Ultrasound element, ultrasound device, and aerial haptics device

Abstract

This ultrasound element comprises a piezoelectric element that generates ultrasound in the range of 20-100 kHz and an acoustic matching layer that is provided on the piezoelectric element and that includes a resin, wherein the maximum thickness from the surface of the piezoelectric element opposite to the surface on which the acoustic matching layer is disposed to the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is disposed is not more than 1.5 mm.

Description

Ultrasonic element, ultrasonic device, and mid-air haptic device

[0001] The present disclosure relates to ultrasonic elements, ultrasonic devices, and airborne haptic devices.

[0002] In recent years, with the spread of virtual reality technology, there has been an increasing demand for airborne haptic devices that stimulate cutaneous sensations without contact. For example, an airborne haptic device collects ultrasonic waves generated with a time delay from a large number of ultrasonic transducers arranged two-dimensionally to form a composite wave, and forms a focus at a targeted position, generating a large acoustic radiation pressure at the focus, thereby stimulating human cutaneous sensations without contact. Known examples of airborne haptic devices include those disclosed in Non-Patent Document 1 below, in which ultrasonic elements with an outer diameter of approximately 10 mm and a thickness of approximately 7 mm are arranged two-dimensionally on a printed circuit board and connected by solder to form an array. Non-Patent Document 1: Journal of the Acoustical Society of Japan, Vol. 76, No. 5 (2020), pp. 271-278

[0003] In an airborne haptic device that uses an array of ultrasonic elements with an outer diameter of approximately 10 mm and a thickness of approximately 7 mm, the individual ultrasonic elements are large, which makes the entire device large, making it difficult to use as a component in a small device.

[0004] An object of the present disclosure is to provide an ultrasonic element that generates high sound pressure and is applicable to a small airborne haptic device, as well as an ultrasonic device and an airborne haptic device that use the same.

[0005] Means for solving the above problems include the following aspects. <1> An ultrasonic element comprising: a piezoelectric element that generates ultrasonic waves of 20 kHz to 100 kHz; and an acoustic matching layer that is provided on the piezoelectric element and contains a resin, wherein the maximum thickness from the surface of the piezoelectric element opposite the surface on which the acoustic matching layer is disposed to the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed is 1.5 mm or less. <2> The ultrasonic element according to <1>, in which the difference between the maximum thickness and the minimum thickness of the acoustic matching layer is 1 μm or more. <3> The ultrasonic element according to <1> or <2>, in which the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed is a curved surface. <4> The ultrasonic element according to any one of <1> to <3>, in which the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed is convex. <5> The ultrasonic element according to any one of <1> to <3>, in which the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed is concave. <6> The ultrasonic element according to any one of <1> to <5>, wherein the maximum diameter of the entire ultrasonic element is 8 mm or less when viewed in a plan view. <7> The ultrasonic element according to any one of <1> to <6>, wherein the acoustic matching layer is provided in contact with the piezoelectric element. <8> The ultrasonic element according to any one of <1> to <6>, further comprising a metal plate between the piezoelectric element and the acoustic matching layer. <9> The ultrasonic element according to any one of <1> to <8>, further comprising at least one of an acoustic reflection layer containing a resin and an acoustic attenuation layer containing a resin, on the side of the piezoelectric element opposite to the side on which the acoustic matching layer is provided. <10> An ultrasonic device comprising: a support; and a plurality of ultrasonic elements according to any one of <1> to <9>, provided on the support and arranged two-dimensionally. <11> The ultrasonic device according to <10>, which is used for an air haptic device. <12> An air haptic device including the ultrasonic device according to <10> or <11>.

[0006] According to the present disclosure, an ultrasonic element that generates high sound pressure and is applicable to a small airborne haptic device, as well as an ultrasonic device and an airborne haptic device that use the same are provided.

[0007] 12 is an end view schematically showing a portion of a cut surface in an example of an ultrasonic element according to an embodiment. FIG. 13 is an end view schematically showing a portion of a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 14 is an end view schematically showing a portion of a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 15 is an end view schematically showing a portion of a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 16 is an end view schematically showing a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 17 is an end view schematically showing a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 18 is an end view schematically showing a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 19 is an end view schematically showing a cut surface in another example of an ultrasonic element according to an embodiment. FIG. 19 is an end view schematically showing a cut surface in another example of an ultrasonic element according to an embodiment. 15 is a perspective view of an ultrasonic wave generating device in the air haptic device shown in Fig. 14. Fig. 16 is a schematic cross-sectional view of the ultrasonic wave generating device shown in Fig. 15.

[0008] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present invention.

[0009] In the present disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, each component may contain multiple types of particles. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" or "film" include cases where the layer or film is formed over the entire area when the area where the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area. In the present disclosure, the term "laminated" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable. In the present disclosure, "(meth)acryloyl group" means at least one of an acryloyl group and a methacryloyl group, and "(meth)acrylic acid" means at least one of acrylic acid and methacrylic acid. When embodiments are described in the present disclosure with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited thereto.

[0010] An ultrasonic element according to an embodiment of the present disclosure includes a piezoelectric element that generates ultrasonic waves of 20 kHz to 100 kHz, and an acoustic matching layer that is provided on the piezoelectric element and contains a resin, wherein the maximum thickness from the surface of the piezoelectric element opposite to the surface on which the acoustic matching layer is disposed to the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is disposed is 1.5 mm or less. Hereinafter, the maximum thickness from the surface of the piezoelectric element opposite to the surface on which the acoustic matching layer is disposed to the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is disposed is also referred to as the “specific thickness.”

[0011] An example of a conventional aerial haptic device is an array of ultrasonic elements with an outer diameter of approximately 10 mm and a thickness of approximately 7 mm, as described above. An example of a conventional aerial haptic device is shown in FIG. 14 . In the aerial haptic device 500 shown in FIG. 14 , a plurality of ultrasonic elements 510 are two-dimensionally arranged and connected to a printed circuit board 502 by solder. FIGS. 15 and 16 show a perspective view and a cross-sectional schematic diagram of the ultrasonic element 510. The ultrasonic element 510 is composed of an ultrasonic generator 520 that generates ultrasonic waves and a connection part 512 that connects to the printed circuit board 502. The ultrasonic generator 520 includes a metal plate 522, a piezoelectric ceramic 524 in contact with one side of the metal plate 522, and a funnel-shaped resonator 526 partially in contact with the other side of the metal plate 522. The metal plate 522, the piezoelectric ceramic 524, and the resonator 526 are covered by a housing 528 having a sound emission hole 528A.

[0012] In the airborne haptic device shown in FIG. 14 , as described above, each ultrasonic element has an outer diameter of approximately 10 mm and a thickness of approximately 7 mm and includes one ultrasonic wave generating unit. Therefore, the entire airborne haptic device is large, heavy, and expensive. Specifically, for example, an airborne haptic device with 100 (10×10) ultrasonic elements connected to a printed circuit board measures approximately 170 mm×170 mm×20 mm. Therefore, it is difficult to use the device as a component in small devices such as virtual reality (VR) glasses, augmented reality (AR) glasses, mixed reality (MR) glasses, and hearable devices.

[0013] On the other hand, the ultrasonic element of this embodiment includes a piezoelectric element that generates ultrasonic waves in the 20 kHz to 100 kHz range and an acoustic matching layer that is disposed on the piezoelectric element and contains a resin. When ultrasonic waves are radiated directly from the piezoelectric element into the air without the aid of an acoustic matching layer, the large difference in acoustic impedance at the interface can result in attenuation of the intensity of the ultrasonic waves radiated into the air and waveform distortion, resulting in a low sound pressure of the ultrasonic waves. In contrast, in this embodiment, the acoustic matching layer is provided, so the acoustic impedance difference between the piezoelectric element and the acoustic matching layer and the acoustic impedance difference between the ultrasonic element and the air are smaller than the acoustic impedance difference between the piezoelectric element and the air. Therefore, ultrasonic waves can be efficiently radiated into the air without providing a funnel-shaped resonator 526, as in the ultrasonic element 510 shown in FIG. 16 . Furthermore, the maximum thickness (i.e., the specific thickness) from the surface of the piezoelectric element opposite the surface on which the acoustic matching layer is disposed to the surface on which the piezoelectric element is disposed opposite the surface on which the acoustic matching layer is disposed is 1.5 mm or less, resulting in an ultrasonic element that generates high sound pressure and is applicable to a small air haptic device. By applying the ultrasonic elements of this embodiment to a small aerial haptic device, ultrasonic waves are emitted into the air from each ultrasonic element while maintaining their intensity and waveform, making it possible to generate high acoustic radiation pressure at the targeted location.

[0014] <Layer Structure> The ultrasonic element of this embodiment only needs to have at least a piezoelectric element and an acoustic matching layer, and may have other layers as necessary. Examples of other layers include a metal plate or the like provided between the piezoelectric element and the acoustic matching layer; an acoustic reflection layer, an acoustic attenuation layer, or the like provided on the side of the piezoelectric element opposite the side on which the acoustic matching layer is provided; and the like. Examples of layer structures in the ultrasonic element of this embodiment are shown in Figures 1 to 4, but the ultrasonic element of this embodiment is not limited to these. Figures 1 to 4 each schematically show a portion of a cross section cut in the thickness direction of the piezoelectric element in an example of the ultrasonic element of this embodiment.

[0015] The ultrasonic element 200 shown in FIG. 1 includes a piezoelectric element 16 and an acoustic matching layer 20 provided in contact with at least a portion of one surface of the piezoelectric element. The acoustic matching layer 20 is the outermost layer in contact with air. In the ultrasonic element 200, the maximum thickness (i.e., the specific thickness) from the surface 16A of the piezoelectric element 16 opposite the surface on which the acoustic matching layer 20 is disposed to the surface 20A of the acoustic matching layer 20 opposite the surface on which the piezoelectric element 16 is disposed is 1.5 mm or less. In the ultrasonic element 200, for example, the acoustic impedance of the acoustic matching layer 20 is a value between the acoustic impedance of the piezoelectric element 16 and the acoustic impedance of air. By providing the acoustic matching layer 20 between the piezoelectric element 16 and the air, the ultrasonic element 200 can efficiently radiate ultrasonic waves generated by the piezoelectric element 16 into the air. Therefore, even if the specific thickness is within the above range, a high sound pressure can be obtained, and the ultrasonic element 200 is applicable to a small air haptic device. Furthermore, in the ultrasonic element 200, since no metal plate is provided between the piezoelectric element 16 and the acoustic matching layer 20, flexibility is imparted to the entire ultrasonic element 200 by using a piezoelectric resin sheet, which will be described later, as the piezoelectric element 16.

