Ultrasonic transducer and ultrasonic sensor

Abstract

To provide an ultrasonic transducer and an ultrasonic sensor that can widen the ultrasonic beam angle even when the receiving surface is large.SOLUTION: An ultrasonic transducer includes a laminate (10) in which a first electrode layer (12A), a piezoelectric layer (11), and a second electrode layer (12B) are laminated in this order, and a plurality of vibration regions (SV1, SV2) having different resonance frequencies, amplitudes, or phases are provided within the plane of the laminate (10).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] One aspect of the present invention relates to an ultrasonic transducer and an ultrasonic sensor. [Background technology]

[0002] Patent Document 1 discloses an ultrasonic sensor using a piezoelectric element made of a flexible polymer material. The ultrasonic sensor of Patent Document 1 includes a base and a piezoelectric sheet placed on the surface of the base. Furthermore, in the ultrasonic sensor of Patent Document 1, the piezoelectric sheet includes a piezoelectric element, a lower electrode laminated on the back side of the piezoelectric element, and an upper electrode laminated on the front side of the piezoelectric element so that at least a portion of the upper electrode faces the lower electrode. In the ultrasonic sensor of Patent Document 1, the piezoelectric sheet is fixed to the base in an area other than the area of ​​the lower electrode that faces the upper electrode in a plan view. In the ultrasonic sensor of Patent Document 1, a foamed resin electret made of, for example, polypropylene (PP) is used as the polymer material constituting the piezoelectric element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2020-67371 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in an ultrasonic sensor using a foamed resin electret as the polymeric material constituting the piezoelectric body, such as that disclosed in Patent Document 1, the sound field intensity at a distance from the ultrasonic sensor on the central axis of the ultrasonic sensor is proportional to the voltage applied to the ultrasonic sensor multiplied by the area of ​​the ultrasonic sensor. Therefore, the ultrasonic sensor of Patent Document 1 has low ultrasonic transmission and reception sensitivity, and therefore requires a large ultrasonic transmission and reception surface. On the other hand, because the ultrasonic sensor of Patent Document 1 transmits and receives ultrasonic waves by thickness vibration of the piezoelectric body, even if the area is increased, the ultrasonic directivity is narrow, and the ultrasonic detection zone cannot be covered over a wide area.

[0005] An object of one aspect of the present invention is to provide an ultrasonic transducer and an ultrasonic sensor that can widen the beam angle of ultrasonic waves even when the area of ​​the transmitting and receiving surface is increased. [Means for solving the problem]

[0006] In order to solve the above problems, the ultrasonic transducer according to aspect 1 of the present invention comprises a laminate in which a first electrode layer including at least one electrode, a piezoelectric layer including an electret sheet made of foamed resin, and a second electrode layer including at least one electrode are stacked in this order, and multiple vibration regions with different resonant frequencies, amplitudes, or phases are provided within the plane of the laminate.

[0007] Aspect 2 of the present invention provides an ultrasonic transducer according to aspect 1, wherein the plurality of vibration regions are made up of parts with different elasticity or mass within the plane of the laminate.

[0008] An ultrasonic transducer according to aspect 3 of the present invention is the same as that of aspect 1, and includes a support layer on one side of the laminate that supports the laminate, and the multiple vibration regions consist of non-fixed portions where a portion of the surface of the laminate is not fixed to the support layer, and fixed portions where a portion of the surface of the laminate is fixed to the support layer.

[0009] A fourth aspect of the present invention provides an ultrasonic transducer according to the first aspect, wherein the plurality of vibration regions are made up of portions of the piezoelectric layer whose polarization directions are different from each other.

[0010] An ultrasonic transducer according to aspect 4 of the present invention is the same as that of aspect 1, in which at least one of the first electrode layer and the second electrode layer comprises a plurality of electrodes, the first electrode layer and the second electrode layer face each other to form a plurality of electrode pairs, and electrical signals of different phases are applied to each of the plurality of electrode pairs.

[0011] A fifth aspect of the present invention provides an ultrasonic transducer according to the first aspect, wherein the plurality of vibration regions are made up of portions of the piezoelectric layer whose polarization directions are different from each other.

[0012] An ultrasonic transducer according to a sixth aspect of the present invention is any one of the first to fifth aspects, wherein the plurality of vibration regions are made up of two types of vibration regions having mutually different resonance frequencies, amplitudes, or phases.

[0013] An ultrasonic transducer according to a seventh aspect of the present invention is any one of the first to fifth aspects, wherein the plurality of vibration regions are made up of m types of vibration regions, the phases of adjacent vibration regions differing by 2π / m (m is an integer of 2 or more).

[0014] An ultrasonic transducer according to aspect 8 of the present invention is the same as in aspect 7, and has a transmitting / receiving surface on one side of the laminate for transmitting and receiving ultrasonic waves. When a virtual point a predetermined distance away from the transmitting / receiving surface is designated as a focus point O, and a plurality of virtual lines Ln are drawn on the transmitting / receiving surface so that the distance Dn from the focus point O to the transmitting / receiving surface is D+n·λ / m (D is an arbitrary fixed distance, n is an integer greater than or equal to 1, and λ is the wavelength of the ultrasonic waves), and the area surrounded by virtual lines Ln and Ln+1 is designated as a vibration area Rn, the vibration area Rn and the vibration area Rn+1 are arranged so that their phases differ from each other by 2π / m.

[0015] An ultrasonic transducer according to a ninth aspect of the present invention is the same as in the seventh aspect, and has a transmitting / receiving surface on one side of the laminate for transmitting and receiving ultrasonic waves. When a virtual line X is defined as a focus line at a predetermined distance from the transmitting / receiving surface, and a plurality of virtual lines Yn are drawn on the transmitting / receiving surface so that a distance Dn from the focus line X to the transmitting / receiving surface is D+n·λ / m (D is an arbitrary fixed distance, n is an integer greater than or equal to 1, and λ is the wavelength of the ultrasonic waves), and the area surrounded by virtual lines Yn and Yn+1 is defined as a vibration area Zn, the vibration area Zn and the vibration area Zn+1 are arranged so that their phases differ from each other by 2π / m.

[0016] An ultrasonic transducer according to a tenth aspect of the present invention is any one of the seventh to ninth aspects, wherein m is four.

[0017] An ultrasonic transducer according to an eleventh aspect of the present invention is the ultrasonic transducer of any one of the first to seventh aspects, wherein the plurality of vibration regions are arranged in a random pattern within the plane of the laminate.

[0018] An ultrasonic transducer according to a twelfth aspect of the present invention is based on any one of the first to eleventh aspects, wherein the first electrode layer includes a ground electrode, and the second electrode layer includes two or more hot electrodes.

[0019] An ultrasonic transducer according to aspect 13 of the present invention is similar to aspect 12 in that the second electrode layer comprises an insulating film, and a first hot electrode is formed on one side of the insulating film, and a second hot electrode different from the first hot electrode is formed on the other side.

[0020] An ultrasonic sensor according to a fourteenth aspect of the present invention includes the ultrasonic transducer according to any one of the first to thirteenth aspects, and an amplifier electrically connected to the ultrasonic transducer. [Effects of the Invention]

[0021] According to one aspect of the present invention, the directivity angle of ultrasonic waves can be widened even if the area of ​​the transmitting and receiving surface is increased. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view showing an example of a basic configuration of an ultrasonic transducer according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram of an ultrasonic sensor according to an embodiment of the present invention; [Figure 3] 1 is a perspective view showing a schematic configuration of an example of a vibration region in an ultrasonic transducer according to an embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view showing a schematic configuration of another example of a vibration region in an ultrasonic transducer according to an embodiment of the present invention. [Figure 5] FIG. 10 is a cross-sectional view showing a schematic configuration of still another example of a vibration region in an ultrasonic transducer according to an embodiment of the present invention. [Figure 6] FIG. 10 is a cross-sectional view showing a schematic configuration of still another example of a vibration region in an ultrasonic transducer according to an embodiment of the present invention. [Figure 7] 7 shows an example of a concentric pattern of multiple vibration regions provided within the plane of a laminate in an ultrasonic transducer according to an embodiment of the present invention, where 701 is a schematic diagram for explaining the setting of the concentric pattern, and 702 is a top view schematically showing the concentric pattern of multiple vibration regions. [Figure 8] This shows an example of a pattern of the vibration area when the attention point O is set outside the area of ​​the transmitting and receiving surface, where 801 is a schematic diagram for explaining the setting of the pattern of the vibration area, and 802 is a top view that schematically shows the pattern of the vibration area. [Figure 9] 9 shows an example of a stripe pattern of a plurality of vibration regions provided within the plane of a laminate in an ultrasonic transducer according to an embodiment of the present invention, where 901 is a schematic diagram for explaining the setting of the concentric circle pattern, and 902 is a top view schematically showing the concentric circle pattern of a plurality of vibration regions. [Figure 10]10 shows an example of a concentric circle pattern of vibration regions when the vibration regions consist of three or more types of vibration regions, where 1001 is a schematic diagram for explaining the setting of the concentric circle pattern, and 1002 is a top view that schematically shows the concentric circle pattern of the vibration regions. [Figure 11] This shows an example of a stripe pattern of vibration areas when the multiple vibration areas consist of three or more types of vibration areas, where 1101 is a schematic diagram for explaining the setting of the stripe pattern, and 1102 is a top view that schematically shows the stripe pattern of the multiple vibration areas. [Figure 12] 1 is a cross-sectional view showing an example of the configuration of a laminate in an ultrasonic transducer according to an embodiment of the present invention, in which a first electrode layer includes a ground electrode. [Figure 13] 13 is a plan view showing a schematic configuration of a pattern of hot electrodes in the laminate shown in FIG. 12 when a plurality of vibration regions provided in the plane of the laminate are in a four-phase concentric circle pattern. FIG. [Figure 14] 10A and 10B are a top view and a cross-sectional view showing another example of the configuration of a laminate in which the first electrode layer includes a ground electrode in an ultrasonic transducer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] [Embodiment 1] Hereinafter, one embodiment of the present invention will be described in detail.

