JP7459736B2 - Piezoelectric Devices - Google Patents

Description

The present invention relates to a piezoelectric device.

Conventionally, there is known an ultrasound diagnostic device that includes an ultrasound probe that transmits ultrasound to an object to be examined and receives ultrasound reflected from within the object to be examined, and that forms an image from the ultrasound received by the ultrasound probe.

In an ultrasonic probe, the transmission efficiency of ultrasonic waves between the object and the object to be inspected is usually increased by increasing the adhesion to the object to be inspected. Therefore, it is conceivable to design the contact surface of the ultrasonic probe that comes into contact with the object to be inspected so as to match the surface shape of the object to be inspected, thereby increasing the adhesion to the object to be inspected. However, if an ultrasonic probe is designed to match the surface shape of a specific object to be inspected, the versatility of the ultrasonic probe will be reduced. Not suitable for human body, etc.).

The following Patent Documents 1 and 2 disclose a sheet-shaped ultrasonic probe in which a piezoelectric layer is embedded in an elastic body. With such an ultrasonic probe, the elastic body undergoes elastic deformation, allowing the contact surface of the ultrasonic probe to follow the surface shape of the test object to a certain extent, and the probe can be applied to test objects whose surface shape changes over time.

Patent No. 6139136 US Patent Application Publication No. 2019/0328354

In the piezoelectric device according to the prior art described above, when the elastic body of the ultrasonic probe is deformed to follow the surface shape of the object to be inspected, the piezoelectric layer within the elastic body undergoes bending deformation, and as a result, the ultrasonic The irradiation area changes.

An object of the present invention is to provide a piezoelectric device in which bending deformation of a piezoelectric layer is suppressed.

を満たす。 A piezoelectric device according to one aspect of the present invention is a piezoelectric device that transmits ultrasonic waves to an object to be inspected and receives ultrasonic waves reflected at the object to be inspected, and has an opposing surface facing the object to be inspected. a piezoelectric layer provided inside the elastic element that extends parallel to the opposing surface and expands and contracts in the thickness direction; and a piezoelectric layer laminated on the side opposite to the opposing surface. The thickness of the piezoelectric layer and the retention layer are T ₁ and T ₂ , respectively, and the tensile modulus of the elastic element, the piezoelectric layer, and the retention layer are E ₀ and E , respectively. ₁ and E ₂ , the following formula (1)

satisfy.

The inventors discovered that a piezoelectric device that satisfies formula (1) can significantly suppress bending deformation of the piezoelectric layer.

In a piezoelectric device according to another embodiment, the laminate further includes an acoustic matching layer laminated on the piezoelectric layer on the opposing surface side.

In a piezoelectric device according to another embodiment, the elastic body has a tensile modulus E ₀ of 0.5 to 1000 MPa, the piezoelectric layer has a tensile modulus E ₁ of 0.1 to 10 GPa, and the support layer has a tensile modulus E ₂ of 2 to 82.7 GPa.

In another embodiment of the piezoelectric device, the piezoelectric layer is made of a material containing a polymer with an electromechanical coupling coefficient of 0.1 or more.

In another embodiment of the piezoelectric device, the piezoelectric layer is made of a material containing polyvinylidene fluoride.

In a piezoelectric device according to another embodiment, the piezoelectric layer is made of a material containing at least one of lead zirconate titanate, barium titanate, lithium niobate, and aluminum nitride.

According to the present invention, a piezoelectric device in which bending deformation of a piezoelectric layer is suppressed is provided.

FIG. 1 is a schematic cross-sectional view of a piezoelectric device according to an embodiment. FIG. 2 is a diagram showing a situation when bending deformation occurs in the piezoelectric layer. FIG. 3 is a schematic cross-sectional view showing a piezoelectric device of a different type. FIG. 4 is a schematic cross-sectional view showing a piezoelectric device of a different type. FIG. 5 is a schematic cross-sectional view showing different types of piezoelectric devices. FIG. 6 is a schematic cross-sectional view showing different types of piezoelectric devices. FIG. 7 is a schematic cross-sectional view showing a piezoelectric device of a different type. FIG. 8 is a schematic cross-sectional view showing different types of piezoelectric devices. FIG. 9 is a schematic cross-sectional view showing different types of piezoelectric devices. FIG. 10 is a schematic cross-sectional view showing a piezoelectric device of a different type. FIG. 11 is a table showing samples according to the embodiment. FIG. 12 is a table showing samples according to comparative examples.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals will be used for the same elements or elements having the same function, and redundant description will be omitted.