[0016] The ultrasonic element 210 shown in FIG. 2 includes a piezoelectric element 16, a metal plate 28 provided on one side of the piezoelectric element 16, and an acoustic matching layer 22 provided on the surface of the metal plate 28 opposite the side on which the piezoelectric element 16 is disposed. That is, the ultrasonic element 210 includes the metal plate 28 between the piezoelectric element 16 and the acoustic matching layer 22. The acoustic matching layer 22 is the outermost layer in contact with air. In the ultrasonic element 210, the maximum thickness from the surface 16A of the piezoelectric element 16 opposite the side on which the acoustic matching layer 22 is disposed to the surface 22A of the acoustic matching layer 22 opposite the side on which the piezoelectric element 16 is disposed is 1.5 mm or less. In the ultrasonic element 210, for example, the acoustic impedance of the acoustic matching layer 22 is a value between the acoustic impedance of the metal plate 28 and the acoustic impedance of air. Furthermore, in the ultrasonic element 210, by having the acoustic matching layer 22 between the metal plate 28 and the air, the ultrasonic waves generated from the piezoelectric element 16 and amplified by the metal plate 28 can be efficiently emitted into the air. Therefore, even if the specific thickness is within the above range, a high sound pressure can be obtained, and the device can be applied to a small mid-air haptic device.

[0017] The ultrasonic element 220 shown in FIG. 3 includes a piezoelectric element 16, an acoustic matching layer 20 provided in contact with at least a portion of one surface of the piezoelectric element, and an acoustic reflection layer 24 provided on the other surface of the piezoelectric element 16, with the acoustic matching layer 20 being the outermost layer in contact with air. That is, the ultrasonic element 220 further includes an acoustic reflection layer 24 on the side of the piezoelectric element 16 opposite the side on which the acoustic matching layer 20 is provided. The ultrasonic element 220 may include an acoustic attenuation layer instead of or in addition to the acoustic reflection layer 24. When an acoustic attenuation layer is provided in addition to the acoustic reflection layer 24, the order of their placement is not particularly limited. From the piezoelectric element 16 side, the acoustic reflection layer 24 and the acoustic attenuation layer may be provided in this order, or the acoustic attenuation layer and the acoustic reflection layer 24 may be provided in this order. That is, the ultrasonic element 220 may include at least one of the acoustic reflection layer 24 and the acoustic attenuation layer on the side opposite the side on which the acoustic matching layer 20 is provided. In the ultrasonic element 220, the maximum thickness from the surface 16A of the piezoelectric element 16 opposite to the surface on which the acoustic matching layer 20 is disposed to the surface 20A of the acoustic matching layer 20 opposite to the surface on which the piezoelectric element 16 is disposed is 1.5 mm or less. Flexibility is imparted to the entire element 200.

[0018] In the ultrasonic element 220, similar to the ultrasonic element 200, for example, the acoustic impedance of the acoustic matching layer 20 is a value between the acoustic impedance of the piezoelectric element 16 and the acoustic impedance of air, thereby enabling efficient radiation of ultrasonic waves generated from the piezoelectric element 16 into the air. Furthermore, in the ultrasonic element 220, by providing an acoustic wave reflecting layer 24 on the other surface of the piezoelectric element 16, ultrasonic waves generated from the piezoelectric element 16 on the side opposite to the side where the acoustic matching layer 20 is disposed are reflected by the acoustic wave reflecting layer 24 and efficiently radiated toward the acoustic matching layer 20. In this way, the ultrasonic element 220 efficiently radiates ultrasonic waves into the air, and even if the specific thickness is within the above-mentioned range, a high sound pressure can be obtained, making it applicable to a small-sized air haptic device. Furthermore, in the ultrasonic element 220, a metal plate is not provided between the piezoelectric element 16 and the acoustic matching layer 20. Therefore, by using a piezoelectric resin sheet (described later) as the piezoelectric element 16, the entire ultrasonic element 220 becomes flexible.

[0019] 4 includes a piezoelectric element 16, a metal plate 28 provided on one side of the piezoelectric element, an acoustic matching layer 22 provided on the surface of the metal plate 28 opposite the side on which the piezoelectric element 16 is disposed, and an acoustic reflection layer 24 provided on the surface of the piezoelectric element 16 opposite the side on which the acoustic matching layer 22 is disposed, with the acoustic matching layer 22 being the outermost layer in contact with air. The ultrasonic element 230 may be provided with an acoustic attenuation layer instead of or in addition to the acoustic reflection layer 24. When an acoustic attenuation layer is provided in addition to the acoustic reflection layer 24, the order of arrangement is not particularly limited, and the acoustic reflection layer 24 and the acoustic attenuation layer may be provided in this order from the piezoelectric element 16 side, or the acoustic attenuation layer and the acoustic reflection layer 24 may be provided in this order. In the ultrasonic element 230, the maximum thickness from the surface 16A opposite to the surface on which the acoustic matching layer 22 of the piezoelectric element 16 is arranged to the surface 22A opposite to the surface on which the piezoelectric element 16 is arranged of the acoustic matching layer 22 is 1.5 mm or less.

[0020] In the ultrasonic element 230, similar to the ultrasonic element 210, for example, the acoustic impedance of the acoustic matching layer 22 is a value between the acoustic impedance of the metal plate 28 and the acoustic impedance of air, so that ultrasonic waves generated from the piezoelectric element 16 and amplified by the metal plate 28 can be efficiently radiated into the air. Furthermore, in the ultrasonic element 230, the acoustic wave reflecting layer 24 is provided on the surface of the piezoelectric element 16 opposite to the surface on which the acoustic matching layer 22 is disposed, so that a portion of the ultrasonic waves generated from the piezoelectric element 16 is reflected by the acoustic wave reflecting layer 24, amplified by the metal plate 28, and then efficiently radiated into the air from the acoustic matching layer 22. In this way, in the ultrasonic element 230, ultrasonic waves are efficiently radiated into the air, and even if the specific thickness is within the above-mentioned range, a high sound pressure can be obtained, and the ultrasonic element 230 is applicable to a small-sized mid-air haptic device.

[0021] <Thickness of Ultrasonic Element> As described above, the specific thickness of the ultrasonic element is 1.5 mm or less, preferably 1.3 mm or less, and more preferably 1.0 mm or less. The specific thickness of the ultrasonic element may be 0.1 mm or more. The thickness of the entire ultrasonic element may be, for example, 2 mm or less, preferably 1.5 mm or less, and more preferably 1.3 mm or less. The thickness of the entire ultrasonic element may be 0.1 mm or more. When the ultrasonic element further has at least one of an acoustic reflection layer and an acoustic attenuation layer, the thickness of the entire ultrasonic element includes the thickness of the acoustic reflection layer and the acoustic attenuation layer. Furthermore, when the ultrasonic element further has other components such as a housing in the thickness direction of the ultrasonic element, the thickness of the entire ultrasonic element means the thickness of the entire ultrasonic element including the housing, etc. Here, the thickness of the layer or member can be measured using a micrometer or the like. When the thickness of the layer or member can be directly measured, it is measured using a micrometer. On the other hand, when the thickness of the layer or member cannot be directly measured, such as when measuring the thickness of one layer or the total thickness of multiple layers, it may be measured by observing the cross-section of the layer to be measured using an electron microscope.

[0022] <Surface Shape of Acoustic Matching Layer> In the ultrasonic element of this embodiment, the shape of the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is arranged is not particularly limited, and may be flat, curved, or a combination of flat and curved. The shape of the surface of the acoustic matching layer facing the piezoelectric element is not particularly limited, and examples thereof include shapes corresponding to the surface shape of the layer (piezoelectric element, metal plate, etc.) with which the acoustic matching layer is in contact. For example, when the acoustic matching layer is provided in contact with the piezoelectric element and the surface of the piezoelectric element facing the acoustic matching layer is flat, examples of the surface of the acoustic matching layer facing the piezoelectric element include flat surfaces. Hereinafter, the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is arranged, i.e., the surface from which ultrasonic waves generated by the piezoelectric element are radiated, is also referred to as the "radiation surface."

[0023] From the viewpoint of obtaining a higher sound pressure, the radiation surface in the ultrasonic element of this embodiment preferably has a shape such that the difference between the maximum thickness and the minimum thickness of the acoustic matching layer is 1 μm or more. From the viewpoint of obtaining a higher sound pressure, the difference between the maximum thickness and the minimum thickness of the acoustic matching layer is more preferably 50 μm or more, even more preferably 100 μm or more, particularly preferably 200 μm or more, and most preferably 400 μm or more. Furthermore, from the viewpoint of obtaining a higher sound pressure, the radiation surface in the ultrasonic element of this embodiment preferably has a shape such that the difference between the maximum thickness and the minimum thickness of the acoustic matching layer is 1 mm or less. From the viewpoint of setting the specific thickness within the above-mentioned range, the difference between the maximum thickness and the minimum thickness of the acoustic matching layer is more preferably 800 μm or less, even more preferably 600 μm or less, and particularly preferably 500 μm or less. The difference between the maximum thickness and the minimum thickness of the acoustic matching layer is preferably 1 μm to 1 mm, more preferably 50 μm to 800 μm, even more preferably 100 μm to 600 μm, and particularly preferably 200 μm to 500 μm. Examples of the shape of the radiation surface of an acoustic matching layer whose difference between the maximum thickness and the minimum thickness is in the above range include a convex shape in which the central part of the radiation surface is higher than the peripheral part, a concave shape in which the central part of the radiation surface is lower than the peripheral part, and an uneven shape in which a plurality of convex parts and a plurality of concave parts are arranged alternately.

[0024] 5 to 10 show examples of ultrasonic elements in which the radiation surface of the acoustic matching layer is convex, concave, or uneven, but the ultrasonic element of this embodiment is not limited to these. Each of the ultrasonic elements shown in Fig. 5 to 10 has a piezoelectric element 16 and an acoustic matching layer 20, but is not limited to this and may have other layers. Note that Fig. 5 to 10 each schematically show a cross section cut in the thickness direction of the piezoelectric element in an example of the ultrasonic element of this embodiment.

