Piezoelectric speaker

Abstract

This invention provides a piezoelectric speaker that produces sound by vibrating a diaphragm using a piezoelectric actuator, and which has good low-frequency characteristics. [Solution] The piezoelectric speaker 10 includes a flexible piezoelectric actuator 35, a diaphragm 41, a fixed surface 17, and an intervening layer 42. The diaphragm 41 is vibrated by the flexible piezoelectric actuator 35. The fixed surface 17 is a surface to be fixed to the support 80. The intervening layer 42 is positioned between the diaphragm 41 and the fixed surface 17. The driving coefficient of the intervening layer 42 is 1[(kg·mm) / (GPa·m)] 3 The above is true. The driving coefficient is a value obtained by dividing the product of the thickness of the intervening layer 42 and the density of the intervening layer 42 by the Young's modulus of the intervening layer 42.

Description

[Technical Field]

[0001] This invention relates to a piezoelectric speaker. [Background technology]

[0002] Piezoelectric speakers, which utilize piezoelectric materials, are known as speakers (for example, Patent Documents 1 and 2). Patent Document 2 describes an estimated vibration mechanism that converts in-plane expansion and contraction of a piezoelectric film into deformation in the thickness direction by constraining one of the main surfaces of the piezoelectric film. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 03-201799 [Patent Document 2] International Publication No. 2019 / 103016 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent Document 2 does not discuss piezoelectric speakers that produce sound by vibrating a diaphragm using a piezoelectric actuator. The object of the present invention is to provide a piezoelectric speaker that produces sound by vibrating a diaphragm using a piezoelectric actuator and has good low-frequency characteristics. [Means for solving the problem]

[0005] The present invention A flexible piezoelectric actuator and A vibrating plate that is vibrated by the aforementioned flexible piezoelectric actuator, A fixing surface to be fixed to the support, The system comprises an intervening layer disposed between the diaphragm and the fixed surface, The driving coefficient of the intervening layer is 1[(kg·mm) / (GPa·m)] 3)]That's all above. Provide a piezoelectric speaker. Here, the driving coefficient is a value obtained by dividing the product of the thickness and density of the intervening layer by the Young's modulus of the intervening layer.

Advantages of the Invention

[0006] According to the present invention, there is provided a piezoelectric speaker that vibrates a diaphragm with a piezoelectric actuator to produce sound, and a piezoelectric speaker with good low-frequency characteristics can be provided.

Brief Description of the Drawings

[0007] [Figure 1] Cross-sectional view of a piezoelectric speaker according to an embodiment of the present invention [Figure 2] Cross-sectional view of a piezoelectric speaker with a release liner according to an embodiment of the present invention [Figure 3] Cross-sectional view of a piezoelectric speaker installation structure according to an embodiment of the present invention [Figure 4] Explanatory drawing of the vibration mechanism of a piezoelectric speaker according to an embodiment of the present invention [Figure 5] Top view of a piezoelectric speaker according to an embodiment of the present invention [Figure 6] Cross-sectional view showing a piezoelectric speaker according to a modification of the present invention [Figure 7] Top view of a piezoelectric speaker according to a modification of the present invention [Figure 8] Explanatory drawing of a bimorph structure according to an example [Figure 9] Cross-sectional view showing a piezoelectric speaker according to a modification [Figure 10] Block diagram showing a measurement system for measuring the frequency-sound pressure level characteristics of samples of Examples 1 to 20, Comparative Examples 1 to 7, and Reference Example 1 [Figure 11] Graph showing the frequency-sound pressure level characteristics of the sample of Example 2 [Figure 12A] Chart showing the evaluation results of samples of Examples 1 to 20 and Reference Example 1 [Figure 12B] Chart showing the evaluation results of samples of Comparative Examples 1 to 7 [Figure 13] Graphs showing the relationship between the driving coefficient of the intervening layer 42 and the sound quality evaluation value for the samples of Examples 1-20, Comparative Examples 1-7, and Reference Example 1. [Figure 14] Graph showing the frequency-sound pressure level characteristics of the sample from Example 21 and the sample from Comparative Example 8. [Figure 15] Cross-sectional view of the piezoelectric speaker in Patent Document 1 [Figure 16] Diagram illustrating the estimated vibration mechanism of the piezoelectric speaker in Patent Document 2 [Modes for carrying out the invention]

[0008] In this specification, a bendable piezoelectric actuator refers to a piezoelectric actuator that, when a voltage is applied to the piezoelectric actuator, bends and vibrates itself.

[0009] In this specification, "metal" is a concept that includes alloys. "Resin" is a concept that includes rubber and elastomers. "Polymer" means a polymer with a weight-average molecular weight greater than 10,000.

[0010] In this specification, the phrase "an element contains material" may be used. This phrase is not intended to limit the percentage or amount of material contained in that element. When an element contains material, it may contain the material in any amount by mass, such as 10% to 100%, 30% to 100%, 50% to 100%, 70% to 100%, 90% to 100%, or 100%. For example, when it is stated that a diaphragm contains resin, the diaphragm may contain resin in any amount by mass, such as 10% to 100%, 30% to 100%, 50% to 100%, 70% to 100%, 90% to 100%, or 100%. The same applies to expressions such as "an intervening layer contains resin" or "a piezoelectric body contains piezoelectric ceramic."

[0011] In this specification, unless otherwise specified, the thickness of an element refers to the thickness of the element in its standalone state, not the thickness of the element when it is incorporated into a piezoelectric speaker. For example, even if the intervening layer is compressed in its thickness direction when incorporated into a piezoelectric speaker, the thickness of the intervening layer refers to the thickness of the intervening layer in its standalone state when it is not incorporated into a piezoelectric speaker.

[0012] In this specification, unless otherwise specified, "when the diaphragm is observed in a plan view" means when the diaphragm of a stationary piezoelectric speaker is observed in a plan view.

[0013] In this specification, the terms "plate" and "film" are not intended to distinguish between different thicknesses. Following convention, the term "diaphragm" is used in this specification, but this term is not intended to limit the thickness. Similarly, the term "film" is used in this specification, but this term is not intended to limit the thickness.

[0014] In this specification, "adhesive" means an agent that is liquid before use and becomes solid when applied. "Pressure-sensitive adhesive" means an agent that remains wet. "Adhesive layer" means a layer containing an adhesive. "Pressure-sensitive layer" means a layer containing a pressure-sensitive adhesive.

[0015] In this specification, "audible range" means the frequency range from 20 Hz to 20 kHz.

[0016] In this specification, the “principal face” of an element means the face perpendicular to the thickness direction of that element. The “in-plane direction” of an element means the direction perpendicular to the thickness direction of that element.

[0017] In this specification, terms such as "up," "down," and "front" are used to specify the relative positions of elements and are not intended to limit the orientation of these elements when the piezoelectric speaker is in use.

[0018] The embodiments of the present invention will be described below with reference to the attached drawings, but the following are merely illustrative examples of embodiments of the present invention and are not intended to limit the invention. In addition, identical or similar components may be denoted by the same reference numerals, and their descriptions may be omitted.

[0019] ≪≪1. Configuration of piezoelectric speaker 10, piezoelectric speaker 110 with peel-off liner, and piezoelectric speaker mounting structure 210≫≫ Figure 1 is a cross-sectional view of a piezoelectric speaker 10 according to an embodiment of the present invention. The piezoelectric speaker 10 includes, in this order, a bendable piezoelectric actuator 35, a diaphragm 41, an intervening layer 42, and a fixed surface 17. The bendable piezoelectric actuator 35 includes, in this order, an electrode 61, a piezoelectric body 30, and an electrode 62.

[0020] In this embodiment, the piezoelectric speaker 10 further includes a bonding layer 51, a bonding layer 52, and a bonding layer 53. The bonding layer 51 is positioned between the diaphragm 41 and the electrode 62 of the bendable piezoelectric actuator 35. The bonding layer 52 is positioned between the diaphragm 41 and the intervening layer 42. The bonding layer 53 is positioned on the opposite side of the bonding layer 52 from the intervening layer 42. The bonding layer 53 forms a fixed surface 17.

[0021] Thus, in the piezoelectric speaker 10, the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, the bonding layer 51, the electrode 62, the piezoelectric body 30, and the electrode 61 are stacked in this order from bottom to top. Specifically, the bonding layer 53 and the intervening layer 42 are in contact, the intervening layer 42 and the bonding layer 52 are in contact, the bonding layer 52 and the diaphragm 41 are in contact, the diaphragm 41 and the bonding layer 51 are in contact, the bonding layer 51 and the electrode 62 are in contact, the electrode 62 and the piezoelectric body 30 are in contact, and the piezoelectric body 30 and the electrode 61 are in contact. The bottom surface of the piezoelectric speaker 10 is the bottom surface of the bonding layer 53 and is the fixed surface 17.

