JPH07111458B2 - Ultrasonic rangefinder - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ultrasonic range finder that transmits and receives ultrasonic waves in the air to measure a distance.

More specifically, the present invention relates to an improvement in the structure of a transducer of an ultrasonic range finder.

<Prior Art> FIG. 11 is an explanatory view of a configuration of a conventional example which is generally used in the past.

In the figure, 1a is a cylindrical piezoelectric vibrator made of ceramics. 2a is a plastic case that also serves as an acoustic matching layer. 3a is a damping material for braking the piezoelectric vibrator 1a. Reference numeral 4a is a reflector for changing the direction of ultrasonic waves transmitted / received by the piezoelectric vibrator 1a to have directivity.

In the above configuration, (1) In case of transmitting ultrasonic wave When an electric pulse is applied to the piezoelectric vibrator 1a, the piezoelectric vibrator 1a
Causes respiratory vibrations in the radial direction and generates ultrasonic waves toward the air in the normal direction of the outer peripheral portion. This ultrasonic wave is converted in its traveling direction by the reflector 4a and becomes a donut-shaped beam as shown in FIG. 12 and travels downward in FIG.

(2) In the case of receiving ultrasonic waves Ultrasonic waves that have entered from below in Fig. 11 are converged by the reflector 4a, pass through the case 2a, and apply stress to the outer peripheral portion of the piezoelectric vibrator 1a. The piezoelectric vibrator 1a generates an electric field in the sense of electrodes according to the applied stress.

<Problems to be Solved by the Invention> An ultrasonic distance meter based on such a principle is required to have the following characteristics.

(1) High Damping Characteristics An ultrasonic range finder is an instrument for determining a distance L to an object by radiating an ultrasonic wave toward the object and measuring a time t until the ultrasonic wave returns and returns.

Here, L = (1/2) Ct (1) C; sound velocity in the propagation medium However, since the ceramic-based piezoelectric vibrator 1a generally has large inertia, the electric drive pulse shown in FIG. As shown in Fig. 13 (B),
Damping vibration b continues. This is called residual vibration b. When the distance to the measurement target is short, as shown in FIG. 13 (C), while residual vibration b remains, In some cases, the reflected wave C arrives, making it impossible to separate and distinguish the two. That is, it becomes difficult to measure the closest distance.

On the other hand, when the distance to the measurement target is long, the reflected wave amplitude becomes extremely small as shown in FIG. 13 (D), so that it becomes necessary to electrically amplify the received voltage. At this time, since the electromotive force due to the residual vibration b is also amplified at the same time, in order not to detect the residual vibration b by mistake,
Until the amplitude of the residual vibration b becomes smaller than the amplitude of the reflected wave c, the detection prohibited area (dead zone) e of the reflected wave c is
It needs to be provided as shown in FIG.

From the above, when trying to measure a long distance, it becomes impossible to measure a short distance. On the other hand, when it is possible to measure up to a short distance (shortening the dead zone), a long distance with a small reflection occurs. The problem arises that measurement becomes difficult.

In order to avoid this situation, generally, a method of braking the piezoelectric vibrator 1a by the damping material 3a shown in FIG. 11 is adopted, but this method has the following two problems. There is.

It is extremely difficult to select a damping material having a satisfactory or appropriate braking effect in a wide temperature range. That is, the physical properties of many viscous substances change greatly depending on the temperature, and in reality, it is difficult to find a damping material that can obtain the necessary and sufficient braking characteristics from low temperatures to high temperatures.

Applying damping with a damping material means suppressing vibration, which leads to a reduction in sound pressure generated during transmission.

(2) High-efficiency transmission / reception characteristics It is desirable that sound can be transmitted / received with low power in terms of energy saving and safety.

However, the transmitter / receiver shown in the conventional example of FIG. 11 has the following two problems.

Since damping is applied by the damping material 3a, in order to obtain the desired oscillator vibration amplitude, it is necessary to give a driving power that is considerably larger than that of the piezoelectric oscillator 1a alone, for example, 10 times, or 1 KV when expressed in terms of voltage. is there.