[0025] In the ultrasonic element 200A shown in Fig. 5, the radiation surface of the acoustic matching layer 20, i.e., the surface 20A of the acoustic matching layer 20 opposite to the surface on which the piezoelectric element 16 is arranged, is curved and convex, and the central portion of the radiation surface is higher than the peripheral portion. Therefore, in the surface direction of the acoustic matching layer 20 (i.e., the surface direction perpendicular to the thickness direction), the thickness of the acoustic matching layer 20 in the central portion is thicker than the thickness of the acoustic matching layer 20 in the peripheral portion. As a result, a higher sound pressure can be obtained compared to when the radiation surface of the acoustic matching layer 20 is flat and the thickness of the acoustic matching layer 20 is uniform. Also, in the ultrasonic element 200B shown in Fig. 6, the radiation surface of the acoustic matching layer 20 is conical. Therefore, in the surface direction of the acoustic matching layer 20, the thickness of the acoustic matching layer 20 in the central portion is thicker than the thickness of the acoustic matching layer 20 in the peripheral portion. As a result, a higher sound pressure can be obtained compared to when the thickness of the acoustic matching layer 20 is uniform, as with the ultrasonic element 200A shown in Fig. 5.

[0026] In the ultrasonic element 200C shown in FIG. 7 , the radiation surface of the acoustic matching layer 20 is curved and concave, and the central portion of the radiation surface is lower than the peripheral portion. Therefore, the thickness of the acoustic matching layer 20 in the central portion in the surface direction of the acoustic matching layer 20 is thinner than the thickness of the acoustic matching layer 20 in the peripheral portion. As a result, a higher sound pressure can be obtained compared to when the radiation surface of the acoustic matching layer 20 is flat and the thickness of the acoustic matching layer 20 is uniform. Furthermore, in the ultrasonic element 200D shown in FIG. 8 , the radiation surface of the acoustic matching layer 20 is in the shape of an inverted cone. Therefore, the thickness of the acoustic matching layer 20 in the central portion in the surface direction of the acoustic matching layer 20 is thinner than the thickness of the acoustic matching layer 20 in the peripheral portion. As with the ultrasonic element 200C shown in FIG. 7 , a higher sound pressure can be obtained compared to when the thickness of the acoustic matching layer 20 is uniform.

[0027] In the ultrasonic element 200E shown in Fig. 9, the radiation surface of the acoustic matching layer 20 is composed of a plurality of curved surfaces and is uneven, with a plurality of convex portions and a plurality of concave portions arranged alternately. Therefore, the thickness of the acoustic matching layer 20 at the convex portions is greater than the thickness of the acoustic matching layer 20 at the concave portions. This allows for a higher sound pressure to be obtained compared to when the radiation surface of the acoustic matching layer 20 is flat and the thickness of the acoustic matching layer 20 is uniform. Furthermore, in the ultrasonic element 200F shown in Fig. 10, the radiation surface of the acoustic matching layer 20 is composed of a plurality of quadrangular pyramids and is uneven. Therefore, the thickness of the acoustic matching layer 20 at the convex portions is greater than the thickness of the acoustic matching layer 20 at the concave portions. As with the ultrasonic element 200E shown in Fig. 9, a higher sound pressure can be obtained compared to when the thickness of the acoustic matching layer 20 is uniform.

[0028] <Diameter of Ultrasonic Element> When the ultrasonic element is viewed in a plane, the maximum diameter of the entire ultrasonic element is preferably 8 mm or less. By applying ultrasonic elements whose maximum diameter of the entire ultrasonic element is within the above range to an air haptic device, the spatial resolution of acoustic radiation pressure can be increased. Specifically, for example, by arranging ultrasonic elements whose maximum diameter of the entire ultrasonic element is within the above range in two dimensions, the distance between ultrasonic generating units can be reduced, and it is thought that the spatial resolution of acoustic radiation pressure can be increased.

[0029] Here, the maximum diameter of the entire ultrasonic element refers to the largest diameter of the entire ultrasonic element in the plane direction of the piezoelectric element. For example, if the shape of the entire ultrasonic element in the plane direction is elliptical, the maximum diameter means the major axis, and if the shape is square, the maximum diameter means the length of the diagonal.

[0030] Hereinafter, each layer constituting the ultrasonic element of this embodiment will be described.

[0031] <Piezoelectric element> The piezoelectric element is not particularly limited as long as it is an element that generates ultrasonic waves of 20 kHz to 100 kHz, and among them, an element that generates ultrasonic waves of 20 kHz to 80 kHz is preferable, and an element that generates ultrasonic waves of 40 kHz to 70 kHz is more preferable. Examples of piezoelectric elements include piezoelectric ceramics, piezoelectric resin sheets, and piezoelectric single crystals.

[0032] Examples of piezoelectric ceramics include ceramic piezoelectric bodies with electrodes provided thereon. Examples of ceramic piezoelectric body materials include lead zirconate titanate (PZT), barium titanate, and lead titanate. The maximum thickness of the piezoelectric ceramics is, for example, 200 μm or less. The shape of the piezoelectric ceramics in the planar direction is not particularly limited, and examples include circles and polygons. The maximum diameter of the piezoelectric ceramics in the planar direction is, for example, 6.5 mm or less. The acoustic impedance of the piezoelectric ceramics is, for example, 30 MRayls. The acoustic impedance of the piezoelectric ceramics is not limited to 30 MRayls, and may be 25 MRayls to 50 MRayls.

[0033] An example of a piezoelectric resin sheet is a sheet-shaped piezoelectric body made of resin with electrodes provided thereon. Examples of materials for the resin piezoelectric body include polyvinylidene fluoride (PVDF) and polylactic acid (PLA). An example of the acoustic impedance of the piezoelectric resin sheet is 4.5 MRayls. The acoustic impedance of the piezoelectric resin sheet is not limited to 4.5 MRayls, and may be 1 MRayls to 25 MRayls.

[0034] <Acoustic Matching Layer> The acoustic matching layer contains at least a resin and propagates ultrasonic waves generated from a piezoelectric element into the air while maintaining their intensity and waveform. Specifically, the acoustic impedance of the acoustic matching layer is set to a value between the acoustic impedance of the layer with which the acoustic matching layer is in contact and the acoustic impedance of air. Specifically, for example, when the acoustic matching layer 20 is provided in contact with the piezoelectric element 16, as in the ultrasonic element 200 shown in FIG. 1, the acoustic impedance of the acoustic matching layer 20 is set to a value between the acoustic impedance of the piezoelectric element 16 and the acoustic impedance of air. Furthermore, for example, when the acoustic matching layer 22 is provided in contact with a metal plate 28, as in the ultrasonic element 210 shown in FIG. 2, the acoustic impedance of the acoustic matching layer 22 is set to a value between the acoustic impedance of the metal plate 28 and the acoustic impedance of air. This reduces the difference in acoustic impedance between the layer with which the acoustic matching layer is in contact and the air, making it less likely that ultrasonic waves generated from the piezoelectric element will be reflected at the interface between the ultrasonic element and the air, and more likely to propagate through the air while maintaining their intensity and waveform.

[0035] The acoustic matching layer may have a single-layer structure or a multi-layer structure. Examples of acoustic matching layers with a multi-layer structure include a layer formed by stacking an acoustic matching layer having an acoustic impedance value close to the acoustic impedance of the layer to which the acoustic matching layer is in contact, and an acoustic matching layer having an acoustic impedance value close to the acoustic impedance of air. By gradually changing the acoustic impedance of the acoustic matching layer from the piezoelectric element side to the air side, ultrasonic waves generated from the piezoelectric element are more likely to propagate through the air while maintaining their intensity and waveform. When the acoustic matching layer has a multi-layer structure, the acoustic matching layer may have a two-layer structure or a laminated structure of three or more layers.

[0036] The acoustic impedance value of the entire acoustic matching layer is preferably a value between the acoustic impedance of air (e.g., 0.0004 MRayls) and the acoustic impedance of the layer with which the acoustic matching layer is in contact, and is preferably set according to the acoustic impedance value of the layer with which the acoustic matching layer is in contact. For example, when the acoustic matching layer is provided in contact with a piezoelectric element that is a piezoelectric ceramic, the acoustic impedance of the entire acoustic matching layer is preferably 0.01 MRayls to 1 MRayls. When the acoustic matching layer is provided in contact with a piezoelectric element that is a piezoelectric resin sheet, the acoustic impedance of the entire acoustic matching layer is preferably 0.001 MRayls to 1 MRayls. When the acoustic matching layer is provided in contact with a metal plate, the acoustic impedance of the entire acoustic matching layer is preferably 0.01 MRayls to 1 MRayls, more preferably 0.03 MRayls to 0.5 MRayls, and even more preferably 0.05 MRayls to 0.3 MRayls.

[0037] Here, "the acoustic impedance value of the entire acoustic matching layer" refers to the value of the entire multilayer structure when the acoustic matching layer has a multilayer structure. When the acoustic matching layer has a multilayer structure, the acoustic impedance of the entire multilayer structure may be within the above range. The acoustic impedance of each layer constituting the multilayer structure may be within the above range, or the acoustic impedance of at least one layer may be outside the above range. In other words, the acoustic impedance of the entire multilayer structure may be within the above range, and the acoustic impedance of at least one layer constituting the multilayer structure may be outside the above range. A multilayer acoustic matching layer may include, for example, a first acoustic matching layer disposed on the layer side with which the acoustic matching layer contacts and having an acoustic impedance value of 3 MRayls or more, and a second acoustic matching layer disposed closer to the air than the first acoustic matching layer and having an acoustic impedance value of less than 3 MRayls. The acoustic impedance of the acoustic matching layer can be calculated from the sound speed and density of the acoustic matching layer, as described below, using the following formula: Formula: Acoustic impedance=(Sound velocity×Density) The density can be determined, for example, by preparing a sample of 10 mm square and measuring the average thickness and mass of the sample.

[0038] Methods for controlling the acoustic impedance value of the acoustic matching layer include, for example, selecting the type of resin contained in the acoustic matching layer, adjusting the resin content relative to the entire acoustic matching layer, incorporating a filler into the acoustic matching layer and adjusting the type of filler and the filler content relative to the entire acoustic matching layer, and incorporating air bubbles into the acoustic matching layer. The method for controlling the acoustic impedance value of the acoustic matching layer is selected depending on the target acoustic impedance value. Hereinafter, an acoustic matching layer having an acoustic impedance of 3 MRayls or more will be referred to as "acoustic matching layer A," and an acoustic matching layer having an acoustic impedance of less than 3 MRayls will be referred to as "acoustic matching layer B," and acoustic matching layer A and acoustic matching layer B will be described separately.