[0022] Figure 2 is a cross-sectional view of a piezoelectric speaker 110 with a release liner according to an embodiment of the present invention. In the piezoelectric speaker 110 with a release liner, the fixed surface 17 of the piezoelectric speaker 10 is covered by the release liner 20.

[0023] Figure 3 is a cross-sectional view of a piezoelectric speaker mounting structure 210 according to an embodiment of the present invention. In the piezoelectric speaker mounting structure 210, the fixing surface 17 of the piezoelectric speaker 10 is fixed to the support 80. In the piezoelectric speaker mounting structure 210, sound is emitted from the piezoelectric speaker 10. Typically, the piezoelectric speaker 10 emits sound in the audible range.

[0024] The piezoelectric speaker mounting structure 210 can be constructed starting from the piezoelectric speaker 110 with a peel-off liner as follows: Remove the peeling liner 20 from the piezoelectric speaker 110 with the peeling liner. This results in a piezoelectric speaker 10 with an exposed fixed surface 17. The fixing surface 17 of the piezoelectric speaker 10 is fixed to the support 80. This provides a piezoelectric speaker mounting structure 210.

[0025] The piezoelectric speaker 10 can be used both as a speaker for listening to sound and as a speaker for noise reduction using active noise control (ANC), etc.

[0026] An exemplary speaker system, not shown in the illustration, includes a control device and a piezoelectric speaker 10. The control device transmits a control signal to the piezoelectric speaker 10. The piezoelectric speaker 10 emits sound based on the control signal.

[0027] ≪1-1. Flexible Piezoelectric Actuator≫ The flexible piezoelectric actuator 35 vibrates when a voltage is applied. Specifically, a voltage is applied between electrodes 61 and 62 via a voltage path (not shown in the diagram). This applies a voltage to the piezoelectric element 30. The voltage path is constructed, for example, using a flexible printed circuit (FPC).

[0028] The piezoelectric element 30 has a film shape. The piezoelectric element 30 may be non-porous or porous.

[0029] In this embodiment, the piezoelectric element 30 includes a piezoelectric ceramic. Including a piezoelectric ceramic in the piezoelectric element 30 is advantageous from the viewpoint of improving the sound pressure level that the piezoelectric speaker 10 can form. Examples of piezoelectric ceramics included in the piezoelectric element 30 include lead zirconate, lead zirconate titanate, lead zirconate titanate lanthanate, barium titanate, Bi layered compounds, tungsten bronze structured compounds, and solid solutions of barium titanate and bismuth ferrite.

[0030] The piezoelectric element 30 may contain a piezoelectric resin. Examples of piezoelectric resins included in the piezoelectric element 30 include polyvinylidene fluoride and polylactic acid. The piezoelectric resin may also contain polyolefins such as polyethylene and polypropylene.

[0031] The thickness of the piezoelectric material 30 is, for example, 10 μm or more and 5000 μm or less, and may be 50 μm or more and 2000 μm or less, or 100 μm or more and 1000 μm or less.

[0032] Electrodes 61 and 62 are in contact with the piezoelectric element 30, sandwiching it between them. Electrodes 61 and 62 have a film shape. Electrodes 61 and 62 can be formed on the piezoelectric element 30 by vapor deposition, plating, sputtering, etc. Metal foil can also be used as electrodes 61 and 62.

[0033] Electrodes 61 and 62 contain, for example, metals. Examples of metals contained in electrodes 61 and 62 include gold, platinum, silver, copper, palladium, chromium, molybdenum, iron, tin, aluminum, and nickel. Electrodes 61 and 62 may also contain alloys of these metals. Electrodes 61 and 62 may also contain carbon, conductive polymers, glass components, etc.

[0034] The thickness of electrode 61 and electrode 62 is, for example, 5 nm to 200 μm, but may also be 10 nm to 150 μm, or 20 nm to 100 μm.

[0035] In this embodiment, electrode 61 covers the entire main surface of one of the piezoelectric elements 30. However, electrode 61 may cover only a portion of the main surface of the piezoelectric element 30. Electrode 62 covers the entire other main surface of the piezoelectric element 30. However, electrode 62 may cover only a portion of the main surface of the other main surface of the piezoelectric element 30.

[0036] ≪1-2. Configuration of the diaphragm 41≫ The diaphragm 41 amplifies the amplitude of vibrations transmitted from the flexible piezoelectric actuator 35. The diaphragm 41 has a film shape. In this embodiment, the diaphragm 41 contains a resin, specifically a polymer. The diaphragm 41 is a non-porous material. However, the diaphragm 41 may be a porous material.

[0037] Examples of polymers included in the diaphragm 41 include polycarbonate (PC), polyethylene terephthalate (PET), polyolefin, polyvinyl chloride (PVC), and acrylic resin. Examples of polyolefins included in the diaphragm 41 include polyethylene (PE) and polypropylene (PP). The diaphragm 41 may contain paper, wood, or metal. Examples of metals included in the diaphragm 41 include aluminum, iron, copper, stainless steel, and phosphor bronze.

[0038] The Young's modulus (tensile modulus) of the diaphragm 41 is, for example, 0.1 GPa or more and 250 GPa or less, but may also be 0.5 GPa or more and 130 GPa or less, or 1.0 GPa or more and 10 GPa or less. The density of the diaphragm 41 is, for example, 200 kg / m³. 3 More than 20000kg / m 3 The following is true: 400 kg / m 3 More than 10000kg / m 3 It may also be less than 500 kg / m 3 More than 2000kg / m 3 The thickness of the diaphragm 41 may be, for example, 0.001 mm or more and 10 mm or less, and may be 0.002 mm or more and 5 mm or less, or 0.005 mm or more and 2 mm or less.

[0039] ≪1-3. Composition of the intervening layer 42≫ The intervening layer 42 is positioned between the diaphragm 41 and the fixed surface 17. The intervening layer 42 has a film shape. In this embodiment, the intervening layer 42 contains resin and is porous. In this embodiment, the intervening layer 42 is neither an adhesive layer nor a sticky layer. However, the intervening layer 42 does not have to contain resin, may be non-porous, or may be an adhesive layer or a sticky layer. Specifically, the porous material that constitutes the intervening layer 42 may be a foam.

[0040] Examples of resins included in the intervening layer 42 include ethylene propylene (EPDM) rubber, butyl rubber, nitrile rubber, natural (NR) rubber, styrene-butadiene rubber, acrylonitrile-butadiene (NBR) rubber, silicone, urethane, and acrylic resin. Specifically, examples of porous intervening layers 42 containing resin include ethylene propylene rubber foam layers, butyl rubber foam layers, nitrile rubber foam layers, natural rubber foam layers, styrene-butadiene rubber foam layers, acrylonitrile-butadiene rubber foam layers, silicone foam layers, and urethane foam layers. Examples of non-porous intervening layers 42 containing resin include acrylic resin layers. Examples of porous intervening layers 42 that do not contain resin include porous metals. The intervening layer 42 may also be a blend of two or more materials.

[0041] Preferably, the intervening layer 42 is a foamed layer containing rubber. More preferably, the intervening layer 42 is a foam containing ethylene propylene rubber.

[0042] The foam formed by the intervening layer 42 may have an open cell structure, a closed cell structure, or a semi-open semi-closed cell structure. The open cell structure refers to a structure with an open cell ratio of 100%. The closed cell structure refers to a structure with an open cell ratio of 0%. The semi-open semi-closed cell structure refers to a structure with an open cell ratio greater than 0% and less than 100%. Here, the open cell ratio can be calculated, for example, by performing a test of submerging the foam in water and using the formula: open cell ratio [%] = {(volume of water absorbed) / (volume of the cell part)} × 100. In a specific example, the "volume of water absorbed" is obtained by measuring the mass of the water replaced with the air in the cells of the foam after submerging the foam in water and leaving it for 3 minutes under a reduced pressure of -750 mmHg, and converting the mass to volume with the density of water being 1.0 g / cm 3 and converting it to volume. The "volume of the cell part" is a value calculated using the formula: volume of the cell part [cm 3 = {(mass of the foam) / (apparent density of the foam)} - {(mass of the foam) / (material density)}. The "material density" is the density of the base material (solid body) forming the foam.

[0043] The expansion ratio (density ratio before and after expansion) of the foam formed by the intervening layer 42 is, for example, 5 times or more and 40 times or less, and may be 10 times or more and 40 times or less.

[0044] <0000​​​​​​More than 1500kg / m 3 The following applies: 20 kg / m 3 More than 500kg / m 3 It may also be less than 30 kg / m 3 More than 200kg / m 3 The thickness of the intervening layer 42 may be, for example, 0.1 mm or more and 30 mm or less, and may be 0.5 mm or more and 25 mm or less, or 1 mm or more and 20 mm or less.