Since the acoustic impedance (ρc ;; density, c; speed of sound) of the piezoelectric vibrator 1a is about 5 orders of magnitude higher than the acoustic impedance of air, even if the piezoelectric vibrator 1a vibrates, the energy transmitted to the air is extremely small. . In order to improve this, sound is emitted into the air through a case 2a made of plastic that is acoustically softer (smaller acoustic impedance ρc) than the piezoelectric vibrator 1a as an acoustic matching layer. ing. Also, this plastic layer 2a
When the thickness is 1/4 wavelength, the energy transmission efficiency becomes maximum. However, if the sound velocity of the plastic changes due to temperature change, the equivalent plastic layer thickness will deviate from 1/4 wavelength, and the sound propagation efficiency will deteriorate. After all,
The presence of the matching layer 2a appears as a temperature change of the transmission / reception characteristics.

(3) Simple structure As described above, the transducer of the conventional example shown in FIG. 11 has the damping material 3a and the acoustic matching in addition to the piezoelectric vibrator 1a in order to approach the characteristics of the transducer. The additional elements such as the layer 2a are required, and as a result, the characteristics are greatly affected by these elements with respect to temperature changes and the like.

Ideally, there should be no such extra elements.

The present invention solves this problem.

An object of the present invention is to provide an ultrasonic rangefinder having a simple structure, high damping characteristics, high efficiency, and good waterproofing when submerged in water.

<Means for Solving the Problem> In order to achieve this object, the present invention provides a cylindrical holder, a ring-shaped recess that leaves both ends of the peripheral surface of the holder, and A cylindrical polymeric piezoelectric film that is fixed to a portion other than the concave portion on the peripheral surface of the holding body to form the concave portion and a chamber, and electrode plates provided on the outer peripheral surface and the inner peripheral surface of the polymeric piezoelectric film, respectively. And a conical reflector that is attached to one end of the holding body on the head side to give directivity in the axial direction of the holding body to ultrasonic waves transmitted and received, and communicates the chamber provided on the holding body with the outside. And a plate-like sealing lid that is provided to face the external opening of the pressure equalizing hole and that seals the external opening of the pressure equalizing hole with water pressure. This is an ultrasonic rangefinder.

<Operation> In the above configuration, when an electric pulse is applied to the polymeric piezoelectric film, the polymeric piezoelectric film causes respiratory oscillation in the radial direction.
The ultrasonic waves generated by the respiratory vibrations are changed in direction of travel by the reflector and travel as a donut-shaped beam.

On the other hand, when pressure is applied to the polymer piezoelectric film from the outside, the polymer piezoelectric film expands and contracts to generate a voltage between the electrodes.

Then, if the transducer is submerged in water, due to water pressure,
The outer opening of the pressure equalizing hole is sealed by a sealing lid.

Hereinafter, detailed description will be given based on examples.

<Embodiment> FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

In the figure, 1 is a cylindrical polymer piezoelectric film. The polymeric piezoelectric film 1 is stretched in the circumferential direction α as shown in FIG. 2 and then formed into a cylindrical shape as shown in FIG. In this case, polyvinylidene fluoride (PVDF) is used.

Electrodes 11 and 12 are provided on both sides of the piezoelectric polymer film 1. 111 and 112 are lead wires having one ends attached to the electrodes 11 and 12, respectively.

Reference numeral 2 is a cylindrical holder that holds the polymeric piezoelectric film 1 on the upper and lower end surfaces thereof so as not to hinder the respiratory vibration. The holder 2 is made of plastic having excellent weather resistance such as Teflon and vinyl chloride.

21 is provided on the peripheral surface of the holder 2, and the piezoelectric polymer film 1 and the chamber 3 are provided.
It is a concave portion that constitutes.

Reference numeral 4 is a conical reflector having a head side attached to one end of the polymeric piezoelectric film 1 and imparting directivity to ultrasonic waves to be transmitted and received.

Reference numeral 5 is a pressure equalizing hole provided in the holding body 2 to connect the chamber 3 and the outside.

Reference numeral 6 denotes a plate-like sealing lid which is provided so as to face the external opening of the pressure equalizing hole 5 and seals the external opening of the pressure equalizing hole 5 by water pressure. One end of the sealing lid 6 is fixed to the holding body 2, and in this case, it is made of an elastic body. Normally, a gap 61 exists between the sealing lid 6 and the holding body 2.

