Ultrasound transducer, ultrasound generating device, and pest control system

Abstract

This ultrasonic transducer includes at least one piezoelectric oscillator. This piezoelectric vibrator includes at least one flat piezoelectric body, and a pair of electrodes disposed with the piezoelectric body being interposed. The piezoelectric oscillator generates ultrasonic waves having a frequency of 18 to 70 kHz.

Description

Ultrasonic Transducer, Ultrasonic Generator, and Pest Control System 【0001】 The present invention relates to an ultrasonic transducer, an ultrasonic generator, and a pest control system. 【0002】 In recent years, damage caused by pests and diseases due to climate change and the like has been expanding, and damage caused by pests and diseases has been increasing on a global scale. On the other hand, regarding pest control using conventional pesticides, there have been social efforts in the direction of reducing the usage amount due to negative impacts on the environment, such as the impact on organisms other than the target pests and the problem of pollution to soil and water resources. 【0003】 In such a social background, focusing on the characteristic that insects avoid the ultrasonic waves emitted by bats, a method of controlling pests using ultrasonic waves has been proposed. For example, Patent Document 1 discloses an ultrasonic generator for pest control that prevents pests from approaching a vegetable field by pseudo-generating ultrasonic waves emitted by bats, which are natural enemies of pests. Further, Patent Document 2 discloses a pest control system in a crop cultivation field, comprising ultrasonic transmitting means for generating and outputting ultrasonic waves in the wavelength range of ultrasonic waves emitted by bats, moving means for moving the ultrasonic transmitting means, and control means for controlling the operations of the ultrasonic transmitting means and the moving means. 【0004】 Japanese Patent Application Laid-Open No. 2008-48717 Japanese Patent Application Laid-Open No. 2011-205981 【0005】 The ultrasonic generating means (also called an ultrasonic transducer) used in conventional pest control systems has a high directivity of the generated ultrasonic waves, and the emission direction tends to be limited to a narrow range. Therefore, there is a problem that a large number of ultrasonic transducers are required to cover a large field. 【0006】 An object of the present invention is to provide an ultrasonic transducer for pest control that has a smaller directivity and can efficiently generate ultrasonic waves in more directions. 【0007】[1] An ultrasonic transducer according to one aspect of the present invention is an ultrasonic transducer for pest control. This ultrasonic transducer has at least one piezoelectric vibrator, which includes at least one flat piezoelectric body and a pair of electrodes arranged with the piezoelectric body in between. The piezoelectric vibrator generates ultrasonic waves with a frequency of 18 kHz or more and 70 kHz or less. 【0008】 [2] In the ultrasonic transducer described in [1], the piezoelectric vibrator may be driven at a non-resonant frequency. 【0009】 [3] In the ultrasonic transducer described in [1] or [2], the piezoelectric material may be a lead-free piezoelectric ceramic. 【0010】 [4] In the ultrasonic transducer described in any of [1] to [3], the piezoelectric vibrator further comprises a flat metal plate, the piezoelectric body includes two piezoelectric bodies arranged with the metal plate in between, and the pair of electrodes may include two pairs of electrodes arranged with each of the two piezoelectric bodies in between. 【0011】 [5] In the ultrasonic transducer described in any of [1] to [3], the piezoelectric vibrator may further have a flat metal plate disposed on one side of the piezoelectric body. 【0012】 [6] In the ultrasonic transducer described in any of [1] to [5], the piezoelectric vibrator may be in the shape of a rectangular flat plate. 【0013】 [7] In the ultrasonic transducer described in [6], the length of the shorter side of the piezoelectric vibrator, which is a rectangular flat plate, may be one wavelength or more of the wave generated by the frequency at which the piezoelectric vibrator is driven. 【0014】 [8] In the ultrasonic transducer described in any of [1] to [5], the piezoelectric vibrator may be in the shape of a circular or elliptical flat plate. 【0015】[9] In the ultrasonic transducer described in [8], the diameter of the piezoelectric vibrator, which is a circular flat plate, or the minor axis of the piezoelectric vibrator, which is an elliptical flat plate, may be one wavelength or more of the wave generated by the frequency at which the piezoelectric vibrator is driven. 【0016】

[10] The ultrasonic transducer described in any of [1] to [9] may further have a support portion that fixes the piezoelectric vibrator at the central part of the piezoelectric vibrator. 【0017】

[11] The ultrasonic transducer described in any of [1] to

[10] may further have a waterproof layer covering the piezoelectric vibrator. 【0018】

[12] In the ultrasonic transducer described in any of [1] to

[11] , the piezoelectric vibrator may be driven by bending vibration. 【0019】

[13] Another aspect of the present invention relates to an ultrasonic generator comprising a plurality of ultrasonic transducers as described in any of [1] to [2]. 【0020】

[14] The ultrasonic generator described in

[13] may further include a detection unit for detecting ultrasonic waves emitted from the piezoelectric transducer. 【0021】

[15] Another aspect of the present invention relates to a pest control system comprising at least one ultrasonic generator as described in

