Piezoelectric loudspeaker

Abstract

The present invention relates to a piezoelectric speaker. A piezoelectric speaker (10) has a piezoelectric film (35), a first bonding layer (51), and an intermediate layer (40). The piezoelectric film (35) includes a first electrode (61), a second electrode (62), and a piezoelectric body (30) sandwiched between the first electrode (61) and the second electrode (62). The first bonding layer (51) is an adhesive or cohesive layer. The intermediate layer (40) is disposed between the piezoelectric film (35) and the first bonding layer (51). The entire main surface of both main surfaces of the piezoelectric film (35) vibrates up and down.

Description

[0001] This application is a divisional application of Chinese patent application No. 202310171873.8, filed on November 20, 2018; Chinese patent application No. 202310171873.8 is a divisional application of Chinese patent application No. 201880075004.2, filed on November 20, 2018. Technical Field

[0002] This invention relates to a piezoelectric loudspeaker. Background Technology

[0003] In recent years, piezoelectric loudspeakers (hereinafter sometimes referred to as piezoelectric loudspeakers) have been used in acoustic devices or for noise reduction. Piezoelectric loudspeakers have the advantages of small size and light weight.

[0004] Patent document 1 describes an example of a piezoelectric loudspeaker.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 63-149997

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-122187 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] To ensure sufficient volume, in the piezoelectric loudspeaker of Patent Document 1, the edge of the piezoelectric diaphragm is fixed by a support member, and the piezoelectric diaphragm is kept in a curved shape. However, from the viewpoint of realizing a piezoelectric loudspeaker with fewer restrictions on the installation location, it is preferable that the piezoelectric diaphragm does not need to be curved.

[0011] The object of the present invention is to provide a piezoelectric loudspeaker that exhibits practical acoustic properties even when the piezoelectric diaphragm does not maintain a curved shape.

[0012] means for solving problems

[0013] This invention provides a piezoelectric loudspeaker, wherein the piezoelectric loudspeaker has: A piezoelectric film, the piezoelectric film comprising a first electrode, a second electrode, and a piezoelectric element sandwiched between the first electrode and the second electrode; The first bonding layer with adhesive or gluing properties; and An intermediate layer is disposed between the piezoelectric film and the first bonding layer, and The entire main surface of the two main surfaces of the piezoelectric film vibrates up and down.

[0014] Invention Effects

[0015] For a piezoelectric loudspeaker that vibrates up and down on the entire principal surface of the two principal surfaces of the piezoelectric diaphragm, practical acoustic characteristics can be exhibited even if the piezoelectric diaphragm does not maintain a curved shape. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view of a piezoelectric loudspeaker with its cross-section parallel to the thickness direction.

[0017] Figure 2 This is a top view of the piezoelectric loudspeaker viewed from the side opposite to the first mating surface.

[0018] Figure 3 This diagram illustrates the state in which a piezoelectric loudspeaker is fixed to a support.

[0019] Figure 4A A diagram illustrating the vibration of a piezoelectric film.

[0020] Figure 4B A diagram illustrating the vibration of a piezoelectric film.

[0021] Figure 5 This is a diagram used to illustrate the structure of the sample used for measurement.

[0022] Figure 6 This is a block diagram of the output system.

[0023] Figure 7 This is a block diagram for evaluating the system.

[0024] Figure 8A A table representing the evaluation results of the samples.

[0025] Figure 8B A table representing the evaluation results of the samples.

[0026] Figure 9 A graph showing the relationship between the constraint degree of the intermediate layer and the frequency at which the sound begins to be emitted.

[0027] Figure 10 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 1.

[0028] Figure 11 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 2.

[0029] Figure 12 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 3.

[0030] Figure 13 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 4.

[0031] Figure 14 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 5.

[0032] Figure 15 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 6.

[0033] Figure 16 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 7.

[0034] Figure 17 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 8.

[0035] Figure 18 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 9.

[0036] Figure 19 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 10.

[0037] Figure 20 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 11.

[0038] Figure 21 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 12.

[0039] Figure 22 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 13.

[0040] Figure 23 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 14.

[0041] Figure 24 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 15.

[0042] Figure 25 A graph showing the frequency characteristics of the sound pressure level of the sample in Example 16.

[0043] Figure 26 A graph showing the frequency characteristics of the sound pressure level of the sample in Reference Example 1.

[0044] Figure 27 A graph showing the frequency response of background noise sound pressure levels.

[0045] Figure 28 This is a diagram illustrating the support structure of the piezoelectric film. Detailed Implementation

[0046] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the following are merely illustrative examples of embodiments of the present invention and are not intended to limit the present invention.

[0047] [First Implementation Method]

[0048] use Figure 1 and Figure 2 The piezoelectric loudspeaker according to the first embodiment will be described. The piezoelectric loudspeaker 10 has: a piezoelectric film 35, a first bonding layer 51, an intermediate layer 40, and a second bonding layer 52. The first bonding layer 51, the intermediate layer 40, the second bonding layer 52, and the piezoelectric film 35 are stacked sequentially.

[0049] The piezoelectric film 35 includes a piezoelectric body 30, an electrode 61, and an electrode 62. The piezoelectric film 35 has a film shape.

[0050] The piezoelectric element 30 has a film shape. The piezoelectric element 30 vibrates when a voltage is applied. The piezoelectric element 30 can be a ceramic film, a resin film, etc. Examples of materials for the ceramic film piezoelectric element 30 include: lead zirconate, lead zirconate titanate, lanthanum lead zirconate titanate, barium titanate, Bi layered compounds, tungsten bronze structure compounds, and solid solutions of barium titanate and bismuth ferrite. Examples of materials for the resin film piezoelectric element 30 include: polyvinylidene fluoride, polylactic acid, etc. The material for the resin film piezoelectric element 30 can also be polyolefins such as polyethylene and polypropylene. Furthermore, the piezoelectric element 30 can be a non-porous body or a porous body.

[0051] The thickness of the piezoelectric element 30 can be in the range of 10 μm to 300 μm, or in the range of 30 μm to 110 μm.

[0052] Electrodes 61 and 62 sandwich the piezoelectric body 30 in the middle. Specifically, the piezoelectric body 30 is in contact with electrodes 61 and 62. The first electrode 61 and the second electrode 62 have a film shape. The first electrode 61 and the second electrode 62 are each connected to a lead (not shown). The first electrode 61 and the second electrode 62 can be formed on the piezoelectric body 30 by vapor deposition, electroplating, sputtering, etc. Metal foil can also be used as the first electrode 61 and the second electrode 62. The metal foil can be attached to the piezoelectric body 30 by double-sided tape, adhesive, glue, etc. Metals can be used as materials for the first electrode 61 and the second electrode 62, specifically: gold, platinum, silver, copper, palladium, chromium, molybdenum, iron, tin, aluminum, nickel, etc. Carbon and conductive polymers can also be used as materials for the first electrode 61 and the second electrode 62. Alloys of the above materials can also be used as materials for the first electrode 61 and the second electrode 62. The first electrode 61 and the second electrode 62 can also contain glass components, etc.

