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DESCRIPTION JPS63275974

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DESCRIPTION JPS63275974
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
transducer of an ultrasonic rangefinder which transmits and receives ultrasonic waves in the air.
More specifically, the present invention relates to the improvement of the characteristics of the
ultrasonic range finder transducer. (Prior Art) FIG. 7 is an explanatory view of the configuration
of a conventional example generally used conventionally. In the figure, h is a cylindrical
piezoelectric vibrator made of a ceramic system. h is a case of plastics which also serves as an
acoustic matching layer. Reference numeral 31 denotes a damping material for damping the
piezoelectric vibrator. Reference numeral 4 @ is a reflector for directing the transmission of the
ultrasonic wave from the piezoelectric vibrator 11 and changing the direction of the received
sound. In the above configuration, in the case of (1) transmission of an ultrasonic wave, when an
electric pulse is applied to the piezoelectric vibrator 1a, the piezoelectric vibrator 1 causes
respiratory vibration in the radial direction, and is in air normal to the outer peripheral portion. It
generates ultrasonic waves toward it. This ultrasonic wave changes its traveling direction by the
reflection self 4I and travels downward in FIG. 7 as a donut shaped beam as shown in FIG. (2) In
the case of reception of ultrasonic waves The ultrasonic waves incident from the lower side of
FIG. 7 are converged by the reflecting umbrella 41, pass through the case 21, and the
piezoelectric vibrator! Apply stress to the periphery of the turtle. The piezoelectric vibrator 1 @
generates an electric field between the electrodes in response to the applied stress. (Problems to
be Solved by the Invention) As a specific application of the ultrasonic transmitter-receiver based
on such a principle, there is a distance meter or a level meter. In such a thing, the following
characteristics are required. (1) High Damping Characteristic The ultrasonic distance meter is an
instrument for determining the distance ML to the object by measuring the time t until the object
emits an ultrasonic wave and reflects it back. Here, C: the velocity of sound in the propagation
medium However, since the ceramic piezoelectric vibrator 1 generally has a large inertia, even
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after the electric drive pulse a shown in FIG. As shown in FIG. 9 (B), when the damping vibration
is continued and this is called the residual vibration, when the distance to the object to be
measured is short, as shown in FIG. 9 (C), While the residual vibration remains, the reflected
wave C may reach, and separation and determination of the both may be impossible. That is, it
becomes difficult to measure the close distance. On the other hand, when the distance to the
object to be measured is long, as shown in FIG. 9 (D), the reflected wave amplitude becomes
extremely small, and therefore, it is necessary to electrically amplify the received voltage. At this
time, since the electromotive force due to the residual vibration is also amplified at the same
time, in order not to detect the residual vibration erroneously, until the amplitude of the residual
vibration becomes smaller than the amplitude of the wave C, It is necessary to provide a
detection prohibited area (dead zone) e of the reflected wave C as shown in FIG. 9 (E).
From the above, if it is going to measure a long distance, it will become impossible to measure at
a short distance, while if it is possible to measure to a short distance (shortening the dead zone),
it will be a long distance measurement with small reflection. The problem of difficulty arises. In
order to avoid this situation, generally, a method of damping the piezoelectric vibrator is taken
by the damping member 31 shown in FIG. 7, but there are two problems of blowing in this
method. There is. ? It is extremely difficult to select a damping material that has a satisfactory
or normal braking effect over a wide temperature range. That is, many viscous substances,
Because the physical properties change greatly depending on the R degree, in reality, it is
difficult to find a damping material that can obtain necessary and sufficient damping
characteristics from low temperature to high temperature. ? Applying damping with damping
material means suppressing vibration, which leads to a reduction in the sound pressure
generated during transmission. (2) High efficiency of transmission and reception characteristics
It is desirable to be able to transmit and receive sound with low power in terms of energy saving
and safety. However, the transducer shown in FIG. 7 prior art has the following two problems. (2)
Since damping is applied by the damping member 31, in order to obtain a desired vibrator
vibration amplitude, it is necessary to give a driving power considerably higher than that of the
piezoelectric vibrator 11 alone, for example, about lkV when expressed in voltage by 10 times.