In the above configuration, when an electric pulse is applied to the polymeric piezoelectric film 1, the polymeric piezoelectric film 1 expands and contracts in the stretching direction α,
Since the polymer piezoelectric film 1 is formed into a cylindrical shape, it is converted into respiratory vibration in the radial direction. The ultrasonic wave generated by this respiratory vibration has its traveling direction changed by the reflector 4.
It becomes a donut-shaped beam and travels downward in FIG.

On the other hand, when pressure is applied to the polymeric piezoelectric film 1 from the outside, the polymeric piezoelectric film 1 expands and contracts, and a voltage is generated between the electrodes 11 and 12.

That is, the transmitter / receiver shown in FIG. 1 performs the same operation as that of the conventional example shown in FIG.

Then, if the transducer is submerged in water, due to water pressure,
The outer opening of the pressure equalizing hole is sealed by a sealing lid.

The polymeric piezoelectric film 1 has (1) a low acoustic impedance and is easily matched with water, air, and the like.

(2) Pulses of short duration can be transmitted / received due to large energy attenuation inside.

(3) Since it is flexible, it can be easily manufactured and processed into a thin film.

It has the feature.

Taking advantage of these characteristics, as shown in FIG. 1, the vibration in the length direction of the film is converted into the vibration in the radial direction for use.

The resonance frequency f ₀ of the film at this time is expressed by the half radius of curvature of the film R,
If the elastic modulus is represented by E and the density is represented by ρ, the equation (2) is obtained.

f ₀ = {1 / (2πR)} (E / ρ) ^1/2 (2) Therefore, suppose now that E = 11.3 × 10 ⁹ (N / m ² ), ρ = 1.8 ×
If 10 ³ 8Kg / m), in a first view, by a radius of the holder 2 and 10 mm, it is possible to transmit and receive ultrasonic waves of about 40 KHz.

Hereinafter, the advantage of using the polymer piezoelectric film 1 will be specifically described in comparison with a ceramic-based piezoelectric vibrator.

(1) In case of transmission The absolute value of the sound pressure radiated in the air is proportional to the velocity V of the vibration source if the frequency and radiation area of the vibration source are the same. Since the velocity V is proportional to the displacement X of the vibration source if the frequency is constant, the conversion efficiency between the voltage V applied to the polymer piezoelectric film 1 and the displacement X will be considered.

If a voltage V is applied between the electrodes 11 and 12 provided on both sides of the polymeric piezoelectric film 1, the stretching direction of the polymeric piezoelectric film 1, that is, the elongation Δl of the outer circumference of the cylinder can be calculated by the following equation.

│Δl / l | = | S | = d ₃₁ E = d ₃₁ · V / t (3) where, 1 is the length of the piezoelectric polymer film 1 (= 2πr, r = radius), and t is high. The thickness of the molecular piezoelectric film 1, d ₃₁ is a piezoelectric strain constant.

From the equation (3), Δl becomes larger as the piezoelectric strain constant d ₃₁ becomes larger.
It can be seen that the smaller the thickness t, the larger the value. Is larger, the amplitude X of the respiratory vibration of the polymer piezoelectric film 1 is also larger.

The piezoelectric strain constant d ₃₁ of the polymer piezoelectric film 1 is generally one digit smaller than the piezoelectric strain constant d ₃₁ of the ceramic type piezoelectric vibrator 1a, for example, pzt, but conversely the plate thickness t is extremely small. It is possible to make things. After all, it is possible to obtain a large Δl / l with efficiency that is several times more efficient than PZT.

As an example, the piezoelectric strain constant of the polymer piezoelectric film 1 d ₃₁ = 10
× 10 ^-12 (C / N), thickness t = 4 μm, piezoelectric strain constant of PZT d ₃₁
= 100 × 10 ^-12 (C / N) and thickness t = 2μm, Δl / l
The value of is (piezoelectric film / PZT) = 5.

That is, in a ceramic-based piezoelectric vibrator, it is impossible to form a cylindrical film having a thickness of the order of 10 μm from a place vulnerable to impact, whereas the polymer piezoelectric film 1 can be made extremely thin. It is possible to compensate for the small distortion constant d ₃₁ .

Since the polymer piezoelectric film 1 is a polymer, the internal energy is greatly attenuated. This appears as a high damping effect of vibration, and it is not necessary to apply braking by the special damping material 3a unlike the ultrasonic transmitter / receiver of the conventional example.