[0039] An example of an acoustic matching layer A having an acoustic impedance of 3 MRayls or more is a cured film of a resin composition containing a resin and a filler having a specific gravity of 2.0 or more. Specific examples of resins include epoxy resins and acrylic resins, among the specific examples of resins described below. Examples of fillers having a specific gravity of 2.0 or more include insulating fillers such as aluminum oxide and bismuth oxide, among the specific examples of fillers described below. The acoustic velocity in the acoustic matching layer A is not particularly limited and may be, for example, 1500 m / s to 5000 m / s, with 1900 m / s to 4500 m / s being preferred. The acoustic velocity in the acoustic matching layer can be determined by using an ultrasonic sound velocimeter (ZX-5, manufactured by Dakota Japan) and inputting the thickness of the acoustic matching layer measured using a micrometer. The density of the acoustic matching layer A is not particularly limited and may be, for example, 1.0 g / cm. ３ ~6.0 g / cm ３ and 1.2 g / cm ３ ~5.5g / cm ３ The density of the acoustic matching layer can be determined, for example, by preparing a sample of 10 mm square and measuring the average thickness and mass of the sample.

[0040] From the viewpoint of controlling the sound velocity within the above range, the elastic modulus of the acoustic matching layer A at 20°C is preferably 1.0 GPa or more, more preferably 7.0 GPa or more, and even more preferably 10.0 GPa or more. The elastic modulus of the acoustic matching layer at 20°C is determined by measurement in tension mode using a viscoelasticity measuring device DMA7100 (Hitachi High-Technologies Corporation) under conditions of a temperature rise rate of 5°C / min and a frequency of 10 Hz.

[0041] The volume resistivity of the acoustic matching layer A is, for example, 1.0×10 ６ Ω cm or more, and 1.0 × 10 ７ It may be in the range of Ω cm or more, and may be 1.0 × 10 ８ The upper limit of the volume resistivity of the acoustic matching layer A is not particularly limited, and may be, for example, 1.0×10 １６ The volume resistivity of the acoustic matching layer can be calculated from the area and thickness of the electrode contact surface by measuring the insulation resistance value using an insulation resistance meter (for example, 8340A manufactured by Advantest) in accordance with JIS C 2139-3-1:2018.

[0042] Examples of acoustic matching layer B having an acoustic impedance of less than 3 MRayls include a cured film of a resin composition containing a resin and a filler having a specific gravity of less than 2.0, a cured film of a resin composition containing a resin and a foaming agent, and a cured film of a resin composition containing a resin, a filler having a specific gravity of less than 2.0, and a foaming agent. Specific examples of resins include epoxy resins and acrylic resins, among the specific examples of resins described below. The acoustic matching layer B may have any sound velocity, but is not particularly limited, and may be, for example, 500 m / s to 3000 m / s, preferably 500 m / s to 2000 m / s, and more preferably 500 m / s to 1500 m / s. The acoustic matching layer B may have any density, but is not particularly limited, and may have a density of, for example, 0.1 g / cm. ３ ~2.0 g / cm ３ and 0.1 g / cm ３ ~1.3 g / cm ３ is preferred, and 0.1 g / cm ３ ~1.0 g / cm ３From the viewpoint of controlling the sound velocity within the above range, the elastic modulus of the acoustic matching layer B at 20°C is preferably 4 GPa or less, and more preferably 0.01 GPa or less. From the viewpoint of controlling the sound velocity within the above range, the elastic modulus of the acoustic matching layer B at 20°C is preferably 0.001 GPa or more. The volume resistivity of the acoustic matching layer B is, for example, 1.0 × 10 ６ Ω cm or more, and 1.0 × 10 ７ It may be in the range of Ω cm or more, and may be 1.0 × 10 ８ The upper limit of the volume resistivity of the acoustic matching layer B is not particularly limited, and may be, for example, 1.0×10 １６ Ω·cm can be given as an example.

[0043] The acoustic matching layer may be provided on at least a portion of the layer (e.g., a piezoelectric element or a metal plate) that the acoustic matching layer contacts. The acoustic matching layer is preferably provided on 50% or more of the surface area of ​​the layer that the acoustic matching layer contacts, more preferably 80% or more, and even more preferably covering the entire layer that the acoustic matching layer contacts. Furthermore, it is preferable that at least a portion of the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed (i.e., the radiation surface) be in contact with air, more preferably 50% or more of the surface area of ​​the radiation surface be in contact with air, even more preferably 80% or more.

[0044] The maximum thickness of the acoustic matching layer is, for example, 1 mm or less, and from the viewpoint of miniaturizing the ultrasonic element, it is preferably 900 μm or less, and more preferably 800 μm or less. From the viewpoint of maintaining the intensity of the ultrasonic waves, the maximum thickness of the acoustic matching layer is preferably 200 μm or more, more preferably 400 μm or more, and even more preferably 500 μm or more. The method for measuring the thickness is as described above.

[0045] As described above, the acoustic matching layer contains at least a resin. The resin content relative to the entire acoustic matching layer is adjusted depending on the type of resin and the desired acoustic impedance value. From the viewpoint of ensuring flexibility of the acoustic matching layer, the resin content may be 2% by mass or more, 3% by mass or more, or 4% by mass or more relative to the entire acoustic matching layer. From the viewpoint of ensuring flexibility of the film, the resin content may be 9% by mass or more, 10% by mass or more, or 13% by mass or more. Furthermore, the resin content may be 100% by mass or less, 99% by mass or less, 95% by mass or less, 25% by mass or less, 12% by mass or less, 10% by mass or less, or 9% by mass or less relative to the entire acoustic matching layer. Examples of the resin include resins contained in the resin composition described below and cured products thereof.

[0046] As described above, the acoustic matching layer may contain a filler, if necessary. The filler content relative to the entire acoustic matching layer is adjusted depending on the type of filler and the desired acoustic impedance value. For example, when the acoustic matching layer is the acoustic matching layer A and an insulating filler described below is used as the filler, the insulating filler content may be 90 vol% or less, 80 vol% or less, 70 vol% or less, less than 50 vol%, 45 vol% or less, 35 vol% or less, 25 vol% or less, or 15 vol% or less relative to the entire acoustic matching layer A. Furthermore, the insulating filler content may be 1 vol% or more, 5 vol% or more, 15 vol% or more, 25 vol% or more, 35 vol% or more, 50 vol% or more, 60 vol% or more, or 70 vol% or more relative to the entire acoustic matching layer A. Examples of the insulating filler include the insulating fillers contained in the resin composition described below.

[0047] Similarly, when the acoustic matching layer is the acoustic matching layer B and hollow particles, which will be described later, are used as the filler, the content of the hollow particles may be 90% by volume or less, 80% by volume or less, 70% by volume or less, less than 50% by volume, 45% by volume or less, 35% by volume or less, 25% by volume or less, or 15% by volume or less, based on the entire acoustic matching layer B. Furthermore, the content of the hollow particles may be 1% by volume or more, 5% by volume or more, 15% by volume or more, 25% by volume or more, 35% by volume or more, 50% by volume or more, 60% by volume or more, or 70% by volume or more, based on the entire acoustic matching layer B. Examples of types of hollow particles include hollow particles contained in resin compositions, which will be described later.

[0048] The acoustic matching layer may contain other components in addition to the resin and filler, as necessary. The types and contents of the other components are the same as those of the other components contained in the resin composition described below and their contents relative to the total solid content of the resin composition.

[0049] The acoustic matching layer may contain bubbles, if necessary. Examples of acoustic matching layers containing bubbles include a cured film of a resin composition containing a foaming agent, as described below. When the acoustic matching layer is the acoustic matching layer B containing bubbles, the bubble content may be 90% by volume or less, 80% by volume or less, 70% by volume or less, less than 50% by volume, 45% by volume or less, 35% by volume or less, 25% by volume or less, or 15% by volume or less, based on the entire acoustic matching layer B. Furthermore, the bubble content may be 1% by volume or more, 5% by volume or more, 15% by volume or more, 25% by volume or more, 35% by volume or more, 50% by volume or more, 60% by volume or more, or 70% by volume or more, based on the entire acoustic matching layer B.

[0050] The bubble content is measured using the relationship between the apparent density (ρ) and true density (ρ0) of the sample according to the water immersion method. Formula: Porosity (%) = {1 - (ρ / ρ0)} x 100. The apparent density (ρ) is calculated by measuring the weight in air and the weight in water using the water gravimetric method (water immersion method), determining the apparent volume based on Archimedes' principle, and then dividing the weight in air by the apparent volume. The true density (ρ0) is measured by thoroughly crushing the sample to remove open pores and using a Gay-Lussac pycnometer. Specifically, the voids in the sample are completely degassed and replaced with liquid, and the relationship between the weight and volume is calculated to determine the true density.

[0051] An example of an acoustic matching layer is a cured film of a resin composition containing a resin. The cured film may be a film obtained by curing a dried film of the resin composition, or may be a film obtained by curing a resin composition without first drying the film. Here, the cured film may be a film whose hardness has increased due to a chemical reaction that results in a different chemical structure from before curing, or a film whose hardness has increased due to solidification of a molten resin composition whose chemical structure remains the same as before curing. Hereinafter, an acoustic matching layer that is a cured film of a resin composition will be described as an example of an acoustic matching layer.

[0052] (Resin Composition) The resin composition contains at least a resin, and may contain a filler, a solvent, other components, and the like, as needed.

[0053] Resin: The type of resin is not particularly limited, and may be a thermosetting resin, a thermoplastic resin, or a combination thereof. The resin may be in the form of a monomer having a functional group that can undergo a polymerization reaction upon heating, or in the form of an already polymerized polymer.

[0054] The resin is preferably a resin having a polar group. By using a resin having a polar group as the resin, the interaction with the surface of the contacting member is improved, and a layer with high adhesiveness is obtained. A polar group refers to an atomic group that has polarity due to the bond between atoms with different electronegativity. Examples of polar groups include groups having heteroatoms other than carbon atoms and hydrogen atoms, and more specifically, groups containing at least one heteroatom selected from the group consisting of nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, phosphorus atoms, and silicon atoms. Among these, groups containing at least one heteroatom selected from the group consisting of nitrogen atoms, oxygen atoms, and sulfur atoms are preferred as polar groups. More specifically, examples of the polar group include an amino group, an amido group, an imido group, a cyano group, a nitro group, an epoxy group, a hydroxy group, a carboxy group, a carbonyl group, a thiol group, a sulfo group, a thionyl group, an ester bond, an ether bond, a sulfide bond, a urethane bond, and a urea bond, and at least one selected from the group consisting of an amido group, an imido group, an epoxy group, a hydroxy group, an amino group, a carboxy group, a carbonyl group, an ether bond, and a urea bond is preferred. The polar group may be present in the main chain or in a side chain of the resin.