There is. ? Piezoelectric vibrator 1 The acoustic impedance of heat (? C: :: density, C: sound
velocity) is about 5 orders of magnitude greater than the acoustic impedance of air, so even if the
piezoelectric vibrator Is vibrates, the energy transmitted to the air is very small It is. In order to
improve this, sound is emitted into the air through a case 21 made of plastic (as small as acoustic
impedance CC) which is softer as sound ? than the piezoelectric vibrator 11 as an acoustic
matching layer. Further, when the thickness of the plastic layer 21 is 174 wavelengths, the
energy transmission efficiency is maximized. However, when the speed of sound of plastic
changes due to temperature change, equivalent plastic layer thickness! As a result, the sound
propagation efficiency is degraded. After all, the presence of the matching layer 21 can be
regarded as a temperature change of the transmission and reception characteristics. (2) Simple
Structure As described above, the transducer of the prior art shown in FIG. 7 has the damping
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material 31 and the acoustic matching layer 21 in addition to the piezoelectric vibrator 1i in
order to bring its characteristics closer to an ideal one. And so on, and as a result, the
characteristics are greatly affected by these factors against temperature change and the like.
Ideally, it is desirable not to have these extra elements. The present invention solves these
problems. An object of the present invention is to provide an ultrasonic transducer having a
simple structure, high damping characteristics and good efficiency. (Means for Solving the
Problems) In order to achieve this object, the present invention provides a cylindrical holder, and
a recess provided in a ring shape leaving both end portions of the circumferential surface of the
holder. A cylindrical polymeric piezoelectric film fixed to both end portions of the peripheral
surface of the holder and constituting the recess and the chamber, and an electrode plate
provided on the outer periphery and the inner peripheral surface of the polymeric piezoelectric
film And a conical reflector for attaching the head side to one end of the holding body and
imparting directivity of the axial direction of the holding body to ultrasonic waves transmitted
and received, and the chamber and the outside provided on the holding body. A transducer of an
ultrasonic rangefinder comprising a communicating pressure equalizing hole is constructed. In
the above configuration, when an electric pulse is applied to the polymer piezoelectric film, the
polymer piezoelectric film causes respiratory vibration in the radial direction. The ultrasonic
waves generated by this respiratory vibration are converted in the traveling direction by the
reflector and travel as a donut shaped beam. On the other hand, when pressure is applied to the
polymeric piezoelectric film from the outside, expansion and contraction of the polymeric
piezoelectric film 1 occur, and a voltage is generated between the electrodes. Hereinafter, the
present invention will be described in detail based on examples. (Embodiment) FIG. 1 is a view
for explaining the construction of an embodiment of the present invention. In the figure, 1 is a
cylindrical polymeric piezoelectric film. The polymeric piezoelectric film 1 is formed in a
cylindrical shape as shown in FIG. 3 after being stretched in the circumferential direction ? as
shown in FIG. In this case, polyvinylidene fluoride (pvDF) is used. II and +2 are electrodes
provided on both sides of the polymer piezoelectric film 1. Ill and 12+ are lead wires attached at
one end to the electric wire 44 + 1j12 respectively. Reference numeral 2 denotes a cylindrical
holding body for holding the polymeric piezoelectric film 1 at the upper and lower end faces so
as not to hear the respiratory vibration as much as possible. The holding body 2 is a plastic
excellent in weather resistance and the like, for example, Teflon. Environmental vinyl is used.
Denoted at 2 I is a recess provided on the circumferential surface of the holder 2 and
constituting the polymeric piezoelectric film 1 and the chamber 3. A conical reflector 4 has a
head side attached to the end of the polymeric piezoelectric film I to impart directivity to
ultrasonic waves transmitted and received. Reference numeral 5 denotes a pressure equalizing
hole which is provided in the holder 2 and communicates the chamber 3 with the outside. In the
above configuration, polymer pressure? ! ! When an electric pulse is applied to the film 1, the
polymeric piezoelectric film 1 expands and contracts in the stretching direction ?, but since the
polymeric piezoelectric film 1 is formed in a cylindrical shape, it is converted into respiratory
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vibration in the radial direction.
The ultrasonic waves generated by this respiratory vibration are converted in the direction of
travel by the reflector 4, and travel as a doughnut-shaped beam downward in FIG. On the other
hand, when pressure is applied to the polymer piezoelectric film 1 from the outside, expansion
and contraction of the polymer pressure film 1 occurs, and a voltage is generated between the
electrodes 11.12. That is, the transducer shown in FIG. 1 performs the same operation as that of
the conventional example shown in FIG. The polymeric piezoelectric film 1 has a small acoustic
impedance () and is easy to match with water, air, and the like. (2) It is possible to transmit and
receive pulses with a short duration, because the internal energy breakdown is large. (3) The
flexibility makes it easy to manufacture and process thin films. It has the feature of. Taking
advantage of these characteristics, as shown in FIG. 1, vibration in the longitudinal direction of
the membrane is converted to radial vibration and used. The resonance frequency fo of the
crucible at this time is expressed by equation (2) if the curvature radius of the film is indicated by
C, and the density is indicated by ?. Therefore, assuming that C = 113 О lo ? ? (N / m ?) and
== 1.8 О 11 ? (kg / m ?) for the metal plate, the radius of the holding body 2 is IQ + nm in FIG.