[0053] The thicknesses of the first electrode 61 and the second electrode 62 are, for example, in the range of 10 nm to 150 μm, or in the range of 20 nm to 100 μm.

[0054] exist Figure 1 and Figure 2 In the example, the first electrode 61 covers the entire main surface of the piezoelectric body 30. However, the first electrode 61 may also cover only a portion of that main surface of the piezoelectric body 30. The second electrode 62 covers the entire other main surface of the piezoelectric body 30. However, the second electrode 62 may also cover only a portion of that other main surface of the piezoelectric body 30.

[0055] An intermediate layer 40 is disposed between the piezoelectric film 35 and the first bonding layer 51. The intermediate layer 40 can be a layer other than an adhesive layer or a bonding layer, or it can be an adhesive layer or a bonding layer. In this embodiment, the intermediate layer 40 is a porous layer and / or a resin layer. Here, the resin layer is a concept that includes a rubber layer and an elastomer layer; therefore, the intermediate layer 40, which is a resin layer, can also be a rubber layer or an elastomer layer. Examples of intermediate layers 40 that are resin layers include: ethylene propylene rubber layers, butyl rubber layers, nitrile rubber layers, natural rubber layers, styrene-butadiene rubber layers, polysiloxane layers, polyurethane layers, acrylic resin layers, etc. Examples of intermediate layers 40 that are porous layers include foam layers, etc. Specifically, examples of intermediate layers 40 that are both porous layers and resin layers include: ethylene propylene rubber foam layers, butyl rubber foam layers, nitrile rubber foam layers, natural rubber foam layers, styrene-butadiene rubber foam layers, polysiloxane foam layers, polyurethane foam layers, etc. As an intermediate layer 40 that is not a porous layer but a resin layer, examples include acrylic resin layers. As an intermediate layer 40 that is not a resin layer but a porous layer, examples include metal porous layers. Here, a resin layer refers to a layer containing resin, which can contain more than 30% resin, more than 45% resin, more than 60% resin, or more than 80% resin. The same applies to rubber layers, elastomer layers, ethylene propylene rubber layers, butyl rubber layers, nitrile rubber layers, natural rubber layers, styrene-butadiene rubber layers, polysiloxane layers, polyurethane layers, acrylic resin layers, metal layers, resin films, ceramic films, etc. The intermediate layer 40 can also be a blend layer of two or more materials.

[0056] The elastic modulus of the intermediate layer 40 is, for example, 10000 N / m. 2 ~10,000,000 N / m 2 It can also be 20000 N / m 2 ~100000N / m 2 .

[0057] In one example, the pore size of the intermediate layer 40, which is a porous layer, is 0.1 mm to 7.0 mm, or 0.3 mm to 5.0 mm. In another example, the pore size of the intermediate layer 40, which is a porous layer, is, for example, 0.1 mm to 2.5 mm, or 0.2 mm to 1.5 mm, or 0.3 mm to 0.7 mm. The porosity of the intermediate layer 40, which is a porous layer, is, for example, 70% to 99%, or 80% to 99%, or 90% to 95%.

[0058] As the intermediate layer 40 of the foamed body layer, a known foaming material can be used (for example, the foaming material of Patent Document 2 can be used). The intermediate layer 40 of the foamed body layer can have a continuous bubble structure, an independent bubble structure, or a semi-independent / semi-continuous bubble structure. A continuous bubble structure refers to a structure with a continuous bubble rate of 100%. An independent bubble structure refers to a structure with a continuous bubble rate of 0%. A semi-independent / semi-continuous bubble structure refers to a structure with a continuous bubble rate greater than 0% and less than 100%. Here, the continuous bubble rate can be calculated, for example, by conducting an experiment immersing the foamed body layer in water and using the formula: Continuous bubble rate (%) = {(volume of absorbed water) / (volume of bubble portion)} × 100. In a specific example, the "volume of absorbed water" is obtained as follows: the foamed body layer is immersed in water, placed under a reduced pressure of -750 mmHg for 3 minutes, and then the mass of water displaced by the air in the bubbles of the foamed body layer is measured, with the density of the water set to 1.0 g / cm³. 3 Then convert it to volume. The "volume of the bubble portion" is calculated using the formula: Volume of the bubble portion (cm³) 3 The value is calculated as: ) = {(mass of the foam layer) / (apparent density of the foam layer)} - {(mass of the foam layer) / (material density)}. "Material density" refers to the density of the substrate (solid material) that forms the foam layer.

[0059] The foaming ratio (density ratio before and after foaming) of the intermediate layer 40, which is part of the foamed body layer, is, for example, 5 to 40 times, or 10 to 40 times.

[0060] The thickness of the intermediate layer 40 in the uncompressed state is, for example, in the range of 0.1 mm to 30 mm, or in the range of 1 mm to 30 mm, or in the range of 1.5 mm to 30 mm, or in the range of 2 mm to 25 mm. Typically, in the uncompressed state, the intermediate layer 40 is thicker than the piezoelectric film 35. In the uncompressed state, the ratio of the thickness of the intermediate layer 40 to the thickness of the piezoelectric film 35 is, for example, more than 3 times, or more than 10 times, or more than 30 times. In addition, typically, in the uncompressed state, the intermediate layer 40 is thicker than the first bonding layer 51.

[0061] The first bonding layer 51 is an adhesive or glue-like layer. In other words, the first bonding layer 51 is an adhesive layer or bonding layer. The first bonding layer 51 can be adhered to the support. Figure 1 In the example, the first bonding layer 51 is in contact with the intermediate layer 40. The first bonding layer 51 is used to bond the intermediate layer 40 to the support. Specifically, the first bonding layer 51 has a first bonding surface 17 for adhering to the support. Examples of the first bonding layer 51 include double-sided tape having a substrate and adhesive coated on both sides of the substrate. Examples of the substrate for the double-sided tape used as the first bonding layer 51 include non-woven fabrics. Examples of the adhesive for the double-sided tape used as the first bonding layer 51 include adhesives containing acrylic resins. However, the first bonding layer 51 may also be an adhesive layer without a substrate.

[0062] The thickness of the first bonding layer 51 is, for example, 0.01 mm to 1.0 mm, or 0.05 mm to 0.5 mm.