This can further avoid the reduction of the vibration amplitude due to the damping material 3a (in the conventional example, it was reduced to about 1/10 or less, for example). Considering the difference in efficiency in the above term, the value of the amplitude X obtained when the same voltage V is applied reaches several tens to several hundreds of times that of the conventional example.

On the other hand, the transmittance T of energy from the oscillator to the air
Is T = 4Z ₁ Z ₂ / (Z ₁ + Z ₂ ) ² (4) Z ₁ ; Acoustic impedance of oscillator Z ₂ ; Acoustic impedance of air.

Z ₁ 3 × 10 ⁶ (NS / m ³ ) of polymer piezoelectric film 1, Z ₁ 30 of PZT
Applying × 10 ⁶ (NS / m ³ ) and Z ₂ 400 (NS / m ³ ) of air, T ₁ / T ₂ = (0.53 × 10 ^-3 ) / (0.053 × 10 ^-3 ) = 10 T ₁ ; Transmittance between polymer piezoelectric film 1 and air T ₂ ; Transmittance between PZT and air In the conventional example using PZT, acoustic matching layer 2a is used to improve the low transmittance. However, in the piezoelectric polymer film 1, even if such a means is not used,
Propagation is possible with relatively good efficiency.

(2) In the case of reception The open-end voltage V generated between both surfaces of the polymer piezoelectric film 1 by the force F (direction is the extending direction of the polymer piezoelectric film 1) applied from the outside at the time of reception is expressed by the following equation. .

| E | ＝ | V / t | ＝ g ₃₁・ ρ ＝ g ₃₁・ F / l ・ t ∴ | V | ＝ g ₃₁・ F / l (5) ρ; Stress g ₃₁ ; Voltage output constant Polymer piezoelectric film Since the value of the voltage output constant g ₃₁ of 1 is about 10 to 20 times the value of the voltage output constant g ₃₁ of a ceramic system, for example, PZT, a large | V | can be obtained even with the same force F.

Since the effect of the presence or absence of damping material described in the case of transmission is established even at the time of reception, comprehensively several tens even at the time of reception.
Up to 200 times more efficient is possible.

As a result, according to the present invention, it is possible to realize the functions and the transmission / reception efficiencies that are equal to or higher than those of the method using the conventional ceramic-based vibrator with the power consumption of 1/1000 or less.

Next, the characteristics of the prototyped transmitter / receiver will be described with reference to specific examples.

In a device in which a holder 2 has a radius of 10 mm and a height of 30 mm, a polymer piezoelectric film 1 having a thickness of 50 μm is attached to and supported by the holder 2 with a width of 2 mm at each of upper and lower ends.
The following values were obtained for the transmission and reception sensitivities at a distance of 800 mm over the entire surface.

Transmission; 120 dB (0 dB = 2 x 10 ^-4 µbar) Reception; -30 dB (0 dB = 1 V / µ bar) This is a total transmission and reception characteristics of 500 to 1000 times compared to the conventional transducer of Fig. 11. It shows an improvement.

In the measurement of the transmission / reception sensitivity, the drive voltage of the drive circuit is set to 10 V _PP, and in order to eliminate the ineffective component due to the capacitance component of the polymer piezoelectric film 1, the inductance is matched with each other.

Further, the thickness of the piezoelectric polymer film 1 is 50 μm in the above specific example.
However, if this thickness is too thin, it is not possible to maintain the self-tension required for transmission and reception in the case of a cylindrical shape. Also,
Problems such as difficulty in manufacturing occur.

On the other hand, if it is too thick, the problem that the transmission / reception sensitivity decreases due to the equation (3) occurs.

A practically usable value is 25 to 10 μm.

FIG. 5 is a graph comparing transmission and reception total sensitivities with and without the pressure equalizing hole 5 in the configuration of FIG. Shows the case where there is no pressure equalizing hole 5, and shows the case where there is a pressure equalizing hole 5.

When the pressure increases due to a change in the ambient pressure, the sensitivity sharply decreases as the pressure increases when the pressure equalizing hole 5 does not exist, whereas when the pressure equalizing hole 5 exists, the sensitivity decreases sharply. No reduction in sensitivity has occurred.

FIG. 6 shows the directivity indicating the magnitude of the reflected sound from the reflector 4 3 m in front of the transmitter / receiver.

