JP5481184B2 - Ultrasonic receiver - Google Patents

Description

  The present invention relates to an ultrasonic receiver used for measuring a distance by measuring the intensity of ultrasonic waves emitted from an ultrasonic transmission source using a piezoelectric element, and in particular, it is 360 ° in the horizontal direction. The present invention relates to an ultrasonic receiver in which a piezoelectric element has a cylindrical structure so that substantially uniform received sensitivity can be obtained in all directions.

  Conventionally, a cylindrical piezoelectric element has been used in a sound wave transmitter / receiver for generating and receiving a uniform sound pressure in all 360 ° directions in the horizontal direction. As a transmitter, for example, as described in Patent Document 1 and Patent Document 2, electrodes are formed on an inner peripheral surface and an outer peripheral surface of a cylindrical piezoelectric element, and an AC voltage is applied between them. Has proposed a loudspeaker that emits sound waves in a direction of 360 ° perpendicular to the central axis of the cylinder.

As an ultrasonic transmitter / receiver , an ultrasonic transmitter / receiver in which a plurality of cylindrical piezoelectric elements are arranged in the direction of the central axis of a cylinder via a sound insulating material has been proposed. FIG. 8 is a cross-sectional view showing an example of the structure of such a conventional ultrasonic transducer. In this ultrasonic transducer, a plurality of cylindrical piezoelectric elements 11a, 11b, 11c, and 11d that have electrodes on the inner peripheral surface and the outer peripheral surface and perform vibrations that expand in diameter are arranged with their cylindrical axes aligned in the height direction. The metal lids 17a and 17b are arranged at both ends of the arranged piezoelectric elements, the inner peripheral surface electrodes 13 of the piezoelectric elements are connected to each other by lead wires 14, and one end thereof is built in the piezoelectric element. It is connected to the output terminal of the oscillation circuit block 18. The other end of the output end of the oscillation circuit block 18 is connected to a metallic lid 17a. Except for the outer peripheral surface electrode 12 of each piezoelectric element, watertightness is provided between the piezoelectric elements and between the piezoelectric elements at both ends and the lids 17a and 17b and between the inner peripheral surface of the piezoelectric element and the outer peripheral surface of the inner cylinder 16. There is molded with a resin 15 having a hardness sufficient to support the piezoelectric element and does not hinder the vibration of the piezoelectric element. When this ultrasonic transducer is submerged in water, the lid 17a and the outer peripheral surface electrode 12 of the piezoelectric element have the same potential, so that each piezoelectric element is electrically connected to the oscillation circuit block 18 in parallel.

Japanese Patent Laid-Open No. 9-327092 Japanese Patent Laid-Open No. 9-327093 JP-A-8-307994

  The above-mentioned ultrasonic transmitter / receiver can function in principle as a transmitter and a receiver. However, when attention is paid to the sensitivity when used as an ultrasonic receiver, the above-described conventional transmitter / receiver structure cannot provide sufficient performance. In other words, since it is assumed that the transmitter is driven with relatively high power, almost the entire cylindrical surface vibrates and contributes to transmission. However, when viewed as a receiver, the piezoelectric element that produces sensitivity is effective. Because there is only a part of the cylindrical surface with respect to the sound pressure input from a specific direction, that is, the plane part perpendicular to the incident direction of the input sound pressure is only part of the linear part of the cylindrical surface. This is because it is difficult to obtain sufficient sensitivity.

  Further, in the configuration of the above conventional transmitter / receiver, each piezoelectric element is electrically connected in parallel in order to stably obtain the directivity of the transmitted sound pressure in all 360 ° directions in the horizontal direction. Each piezoelectric element is driven so as to vibrate in the same phase, but as a receiver, inactive parts that do not contribute to mechanical-electrical conversion other than a small part that generates electric charge due to the piezoelectric phenomenon from the input sound pressure Since this part also has a capacitance, when connected in parallel, the capacitance of the inactive part further increases and absorbs the generated charge, so that the voltage obtained by reception decreases and the reception There was a problem that the sensitivity was lowered.

  Accordingly, an object of the present invention is to provide an ultrasonic receiver capable of increasing the receiving sensitivity as compared with the conventional one without impairing the directivity.