[0024] <Ultrasonic sensor> FIG. 2 is a schematic diagram of the ultrasonic sensor 100. The ultrasonic sensor 100 is a sensor that emits ultrasonic waves and receives the ultrasonic waves reflected by an object. Ultrasonic waves refer to sound waves having a frequency of 20 kHz or higher. As shown in FIG. 2, the ultrasonic sensor 100 includes an ultrasonic transducer 1 and an amplifier 51.

[0025] The ultrasonic transducer 1 emits ultrasonic waves by converting an electrical signal supplied from a power source (not shown) into mechanical vibrations. The ultrasonic transducer 1 also converts mechanical vibrations generated by ultrasonic waves received from outside into electrical signals. The amplifier 51 amplifies the voltage or current electrical signal converted by the ultrasonic transducer 1. Examples of the amplifier 51 include a normal amplifier, an instrumentation amplifier, and an operational amplifier. The ultrasonic transducer 1 only needs to have the function of converting ultrasonic waves into electrical energy and vice versa. The ultrasonic sensor 100 only needs to have the function of receiving or transmitting (emitting) ultrasonic waves. In this case, the ultrasonic sensor 100 does not need to have the amplifier 51.

[0026] <Basic configuration of ultrasonic transducer> Fig. 1 is a schematic cross-sectional view showing an example of the basic configuration of an ultrasonic transducer 1. In Fig. 1, the direction from the second electrode layer 12B toward the first electrode layer 12A is the upward direction (stacking direction, +Z-axis direction), and the opposite direction is the downward direction (-Z-axis direction). The direction perpendicular to the up-down direction is the horizontal direction (direction on the XY plane). Fig. 1 is a cross-sectional view of the ultrasonic transducer 1 cut along a plane parallel to the up-down direction.

[0027] As shown in FIG. 1, the ultrasonic transducer 1 includes a laminate 10, a first extraction electrode 13A, and a second extraction electrode 13B. The laminate 10 includes a piezoelectric layer 11, a first electrode layer 12A, and a second electrode layer 12B, with the piezoelectric layer 11 sandwiched between the first electrode layer 12A and the second electrode layer 12B. That is, the laminate 10 includes the first electrode layer 12A, the piezoelectric layer 11, and the second electrode layer 12B stacked in this order. The ultrasonic transducer 1 also includes a transmitting / receiving surface 10A on the first electrode layer 12A side that emits or receives ultrasonic waves. As will be described later, each layer may be a thin film (sheet-like).

[0028] (Piezoelectric layer) The piezoelectric layer 11 is located between the first electrode layer 12A and the second electrode layer 12B. The piezoelectric layer 11 is made of a thin-film piezoelectric material (piezoelectric film). The polarization direction of the piezoelectric layer 11 is the upward direction.

[0029] The piezoelectric layer 11 is an electret made of foamed resin. An electret made of foamed resin is called a foamed resin electret. The foamed resin electret can be made by foaming a flexible resin material.

[0030] Examples of resin materials include thermoplastic resins, such as polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P(VDF / TrFE)), and vinylidene cyanide-vinyl acetate copolymer (P(VDCN / VAc)). Only one of these resin materials may be used, or multiple types may be combined. These resin materials are foamed to form bubbles within the resin material. The foamed resin material may then be stretched to form flat bubbles. Each pore is then polarized and charged, for example, by corona discharge. This converts the foamed resin (foamed resin) into an electret.

[0031] From the viewpoint of increasing the compatibility between the piezoelectric layer 11 and air and easily widening the frequency band of the ultrasonic waves emitted by the piezoelectric layer 11, the resin material is preferably PP or PE.

[0032] A foamed resin electret, which is made by foaming the resin material, has a low acoustic impedance and high compatibility with air, resulting in a high conversion efficiency between ultrasonic waves and electricity. In particular, the acoustic impedance of a foamed resin electret is smaller than that of non-foamed materials commonly used as piezoelectric bodies, and is close to the acoustic impedance of air, making it suitable for use as a piezoelectric layer. Therefore, by using a foamed electret with a high conversion efficiency as the piezoelectric layer, the Q value of the ultrasonic transducer 1 is reduced, allowing it to emit ultrasonic waves over a relatively wide frequency band.

[0033] In general, the directivity of a sensor using a sound source that vibrates in a piston-like manner (vibrates uniformly in the thickness direction) is determined by the frequency, the shape of the vibration region, and the size of the vibration region. The thickness, shape, and size of the vibration region of a foamed resin electret can be easily adjusted. Therefore, by using a foamed resin electret as the piezoelectric layer 11, the thickness longitudinal vibration and the shape and size of the piezoelectric layer 11 can be designed independently. This makes it easy to adjust the directivity of the ultrasonic waves emitted by the ultrasonic transducer 1. For example, the area of ​​the ultrasonic wave emitting surface (receiving surface) of the foamed resin electret can be designed to be large. Generally, the larger the area of ​​the ultrasonic wave emitting surface of a sensor, the higher the directivity. Therefore, in this case, the ultrasonic transducer 1 can emit ultrasonic waves with high directivity.

[0034] The piezoelectric constant d33 of the foamed resin electret is relatively large, being comparable to that of lead zirconate titanate (PZT). Furthermore, the elastic modulus of the foamed resin electret in the thickness direction is smaller than that of other materials. Therefore, the foamed resin electret requires a smaller voltage to displace it in the thickness direction than other materials. Furthermore, the foamed resin electret has a small dielectric constant, and the current that flows during driving is also small. Therefore, the power consumption of the ultrasonic transducer 1 can be reduced.

[0035] Furthermore, since the Q value of the foamed resin electret is small, the reverberation of the ultrasonic waves is small and the resolution in the direction of propagation of the ultrasonic waves is high. Therefore, the ultrasonic transducer 1 can accurately measure the distance to the object to be measured, even if the object is close.

[0036] For example, when piezoelectric ceramics, quartz crystal, or polyvinylidene fluoride (unfoamed) is used as the piezoelectric body, the large elastic modulus of the piezoelectric body results in small displacement. To solve this problem, a vibration mode is used in which the resonant frequency is determined by the size of the direction perpendicular to the sound wave radiation direction, such as flexural vibration. Increasing the area of ​​the piezoelectric body reduces the vibration frequency accordingly, making it difficult to design thickness longitudinal vibration and the shape and size of the piezoelectric body independently. Therefore, in this case, it is not easy to adjust the directivity.

[0037] Although it is possible to adjust the directivity by attaching a horn, the horn becomes a protruding part, and its attachment is limited. Furthermore, there is no established theory for designing the directivity of a horn, which makes the design of the ultrasonic transducer more difficult and requires time for development. Furthermore, when attempting to utilize thickness vibration as in one embodiment of the present invention, these piezoelectric materials tend to be thicker due to the high ultrasonic velocity. Therefore, it is difficult to use the frequency band of the ultrasonic waves emitted by the ultrasonic transducer at relatively low frequencies (100 kHz or less) where the absorption attenuation of the ultrasonic waves is small.

[0038] The thickness of the piezoelectric layer 11 is preferably 5 mm or less, more preferably 1 mm or less, even more preferably 500 μm or less, and particularly preferably 300 μm or less. There is no particular lower limit to the thickness of the piezoelectric layer 11, but from the viewpoint of mechanical strength, 10 μm or more is preferred.

[0039] Generally, the resonant frequency of a vibrating body is inversely proportional to the square root of the vibrating body's weight. Therefore, the lighter the vibrating body, the higher the resonant frequency of the vibrating body can be, and the higher the frequency of the ultrasonic waves emitted from the vibrating body can be. Therefore, for the same density, the thinner the piezoelectric layer 11, the easier it is to increase the frequency of the ultrasonic waves emitted by the ultrasonic transducer 1. Increasing the frequency of the ultrasonic waves emitted by the ultrasonic transducer 1 increases the possibility of using the ultrasonic transducer 1 as a general-purpose ultrasonic transducer (for example, as a rear sonar for automobiles).

[0040] The average bubble diameter in the thickness direction of the piezoelectric layer 11 is preferably 10 μm or more and 400 μm or less. When the average bubble diameter in the thickness direction is equal to or more than the above-mentioned lower limit, it becomes easier to suppress the attenuation of ultrasonic waves in the piezoelectric layer 11. When the average bubble diameter in the thickness direction is equal to or less than the above-mentioned upper limit, it becomes easier to reduce the thickness of the piezoelectric layer 11, and therefore it becomes easier to increase the frequency of ultrasonic waves.

[0041] The average number of bubbles in the thickness direction of the piezoelectric layer 11 is preferably small, for example, preferably 5 or less, more preferably 3 or less, and most preferably 1. When the average number of bubbles in the thickness direction is equal to or less than the above upper limit, the thickness of the piezoelectric layer 11 can be easily reduced, which makes it easier to increase the frequency of the ultrasonic waves.