As shown in FIG. 1, the piezoelectric device 10 includes an elastic body 20 and a laminate 30 provided inside the elastic body 20. The piezoelectric device 10 according to the embodiment is an ultrasound probe used in an ultrasound diagnostic apparatus. The piezoelectric device 10 transmits ultrasonic waves to the object to be inspected 1 and receives ultrasonic waves reflected within the object to be inspected 1 .

The elastic body 20 has a sheet-like outer shape, and has a contact surface 20a (opposing surface) that contacts the inspection object 1, and an upper surface 20b located opposite to the contact surface 20a. The contact surface 20a is an opposing surface facing the object 1 to be inspected, and directly (or indirectly) contacts the surface of the object 1 to be inspected. The elastic body 20 is made of, for example, polyester, silicone rubber, or the like. The elastic body 20 can be obtained, for example, by molding. The constituent material of the elastic body 20 has a tensile modulus (E ₀ ) of 0.5 to 1000 MPa. In this embodiment, the elastic body 20 has a rectangular shape in plan view.

The laminate 30 is composed of a piezoelectric layer 32, a retaining layer 34, and an acoustic matching layer 36. The layers 32, 34, and 36 of the laminate 30 are stacked along the thickness direction of the piezoelectric device 10 (the vertical direction in FIG. 1). The layers 32, 34, and 36 of the laminate 30 are formed, for example, by coating or lamination. The entire surface of the laminate 30, including the top and bottom surfaces, is covered by the elastic element 20.

The piezoelectric layer 32 is made of a piezoelectric material such as an organic piezoelectric material or a piezoelectric ceramic. The organic piezoelectric material constituting the piezoelectric layer 32 is preferably a material containing a polymer having an electromechanical coupling coefficient of 0.1 or more, for example, polyvinylidene fluoride (PVDF). The piezoelectric ceramic constituting the piezoelectric layer 32 is made of a material containing at least one of lead zirconate titanate, barium titanate, lithium niobate, and aluminum nitride. The material constituting the piezoelectric layer 32 has a tensile modulus (E ₁ ) of 3 to 10 GPa. In this embodiment, the piezoelectric layer 32 has a rectangular shape of 10 mm x 10 mm in a plan view and extends parallel to the contact surface 20a of the elastic body 20. The piezoelectric layer 32 has a substantially uniform thickness, and the thickness (T ₁ ) is, for example, 10 to 5000 μm (100 μm as an example). A pair of electrode layers (not shown) are provided on the upper and lower sides of the piezoelectric layer 32, and when a pulse voltage is repeatedly applied between the pair of electrode layers, the piezoelectric layer 32 oscillates so as to repeatedly expand and contract in its thickness direction, thereby outputting ultrasonic waves.

The retaining layer 34 is a layer that retains the piezoelectric layer 32, and is laminated on the upper side of the piezoelectric layer 32 (i.e., the side opposite the contact surface 20a). The retaining layer 34 is made of, for example, a resin material such as polyamide resin or methacrylic resin, or solder. The material that constitutes the retaining layer 34 has a tensile modulus (E ₂ ) of 2 to 82.7 GPa. In this embodiment, the retaining layer 34 has the same shape (i.e., rectangular) and dimensions as the piezoelectric layer 32 in a plan view. The retaining layer 34 has a substantially uniform thickness, and the thickness (T ₂ ) is, for example, 10 to 20,000 μm (360 μm as an example).

The acoustic matching layer 36 is a layer for increasing the incidence efficiency of ultrasonic waves into the inspection object 1, and is laminated on the lower side of the piezoelectric layer 32 (that is, on the contact surface 20a side). The acoustic matching layer 36 is made of a resin material such as polystyrene. In this embodiment, the acoustic matching layer 36 has the same shape (ie, rectangular shape) and the same dimensions as the piezoelectric layer 32 in plan view. The acoustic matching layer 36 has a substantially uniform thickness, and the thickness (T ₃ ) is, for example, 2 to 1000 μm (20 μm as an example).