[13] or

[14] . 【0022】 According to one aspect of the present invention, it is possible to provide an ultrasonic transducer for pest control that has less directivity and can efficiently generate ultrasonic waves in a wider range of directions. According to an ultrasonic generator equipped with an ultrasonic transducer according to one aspect of the present invention, it is possible to provide a pest control system that can efficiently control pests over a wide range of crops with less power consumption. The pest control system according to one aspect of the present invention can be effectively used to control lepidopteran pests, including noctuid moths, using ultrasound. 【0023】Figure 1 is a perspective view showing the external configuration of an ultrasonic generator according to the first embodiment. Figure 1 is a block diagram showing the internal configuration of the ultrasonic generator shown in Figure 1. Figure 1 is a schematic diagram of a field where the ultrasonic generator shown in Figure 1 is installed. Figure 1 is a schematic cross-sectional diagram showing the general configuration of an ultrasonic transducer provided in the ultrasonic generator shown in Figure 1. (a) is a plan view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer. (b) is a cross-sectional view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer. (a) and (b) are schematic diagrams for explaining the movement of the piezoelectric vibrator inside the ultrasonic transducer. Figure 1 is a schematic cross-sectional diagram showing the configuration of a piezoelectric vibrator according to a modified example. (a) is a plan view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer according to a modified example. (b) is a cross-sectional view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer according to a modified example. (a) is a plan view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer according to a modified example. (b) is a cross-sectional view showing the configuration of the piezoelectric vibrator and support part of the ultrasonic transducer according to a modified example. This is an image diagram showing the configuration of the pest control system according to the second embodiment. This is a graph showing the frequency characteristics of the impedance of the piezoelectric vibrator used in Example 1. This figure shows the simulation analysis results of the sound pressure level distribution in the X-axis cross-section when the piezoelectric vibrator of Example 1 is driven at a non-resonant frequency (20 kHz). This figure shows the simulation analysis results of the sound pressure level distribution in the Y-axis cross-section when the piezoelectric vibrator of Example 1 is driven at a non-resonant frequency (20 kHz). This figure shows the simulation analysis results of the sound pressure level distribution in the X-axis cross-section when the piezoelectric vibrator of Example 1 is driven at a resonant frequency (3.448 kHz). This figure shows the simulation analysis results of the sound pressure level distribution in the Y-axis cross-section when the piezoelectric vibrator of Example 1 is driven at a resonant frequency (3.448 kHz). This figure shows the measured sound pressure level in the long-side direction when the piezoelectric vibrator of Example 1 is driven at a non-resonant frequency (20 kHz). This figure shows the measured sound pressure level in the short-side direction when the piezoelectric vibrator of Example 1 is driven at a non-resonant frequency (20 kHz).This figure shows the lateral directivity measurement results of the sound pressure level distribution of the emitted ultrasound when the ultrasonic generator of Example 2 is driven at a non-resonant frequency (20 kHz). This figure shows the vertical directivity measurement results of the sound pressure level distribution of the emitted ultrasound when the ultrasonic generator of Example 2 is driven at a non-resonant frequency (20 kHz). 【0024】 Embodiments of the present invention will be described below with reference to the drawings. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated. 【0025】 <First Embodiment> In this embodiment, an ultrasonic generator 10, which is an example of an ultrasonic generator, will be described as an example. The ultrasonic generator 10 is equipped with a plurality of ultrasonic transducers 50. The ultrasonic transducers 50 are an example of an ultrasonic transducer according to the present invention. 【0026】 The ultrasonic generator 10 generates ultrasonic waves equivalent to those emitted by bats (for example, sound waves included in the wavelength band from 18 kHz to 70 kHz). Generally, lepidopteran pests known to feed on crops (for example, noctuid moths such as the beet armyworm, tobacco budworm, and akebia leafminer, as well as suckers and corn borers) have bats as natural enemies and have the characteristic of fleeing from ultrasonic waves emitted by bats. Therefore, the ultrasonic generator 10 is suitably installed in a field F of crops that are susceptible to damage from pests that use bats as natural enemies. 【0027】 (Overall configuration of the ultrasonic generator) Figure 1 shows the external configuration of the ultrasonic generator 10. As shown in Figure 1, the ultrasonic generator 10 includes an ultrasonic generating unit 11, a support column 12, a housing 13, a support rope 15, and a solar panel 32, etc. 【0028】The ultrasonic generating unit 11 has a plurality of ultrasonic transducers 50. In this embodiment, the plurality of ultrasonic transducers 50 are arranged at equal intervals around the outer circumference of a substantially cylindrical column 51 having an axis extending in the vertical direction. The ultrasonic generating unit 11 is supported by a support column 12 and is positioned at a certain height (for example, 0.3 m to 3.0 m) above the ground. In another embodiment, the ultrasonic generating unit 11 may have only one ultrasonic transducer 50. 【0029】 The support column 12 is formed, for example, from an iron column. The support column 12 supports the ultrasonic generating unit 11. The support column 12 is further supported by a plurality of support ropes 15. Wiring (not shown) for communication with the control unit 20 located inside the housing 13 is arranged on the support column 12. 