[0042] Although the area of ​​the piezoelectric layer 11 is not particularly limited, the larger the area, the more efficiently ultrasonic waves with low energy can be received, thereby reducing the energy required for transmitting and receiving ultrasonic waves. 2 It may be more than 100cm 2 It may be more than 1000 cm 2 It may be more than that.

[0043] (electrode layer) The first electrode layer 12A and the second electrode layer 12B vibrate the piezoelectric layer 11 by applying a voltage to the piezoelectric layer 11. Furthermore, the first electrode layer 12A and the second electrode layer 12B generate a voltage or a current between the first electrode layer 12A and the second electrode layer 12B due to a change in voltage generated in the piezoelectric layer 11 by an external force (ultrasonic wave).

[0044] The first electrode layer 12A is an electrode layer located on the upper surface of the piezoelectric layer 11. The second electrode layer 12B is an electrode layer located on the lower surface of the piezoelectric layer 11. Each of the first electrode layer 12A and the second electrode layer 12B includes at least one electrode.

[0045] In this embodiment, the first electrode layer 12A and the second electrode layer 12B are described as being formed by a single electrode. However, the first electrode layer 12A may include multiple electrodes. The second electrode layer 12B may also include multiple electrodes. Both the first electrode layer 12A and the second electrode layer 12B may include multiple electrodes, or only one of the first electrode layer 12A and the second electrode layer 12B may include multiple electrodes. In these cases, the electrodes included in the first electrode layer 12A and the electrodes included in the second electrode layer 12B face each other. This allows ultrasonic waves to be emitted and received in each region of the piezoelectric layer 11 between the facing electrodes. Therefore, for example, the ultrasonic transducer 1 can be arrayed and the direction in which ultrasonic waves can be transmitted and received can be changed using phased array technology.

[0046] The thickness of each of the first electrode layer 12A and the second electrode layer 12B is preferably 300 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. In this case, it becomes easier to increase the frequency of the ultrasonic waves. The lower limit of the thickness of the first electrode layer 12A and the second electrode layer 12B is not particularly limited and may be, for example, 1 μm or more.

[0047] The first electrode layer 12A and the second electrode layer 12B may each be in contact with a portion of the surface of the piezoelectric layer 11. The material of the first electrode layer 12A and the second electrode layer 12B may be a metal such as aluminum. When the material is a metal, it may be a foil or a vapor-deposited layer.

[0048] A first extraction electrode 13A and a second extraction electrode 13B are electrically connected to the electrodes of the first electrode layer 12A and the second electrode layer 12B, respectively. The first extraction electrode 13A and the second extraction electrode 13B extend from the first electrode layer 12A and the second electrode layer 12B to the outside of the laminate 10. The first electrode layer 12A and the second electrode layer 12B are connected to a power supply and amplifier 51 included in the ultrasonic sensor 100.

[0049] The material of the first extraction electrode 13A and the second extraction electrode 13B may be, for example, the same as or different from the material of the first electrode layer 12A and the second electrode layer 12B. For example, the first extraction electrode 13A and the first electrode layer 12A may be integrally formed with the second extraction electrode 13B and the second electrode layer 12B. Alternatively, for example, the first electrode layer 12A and the second electrode layer 12B may be formed using aluminum, which has a low density and is inexpensive, and the first extraction electrode 13A and the second extraction electrode 13B may be formed using copper, which is easy to solder.

[0050] The first extraction electrode 13A and the second extraction electrode 13B may have a first conductive tack surface (not shown) and a second conductive tack surface (not shown) on the surfaces facing the first electrode layer 12A and the second electrode layer 12B, respectively. The first conductive tack surface and the second conductive tack surface may be surfaces on which a conductive tack sheet is attached to the first extraction electrode 13A and the second extraction electrode 13B, respectively, or may be surfaces on which a conductive adhesive is applied. The first extraction electrode 13A and the second extraction electrode 13B themselves may be conductive tack sheets.

[0051] Furthermore, the entire surface of one of the first and second extraction electrodes 13A and 13B may be the first and second conductive tack surfaces, or only a portion of the surface may be the first and second conductive tack surfaces.

[0052] In this embodiment, the first electrode layer 12A and the piezoelectric layer 11 are in contact with each other without being bonded with an adhesive or the like. The second electrode layer 12B and the piezoelectric layer 11 are in contact with each other without being bonded with an adhesive or the like. Even in this case, they can be bonded together by static electricity or the like. In this case, the first electrode layer 12A, the piezoelectric layer 11, and the second electrode layer 12B can be easily disassembled. Therefore, when the piezoelectric layer 11 deteriorates, it can be easily replaced. Furthermore, the ultrasonic transducer 1 can be easily manufactured.

[0053] However, at least one of the first electrode layer 12A and the second electrode layer 12B may be bonded to the piezoelectric layer 11. For example, a first adhesive layer (not shown) that bonds the first electrode layer 12A to the piezoelectric layer 11 and a second adhesive layer (not shown) that bonds the second electrode layer 12B to the piezoelectric layer 11 may be provided. In this case, bonding the first electrode layer 12A, the piezoelectric layer 11, and the second electrode layer 12B together makes it easier to increase the frequency band of the ultrasonic waves emitted by the ultrasonic transducer 1. The first adhesive layer and the second adhesive layer may be formed of an adhesive such as a spray glue. When the first adhesive layer and the second adhesive layer are provided, the thickness of each of the first adhesive layer and the second adhesive layer is preferably 200 μm or less.

[0054] When the thickness (film thickness) of the piezoelectric layer 11 is sufficiently thin and the piezoelectric layer 11 is bonded to the first electrode layer 12A and the second electrode layer 12B, as in this embodiment, the lateral expansion of the piezoelectric layer 11 is constrained by the first electrode layer 12A and the second electrode layer 12B. Therefore, when the piezoelectric layer 11 is bonded to the first electrode layer 12A and the second electrode layer 12B, the spring constant of the piezoelectric layer 11 is larger than when the piezoelectric layer 11 is not bonded to the first electrode layer 12A and the second electrode layer 12B. This increases the resonant frequency of the piezoelectric layer 11. Therefore, the ultrasonic transducer 1 can widen the frequency band of the ultrasonic waves it emits.

[0055] The ultrasonic transducer 1 may also include an electrode support layer that supports the first electrode layer 12A and the second electrode layer 12B.

[0056] (Support layer) The ultrasonic transducer 1 includes a support layer 40 that supports the laminate 10 at a position facing the lower surface of the second electrode layer 12B. The support layer 40 is a sheet-like member that includes a substrate 41 that contacts the second electrode layer 12B and a base 42 on which the substrate 41 is provided. An upper surface 40US of the support layer 40 contacts the second electrode layer 12B.

[0057] The substrate 41 only needs to be provided in at least an area that overlaps with the first electrode layer 12A and the second electrode layer 12B in a plan view. The material of the substrate 41 may be, for example, resin. The material of the base 42 may be, for example, rubber or balsa. The thickness of the substrate 41 may be 50 μm or more and 10 mm or less, and the thickness of the base 42 may be 500 μm or more and 10 mm or less. By adjusting the material and thickness of the substrate 41, the acoustic characteristics and electrical characteristics of the ultrasonic transducer 1 can be adjusted.

[0058] <Thickness of each layer> As described above, the thickness of each layer of the ultrasonic transducer 1 is adjusted to be thin. That is, each layer of the ultrasonic transducer 1 is in a sheet shape. Therefore, the ultrasonic transducer 1 can be made thin, and therefore the ultrasonic transducer 1 can be installed in various locations. Also, as described above, since each layer is in a sheet shape, the frequency band can be increased. Furthermore, by using a large-area ultrasonic transducer, scattered or reflected ultrasonic waves can be efficiently received, and the power required for transmitting waves can be reduced accordingly.

[0059] <Method of manufacturing ultrasonic transducer> An example of a method for manufacturing the ultrasonic transducer 1 will be described.

[0060] The first extraction electrode 13A is bonded to the first electrode layer 12A. Furthermore, the second extraction electrode 13B is bonded to the second electrode layer 12B. Thereafter, the first electrode layer 12A and the second electrode layer 12B are bonded to the piezoelectric layer 11 to produce the laminate 10. As described above, the piezoelectric layer 11 and the first electrode layer 12A do not have to be bonded together. Furthermore, the piezoelectric layer 11 and the second electrode layer 12B do not have to be bonded together. Thereafter, the laminate 10 is bonded to a base 42 via a substrate 41.

[0061] A plurality of laminates 10 may be produced for one base 42. A plurality of ultrasonic transducers 1 may be manufactured by cutting a plurality of laminates 10.

[0062] <Features of the ultrasonic transducer according to this embodiment> As described above, the ultrasonic transducer according to this embodiment is based on a configuration including a laminate 10 in which a first electrode layer 12A including at least one electrode, a piezoelectric layer 11 including an electret sheet made of a foamed resin, and a second electrode layer 12B including at least one electrode are laminated in this order. Ultrasonic sensors including such ultrasonic transducers generally have low sensitivity. Therefore, to improve sensitivity, it is necessary to increase the area of ​​the transmitting and receiving surfaces of the ultrasonic transducer. On the other hand, as described above, the larger the area of ​​the transmitting and receiving surfaces of the ultrasonic sensor, the higher the directivity (narrower the beam angle), and the sound field distribution of the ultrasonic waves becomes approximately parallel. Furthermore, the narrow beam angle of the ultrasonic waves makes it difficult to cover a wide detection range of the ultrasonic sensor.