[0046] ≪1-4. Composition of the bonding layer 51≫ The bonding layer 51 is positioned between the diaphragm 41 and the flexible piezoelectric actuator 35. The bonding layer 51 joins the diaphragm 41 and the flexible piezoelectric actuator 35. Specifically, the bonding layer 51 is positioned between the diaphragm 41 and the electrode 62. The bonding layer 51 joins the diaphragm 41 and the electrode 62. In this embodiment, the bonding layer 51 is an adhesive layer. However, the bonding layer 51 may be an adhesive layer.

[0047] The bonding layer 51 can be a double-sided tape having a base material and an adhesive applied to both sides of the base material. The base material of the double-sided tape used as the bonding layer 51 can be a nonwoven fabric or the like. The adhesive of the double-sided tape used as the bonding layer 51 can be an adhesive containing acrylic resin, an adhesive containing silicone, or the like. The bonding layer 51 may also be a layer of adhesive without a base material.

[0048] The thickness of the bonding layer 51 is, for example, 0.01 mm or more and 1.0 mm or less, and may be 0.05 mm or more and 0.5 mm or less.

[0049] ≪1-5. Composition of the bonding layer 52≫ The bonding layer 52 is positioned between the intervening layer 42 and the diaphragm 41. The bonding layer 52 joins the intervening layer 42 and the diaphragm 41. In this embodiment, the bonding layer 52 is an adhesive layer. However, the bonding layer 52 may be an adhesive layer.

[0050] The bonding layer 52 may include a double-sided tape having a base material and an adhesive applied to both sides of the base material. The base material of the double-sided tape used as the bonding layer 52 may be a nonwoven fabric or the like. The adhesive of the double-sided tape used as the bonding layer 52 may include an adhesive containing acrylic resin or an adhesive containing silicone. The bonding layer 52 may also be a layer of adhesive without a base material.

[0051] The thickness of the bonding layer 52 is, for example, 0.01 mm or more and 1.0 mm or less, and may be 0.05 mm or more and 0.5 mm or less.

[0052] ≪1-6. Composition of the bonding layer 53≫ The bonding layer 53 forms a fixed surface 17 by its main surface. In this embodiment, the bonding layer 53 is an adhesive layer. That is, the fixed surface 17 is an adhesive surface. However, the bonding layer 53 may be an adhesive layer. That is, the fixed surface 17 may be an adhesive surface.

[0053] The bonding layer 53 can be a double-sided tape having a base material and an adhesive applied to both sides of the base material. The base material of the double-sided tape used as the bonding layer 53 can be a nonwoven fabric or the like. The adhesive of the double-sided tape used as the bonding layer 53 can be an adhesive containing acrylic resin, an adhesive containing silicone, or the like. The bonding layer 53 may also be a layer of adhesive without a base material.

[0054] The thickness of the bonding layer 53 is, for example, 0.01 mm or more and 1.0 mm or less, and may be 0.05 mm or more and 0.5 mm or less.

[0055] ≪1-7. Composition of the release liner 20≫ As shown in Figure 2, in the piezoelectric speaker 110 with a release liner, the release liner 20 is bonded to the fixed surface 17. Typically, the release liner 20 covers the entire fixed surface 17. The release liner 20 may consist of a film and a release agent applied to the main surface 21 of the film on the bonding layer 53 side. The film of the release liner 20 may be paper, a resin film, etc. The release agent of the release liner 20 may be a polymer having a long-chain alkyl group, a compound or polymer containing a fluorine atom, a polymer containing silicone, etc.

[0056] ≪1-8. Composition of Support 80≫ As shown in Figure 3, in the piezoelectric speaker mounting structure 210, the support 80 is joined to the fixed surface 17. In this embodiment, the main surface 81 of the support 80 is flat, and the fixed surface 17 is joined to that flat surface. However, if the main surface 81 is curved, the fixed surface 17 may be joined to that curved surface. In the example of Figure 3, when the fixed surface 17 is joined to the flat main surface 81 of the piezoelectric speaker 10, the main surface of the diaphragm 41 and the main surface of the intervening layer 42 are configured to be parallel to the main surface 81.

[0057] In this embodiment, the support 80 contains a resin. Examples of resins included in the support 80 include acrylic resin. The thickness of the support 80 is, for example, 0.1 mm to 1000 mm, and may be 0.5 mm to 500 mm, or 2 mm to 100 mm. In one specific example, the support 80 is a 3 mm thick acrylic plate. Here, the acrylic plate is a plate containing acrylic resin. The support 80 may also contain metal. Examples of metals included in the support 80 include stainless steel. The support 80 is, for example, a partition and is used, for example, as a room divider.

[0058] ≪≪2. Operation of the Piezoelectric Speaker 10≫≫ In this embodiment, the piezoelectric speaker 10 operates as follows: When a voltage is applied to the flexible piezoelectric actuator 35, the flexible piezoelectric actuator 35 vibrates; The flexible piezoelectric actuator 35 causes the diaphragm 41, specifically the diaphragm 41 and the intervening layer 42, to vibrate.

[0059] Here, the vibration mechanism of the piezoelectric speaker 10 according to this embodiment will be explained in comparison with the estimated vibration mechanism of the piezoelectric speaker 800 described in Patent Document 2. Figure 16 is an explanatory diagram of the estimated vibration mechanism of the piezoelectric speaker 800 described in Patent Document 2. Figure 4 is an explanatory diagram of the vibration mechanism of the piezoelectric speaker 10 according to an embodiment of the present invention. In Figure 4, the bonding layers 51, 52, and 53 are not shown. In Figure 16, the bonding layers are also not shown.

[0060] As shown in Figure 16, in the piezoelectric speaker 800, a piezoelectric film 835 is bonded to the intervening layer 842. The estimated vibration mechanism of the piezoelectric speaker 800 is as follows: When a voltage is applied to the piezoelectric film 835, the piezoelectric film 835 expands and contracts in the in-plane direction. When the piezoelectric film 835 is appropriately constrained by the intervening layer 842, the above-mentioned in-plane expansion and contraction occurs, and this in-plane expansion and contraction is converted into vibration in the thickness direction of the piezoelectric film 835. This causes bending vibrations in the piezoelectric film 835 and the intervening layer 842.

[0061] In contrast, as shown in Figure 4, the vibration mechanism of the piezoelectric speaker 10 of this embodiment is as follows: When a voltage is applied to the flexible piezoelectric actuator 35, bending vibration occurs in the flexible piezoelectric actuator 35. The bending vibration described above applies a bending moment to the diaphragm 41. This causes the diaphragm 41 to vibrate.

[0062] Specifically, the vibration mechanism of the piezoelectric speaker 10 in this embodiment is as follows: When a voltage is applied to the flexible piezoelectric actuator 35, bending vibration occurs in the flexible piezoelectric actuator 35. The bending vibration described above applies a bending moment to the diaphragm 41 and the intervening layer 42. This causes the diaphragm 41 and the intervening layer 42 to vibrate.

[0063] According to the inventors' research, the vibration mechanism described with reference to Figure 4 is advantageous compared to the estimated vibration mechanism described with reference to Figure 16 in terms of improving the sound pressure level generated by the piezoelectric speaker 10.

[0064] In this embodiment, when the diaphragm 41 is observed in a plan view, the diaphragm 41 occupies a region of 50% to 100% of the area of ​​the intervening layer 42. In the vibration mechanism described with reference to Figure 4, a larger area of ​​the diaphragm 41 relative to the area of ​​the intervening layer 42 is advantageous from the viewpoint of improving the sound pressure level emitted by the piezoelectric speaker 10. Preferably, when the diaphragm 41 is observed in a plan view, the diaphragm 41 occupies a region of 75% to 100% of the area of ​​the intervening layer 42. More preferably, when the diaphragm 41 is observed in a plan view, the diaphragm 41 occupies a region of 90% to 100% of the area of ​​the intervening layer 42. Even more preferably, when the diaphragm 41 is observed in a plan view, the diaphragm 41 occupies a region of 100% of the area of ​​the intervening layer 42.

[0065] Here, if the diaphragm 41 is a porous material, the proportion of the area in which the diaphragm 41 exists is determined from a macroscopic perspective, rather than from a microscopic perspective that takes into account the pores resulting from its porous structure. This also applies to other elements such as the intervening layer 42. For example, if the intervening layer 42 and the diaphragm 41 have a common contour when observed in a plan view, the diaphragm 41 is said to exist in an area of ​​100% of the area of ​​the intervening layer 42, regardless of the porosity of the intervening layer 42 and the diaphragm 41.

[0066] In the vibration mechanism described with reference to Figure 4, the piezoelectric element 30 only needs to have a limited area. Figure 5 is a top view of a piezoelectric speaker 10 according to an embodiment of the present invention. In this embodiment, when the diaphragm 41 is observed in plan view, the piezoelectric element 30 exists in a region greater than 0% but less than 100% of the area of ​​the diaphragm 41. Specifically, when the diaphragm 41 is observed in plan view, the piezoelectric element 30 exists in a region of 1% to 75% of the area of ​​the diaphragm 41. More specifically, when the diaphragm 41 is observed in plan view, the piezoelectric element 30 exists in a region of 5% to 50% of the area of ​​the diaphragm 41.