[0063] The second bonding layer 52 is disposed between the intermediate layer 40 and the piezoelectric film 35. In this embodiment, the second bonding layer 52 is an adhesive or glue-like layer. In other words, the second bonding layer 52 is an adhesive layer or bonding layer. The second bonding layer 52 is in contact with the intermediate layer 40 and the piezoelectric film 35. The second bonding layer 52 bonds the intermediate layer 40 and the piezoelectric film 35. As the second bonding layer 52, examples include double-sided tape having a substrate and an adhesive coated on both sides of the substrate. As the substrate of the double-sided tape used as the second bonding layer 52, examples include non-woven fabrics, etc. As the adhesive of the double-sided tape used as the second bonding layer 52, examples include adhesives containing acrylic resins, etc. However, the second bonding layer 52 may also be an adhesive layer without a substrate.

[0064] The thickness of the second bonding layer 52 is, for example, 0.01 mm to 1.0 mm, or 0.05 mm to 0.5 mm.

[0065] In this embodiment, the piezoelectric film 35 is integrated with the layer on one side of the first bonding surface 17 by contacting the second bonding layer 52 with the piezoelectric film 35.

[0066] exist Figure 3 The diagram shows the first mating surface 17 connecting the two parts. Figure 1 The piezoelectric speaker 10 is attached to the support 80. In this state, a voltage is applied to the piezoelectric diaphragm 35 via leads. This causes the piezoelectric diaphragm 35 to vibrate, emitting sound. Figure 3In the example, the support 80 has a flat surface on which the piezoelectric speaker 10 is attached, and the piezoelectric diaphragm 35 is unfolded in a planar shape. This is advantageous from the viewpoint that the sound waves emitted from the piezoelectric diaphragm 35 are close to plane waves. However, if the support 80 has a curved surface, the piezoelectric speaker 10 can also be attached to the curved surface.

[0067] Typically, the area of ​​the surface of the support 80 opposite to the first mating surface 17 is greater than or equal to the area of ​​the first mating surface 17. The area of ​​the surface of the support 80 opposite to the first mating surface 17 is, for example, more than 1.0 times, or more than 1.5 times, or more than 5 times the area of ​​the first mating surface 17. Typically, compared to the intermediate layer 40, the support 80 has greater rigidity (the product of Young's modulus and the moment of inertia of the section), greater Young's modulus, and / or greater thickness. However, the support 80 may also have the same rigidity, Young's modulus, and / or thickness as the intermediate layer 40, or it may have less rigidity, Young's modulus, and / or thickness than the intermediate layer 40. The Young's modulus of the support 80 is, for example, more than 1 GPa, or more than 10 GPa, or more than 50 GPa. There is no particular upper limit to the Young's modulus of the support 80, for example, 1000 GPa. Since various materials can be used as the support 80, it is difficult to specify its thickness range. However, the thickness of the support 80 can be, for example, 0.1 mm or more, 1 mm or more, 10 mm or more, or 50 mm or more. There is no particular upper limit to the thickness of the support 80, for example, 1 mm. Typically, regardless of the piezoelectric speaker 10, the position and / or shape of the support 80 are fixed. Typically, the support 80 is a support designed to be non-bending.

[0068] The piezoelectric speaker 10 fixed on the support 80 can be used as an acoustic speaker or as a noise reduction speaker.

[0069] In the piezoelectric loudspeaker 10, the entire main surface of the two main surfaces of the piezoelectric diaphragm 35 vibrates up and down. Such a piezoelectric loudspeaker 10 can exhibit practical acoustic characteristics even if the piezoelectric diaphragm 35 does not maintain a curved shape.

[0070] In detail, when the first bonding surface 17, which is the main surface of the first bonding layer 51 opposite to the intermediate layer 40, is attached to the support 80, and a voltage is applied between the first electrode 61 and the second electrode 62, the entire main surface of the two main surfaces of the piezoelectric film 35 vibrates up and down. The up and down vibration of the entire main surface means that, based on the position of the main surface when no voltage is applied between the first electrode 61 and the second electrode 62, the main surface vibrates by displacing to one side and the other side in the thickness direction of the piezoelectric film 35.

[0071] It should be noted that "the entire main surface of the two main surfaces of the piezoelectric film 35 vibrates vertically" is a concept that includes not only the complete vibration of the two main surfaces, but also the vibration of substantially all the areas of the two main surfaces. Specifically, "the entire main surface of the two main surfaces of the piezoelectric film 35 vibrates vertically" means that more than 90% of the area of ​​one of the two main surfaces (the supported surface 16) vibrates vertically, and more than 90% of the area of ​​the other main surface vibrates vertically. This can be more than 95% of the area of ​​one surface, or 100% of the area of ​​the other surface.

[0072] The outer edge of one side of the piezoelectric film 35 is formed by a closed profile. Typically, more than 90% of the closed profile vibrates up and down. It is possible for more than 95% of the closed profile to vibrate up and down, or even for 100% of the closed profile to vibrate up and down.

[0073] The outer edge of the other side of the piezoelectric film 35 is formed by a closed profile. Typically, more than 90% of this closed profile vibrates up and down. It is possible for more than 95% of the closed profile to vibrate up and down, or even for 100% of the closed profile to vibrate up and down.

[0074] Typically, when a voltage is applied between the first electrode 61 and the second electrode 62 while the entire first mating surface 17 is attached to the support body 80, the piezoelectric loudspeaker 10 does not have a fixing member (screw, rivet, etc.) that fixes a portion of the piezoelectric film 35 to the support body 80 and makes that portion function as a node for the vibration of the piezoelectric film 35.

[0075] In a non-limiting manner, the entire main surface of the piezoelectric film 35 side of the intermediate layer 40 vibrates up and down. Specifically, when a voltage is applied between the first electrode 61 and the second electrode 62 while the entire first bonding surface 17 is adhered to the support 80, the entire main surface of the piezoelectric film 35 side of the intermediate layer 40 vibrates up and down.

[0076] "The entire main surface of the piezoelectric film 35 on one side of the intermediate layer 40 vibrates up and down" is a concept that includes not only the complete vibration of the main surface, but also the vibration of substantially the entire area of ​​the main surface. Specifically, "the entire main surface of the piezoelectric film 35 on one side of the intermediate layer 40 vibrates up and down" means that more than 90% of the area of ​​the main surface vibrates up and down. It can be more than 95% of the area of ​​the main surface vibrating up and down, or it can be 100% of the area of ​​the main surface vibrating up and down.

[0077] Reference Figure 4A and Figure 4B The vibration of the piezoelectric film 35 is explained. Figure 4A and Figure 4B In this context, the reference position RP represents the position of the supported surface 16 of the piezoelectric film 35 when it is not vibrating. Here, the supported surface 16 refers to the main surface on one side of the intermediate layer 40 of the piezoelectric film 35. Figure 4A and Figure 4B The illustrations of the first bonding layer 51 and the second bonding layer 52 are omitted. In use... Figure 4A and Figure 4B In the description, the thickness direction refers to the thickness direction of the unvibrated piezoelectric film 35, and the in-plane direction refers to the direction orthogonal to its thickness direction.