[0063] Therefore, as a result of intensive research aimed at developing an ultrasonic sensor that can widen the beam angle of ultrasonic waves even when the area is increased, the inventors focused on the vibration mode of ultrasonic waves (resonance frequency or amplitude, or phase) on the transmitting and receiving surface and thought that if the vibration mode of ultrasonic waves is made non-uniform, the beam angle of ultrasonic waves can be widened. Then, they thought that if vibration regions with different vibration modes, such as resonance frequency, amplitude, or phase, are formed on the transmitting and receiving surface, ultrasonic waves with a wide beam angle can be emitted, and arrived at the ultrasonic transducer according to this embodiment.

[0064] That is, the ultrasonic transducer according to this embodiment is characterized in that a plurality of vibration regions with different resonant frequencies, amplitudes, or phases are provided within the plane of the laminate, thereby realizing an ultrasonic sensor that can widen the beam angle of ultrasonic waves even when the transmitting and receiving surface is large.

[0065] An example of a plurality of vibration regions in the ultrasonic transducer according to this embodiment will be described below.

[0066] (1) Non-uniformity of vibration modes due to the addition of mass Fig. 3 is a perspective view showing a schematic configuration of an example of a vibration region in the ultrasonic transducer according to this embodiment. Fig. 3 shows an example in which a plurality of vibration regions are made up of parts with different elasticity or mass within the plane of the laminate 10. As shown in Fig. 3, in the ultrasonic transducer according to this embodiment, mass addition portions 14a to 14g may be provided on the transmitting / receiving surface 10A of the laminate 10. Examples of materials for the mass addition portions 14a to 14g include a resin film and an aluminum film. In the transmitting / receiving surface 10A of the ultrasonic transducer, the regions where the mass addition portions 14a to 14g are provided respectively become vibration regions SVa to SVg.

[0067] In the transmitting / receiving surface 10A, the vibration regions SVa to SVg have a larger mass than regions where the mass adding portions 14a to 14g are not provided. When a voltage is applied to a laminate with such a configuration, the resonant frequency and amplitude of the vibration regions SVa to SVg are smaller than those of the regions where the mass adding portions 14a to 14g are not provided. For this reason, in the configuration shown in Fig. 3, within the plane of the laminate 10 (transmitting / receiving surface 10A), at least the resonant frequency or amplitude of the vibration regions SVa to SVg differs from that of the regions where the mass adding portions 14a to 14g are not provided.

[0068] If the mass adding portions 14a to 14g have the same thickness in the Z direction, the resonant frequency or amplitude will be the same in the vibration regions SVa to SVg. Therefore, in this case, two types of vibration regions with different vibration modes are provided within the plane of the laminate 10. The two types of vibration regions are the regions where the mass adding portions 14a to 14g are not provided and the vibration regions SVa to SVg.

[0069] 3, instead of the mass adding portions 14a to 14g, regions with partially different elasticity may be provided in predetermined regions within the plane of the laminate 10. In the regions with partially different elasticity, the resonance frequency or amplitude differs from that of other regions, and therefore multiple vibration regions are provided within the plane of the laminate 10. Examples of methods for providing regions with partially different elasticity include a method of combining multiple foamed resins with different expansion ratios to form an electret sheet, and a method of providing regions with partially different cross-linking degrees in the foamed resin that forms the electret sheet.

[0070] (2) Non-uniform vibration modes due to the fixing configuration between the laminate and the support layer Fig. 4 is a cross-sectional view showing a schematic configuration of another example of a vibration region in the ultrasonic transducer according to this embodiment. Fig. 4 shows an example in which the multiple vibration regions are composed of non-fixed portions where a portion of the surface of the laminate 10 is not fixed to the support layer 40, and fixed portions where a portion of the surface of the laminate 10 is fixed to the support layer 40. As shown in Fig. 4, in the ultrasonic transducer according to this embodiment, a plurality of fixing portions 43 for fixing the lower surface of the laminate 10 are provided on the surface of the support layer 40 facing the laminate 10. The fixing portions 43 protrude from the upper surface of the base material 41 and are adhered to the lower surface of the laminate 10. The laminate 10 is fixed to the support layer 40 via the fixing portions 43.

[0071] 4, a vibration region SV1 (fixed portion) where the support layer 40 and the laminate 10 are fixed via a fixing portion 43, and a vibration region SV2 (unfixed portion) where the support layer 40 and the laminate 10 are not fixed to the fixing portion 43 are provided within the plane of the laminate 10. When a voltage is applied to the laminate 10 configured in this way, the resonance frequencies of the vibration region SV1 and the vibration region SV2 differ from each other.

[0072] The fixing portion 43 is not particularly limited as long as it is configured to be able to fix the laminate 10 and the support layer 40 via the fixing portion 43. The base material 41 and the fixing portion 43 may be integrally formed or may be separate bodies.

[0073] Furthermore, the fixing portion 43 may be made of the same material as or a different material from the second electrode layer 12B or the base material 41. The fixing portion 43 may be made of an adhesive or double-sided tape.

[0074] 4, the fixing portions 43 may be made of different materials. In this manner, more vibration regions with different resonance frequencies can be formed within the plane of the laminate 10.

[0075] (3) Non-uniformity of the vibration mode due to a change in the polarization direction of the piezoelectric layer 11 FIG. 5 is a cross-sectional view showing a schematic configuration of yet another example of a vibration region in an ultrasonic transducer according to this embodiment. FIG. 5 shows an example in which multiple vibration regions are composed of portions (segments) in a piezoelectric layer 11, each having a different polarization direction P. As shown in FIG. 5, piezoelectric portions 11A and 11B are provided on the piezoelectric layer 11 of a laminate 10. The piezoelectric portions 11A and 11B have opposite polarization directions P. When a voltage is applied to a laminate 10 having such a configuration, a vibration region SV3 corresponding to the piezoelectric portion 11A and a vibration region SV4 corresponding to the piezoelectric portion 11B vibrate in a plane of the laminate 10, with their phases shifted from each other. In the configuration shown in FIG. 5, the multiple vibration regions provided in the plane of the laminate 10 are composed of two types of vibration regions SV3 and SV4 with different phases. Although the segments are depicted with the same width in FIG. 5, the widths do not have to be the same.

[0076] The piezoelectric layer 11 having the piezoelectric portions 11A and 11B can be manufactured, for example, by the following method. That is, first, two foamed resin electrets are prepared, each charged so that the polarization directions are different from each other. Next, the two prepared foamed resin electrets are each cut out to a predetermined size. Then, the two cut-out foamed resin electrets are arranged alternately in the XY plane.

[0077] (4) Non-uniformity of vibration modes due to the first electrode layer 12A and the second electrode layer 12B FIG. 6 is a cross-sectional view showing a schematic configuration of yet another example of the vibration region of the ultrasonic transducer according to this embodiment. In the configuration shown in FIG. 6, the first electrode layer 12A includes four first electrodes 15A1-15A4. The second electrode layer 12B includes four second electrodes 15B1-15B4. The four first electrodes 15A1-15A4 included in the first electrode layer 12A and the four second electrodes 15B1-15B4 included in the second electrode layer 12B face each other. Electrical signals of different phases are applied to the facing first electrodes 15A1-15A4 and second electrodes 15B1-15B4, respectively. The widths of the segments may be different. As described above, according to the configuration shown in FIG. 6, the first electrode layer 12A and the second electrode layer 12B include a plurality of electrodes (first electrodes 15A1-15A4, second electrodes 15B1-15B4). The first electrode layer 12A and the second electrode layer 12B face each other to form a plurality of electrode pairs. The plurality of electrode pairs corresponds to pairs of first electrodes 15A1 to 15A4 and second electrodes 15B1 to 15B4, respectively. Electric signals of different phases are applied to the plurality of electrode pairs, respectively.

[0078] A vibration region SV5 corresponding to the first electrode 15A1 and the second electrode 15B1 facing each other, a vibration region SV6 corresponding to the first electrode 15A2 and the second electrode 15B2 facing each other, a vibration region SV7 corresponding to the first electrode 15A3 and the second electrode 15B3 facing each other, and a vibration region SV8 corresponding to the first electrode 15A4 and the second electrode 15B4 facing each other are provided within the plane of the laminate 10. When electrical signals of different phases are applied to the first electrode 15A1 and the second electrode 15B1, the first electrode 15A2 and the second electrode 15B2, the first electrode 15A3 and the second electrode 15B3, and the first electrode 15A4 and the second electrode 15B4, respectively, the vibration regions SV5, SV6, SV7, and SV8 vibrate with different phases.

[0079] In the ultrasonic transducer according to this embodiment, from the viewpoint of simplifying the multiple vibration regions provided in the plane of the laminate 10, the multiple vibration regions preferably consist of two types of vibration regions with mutually different resonance frequencies, amplitudes, or phases. The non-uniformity of the vibration modes described above in (1) to (4) makes it possible to realize such two types of vibration regions. For example, in the configuration shown in FIG. 3, two types of vibration regions with different resonance frequencies can be realized by making the Z-direction thicknesses of the mass adding portions 14a to 14g the same. Furthermore, in the configuration shown in FIG. 4, two types of vibration regions with different resonance frequencies can be realized by making the thicknesses of the multiple fixing portions 43 the same material. In the configuration shown in FIG. 5, the polarization direction P of the piezoelectric portion 11A and the polarization direction P of the piezoelectric portion 11B are opposite to each other in the Z direction, thereby realizing two types of vibration regions with mutually different phases. Furthermore, in the configuration shown in FIG. 6, for example, by (I) making the phases of the first electrical signals applied to the first electrode 15A1 and the second electrode 15B1 the same as those of the first electrode 15A3 and the second electrode 15B3, (II) making the phases of the second electrical signals applied to the first electrode 15A2 and the second electrode 15B2 the same as those of the first electrode 15A4 and the second electrode 15B4, and (III) making the first electrical signal and the second electrical signal different in phase, two types of vibration regions with different phases can be realized.