[0055] Specific examples of resins having polar groups include vinyl polymerization resins, acrylic resins, polyamide resins, polyimide resins, polyamideimide resins, polyurethane resins, polyester resins, polyether resins, epoxy resins, oxazine resins, bismaleimide resins, phenolic resins, unsaturated polyester resins, silicone resins, and phenoxy resins. Among these, the resin having polar groups preferably includes at least one selected from the group consisting of polyamideimide resins, epoxy resins, acrylic resins, polyester resins, and polyether resins. The resins having polar groups may be used alone or in combination of two or more.

[0056] In addition to the resin having a polar group, the resin composition may also contain a resin not having a polar group. Examples of resins not having a polar group include SBR resin (styrene-butadiene-random copolymer resin), SBS resin (styrene-butadiene block copolymer resin), SIS (styrene-isoprene block copolymer), SEBS (styrene-ethylene-butylene block copolymer resin), SEPS (styrene-ethylene-propylene block copolymer resin), polyethylene, polypropylene, polybutadiene, polyisoprene, polystyrene, and cycloolefin polymers, as well as hydrogenated versions thereof. The content of the resin having a polar group relative to the total amount of resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The content of the resin having a polar group relative to the total amount of resin may be 100% by mass or may be 95% by mass or less.

[0057] From the viewpoint of durability, the resin preferably contains a thermosetting resin, and more preferably contains a thermosetting resin having a polar group. The thermosetting resin may have an aromatic ring or a fused ring in which two or more aromatic rings are fused. Examples of the fused ring include a naphthalene ring, an anthracene ring, and a phenanthrene ring.

[0058] Examples of the thermosetting resin having a polar group include epoxy resin, phenol resin, melamine resin, urea resin, thermosetting polyimide resin, acrylic resin, polyurethane resin, etc. Among these, as the thermosetting resin having a polar group, from the viewpoint of durability, epoxy resin, phenol resin, and acrylic resin are preferred, and epoxy resin is more preferred.

[0059] The epoxy resin is not particularly limited as long as it has two or more epoxy groups in one molecule. Specific examples of the epoxy resin include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, hydrogenated bisphenol A epoxy resin, phenol novolac epoxy resin, cresol novolac epoxy resin, naphthalene epoxy resin, anthracene epoxy resin, biphenol epoxy resin, biphenyl novolac epoxy resin, and cycloaliphatic epoxy resin.

[0060] Specific preferred examples of the epoxy resin include the above-mentioned epoxy resins having a substituent such as an ether group, an alicyclic epoxy group, etc. The epoxy resin is preferably an epoxy resin having a heteroatom other than an oxygen atom derived from the epoxy group or glycidyloxy group of the epoxy resin.

[0061] The epoxy resin may be, for example, an epoxy resin containing a nitrogen atom and a hydrogen atom bonded to the nitrogen atom. In a preferred embodiment, the epoxy resin may have a heterocyclic structure containing a nitrogen atom and a hydrogen atom bonded to the nitrogen atom. An example of such a heterocyclic structure is a glycoluril structure.

[0062] The molecular weight of the epoxy resin is not particularly limited, and may be, for example, 100 to 1,500, or may be 150 to 1,000, or may be 200 to 500.

[0063] When the resin composition contains an epoxy resin, the content of the epoxy resin relative to the total amount of resin may be 80% by mass or more, 90% by mass or more, or even 100% by mass, and the content of the epoxy resin relative to the total amount of resin may be 10% by mass to 90% by mass, 20% by mass to 80% by mass, 30% by mass to 80% by mass, or 40% by mass to 80% by mass.

[0064] The acrylic resin is not particularly limited as long as it has two or more (meth)acryloyl groups in the molecule. Specific examples of the acrylic resin include polyfunctional (meth)acrylic acid esters such as 1,9-nonanediol diacrylate, ethylene glycol diacrylate, and propylene glycol diacrylate.

[0065] When the resin composition contains the acrylic resin, the resin composition may further contain an acrylic compound other than the acrylic resin. Examples of the acrylic compound other than the acrylic resin include acrylic nitrile group-containing monomers such as acrylonitrile and methacrylonitrile; monofunctional (meth)acrylic acid esters such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate, 3-ethoxypropyl acrylate, oxycarbonyl tetramethacrylate, methyl acrylate, isopropyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, n-propyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, ethyl methacrylate, 2-nitro-2-methylpropyl methacrylate, 1,1-diethylpropyl methacrylate, methyl methacrylate, isodecyl acrylate, tricyclodecyl acrylate, and glycidyl methacrylate.

[0066] When the resin composition contains an acrylic resin, the total content of the acrylic resin and the acrylic compound other than the acrylic resin relative to the total amount of the resin may be 5% by mass to 100% by mass, or may be 10% by mass to 50% by mass.

[0067] When the resin contains a thermosetting resin, the resin composition may further contain a curing agent. For example, when an epoxy resin is used as the thermosetting resin, a curing agent such as a polyaddition-type curing agent such as an acid anhydride-based curing agent, an amine-based curing agent, a phenol-based curing agent, or a mercaptan-based curing agent, or a latent curing agent such as imidazole may be used in combination. Furthermore, when an acrylic resin is used as the thermosetting resin, a curing agent such as a peroxide or an azo compound may be used in combination. When the resin is polymerized using a curing agent in combination, the polar group contained in the resin having a polar group may be a polar group generated as a result of the polymerization reaction.

[0068] From the viewpoint of flexibility, the resin preferably contains a thermoplastic resin, and preferably contains a thermoplastic resin having a polar group. Examples of the thermoplastic resin include phenoxy resin, polyamideimide resin, polyethylene resin, polypropylene resin, and SBR resin. Among them, from the viewpoint of flexibility, the thermoplastic resin is preferably phenoxy resin, polyamideimide resin, polyethylene resin, or SBR resin, and more preferably polyamideimide resin, phenoxy resin, or SBR resin.

[0069] The phenoxy resin is not particularly limited as long as it has a phenoxy structure in its molecular structure. Here, the "phenoxy structure" refers to a structure in which an oxygen atom is bonded to a benzene ring, and is a phenoxy group (C ６ H ５ —O—), as well as those in which a part of the phenoxy group has been substituted, and those in which a part of the phenoxy group has been reacted by hydrogenation or the like are also included.

[0070] Examples of phenoxy resins include phenoxy resins having a bisphenol skeleton, phenoxy resins having a novolac skeleton, phenoxy resins having a naphthalene skeleton, and phenoxy resins having a biphenyl skeleton. Among these, from the viewpoint of versatility, the phenoxy resin is preferably a phenoxy resin having a bisphenol skeleton. Examples of phenoxy resins having a bisphenol skeleton include bisphenol A phenoxy resins, bisphenol F phenoxy resins, copolymer phenoxy resins of bisphenol A and bisphenol F, bisphenol S phenoxy resins, brominated bisphenol A phenoxy resins, and hydrogenated bisphenol A phenoxy resins. These phenoxy resins may be used alone or in combination of two or more.

[0071] A polyamide-imide resin is a resin having an amide bond and an imide bond in the main chain. A preferred example of the polyamide-imide resin is a polyamide-imide resin having at least one structure selected from the group consisting of a polyalkylene oxide structure and a polysiloxane structure. These polyamide-imide resins are preferred from the viewpoint of mitigating stress due to deformation of the polyamide-imide resin. These polyamide-imide resins may be synthesized using, for example, a polyalkylene oxide-modified diamine and a polysiloxane-modified diamine, respectively.

[0072] As the unit structure of the polyalkylene oxide structure that may be contained in the polyamide-imide resin, an alkylene oxide structure having 1 to 10 carbon atoms is preferred, an alkylene oxide structure having 1 to 8 carbon atoms is more preferred, and an alkylene oxide structure having 1 to 4 carbon atoms is even more preferred. Of these, a polypropylene oxide structure is preferred as the polyalkylene oxide structure. The alkylene group in the alkylene oxide structure may be linear or branched. The unit structure in the polyalkylene oxide structure may be of one type or two or more types.

[0073] Examples of the polysiloxane structure that may be contained in the polyamide-imide resin include polysiloxane structures in which some or all of the silicon atoms in the polysiloxane structure are substituted with alkyl groups having 1 to 20 carbon atoms or aryl groups having 6 to 18 carbon atoms. Another preferred embodiment of the polyamide-imide resin is a polyamide-imide resin having a structural unit derived from diimide carboxylic acid or a derivative thereof and a structural unit derived from aromatic diisocyanate or aromatic diamine.

[0074] The SBR resin is not particularly limited as long as it is a copolymer of styrene and butadiene. Furthermore, the ratio of the styrene-derived units and the butadiene-derived units constituting the SBR resin is not particularly limited, and the molecular weight of the SBR resin is also not particularly limited. The SBR resin may be one in which the unsaturated double bonds of the butadiene-derived units remain in order to react with a thermosetting resin, or one in which the unsaturated double bonds have been hydrogenated to increase durability.

[0075] When the resin contains a thermoplastic resin, the thermoplastic resin may be combined with a thermosetting resin from the viewpoints of improving the strength of the film after film formation and suppressing cure shrinkage during curing.

[0076] The total content of the resin in the resin composition may be 2% by mass or more, 3% by mass or more, or 4% by mass or more relative to the solid content of the resin composition, and from the viewpoint of obtaining flexibility of the film, it may be 9% by mass or more, 10% by mass or more, or 13% by mass or more. Furthermore, the total content of the resin in the resin composition may be 100% by mass or less, 99% by mass or less, 95% by mass or less, 25% by mass or less, 12% by mass or less, 10% by mass or less, or 9% by mass or less relative to the solid content of the resin composition.