【0030】 The housing 13 is positioned on the ground near the support column 12. Various electrical components constituting the control unit 20 and the power supply unit 30 are housed inside the housing 13. The solar panel 32 is positioned near the support column 12 and the housing 13. The solar panel 32 is connected to the battery 31 inside the housing 13. The electrical energy generated by the solar panel 32 charges the battery 31. In another embodiment, the solar panel 32 may be installed at a location somewhat far from the support column 12 (for example, a location adjacent to field F). 【0031】 Figure 2 shows the internal configuration of the ultrasonic generator 10. The ultrasonic generator 10 mainly includes an ultrasonic generating unit 11, a control unit 20, a power supply unit 30, and a detection unit 40. As described above, the ultrasonic generating unit 11 has a plurality of ultrasonic transducers 50. The ultrasonic transducers 50 generate ultrasonic waves at a predetermined frequency (for example, a non-resonant frequency of 20 kHz) within the range of 18 kHz to 70 kHz. Note that ultrasonic waves at frequencies other than the predetermined frequency may also be included as noise. 【0032】The control unit 20 includes an ultrasonic oscillation circuit 21, an amplification circuit 22, a power supply circuit 23, a memory 26, and a timer 27. The ultrasonic oscillation circuit 21 oscillates an ultrasonic signal of a predetermined frequency generated from the ultrasonic transducer 50. The amplification circuit 22 amplifies the ultrasonic signal generated by the ultrasonic oscillation circuit 21. The power supply circuit 23 generates an electrical signal using electrical energy supplied from the power supply unit 30. This electrical signal is used as a power source for various electrical components within the ultrasonic generator 10 (for example, the ultrasonic oscillation circuit 21, the amplification circuit 22, the memory 26, etc.). 【0033】 The memory 26 includes ROM (read-only memory) and RAM (Random Access Memory). The memory 26 stores the operation programs and calculation results of various electrical components within the ultrasonic generator 10. 【0034】 The power supply unit 30 supplies power to various components within the device (for example, the control unit 20). The power supply unit 30 includes a battery 31 and a solar panel 32. The solar panel 32 generates electricity based on solar energy. The electricity obtained by the solar panel 32 is used to charge the battery 31. By using sunlight as the power source for the power supply unit 30, the running costs of the ultrasonic generator 10 can be reduced. In addition, it becomes unnecessary to install power lines from the commercial power supply to the ultrasonic generator 10, thus simplifying the equipment. In another embodiment, the power supply unit 30 may use a commercial power supply. 【0035】 The detection unit 40 detects the ultrasonic waves emitted from the piezoelectric transducer 60. For example, the detection unit 40 can be a conventionally known ultrasonic sensor, a microphone capable of detecting ultrasonic waves, etc. The presence of the detection unit 40 in the ultrasonic generator 10 allows for confirmation of whether or not ultrasonic waves are being emitted normally from the ultrasonic transducer 50. 【0036】The ultrasonic generator 10 may be configured to communicate with external devices. To achieve this, the ultrasonic generator 10 may have a communication interface 29. The communication interface 29 is implemented by an antenna, connector, etc. The communication interface 29 can transmit and receive signals and data with servers and repeaters, etc., via wide-area wireless communication means such as the Internet, LTE, or carrier network. 【0037】 The ultrasonic generator 10 is installed in fields such as orchards of peaches, pears, and strawberries, and vegetable fields of onions, lettuce, and cabbage. Figure 3 schematically shows a field F in which the ultrasonic generator 10 is installed. In field F, for example, several peach trees P are planted. Also, there is a grove of trees surrounding field F that serves as a habitat for noctuid moths. 【0038】 It is preferable that field F is located within the effective range R of the ultrasonic waves emitted by the ultrasonic generator 10. If the area of ​​field F exceeds the effective range R of one ultrasonic generator 10, it is preferable to arrange multiple ultrasonic generators 10 at predetermined intervals such that their effective ranges R overlap, according to the area of ​​the field. 【0039】 For example, in the case of an ultrasonic generator 10 having a rectangular piezoelectric transducer 60 as shown in Figure 6(a), the effective range R is, for example, a spherical area with a radius of 25 m centered on the ultrasonic generator 10. 【0040】 (Configuration of the ultrasonic transducer) Next, the specific configuration of the ultrasonic transducer 50 provided in the ultrasonic generator 10 will be described. Figure 4 shows the configuration of the ultrasonic transducer 50. Figure 4 shows the cross-sectional configuration of the piezoelectric vibrator 60 included in the ultrasonic transducer 50. The piezoelectric vibrator 60 shown in Figure 4 is a bimorph type piezoelectric vibrator. 【0041】FIGS. 5(a) and 5(b) schematically show the configurations of the piezoelectric vibrator 60 and the support portion 55 that constitute the ultrasonic transducer 50. FIG. 6(a) shows an image of the movement of the piezoelectric vibrator 60 in the ultrasonic transducer 50 during operation (during ultrasonic generation). 【0042】 As shown in FIG. 4, the ultrasonic transducer 50 has a piezoelectric vibrator 60, a support portion 55, etc. In FIG. 4, a power source (e.g., the control unit 20, the power supply unit 30, etc.) that supplies an ultrasonic signal to the ultrasonic transducer 50 is also shown. 【0043】 The piezoelectric vibrator 60 includes at least one flat piezoelectric body 62 and a pair of electrodes disposed with the piezoelectric body interposed therebetween. For example, the piezoelectric vibrator 60 is of the bimorph type and has two piezoelectric bodies 62 (specifically, the first piezoelectric body 62a and the second piezoelectric body 62b). 【0044】 In the present embodiment, the piezoelectric vibrator 60 has a flat metal plate 61 (also called a shim material), two piezoelectric bodies 62 (i.e., the first piezoelectric body 62a and the second piezoelectric body 62b) disposed with the metal plate 61 interposed therebetween, and two sets of electrode pairs 63 and 64 disposed with each of the two piezoelectric bodies 62 interposed therebetween. 