The inventors have found that the piezoelectric device 10 that satisfies the following formula (1) can significantly suppress bending deformation of the piezoelectric layer 32. It is believed that in the piezoelectric device 10, the retention layer 34 contributes to suppressing bending deformation of the piezoelectric layer 32.

Figure 2 shows the state when bending deformation occurs in the piezoelectric layer 32. As shown in Figure 2, when the surface of the test object 1 is curved so as to protrude toward the piezoelectric device 10, the elastic body 20 elastically deforms to follow the surface shape of the test object 1. At this time, bending deformation occurs in the piezoelectric layer 32 provided inside the elastic body 20 so as to protrude from the contact surface 20a side toward the upper surface 20b side of the elastic body 20.

When bending deformation occurs in the piezoelectric layer 32 as shown in FIG. ), as a result, the inspection area becomes narrower.

Conversely, if bending deformation (opposite to the bending deformation shown in FIG. 2) occurs in the piezoelectric layer 32 such that it protrudes from the upper surface 20b side of the elastic body 20 toward the contact surface 20a side, the irradiation area A of the ultrasonic waves emitted from the piezoelectric layer 32 diverges (i.e., gradually expands toward the inside of the object to be inspected 1), and as a result, the piezoelectric layer 32 is no longer able to receive the ultrasonic waves reflected within the object to be inspected 1.

In the piezoelectric device 10 described above, bending deformation of the piezoelectric layer 32 is suppressed, thereby suppressing convergence and divergence of ultrasonic waves, allowing for proper transmission and reception of ultrasonic waves.

The piezoelectric device 10 can take various forms as long as the above formula (1) is satisfied. Modifications of the piezoelectric device 10 are shown in FIGS. 3 to 10.

The piezoelectric device 10A shown in FIG. 3 differs from the piezoelectric device 10 in that it does not include the acoustic matching layer 36. That is, the piezoelectric device can omit the acoustic matching layer if necessary.

The piezoelectric device 10B shown in Fig. 4 differs from the piezoelectric device 10 in that the width _W2 of the retention layer ₃₄ is narrower than the width W1 of the piezoelectric layer 32. The piezoelectric device 10C shown in Fig. 5 differs from the piezoelectric device 10B in that the retention layer 34 is further thinned.

The piezoelectric device 10D shown in FIG. 6 differs from the piezoelectric device 10 only in that the width _W2 of the retention layer ₃₄ is wider than the width W1 of the piezoelectric layer 32. The piezoelectric device 10E shown in FIG. 7 differs from the piezoelectric device 10 only in that the width W ₃ of the acoustic matching layer 36 is wider than the width W ₁ of the piezoelectric layer 32 . The piezoelectric device 10F shown in FIG. 8 differs from the piezoelectric device 10 only in that the width W ₂ of the retention layer ₃₄ and the width W ₃ of the acoustic matching layer 36 are wider than the width W 1 of the piezoelectric layer 32. In the piezoelectric device 10F, the width W ₂ of the holding layer 34 and the width W ₃ of the acoustic matching layer 36 may be the same or different. The piezoelectric device 10G shown in FIG. 9 differs from the piezoelectric device 10 in that the width _W2 of the holding layer 34 is narrower than the width _W1 of the piezoelectric layer 32, and the width _W3 of the acoustic matching layer 36 is wider. It's different.

The piezoelectric device 10H shown in FIG. 10 differs from the piezoelectric device 10 in that the laminate 30 is biased toward the top surface 20b. In the piezoelectric device 10H, the distance between the laminate 30 and the contact surface 20a is longer than the distance between the laminate 30 and the top surface 20b. From the perspective of suppressing attenuation of ultrasonic waves, it is preferable that the distance d between the laminate 30 and the contact surface 20a (i.e., the thickness of the elastic body 20 on the contact surface 20a side of the laminate 30) is short. The distance d between the laminate 30 and the contact surface 20a is, for example, 10 to 2000 μm.