[0078] Figure 4A This indicates the vibration of the piezoelectric film 35 at a relatively low frequency.

[0079] exist Figure 4A In the example shown, at a certain moment, the piezoelectric film 35 is in the state to the left of the square arrow. In this state, when viewed from the reference position RP in the central region in the in-plane direction, the supported surface 16 of the piezoelectric film 35 is displaced towards the support body 80, and when viewed from the reference position RP in the peripheral region, the supported surface 16 of the piezoelectric film 35 is displaced towards the side opposite to the support body 80. Similarly, the main surface of the piezoelectric film 35 on the side opposite to the supported surface 16 also undergoes displacement, based on the position of this main surface when not vibrating.

[0080] exist Figure 4A In the example shown, at another moment, the piezoelectric film 35 is in the state to the right of the square arrow. In this state, when viewed from the reference position RP in the central region in the in-plane direction, the supported surface 16 of the piezoelectric film 35 is displaced to the side opposite to the support 80, and when viewed from the reference position RP in the peripheral region, the supported surface 16 of the piezoelectric film 35 is displaced towards the support 80. Similarly, displacement also occurs on the main surface of the piezoelectric film 35 on the side opposite to the supported surface 16, based on the position of this main surface when not vibrating.

[0081] Figure 4B This indicates the vibration of the piezoelectric film 35 at a relatively high frequency.

[0082] exist Figure 4BIn the example shown, at a certain moment, the piezoelectric film 35 is in the state to the left of the square arrow. In this state, in the piezoelectric film 35, regarding the in-plane direction, the portions of the supported surface 16 that are displaced to the side opposite to the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 that are displaced to the side of the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 that are displaced to the side opposite to the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 that are displaced to the side of the support body 80 when viewed from the reference position RP, and the portions of the supported surface 16 that are displaced to the side opposite to the support body 80 when viewed from the reference position RP are arranged in sequence. For the main surface of the piezoelectric film 35 on the side opposite to the supported surface 16, displacement also occurs similarly with the position of this main surface when there is no vibration as a reference.

[0083] exist Figure 4B In the example shown, at another moment, the piezoelectric film 35 is in the state to the right of the square arrow. In this state, in the piezoelectric film 35, regarding the in-plane direction, the portions of the supported surface 16 displaced towards the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 displaced towards the opposite side of the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 displaced towards the support body 80 when viewed from the reference position RP, the portions of the supported surface 16 displaced towards the opposite side of the support body 80 when viewed from the reference position RP, and the portions of the supported surface 16 displaced towards the support body 80 when viewed from the reference position RP are arranged in sequence. For the main surface of the piezoelectric film 35 on the side opposite to the supported surface 16, displacement also occurs similarly with the position of this main surface when there is no vibration as a reference.

[0084] exist Figure 4A and Figure 4B In the manner shown, the entire main surface of the piezoelectric film 35 side of the intermediate layer 40 also vibrates in the vertical direction.

[0085] From the viewpoint of maximizing the practical acoustic properties of the piezoelectric diaphragm 35, it is advantageous for the entire main surface of both main surfaces of the piezoelectric diaphragm 35 to vibrate vertically. Furthermore, in this embodiment, an intermediate layer 40 is disposed between the piezoelectric diaphragm 35 and the first bonding layer 51. The presence of the intermediate layer 40 is considered to contribute to maximizing the practical acoustic properties of the piezoelectric diaphragm 35. Hereinafter, the piezoelectric loudspeaker 10 according to this embodiment, including the intermediate layer 40, will be further described.

[0086] In this embodiment, the intermediate layer 40 prevents the low-frequency side of the audible range from being difficult to produce due to the first mating surface 17 of the piezoelectric speaker 10 being adhered to the support 80. Details of its function require further investigation, but it is possible that by appropriately constraining one main surface of the piezoelectric film 35 using the intermediate layer 40, it may be easier to produce low-frequency side of the audible range from the piezoelectric film 35.

[0087] The aforementioned "appropriate constraint" can be considered to be achieved through the appropriately selected constraint degree of the intermediate layer 40. For example, the constraint degree of the intermediate layer 40 is 5 × 10. 8 N / m 3 The following is an example of a 40-degree constraint in the intermediate layer: 1×10. 4 N / m 3 The above. The preferred constraint degree of the intermediate layer 40 is 2×10. 8 N / m 3 Hereinafter, 1×10 is more preferred. 5 N / m 3 ~5×10 7 N / m 3 Here, the constraint degree of the intermediate layer 40 (N / m) 3 The elastic modulus (N / m) of the intermediate layer 40 is shown in the following formula. 2 The value is obtained by dividing the product of the surface filling rate of the piezoelectric film 35 and the surface filling rate of the intermediate layer 40 by the thickness (m) of the intermediate layer 40. The surface filling rate of the intermediate layer 40 is the filling rate of the main surface on one side of the piezoelectric film 35 of the intermediate layer 40 (the value obtained by subtracting the porosity from 1). When the pores of the intermediate layer 40 are uniformly distributed, the surface filling rate can be regarded as equal to the three-dimensional filling rate of the intermediate layer 40.

[0088] Constraint degree (N / m) 3 ) = Elastic modulus (N / m 2 × Surface filling rate ÷ Thickness (m)

[0089] The degree of constraint can be considered a parameter representing the degree of constraint of the piezoelectric film 35 generated by the intermediate layer 40. As shown in the above equation, the greater the elastic modulus of the intermediate layer 40, the greater the degree of constraint. As shown in the above equation, the greater the surface fill rate of the intermediate layer 40, the greater the degree of constraint. As shown in the above equation, the smaller the thickness of the intermediate layer 40, the greater the degree of constraint. The relationship between the degree of constraint of the intermediate layer 40 and the sound generated from the piezoelectric film 35 requires further research. However, if the constraint is too large, it may hinder the deformation of the piezoelectric film 35 required to generate low-frequency sound. Conversely, if the constraint is too small, the piezoelectric film 35 may not deform sufficiently in its thickness direction, but only stretch and contract in its in-plane direction (the direction perpendicular to the thickness direction), thus hindering the generation of low-frequency sound. It can be considered that by setting the degree of constraint of the intermediate layer 40 within an appropriate range, the in-plane stretching and contraction of the piezoelectric film 35 is appropriately converted into deformation in the thickness direction, and the piezoelectric film 35 as a whole is appropriately bent, thereby facilitating the generation of low-frequency sound.

[0090] As can be understood from the above description, a layer different from the intermediate layer 40 may exist between the piezoelectric film 35 and the first bonding surface 17. This different layer is, for example, the second bonding layer 52.