Due to the effect of the reflector 4, sharp directivity within a half-angle of 4 can be obtained, and ideal characteristics as a distance meter or level meter can be realized.

As a result, (1) since the polymeric piezoelectric film 1 itself has a large internal attenuation, it is possible to transmit and receive ultrasonic waves having 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 / reception is possible.

(3) Since the acoustic impedance of the polymeric piezoelectric film 1 is an order of magnitude smaller than the acoustic impedance of the ceramic-based vibrator, the sound transmission / reception efficiency into the air is good.

(4) Since the polymer piezoelectric film 1 can be made thin, the electric field strength can be increased during transmission, and the transmission efficiency (the amount of displacement of the polymer piezoelectric film 1) can be increased.

Also, upon reception, this thinness does not affect the output. On the other hand, a high open circuit voltage can be obtained due to the high piezoelectric output constant g _{31 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 changes in the temperature characteristics due to changes in these physical properties.

(6) Therefore, as compared with the conventional example shown in FIG. 11, high performance can be realized with extremely low power consumption.

(7) Since the polymeric piezoelectric film 1 is fixed only to the upper and lower end faces, free breathing vibration without restraint can be obtained, and as a result, a large transmission / reception sensitivity can be obtained.

(8) By having the pressure equalizing hole 5, it is possible to realize a transducer in which the sensitivity is not influenced by the ambient pressure.

(9) By using the reflector 4, it is possible to realize a transmitter / receiver having a good directivity, which is optimum for a rangefinder.

(10) When the transducer is submerged in water, the sealing lid automatically closes the outer opening of the pressure equalizing hole due to the water pressure when the water is submerged, thus preventing water from entering the pressure equalizing hole. It is possible to prevent a decrease in the sensitivity of the transducer after the death.

FIG. 7 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

In this embodiment, a continuous protrusion 22 is provided around the pressure equalizing hole 5 of the holder 2.

A more complete seal between the pressure equalizing hole 5 and the sealing lid 6 can be obtained.

FIG. 8 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

In the present embodiment, the sealing lid 6 has a buoyant body 62 with a large buoyancy.
Is attached to increase the sealing pressure due to the buoyancy of the sealing lid 6.

FIG. 9 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

In the present embodiment, the sealing lid 6 is not made of an elastic material, but a sealing body 63 is provided on the sealing surface with the pressure equalizing hole 5, and a hinge 64 is used to attach the sealing lid 6 to the holding body 2. is there. Reference numeral 65 is a sealing lid retainer.

FIG. 10 is an explanatory view of a main part configuration of another embodiment of the present invention.

In this embodiment, a guide rod 65 is provided on the holder 2 so that the sealing lid 6 can move along the guide rod 66.

In addition, in the above-described embodiments, the holder 2 is described as being made of a plastic material, but is made of metal such as stainless steel,
Of course, this may also be used as an electrode lead-out portion (lead portion) from the inner electrode of the polymer piezoelectric film 1.

Further, if the holding body 2 is made of ceramics such as alumina, it is possible to integrally burn a complicated shape, the additional work can be suppressed to the minimum, and the manufacturing cost can be reduced.

Further, ceramics also have a feature that they have excellent weather resistance and chemical resistance.

Further, if a metal coating (metallizing) is applied to the surface of the ceramics, the advantage that it can be used as a lead-out portion of the inner electrode can be added.

Although the polymer piezoelectric film 1 is described to be made of polyvinylidene fluoride (PVDE) in the above-mentioned embodiments, the invention is not limited to this, and for example, a copolymer of vinylidene fluoride and trifluoroethylene (P ( VDF-TrFE)), a copolymer of vinylidene fluoride and tetrafluoroethylene (P
(VDF-TeFE)) or an alternating copolymer of cyanovinylidene and vinyl acetate (P (VCN-VAC)), in short, as long as it shows good piezoelectricity. In these materials, the stretching operation is not always necessary,
Only the polarization operation by applying a high voltage may be performed.

Further, in the above description, it was explained that the sealing lid 6 has one end fixed to the holding body 2, but it is sufficient that the gap 61 is formed, and the pressure equalizing hole 5 is not sealed by the sealing lid 6. Of course, most of the sealing lid 6 may be fixed to the holding body 2.

