 is superior to that in FIG. 2 in ability of detecting the
delayed electric signal at output interdigital transducer 3 because
first piezoelectric zone part 20 and second piezoelectric zone part
21 are electrically separated by nonpiezoelectric zone part 22.
FIG. 14 shows a sectional view of other detecting assembly used
in place of the detecting assembly in FIG. 2. The detecting assembly
in FIG. 14 has the same construction as FIG. 2 except for using
nonpiezoelectric plate 23 first piezoelectric substrate 24 and
second piezoelectric substrate 25 in place of substrate 1. One
end surface of nonpiezoelectric plate 23 is in contact with the
liquid in FIG. 1. First piezoelectric substrate 24 and second piezoelectric
substrate 25 are cemented with the other end surface of nonpiezoelectric
plate 23 under an electrically separated condition. Input interdigital
transducer 2 and output interdigital transducer 3 can be formed
on either end surface of first piezoelectric substrate 24 and second
piezoelectric substrate 26 respectively. The detecting assembly
in FIG. 14 id superior to that in FIG. 2 in mechanical intensity
and ability of detecting the delayed electric signal at output interdigital
transducer 3.
FIG. 15 shows a plan view of a further detecting assembly used
in place of the detecting assembly in FIG. 2. The detecting assembly
in FIG. 15 has the same construction as FIG. 2 except for using
input interdigital transducer 26 and output interdigital transducer
27 in place of input interdigital transducer 2 and output interdigital
transducer 3 respectively. Input interdigital transducer 26 and
output interdigital transducer 27 have an arch-shaped electrode
pattern and are made of an aluminum thin film, respectively. Input
interdigital transducer 26 and output interdigital transducer 27
are arranged such that they make a pair with a concentric center.
The detecting assembly in FIG. 15 is superior to that in FIG. 2
in ability of radiating the longitudinal wave in the liquid by input
interdigital transducer 26 and detecting the delayed electric signal
at output interdigital transducer 27 because input interdigital
transducer 26 and output interdigital transducer 27 have an arch-shaped
electrode pattern, respectively, and are arranged such that they
make the pair with the concentric center.
In FIGS. 12 13 and 14 it is possible to use input interdigital
transducer 26 and output interdigital transducer 27 in place of
input interdigital transducer 2 and output interdigital transducer
3 respectively. Such an arrangement having input interdigital transducer
26 and output interdigital transducer 27 is superior to that having
input interdigital transducer 2 and output interdigital transducer
3 in a radiation ability of the longitudinal wave into the liquid
and a detecting ability of the delayed electric signal.
FIG. 16 shows an illustration in case of measuring a flowing speed
of a liquid in pipe 28 by using the ultrasonic Doppler flow-meter
in FIG. 1. The liquid includes material 29 which moves in accordance
with the flowing speed of the liquid and reflects a longitudinal
wave in the liquid. In the same way as FIG. 1 the flowing speed
of the liquid is obtained from the frequency difference .DELTA.f
between the carrier frequency f.sub.0 and the Doppler frequency
f. Thus, for example, it is possible to obtain a human blood-flow
speed, a flowing speed in a water pipe or a drainpipe, and so on.
While this invention has been described in connection with what
is presently considered to be the most practical and preferred embodiment,
it is to be understood that the invention is not limited to the
disclosed embodiment, but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims. |