【0045】 The first electrode pair 63 has electrodes 63a and 63b disposed with the first piezoelectric body 62a interposed therebetween. The second electrode pair 64 has electrodes 64a and 64b disposed with the second piezoelectric body 62b interposed therebetween. The first piezoelectric body 62a having the first electrode pair 63 is disposed on one surface of the metal plate 61, and the second piezoelectric body 62b having the second electrode pair 64 is disposed on the other surface of the metal plate 61. An ultrasonic signal transmitted from the control unit 20 is applied to each of the electrode pairs 63 and 64. 【0046】 The metal plate 61 and the piezoelectric body 62 are both in the shape of a rectangular flat plate. The shape of the piezoelectric vibrator 60 formed by laminating these is also in the shape of a rectangular flat plate. In another embodiment, the shape of the piezoelectric vibrator 60 may be in the shape of a circular or elliptical flat plate. 【0047】The metal plate 61 is formed of a metal material such as, for example, 42 alloy (42% Ni-Fe), stainless steel, titanium, nickel alloy, brass, etc. The thickness of the metal plate 61 is, for example, 0.05 mm or more and 0.3 mm or less. The metal plate 61 has a ground potential. 【0048】 The thickness of the piezoelectric body 62 is, for example, 0.05 mm or more and 0.5 mm or less. 【0049】 The piezoelectric body 62 is formed of, for example, ceramics exhibiting piezoelectricity. Examples of the ceramics exhibiting piezoelectricity include, for example, lead-free piezoelectric ceramics, PZT (lead zirconate titanate) -based ceramics, etc. Among these, lead-free piezoelectric ceramics are preferably used in terms of having less environmental impact. As the lead-free piezoelectric ceramics, those containing, for example, an alkali niobate-based perovskite-type oxide as a main component are preferably used. 【0050】 As shown in FIG. 4, the ultrasonic transducer 50 has a waterproof layer 66 covering the piezoelectric vibrator 60. The waterproof layer 66 is formed of a conventionally known general waterproof coating agent (for example, fluorine-based, silicon-based, organic-based, etc.). The waterproof layer 66 can be formed, for example, by spraying a liquid waterproof coating agent and solidifying it after laminating the metal plate 61, the piezoelectric body 62 including electrodes, etc. to form the piezoelectric vibrator 60. By covering the piezoelectric vibrator 60 with the waterproof layer 66, it is possible to suppress the fouling of the edge portions of each electrode and the intrusion of water into the vibrator interior. 【0051】 The support portion 55 fixes the piezoelectric vibrator 60. Two support portions 55 are provided so as to sandwich the flat piezoelectric vibrator 60. One support portion 55 is disposed at substantially the center of one surface 60a of the flat piezoelectric vibrator 60 (see FIG. 5(a)). Also, the other support portion 55 is disposed at substantially the center of the other surface 60b of the flat piezoelectric vibrator 60 (that is, at a position corresponding in plan view to the one support portion 55) (see FIG. 4). The shape of the support portion 55 is not particularly limited, and is, for example, a cylindrical shape, a frustum of a cone shape, a prismatic shape, a hemispherical shape, etc. 【0052】The support portion 55 includes a screw 56 and a spacer 57 (or a nut). The screw 56 may be composed of two members and be positioned to sandwich the piezoelectric vibrator 60, or it may be composed of a single member and be positioned to pass through the piezoelectric vibrator 60. The spacers 57, 57 are positioned on the upper and lower surfaces of the piezoelectric vibrator 60, respectively, surrounding the screw 56. The piezoelectric vibrator 60 is supported and fixed to the base portion of the ultrasonic transducer 50 by the support portion 55 having the screw 56. 【0053】 The support section 55 is provided with a wiring structure for supplying electrical signals (ultrasonic signals) to each electrode pair 63 and 64. This allows electrical signals to be transmitted from the control unit 20 to the piezoelectric transducer 60 via the wiring within the support section 55. Specifically, ultrasonic signals of a particular frequency, generated by the power supply circuit 23, ultrasonic oscillation circuit 21, and amplification circuit 22 within the control unit 20, are transmitted to each electrode pair 63 and 64 of the piezoelectric transducer 60. The ultrasonic signals transmitted from the control unit 20 are then applied to the entire piezoelectric transducer 60 from the support section 55, which is located in the center of the rectangular, flat piezoelectric transducer 60. 【0054】 Figure 6(a) schematically shows the movement of the piezoelectric vibrator 60 at this time. Figure 6(b) shows the state of the piezoelectric vibrator 60 when it is driven at a frequency of 20 kHz. When an ultrasonic signal is supplied to the electrode pair 63 and 64, the piezoelectric vibrator 60, supported by the support part 55, is driven by a bending motion (see Figures 6(a) and 6(b)). 【0055】When the piezoelectric vibrator 60 is driven by bending motion, it means that when an ultrasonic signal is applied to each electrode of the piezoelectric vibrator 60, the flat piezoelectric vibrator (diaphragm) itself vibrates in a wave-like, undulating motion (see Figure 6(b)). At this time, at a given moment, the surface of one diaphragm faces in various directions, and ultrasonic waves are emitted directly from the surface of the diaphragm in those various directions. As a result, the ultrasonic waves emitted from the piezoelectric vibrator 60 do not have directivity in any particular direction. Therefore, it becomes possible to efficiently emit ultrasonic waves in multiple directions (preferably all directions) from the surface of the flat piezoelectric vibrator 60. 【0056】 The frequency of the current input to the piezoelectric transducer 60 is equivalent to the frequency of ultrasound emitted by bats (specifically, a frequency within the range of 18 kHz to 70 kHz). As a result, the ultrasonic transducer 50 emits ultrasound equivalent to that emitted by bats, thus keeping pests that use bats as natural enemies away from crops around the ultrasonic transducer 50. 