[0080] <Pattern of multiple vibration regions within the plane of the laminate> In the ultrasonic transducer according to this embodiment, the pattern of the multiple vibration regions provided within the plane of the laminate 10 is not particularly limited as long as it can widen the directivity angle of the ultrasonic waves. In the ultrasonic transducer according to this embodiment, the multiple vibration regions may be arranged in a random pattern within the plane of the laminate 10.

[0081] In the ultrasonic transducer according to this embodiment, from the viewpoint of easily adjusting the directivity angle of the ultrasonic waves, it is preferable that the multiple vibration regions provided in the plane of the laminate 10 consist of m types of vibration regions in which the phases of adjacent vibration regions differ by 2π / m (m is an integer equal to or greater than 2). An example of a pattern of such multiple vibration regions will be described below.

[0082] (a-1) Concentric circle pattern When the multiple vibration regions are made up of m types of vibration regions with adjacent vibration regions differing in phase by 2π / m, the pattern of the multiple vibration regions may be, for example, a concentric circle pattern as shown in FIG.

[0083] Fig. 7 shows an example of a concentric pattern of multiple vibration regions provided in the plane of the laminate 10, where 701 in Fig. 7 is a schematic diagram for explaining the setting of the concentric pattern, and 702 in Fig. 7 is a top view schematically showing the concentric pattern of multiple vibration regions. As shown in Fig. 7, the pattern of multiple vibration regions provided in the plane of the laminate 10 may be a concentric pattern with a focus point O at the center.

[0084] The method for setting the concentric circle pattern can be generalized as follows. First, a virtual point a predetermined distance away from the transmitting / receiving surface 10A of the laminate 10 is defined as the attention point O. Next, multiple virtual lines Ln are drawn on the transmitting / receiving surface 10A so that the distance Dn from the attention point O to the transmitting / receiving surface 10A is D+n·λ / m (D is an arbitrary fixed distance, n is an integer greater than or equal to 1, and λ is the wavelength of the ultrasonic wave). Then, if the area surrounded by the virtual lines Ln and Ln+1 is defined as a vibration area Rn, the vibration areas Rn and Rn+1 are arranged so that their phases differ by 2π / m. Note that the attention point O is a point where the sound pressure is stronger than at other points, and the sensitivity and S / N ratio increase near the attention point O.

[0085] 7 will be described when m is 2. First, a virtual point located a predetermined distance away from the transmitting / receiving surface 10A of the laminate 10 is set as a target point O.

[0086] Next, three imaginary lines L1 to L3 are drawn on the transmitting and receiving surface 10A so that the distance Dn from the attention point O to the transmitting and receiving surface 10A is D+n·λ / 2 (D is an arbitrary fixed distance, n is an integer between 1 and 3, and λ is the wavelength of the ultrasonic wave). In the example shown in 701 and 702 of FIG. 7, D is D0-λ / 4 (D0 is the minimum distance from the transmitting and receiving surface 10A to the attention point O), and the imaginary lines L1 to L3 are concentric circles. The imaginary line L1 is a concentric circle where the distance D1 from the attention point O to the transmitting and receiving surface 10A is D0+λ / 4. The imaginary line L2 is a concentric circle where the distance D2 from the attention point O to the transmitting and receiving surface 10A is D0+3λ / 4. The imaginary line L3 is a concentric circle where the distance D3 from the attention point O to the transmitting and receiving surface 10A is D0+5λ / 4. Note that the fixed distance D may be set arbitrarily and is not limited to the above setting. For example, D may be D=D0.

[0087] The region surrounded by virtual line L1 is defined as vibration region R1, the region surrounded by virtual line L1 and virtual line L2 is defined as vibration region R2, and the region surrounded by virtual line L2 and virtual line L3 is defined as vibration region R3. The vibration regions R1 and R2 are set to have a phase difference of π. The vibration regions R2 and R3 are set to have a phase difference of π. For example, when the vibration mode is made non-uniform by changing the polarization direction of the piezoelectric layer 11, the polarization direction P of the vibration regions R1 and R3 is set to be upward, while the polarization direction P of the vibration region R2 is set to be downward.

[0088] As described above, by setting the vibration area pattern to a concentric circle pattern, the ultrasonic beam angle can be widened. For example, if the attention point O is set on the central axis of the transmitting / receiving surface 10A of the laminate 10, and the angle formed by an imaginary line passing through the edge of the vibration area and the attention point O with respect to the central axis is θ, the ultrasonic beam angle will be ±θ with the attention point O as the reference. Specifically, when θ = 45°, the ultrasonic beam angle will be ±45°.

[0089] It is also possible to set the attention point O outside the area of ​​the transmitting / receiving surface 10A, as shown by 801 and 802 in Fig. 8. In this case, the imaginary lines L1 to L3 are arcs rather than concentric circles.

[0090] (a-2) Striped pattern When the multiple vibration regions are made up of m types of vibration regions in which the phases of adjacent vibration regions differ by 2π / m, the pattern of the multiple vibration regions may be, for example, a striped pattern as shown in FIG.

[0091] Fig. 9 shows an example of a striped pattern of multiple vibration regions provided in the plane of the laminate 10, where 901 in Fig. 9 is a schematic diagram for explaining the setting of the striped pattern, and 902 in Fig. 9 is a top view schematically showing the striped pattern of multiple vibration regions. As shown in Fig. 9, the pattern of the multiple vibration regions provided in the plane of the laminate 10 may be a striped pattern with the attention line X as the center line.

[0092] The method for setting the striped pattern can be generalized as follows. First, an imaginary line a predetermined distance away from the transmitting / receiving surface 10A is defined as the attention line X. Next, multiple imaginary lines Yn are drawn on the transmitting / receiving surface 10A so that the distance Dn from the attention line X to the transmitting / receiving surface 10A is D+n·λ / m (D is an arbitrary fixed distance, n is an integer greater than or equal to 1, and λ is the wavelength of the ultrasonic wave). Then, if the area surrounded by the imaginary lines Yn and Yn+1 is defined as the vibration area Zn, the vibration area Zn and the vibration area Zn+1 are set so that they have a phase difference of 2π / m. Note that the attention line X is an imaginary line consisting of points where the sound pressure is stronger than other points, and the sensitivity and S / N ratio increase near the attention line X.

[0093] As a specific setting method, a method for setting the striped pattern shown in FIG. 9 when m is 2 will be described. First, a virtual line that is a predetermined distance away from the transmitting / receiving surface 10A of the laminate 10 is set as the attention line X. In the example shown in FIG. 9, the attention line X extends in the Y direction parallel to the transmitting / receiving surface 10A. Note that the direction in which the attention line X extends does not have to be parallel to the transmitting / receiving surface 10A.

[0094] Next, imaginary lines Y1 to Y3 are drawn on the transmitting and receiving surface 10A so that the distance Dn from the observation line X to the transmitting and receiving surface 10A is D+n·λ / 2 (D is an arbitrary fixed distance, n is an integer between 1 and 3, and λ is the wavelength of the ultrasonic wave). In the examples shown in 901 and 902 of FIG. 9, D is D0-λ / 4 (D0 is the minimum distance from the transmitting and receiving surface 10A to the observation line X), and the imaginary lines Y1 to Y3 are each two straight lines. The two imaginary lines Y1·Y1 are each a straight line such that the distance D1 from the observation line X to the transmitting and receiving surface 10A is D0+λ / 4. The two imaginary lines Y2·Y2 are each a straight line such that the distance D2 from the observation line X to the transmitting and receiving surface 10A is D0+3λ / 4. The two imaginary lines Y3·Y3 are each a straight line such that the distance D3 from the observation line X to the transmitting and receiving surface 10A is D0+5λ / 4. The fixed distance D may be set arbitrarily and is not limited to the above setting. For example, D=D0 may be used.

[0095] The region surrounded by the imaginary line Y1-Y1 is defined as vibration region Z1, the region surrounded by the imaginary line Y1-Y1 and the imaginary line Y2-Y2 is defined as vibration region Z2, and the region surrounded by the imaginary line Y2-Y2 and the imaginary line Y3-Y3 is defined as vibration region Z3. The vibration regions Z1 and Z2 are set to have a phase difference of π. The vibration regions Z2 and Z3 are set to have different resonant frequencies, amplitudes, or phases. For example, when the vibration mode is made non-uniform by changing the polarization direction of the piezoelectric layer 11, the polarization direction P of the vibration regions Z1 and Z3 is set upward, while the polarization direction P of the vibration region Z2 is set downward.

[0096] As described above, by setting the pattern of the vibration area to a striped pattern, the directivity angle of the ultrasonic waves can be widened. For example, if the attention line X is set so as to intersect with the central axis of the transmitting / receiving surface 10A of the laminate 10, and the angle formed by an imaginary line connecting the edge of the vibration area and the attention line X at the minimum distance with respect to the central axis is θ, the directivity angle of the ultrasonic waves will be ±θ with respect to the attention line X. Specifically, when θ = 45°, the directivity angle of the ultrasonic waves will be ±45°.