The inventors conducted an experiment to confirm the effects of the respective thicknesses of the piezoelectric layer and the retention layer, and the tensile modulus of each of the elastic body, the piezoelectric layer, and the retention layer on the bending deformation of the piezoelectric layer. . Specifically, the radius of curvature was determined for each of a plurality of samples having the same configuration as the piezoelectric device 10 (or piezoelectric device 10A) described above, but each layer having different constituent materials and film thicknesses. The constituent materials and film thicknesses of each sample are as shown in FIGS. 11 and 12. Note that the film thickness of the elastic body in this example corresponds to the above-mentioned separation distance d (separation distance between the laminate and the contact surface). In addition, the dimensions of each sample in plan view were 10 mm x 10 mm for the piezoelectric layer and 20 mm x 20 mm for the elastic body.

(Examples 1 to 11)
Each sample according to Examples 1 to 11 includes a piezoelectric layer made of polyvinylidene fluoride (1) (PVDF1 in the table of FIG. 11). Polyvinylidene fluoride (1) according to Examples 1 to 11 has a tensile modulus of 2.1 GPa.

Each sample in Examples 1 to 4 includes an acoustic matching layer, an elastic element, and a retaining layer in addition to a piezoelectric layer. In the samples in Examples 1 to 4, the acoustic matching layer, the elastic element, and the retaining layer are all made of the same material, with the acoustic matching layer being made of polystyrene (tensile modulus of elasticity 2.7 GPa), the elastic element being made of polyester, and the retaining layer being made of polyamide. The polyester in Examples 1 to 4 is polyester (model number: Hi-Trail 3046) manufactured by Toray DuPont Co., Ltd., and has a tensile modulus of elasticity of 0.019 GPa. The polyamide in Examples 1 to 4 is polyamide (model number: RUN35-C25) manufactured by Unitika Ltd., and has a tensile modulus of elasticity of 18.4 GPa.

In the samples according to Examples 1 to 4, the piezoelectric layer, acoustic matching layer, elastic body, and retention layer have different thicknesses. That is, the film thicknesses of the piezoelectric layer, acoustic matching layer, elastic body, and retention layer according to Example 1 are 42 μm, 10 μm, 20 μm, and 125 μm, respectively. The film thicknesses of the piezoelectric layer, acoustic matching layer, elastic body, and retention layer according to Example 2 are 100 μm, 25 μm, 50 μm, and 375 μm, respectively. The film thicknesses of the piezoelectric layer, acoustic matching layer, elastic body, and retention layer according to Example 3 are 400 μm, 250 μm, 400 μm, and 400 μm, respectively. The film thicknesses of the piezoelectric layer, acoustic matching layer, elastic body, and retention layer according to Example 4 are 2000 μm, 1250 μm, 1000 μm, and 1000 μm, respectively.

The sample of Example 5 includes an elastic body and a retaining layer in addition to a piezoelectric layer. The sample of Example 5 has the same configuration as the sample of Example 3, except that it does not include an acoustic matching layer.

Each sample according to Examples 6 to 8 includes an acoustic matching layer, an elastic body, and a retention layer in addition to the piezoelectric layer. In the samples according to Examples 6 to 8, the acoustic matching layer and the retention layer are both made of the same material, the acoustic matching layer is made of polystyrene (tensile modulus 2.7 GPa), and the retention layer is made of polyamide ( It has a tensile modulus of elasticity of 18.4 GPa). In the samples according to Examples 6 to 8, the thickness of the acoustic matching layer was 25 μm, and the thickness of the holding layer was 500 μm.

In the samples according to Examples 6 to 8, the film thicknesses of the elastic bodies were the same (50 μm), and the constituent materials of the elastic bodies were different. In the sample according to Example 6, the elastic body is made of polyamide elastomer. The polyamide elastomer according to Example 6 is a polyamide elastomer manufactured by Daicel (model number: E40-S1), and its tensile modulus is 80 MPa. In the sample according to Example 7, the elastic body was made of polyimide silicone. The polyimide silicone according to Example 7 is a polyimide silicone manufactured by Shin-Etsu Chemical Co., Ltd. (model number: SMP-7004), and its tensile modulus is 160 MPa. In the sample according to Example 8, the elastic body was made of polyolefin. The polyolefin according to Example 8 is a polyolefin manufactured by Sumitomo Chemical Co., Ltd. (model number: S131), and its tensile modulus is 650 MPa.