【0057】 Furthermore, it is preferable that the frequency of the current input to the piezoelectric vibrator 60 be a non-resonant frequency. That is, the piezoelectric vibrator 60 is driven at a non-resonant frequency. Here, a non-resonant frequency means that the frequency of the ultrasound emitted from the piezoelectric vibrator, which undergoes bending motion when an ultrasonic signal is applied, is a frequency other than the resonant frequency, and not the resonant frequency caused by the physical properties and structure of the piezoelectric material itself. 【0058】 By driving the piezoelectric vibrator 60 at a non-resonant frequency, the flat vibrator (diaphragm) can avoid vibrating (bending) in a specific vibration mode at the resonant frequency, thereby reducing the directivity of the ultrasonic waves emitted from the diaphragm. In addition, a decrease in the impedance of the diaphragm can be prevented, and power consumption during operation can be reduced. 【0059】Preferably, the length of the shorter side of the piezoelectric transducer 60, which is a rectangular flat plate, is one wavelength or more of the wave generated by the frequency at which the piezoelectric transducer 60 is driven. This allows the piezoelectric transducer 60 to form vibration nodes of one wavelength or more not only in the direction of the longer side but also in the direction of the shorter side within a single rectangular flat plate piezoelectric transducer 60 during its own bending motion when an ultrasonic signal is applied to it. As a result, the sound pressure level of the ultrasonic waves radiated from the ultrasonic transducer 50 can be maintained above a predetermined value. Furthermore, the directivity of the ultrasonic waves is weakened, and the variation in sound pressure level depending on the direction can be reduced. 【0060】 In one example, the length of the short side (X-axis) of the flat plate of the rectangular piezoelectric vibrator 60 is preferably 10 mm to 50 mm, and more preferably about 20 mm or more. The length of the long side (Y-axis) of the flat plate of the rectangular piezoelectric vibrator 60 is preferably 10 mm to 100 mm, and more preferably about 20 mm or more (see Figure 6(a)). 【0061】 Furthermore, if the piezoelectric vibrator 60 is a circular flat plate, it is preferable that the diameter of the circular piezoelectric vibrator is at least one wavelength of the wave generated by the frequency at which the piezoelectric vibrator 60 is driven. Also, if the piezoelectric vibrator 60 is an elliptical flat plate, it is preferable that the minor axis of the elliptical piezoelectric vibrator 60 is at least one wavelength of the wave generated by the frequency at which the piezoelectric vibrator 60 is driven. This allows the same effects as described above to be obtained. 【0062】 (Modified Piezoelectric Vibrators) In the above embodiment, a bimorph-type piezoelectric vibrator 60 was used as an example, but the configuration of the piezoelectric vibrator is not limited to this. Modified piezoelectric vibrators will be described below. 【0063】Figure 7 shows the cross-sectional configuration of a unimorph type piezoelectric vibrator 60B. The piezoelectric vibrator 60B has a flat metal plate 61 (also called a shim) arranged on one side of the piezoelectric body 62. Specifically, the piezoelectric vibrator 60B has a flat metal plate 61, a piezoelectric body 62 arranged on either side of the metal plate 61, and an electrode pair 63 arranged with the piezoelectric body 62 in between. The electrode pair 63 has electrodes 63a and 63b. Similar to the piezoelectric vibrator 60, the shape of the piezoelectric vibrator 60B may be a rectangular flat plate, or a circular or elliptical flat plate. 【0064】 In another variation, the piezoelectric vibrator may be a bimorph type with a shimless structure that does not have shim material. 【0065】 Figures 8(a) and 8(b) show modified configurations for supporting the piezoelectric vibrator 60. As shown in Figure 8(a), the piezoelectric vibrator 60 is supported and fixed by hemispherical support portions 55 located approximately in the center of its upper and lower surfaces. Two beam portions 155 and 155 are provided approximately in the center of the long side of the rectangular piezoelectric vibrator, crossing in the short side direction. The piezoelectric vibrator 60, supported by the support portions 55, is positioned between the two beam portions 155 and 155. The two beam portions 155 and 155 are fixed by beam fixing portions 156. 【0066】 In another modified configuration, the support portion 55 may not be provided. In such a configuration, two beam portions 155 and 155 are provided so as to sandwich the piezoelectric vibrator 60 from above and below, and the piezoelectric vibrator 60 may be directly supported by the beam portions 155 and 155. 【0067】 Figures 9(a) and (b) show yet another modification of the configuration for supporting the piezoelectric vibrator 60. In this modification, a portion of the metal plate 61 included in the bimorph-type piezoelectric vibrator 60 extends in a beam-like manner beyond the width of the short side of the piezoelectric body 62, forming an overhang 61a. This overhang 61a is fixed by a support portion 55 including screws 56 and spacers 57. 【0068】(Summary of the First Embodiment) As described above, the ultrasonic transducer 50 according to this embodiment has at least one piezoelectric transducer 60. The piezoelectric transducer 60 has at least one flat piezoelectric body 62 (more specifically, a first piezoelectric body 62a and a second piezoelectric body 62b) and a pair of electrodes (specifically, a first electrode pair 63 and a second electrode pair 64) arranged with the piezoelectric body 62 in between. The piezoelectric transducer 60 generates ultrasonic waves with a frequency of 18 kHz to 70 kHz. The ultrasonic transducer 50 according to this embodiment is used for pest control. 【0069】 According to the above configuration, an ultrasonic transducer can be obtained that has less directivity and can efficiently generate ultrasound in more directions. 【0070】 Furthermore, regarding the size of the flat-plate piezoelectric transducer 60, it is preferable to make the size of the shorter side (for example, in the case of a rectangular shape) or the diameter (for example, in the case of a circular or elliptical shape) larger than one wavelength in the bending vibration of the flat plate. As a result, when an ultrasonic signal is applied to the piezoelectric transducer 60, the bending mode vibration will have multiple nodes (non-vibrating points between the irregularities) on the surface of the flat-plate transducer, so that the vibrating surface can simultaneously vibrate the air in many directions. Therefore, it becomes possible to broaden the direction of ultrasonic radiation from the surface of the piezoelectric transducer 60. In principle, it is possible to generate ultrasonic waves in all 360° directions with a single transducer. 