[0077] Filler Among fillers, examples of insulating fillers used in producing the acoustic matching layer A include oxides such as aluminum oxide, zirconium oxide, titanium oxide, bismuth oxide, silicon dioxide, cerium oxide, tantalum oxide, tungsten oxide, and sintered uranium oxide; barium titanate, tungsten carbide, tungsten, and zirconium. One type of insulating filler may be used alone, or two or more types may be used in combination.

[0078] Among these, the insulating filler preferably contains at least one selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, bismuth oxide, silicon dioxide, tantalum oxide, and tungsten oxide. Furthermore, from the viewpoints of high hardness and uniform particle shape, the insulating filler preferably contains at least one selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, barium titanate, and bismuth oxide, and more preferably contains at least one selected from the group consisting of aluminum oxide, zirconium oxide, and bismuth oxide.

[0079] The volume resistivity of the insulating filler at 25°C is 1 x 10 ６ It is preferable that the resistance is Ω cm or more, and 1×10 ８ More preferably, it is 1×10 Ω cm or more. １０ It is more preferable that the resistivity is Ω·cm or more.

[0080] From the viewpoint of thinning the resin composition layer, the volume average particle diameter D50 of the insulating filler is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. The lower limit of the volume average particle diameter D50 of the insulating filler is not particularly limited, and may be 0.001 μm or more. From the above viewpoints, the volume average particle diameter D50 of the insulating filler is preferably 0.001 μm to 5.0 μm, more preferably 0.001 μm to 3.0 μm, and even more preferably 0.001 μm to 2.0 μm.

[0081] Here, the volume average particle diameter D50 of the insulating filler contained in the resin composition and the volume average particle diameter D50 of the insulating filler contained in the film formed using the resin composition are determined as follows. Specifically, the volume average particle diameter D50 is the particle diameter at which the cumulative total from the small diameter side reaches 50% in the volume-based particle size distribution curve. The particle size distribution curve of the insulating filler contained in the resin composition is obtained by observing the cross section of the cured resin composition with a scanning electron microscope (SEM) and determining the circle equivalent diameter of 20 insulating fillers. Note that when determining the volume average particle diameter D50 of the insulating filler alone (for example, the insulating filler that is a raw material for the resin composition), it may be determined by a laser diffraction / scattering particle size distribution measurement method using, for example, a particle size distribution measurement device that utilizes laser light scattering (for example, the "SALD-3000" manufactured by Shimadzu Corporation).

[0082] The shape of the insulating filler is not particularly limited, and may be spherical, powdery, needle-like, fibrous, plate-like, angular, polyhedral, scale-like, or the like. From the viewpoint of thinning the resin composition layer, the shape of the insulating filler is preferably polyhedral or spherical, and more preferably spherical. From the viewpoint of thinning the resin composition layer, the aspect ratio of the insulating filler is preferably 5 or less, preferably 4 or less, and more preferably 3 or less. The aspect ratio of the insulating filler contained in the resin composition is determined by observing a cross section of a cured product of the resin composition with a scanning electron microscope (SEM) and averaging the aspect ratios of 20 insulating fillers.

[0083] The specific gravity of the insulating filler is not particularly limited and may be adjusted appropriately depending on the application of the resin composition. The specific gravity of the insulating filler may be 2.0 or more, 3.0 or more, 5.0 or more, 6.0 or more, or 7.0 or more. The upper limit of the specific gravity of the insulating filler is not particularly limited. The specific gravity of the insulating filler may be, for example, 10.0 or less. In the present disclosure, the specific gravity of the filler represents the ratio of the true specific gravity of the measurement sample to the true specific gravity of water, measured in accordance with JIS K 0061:2001 and JIS Z 8807:2012, as the ratio of the mass of the measurement sample to the mass of the same volume of pure water under atmospheric pressure. Note that when the resin composition contains two or more types of fillers, the specific gravity of the fillers refers to the value for the mixture of fillers contained in the resin composition.

[0084] The content of the insulating filler in the total solid content of the resin composition may be 90% by volume or less, 85% by volume or less, 80% by volume or less, less than 50% by volume, 45% by volume or less, 35% by volume or less, 25% by volume or less, or 15% by volume or less. Also, from the viewpoint of increasing the acoustic impedance of the film, the content of the insulating filler in the total solid content of the resin composition may be 1% by volume or more, 5% by volume or more, 15% by volume or more, 25% by volume or more, 35% by volume or more, 50% by volume or more, 55% by volume or more, or 60% by volume or more.

[0085] The content of the insulating filler in the total solid content of the resin composition may be 99% by mass or less, or from the viewpoint of achieving both flexibility and wide acoustic impedance control, may be 87% by mass or less, 70% by mass or less, 65% by mass or less, less than 65% by mass, 60% by mass or less, 50% by mass or less, or 40% by mass or less. Furthermore, the content of the insulating filler in the total solid content of the resin composition may be 1% by mass or more, 5% by mass or more, 20% by mass or more, 70% by mass or more, 80% by mass or more, 88% by mass or more, 90% by mass or more, or 92% by mass or more.

[0086] Among fillers, hollow particles used in producing the acoustic matching layer B include hollow inorganic particles and hollow organic particles. Examples of hollow inorganic particles include hollow oxide particles such as hollow silica particles, hollow titania particles, hollow zirconia particles, and hollow tin oxide particles; hollow silicon particles; and hollow carbon particles. Examples of hollow organic particles include hollow polymer particles, and specific examples include hollow particles made of vinyl polymerization resin, acrylic resin, polyamide resin, polyimide resin, polyamideimide resin, polyurethane resin, polyester resin, polyether resin, epoxy resin, oxazine resin, bismaleimide resin, phenol resin, unsaturated polyester resin, silicone resin, phenoxy resin, SBR resin (styrene-butadiene-random copolymer resin), SBS resin (styrene-butadiene block copolymer resin), SIS (styrene-isoprene block copolymer), SEBS (styrene-ethylene-butylene block copolymer resin), SEPS (styrene-ethylene-propylene block copolymer resin), polyethylene, polypropylene, polybutadiene, polyisoprene, polystyrene, and cycloolefin polymer, as well as hydrogenated versions of these.

[0087] From the viewpoint of thinning the resin composition layer, the volume average particle diameter D50 of the hollow particles is preferably 100.0 μm or less, more preferably 50.0 μm or less, and even more preferably 30.0 μm or less. The lower limit of the volume average particle diameter D50 of the hollow particles is not particularly limited and may be 1 μm or more. From the above viewpoints, the volume average particle diameter D50 of the hollow particles is preferably 1 μm to 100.0 μm, more preferably 1 μm to 50.0 μm, and even more preferably 1 μm to 30.0 μm. The volume average particle diameter D50 of the hollow particles contained in the resin composition and the volume average particle diameter D50 of the hollow particles contained in the film formed using the resin composition are determined in the same manner as the volume average particle diameter D50 of the insulating filler described above. The shape of the hollow particles is not particularly limited, and examples thereof include spherical shapes.

[0088] The specific gravity of the hollow particles is not particularly limited and may be adjusted appropriately depending on the application of the resin composition. The specific gravity of the hollow particles may be less than 2.0, may be 0.1 or less, or may be 0.01 or less.

[0089] -Foaming Agent- Examples of the foaming agent include organic foaming agents and inorganic foaming agents. Examples of organic foaming agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), and hydrazodicarbonamide (HDCA). Examples of inorganic foaming agents include sodium bicarbonate. The decomposition temperature of the foaming agent is not particularly limited and may be, for example, 50°C to 200°C, 80°C to 200°C, or 130°C to 200°C. The content of the foaming agent in the resin composition is preferably set appropriately depending on the type of foaming agent, etc. For example, when the organic foaming agent azodicarbonamide is used as the foaming agent, from the viewpoint of foamability, the content of the organic foaming agent in the resin composition is preferably in the range of 0.05% by mass to 1.0% by mass, and more preferably in the range of 0.1% by mass to 0.5% by mass.

[0090] -Solvent- The resin composition may contain a solvent in order to adjust the viscosity. In order to prevent the composition from drying out during the step of applying the composition, the solvent preferably has a boiling point of 70°C or higher, and more preferably has a boiling point of 100°C or higher. In order to suppress the generation of voids, the solvent more preferably has a boiling point of 300°C or lower.

[0091] The type of solvent is not particularly limited, and examples thereof include alcohol-based solvents, ether-based solvents, ketone-based solvents, amide-based solvents, aromatic hydrocarbon-based solvents, ester-based solvents, and nitrile-based solvents. More specific examples of the solvent include methyl isobutyl ketone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, γ-butyrolactone, sulfolane, cyclohexanone, methyl ethyl ketone, dimethylpropanamide, 2-(2-hexyloxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol, diethylene glycol monoethyl ether, terpineol, stearyl alcohol, tripropylene glycol methyl ether, diethylene glycol, propylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol-n-butyl ether, 1,3-butanediol, 1,4-butanediol, p-phenylphenol, propylene glycol phenyl ether, tributyl citrate, 4-methyl-1,3-dioxolan-2-one, paraffin, toluene, etc. One solvent may be used alone, or two or more solvents may be used in combination.

[0092] From the viewpoints of viscosity, shortening the heating process, etc., the solvent content is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 20% by mass or less, relative to the total amount of the resin composition. The lower limit of the solvent content is not particularly limited, and the resin composition may not contain a solvent. The solvent content may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or less.

[0093] Other Components The resin composition may contain other components as needed, such as additives such as dispersants, coupling agents, and thixotropic agents.

[0094] The resin composition may contain a dispersant from the viewpoint of filler dispersibility. Examples of dispersants include dispersants compatible with the resin. Use of a dispersant compatible with the resin tends to favorably disperse the filler and improve adhesion to the substrate. Specific examples of dispersants include phosphates, carboxylates, and amine carboxylates. The content of the dispersant may be 0.01% by mass to 5% by mass, 0.05% by mass to 3% by mass, 0.1% by mass to 1% by mass, or 0.1% by mass to 0.5% by mass, based on the total solid content of the resin composition.

[0095] The type of coupling agent is not particularly limited, and examples of the coupling agent include silane compounds, titanium compounds, aluminum chelate compounds, and aluminum / zirconium compounds. Among them, silane coupling agents are preferred from the viewpoint of adhesion to substrates such as glass. The coupling agents may be used alone or in combination of two or more. When the resin composition contains a coupling agent, the adhesion of the resulting film to the substrate tends to be improved.