[0067] For example, the thickness of the diaphragm 41 is 0.5% or more and 1000% or less of the thickness of the piezoelectric element 30. The thickness of the diaphragm 41 may be 1.0% or more and 500% or less of the thickness of the piezoelectric element 30. The thickness of the diaphragm 41 may be 1.5% or more and 300% or less of the thickness of the piezoelectric element 30.

[0068] As shown in Figure 4, in this embodiment, when the diaphragm 41 is observed in a plan view, it has an overlapping region 41a that overlaps with the bendable piezoelectric actuator 35 and an outer region 41b located outside the bendable piezoelectric actuator 35. In the piezoelectric speaker 10, the diaphragm 41 vibrates such that the amplitude of the outer region 41b is larger than the amplitude of the overlapping region 41a. Typically, when the diaphragm 41 is observed in a plan view, the outer region 41b surrounds the overlapping region 41a.

[0069] In this embodiment, in the piezoelectric speaker 10, the intervening layer 42 deforms and vibrates in accordance with the deformation caused by the vibration of the diaphragm 41. Specifically, the upper surface of the intervening layer 42 deforms and vibrates in accordance with the deformation caused by the vibration of the lower surface of the diaphragm 41.

[0070] In this embodiment, when the diaphragm 41 is observed in a plan view, an area of ​​90% to 100% of the diaphragm 41 vibrates vertically. This is advantageous from the viewpoint of improving the sound pressure level emitted by the piezoelectric speaker 10. Typically, when the diaphragm 41 is observed in a plan view, the entire diaphragm 41 vibrates vertically.

[0071] In this embodiment, qualitatively, the diaphragm 41 acts like a "spring" that amplifies vibrations from the flexible piezoelectric actuator 35. The intervening layer 42 acts to reduce the "spring constant" of the above-mentioned "spring," thereby extending the frequency range of sound that the piezoelectric speaker 10 can output to the lower frequency side. In addition, the intervening layer 42 acts to suppress the Q value of the vibration.

[0072] Figure 15 is a cross-sectional view of the piezoelectric speaker 700 of Patent Document 1. In the piezoelectric speaker 700 of Patent Document 1 shown in Figure 15, the peripheral edge of the metal diaphragm 702 to which the piezoelectric ceramic 701 is attached is fixed by a frame 703. In this configuration, the central part of the metal diaphragm 702 vibrates freely. In this case, odd-order mode vibrations tend to appear in a way that degrades sound quality. In contrast, the intervening layer 42 according to the embodiment can suppress the appearance of odd-order mode vibrations that degrade sound quality by supporting a large area of ​​the diaphragm 41.

[0073] In this embodiment, the intervening layer 42 is bonded to a part of the diaphragm 41, not the entire diaphragm 41. Specifically, the intervening layer 42 is bonded to only one of the two main surfaces of the diaphragm 41. This configuration allows the diaphragm 41 to exhibit vibration amplification while the intervening layer 42 easily expands the frequency range of sound that the piezoelectric speaker 10 can output to the lower frequency side. In this embodiment, the intervening layer 42 is bonded to the diaphragm 41 via a bonding layer 51. If the intervening layer 42 is an adhesive or tacky layer, the intervening layer 42 may be directly bonded to the diaphragm 41.

[0074] In this embodiment, the thickness of the diaphragm 41 is less than the thickness of the intervening layer 42. With this configuration, the relatively thin diaphragm 41 exhibits vibration amplification while the relatively thick intervening layer 42 makes it easier to extend the frequency range of sound that the piezoelectric speaker 10 can output to the lower frequency side. The thickness of the diaphragm 41 may be 0.0005 times or more and 0.8 times or less the thickness of the intervening layer 42. The thickness of the diaphragm 41 may be 0.001 times or more and 0.5 times or less the thickness of the intervening layer 42. The thickness of the diaphragm 41 may be 0.002 times or more and 0.3 times or less the thickness of the intervening layer 42.

[0075] As described above, the diaphragm 41 may contain a polymer. The inclusion of a polymer in the diaphragm 41 may be advantageous from the viewpoint of improving the "spring" effect, that is, from the viewpoint of amplifying the vibrations from the flexible piezoelectric actuator 35.

[0076] In this embodiment, the intervening layer 42 has a substantially constant thickness in the in-plane direction when incorporated into the piezoelectric speaker 10. This may be advantageous from the viewpoint of allowing the intervening layer 42 to exert the above-mentioned effect of extending the frequency range of sound that the piezoelectric speaker 10 can output to the lower frequency side. Note that "having a substantially constant thickness" means, for example, that the minimum thickness is 70% or more and 100% or less of the maximum thickness, and more specifically, that the minimum thickness is 85% or more and 100% or less of the maximum thickness.

[0077] In this embodiment, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in a region of 50% to 100% of the area of ​​the diaphragm 41. This is advantageous from the viewpoint of allowing the intervening layer 42 to exert the above-mentioned effect of extending the frequency range of sound that the piezoelectric speaker 10 can output to the lower frequency side. Preferably, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in a region of 75% to 100% of the area of ​​the diaphragm 41. More preferably, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in a region of 90% to 100% of the area of ​​the diaphragm 41. Even more preferably, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in a region of 100% of the area of ​​the diaphragm 41.

[0078] In this embodiment, when the diaphragm 41 is observed in a plan view, the fixing surface 17 is present in an area of ​​50% to 100% of the area of ​​the diaphragm 41. This makes it easy to fix the piezoelectric speaker 10 to the support 80. Preferably, when the diaphragm 41 is observed in a plan view, the fixing surface 17 is present in an area of ​​75% to 100% of the area of ​​the diaphragm 41. More preferably, when the diaphragm 41 is observed in a plan view, the fixing surface 17 is present in an area of ​​90% to 100% of the area of ​​the diaphragm 41. Even more preferably, when the diaphragm 41 is observed in a plan view, the fixing surface 17 is present in an area of ​​100% of the area of ​​the diaphragm 41.

[0079] In this embodiment, when the diaphragm 41 is observed in plan view, a laminated structure 70 is formed in a region of 50% to 100% of the area of ​​the diaphragm 41, including the fixed surface 17, the intervening layer 42, and the diaphragm 41 in that order. Therefore, the fixed surface 17 can be pressed against the support 80 via the intervening layer 42, making it easy to fix the piezoelectric speaker 10 to the support 80. Preferably, when the diaphragm 41 is observed in plan view, the laminated structure 70 is formed in a region of 75% to 100% of the area of ​​the diaphragm 41. More preferably, when the diaphragm 41 is observed in plan view, the laminated structure 70 is formed in a region of 90% to 100% of the area of ​​the diaphragm 41. Even more preferably, when the diaphragm 41 is observed in plan view, the laminated structure 70 is formed in a region of 100% of the area of ​​the diaphragm 41.

[0080] Specifically, in the laminated structure, multiple layers are stacked without gaps. More specifically, the laminated structure 70 includes a bonding layer 53, an intervening layer 42, another bonding layer 52, and a diaphragm 41 in that order. More specifically, the laminated structure 70 includes a bonding layer 53, an intervening layer 42, another bonding layer 52, a diaphragm 41, and another bonding layer 51 in that order.

[0081] In this embodiment, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in an area of ​​50% to 100% of the area of ​​the flexible piezoelectric actuator 35. Specifically, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in an area of ​​75% to 100% of the area of ​​the flexible piezoelectric actuator 35. More specifically, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in an area of ​​90% to 100% of the area of ​​the flexible piezoelectric actuator 35. Even more specifically, when the diaphragm 41 is observed in a plan view, the intervening layer 42 is present in an area of ​​100% of the area of ​​the flexible piezoelectric actuator 35.

[0082] In this embodiment, when the diaphragm 41 is observed in a plan view, the fixed surface 17 exists in an area of ​​50% to 100% of the area of ​​the flexible piezoelectric actuator 35. Specifically, when the diaphragm 41 is observed in a plan view, the fixed surface 17 exists in an area of ​​75% to 100% of the area of ​​the flexible piezoelectric actuator 35. More specifically, when the diaphragm 41 is observed in a plan view, the fixed surface 17 exists in an area of ​​90% to 100% of the area of ​​the flexible piezoelectric actuator 35. Even more specifically, when the diaphragm 41 is observed in a plan view, the fixed surface 17 exists in an area of ​​100% of the area of ​​the flexible piezoelectric actuator 35.