It is possible to transmit and receive ultrasonic waves of about 40 kHz. Hereinafter, the
advantage of using the polymer piezoelectric material vl will be specifically described in
comparison with a ceramic piezoelectric vibrator. (1) In the case of transmission: The absolute
value of the sound pressure radiated into the air is proportional to the velocity V of the vibration
source if the frequency of the vibration source and the radiation surface Jfi are the same. Since
the velocity {circle over (1)} is proportional to the displacement X of the vibration source if the
frequency is constant, let us consider the conversion efficiency of the voltage V applied to the
polymeric piezoelectric film 1 and the displacement X. Assuming that a voltage ? is applied
between the electrodes II and H provided on both sides of the polymeric piezoelectric film 1, the
stretching direction of the polymeric piezoelectric film 1, that is, the elongation 6g of the outer
periphery of the cylinder can be calculated by the following equation. 1 ? ffi / R l = 1 S l = d, E =
av / l (3) where Q is the length of the polymer piezoelectric film 1 = 2?r: r = radius), the point is
the polymer piezoelectric film l The thickness d31 is a piezoelectric strain constant. From
equation (3), it can be seen that ?Q becomes larger as the piezoelectric strain constant d31
increases and the thickness t decreases. As the ?? is larger, the amplitude X of the respiratory
vibration of the polymer piezoelectric film l is also larger. The piezoelectric strain constant dS +
of the polymer piezoelectric film 1 is generally one order of magnitude smaller than the ceramic
piezoelectric vibrator 11, for example, the piezoelectric strain constant d31 of P2T, but
conversely, the plate thickness t is extremely small. It is possible to make.
As a whole, it is possible to obtain a large ?l / Q several times more efficiently than FAT. For
example, the piezoelectric strain constant d of the polymer piezoelectric film 1, = 10xlO-"(C / N),
thickness t = 40?m, P2T piezoelectric strain constant d3. Assuming that 100 О IQ? ? ? (C /
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N) and thickness t = 2 mm, the f city of ?1 / 1 is (piezoelectric m / PI) = 5. That is, while it is
impossible to form a cylindrical crucible with a thickness on the order of 10 ?m from the point
of being vulnerable to impact, the piezoelectric ceramic film 1 can be made extremely thin.
Therefore, it can be compensated that the piezoelectric distortion constant d11 is small. {Circle
over (2)} Since the polymeric piezoelectric film 1 is a polymer, the attenuation of energy inside is
large. This is considered to be a high damping effect of vibration, and it is not necessary to apply
damping by a special damping member 31 as in the conventional ultrasonic transducer. ? This
further reduces the vibration amplitude due to the damping material 3 (in the conventional
example, for example, about-or less! It was decreasing below fl. ) Can be avoided. Taking into
consideration the difference in efficiency in the item (1), the value of the amplitude X obtained
when the same voltage (2) is applied is the number of conventional examples! The size reaches
? times to several hundred times. (1) Force, permeability T of energy from the transducer to air:
z: acoustic impedance of the transducer z: acoustic impedance of air. 2. of polymer piezoelectric
film Applying # 3X IQ '(MS / m "), PAT zlm 3Qx IQ' (Is / m") and air 2i-4QQ (83-83), Tl;
Permeability of polymer piezoelectric film and air T,: P2T and the transmittance of air P2T In the
conventional example, the acoustic matching layer 21 is used to improve the low transmittance,
but in the polymer piezoelectric film, it is particularly It is possible to propagate with relatively
good efficiency without using any means. (2) In the case of reception {circle over (2)} The open
end voltage V generated between both surfaces of the polymeric piezoelectric film 1 by the force
F applied from the outside at the time of reception (the direction is the stretching direction of the
polymeric piezoelectric film 1) It is shown again. l E l = l v / l l = g x + и o = gs + и F / Q и t "l V l = K
31 и F / ? (5) :: stress g 31: voltage ratio ? force constant polymer piezoelectric film 1 Since the
value of the voltage output constant gs + is about 10 to 20 times as large as that of the ceramic
system, for example, the voltage output constant gx + of P2T, a large IVI can be obtained even
with the same force F.