【0071】 Thus, in this embodiment, the emission angle of ultrasonic waves from the piezoelectric transducer 60 can be set to 360° in principle, which reduces the constraints on the orientation of the ultrasonic transducer 50 when installing the ultrasonic generator 10. 【0072】Furthermore, the ultrasonic transducer 50 of this embodiment can generate ultrasonic waves with an effective sound pressure level using a small amount of driving power. Therefore, even when using power generated by a solar panel as the power source, it can emit ultrasonic waves sufficient to exert a pest control effect. Accordingly, the ultrasonic generator 10 having the ultrasonic transducer 50 can be easily used even in environments where power infrastructure is not well-developed, such as mountainous areas. 【0073】 <Second Embodiment> In this embodiment, an example of the present invention, a pest control system 100, will be described. The pest control system 100 includes at least one ultrasonic generator. An example of an ultrasonic generator is the ultrasonic generator 10 described in the first embodiment. 【0074】 Figure 10 schematically shows the overall configuration of the pest control system according to this embodiment (hereinafter also simply referred to as system 100). System 100 includes at least one ultrasonic generator 10. 【0075】 The system 100 preferably includes multiple ultrasonic generators 10. This makes it possible to realize a pest control system for a larger area of ​​field F that cannot be covered by the effective range R of a single ultrasonic generator 10. 【0076】 In the example shown in Figure 10, three ultrasonic generators 10 are arranged in the field F at predetermined intervals. It is preferable that the ultrasonic generators 10 are arranged at intervals such that the effective range R of the ultrasonic waves emitted from each individual device 10 partially overlaps with each other. 【0077】 In another embodiment, the system 100 may provide pest control for multiple fields F located in different locations. In this case, at least one ultrasonic generator 10 is placed in each field F. 【0078】 The pest control system 100 includes, as its main components, an ultrasonic generator 10, a server 70, and a communication terminal (for example, a tablet terminal) 80. 【0079】The ultrasonic generator 10 can send and receive signals and data to and from the server 70 via the communication interface 29. 【0080】 For example, a server on the cloud can be used as server 70. Other servers such as VPS, shared servers, and dedicated servers can also be used as appropriate. Each ultrasonic generator 10 and the communication terminal 80 and other devices within the system 100 are configured to be able to connect wirelessly to server 70 via wide-area wireless communication means such as the internet, LTE, or carrier network. Server 70 is equipped with a CPU (control unit) for controlling each device within the system 100, such as the ultrasonic generator 10. 【0081】 For example, a tablet device can be used as the communication terminal 80. The communication terminal 80 is configured to be able to connect wirelessly to the server 70 via, for example, the internet, LTE, or a carrier network. As a result, the communication terminal 80 receives information such as the operation of the ultrasonic generator 10 located in the field F and detection information from the detection unit 40. Therefore, a user of the communication terminal 80 can, for example, monitor the ultrasonic waves emitted from the ultrasonic generator 10 from a location away from the field F. Note that the communication terminal 80 is not limited to a tablet device; it may also be a personal computer or a smartphone. 【0082】 According to this embodiment, a pest control system 100 can be provided that uses ultrasound to control lepidopteran pests, including moths, and can efficiently control pests over a wide area of ​​crops with less power consumption. Therefore, it is possible to reduce damage to crops caused by lepidopteran pests. 【0083】 [Examples] Examples of the present invention will be described below. However, the present invention is not limited to the following examples. 【0084】(Example 1) As the material for the piezoelectric element 62, lead-free piezoelectric ceramic LF04A (potassium sodium niobate (KNN) based piezoelectric element manufactured by NGK Spark Plug Co., Ltd.) was used to form a bimorph-type rectangular flat piezoelectric vibrator 60 (metal plate 61 thickness 0.1 mm, piezoelectric element thickness 0.1 mm). The dimensions of the rectangular flat plate (long side × short side) were 60 mm × 20 mm. Then, as shown in Figure 6(a), an ultrasonic transducer 50 was fabricated with a support part 55 placed approximately in the middle of the rectangular flat piezoelectric vibrator 60. 【0085】 Figure 11 shows the frequency characteristics (calculated values) of the impedance of the fabricated ultrasonic transducer 50. In the graph of Figure 11, a dashed line is marked at a frequency of 20 kHz. As shown in this figure, it can be confirmed that the ultrasonic transducer 50 does not resonate at 20 kHz. 【0086】 This ultrasonic transducer 50 was driven with a 20 kHz - 20 Vp - p sine wave, which is a non-resonant frequency. A waveform generator (product name: KEYSIGHT_33500B Waveform Generator) and an audio amplifier were used for this purpose. 【0087】 The distribution (directivity) of the sound pressure level of the ultrasound emitted from the ultrasonic transducer 50 was measured using an ultrasonic microphone (MI-1531, manufactured by Ono Sokki Co., Ltd.), a microphone amplifier (MI-3140, manufactured by Ono Sokki Co., Ltd.), and an FFT (CF-9200, manufactured by Ono Sokki Co., Ltd.). 【0088】 Figures 12 and 13 show the sound pressure level distribution obtained by analyzing the measurement results in advance using simulation. Figure 12 shows the sound pressure level distribution in the cross-section of the long side (X-axis) of the piezoelectric vibrator 60 when driven at a non-resonant frequency (20 kHz). Figure 13 shows the sound pressure level distribution in the cross-section of the short side (Y-axis) of the piezoelectric vibrator 60 when driven at a non-resonant frequency (20 kHz). 