[0083] In this embodiment, when the diaphragm 41 is observed in a plan view, the laminated structure 70 is formed in an area of ​​50% to 100% of the area of ​​the bendable piezoelectric actuator 35. Specifically, when the diaphragm 41 is observed in a plan view, the laminated structure 70 is formed in an area of ​​75% to 100% of the area of ​​the bendable piezoelectric actuator 35. More specifically, when the diaphragm 41 is observed in a plan view, the laminated structure 70 is formed in an area of ​​90% to 100% of the area of ​​the bendable piezoelectric actuator 35. Even more specifically, when the diaphragm 41 is observed in a plan view, the laminated structure 70 is formed in an area of ​​100% of the area of ​​the bendable piezoelectric actuator 35.

[0084] In the vibration mechanism described with reference to Figure 4, the low-frequency characteristics of the piezoelectric speaker 10 can be improved by appropriately configuring the diaphragm 41. In this embodiment, the bending coefficient of the diaphragm 41 is 100 [kg / (GPa·mm·m 3 )] That's all. Having the coefficient of inflection within this range makes it possible to improve the low-frequency characteristics of the piezoelectric speaker 10.

[0085] Here, the bending coefficient of the diaphragm 41 is given by the density of the diaphragm 41 [kg / m³], as shown in Equation 1 below. 3 This value is obtained by dividing the result by the product of the Young's modulus [GPa] of the diaphragm 41 and the thickness [mm] of the diaphragm 41.

number

[0086] The bending coefficient of the diaphragm 41 is preferably 100 [kg / (GPa·mm·m 3 )] more than 200000mm 2 / [kg / (GPa·mm·m 3 )] or less, more preferably 200 [kg / (GPa·mm·m 3 )] or more 100,000 [kg / (GPa·mm·m 3 ) or less, and more preferably 290 [kg / (GPa·mm·m 3 )] or more 90000 [kg / (GPa·mm·m 3 )] The following:

[0087] In the vibration mechanism described with reference to Figure 4, the low-frequency characteristics of the piezoelectric speaker 10 can be improved by appropriately configuring the intervening layer 42. In this embodiment, the driving coefficient of the intervening layer 42 is 1[(kg·mm) / (GPa·m 3 )] That's all. Having the driving coefficient within this range makes it possible to improve the low-frequency characteristics of the piezoelectric speaker 10.

[0088] Here, the driving coefficient of the intervening layer 42 is given by the density of the intervening layer 42 [kg / m³], as shown in Equation 2 below.3 This value is obtained by dividing ] by the product of the Young's modulus [GPa] of the intervening layer 42 and the thickness [mm] of the intervening layer 42.

number

[0089] The driving coefficient of the intervening layer 42 is preferably 1 [(kg·mm) / (GPa·m)]. 3 ) 500mm or more 2 / [(kg·mm) / (GPa·m 3 ) or less, more preferably 1.5 [(kg·mm) / (GPa·m 3 )] Above 300 [(kg·mm) / (GPa·m 3 ) or less, and more preferably 4[(kg·mm) / (GPa·m 3 )] Above 150 [(kg·mm) / (GPa·m 3 )] The following:

[0090] Figure 6 is a cross-sectional view showing a piezoelectric speaker 10a according to a modified example of the present invention. Figure 7 is a top view of the piezoelectric speaker 10a according to a modified example of the present invention. In the piezoelectric speaker 10a according to the modified example, the bendable piezoelectric actuator 35a includes a plurality of actuator parts 35p spaced apart from each other. The electrode 61a includes a plurality of electrode parts 61p spaced apart from each other. The electrode 62a includes a plurality of electrode parts 62p spaced apart from each other. The piezoelectric body 30a includes a plurality of piezoelectric parts 30p spaced apart from each other. Each actuator part 35p includes an electrode part 61p, a piezoelectric part 30p, and an electrode part 62p in that order. Specifically, in the modified examples shown in Figures 6 and 7, there are two actuator parts 35p. The same applies to the electrode parts 61p, 62p, and 30p.

[0091] In the modified examples shown in Figures 6 and 7, when the diaphragm 41 is observed in a plan view, the piezoelectric element 30 may exist in a region greater than 0% but less than 100% of the area of ​​the diaphragm 41. Specifically, when the diaphragm 41 is observed in a plan view, the piezoelectric element 30a may exist in a region of 1% to 75% of the area of ​​the diaphragm 41. More specifically, when the diaphragm 41 is observed in a plan view, the piezoelectric element 30a may exist in a region of 5% to 50% of the area of ​​the diaphragm 41. In the modified examples, the region in which the piezoelectric element 30 exists refers to a combination of regions in which multiple piezoelectric elements 30p exist.

[0092] In this embodiment, a unimorph structure is configured in which a flexible piezoelectric actuator 35 is joined to one side of the diaphragm 41. However, a bimorph structure may be configured in which a flexible piezoelectric actuator 35 is joined to each of the two sides of the diaphragm 41.

[0093] Figure 8 is an explanatory diagram of a bimorph structure as an example. In the bimorph structure of Figure 8, the first flexible piezoelectric actuator 35, the first bonding layer 51, the diaphragm 41, the second bonding layer 51, and the second flexible piezoelectric actuator 35 are stacked in this order from bottom to top. The bimorph structure of Figure 8 can be provided on a structure that includes the bonding layer 53, the intervening layer 42, and the bonding layer 52 in this order, as explained with reference to Figure 1.

[0094] In a modified example not shown in the illustration, a protective coating is formed to cover the flexible piezoelectric actuator 35. The protective coating may be beneficial for the commercialization of the piezoelectric speaker 10. The protective coating typically has a film form. The protective coating includes, for example, polyester.

[0095] In this embodiment, when the diaphragm 41 is observed in plan view, the contours of the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, and the bonding layer 51 coincide. However, it is acceptable for these contours to be misaligned.

[0096] Figure 9 is a cross-sectional view showing a modified piezoelectric speaker 10b. In the piezoelectric speaker 10b, when the diaphragm 41 is observed in a plan view, the contours of the bonding layer 53, the intervening layer 42, the bonding layer 52, and the diaphragm 41 coincide. The contours of the bonding layer 51, the electrode 61, the piezoelectric body 30, and the electrode 62 coincide.

[0097] When the diaphragm 41 is observed in plan view, the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, the bonding layer 51, the electrode 62, the piezoelectric body 30, and the electrode 61 may be square, rectangular, circular, or elliptical.

[0098] As described above, in the embodiment, the fixed surface 17 is formed by a bonding layer 53. In a modified example not shown, the fixed surface 17 is formed by an intervening layer 42. In the modified example, the intervening layer 42 may be an adhesive layer or a tack layer. The expression "including the flexible piezoelectric actuator 35, the diaphragm 41, the intervening layer 42, and the fixed surface 17 in this order" is intended to include not only the form in which the fixed surface 17 is formed by an element other than the intervening layer 42, but also the form in which the fixed surface 17 is formed by the intervening layer 42. Similarly, the expression "the intervening layer 42 is positioned between the diaphragm 41 and the fixed surface 17" is intended to include not only the form in which the fixed surface 17 is formed by an element other than the intervening layer 42, but also the form in which the fixed surface 17 is formed by the intervening layer 42.

[0099] Furthermore, the expression "When the diaphragm 41 is observed in a plan view, the fixed surface 17 exists in a region of 50% to 100% of the area of ​​the diaphragm 41" will be explained. This expression means that when the diaphragm 41 is observed in a plan view, the fixed surface 17 overlaps with the diaphragm 41 in a region of 50% to 100% of the area of ​​the diaphragm 41. Therefore, this expression includes a configuration in which, when the diaphragm 41 is observed in a plan view, the fixed surface 17 overlaps with the diaphragm 41 in a region of 100% of the area of ​​the diaphragm 41, and there is a portion of the fixed surface 17 that extends beyond the diaphragm 41. Furthermore, this expression encompasses a configuration in which, when the diaphragm 41 is observed in a plan view, the fixed surface 17 overlaps with the diaphragm 41 in an area of ​​50% to 100% of the diaphragm 41's area, and there is no portion of the fixed surface 17 that extends beyond the diaphragm 41. The same applies to other similar expressions. [Examples]

[0100] The present invention will be described in detail with reference to examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to these examples.

[0101] (Example 1) The piezoelectric speaker mounting structure 210 shown in Figure 3 was fabricated using the following components and served as a sample for Example 1: A 3mm thick acrylic sheet was used as the support 80. As the bonding layer 53, a 0.16 mm thick adhesive sheet (double-sided tape) was used, in which an acrylic adhesive was impregnated on both sides of a nonwoven fabric. As the intervening layer 42, a closed-cell foam with a thickness of 3 mm was used, which was obtained by foaming a mixture containing ethylene propylene (EPDM) rubber and butyl rubber at a foaming ratio of approximately 10 times. As the bonding layer 52, a 0.16 mm thick adhesive sheet (double-sided tape) was used, in which an acrylic adhesive was impregnated on both sides of a nonwoven fabric. A 1.0 mm thick polycarbonate sheet was used as the diaphragm 41. As the bonding layer 51, an adhesive sheet (double-sided tape) with a thickness of 0.16 mm was used, in which an acrylic adhesive was impregnated on both sides of a nonwoven fabric. As the flexible piezoelectric actuator 35, a flexible piezoelectric actuator with a thickness of 0.49 mm was used, in which the piezoelectric body 30 is a piezoelectric ceramic, the electrodes 61 and 62 are conductors that are sufficiently thin relative to the piezoelectric body 30, and a voltage path composed of a flexible printed circuit is attached.