[0091] The support 80 can have a greater degree of constraint than the intermediate layer 40. Even in this case, low-frequency sound can still be generated from the piezoelectric film 35 through the action of the intermediate layer 40. However, the support 80 can also have the same degree of constraint as the intermediate layer 40, or it can have a smaller degree of constraint than the intermediate layer 40. Here, the degree of constraint of the support 80 (N / m) 3 ) is the elastic modulus (N / m) of the support 80. 2 The value is obtained by dividing the product of the piezoelectric film 35 and the surface filling rate of the support 80 by the thickness (m) of the support 80. The surface filling rate of the support 80 is the filling rate of the main surface of the piezoelectric film 35 on one side of the support 80 (the value obtained by subtracting the porosity from 1).

[0092] In the piezoelectric loudspeaker 10 of this embodiment, the intermediate layer 40 and the first bonding layer 51 both support the entire supported surface 16.

[0093] It should be noted that "the intermediate layer 40 and the first bonding layer 51 together support the entire supported surface 16" is a concept that includes not only the case where the intermediate layer 40 and the first bonding layer 51 together support the entire area of ​​the supported surface 16, but also the case where the intermediate layer 40 and the first bonding layer 51 together support substantially the entire area of ​​the supported surface 16. Specifically, "the intermediate layer 40 and the first bonding layer 51 together support the entire supported surface 16" means that the intermediate layer 40 supports more than 90% of the area of ​​the supported surface 16, and the first bonding layer 51 supports more than 90% of the area of ​​the supported surface 16. The intermediate layer 40 can support more than 95% of the area of ​​the supported surface 16, and the intermediate layer 40 can also support 100% of the area of ​​the supported surface 16. The first bonding layer 51 can support more than 95% of the area of ​​the supported surface 16, and the first bonding layer 51 can also support 100% of the area of ​​the supported surface 16.

[0094] The piezoelectric speaker 10 described above can be easily attached to the support 80. Furthermore, the piezoelectric speaker 10 exhibits practical acoustic characteristics when attached to the support 80.

[0095] In this embodiment, when a voltage is applied to the first electrode 61 and the second electrode 62 while the first bonding layer 51 is attached to the support body 80, the intermediate layer 40 and the first bonding layer 51 support the entire supported surface 16 while allowing the piezoelectric film 35 to vibrate.

[0096] In this embodiment, the intermediate layer 40 is bonded to the entire supported surface 16. Specifically, the second bonding layer 52 bonds the entire supported surface 16 to the intermediate layer 40. More specifically, the second bonding layer 52 is in contact with the entire supported surface 16. When a voltage is applied to the first electrode 61 and the second electrode 62 while the first bonding layer 51 is attached to the support 80, the piezoelectric film 35 vibrates while the entire supported surface 16 is bonded to the intermediate layer 40 via the second bonding layer 52.

[0097] The piezoelectric loudspeaker 10 of the present invention can also be described in the following manner: The piezoelectric loudspeaker 10 has: A piezoelectric film 35, the piezoelectric film 35 comprising a first electrode 61, a second electrode 62 and a piezoelectric body 30 sandwiched between the first electrode 61 and the second electrode 62; The first bonding layer 51 is adhesive or glue-like; and An intermediate layer 40 is disposed between the piezoelectric film 35 and the first bonding layer 51, and When the main surface of one side of the intermediate layer 40 of the piezoelectric film 35 is defined as the supported surface 16, The intermediate layer 40 is joined to the entire supported surface 16.

[0098] For such a piezoelectric speaker 10, even if the piezoelectric diaphragm 35 does not maintain a curved shape, it can still exhibit practical acoustic characteristics.

[0099] It should be noted that "intermediate layer 40 engages with the entire supported surface 16" is a concept that includes not only the case where intermediate layer 40 engages with the entire area of ​​supported surface 16, but also the case where intermediate layer 40 engages with substantially the entire area of ​​supported surface 16. Specifically, "intermediate layer 40 engages with the entire supported surface 16" means that intermediate layer 40 engages with more than 90% of the area of ​​supported surface 16. Intermediate layer 40 can engage with more than 95% of the area of ​​supported surface 16, or intermediate layer 40 can engage with 100% of the area of ​​supported surface 16. In the context of "second engagement layer 52 engages the entire supported surface 16 with intermediate layer 40," "the entire supported surface 16" can also be interpreted as more than 90% of the area of ​​supported surface 16, more than 95% of the area of ​​supported surface 16, or 100% of the area of ​​supported surface 16.

[0100] Similarly, "the second bonding layer 52 is in contact with the entire supported surface 16" is a concept that includes not only the case where the second bonding layer 52 is in contact with the entire area of ​​the supported surface 16, but also the case where the second bonding layer 52 is in contact with substantially the entire area of ​​the supported surface 16. Specifically, "the second bonding layer 52 is in contact with the entire supported surface 16" means that the second bonding layer 52 is in contact with more than 90% of the area of ​​the supported surface 16. The second bonding layer 52 may be in contact with more than 95% of the area of ​​the supported surface 16, or the second bonding layer 52 may be in contact with 100% of the area of ​​the supported surface 16.

[0101] As can be understood from the above description, in the piezoelectric loudspeaker 10, when the piezoelectric film 35 is viewed in a top view, the intermediate layer 40 can be disposed in an area covering more than 90% of the area of ​​the piezoelectric film 35, more than 95% of the area of ​​the piezoelectric film 35, or even 100% of the area of ​​the piezoelectric film 35. When the piezoelectric film 35 is viewed in a top view, the first bonding layer 51 can be disposed in an area covering more than 90% of the area of ​​the piezoelectric film 35, more than 95% of the area of ​​the piezoelectric film 35, or even 100% of the area of ​​the piezoelectric film 35. Furthermore, when viewing the piezoelectric film 35 in a top view, the second bonding layer 52 can be disposed in an area covering more than 90% of the area of ​​the piezoelectric film 35, or in an area covering more than 95% of the area of ​​the piezoelectric film 35, or in an area covering 100% of the area of ​​the piezoelectric film 35.

[0102] Here, when the intermediate layer 40 is a porous body, the ratio of the area where the intermediate layer 40 is disposed is defined not from a microscopic point of view considering the pores produced by the porous structure, but from a more macroscopic point of view. For example, when the piezoelectric film 35 and the intermediate layer 40, which is a porous body, are plate-like bodies with a common outline in a top view, it is indicated that the intermediate layer 40 is disposed in an area covering 100% of the area of ​​the piezoelectric film 35.

[0103] The piezoelectric film 35 can form more than 50% of the main surface 15 of the piezoelectric speaker 10 on the side opposite to the first mating surface 17. It can also form more than 75% of the main surface 15, or the entire main surface 15 can be formed by the piezoelectric film 35.