Each sample according to Examples 9 to 11 includes an acoustic matching layer, an elastic body, and a retention layer in addition to the piezoelectric layer. In the samples according to Examples 9 to 11, the acoustic matching layer and the elastic body were both made of the same material, the acoustic matching layer was made of polystyrene (tensile modulus of elasticity 2.7 GPa), and the elastic body was made of polystyrene (tensile modulus of elasticity 2.7 GPa). It is made of polyester (tensile modulus 0.019 GPa). In the samples according to Examples 9 to 11, the thickness of the acoustic matching layer was 25 μm, and the thickness of the elastic body was 50 μm.

In the samples according to Examples 9 to 11, the retention layers were different from each other. In the sample according to Example 9, the holding layer is made of methacrylic resin and has a thickness of 400 μm. The methacrylic resin according to Example 9 is a methacrylic resin (model number: Deglass A) manufactured by Asahi Kasei Group, and its tensile modulus is 3.2 GPa. In the sample according to Example 10, the holding layer is made of epoxy resin and has a thickness of 400 μm. The epoxy resin according to Example 10 is an epoxy resin manufactured by Cemedine (model number: EP811), and its tensile modulus is 6.6 GPa. In the sample according to Example 11, the holding layer is made of solder and has a thickness of 100 μm. The solder according to Example 11 is a solder manufactured by Harima Kasei Co., Ltd. (model number: PS48BR-600-LSP), and its tensile modulus is 51 GPa.

(Examples 12 to 15)
The samples according to Examples 12 to 15 each include an acoustic matching layer, an elastic element, and a retaining layer in addition to a piezoelectric layer. The piezoelectric layers according to Examples 12 to 15 are different from each other and from the piezoelectric layers according to Examples 1 to 11.

In the sample of Example 12, the piezoelectric layer is made of polyvinylidene fluoride (2) (PVDF2 in the table of FIG. 11). The polyvinylidene fluoride (2) of Example 12 has a tensile modulus of elasticity of 0.38 GPa. The thickness of the piezoelectric layer of Example 12 is 100 μm. In the sample of Example 12, the acoustic matching layer is made of polystyrene (tensile modulus of elasticity 2.7 GPa) and has a thickness of 20 μm. In the sample of Example 12, the elastic element is made of polyester (tensile modulus of elasticity 0.019 GPa) and has a thickness of 50 μm. In the sample of Example 12, the retention layer is made of polyamide (tensile modulus of elasticity 18.4 GPa) and has a thickness of 200 μm.

In the sample according to Example 13, the piezoelectric layer is made of a material containing ceramics. The ceramic according to Example 13 is composed of a mixture of polyvinylidene fluoride (1) and lead zirconate titanate (tensile modulus of 3.5 GPa), and the content of lead zirconate titanate is 58 wt%. . The thickness of the piezoelectric layer according to Example 13 is 150 μm. In the sample according to Example 13, the acoustic matching layer is made of polystyrene (tensile modulus of 2.7 GPa) and has a film thickness of 40 μm. In the sample according to Example 13, the elastic body is made of polyimide silicone (tensile modulus of 0.16 GPa), and its film thickness is 50 μm. In the sample according to Example 13, the holding layer is made of polyamide (tensile modulus of 18.4 GPa) and has a film thickness of 300 μm.

In the sample according to Example 14, the piezoelectric layer is made of a material containing ceramics. The ceramic according to Example 14 is composed of a mixture of polyvinylidene fluoride (1) and barium titanate (tensile modulus of 3.0 GPa), and the content of barium titanate is 10 wt%. The thickness of the piezoelectric layer according to Example 14 is 65 μm. In the sample according to Example 14, the acoustic matching layer is made of polystyrene (tensile modulus of 2.7 GPa) and has a thickness of 16 μm. In the sample according to Example 14, the elastic element was made of polyimide silicone (tensile modulus of 0.16 GPa), and its film thickness was 100 μm. In the sample according to Example 14, the holding layer is made of epoxy resin (tensile modulus of 6.6 GPa) and has a thickness of 300 μm.