[0096] Examples of the silane coupling agent include silane coupling agents having a vinyl group, an epoxy group, a methacrylic group, an acrylic group, an amino group, an isocyanurate group, a ureido group, a mercapto group, an isocyanate group, an acid anhydride group, etc. Among them, a silane coupling agent having an epoxy group or an amino group is preferred, and a silane coupling agent having an epoxy group or an anilino group is more preferred. In particular, when at least one selected from the group consisting of a polyamideimide resin and an epoxy resin is used as the resin, it is preferred to use a silane coupling agent having an epoxy group or an amino group, and more preferred to use a silane coupling agent having an epoxy group or an anilino group, from the viewpoint of good compatibility with the polyamideimide resin and the epoxy resin.

[0097] Specific examples of the silane coupling agent include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-ureidopropyltriethoxysilane.

[0098] When the resin composition contains a coupling agent, the content of the coupling agent in the resin composition is not particularly limited, and is preferably 0.05% by mass to 5% by mass, and more preferably 0.1% by mass to 2.5% by mass, relative to the solid content of the resin composition.

[0099] Examples of thixotropic agents include 12-hydroxystearic acid, 12-hydroxystearic acid triglyceride, ethylene bisstearic acid amide, hexamethylene bisoleic acid amide, N,N'-distearyl adipic acid amide, and fumed silica. One type of thixotropic agent may be used alone, or two or more types may be used in combination. The content of the thixotropic agent is not particularly limited, and may be 0.01% by mass to 5% by mass, 0.05% by mass to 3% by mass, or 0.1% by mass to 1% by mass, based on the total solid content of the resin composition.

[0100] The resin composition may or may not contain a conductive filler as another component. From the viewpoint of obtaining an insulating film, the content of the conductive filler relative to the total solid content of the resin composition is preferably less than 1% by volume, more preferably less than 0.1% by volume, and even more preferably less than 0.01% by volume. The conductive filler is a filler having a volume resistivity of 1×10 at 25° C. ６The term "conductive filler" refers to a filler having a resistivity of less than Ω·cm. Examples of conductive fillers include metals, conductive metal oxides, and carbon black.

[0101] - Preparation and Properties of Resin Composition - The method for preparing the resin composition is not particularly limited, and examples thereof include a method in which the components contained in the resin composition described above are mixed in predetermined amounts using a mixer or the like.

[0102] From the viewpoint of handleability, the viscosity of the resin composition is preferably 10 Pa·s to 300 Pa·s, more preferably 20 Pa·s to 250 Pa·s, and even more preferably 30 Pa·s to 200 Pa·s at 25° C. The viscosity of the resin composition is measured in accordance with JIS Z 3284-3:2014 using an E-type rotational viscometer equipped with an SPP rotor, at 25° C., at a rotation speed of 2.5 revolutions per minute (rpm) for 144 seconds, and is the average value of two measurements.

[0103] (Method for Manufacturing Acoustic Matching Layer) The acoustic matching layer can be obtained, for example, as follows. Specifically, for example, the above-described resin composition is first applied to an object on which the acoustic matching layer is to be mounted to form a resin composition layer, and the resin composition layer is then dried and cured to obtain an acoustic matching layer that is a cured film of the resin composition. Alternatively, the above-described resin composition may be applied to the surface of a substrate to form a resin composition layer, the resin composition layer is dried to obtain a dried film, and the dried film peeled from the surface of the substrate is then provided on the object on which the acoustic matching layer is to be mounted and cured to obtain an acoustic matching layer that is a cured film of the resin composition. Alternatively, the above-described resin composition may be applied to the surface of a substrate to form a resin composition layer, the resin composition layer is dried and cured to obtain a cured film of the resin composition, and the cured film peeled from the surface of the substrate is then provided on the object on which the acoustic matching layer is to be mounted to obtain an acoustic matching layer that is a cured film of the resin composition. Alternatively, the acoustic matching layer may be obtained by forming a molded product of the resin composition by injection molding, extrusion molding, or the like, and then providing the cured film on the object on which the acoustic matching layer is to be mounted to obtain an acoustic matching layer that is a cured film of the resin composition.

[0104] When the acoustic matching layer has a multilayer structure, the acoustic matching layer may be a cured film obtained by curing a laminate in which a plurality of dry films are stacked. Specifically, the acoustic matching layer may be a cured film obtained by peeling dry films formed on a plurality of different substrates from each other, bonding them together, and curing them to form an integrated film. Alternatively, the acoustic matching layer may be a cured film obtained by further applying a resin composition onto a dry film, drying the composition, and then curing the laminate in which a plurality of dry films are stacked.

[0105] The method for applying the resin composition is not particularly limited, and examples thereof include spraying, screen printing, spin coating, spin coating, and bar coating. The substrate to which the resin composition is applied is not particularly limited, and examples thereof include glass, metal, resin material, metal vapor deposition film, metal oxide, ceramic, nonwoven fabric, glass fiber, aramid fiber, carbon fiber, glass fiber prepreg, aramid fiber prepreg, and carbon fiber prepreg. The method for drying the resin composition layer is not particularly limited, and examples thereof include heat treatment using a device such as a hot plate or oven, and natural drying. The conditions for drying by heat treatment are not particularly limited as long as the solvent in the resin composition is sufficiently evaporated, and may be 80°C to 150°C for about 5 minutes to 120 minutes.

[0106] The curing method for obtaining a cured film is not particularly limited, and curing can be performed by heat treatment, etc. Curing by heat treatment can be performed using a box dryer, a hot air conveyor dryer, a quartz tube furnace, a hot plate, a rapid thermal annealer, a vertical diffusion furnace, an infrared curing furnace, an electron beam curing furnace, a microwave curing furnace, a laminator, a hot plate press, etc. Alternatively, a cured film can be obtained by curing the resin composition by heat treatment during molding using a molding machine such as an injection molding machine or an extrusion molding machine.

[0107] <Metal Plate> The metal plate is provided as needed, and is a layer that amplifies ultrasonic waves generated from the piezoelectric element and propagates them to the acoustic matching layer. The material of the metal plate is not particularly limited, and examples thereof include aluminum, stainless steel, iron, and copper. The maximum thickness of the metal plate is, for example, 500 μm or less, and from the viewpoint of obtaining a high sound pressure and setting the specific thickness within the above-mentioned range, a thickness of 100 μm to 500 μm is preferred.

[0108] The metal plate may be provided on at least a portion of the surface of the piezoelectric element facing the acoustic matching layer, and from the viewpoint of efficiently amplifying ultrasonic waves generated by the piezoelectric element, it is preferable that the metal plate be provided so as to cover the entire surface facing the acoustic matching layer. The size of the metal plate in the planar direction may be larger than the surface of the piezoelectric element facing the acoustic matching layer. The shape of the metal plate in the planar direction is not particularly limited, and examples include a circle, a polygon, and the like. When viewed in a plane, the maximum diameter of the metal plate is, for example, 8 mm or less.

[0109] <Sound Reflecting Layer> The sound reflecting layer contains at least a resin and reflects ultrasonic waves generated from the piezoelectric element on the side opposite the acoustic matching layer. Specifically, the acoustic impedance value of the sound reflecting layer is set to a value significantly different from the acoustic impedance value of the layer with which the sound reflecting layer is in contact. This makes it easier for ultrasonic waves generated from the piezoelectric element to be reflected at the interface between the sound reflecting layer and the layer with which the sound reflecting layer is in contact. Methods for controlling the acoustic impedance value of the sound reflecting layer include methods similar to those for controlling the acoustic impedance value of the acoustic matching layer described above. The composition and formation method of the sound reflecting layer are the same as those of the acoustic matching layer described above, except for the different acoustic impedance value. The average thickness of the sound reflecting layer is not particularly limited, and can be, for example, 500 μm or less. The definition of average thickness and the method for measuring thickness are as described above.

[0110] <Acoustic Attenuation Layer> The acoustic attenuation layer contains at least a resin and attenuates ultrasonic waves generated from the piezoelectric element on the side opposite to the acoustic matching layer. The acoustic attenuation layer may be any layer that is impervious to acoustic waves, such as a layer that reflects acoustic waves to impair their transmission, a layer that absorbs acoustic waves to impair their transmission, or a layer that reflects and absorbs acoustic waves to impair their transmission.

[0111] In the acoustic attenuation layer, as with the acoustic reflection layer described above, by setting the acoustic impedance value to a value significantly different from the acoustic impedance value of the layer with which the acoustic attenuation layer is in contact, the reflectivity of the acoustic waves can be increased and the acoustic waves can be made less likely to transmit. Furthermore, the acoustic attenuation layer can weaken the signal strength of the ultrasonic waves during propagation by converting them into thermal energy, diffusing, scattering, delaying, etc. The composition and formation method of the acoustic attenuation layer are the same as those of the acoustic matching layer described above, except for the different acoustic impedance value. The average thickness of the acoustic attenuation layer is not particularly limited, and can be, for example, 500 μm or less. The definition of the average thickness and the method for measuring the thickness are as described above.

[0112] If the acoustic attenuation layer is a layer with a high acoustic absorption rate, it is preferable to increase the thermal conductivity of the acoustic attenuation layer so that the heat generated by absorbing acoustic waves does not easily accumulate. One method for increasing the thermal conductivity of the acoustic attenuation layer is to include a highly thermally conductive filler. Examples of highly thermally conductive fillers include aluminum oxide.

[0113] An ultrasonic device according to an embodiment of the present disclosure includes a support and a plurality of ultrasonic elements provided on the support and arranged two-dimensionally. In this embodiment, the ultrasonic elements according to the embodiment described above are used as the ultrasonic elements, and therefore the device is applicable to a small-sized mid-air haptic device. In addition, ultrasonic waves are emitted into the air from each ultrasonic element while maintaining their intensity and waveform, making it possible to generate a high acoustic radiation pressure at a targeted position.

[0114] <Support> The support is not particularly limited as long as it is a member that supports the ultrasonic element. Below, the configuration of an example of an ultrasonic device according to the present disclosure will be described with reference to the drawings, but the ultrasonic device according to the present disclosure is not limited thereto.

[0115] <First Embodiment> Fig. 11 is a perspective view showing an example of an ultrasonic device according to a first embodiment, and Fig. 12 is a schematic view showing a cross section cut in the thickness direction of the ultrasonic device of Fig. 11. The ultrasonic device 100 shown in Fig. 11 and Fig. 12 has a support body 10 and a plurality of ultrasonic elements 12 provided on the support body 10. Each of the plurality of ultrasonic elements 12 is the ultrasonic element according to the above-described embodiment, and as shown in Fig. 11, is arranged two-dimensionally on the surface of the support body 10 to form an array.