[0104] In this embodiment, layers existing between and adjacent to each other, such as the piezoelectric film 35 and the first bonding surface 17, are bonded together. Here, "between the piezoelectric film 35 and the first bonding surface 17" includes both the piezoelectric film 35 and the first bonding surface 17. Specifically, the first bonding layer 51 is bonded to the intermediate layer 40, the intermediate layer 40 is bonded to the second bonding layer 52, and the second bonding layer 52 is bonded to the piezoelectric film 35. Therefore, regardless of the mounting configuration of the piezoelectric speaker 10 on the support 80, the piezoelectric film 35 can be stably configured, and the piezoelectric speaker 10 can be easily mounted onto the support 80. Furthermore, thanks to the action of the intermediate layer 40, sound can be emitted from the piezoelectric film 35 regardless of the mounting configuration. Therefore, in this embodiment, these layers are combined to realize a convenient piezoelectric speaker 10.

[0105] In this embodiment, the first bonding layer 51 has a uniform thickness. The intermediate layer 40 has a uniform thickness. The piezoelectric film 35 has a uniform thickness. In most cases, this is advantageous from various viewpoints such as the storage of the piezoelectric speaker 10, ease of use, and control of the sound emitted from the piezoelectric film 35. It should be noted that "having a uniform thickness" means, for example, that the minimum thickness is more than 70% and less than 100% of the maximum thickness. The minimum thickness of each of the first bonding layer 51, the intermediate layer 40, and the piezoelectric film 35 can be more than 85% and less than 100% of their respective maximum thicknesses. The minimum thickness of each of the first bonding layer 51, the intermediate layer 40, and the piezoelectric film 35 can be more than 90% and less than 100% of their respective maximum thicknesses. In addition, "having a uniform thickness" means that the thickness is uniform in a non-vibrating state.

[0106] exist Figure 1 In the example shown, the first bonding surface 17 of the first bonding layer 51 is exposed. However, the first bonding surface 17 can be covered by a release layer that can be peeled off from the first bonding surface 17. Typically, the release layer covers 100% of the area of ​​the first bonding surface 17. Examples of release layers include those having a film and a release agent coated on the main surface of the film on one side of the first bonding surface 17. Examples of films that can be used as release layers include paper, resin films, etc. Examples of release agents that can be used as release layers include polymers having long-chain alkyl groups, compounds or polymers containing fluorine atoms, polysiloxane polymers, etc. By attaching the first bonding surface 17 to the support 80 in the state after removing the release layer, the piezoelectric film 35 and the intermediate layer 40 can be fixed to the support 80. Such an attachment operation is less burdensome for the operator.

[0107] Incidentally, compared to ceramics, resin is a material less prone to cracking. In a specific example, the piezoelectric element 30 of the piezoelectric film 35 is a resin film, and the intermediate layer 40 is a resin layer that does not function as a piezoelectric film. This arrangement is advantageous from the viewpoint that cutting the piezoelectric speaker 10 with scissors, hands, etc., will not cause cracks in the piezoelectric element 30 or the intermediate layer 40. Furthermore, with this arrangement, even if the piezoelectric speaker 10 is bent, cracks are less likely to occur in the piezoelectric element 30 or the intermediate layer 40. Additionally, from the viewpoint that fixing the piezoelectric speaker 10 to a curved surface will not cause cracks in the piezoelectric element 30 or the intermediate layer 40, it is advantageous that the piezoelectric element 30 is a resin film and the intermediate layer 40 is a resin layer.

[0108] exist Figure 1 In the example, the piezoelectric film 35, the intermediate layer 40, the first bonding layer 51, and the second bonding layer 52 are rectangles with both short and long sides in the top view. However, they can also be squares, circles, ellipses, etc.

[0109] In addition, piezoelectric loudspeakers may also include, except for Figure 1 Layers other than those shown.

[0110] Example

[0111] The present invention will be described in detail through embodiments. However, the following embodiments illustrate one example of the invention, and the invention is not limited to the following embodiments.

[0112] (Example 1)

[0113] The piezoelectric loudspeaker 10 was manufactured by attaching its first mating surface 17 to a fixed support member, thereby utilizing the aforementioned support member as a... Figure 3The structure of the support 80 is as follows: Specifically, a stainless steel plate (SUS plate) with a thickness of 5 mm is used as the support member. As the first bonding layer 51, an adhesive sheet (double-sided tape) with a thickness of 0.16 mm is used, which is impregnated with acrylic adhesive on both sides of the nonwoven fabric. As the intermediate layer 40, an independent bubble-type foam with a thickness of 3 mm is used, obtained by foaming a mixture containing ethylene propylene rubber and butyl rubber at approximately 10 times the foaming ratio. As the second bonding layer 52, an adhesive sheet (double-sided tape) with a thickness of 0.15 mm is used, which is based on nonwoven fabric and coated on both sides with a solvent-free adhesive containing acrylic resin. As the piezoelectric film 35, a polyvinylidene fluoride film (total thickness of 33 μm) with copper electrodes (containing nickel) deposited on both sides is used. In Embodiment 1, the first bonding layer 51, intermediate layer 40, second bonding layer 52, and piezoelectric film 35 have dimensions of 37.5 mm longitudinally and 37.5 mm laterally in a top view, and have a non-segmented, non-framed plate shape with overlapping contours (as in the embodiments and reference examples described later). The support member 80 has dimensions of 50 mm longitudinally and 50 mm laterally in a top view and completely covers the first bonding layer 51. A structure with... Figure 3 The sample of Example 1 of the structure shown.

[0114] (Example 2)

[0115] As the intermediate layer 40, a semi-independent, semi-continuous bubble-type foam with a thickness of 3 mm was used, obtained by foaming a mixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. This foam is a sulfur-containing foam. In addition, a sample of Example 2 was prepared in the same manner as in Example 1.

[0116] (Example 3)

[0117] In Example 3, a 5 mm thick foam with the same material and structure as the intermediate layer 40 in Example 2 was used as the intermediate layer 40. Otherwise, the sample of Example 3 was prepared in the same manner as in Example 2.

[0118] (Example 4)

[0119] In Example 4, a 10 mm thick foam with the same material and structure as the intermediate layer 40 in Example 2 was used as the intermediate layer 40. Otherwise, the sample of Example 4 was prepared in the same manner as in Example 2.

[0120] (Example 5)

[0121] In Example 5, a 20 mm thick foam with the same material and structure as the intermediate layer 40 in Example 2 was used as the intermediate layer 40. Otherwise, the sample of Example 5 was prepared in the same manner as in Example 2.

[0122] (Example 6)

[0123] As the intermediate layer 40, a semi-independent, semi-continuous bubble-type foam with a thickness of 20 mm was used, obtained by foaming a mixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. This foam is sulfur-free and is softer than the foams used as intermediate layers 40 in Examples 2-5. In addition, a sample of Example 6 was prepared in the same manner as in Example 1.

[0124] (Example 7)

[0125] As the intermediate layer 40, a semi-independent, semi-continuous bubble-type foam with a thickness of 20 mm was used, obtained by foaming a mixture containing ethylene propylene rubber at a foaming ratio of approximately 20 times. In addition, the sample of Example 7 was prepared in the same manner as in Example 1.