[0102] In Example 1, when the diaphragm 41 is observed in plan view, the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, and the bonding layer 51 have dimensions of 50 mm in length and 50 mm in width, and their contours overlap. When the diaphragm 41 is observed in plan view, the bendable piezoelectric actuator 35 has dimensions of 30 mm in length and 30 mm in width. When the diaphragm 41 is observed in plan view, the support 80 has dimensions of 600 mm in length and 450 mm in width, and completely covers the bonding layer 53. These points are also true in Examples 2 to 20, Comparative Examples 1 to 7, and Reference Example 1, which will be described later.

[0103] (Example 2) As the intervening layer 42, a closed-cell foam with a thickness of 5 mm was used, which was obtained by foaming a mixture containing ethylene propylene rubber and butyl rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 2 was prepared in the same manner as in Example 1.

[0104] (Example 3) As the intervening layer 42, a 10 mm thick, closed-cell foam was used, which was obtained by foaming a mixture containing ethylene propylene rubber and butyl rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 3 was prepared in the same manner as in Example 1.

[0105] (Example 4) As the intervening layer 42, a closed-cell foam with a thickness of 15 mm was used, which was obtained by foaming a mixture containing ethylene propylene rubber and butyl rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 4 was prepared in the same manner as in Example 1.

[0106] (Example 5) As the intervening layer 42, a 5 mm thick, closed-cell sulfur-containing foam was used, which was obtained by foaming an ethylene propylene rubber mixture at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 5 was prepared in the same manner as in Example 1.

[0107] (Example 6) As the intervening layer 42, a 10 mm thick, closed-cell sulfur-containing foam was used, which was obtained by foaming an ethylene propylene rubber mixture at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 6 was prepared in the same manner as in Example 1.

[0108] (Example 7) As the intervening layer 42, a 5 mm thick, semi-closed, semi-open-cell sulfur-containing foam was used, which was obtained by foaming an ethylene propylene rubber mixture at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 7 was prepared in the same manner as in Example 1.

[0109] (Example 8) As the intervening layer 42, a 10 mm thick, semi-closed, semi-open-cell sulfur-containing foam was used, which was obtained by foaming an ethylene propylene rubber mixture at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 8 was prepared in the same manner as in Example 1.

[0110] (Example 9) As the intervening layer 42, a 3 mm thick, semi-closed, semi-open-cell, sulfur-free foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 9 was prepared in the same manner as in Example 1.

[0111] (Example 10) As the intervening layer 42, a sulfur-free foam with a thickness of 5 mm and semi-closed, semi-open-cell structure was used, which was obtained by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 10 was prepared in the same manner as in Example 1.

[0112] (Example 11) As the intervening layer 42, a 10 mm thick, semi-closed, semi-open-cell, sulfur-free foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 11 was prepared in the same manner as in Example 1.

[0113] (Example 12) As the intervening layer 42, a 15 mm thick, semi-closed, semi-open-cell, sulfur-free foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 12 was prepared in the same manner as in Example 1.

[0114] (Example 13) As the intervening layer 42, a closed-cell foam with a thickness of 5 mm was used, which was obtained by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 20 times. Otherwise, the sample for Example 13 was prepared in the same manner as in Example 1.

[0115] (Example 14) As the intervening layer 42, a 10 mm thick, closed-cell foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 20 times. Otherwise, the sample for Example 14 was prepared in the same manner as in Example 1.

[0116] (Example 15) As the intervening layer 42, a 5 mm thick, semi-closed, semi-open-cell foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 20 times. Otherwise, the sample for Example 15 was prepared in the same manner as in Example 1.

[0117] (Example 16) As the intervening layer 42, a 10 mm thick, semi-closed, semi-open-cell foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 20 times. Otherwise, the sample for Example 16 was prepared in the same manner as in Example 1.

[0118] (Example 17) As the intervening layer 42, a closed-cell foam with a thickness of 5 mm was used, which was obtained by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 17 was prepared in the same manner as in Example 1.

[0119] (Example 18) As the intervening layer 42, a 10 mm thick, closed-cell foam was used, which was obtained by foaming an admixture containing ethylene propylene rubber at an expansion ratio of approximately 10 times. Otherwise, the sample for Example 18 was prepared in the same manner as in Example 1.

[0120] (Example 19) As the intervening layer 42, a 5 mm thick, semi-closed, semi-open-cell foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 19 was prepared in the same manner as in Example 1.

[0121] (Example 20) As the intervening layer 42, a 10 mm thick, semi-closed, semi-open-cell foam was used, which was produced by foaming an admixture containing ethylene propylene rubber at a foaming ratio of approximately 10 times. Otherwise, the sample for Example 20 was prepared in the same manner as in Example 1.

[0122] (Comparative Example 1) As the intervening layer 42, a 1 mm thick, non-porous acrylonitrile butadiene (NBR) rubber with a hardness of 60 was used. Otherwise, the sample for Comparative Example 1 was prepared in the same manner as in Example 1. In this specification, hardness refers to Shore A hardness.

[0123] (Comparative Example 2) As the intervening layer 42, a 3 mm thick, non-porous acrylonitrile butadiene rubber with a hardness of 60 was used. Otherwise, the sample for Comparative Example 2 was prepared in the same manner as in Example 1.

[0124] (Comparative Example 3) As the intervening layer 42, a 1 mm thick, non-porous natural (NR) rubber with a hardness of 65 was used. Otherwise, the sample for Comparative Example 3 was prepared in the same manner as in Example 1.

[0125] (Comparative Example 4) As the intervening layer 42, a non-porous natural rubber with a hardness of 65 and a thickness of 8 mm was used. Otherwise, the sample for Comparative Example 4 was prepared in the same manner as in Example 1.

[0126] (Comparative Example 5) As the intervening layer 42, a 1 mm thick, non-porous silicone with a hardness of 50 was used. As the bonding layer 53 and bonding layer 52, an adhesive sheet (double-sided tape) with a thickness of 0.085 mm was used, in which an acrylic adhesive was impregnated on one side of a nonwoven fabric and a silicone adhesive was impregnated on both sides. The silicone adhesives of bonding layer 53 and bonding layer 52 were brought into contact with the intervening layer 42. Otherwise, a sample of Comparative Example 5 was prepared in the same manner as in Example 1.

[0127] (Comparative Example 6) As the intervening layer 42, a 3 mm thick, non-porous silicone with a hardness of 50 was used. Otherwise, the sample for Comparative Example 6 was prepared in the same manner as for Comparative Example 5.

[0128] (Comparative Example 7) As the intervening layer 42, a 5 mm thick, non-porous silicone with a hardness of 50 was used. Otherwise, the sample for Comparative Example 7 was prepared in the same manner as for Comparative Example 5.

[0129] (Reference example 1) The intervening layer 42 and the bonding layer 52 were omitted, and the bonding layer 53 and the diaphragm 41 were brought into contact with each other. Otherwise, a sample of Reference Example 1 was prepared in the same manner as in Example 1.

[0130] The evaluation methods for the samples related to Examples 1-20, Comparative Examples 1-7, and Reference Example 1 are as follows.

[0131] <thickness> The thickness of the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, the bonding layer 51, and the bendable piezoelectric actuator 35 were measured using a thickness gauge. The thickness of each element is the thickness of the element in its standalone state, before it is incorporated into the piezoelectric speaker.

[0132] <Young's modulus of intervening layer 42> Small pieces were cut from the intervening layer 42. Compression tests were performed on these pieces at room temperature using a tensile testing machine (TA Instruments "RSA-G2"). A stress-strain curve was obtained. Young's modulus was calculated from the initial slope of the stress-strain curve.

[0133] <Density of the intervening layer 42> A rectangular prism-shaped piece was cut out from the interlayer 42. The apparent density was determined from the volume and mass of the cut-out piece. This apparent density was taken as the density of the interlayer 42.

[0134] <Frequency characteristics of the sound pressure level of the sample> Figure 10 is a block diagram showing a measurement system 300 for measuring the frequency characteristics (hereinafter referred to as frequency-sound pressure level characteristics) of the sound pressure levels of the samples in Examples 1-20, Comparative Examples 1-7, and Reference Example 1. The measurement system 300 includes a speaker output system 400, a microphone input system 500, and sound-absorbing material 350. As will be described later, the measurement system 300 was also used to measure the frequency-sound pressure level characteristics of the samples in Example 21 and Comparative Example 8, which will be described later.