In order to solve the above-mentioned problems, a piezoelectric element having a cylindrical shape and independent electrodes on the inner peripheral surface and the outer peripheral surface, polarized in the thickness direction, and having the same outer diameter is arranged so that the central axes coincide with each other. A plurality of stacks arranged in a direction, and lead wires of cables to be taken out to the outside are connected to the electrodes, and at least two of the piezoelectric elements are electrically connected in series, and a direction perpendicular to the outer peripheral surface of the piezoelectric elements a sound received ultrasound machine having a receiving sensitivity to pressure, the capped one end of the piezoelectric element by an elastic member, between said piezoelectric element, a plurality of piezoelectric elements stacked above and the elastic member A sound absorbing material is disposed between and inside the piezoelectric element, and the sound absorbing material inside the piezoelectric element is disposed so as not to buffer the lead wire .

  The outer peripheral surface of the piezoelectric element and the exposed surface of the sound absorbing material may be molded with resin.

  In this case, the difference in electrical impedance between the resin when the outer peripheral surface of the piezoelectric element is molded with the resin is within 20 dB relative to the electrical impedance of the piezoelectric element when the resin is not present. A resin is desirable. The elastic body may be a metal.

  Further, it is desirable that the variation of the reception sensitivity is within ± 1 dB in all directions perpendicular to the outer peripheral surface of the piezoelectric element.

  In the present invention, as described above, the capacitance of the inactive portion is reduced by electrically connecting each piezoelectric element in series, and the voltage generated from the generated charges caused by the distortion caused by the sound pressure is increased compared to the conventional case. Thus, the reception sensitivity is improved.

  Also, in the ultrasonic receiver according to the present invention, the outer side of each piezoelectric element and the exposed surface of the sound absorbing material are molded with a resin having a hardness that does not hinder vibrations, thereby improving the pressure resistance and waterproofness in water. It is possible to increase the reception sensitivity.

  As described above, according to the present invention, it is possible to obtain an ultrasonic wave receiver capable of increasing the reception sensitivity as compared with the conventional one without impairing the directivity.

The perspective view which shows an example of the structure of the piezoelectric element used for the ultrasonic receiver by this invention. 1 is an external perspective view showing the configuration of a first embodiment of an ultrasonic receiver according to the present invention. Sectional drawing which shows the internal structure of 1st Embodiment of the ultrasonic receiver by this invention. Sectional drawing which shows the structure of 2nd Embodiment of the ultrasonic receiver by this invention. Sectional drawing which shows the internal structure of the comparative example of the ultrasonic receiver of the same structure as the past. The figure which shows the measurement result of the relationship between a receiving sensitivity and the distance from a sound source about an Example and a comparative example. The figure which shows the measurement result of the directivity characteristic of the received voltage in the distance of 1 m from a sound source. Sectional drawing which shows an example of the structure of the conventional ultrasonic transducer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an example of the structure of a piezoelectric element used in an ultrasonic receiver according to the present invention. As shown in FIG. 1, the piezoelectric element 1 has a cylindrical shape, and an inner peripheral surface electrode 2 is formed on the inner peripheral surface, and an outer peripheral surface electrode 3 is formed on the outer peripheral surface by baking a silver paste. The piezoelectric element 1 is polarized in the thickness direction using the inner peripheral surface electrode 2 and the outer peripheral surface electrode 3, and generates an electric charge when an external force such as a sound wave is applied to the outer peripheral surface to cause distortion.

  FIG. 2 is an external perspective view showing the configuration of the first embodiment of the ultrasonic receiver according to the present invention. Two piezoelectric elements 1a and 1b having the same shape and configured as shown in FIG. 1 are stacked in the height direction of the cylinders so that the central axes of the cylinders coincide with each other. The piezoelectric elements 1a and 1b are stacked via a sound absorbing material 4b, and a metal lid 5 is bonded to the upper surface of the piezoelectric element 1a via the sound absorbing material 4a. A metal mount 6 is bonded to the lower surface of the piezoelectric element 1b via a sound absorbing material 4c. The lid 5 and the gantry 6 are made of metal in the present embodiment. However, the lid 5 and the gantry 6 are not limited to metal, but the same effect can be obtained as long as the elastic body is strong enough to maintain the outer shape and support the piezoelectric elements 1a and 1b. can get. For example, phenol resin can be used. The piezoelectric elements 1a and 1b are electrically connected inside and taken out by a cable 7 to the outside.