[0126] (Example 8)

[0127] As the intermediate layer 40, a porous metal is used. This porous metal is made of nickel, has a pore size of 0.9 mm, and a thickness of 2.0 mm. As the second bonding layer 52, the same adhesive layer as the first bonding layer 51 of Example 1 is used. Otherwise, the sample of Example 8 was prepared in the same manner as in Example 1.

[0128] (Example 9)

[0129] As the intermediate layer 40, a substrate-free adhesive sheet with a thickness of 3 mm made of acrylic adhesive was used. In addition, the sample of Example 9 was prepared in the same manner as in Example 8.

[0130] (Example 10)

[0131] As the intermediate layer 40, a 5 mm thick polyurethane foam was used. Otherwise, the sample of Example 10 was prepared in the same manner as in Example 8.

[0132] (Example 11)

[0133] As the intermediate layer 40, a polyurethane foam with a thickness of 10 mm was used. The pore size of this polyurethane foam was smaller than that of the polyurethane foam used as the intermediate layer 40 in Example 10. Otherwise, a sample of Example 11 was prepared in the same manner as in Example 8.

[0134] (Example 12)

[0135] As the intermediate layer 40, a 5 mm thick, independently bubble-type nitrile rubber foam was used. In addition, the sample of Example 12 was prepared in the same manner as in Example 8.

[0136] (Example 13)

[0137] As the intermediate layer 40, a 5 mm thick, independently bubble-type ethylene propylene rubber foam was used. In addition, the sample of Example 13 was prepared in the same manner as in Example 8.

[0138] (Example 14)

[0139] As the intermediate layer 40, a 5 mm thick, individually bubble-type foam made from a blend of natural rubber and styrene-butadiene rubber was used. In addition, the sample of Example 14 was prepared in the same manner as in Example 8.

[0140] (Example 15)

[0141] As the intermediate layer 40, a 5 mm thick, independently bubble-type polysiloxane foam was used. Otherwise, the sample of Example 15 was prepared in the same manner as in Example 8.

[0142] (Example 16)

[0143] As the intermediate layer 40, a foam with a thickness of 10 mm was used, which had the same material and structure as the intermediate layer 40 in Example 1. As the second bonding layer 52, an adhesive sheet, the same as in Example 1, was used. As the piezoelectric element 30 of the piezoelectric film 35, a resin sheet with a thickness of 35 μm, using polylactic acid derived from corn as the main raw material, was used. The first electrode 61 and the second electrode 62 of the piezoelectric film 35 were each aluminum films with a thickness of 0.1 μm and were formed by vapor deposition. In this way, a piezoelectric film 35 with a total thickness of 35.2 μm was obtained. In addition, the sample of Example 16 was prepared in the same manner as in Example 1.

[0144] (Refer to Example 1)

[0145] The piezoelectric film 35 of Example 1 was used as a sample in Reference Example 1. In Reference Example 1, the sample was placed on a platform parallel to the ground without being glued.

[0146] The evaluation methods for the samples involved in the examples and reference examples are as follows.

[0147] <Thickness of the intermediate layer (uncompressed state)>

[0148] The thickness of the intermediate layer was measured using a thickness gauge.

[0149] <Elastic modulus of the intermediate layer>

[0150] Small pieces were cut from the middle layer. These pieces were then subjected to compression tests at room temperature using a tensile testing machine (TA Instruments "RSA-G2"). This yielded stress-strain curves. The elastic modulus was calculated based on the initial slope of the stress-strain curves.

[0151] <Aperture of the intermediate layer>

[0152] A magnified image of the intermediate layer was obtained using a microscope. The average aperture of the intermediate layer was determined through image analysis of this magnified image. This average aperture was then used as the aperture size of the intermediate layer.

[0153] <Porosity of the intermediate layer>

[0154] Small rectangular pieces are cut from the intermediate layer. The apparent density is calculated based on the volume and mass of the cut pieces. The apparent density is divided by the density of the substrate (solid) forming the intermediate layer. The fill power is then calculated. The fill power is then subtracted from 1. The porosity is thus obtained.

[0155] <Surface fill rate of the intermediate layer>

[0156] For Examples 2-15, the above-mentioned fill rate is used as the surface fill rate. In Examples 1 and 16, since the intermediate layer has a surface layer, the surface fill rate is set to 100%.

[0157] <Frequency characteristics of the sample's sound pressure level>

[0158] exist Figure 5 The diagram shows the structure of the samples used for testing Examples 1-16. Conductive copper foil tape 70 (3M Corporation CU-35C), with a thickness of 70 μm and a length of 5 mm × 70 mm, is attached to the corners of both sides of the piezoelectric film 35. Additionally, wire clips 75 are attached to these conductive copper foil tapes 70. The conductive copper foil tapes 70 and wire clips 75 constitute part of a circuit for applying an alternating current voltage to the piezoelectric film 35.

[0159] The structure of the sample used for measuring Reference Example 1 was modeled after... Figure 5 The structure. Specifically, imitating Figure 5 Conductive copper foil tape 70 is attached to the corners of both sides of the piezoelectric film 35, and wire clips 75 are attached to these conductive copper foil tapes 70. The assembly obtained in this way is placed on a platform parallel to the ground without being glued.

[0160] exist Figure 6 and Figure 7 The diagram shows a block diagram for determining the acoustic properties of a sample. Specifically, Figure 6 The output system is shown. Figure 7 The evaluation system is shown.

[0161] exist Figure 6 In the output system shown, the sound output is sequentially connected to a personal computer (hereinafter sometimes referred to as PC) 401, an audio interface 402, a speaker amplifier 403, and a sample 404 (the piezoelectric speaker in the embodiment and reference example). The speaker amplifier 403 is also connected to an oscilloscope 405 so that the output from the speaker amplifier 403 to the sample 404 can be verified.

[0162] WaveGene is installed in the audio output PC 401. WaveGene is free software for generating test audio signals. The audio interface 402 uses a QUAD-CAPTURE manufactured by Roland Corporation. The sampling frequency of the audio interface 402 is set to 192kHz. The speaker amplifier 403 uses an A-924 manufactured by Onkyo Corporation. The oscilloscope 405 uses a DPO2024 manufactured by Tektronix.

[0163] exist Figure 7 In the evaluation system shown, microphone 501, acoustic evaluation device (PULSE) 502 and acoustic evaluation PC 503 are connected in sequence.

[0164] The microphone 501 used is a Type 4939-C-002 manufactured by B&K Corporation. The microphone 501 is positioned at a distance of 1 m from the sample 404. The acoustic evaluation device 502 used is a Type 3052-A-030 manufactured by B&K Corporation.