In the sample according to Example 15, the piezoelectric layer is made of a material containing ceramics. The ceramic according to Example 15 is made of a mixture of an epoxy resin and lead zirconate titanate (tensile modulus of elasticity 11 GPa), and the content of lead zirconate titanate is 69 wt%. The thickness of the piezoelectric layer according to Example 15 is 100 μm. In the sample according to Example 15, the acoustic matching layer is made of polystyrene (tensile modulus of 2.7 GPa) and has a film thickness of 25 μm. In the sample according to Example 15, the elastic body is made of polyimide silicone (tensile modulus of 0.16 GPa), and its film thickness is 100 μm. In the sample according to Example 15, the holding layer is made of epoxy resin (tensile modulus of 6.6 GPa) and has a film thickness of 500 μm.

(Comparative Examples 1 to 3)
Each of the samples according to Comparative Examples 1 to 3 includes a piezoelectric layer made of polyvinylidene fluoride (1), similar to Examples 1 to 11. The thickness of the piezoelectric layer in each of Comparative Examples 1 to 3 is 100 μm. Each of the samples according to Comparative Examples 1 to 3 includes an acoustic matching layer, an elastic element, and a retaining layer in addition to the piezoelectric layer. The acoustic matching layer in each of Comparative Examples 1 to 3 is made of polystyrene (tensile modulus of elasticity: 2.7 GPa), and has a thickness of 25 μm.

The elastic element of Comparative Example 1 is made of the same polyolefin (tensile modulus 0.65 GPa) as the constituent material of the elastic element of Example 8, and has a film thickness of 50 μm. The retaining layer of Comparative Example 1 is made of the same polyamide (tensile modulus 18.4 GPa) as the constituent material of the retaining layers of Examples 1 to 8, and has a film thickness of 100 μm. The sample of Comparative Example 1 differs from the sample of Example 8 only in the film thickness of the retaining layer.

The elastic body according to Comparative Example 2 is made of silicone rubber, and has a film thickness of 50 μm. The silicone rubber according to Comparative Example 2 is a silicone rubber manufactured by Shin-Etsu Chemical Co., Ltd. (model number: KER-4301), and its tensile modulus is 2.5 GPa. The retaining layer according to Comparative Example 2 is made of the same polyamide (tensile modulus of elasticity 18.4 GPa) as the constituent material of the retaining layers according to Examples 1 to 8, 12, and 13, and its film thickness is 125 μm. The sample according to Comparative Example 2 differs from the samples according to Examples 6 to 8 only in the constituent material of the elastic body and the thickness of the retention layer.

The elastic body according to Comparative Example 3 is made of polyester (tensile modulus: 0.019 GPa), and has a film thickness of 50 μm. The holding layer of Comparative Example 3 is made of the same methacrylic resin (tensile modulus of elasticity 3.2 GPa) as the constituent material of the holding layer according to Example 9, and its film thickness is 50 μm. The sample according to Comparative Example 3 differs from the sample according to Example 2 only in the constituent material and film thickness of the holding layer.

(Comparative Example 4)
The sample according to Comparative Example 4 has a piezoelectric layer made of a mixture (tensile modulus 3.5 GPa) of polyvinylidene fluoride (1) and lead zirconate titanate, like the sample according to Example 13. The thickness of the piezoelectric layer according to Comparative Example 4 is 150 μm. The sample according to Comparative Example 4 has an acoustic matching layer, an elastic element, and a retaining layer in addition to the piezoelectric layer. The acoustic matching layer according to Comparative Example 4 is made of polystyrene (tensile modulus 2.7 GPa) and has a thickness of 40 μm. The elastic element according to Comparative Example 4 is made of silicone rubber (tensile modulus 2.5 GPa), which is the same material as the elastic element according to Comparative Example 2, and has a thickness of 50 μm. The retaining layer according to Comparative Example 4 is made of polyamide (tensile modulus 18.4 GPa), which is the same material as the retaining layer according to Examples 1 to 8, 12, and 13, and has a thickness of 300 μm. The sample according to Comparative Example 4 differs from the sample according to Example 13 only in the material of the elastic element.