{Circle over (2)} Since the effect of the presence or absence of the damping material described in
the section of transmission is established also at the time of reception, the efficiency can be
increased by several 10 to 2 H times or more at the time of reception as a whole. As a result of
the above, according to the device of the present invention, functions and transmission /
reception efficiency equal to or more than those of the method using the conventional ceramic
vibrator can be realized with a power consumption of I / 1006 or less. Next, the characteristics of
the prototyped transducer will be described using a specific example. In a device in which the
polymer piezoelectric film 1 with a thickness of 56 ?m is bonded to the holder 2 at the upper
end and the lower end with a width of 2 mm so that the radius of the holder 2 is 30 mm and the
diameter is 30 mm. The transmission and reception sensitivities at a distance of 800 familiar
were obtained as follows. Transmission; 120 dB (O dB = 2 x l [l-'? her) reception (F f; -30 dB (O
dB = IV / u btr) This corresponds to a total of 500 to It shows the same property as that of 0a. In
the measurement of the transmission sensitivity, the drive voltage of the drive circuit is l'0 Vp-p,
and in order to eliminate the reactive component due to the polymer pressure and the
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capacitance component of ? pattern 1, match both with appropriate inductance. ing. Further,
although the thickness of the polymeric piezoelectric film 1 is 5 О 1 ?m in the above specific
example, if this thickness is too thin, it can not maintain its own tension necessary for
transmission and reception if it is cylindrical. In addition, problems such as difficulty in
manufacturing also occur. On the other hand, if it is too thick, there arises a problem that the
transmission sensitivity is reduced by the equation (3) of ll'iJ. 25 to 10 ?m is suitable as a
practical one that can be used. Further, in the embodiment of FIG. 1, the fixation of the polymeric
piezoelectric film l is made only to the upper and lower end faces because the respiratory
vibration of the polymeric piezoelectric material M 1 is considered to be restrained as little as
possible. The transmission and reception sensitivities are sharply reduced if the point of
attachment (fixed point) is provided. That is, for example, as shown in FIG. 4, the transmission
and reception sensitivities are respectively reduced to transmission; 115 dB reception; That is, by
fixing only the upper and lower ends of the polymeric piezoelectric film 1 to the holder 2, a film
having high sensitivity can be obtained. FIG. 5 is a graph comparing the total sensitivity of
transmission and reception depending on the presence or absence of the pressure equalizing
hole 5 in the configuration of FIG. In the case where there is no pressure equalizing hole 5, the
case where there is a pressure equalizing hole 5 is shown. When the pressure increases due to
the change in ambient pressure, the sensitivity sharply decreases with the increase in pressure
when there is no pressure equalization hole 5, while when the pressure equalization hole 5 is
present, the sensitivity There has been no decline.
FIG. 6 shows the directivity of the counter 8 at the front 3 m of the transducer showing the
magnitude of the reflected sound from the umbrella 4. Due to the effect of the reflector 4, sharp
directivity within a half angle of 4 can be obtained, and an ideal characteristic as a distance meter
or level meter can be realized. As a result (1) Since the internal attenuation of the polymeric
piezoelectric film 1 itself is large, transmission and reception of ultrasonic waves with high
damping characteristics become possible without using a damping material. (2) Since no
damping material is used, there is no energy loss due to it, and high efficiency transmission and
reception (a) becomes possible. (3) The acoustic impedance of the polymeric piezoelectric film 1
is smaller by one digit than the acoustic impedance of the ceramic vibrator, so that the
transmission and reception efficiency of sound into the air is good. (4) Since the thickness of the
polymeric piezoelectric film 1 can be reduced, the electric field strength can be increased at the
time of transmission, and the transmission efficiency (displacement of the polymeric piezoelectric
film l) can be increased. Also, when receiving, this thinness does not affect the output. On the
other hand, a high open end voltage can be obtained by the high voltage output constant gs + of
the polymeric piezoelectric film 1 itself. That is, the transmission and reception efficiency can be
greatly improved. (5) Since it is not necessary to use a damping material, an acoustic matching
layer, etc., it is possible to avoid a change in temperature characteristics caused by a change in
physical properties of these. (6) Therefore, high performance can be realized with extremely low
power consumption as compared with the prior art shown in FIG. (7) Polymer Piezoelectric ll!