[0097] (b-1) Concentric circle pattern (when m is 4) Fig. 10 shows an example of a concentric circle pattern of vibration regions when m is 4, where 1001 in Fig. 10 is a schematic diagram for explaining the setting of the concentric circle pattern, and 1002 in Fig. 10 is a top view schematically showing the concentric circle pattern of multiple vibration regions. As shown in Fig. 10, the pattern of multiple vibration regions provided in the plane of the laminate 10 is a concentric circle pattern centered on a focus point A. Note that Fig. 10 shows the setting of the concentric circle pattern when m=4 and the phases of the vibration regions are made non-uniform by changing the configurations of the first electrode layer 12A and the second electrode layer 12B (i.e., by the method (4) above).

[0098] As shown in FIG. 10, first, a virtual point that is a predetermined minimum distance D0 away from the transmitting / receiving surface 10A of the laminated body 10 is set as a target point A.

[0099] Next, four imaginary lines B1 to B4 are drawn on the transmitting and receiving surface 10A so that the distance Dn from the attention point A to the transmitting and receiving surface 10A is D+n·λ / 4 (D is an arbitrary fixed distance, n is an integer between 1 and 4, and λ is the wavelength of the ultrasonic wave). In the example shown in 1001 and 1002 in FIG. 10, D is D0-λ / 8 (D0 is the minimum distance from the transmitting and receiving surface 10A to the attention point A), and the imaginary lines B1 to B4 are concentric circles. The imaginary line B1 is a concentric circle where the distance D1 from the attention point O to the transmitting and receiving surface 10A is D0+3λ / 8. The imaginary line B2 is a concentric circle where the distance D2 from the attention point O to the transmitting and receiving surface 10A is D0+5λ / 8. The imaginary line B3 is a concentric circle where the distance D3 from the attention point A to the transmitting and receiving surface 10A is D0+7λ / 8. The virtual line B4 is a concentric circle with a distance D4 from the point of interest A to the transmitting / receiving surface 10A being D0+9λ / 8. Note that the setting of the fixed distance D is arbitrary and is not limited to the above setting. For example, D=D0 may be used.

[0100] The area surrounded by the virtual line B1 is defined as vibration area C1, the area surrounded by the virtual line B1 and the virtual line B2 is defined as vibration area C2, the area surrounded by the virtual line B2 and the virtual line B3 is defined as vibration area C3, and the area surrounded by the virtual line B3 and the virtual line B4 is defined as vibration area C4.

[0101] Here, the polarization direction P of the piezoelectric layer 11 is unidirectional within the plane of the transmitting / receiving surface 10A. The first electrode layer 12A includes concentric first electrodes 15Aa-15Ad. The second electrode layer 12B includes concentric second electrodes 15Ba-15Bd. The first electrodes 15Aa-15Ad and the second electrodes 15Ba-15Bd face each other and are set in accordance with the settings of the vibration regions C1-C4. Specifically, the vibration region C1 corresponds to the first electrode 15Aa and the second electrode 15Ba facing each other, the vibration region C2 corresponds to the first electrode 15Ab and the second electrode 15Bb facing each other, the vibration region C3 corresponds to the first electrode 15Ac and the second electrode 15Bc facing each other, and the vibration region C4 corresponds to the first electrode 15Ad and the second electrode 15Bd facing each other. There are slight gaps between the first electrodes 15Aa to 15Ad. Note that there are gaps between adjacent first electrodes 15Aa to 15Ad. Similarly, there are gaps between adjacent second electrodes 15Ba to 15Bd. This is because, if there were no gaps, the electrodes would be short-circuited.

[0102] The phase φ2 of the vibrating region C2 is set to be shifted by π / 2 from the phase φ1 of the vibrating region C1. The phase φ3 of the vibrating region C3 is set to be shifted by π / 2 from the phase φ2 of the vibrating region C2. The phase φ4 of the vibrating region C4 is set to be shifted by π / 2 from the phase φ3 of the vibrating region C3. Specifically, when the phase φ1 is 0, the phase φ2 is π / 2, the phase φ3 is π, and the phase φ4 is 3π / 2.

[0103] The phase setting of each vibration region as described above can be achieved by adjusting the phase of the electrical signal applied to the first and second electrodes facing each other and corresponding to each vibration region. Therefore, in the above setting, four power supplies are required to apply electrical signals of different phases to each vibration region. Furthermore, if pairs of positive and negative electrodes are alternately arranged in the first electrodes 15Aa to 15Ad and the second electrodes 15Ba to 15Bd, only two power supplies are required.

[0104] In the concentric circle pattern shown in FIG. 7, a virtual image of attention point O exists on the opposite side of attention point O with respect to laminate 10. Therefore, in the configuration shown in FIG. 7, the sound field of ultrasonic waves with a directivity angle based on attention point O is formed with the sound field of ultrasonic waves with a directivity angle based on the virtual image of attention point O. The sound field of ultrasonic waves with a virtual image of attention point O as a reference has a distribution similar to the sound field of ultrasonic waves with the virtual image of attention point O as a reference. For this reason, in the configuration shown in FIG. 7, interference fringes may occur in the sound field of the radiated ultrasonic waves. On the other hand, in the concentric circle pattern setting shown in FIG. 10, a virtual image of attention point A does not occur, and only ultrasonic waves with a directivity angle based on attention point A are radiated, so interference fringes do not occur in the sound field.

[0105] (b-2) Striped pattern FIG. 11 shows an example of a stripe pattern of vibration regions when m is 4, where 1101 in FIG. 11 is a schematic diagram for explaining the setting of the stripe pattern, and 1102 in FIG. 11 is a top view showing the stripe pattern of multiple vibration regions. As shown in FIG. 11, the pattern of multiple vibration regions provided in the plane of the laminate 10 is a stripe pattern with a focus line as the center line. Note that FIG. 11 shows the setting of a stripe pattern when m=4 and the phases of the vibration regions are made non-uniform by changing the configurations of the first electrode layer 12A and the second electrode layer 12B (i.e., by the method (4) above).

[0106] 11, first, a virtual line that is a predetermined minimum distance D0 away from the transmitting / receiving surface 10A of the laminate 10 is defined as a line of interest H. In the example shown in Fig. 11, the line of interest H extends in the Y direction parallel to the transmitting / receiving surface 10A. Note that the direction in which the line of interest H extends does not have to be parallel to the transmitting / receiving surface 10A.

[0107] Next, four imaginary lines I1 to I4 are drawn on the transmitting and receiving surface 10A so that the distance Dn from the observation line H to the transmitting and receiving surface 10A is D+n·λ / 4 (D is an arbitrary fixed distance, n is an integer between 1 and 4, and λ is the wavelength of the ultrasonic wave). In the examples shown in 1101 and 1102 of FIG. 11, D is D0-λ / 8 (D0 is the minimum distance from the transmitting and receiving surface 10A to the observation line X), and the imaginary lines I1 to I4 are each two straight lines. The two imaginary lines I1 and I1 are each a straight line such that the distance D1 from the observation line H to the transmitting and receiving surface 10A is D0+3λ / 8. The two imaginary lines I2 and I2 are each a straight line such that the distance D2 from the observation line H to the transmitting and receiving surface 10A is D0+5λ / 8. The two imaginary lines I3 and I3 are each a straight line such that the distance D3 from the observation line X to the transmitting and receiving surface 10A is D0+7λ / 8. The two imaginary lines I4-I4 are straight lines such that the distance D4 from the point of interest A to the transmitting / receiving surface 10A is D0+9λ / 8. Note that the setting of the fixed distance D is arbitrary and is not limited to the above setting. For example, D=D0 may be used.

[0108] The area surrounded by the imaginary lines I1·I1 is defined as vibration area J1, the area surrounded by the imaginary lines I1·I1 and I2·I2 is defined as vibration area J2, the area surrounded by the imaginary lines I2·I2 and I3·I3 is defined as vibration area J3, and the area surrounded by the imaginary lines I3·I3 and I4·I4 is defined as vibration area J4.

[0109] Here, the polarization direction P of the piezoelectric layer 11 is unidirectional within the plane of the transmitting / receiving surface 10A. The first electrode layer 12A includes first electrodes 15Aw to 15Az. The second electrode layer 12B includes second electrodes 15Bw to 15Bz. The first electrodes 15Aw to 15Az and the second electrodes 15Bw to 15Bz face each other and are set in accordance with the settings of the vibration regions J1 to J4. Specifically, the vibration region J1 corresponds to the first electrode 15Aw and the second electrode 15Bw facing each other, the vibration region J2 corresponds to the first electrode 15Ax and the second electrode 15Bx facing each other, the vibration region J3 corresponds to the first electrode 15Ay and the second electrode 15By facing each other, and the vibration region J4 corresponds to the first electrode 15Az and the second electrode 15Bz facing each other. Note that, among the first electrodes 15Aw to 15Az, a gap is provided between adjacent electrodes. Similarly, among the second electrodes 15Bw to 15Bz, a gap is provided between adjacent electrodes. This is because, if there were no gap, a short circuit would occur between the electrodes.

[0110] The phase φ2 of the vibrating region J2 is set to be shifted by π / 2 from the phase φ1 of the vibrating region J1. The phase φ3 of the vibrating region J3 is set to be shifted by π / 2 from the phase φ2 of the vibrating region J2. The phase φ4 of the vibrating region J4 is set to be shifted by π / 2 from the phase φ3 of the vibrating region J3. Specifically, when the phase φ1 is 0, the phase φ2 is π / 2, the phase φ3 is π, and the phase φ4 is 3π / 2.