Shape observation of the radius of curvature of the piezoelectric layer from the side direction when each sample according to Examples 1 to 15 and Comparative Examples 1 to 4 described above is attached to an inspection object having a curved surface shape with a radius of curvature of 30 mm. It was determined by Specifically, each specimen was attached to the outer curved surface of a cylindrical object to be inspected, a specimen was encapsulated in epoxy resin, and the central cross section of each specimen was exposed by polishing the specimen. . Then, the exposed center cross section of the sample was observed with an optical microscope to obtain the coordinates of a plurality of feature points on the lower surface of the piezoelectric layer, and the radius of curvature of the piezoelectric layer was obtained from the coordinates of the plurality of feature points.

The radius of curvature of the test object is set to 30 mm, assuming the radius of curvature of a curved surface shape such as the forearm or upper arm. Since the radius of curvature of the forearm or upper arm, where the piezoelectric device (ultrasonic probe in the embodiment) is thought to be attached, is approximately 30 mm, it was thought that the radius of curvature of the test object is appropriate at 30 mm. In addition, if the radius of curvature of the piezoelectric layer is 50 mm or more, the ultrasonic waves emitted from the piezoelectric layer propagate without converging from the attachment surface on which the sample is attached to the outer curved surface of the test object to the surface opposite the attachment surface, making it possible to propagate the ultrasonic waves to a sufficient depth. Therefore, it was determined that deformation of the piezoelectric layer can be suppressed if the radius of curvature of the piezoelectric layer is 50 mm or more.

In the samples according to Examples 1 to 15 satisfying the above formula (1), the radius of curvature of the piezoelectric layer was all 50 mm or more. On the other hand, in the samples according to Comparative Examples 1 to 4 that do not satisfy formula (1), the radius of curvature of the piezoelectric layer was all smaller than 50 mm. From this result, it was found that bending deformation of the piezoelectric layer was significantly suppressed in the piezoelectric device satisfying the formula (1). Further, from a comparison of Examples 6 to 8, it was found that the smaller the tensile modulus of the elastic body, the larger the radius of curvature of the piezoelectric layer (that is, the bending deformation was suppressed). Further, from a comparison of Examples 9 to 11, it was found that the larger the tensile modulus of the retention layer, the larger the radius of curvature of the piezoelectric layer.

The present invention is not limited to the above-described embodiment, but can take various forms. For example, the piezoelectric device is not limited to an ultrasonic probe, but may be, for example, a pressure sensor, etc.

10, 10A to 10H... piezoelectric device, 20... elastic body, 20a... contact surface, 30... laminate, 32... piezoelectric layer, 34... support layer, 36... acoustic matching layer.

Claims (6)

A piezoelectric device that transmits ultrasonic waves to an object to be inspected and receives ultrasonic waves reflected by the object to be inspected,
an elastic body having a facing surface facing the inspection object;
a laminate including a piezoelectric layer provided inside the elastic body, extending parallel to the opposing surface and expanding and contracting in a thickness direction, and a retaining layer laminated on the piezoelectric layer on a side opposite to the opposing surface,
When the thicknesses of the piezoelectric layer and the holding layer are T ₁ and T ₂ , respectively, and the tensile moduli of the elastic body, the piezoelectric layer, and the holding layer are E ₀ , E ₁ , and E ₂ , respectively, the following formula (1) is satisfied:

Meet the piezoelectric device. The piezoelectric device according to claim 1, wherein the laminate further includes an acoustic matching layer laminated on the piezoelectric layer on the opposing surface side. The elastic element has a tensile modulus E ₀ of 0.5 to 1000 MPa, the piezoelectric layer has a tensile modulus E ₁ of 3 to 10 GPa, and the retention layer has a tensile modulus E ₂ of 2 to 82.7 GPa. The piezoelectric device according to claim 1 or 2. The piezoelectric device according to any one of claims 1 to 3, wherein the piezoelectric layer is made of a material containing a polymer having an electromechanical coupling coefficient of 0.1 or more. The piezoelectric device according to claim 4, wherein the piezoelectric layer is made of a material containing polyvinylidene fluoride. 5. The piezoelectric device according to claim 1, wherein the piezoelectric layer is made of a material containing at least one of lead zirconate titanate, barium titanate, lithium niobate, and aluminum nitride.

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