【0089】Figures 14 and 15 show the simulation analysis results of the sound pressure level distribution when the piezoelectric vibrator 60 is driven at the resonant frequency (3.448 kHz) as a comparative example. Figure 14 shows the sound pressure level distribution in the X-axis cross-section of the piezoelectric vibrator. Figure 15 shows the sound pressure level distribution in the Y-axis cross-section of the piezoelectric vibrator. 【0090】 Figures 12 to 15 show the distribution of sound pressure levels when the maximum sound pressure level is set to 1. 【0091】 As shown in these figures, the simulation analysis results show that there are regions of high and low sound wave levels due to ultrasonic interference, measured in wavelength units. However, when driven at the non-resonant frequency (20 kHz), as shown in Figures 12 and 13, the ultrasonic radiation is not biased in any particular direction but is uniformly distributed on both the front and back of the transducer, indicating that ultrasonic waves are emitted in all 360° directions. 【0092】 On the other hand, when driven at the resonant frequency (3.448 kHz), as shown in Figures 14 and 15, there are directions in which the sound pressure is extremely low in the vertical direction on the upper and lower surfaces of the transducer, indicating that the ultrasonic radiation has strong directivity. 【0093】 Figures 16 and 17 show the measured sound pressure levels of the ultrasonic waves emitted when the piezoelectric vibrator 60 is driven at a non-resonant frequency (20 kHz - 20 Vp - p) (microphone distance: 20 cm). Figure 16 shows the measured values ​​in the direction of the long side of the piezoelectric vibrator. Figure 17 shows the measured values ​​in the direction of the short side of the piezoelectric vibrator. 【0094】 In the actual measurements, the sound pressure level was measured by changing the microphone placement angle in the direction of the long and short sides of the piezoelectric transducer 60, directly above the transducer. As a result, as shown in Figures 16 and 17, it was confirmed that ultrasonic waves were uniformly emitted from directly above the transducer up to 90° (directly beside the transducer), with some peaks and valleys in the level, but within a certain range of variation (i.e., between approximately 90 dB and approximately 110 dB). 【0095】(Example 2) In Example 2, eight ultrasonic transducers 50 made in Example 1 were used to create an ultrasonic generator 10 having an ultrasonic generating unit 11 as shown in Figure 1. Then, in a test field F, the ultrasonic generator 10 was used to confirm the directivity of the emitted ultrasonic waves and the power consumption. 【0096】 Figures 18 and 19 show the directional measurement results of the sound pressure level distribution of the ultrasound emitted when each ultrasonic transducer 50 in the device is driven at a non-resonant frequency (20 kHz, 20 Vp-p sine wave). Figure 18 shows the measured value of the horizontal direction H (see Figure 1) of the ultrasonic generating unit 11. Figure 19 shows the measured value of the vertical direction V (see Figure 1) of the ultrasonic generating unit 11. 【0097】 As shown in Figures 18 and 19, the ultrasonic level distribution was confirmed to show a sound pressure level of 60 to 80 dB even when the angle of the ultrasonic generating unit 11 was changed in both the horizontal direction H and the vertical direction Y. This confirmed that the ultrasonic generating unit 11 emits ultrasonic waves in all 360° directions. 【0098】 From these results, it is considered possible to cover a 25m radius around the ultrasonic generator 10 in a spherical shape with ultrasound by installing one such device. Furthermore, it becomes possible to effectively control pests that are repelled by the ultrasound emitted from this ultrasonic generator 10. 【0099】 Furthermore, the power consumption measurements when using this ultrasonic generator 10 were as follows: Power consumption per day (24 hours) (Ah): 5.28 (12V) Power consumption per hour (W): 2.64 【0100】 Based on the above results, one ultrasonic generator 10 can produce an ultrasonic wave with a radius of 25 mm (approximately 2000 m). ２ A pest control system with an effective reach range R can be obtained. Furthermore, the power consumption of the ultrasonic generator 10 was confirmed to be 2.64W, indicating that it can be operated with very low power. 【0101】(Example 3) In Example 3, a pest control system 100 equipped with one ultrasonic generator 10, which was manufactured in Example 2, was used in a peach orchard to conduct a test to confirm the effectiveness of pest control against moths. 【0102】 Figure 3 schematically shows the peach orchard (field F) where the test was conducted. Field F measured 51.25 mm (X direction) x 21.25 mm (Y direction). The ultrasonic generator 10, which was made in Example 2, was installed in the center of this field. In addition, a grove of trees that serves as a source for suction moths, which are pests, was created around field F. 【0103】 The results are shown in Table 1 below. 【0104】 As shown in Table 1, in the comparative example plot where the pest control system 100 was not installed (normal cultivation plot), 11.1% of the harvested peaches were damaged by mites, whereas in the plot where the pest control system 100 was installed, it was confirmed that the damage from mites could be reduced to 1%. From these results, it became clear that the ultrasonic generator 10 can exert a pest control effect in all directions of 360° horizontally. 【0105】 The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. Configurations obtained by combining the configurations of the different embodiments described herein are also included in the scope of the invention. 【0106】 10: Ultrasonic generator 11: Ultrasonic generating unit 20: Control unit 21: Ultrasonic oscillation circuit 22: Amplification circuit 23: Power supply circuit 29: Communication interface 30: Power supply unit 31: Battery 32: Solar panel 40: Detection unit 50: Ultrasonic transducer 55: Support unit 60: Piezoelectric vibrator 61: Metal plate 62: Piezoelectric body 62a: First piezoelectric body 62b: Second piezoelectric body 63: First electrode pair (electrode pair) 63a: Electrode 63b: Electrode 64: Second electrode pair (electrode pair) 64a: Electrode 64b: Electrode 66: Waterproof layer 100: Pest control system 155: Beam F: Field