[0135] In the speaker output system 400, the signal generator 401, audio interface 402, power amplifier 403, and sample 404 are connected in this order. Details of these elements are as follows: A personal computer was used as the signal transmitter 401. • The audio interface 402 used was the OCTA-CAPTURE manufactured by Roland Corporation. • For the power amplifier 403, a Yamaha P2500S was used. Sample 404 was selected from one of the samples in Examples 1-20, Comparative Examples 1-7, and Reference Example 1.

[0136] In the microphone input system 500, the microphone 501, the acoustic evaluation device 502, and the measuring instrument 503 are connected in this order. Details of these elements are as follows: • For microphone 501, a Bruel & Kjær Type 4190-C-001 was used. • As the acoustic evaluation device 502, we used PULSE manufactured by Bruel & Kjær. A personal computer was used as the measuring instrument 503.

[0137] In the measurement system 300, the microphone 501 was placed at an evaluation position 301, 100 cm away from the piezoelectric speaker 10 of sample 404. Sound-absorbing material 350 was placed on the walls and floor of the room where the measurement system 300 was constructed. In this state, a white noise signal voltage with an effective voltage of 3V was applied to the bendable piezoelectric actuator 35 of sample 404. This caused white noise to radiate from the piezoelectric speaker 10 of each sample 404, and the frequency-sound pressure level characteristics of each sample 404 were measured. Figure 11 is a graph showing the frequency-sound pressure level characteristics of the samples in Example 2.

[0138] Next, based on the measurement results of the frequency-sound pressure level characteristics of each sample 404, the sound quality evaluation value [dB] for each sample 404 was calculated. 2 The [dB] was evaluated as shown in equation 3 below. 2[dB] is the value obtained by dividing the product of the summation sound pressure [dB] and the primary peak sound pressure [dB] in the frequency-sound pressure level characteristics of the piezoelectric speaker 10 by the primary resonant frequency [Hz]. The frequency-sound pressure level characteristics represent the relationship between sound frequency and sound pressure level at the evaluation position 301 100 cm in front of the piezoelectric speaker 10. The summation sound pressure [dB] is the overall level of sound pressure from the primary resonant frequency to 2 kHz in the frequency-sound pressure level characteristics. In Figure 11, the primary resonant frequency is denoted as f0. The primary peak sound pressure is the sound pressure level at the primary resonant frequency in the frequency-sound pressure level characteristics.

number

[0139] This section explains the overall sound pressure level from the primary resonant frequency to 2 kHz. When Ln is the sound pressure level at the nth discrete frequency among the N discrete frequencies in the frequency band from the primary resonant frequency to 2 kHz, the sum of the sound pressure levels obtained by the following equation 4 is taken as L.

number

[0140] This section explains the primary resonant frequency. The primary resonant frequency is the lowest peak frequency in the frequency-sound pressure level characteristic. The peak frequency is the frequency at which the sound pressure peaks. Here, the lowest peak frequency is defined as the first frequency at which the sound pressure takes a negative inflection point, i.e., a maximum value, on the frequency-sound pressure level characteristic. However, frequencies at which the sound pressure level is less than ambient noise + 3dB on the frequency-sound pressure level characteristic are not considered the lowest peak frequency.

[0141] Figure 12A is a chart showing the evaluation results of the samples from Examples 1 to 20 and Reference Example 1. Figure 12B is a chart showing the evaluation results of the samples from Comparative Examples 1 to 7. In Figures 12A and 12B, "pores," "thickness," "density," "Young's modulus," and "driving coefficient" refer to the intercalated layer 42 of each sample.

[0142] The thickness, density, and Young's modulus of the diaphragm 41 in Examples 1-20, Comparative Examples 1-7, and Reference Example 1 are as follows. Thickness: 1mm ·Density: 1400kg / m 3 Young's modulus: 4.8 GPa

[0143] Figure 13 shows the driving coefficient of the intervening layer 42 [(kg·mm) / (GPa·m)] for the samples of Examples 1-20, Comparative Examples 1-7, and Reference Example 1. 3 )] and sound quality evaluation value [dB 2 This graph shows the relationship between [Hz]. From Figure 13, it can be seen that the sound quality evaluation values ​​are higher in Examples 1 to 20 compared to Reference Example 1.

[0144] As can be seen from Examples 1 to 20, the piezoelectric speaker 10 of the embodiment can emit audible sounds with its fixed surface 17 fixed to an acrylic plate with a thickness of 3 mm. As can be seen from Examples 1 to 20, the intervening layer 42 of the embodiment can improve the sound quality evaluation value.

[0145] Specifically, the statement that the intervening layer 42 can improve the sound quality evaluation value means that the intervening layer 42 can improve the sound quality evaluation value compared to the case where the intervening layer 42 is omitted, as in Reference Example 1. Similarly, the statement that the diaphragm 41 can improve the sound quality evaluation value means that the diaphragm 41 can improve the sound quality evaluation value compared to the case where the diaphragm 41 is omitted. The sound quality evaluation value is measured by fixing the fixing surface 17 of the piezoelectric speaker 10 to a 3 mm thick acrylic plate, as in Examples 1 to 20.

[0146] Furthermore, although all of the intervening layers 42 in Examples 1-20 and Comparative Examples 1-7 contain rubber, Examples 1-20 obtained better sound quality evaluation values ​​than Comparative Examples 1-7. As can be understood from this, the sound quality evaluation value can be improved by the intervening layer 42 being a foam. Specifically, the sound quality evaluation value can be improved by the intervening layer 42 being a foam containing rubber. More specifically, the sound quality evaluation value can be improved by the intervening layer 42 being a foam containing ethylene propylene rubber.

[0147] (Example 21) The piezoelectric speaker 10a shown in Figures 6 and 7 was fabricated using the following components: • As the bonding layer 53, a bonding layer containing an acrylic adhesive was used. As the intervening layer 42, a 10 mm thick, closed-cell foam was used, which was obtained by foaming a mixture containing ethylene propylene (EPDM) rubber and butyl rubber at a foaming ratio of approximately 10 times. As the bonding layer 52, a 0.16 mm thick adhesive sheet (double-sided tape) was used, in which an acrylic adhesive was impregnated on both sides of a nonwoven fabric. A 1mm thick polycarbonate sheet was used as the diaphragm 41. As the bonding layer 51, an adhesive sheet (double-sided tape) with a thickness of 0.16 mm was used, in which an acrylic adhesive was impregnated on both sides of a nonwoven fabric. A flexible piezoelectric actuator 35 was used, having two actuator sections 35p spaced apart from each other. Here, each actuator section 35p has a piezoelectric section 30p which is a piezoelectric ceramic, and electrode sections 61p and 62p which are conductive materials that are sufficiently thin compared to the piezoelectric section 30p, and is an actuator section with a thickness of 0.76 mm to which a voltage path composed of a flexible printed circuit is attached.

[0148] In Example 21, when the diaphragm 41 is observed in plan view, the bonding layer 53, the intervening layer 42, the bonding layer 52, the diaphragm 41, and the bonding layer 51 have dimensions of 35 cm in length and 50 cm in width, and their contours overlap. When the diaphragm 41 is observed in plan view, each actuator part 35p has dimensions of 30 mm in length and 66 mm in width. The two actuator parts 35p are positioned on the bonding layer 51 such that the 35 cm length of the diaphragm 41 is parallel to the 30 mm length of each actuator part 35p, and the 50 cm width of the diaphragm 41 is parallel to the 66 mm width of each actuator part 35p.

[0149] The support 80 in Example 21 is an acrylic plate with dimensions of 45 cm in length, 60 cm in width, and 0.5 cm in thickness. The fixing surface 17 of the fabricated piezoelectric speaker 10a was fixed to the support 80 so that the 35 cm vertical direction of the diaphragm 41 and the 45 cm vertical direction of the support 80 were parallel, and the 50 cm horizontal direction of the diaphragm 41 and the 60 cm horizontal direction of the support 80 were parallel. In this way, a piezoelectric speaker mounting structure was fabricated and used as the sample for Example 21.

[0150] The sample from Example 21 was incorporated as sample 404 into the measurement system 300 shown in Figure 10. In this state, a white noise signal voltage with an effective voltage of 3V was applied to the two bendable piezoelectric actuators 35a of the sample from Example 21. This caused the piezoelectric speaker 10 of the sample from Example 21 to radiate white noise, and the frequency-sound pressure level characteristics of the sample from Example 21 were measured.

[0151] (Comparative Example 8) A piezoelectric speaker 800, as described in Patent Document 2, was fabricated. The fabricated piezoelectric speaker 800 is a laminate in which a lower bonding layer, an intervening layer 842, an upper bonding layer, and a piezoelectric film 835 are stacked from bottom to top in that order. Specifically: • An acrylic adhesive-based bonding layer was used as the lower bonding layer. As the intervening layer 842, a 10mm thick, closed-cell foam was used, which was obtained by foaming a mixture containing ethylene propylene (EPDM) rubber and butyl rubber at a foaming ratio of approximately 10 times. As the upper bonding layer, a 0.16 mm thick adhesive sheet (double-sided tape) was used, which consisted of a nonwoven fabric impregnated with an acrylic adhesive on both sides. As the piezoelectric film 835, a polyvinylidene fluoride film (total thickness 33 μm) with copper electrodes (containing nickel) deposited on both sides was used.