[0116] The ultrasonic element 12 has a piezoelectric element 16 provided in contact with the support 10, and an acoustic matching layer 20 provided in contact with the piezoelectric element 16. Since each of the ultrasonic elements 12 has the acoustic matching layer 20, the ultrasonic waves generated from the piezoelectric element 16 are propagated into the air while maintaining their intensity and waveform.

[0117] The spacing between the ultrasonic elements 12, i.e., the shortest distance between the centers of the piezoelectric elements 16, is not particularly limited and may be, for example, 500 μm or less. In the ultrasonic device 100 of FIG. 11 , the ultrasonic elements 12 are arranged in a square lattice pattern, but the arrangement shape of the ultrasonic elements 12 is not limited thereto and may be a hexagonal lattice pattern or another arrangement shape. In the ultrasonic device 100, the number of ultrasonic elements 12 arranged in an array on the support 10 is not particularly limited.

[0118] The maximum value of the overall thickness of the ultrasonic device 100, that is, the maximum value of the total thickness of the support 10 and the ultrasonic elements 12, is, for example, 20 mm or less. Here, the maximum value of the overall thickness of the ultrasonic device 100 can be measured using a micrometer or the like.

[0119] The ultrasonic device 100 may or may not further include another layer such as a cover layer on the acoustic matching layer 20. In the ultrasonic device 100, the surface of the piezoelectric element 16 opposite to the surface on which the support 10 is disposed is covered by the acoustic matching layer 20. Therefore, even if a cover layer is not provided, the piezoelectric element 16 is protected by the acoustic matching layer 20. In addition, from the viewpoint of propagating ultrasonic waves into the air while maintaining their intensity and waveform, it is preferable that at least a portion of the acoustic matching layer 20 of the ultrasonic device 100 be in contact with air, and it is more preferable that no other layer be provided on the acoustic matching layer 20.

[0120] Second Embodiment Fig. 13 is a schematic diagram showing a cross section of an example of an ultrasonic device according to a second embodiment. The ultrasonic device according to the second embodiment has one sound-reflecting layer between the support body and the ultrasonic elements so as to cover the entire surface of the support body. Specifically, the ultrasonic device 120 shown in Fig. 13 has a support body 10, a sound-reflecting layer 24 containing resin that is provided on and in contact with the support body 10, and a plurality of ultrasonic elements 12 that are provided on the sound-reflecting layer 24. The support body 10 and the ultrasonic elements 12 in the ultrasonic device 120 are similar to the support body 10 and the ultrasonic elements 12 in the ultrasonic device 100, and therefore a description thereof will be omitted.

[0121] The ultrasonic device 120 includes an acoustic matching layer 20 within the ultrasonic element 12, allowing ultrasonic waves generated from the piezoelectric element 16 to propagate through the air while maintaining their intensity and waveform. Furthermore, the ultrasonic device 120 includes an acoustic reflection layer 24, allowing ultrasonic waves generated from the piezoelectric element 16 and emitted toward the support 10 to be reflected by the acoustic reflection layer 24, making it easier to obtain the intensity of the ultrasonic waves propagating through the air. The ultrasonic device 120 may include an acoustic attenuation layer instead of or in addition to the acoustic reflection layer 24. When the ultrasonic device 120 further includes an acoustic attenuation layer in addition to the acoustic reflection layer 24, the acoustic attenuation layer may be provided on the support 10 side or on the ultrasonic element 12 side relative to the acoustic reflection layer 24. Similar to the ultrasonic device 100, the ultrasonic device 120 may or may not include other layers, such as a cover layer, on the acoustic matching layer 20 of the ultrasonic element 12. If a cover layer is included, another acoustic matching layer may also be provided on the surface of the cover layer opposite the surface on which the acoustic matching layer 20 is disposed. The details of the sound wave reflecting layer 24 in the ultrasonic device 120 are similar to those of the sound wave reflecting layer provided as needed in the ultrasonic element described above, and therefore will not be described here.

[0122] <Applications> The ultrasonic device of the present disclosure is used for an aerial haptic device. The aerial haptic device of the present disclosure is not particularly limited as long as it includes at least the ultrasonic device of the present disclosure. The ultrasonic device according to the above-described embodiment emits ultrasonic waves into the air while maintaining their intensity and waveform from each ultrasonic element, and is capable of generating high acoustic radiation pressure at a targeted position. Furthermore, the ultrasonic device can be miniaturized, making it particularly applicable as a component of a small aerial haptic device. Examples of small aerial haptic devices include wearable devices such as VR (Virtual Reality) glasses, AR (Augmented Reality) glasses, and hearable devices, as well as MR (Mixed Reality) glasses.

[0123] Hereinafter, embodiments of the present disclosure will be described in detail with reference to examples, but the embodiments of the present disclosure are not limited to these.

[0124] Example 1 Using simulation software (manufactured by COMSOL, product name: COMSOL Multiphysics), the following simulation conditions were set, and the sound pressure level of the ultrasound generated from the ultrasonic element in Example 1 was determined. The result was 112.2 dB at a distance of 30 mm from the base of the ultrasonic element. -Simulation conditions- Layer configuration: piezoelectric element, metal plate, and acoustic matching layer Specific thickness: 1.00 mm Shape of the acoustic matching layer on the radiation surface: curved and convex Maximum thickness of the acoustic matching layer: 400 μm Minimum thickness of the acoustic matching layer: 200 μm Maximum diameter of the entire ultrasonic element: 8000 μm Metal plate: (material: iron, maximum thickness: 400 μm, density 7.87 g / cm ３ , elastic modulus 200 GPa, Poisson's ratio 0.29) Piezoelectric element: Piezoelectric ceramics (material: Lead Zirconate Titanate (PZT-5H)), maximum thickness: 200 μm, acoustic impedance: 30 MRayls, center frequency: 40 kHz, maximum diameter in the surface direction: 6.3 mm) Acoustic impedance of acoustic matching layer: 0.500 MRayls Sound velocity of acoustic matching layer: 500 m / s Density of acoustic matching layer: 1.0 g / cm ３ Elastic modulus of acoustic matching layer at 20°C: 0.0025 GPa

[0125] Example 2 The sound pressure level of the ultrasonic waves generated from the ultrasonic element in Example 2 was determined in the same manner as in Example 1, except that the shape of the radiation surface of the acoustic matching layer was curved and concave (maximum thickness: 600 μm, minimum thickness: 200 μm) among the simulation conditions in Example 1. The result was 109.8 dB at a distance of 30 mm from the ultrasonic element base.

[0126] Example 3 The sound pressure level of the ultrasonic waves generated from the ultrasonic element in Example 3 was determined in the same manner as in Example 1, except that, among the simulation conditions in Example 1, the shape of the radiation surface of the acoustic matching layer was set to be flat and the thickness was set to be uniform (maximum thickness and minimum thickness: 600 μm). The result was 97.9 dB at a distance of 30 mm from the ultrasonic element base.

[0127] <Comparative Example 1> The sound pressure level of the ultrasonic waves generated from the ultrasonic element in Comparative Example 1 was determined in the same manner as in Example 1, except that the layer configuration consisted of only a piezoelectric element and a metal plate among the simulation conditions in Example 1. The result was 80.8 dB at a distance of 30 mm from the ultrasonic element base.

[0128] <Reference Example 1> Of the simulation conditions in Example 1, except that the layer configuration was changed to a piezoelectric element, a metal plate, and a resonator (material: aluminum, shape: funnel-shaped, maximum height: 1.0 mm), the sound pressure level of the ultrasound generated from the ultrasonic element in Reference Example 1 was determined in the same manner as in Example 1. The result was 113.9 dB at a distance of 30 mm from the ultrasonic element base.

[0129] All publications, patent applications, and technical standards mentioned in this specification are incorporated herein by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0130] 10 Support 12 Ultrasonic element 16 Piezoelectric element 16A, 20A, 22A Surface 20, 22 Acoustic matching layer 24 Sound wave reflecting layer 26 Sound wave attenuation layer 28 Metal plate 100, 120, 130 Ultrasonic device 200, 200A, 200B, 200C, 200D, 200E, 200F, 210, 220, 230 Ultrasonic element

[0131] 500: Air haptic device 502: Printed circuit board 510: Ultrasonic element 512: Connection part 520: Ultrasonic wave generating part 522: Metal plate 524: Piezoelectric ceramics 526: Resonator 528: Housing 528A: Sound emission hole

Claims

1. An ultrasonic element comprising: a piezoelectric element that generates ultrasonic waves of 20 kHz to 100 kHz; and an acoustic matching layer containing a resin that is provided on the piezoelectric element, wherein the maximum thickness from the surface of the piezoelectric element opposite the surface on which the acoustic matching layer is disposed to the surface of the acoustic matching layer opposite the surface on which the piezoelectric element is disposed is 1.5 mm or less.

2. The ultrasonic element according to claim 1, wherein the difference between the maximum thickness and the minimum thickness of said acoustic matching layer is 1 μm or more.

3. The ultrasonic element according to claim 1, wherein the surface of the acoustic matching layer opposite to the surface on which the piezoelectric element is disposed is a curved surface.

4. The ultrasonic element according to claim 1, wherein the surface of said acoustic matching layer opposite to the surface on which said piezoelectric element is arranged is convex.

5. The ultrasonic element according to claim 1, wherein the surface of said acoustic matching layer opposite to the surface on which said piezoelectric element is disposed is concave.

6. The ultrasonic element according to claim 1, wherein the maximum diameter of the entire ultrasonic element is 8 mm or less when viewed in a plane.

7. The ultrasonic element according to claim 1, wherein the acoustic matching layer is provided in contact with the piezoelectric element.

8. The ultrasonic element according to claim 1, further comprising a metal plate between the piezoelectric element and the acoustic matching layer.

9. The ultrasonic element according to claim 1, further comprising at least one of an acoustic reflection layer containing a resin and an acoustic attenuation layer containing a resin on the side of the piezoelectric element opposite to the side on which the acoustic matching layer is disposed.

10. An ultrasonic device comprising: a support; and a plurality of ultrasonic elements according to any one of claims 1 to 9 provided on the support and arranged two-dimensionally.

11. The ultrasonic device according to claim 10, which is for use as an airborne haptic device.

12. An air haptic device comprising the ultrasonic device according to claim 11.

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