Claims

1. An ultrasonic transducer for pest control, comprising at least one piezoelectric vibrator including at least one flat piezoelectric element and a pair of electrodes arranged with the piezoelectric element in between, wherein the piezoelectric vibrator generates ultrasonic waves with a frequency of 18 kHz to 70 kHz.

2. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is driven at a non-resonant frequency.

3. The ultrasonic transducer according to claim 1, wherein the piezoelectric material is a lead-free piezoelectric ceramic.

4. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator further comprises a flat metal plate, the piezoelectric body includes two piezoelectric bodies arranged with the metal plate in between, and the pair of electrodes includes two pairs of electrodes arranged with each of the two piezoelectric bodies in between.

5. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator further comprises a flat metal plate disposed on one side of the piezoelectric body.

6. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is in the shape of a rectangular flat plate.

7. The ultrasonic transducer according to claim 6, wherein the length of the shorter side of the piezoelectric vibrator, which is a rectangular flat plate, is one wavelength or more of the wave generated by the frequency at which the piezoelectric vibrator is driven.

8. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is in the shape of a circular or elliptical flat plate.

9. The ultrasonic transducer according to claim 8, wherein the diameter of the piezoelectric vibrator, which is a circular plate, or the minor axis of the piezoelectric vibrator, which is an elliptical plate, is one wavelength or more of the wave generated by the frequency at which the piezoelectric vibrator is driven.

10. The ultrasonic transducer according to claim 1, further comprising a support portion for fixing the piezoelectric vibrator at the central part of the piezoelectric vibrator.

11. The ultrasonic transducer according to claim 1, further comprising a waterproof layer covering the piezoelectric vibrator.

12. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is driven by bending vibration.

13. An ultrasonic generator comprising a plurality of ultrasonic transducers as described in claim 1.

14. The ultrasonic generator according to claim 13, further comprising a detection unit for detecting ultrasonic waves emitted from the piezoelectric transducer.

15. A pest control system comprising at least one ultrasonic generator according to claim 13 or 14.

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