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Since the fixation of J1 is limited only to the upper and lower end faces, free and unrestricted
respiratory vibration can be obtained, and as a result, high transmission / reception sensitivity
can be obtained. (8) By having the pressure equalizing hole 5, it is possible to realize a transducer
whose sensitivity is not affected by the ambient pressure. (9) By using the reflector 4, it is
possible to realize a transducer having a good directivity which is optimal for a distance meter. In
the above embodiment, although the holder 2 is described as being made of a plastic material, it
is made of metal such as stainless steel, and it is used as an electrode lead portion (lead portion
from the 11I electrode) in the polymer piezoelectric film 1 Of course it may be good. In addition,
if the material of the holding body 2 is a ceramic such as alumina, it is possible to integrally fire a
complicated shape, it is possible to minimize additional processing, and the manufacturing cost
can be reduced. Ceramics are also characterized by having excellent weather resistance and
chemical resistance. In addition, if a metal coating (metallizing) is applied to the ceramic surface,
it is possible to add an advantage that it can be used as a lead-out portion of the inner electrode.
In the above-mentioned embodiment, although it has been described that the piezoelectric
polymer film 1 is made of polyvinylidene fluoride (PVDE), the present invention is not limited
thereto. For example, a copolymer of vinylidene fluoride and triple ethylene (P ( VDF-TrFI), a
copolymer of vinylidene fluoride and tetrafluoroethylene (P (VDF-TeFE)), or an alternating
copolymer of cyanovinylidene and vinyl acetate (P (VDCN-VAC)). And may be any one that
exhibits good piezoelectricity. In these materials, the stretching operation is not necessarily
required, and only the polarization operation by high voltage application may be performed.
(Effects of the Invention) As described above, according to the present invention, a cylindrical
holding body, a recess provided in a ring shape leaving both end portions of the circumferential
surface of the holding body, and the circumferential surface of the holding body A cylindrical
polymer piezoelectric film fixed to the both end portions and constituting the recess and the
chamber, an electrode plate respectively provided on the outer peripheral surface and the inner
peripheral surface of the polymer piezoelectric film, and one end of the holding body A conical
reflector that imparts directivity in the axial direction of the holder to the ultrasonic wave
attached to the head side and transmitted and received, and a pressure equalizing hole that is
killed by the holder and communicates the chamber and the 41 part The transducer of the
equipped ultrasonic distance meter was constructed. As a result, (1) because the internal
damping of the polymeric piezoelectric film itself is large, it is possible to transmit and receive
ultrasonic waves with high damping characteristics without using a damping material. (2) Since
no damping material is used, there is no energy loss due to it, and highly efficient transmission
and reception become possible. (3) The acoustic impedance of the polymeric piezoelectric film 1
is smaller by one digit than the acoustic impedance of the ceramic vibrator, so that the
transmission and reception efficiency of sound into the air is good. (4) Since the thickness of the
polymeric piezoelectric film can be reduced, the electric field strength can be increased at the
time of transmission, and the transmission efficiency (displacement of the polymeric piezoelectric
film) can be increased. Also, when receiving, this wI does not affect the output. On the other
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hand, a high open @ voltage can be obtained by the high voltage output constant gs + of the
polymer piezoelectric film itself. That is, the transmission and reception efficiency can be greatly
improved. (5) Since it is not necessary to use a damping material, an acoustic matching layer or
the like, it is possible to avoid a change in temperature characteristics caused by a change in
physical properties of these. (6) Therefore, high performance can be realized with extremely low
power consumption as compared to the conventional example. (7) Since the fixation of the
polymeric piezoelectric film is limited only to the upper and lower end faces, free and
unrestricted respiratory vibration can be obtained. As a result, high transmission / reception
sensitivity can be obtained.
(8) By having the pressure equalizing holes, it is possible to realize a transducer whose sensitivity
is not affected by the ambient pressure. (9) By using a reflector, it is possible to realize a
transducer having good directivity which is optimal for a distance meter. Therefore, according to
the present invention, an ultrasonic wave receiver having high damping characteristics and good
efficiency can be realized with a simple structure.
[0002]
Brief description of the drawings
[0003]
1 is an explanatory view of the construction of an embodiment of the present invention, FIG. 2 is
an explanatory view of parts of FIG. 1, FIG. 3 to FIG. 6 are explanatory views of FIG. 1 operation,
and FIG. FIG. 8 is an explanatory view of the configuration of the conventional example used, FIG.
8 and FIG. 9 are operation explanatory views of FIG.
1 иии Polymer piezoelectric film, II j port иии Electrode, 1112 port 1 иии Lead wire, 2 и и и Holding body,
21 иии Recess, 3 и и и и и и и и и , 5 ... pressure equalizing holes. Fig.7 Fig.2 Fig.3 r Sword 0 ?t 1 1
pressure (? m ? ? popular pressure ? 7
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