  FIG. 3 is a cross-sectional view showing the internal structure of the first embodiment of the ultrasonic receiver according to the present invention. As shown in FIG. 3, a central cylinder 8 that fits with the lid 5 and the gantry 6 is installed inside, and the gantry 6 is provided with a recess that fits with the central cylinder 8, and the dent serves as a guide. A central cylinder 8 is set up and a cable 7 is inserted therein. The sound absorbing material 4c, the piezoelectric element 1b, the sound absorbing material 4b, the piezoelectric element 1a, and the sound absorbing material 4a are adhered and stacked on the gantry 6 so that the outer diameters coincide with each other. One lead wire 9b of the cable 7 is connected to the inner peripheral surface electrode 2b of the piezoelectric element 1b by soldering. The other lead wire 9a passes through the sound absorbing material 4a and is taken out to the outer peripheral surface side of the piezoelectric element 1a, and is connected to the outer peripheral surface electrode 3a of the piezoelectric element 1a by soldering. The outer peripheral surface electrode 3b of the piezoelectric element 1b and the inner peripheral surface electrode 2a of the piezoelectric element 1a are connected by a lead wire 9c, and the piezoelectric element 1a and the piezoelectric element 1b are electrically connected in series. A space between the inner peripheral surfaces of the piezoelectric elements 1a and 1b and the central cylinder 8 is filled with a sound absorbing material 4d so as not to buffer the lead wires 9a, 9b and 9c. A recess that fits into the central cylinder 8 is provided inside the lid 5, and the position of the lid 5 is determined and bonded using the recess as a guide.

  FIG. 4 is a cross-sectional view showing a configuration of the second embodiment of the ultrasonic receiver according to the present invention. The basic configuration is the same as that of the first embodiment shown in FIG. 3, but in this embodiment, the outer peripheral surfaces of the stacked piezoelectric elements 1a and 1b and the exposed surfaces of the sound absorbing materials 4a, 4b, and 4c. The difference is that the outside of the lid 5 is molded with resin. That is, considering the use in water, the whole is molded with the polyurethane coating 10 in order to improve waterproofness. Here, the resin to be molded is not limited to polyurethane as long as it does not prevent vibration. In particular, sufficient sensitivity can be obtained if the electrical impedance when the outer peripheral surface of the piezoelectric element is molded with resin is a difference within 20 dB compared to the electrical impedance when there is no resin.

  Next, as an example, the result of actually making a prototype of the ultrasonic receiver of the first embodiment will be described. A piezoelectric element having an outer diameter of 24 mm, an inner diameter of 20 mm, and a height of 10 mm was produced as the piezoelectric elements 1a and 1b in FIGS. The thickness of the sound absorbing materials 4a and 4c was 3 mm, and the thickness of the sound absorbing material 4b was 1 mm. The lid 5 was a stainless steel plate having a thickness of 6 mm, and the gantry was a stainless steel plate having a thickness of 10 mm. The central cylinder 8 is a stainless steel pipe having an outer diameter of 10 mm and an inner diameter of 7 mm.

  In order to confirm the sensitivity improvement effect of the ultrasonic receiver according to the present invention, a comparative example of an ultrasonic receiver having the same structure as that of the conventional example was made at the same time as the embodiment. A sectional view of the internal structure of the comparative example is shown in FIG. The dimensions and configurations of the piezoelectric elements 1a and 1b, the sound absorbing materials 4a, 4b, 4c, and 4d, the lid 5, and the mount 6 are the same as those in the above embodiment. However, in the comparative example, only the connection method of each piezoelectric element and the cable is made to have the same structure as the conventional ultrasonic receiver shown in FIG. That is, the inner peripheral surface electrodes 2a and 2b of the piezoelectric elements 1a and 1b were connected by the lead wire 9d, and this was further connected to one lead wire 9b of the cable 7. The other lead wire 9 a of the cable 7 was connected to the central cylinder 8. By connecting the lead wire 9a to the central cylinder 8 and submerging the ultrasonic receiver having this configuration in water, the outer peripheral surface electrodes 3a and 3b of the piezoelectric elements 1a and 1b, the stainless lid 5, the mount 6, and the central cylinder 8 has the same potential, and the piezoelectric elements 1a and 1b are connected in parallel.

  In the conventional example shown in FIG. 8, the oscillation circuit is housed inside the cylinder. However, in this prototype, since the performance of the receiver is compared, no oscillator is arranged.