[0111] As in the case of the concentric circle pattern shown in Figure 10, the phase of each vibration area can be set by adjusting the phase of the electrical signal applied to the opposing first and second electrodes corresponding to each vibration area.

[0112] In addition, in the striped pattern shown in FIG. 11, as in the case of the concentric circle pattern shown in FIG. 10, only ultrasonic waves with a directivity angle based on the attention line H are emitted, so no interference fringes occur in the sound field.

[0113] <Configuration in which the first electrode layer has a ground electrode> In the ultrasonic transducer according to this embodiment, the first electrode layer may include a ground electrode. Fig. 12 is a cross-sectional view showing an example of the configuration of the laminate 10 in which the first electrode layer 12A includes a ground electrode in the ultrasonic transducer according to this embodiment.

[0114] 12, the laminate 10 includes a first electrode layer 12A, a piezoelectric layer 11, and a second electrode layer 12B. A base material 44 is in contact with the lower surface of the second electrode layer 12B and functions as a support for the laminate 10. The first electrode layer 12A includes a first ground conductive film 12A1 and a second ground conductive film 12A2 as ground electrodes.

[0115] The laminate 10 has a configuration in which the second electrode layer 12B, the piezoelectric layer 11, and the first ground conductive film 12A1 are stacked in this order from the base material 44 toward the Z-axis direction. The second ground conductive film 12A2 is provided in contact with the lower surface of the base material 44. Furthermore, the polarization direction of the piezoelectric layer 11 is unidirectional within the plane of the laminate 10 (within the plane of the transmitting and receiving surface).

[0116] The first ground conductive film 12A1 and the second ground conductive film 12A2 are electrically connected on all side surfaces of the laminate 10, except for the lead-out portion of the second electrode layer 12B. With this configuration, the first ground conductive film 12A1 and the second ground conductive film 12A2 provide a shielding effect, thereby reducing the influence of noise.

[0117] When the first electrode layer 12A includes a ground electrode in this manner, the amplifier forms a wiring connected to the second electrode layer 12B as a signal line (hot). Therefore, the second electrode layer 12B includes two or more hot electrodes. That is, the ultrasonic transducer according to this embodiment may be configured such that the first electrode layer 12A includes a ground electrode and the second electrode layer 12B includes two or more hot electrodes. In the laminate 10 shown in FIG. 12, the second electrode layer 12B includes hot electrodes 16A, 16B, 16C, and 16D.

[0118] The second electrode layer 12B also includes insulating films 17A and 17B. Hot electrodes 16A and 16B are provided on the insulating film 17A, and hot electrodes 16C and 16D are provided on the insulating film 17B. The insulating film 17A provided with hot electrodes 16A and 16B and the insulating film 17B provided with hot electrodes 16C and 16D are stacked in the Z-axis direction. The insulating film 17A has a hot electrode 16A (first hot electrode) formed on one side and a hot electrode 16B (second hot electrode) formed on the other side. Similarly, the insulating film 17B has a hot electrode 16C (first hot electrode) formed on one side and a hot electrode 16D (second hot electrode) formed on the other side. In other words, the insulating film 17A has the hot electrode 16A formed on the side opposite to the side on which the hot electrode 16B is formed. Similarly, in insulating film 17B, hot electrode 16C is formed on the surface opposite to the surface on which hot electrode 16D is formed.

[0119] The first electrode layer 12A and the second electrode layer 12B are connected to a power supply and an amplifier included in the ultrasonic sensor 100. In the second electrode layer 12B, the hot electrode 16A formed on the upper side (+Z axis direction side) of the insulating film 17A is a positive electrode, and the hot electrode 16B formed on the lower side (-Z axis direction side) of the insulating film 17A is a negative electrode. Similarly, the hot electrode 16C formed on the upper side (+Z axis direction side) of the insulating film 17B is a positive electrode, and the hot electrode 16D formed on the lower side (-Z axis direction side) of the insulating film 17B is a negative electrode.

[0120] The base material 44 supports the structure including the piezoelectric layer 11, the first electrode layer 12A, the second electrode layer 12B, etc., and adjusts the acoustic and electrical characteristics. In the example of Fig. 12, the base material 44 is a rubber sheet with a thickness of 2 mm.

[0121] The material of insulating films 17A and 17B is not particularly limited as long as it is an insulating material, and examples thereof include polyester resin, polyolefin resin, polystyrene resin, etc. Furthermore, the thickness of insulating films 17A and 17B is preferably 10 μm to 500 μm, and more preferably 10 μm to 100 μm.

[0122] Furthermore, in order to improve ultrasonic characteristics, it is preferable that the thickness of the first ground conductive film 12A1 in the first electrode layer 12A is thin. The thickness of the first ground conductive film 12A1 is preferably 100 μm or less, and more preferably 50 μm or less. There is no particular lower limit to the thickness of the first ground conductive film 12A1, but it is, for example, 0.1 μm or more. On the other hand, the thickness of the second ground conductive film 12A2 does not require any particular management. Generally, the thickness of the second ground conductive film 12A2 may be within the range of 1 μm to 1000 μm.

[0123] Here, as described above, the hot electrodes 16A to 16D have a specific shape in order to provide a pattern of multiple vibration regions within the surface of the laminate 10. For example, if the multiple vibration regions provided within the surface of the laminate 10 are in a concentric circular pattern, the hot electrodes 16A to 16D are also concentric.

[0124] 12 has a unique configuration in which the piezoelectric layer 11 includes an electret sheet made of a foamed resin. If the piezoelectric layer 11 is made of a piezoelectric material with a large dielectric constant, such as a PVDF piezoelectric film, rather than a foamed resin electret sheet, it is difficult to form a pattern of a predetermined vibration region in the configuration shown in FIG.

[0125] In the laminate 10 shown in FIG. 12, the dielectric constant of the piezoelectric layer 11, which includes a foamed resin electret sheet, is extremely low. Meanwhile, the dielectric constant of the insulating films 17A and 17B is much higher than that of the piezoelectric layer 11, and they are also extremely thin. Therefore, in the second electrode layer 12B, the electrical capacitance between the first electrode layer 12A (ground) and the hot electrode 16A is approximately the same as the electrical capacitance between the first electrode layer 12A (ground) and the hot electrode 16B. Similarly, the electrical capacitance between the first electrode layer 12A (ground) and the hot electrode 16C is approximately the same as the electrical capacitance between the first electrode layer 12A (ground) and the hot electrode 16D. Therefore, the laminate 10 shown in FIG. 12 can form a predetermined vibration region pattern. Meanwhile, if the piezoelectric layer 11 is made of, for example, a PVDF piezoelectric film, the PVDF piezoelectric film has a high dielectric constant, and therefore, even if it is applied to the structure of the laminate 10 shown in FIG. 12, the predetermined performance of this embodiment cannot be achieved.

[0126] Fig. 13 is a plan view showing a schematic configuration of the pattern of hot electrodes 16A to 16D when a plurality of vibration regions provided in the plane of laminate 10 shown in Fig. 12 are in a four-phase concentric circle pattern. The upper side of Fig. 13 shows a schematic configuration of the pattern of hot electrodes 16A to 16D as seen from the +Z-axis direction side, and the lower side of Fig. 13 shows the shape of each of hot electrodes 16A to 16D as seen from the +Z-axis direction side.

[0127] As shown in Fig. 13, when viewed from the +Z-axis direction, the hot electrodes 16A to 16D form concentric ring regions. When viewed from the +Z-axis direction, the concentric ring regions of the hot electrodes 16A to 16D are formed so as not to overlap with each other. In the laminate 10 including the hot electrodes 16A to 16D shown in Fig. 13, multiple vibration regions are formed by the concentric ring regions of the hot electrodes 16A to 16D.

[0128] Here, from the viewpoint of reducing coupling due to electrostatic induction between the hot electrodes, it is preferable that the overlapping areas of the hot electrodes 16A to 16D be small when viewed from the +Z-axis direction. For this reason, as described above, the concentric annular areas of the hot electrodes 16A to 16D are formed so as not to overlap with each other.

[0129] An example of the configuration of the connection wiring to the respective transmission / reception circuits (e.g., a receiving amplifier, a transmitting pulse generator, etc.) of the hot electrodes 16A to 16D is shown in FIG. 13. As shown in FIG. 13, a slit 16AS is formed in the hot electrode 16A so as to cross its concentric annular region in the X direction. Similarly, slits 16BS, 16CS, and 16DS are formed in the hot electrodes 16B, 16C, and 16D, respectively. These slits create cutout regions in the concentric annular regions of the hot electrodes 16A to 16D, resulting in C-shaped regions.

[0130] Loop wiring 16A1, 16B1, 16C1, and 16D1 that connects two ends of the C-shaped region is formed on hot electrodes 16A, 16B, 16C, and 16D. By forming loop wiring 16A1, 16B1, 16C1, and 16D1 in this way, magnetic noise can be reduced.