[0152] In Comparative Example 8, when the piezoelectric film 835 is observed in a plan view, the lower bonding layer, intervening layer 842, upper bonding layer, and piezoelectric film 835 have dimensions of 35 cm vertically and 50 cm horizontally, and their contours overlap. A support 80 similar to the support 80 of Example 21 was prepared. The lower bonding layer of the fabricated piezoelectric speaker 800 was fixed to the support 80 so that the 35 cm vertical direction of the piezoelectric film 835 and the 45 cm vertical direction of the support 80 are parallel, and the 50 cm horizontal direction of the piezoelectric film 835 and the 60 cm horizontal direction of the support 80 are parallel. In this way, a piezoelectric speaker installation structure was fabricated and used as the sample for Comparative Example 8.

[0153] The sample from Comparative Example 8 was incorporated as sample 404 into the measurement system 300 shown in Figure 10. In this state, a white noise signal voltage with an effective voltage of 3V was applied to the piezoelectric film 835 of the Comparative Example 8 sample. This caused the piezoelectric speaker 800 of the Comparative Example 8 sample to radiate white noise, and the frequency-sound pressure level characteristics of the Comparative Example 8 sample were measured.

[0154] Figure 14 is a graph showing the frequency-sound pressure level characteristics of the sample from Example 21 and the sample from Comparative Example 8. From Figure 14, it can be seen that a higher sound pressure level is obtained in the sample from Example 21 compared to the sample from Comparative Example 8. Figure 14 supports the inventor's findings that the vibration mechanism described with reference to Figure 4 is advantageous compared to the estimated vibration mechanism described with reference to Figure 16 in terms of improving the sound pressure level formed by the piezoelectric speaker 10.

[0155] (Note) This disclosure provides for the following technologies:

[0156] (Technology 1) A flexible piezoelectric actuator and A vibrating plate that is vibrated by the aforementioned flexible piezoelectric actuator, A fixing surface to be fixed to the support, The system comprises an intervening layer disposed between the diaphragm and the fixed surface, The driving coefficient of the intervening layer is 1[(kg·mm) / (GPa·m)] 3 ) That's all, Piezoelectric speaker. Here, the driving coefficient is a value obtained by dividing the product of the thickness of the intervening layer and the density of the intervening layer by the Young's modulus of the intervening layer.

[0157] (Technology 2) The aforementioned driving coefficient is 1.5[(kg·mm) / (GPa·m)] 3 )] Above 300 [(kg·mm) / (GPa·m 3 )] The following: A piezoelectric speaker as described in Technology 1.

[0158] (Technology 3) When the diaphragm is observed in a plan view, it has an overlapping region that overlaps with the bendable piezoelectric actuator and an outer region located outside the bendable piezoelectric actuator. The diaphragm vibrates such that the amplitude of the outer region is larger than the amplitude of the overlapping region. A piezoelectric speaker as described in Technology 1 or 2.

[0159] (Technology 4) The intervening layer deforms and vibrates in accordance with the deformation caused by the vibration of the diaphragm. A piezoelectric speaker as described in any one of the three technical specifications.

[0160] (Technology 5) The intervening layer contains a resin and / or is a porous material. A piezoelectric speaker as described in any one of the technical specifications 1 to 4.

[0161] (Technology 6) The intervening layer is a foam. A piezoelectric speaker as described in any one of the technical specifications 1 to 5.

[0162] (Technology 7) The intervening layer is a foam containing rubber. A piezoelectric speaker as described in Technical 6.

[0163] (Technology 8) The intervening layer is a foam containing ethylene propylene rubber. Piezoelectric speaker as described in Technology 7.

[0164] (Technology 9) When the diaphragm is observed in a plan view, the intervening layer is present in a region of 50% to 100% of the area of ​​the diaphragm. A piezoelectric speaker as described in any one of the technical specifications 1 to 8.

[0165] (Technology 10) When the diaphragm is observed in a plan view, the fixed surface exists in a region of 50% to 100% of the area of ​​the diaphragm. A piezoelectric speaker as described in any one of the technical specifications 1 through 9.

[0166] (Technology 11) When the diaphragm is observed in a plan view, a laminated structure is formed in which the fixed surface, the intervening layer, and the diaphragm are included in that order over an area of ​​50% or more of the diaphragm's surface area. A piezoelectric speaker as described in any one of the technical specifications 1 through 10.

[0167] (Technology 12) The aforementioned fixing surface is an adhesive surface or bonding surface. A piezoelectric speaker as described in any one of the technical specifications 1 to 11.

[0168] (Technology 13) The aforementioned flexible piezoelectric actuator includes a piezoelectric element, When the diaphragm is observed in a plan view, the piezoelectric element is present in a region that is greater than 0% and less than 100% of the area of ​​the diaphragm. A piezoelectric speaker as described in any one of the technical specifications 1 to 12. [Industrial applicability]

[0169] According to the present invention, a piezoelectric speaker with good low-frequency characteristics can be provided. According to the present invention, for example, an improved sound environment can be constructed in the low-frequency range. [Explanation of Symbols]

[0170] 10, 10a, 10b, 700, 800 piezoelectric speakers 17 Fixed surface 20 Release Liner 21 Main surface 30, 30a Piezoelectric material 35, 35a Flexible piezoelectric actuator 41 Vibration plate 41a Overlapping area 41b Outer area 42, 842 intervening layer 51, 52, 53 Bonding layer 61, 61a, 62, 62a electrode 70 Laminated structure 80 Support 81 Main surface 110 Piezoelectric speaker with peel-off liner 210 Piezoelectric speaker mounting structure 300 Measurement System 301 Evaluation Position 350 sound-absorbing material 400 speaker output system 401 Signal Transmitter 402 Audio Interface 403 Power Amplifier 404 Samples 500 Microphone Input System 501 Microphone 502 Acoustic evaluation device 503 Measuring Instruments 701 Piezoelectric ceramic 702 Metal diaphragm 703 Frame 835 Piezoelectric film

Claims

1. A flexible piezoelectric actuator and A vibrating plate that is vibrated by the aforementioned flexible piezoelectric actuator, A fixing surface to be fixed to the support, The system comprises an intervening layer disposed between the diaphragm and the fixed surface, The driving coefficient of the intervening layer is 1 [(kg·mm) / (GPa·m)] 3 )] That's all, Piezoelectric speaker. Here, the driving coefficient is a value obtained by dividing the product of the thickness of the intervening layer and the density of the intervening layer by the Young's modulus of the intervening layer.

2. The aforementioned driving coefficient is 1.5 [(kg·mm) / (GPa·m)] 3 ) ] 300 or more [ (kg・mm) / (GPa・m 3 ) ] The following: The piezoelectric speaker according to claim 1.

3. When the diaphragm is observed in a plan view, it has an overlapping region that overlaps with the bendable piezoelectric actuator and an outer region located outside the bendable piezoelectric actuator. The diaphragm vibrates such that the amplitude of the outer region is larger than the amplitude of the overlapping region. The piezoelectric speaker according to claim 1.

4. The intervening layer deforms and vibrates in accordance with the deformation caused by the vibration of the diaphragm. The piezoelectric speaker according to claim 1.

5. The intervening layer contains a resin and / or is a porous material. The piezoelectric speaker according to claim 1.

6. The intervening layer is a foam. The piezoelectric speaker according to claim 1.

7. The intervening layer is a foam containing rubber. The piezoelectric speaker according to claim 6.

8. The intervening layer is a foam containing ethylene propylene rubber. The piezoelectric speaker according to claim 7.

9. When the diaphragm is observed in a plan view, the intervening layer is present in a region of 50% to 100% of the area of ​​the diaphragm. The piezoelectric speaker according to claim 1.

10. When the diaphragm is observed in a plan view, the fixed surface exists in a region of 50% to 100% of the area of ​​the diaphragm. The piezoelectric speaker according to claim 1.

11. When the diaphragm is observed in a plan view, a laminated structure is formed in which the fixed surface, the intervening layer, and the diaphragm are included in that order over an area of ​​50% or more of the diaphragm's surface area. The piezoelectric speaker according to claim 1.

12. The aforementioned fixing surface is an adhesive surface or bonding surface. The piezoelectric speaker according to claim 1.

13. The aforementioned flexible piezoelectric actuator includes a piezoelectric element, When the diaphragm is observed in a plan view, the piezoelectric element is present in a region that is greater than 0% and less than 100% of the area of ​​the diaphragm. The piezoelectric speaker according to claim 1.

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