  FIG. 6 is a diagram showing the measurement results of the relationship between the received wave sensitivity (output voltage) and the distance from the sound source for the above-described examples and comparative examples. A speaker that oscillates an ultrasonic wave having a frequency that matches the anti-resonance frequency of the piezoelectric element is arranged in the anechoic water tank, and the ultrasonic receiver of the example or the comparative example is arranged so that the distance from the speaker is the same. The output voltage from the cable 7 in FIGS. 3, 4 and 5 was directly measured with an oscilloscope. From FIG. 6, the output voltage attenuates according to the distance from the sound source, but at a distance of 1 m, the output voltage is observed to be approximately 2.5 times that of the comparative example in the configuration of the example, and compared with the conventional structure. It was confirmed that an improvement in sensitivity was obtained.

  FIG. 7 is a diagram showing measurement results of the directivity characteristics of the received voltage at a distance of 1 m from the sound source. A speaker that oscillates an ultrasonic wave having a frequency that matches the anti-resonance frequency of the piezoelectric element is placed in the anechoic water tank, and the ultrasonic receiver of the example or the comparative example is attached to the turntable, and the position at a distance of 1 m from the speaker. The output voltage from the cable 7 in FIGS. 3, 4, and 5 when the ultrasonic receiver is rotated while being submerged in water is directly measured with an oscilloscope. Similar to the comparative example, in the example as well, a uniform output voltage could be confirmed over all 360 ° directions, and it was confirmed that it had the same directivity as the conventional structure. It is desirable that the variation in reception sensitivity with respect to all directions is within ± 1 dB in a normal application.

  The ultrasonic receiver according to the present invention can receive ultrasonic waves transmitted from all directions in the same manner as the conventional ultrasonic receiver, and the reception sensitivity is improved as compared with the conventional ultrasonic receiver. The distance from the sound wave transmission source can be detected from a longer distance than in the past. For example, if an ultrasonic receiver is attached to a fish net or the like and an ultrasonic wave is oscillated from a fishing boat, the position and depth of the net can be known.

  Needless to say, the present invention is not limited to the above-described embodiments and examples, and the design can be changed according to the purpose and application. For example, the number of piezoelectric elements stacked in the height direction and the number of piezoelectric elements connected in series, the shape and material of piezoelectric elements, lids, mounts, sound absorbing materials, etc., and the resin material when molding the surface Etc. can be selected according to the purpose.

1, 1a, 1b, 11a, 11b, 11c, 11d Piezoelectric element 2, 2a, 2b, 13 Inner peripheral surface electrode 3, 3a, 3b, 12 Outer peripheral surface electrode 4a, 4b, 4c, 4d Sound absorbing material 5, 17a, 17b Lid 6 Base 7 Cable 8 Center cylinder 9a, 9b, 9c, 9d, 14 Lead wire 10 Polyurethane coating 15 Resin 16 Internal cylinder 18 Oscillation circuit block

Claims (5)

A plurality of piezoelectric elements that are cylindrical and have independent electrodes on the inner and outer peripheral surfaces, polarized in the thickness direction and having the same outer diameter are stacked in the height direction so that the central axes coincide. The lead wire of the cable to be taken out is connected to the electrode, and at least two of the piezoelectric elements are electrically connected in series to receive sound pressure in a direction perpendicular to the outer peripheral surface of the piezoelectric element. An ultrasonic receiver having sensitivity, wherein one end of the piezoelectric element is covered with an elastic body, and sound absorption is performed between the piezoelectric elements, between the elastic body and the piezoelectric elements, and inside the piezoelectric elements. the wood was placed, received ultrasound machine characterized in that the sound absorbing material arranged so as not to buffer with the lead wire in the interior of the piezoelectric element. The ultrasonic receiver according to claim 1 , wherein an outer peripheral surface of the piezoelectric element and an exposed surface of the sound absorbing material are molded with resin. The resin is a resin in which the difference in electrical impedance when the outer peripheral surface of the piezoelectric element is molded with the resin is within 20 dB with respect to the electrical impedance of the piezoelectric element in the absence of the resin. The ultrasonic receiver according to claim 2 . Ultrasonic receiver according to claim 1, wherein the elastic member is a metal. The ultrasonic wave receiver according to any one of claims 1 to 4 , wherein a variation in reception sensitivity is within ± 1 dB in all directions perpendicular to the outer peripheral surface of the piezoelectric element.

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