[0131] Furthermore, in hot electrode 16A, connection wiring 16A2 to the transmitter / receiver circuit is formed inside slit 16AS and extends in the X direction. Similarly, in hot electrodes 16B, 16C, and 16D, connection wiring 16B2, 16C2, and 16D2 to the transmitter / receiver circuit are formed inside slits 16BS, 16CS, and 16DS and extend in the X direction. Because connection wiring 16A2, 16B2, 16C2, and 16D2 are formed inside slits 16AS, 16BS, 16CS, and 16DS, they are extremely thin wires. Therefore, the overlapping areas of connection wiring 16A2, 16B2, 16C2, and 16D2 are extremely small when viewed from the +Z axis direction, reducing coupling due to electrostatic induction between the hot electrodes. The widths of connection wiring 16A2, 16B2, 16C2, and 16D2 can be appropriately set depending on the configuration of the ultrasonic sensor, as long as they can reduce coupling due to electrostatic induction between the hot electrodes. For example, the width of the connection wires 16A2, 16B2, 16C2, and 16D2 is 0.5 mm to 5 mm.

[0132] As described above, according to the configuration shown in FIG. 13, slits 16AS, 16BS, 16CS, and 16DS are provided in hot electrodes 16A, 16B, 16C, and 16D, and connecting wirings 16A2, 16B2, 16C2, and 16D are provided inside the slits 16AS, 16BS, 16CS, and 16DS, thereby reducing coupling due to electrostatic induction between the hot electrodes.

[0133] Furthermore, according to the above configuration, in the laminate 10 shown in Fig. 12, the hot electrodes 16A, 16B, 16C, and 16D are formed in the pattern shown in Fig. 13. That is, in the insulating film 17A, the hot electrode 16A is formed on one surface in the pattern shown in Fig. 13, and the hot electrode 16B is formed on the other surface in the pattern shown in Fig. 13. Similarly, in the insulating film 17B, the hot electrode 16C is formed on one surface in the pattern shown in Fig. 13, and the hot electrode 16D is formed on the other surface in the pattern shown in Fig. 13.

[0134] In this way, since the patterns of hot electrodes 16A and 16B are formed on both sides of insulating film 17A, short circuits are unlikely to occur even if the pitch of connecting wires 16A2 and 16B2 is narrowed. The same effect is also achieved with hot electrodes 16C and 16D formed on insulating film 17B.

[0135] From the viewpoint of making the connection wiring less susceptible to short-circuiting, second electrode layer 12B is not limited to the configuration shown in Fig. 12. That is, in second electrode layer 12B, the number of laminated insulating films on which hot electrodes are formed is not limited to two, but may be one layer, or three or more layers. When the number of laminated insulating films on which hot electrodes are formed is two or more layers, short-circuiting may be prevented by, for example, arranging insulating films on which no hot electrodes are formed between the layers.

[0136] Furthermore, in the ultrasonic transducer according to this embodiment, the configuration in which the first electrode layer 12A includes a ground electrode and the second electrode layer 12B includes two or more hot electrodes is not limited to the configuration shown in Fig. 12. Fig. 14 shows a top view and a cross-sectional view illustrating another example of the configuration of the laminate 10 in the ultrasonic transducer according to this embodiment, in which the first electrode layer 12A includes a ground electrode. In Fig. 14, the cross-sectional view is taken along line A-A' in the top view.

[0137] The configuration shown in Fig. 14 differs from the configurations shown in Fig. 12 and Fig. 13 in that the C-shaped regions of hot electrodes 16A, 16B, 16C, and 16D are all formed on one side of insulating film 17C. Therefore, slits 16S are formed only on one side of insulating film 17C in hot electrodes 16A, 16B, 16C, and 16D. Furthermore, the configuration shown in Fig. 14 does not include loop wiring 16A1, 16B1, 16C1, and 16D1 as shown in Fig. 13.

[0138] In this configuration, on one surface of insulating film 17C, connection wirings 16A2, 16B2, 16C2, and 16D2 are formed within slits 16S. In the configuration shown in FIG. 14, connection wirings 16A2, 16B2, 16C2, and 16D2 are arranged so as not to be electrically connected to one another. For this reason, multiple via holes 18 are formed in connection wirings 16A2, 16B2, 16C2, and 16D2, sandwiching their mutual intersections. These via holes 18 prevent connection wirings 16A2, 16B2, 16C2, and 16D2 from being electrically connected to one another.

[0139] For example, the role of via holes 18 at the intersections of connection wiring 16A2 with connection wiring 16B2, 16C2, and 16D2 will be described with reference to the cross-sectional view of line A-A' in Fig. 14. As shown in the top view of Fig. 14, two via holes 18 are formed in connection wiring 16A2. The intersections of connection wiring 16A2 and connection wiring 16B2, the intersections of connection wiring 16A2 and connection wiring 16C2, and the intersections of connection wiring 16A2 and connection wiring 16D2 are located between the two via holes 18.

[0140] 14, a wiring 16A3 that connects two via holes 18 is formed on the surface of insulating film 17C opposite to the surface on which connection wiring 16A2 is formed. Wiring 16A3 is electrically connected to connection wiring 16A2 through via hole 18. By forming via hole 18 and wiring 16A3 in this manner, electrical connection between connection wiring 16A2 and connection wirings 16B2, 16C2, and 16D2 on one surface of insulating film 17C is avoided.

[0141] 14, a wiring pattern connecting two via holes 18 is formed on the surface of insulating film 17C opposite to the surface on which connection wirings 16B2, 16C2, and 16D2 are formed, thereby preventing electrical connection between connection wirings 16A2, 16B2, 16C2, and 16D2.

[0142] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0143] 1 ultrasonic transducer 11 Piezoelectric layer 12A 1st electrode layer 12B 2nd electrode layer 12A1 First ground conductive film (ground electrode) 12A2 Second ground conductive film (ground electrode) 16A Hot Electrode (First Hot Electrode) 16B Hot electrode (second hot electrode) 16C Hot electrode (first hot electrode) 16D Hot electrode (second hot electrode) 17A insulating film 17B insulating film 17C insulating film 40 Support layer 41, 44 Base material 42 Foundation 51 Amplifier 100 ultrasonic sensors

Claims

1. a first electrode layer including at least one electrode; a piezoelectric layer including an electret sheet made of a foamed resin; a second electrode layer including at least one electrode, and a laminate body in which these are laminated in this order; An ultrasonic transducer in which a plurality of vibration regions having different resonance frequencies, amplitudes, or phases are provided within the plane of the laminate.

2. The ultrasonic transducer according to claim 1 , wherein the plurality of vibration regions are made up of parts having different elasticity or mass within the plane of the laminate.

3. a support layer for supporting the laminate on one surface of the laminate, 2. The ultrasonic transducer of claim 1, wherein the plurality of vibration regions comprise non-fixed portions where a portion of the surface of the laminate is not fixed to the support layer, and fixed portions where a portion of the surface of the laminate is fixed to the support layer.

4. At least one of the first electrode layer and the second electrode layer includes a plurality of electrodes; the first electrode layer and the second electrode layer face each other to form a plurality of electrode pairs, The ultrasonic transducer according to claim 1 , wherein electrical signals of different phases are applied to the plurality of electrode pairs, respectively.

5. The ultrasonic transducer according to claim 1 , wherein the plurality of vibration regions are formed by portions of the piezoelectric layer having different polarization directions.

6. 6. The ultrasonic transducer according to claim 1, wherein the plurality of vibration regions are composed of two types of vibration regions having mutually different resonance frequencies, amplitudes, or phases.

7. The ultrasonic transducer according to any one of claims 1 to 5, wherein the plurality of vibration regions are composed of m types of vibration regions in which the phases of adjacent vibration regions differ by 2π / m (m is an integer of 2 or more).

8. a transmitting / receiving surface for transmitting and receiving ultrasonic waves on one surface of the laminate; When a virtual point a predetermined distance away from the transmitting / receiving surface is taken as a focus point O, and a plurality of virtual lines Ln are drawn on the transmitting / receiving surface so that the distance Dn from the focus point O to the transmitting / receiving surface is D+n λ / m (D is an arbitrary fixed distance, n is an integer equal to or greater than 1, and λ is the wavelength of the ultrasonic wave), 8. The ultrasonic transducer of claim 7, wherein the vibration region Rn is defined as a region surrounded by the virtual lines Ln and Ln+1, and the vibration region Rn and the vibration region Rn+1 are arranged so that their phases differ from each other by 2π / m.

9. a transmitting / receiving surface for transmitting and receiving ultrasonic waves on one surface of the laminate; When a virtual line X is defined as a line of interest that is a predetermined distance away from the transmitting / receiving surface, and a plurality of virtual lines Yn are drawn on the transmitting / receiving surface so that the distance Dn from the line of interest X to the transmitting / receiving surface is D+n λ / m (D is an arbitrary fixed distance, n is an integer of 1 or more, and λ is the wavelength of the ultrasonic wave), 8. The ultrasonic transducer of claim 7, wherein the vibration region Zn is defined as the region surrounded by the virtual lines Yn and Yn+1, and the vibration region Zn and the vibration region Zn+1 are arranged so that their phases differ from each other by 2π / m.

10. 8. The ultrasonic transducer of claim 7, wherein m is 4.

11. 6. The ultrasonic transducer according to claim 1, wherein the plurality of vibration regions are arranged in a random pattern within the plane of the laminate.

12. the first electrode layer includes a ground electrode; The ultrasonic transducer of claim 1 , wherein the second electrode layer comprises two or more hot electrodes.

13. the second electrode layer comprises an insulating film; 13. The ultrasonic transducer according to claim 12, wherein the insulating film has a first hot electrode formed on one surface thereof and a second hot electrode different from the first hot electrode formed on the other surface thereof.

14. An ultrasonic transducer according to any one of claims 1 to 5; an amplifier electrically connected to the ultrasonic transducer.

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