<Effects of the Invention> As described above, according to the present invention, a cylindrical holder, a ring-shaped recess that leaves both ends of the peripheral surface of the holder, and a peripheral surface of the holder are provided. A cylindrical polymeric piezoelectric film which is fixed to a portion other than the concave portion and forms a chamber with the concave portion, electrode plates respectively provided on the outer peripheral surface and the inner peripheral surface of the polymeric piezoelectric film, and the holder A pressure equalizing hole that is provided to communicate between the chamber and the outside, and a plate-like sealing lid that faces the external opening of the pressure equalizing hole and that seals the external opening of the pressure equalizing hole by water pressure. An ultrasonic range finder having a transmitter / receiver having the above is constructed.

As a result, (1) since the piezoelectric polymer film itself has a large internal attenuation, it is possible to transmit and receive ultrasonic waves having 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 / reception is possible.

(3) Since the acoustic impedance of the polymer piezoelectric film is an order of magnitude smaller than the acoustic impedance of the ceramic-based vibrator, the sound transmission / reception efficiency into the air is good.

(4) Since the thickness of the piezoelectric polymer film can be reduced, the electric field strength can be increased during transmission, and the transmission efficiency (the amount of displacement of the piezoelectric polymer film) can be increased.

Also, upon reception, this thinness does not affect the output. On the other hand, due to the high piezoelectric output constant of the polymeric piezoelectric film itself, a high open circuit voltage can be obtained. 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 changes in temperature characteristics due to changes in these physical properties.

(6) Therefore, as compared with the conventional example, high performance can be realized with extremely low power consumption.

(7) Since the fixing of the piezoelectric polymer film is limited to only the upper and lower end surfaces, free breathing vibration without restraint can be obtained. As a result,
Large transmission and reception sensitivity can be obtained.

(8) By having the pressure equalizing hole 5, it is possible to realize a transducer in which the sensitivity is not influenced by the ambient pressure.

(9) By using the reflector 4, it is possible to realize a transmitter / receiver having a good directivity, which is optimum for a rangefinder.

(10) When the transducer is submerged in water, the sealing lid automatically closes the outer opening of the pressure equalizing hole due to the water pressure when the water is submerged, thus preventing water from entering the pressure equalizing hole. It is possible to prevent a decrease in the sensitivity of the layer receiver after the immersion.

Therefore, according to the present invention, it is possible to realize an ultrasonic distance meter having a simple structure, high damping characteristics, high efficiency, and good waterproofing when submerged in water.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part configuration of an embodiment of the present invention, FIG. 2 is an explanatory view of parts of FIG. 1, FIGS. 3 to 6 are operational explanatory views of FIG. 1, and FIG. 7 to FIG. FIG. 10 is an explanatory view of a main part configuration of another embodiment of the present invention, FIG. 11 is an explanatory view of the configuration of a conventional example generally used in the past, and FIGS. 12 and 13 are operational explanations of FIG. It is a figure. 1 ... Polymer piezoelectric film, 11,12 ... electrode, 111,121 ... lead wire, 2 ... holding body, 21 ... concave, 3 ... chamber, 4 ... reflective umbrella, 5 ... pressure equalizing hole, 6 ... Sealing lid, 61 ... Gap, 62 ...
… Floating body, 63 …… Seal body, 64 …… Hinge, 65 …… Seal lid retainer, 66 …… Guide rod.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-140025 (JP, A) Actually opened 53-158227 (JP, U) Actually opened 60-169585 (JP, U) Japanese Patent Publication 4- 63347 (JP, B2) JP-B 4-63348 (JP, B2) JP-B 4-63349 (JP, B2)

Claims (1)

[Claims] 1. A cylindrical holder, a recess provided in a ring shape with both ends of the peripheral surface of the holder remaining, and a recess fixed to a portion other than the recess on the peripheral surface of the holder. And a cylindrical polymer piezoelectric film forming a chamber, electrode plates respectively provided on the outer peripheral surface and the inner peripheral surface of the polymer piezoelectric film, and a head side attached to one end of the holding body for transmitting and receiving. A conical reflector that gives the sound wave directivity in the axial direction of the holding body, a pressure equalizing hole that is provided in the holding body and communicates the chamber with the outside, and faces an external opening of the pressure equalizing hole. An ultrasonic range finder provided with a transducer provided with a plate-like sealing lid that seals the external opening of the pressure equalizing hole by water pressure.