[0165] The output system and evaluation system were configured in this manner, and an AC voltage was applied to the sample 404 from the sound output PC 401 via the audio interface 402 and the speaker amplifier 403. Specifically, a test sound signal with a frequency sweep from 100Hz to 100kHz over 20 seconds was generated using the sound output PC 401. The voltage output from the speaker amplifier 403 was then confirmed using an oscilloscope 405. Furthermore, the sound generated from the sample 404 was evaluated using the evaluation system. The sound pressure frequency response measurement test was conducted in this manner.

[0166] The details of the output system and evaluation system settings are as follows.

[0167] [Output System Settings]

[0168] Frequency range: 100Hz~100kHz

[0169] Scan time: 20 seconds

[0170] Effective voltage: 10V

[0171] Output waveform: sine wave

[0172] [Evaluation System Settings]

[0173] Measurement time: 22 seconds

[0174] Peak hold

[0175] Measurement range: 4Hz~102.4kHz

[0176] Line count: 6400

[0177] <Determining the frequency of the initial sound>

[0178] The lower end of the frequency range where the sound pressure level is more than 3dB higher than the background noise (excluding the steep peaks where the sound pressure level is more than 3dB higher than the background noise and does not meet the ±10% of the peak frequency (the frequency at which the sound pressure level reaches its peak) is determined as the frequency at which the sound begins to be emitted.

[0179] exist Figures 8A to 26 The evaluation results of Examples 1-16 and Reference Example 1 are shown in the figure. Figure 27 The frequency response of the background noise sound pressure level is shown in the figure. It should be noted that... Figure 9 In this context, E1 to E16 correspond to Examples 1 to 16.

[0180] Vibration Evaluation

[0181] Furthermore, by using a reference Figure 6 The output system described applies a 10V, 2000Hz voltage to sample 404 of Example 1, causing sample 404 to vibrate. The displacement in the thickness direction of the piezoelectric film 35 of the vibrating sample 404 was measured non-contactly using a laser-based laser Doppler vibrometer (PSV-400) manufactured by Polytec Co., Ltd. The measurement results show that the entire principal surface of both main surfaces of the piezoelectric film 35 vibrates vertically.

[0182] The same measurements were also performed on samples 404 of Examples 2-7. For samples 404 of Examples 2-7, the measurement results also showed that the entire main surface of the two main surfaces of the piezoelectric film 35 vibrated up and down.

[0183] The voltage frequency was changed from 2000Hz to other frequencies within the audible range, and the same measurements were performed on samples 404 of Examples 1-7. In this case, the measurement results also showed that the entire main surface of both main surfaces of the piezoelectric film 35 vibrated vertically.

[0184] This vibration evaluation indicates that, in reality, it is also like this. Figure 4A and Figure 4BThe piezoelectric film 35 is schematically shown to have two main surfaces that can vibrate up and down.

[0185] [Support structure and degrees of freedom for vibration of piezoelectric films]

[0186] Back Figure 3 Referring to an example of the support structure of the piezoelectric loudspeaker of the present invention, in the piezoelectric loudspeaker 10, the entire surface of the piezoelectric film 35 is fixed to the support body 80 by adhesive layers 51, 52 and intermediate layer 40.

[0187] To ensure that the vibration of the piezoelectric film 35 is not hindered by the support 80, it is also possible to separate the piezoelectric film 35 from the support 80 by supporting a portion of it. Figure 28 The image illustrates a support structure based on this design concept. Figure 28 In the hypothetical piezoelectric loudspeaker 108 shown, the frame 88 supports the periphery of the piezoelectric diaphragm 35 at a position away from the support 80.

[0188] A piezoelectric diaphragm that is pre-bent to one side with a fixed bending direction easily ensures sufficient volume. Therefore, for example, in a piezoelectric speaker 108, a spacer with a convex upper surface and a non-constant thickness can be arranged in the space 48 surrounded by the piezoelectric diaphragm 35, the frame 88, and the support 80, thereby pushing the central portion of the piezoelectric diaphragm 35 upward. However, such a spacer does not engage with the piezoelectric diaphragm 35 so as not to impede the vibration of the piezoelectric diaphragm 35. Therefore, even though a spacer is arranged in the space 48, only the frame 88 supports the piezoelectric diaphragm 35 in a manner that determines its vibration.

[0189] As mentioned above, in Figure 28 The piezoelectric loudspeaker 108 shown employs a partial support structure for the piezoelectric diaphragm 35. In contrast, as... Figure 3 As shown, in the piezoelectric loudspeaker 10, the piezoelectric diaphragm 35 is not specifically supported. Surprisingly, although the entire surface of the piezoelectric diaphragm 35 is fixed to the support 80, the piezoelectric loudspeaker 10 exhibits practical acoustic characteristics. Specifically, in the piezoelectric loudspeaker 10, the piezoelectric diaphragm 35 can vibrate up and down up to its periphery. The piezoelectric diaphragm 35 as a whole can also vibrate up and down. Therefore, compared to the piezoelectric loudspeaker 108, the piezoelectric loudspeaker 10 has a higher degree of vibration freedom, which is relatively advantageous for achieving good sound production characteristics.

Claims

1. A piezoelectric loudspeaker, wherein, The piezoelectric loudspeaker has: A piezoelectric film, the piezoelectric film comprising a first electrode, a second electrode, and a piezoelectric element sandwiched between the first electrode and the second electrode; The first bonding layer with adhesive or glue properties; and An intermediate layer is disposed between the piezoelectric film and the first bonding layer, and When the main surface of one side of the intermediate layer of the piezoelectric film is defined as the supported surface, The intermediate layer is bonded to the entire supported surface. The intermediate layer is an ethylene propylene rubber foam layer. The intermediate layer has an independent bubble structure or a semi-independent, semi-continuous bubble structure.

2. The piezoelectric loudspeaker as claimed in claim 1, wherein, The piezoelectric loudspeaker also has a second bonding layer that bonds the intermediate layer to the entire supported surface, and The second bonding layer is an adhesive or glue-like layer.

3. The piezoelectric loudspeaker as claimed in claim 1, wherein, The thickness of the intermediate layer in the uncompressed state is in the range of 2mm to 25mm.

4. The piezoelectric loudspeaker as claimed in claim 1, wherein, The intermediate layer is a porous layer, and The porosity of the intermediate layer is 80% to 99%.

5. The piezoelectric loudspeaker as claimed in claim 1, wherein, The intermediate layer is a porous layer, and The pore size of the intermediate layer is 0.3mm to 0.7mm.

6. The piezoelectric loudspeaker as claimed in claim 1, wherein, The elastic modulus of the intermediate layer is, for example, 20000 N / m. 2 ~100000N / m 2 .

7. The piezoelectric loudspeaker as claimed in claim 1, wherein, The piezoelectric material is polyvinylidene fluoride or polylactic acid.

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