Driver unit and headphone

Abstract

Provided are: a driver unit which is provided with a piezoelectric film having a curved section that has been molded, and which, when the driver unit is applied to a headphone, can suppress deformation of the curved section of the piezoelectric film when the headphone is worn, and can suppress a decrease in sound quality; an actuator unit is provided with: a piezoelectric thin film having a piezoelectric body layer comprising a polymer composite piezoelectric body in which piezoelectric body particles are contained in a matrix comprising a polymer material, and electrode layers provided on both surfaces of the piezoelectric body layer; and a perforated plate having at least one through hole, the piezoelectric film has a curved portion formed so as to protrude toward one of the main surfaces and to be recessed toward the other main surface, the perforated plate is laminated on the concave surface side of the curved portion of the piezoelectric film, and the through hole communicates a first air chamber defined by the concave surface of the piezoelectric film and the perforated plate with the outside.

Description

Technical Field

[0001] This invention relates to a driver unit and a headset using the driver unit. Background Technology

[0002] A technique for using a piezoelectric film as a thin loudspeaker is proposed, wherein the piezoelectric film consists of an electrode layer and a protective layer sandwiching a piezoelectric layer.

[0003] For example, Patent Document 1 describes an electroacoustic conversion film (piezoelectric film) comprising: a polymer composite piezoelectric body, wherein piezoelectric particles are dispersed in a viscoelastic matrix composed of a polymer material that is viscoelastic at room temperature; and a pair of electrodes, which are stacked on both sides of the polymer composite piezoelectric body. The electroacoustic conversion film has one or more protrusions formed in a convex shape, wherein the protrusions are formed in a convex shape in a manner that protrudes toward a main surface side.

[0004] Previous technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2016 / 017632 Summary of the Invention

[0007] The technical problem to be solved by the invention

[0008] The inventors have researched the use of piezoelectric thin films in the driver unit of headphones. When used as a driver unit for headphones, a small, lightweight design is required, along with the ability to produce high-quality sound over a wide frequency range. Therefore, the inventors believe that, when using piezoelectric thin films in the driver unit of headphones, a structure that utilizes the piezoelectric thin film itself as a diaphragm and can achieve a wide frequency range with a diaphragm (piezoelectric thin film) that can be mounted in headphones is suitable. This structure utilizes the piezoelectric thin film itself as a diaphragm and can achieve a wide frequency range. The diaphragm is formed into a convex shape, protruding towards a main surface.

[0009] In headphones, there is a known method that makes the ear fit tightly against the ear pads, thus making the internal air chamber (within the shell) almost completely sealed. This is called improving the sound pressure level in the low-frequency range by making it a closed or semi-closed type.

[0010] However, according to the inventors' research, the following problems were discovered: when a driver unit with a piezoelectric film (having a curved portion formed into a convex shape protruding towards a main surface) is assembled into a headphone structure, if the ear is made to fit tightly against the ear pads to make the shell substantially sealed, high-frequency resonance and other issues are generated within the shell, causing deviations in frequency characteristics in the high-frequency range (also known as fluctuations in frequency characteristics, peaks, notches, etc.), thus making it impossible to obtain a flat frequency characteristic.

[0011] The present invention addresses the problems of the prior art and provides a driver unit and a headset, the driver unit having a piezoelectric film with a pre-formed curved portion, which improves frequency characteristics when the driver unit is applied to a headset.

[0012] means for solving technical problems

[0013] To address the aforementioned issues, the present invention has the following structure.

[0014] [1] A driver unit having:

[0015] A piezoelectric thin film having a piezoelectric layer and an electrode layer, wherein the piezoelectric layer is composed of a polymer composite piezoelectric containing piezoelectric particles in a matrix comprising a polymer material, and the electrode layer is disposed on both sides of the piezoelectric layer; and

[0016] A perforated plate in the shape of a plate, having at least one through hole.

[0017] The piezoelectric film has a curved portion, which is shaped to protrude toward one of the main surfaces and be recessed toward the other main surface.

[0018] A perforated plate is stacked on the concave side of the curved portion of the piezoelectric film.

[0019] The through hole connects the first air chamber, defined by the concave surface of the piezoelectric film and the perforated plate, to the outside.

[0020] [2] According to the driver unit described in [1], wherein,

[0021] The total area of ​​the through holes is 3% to 70% of the area of ​​the curved portion of the piezoelectric film when viewed from above.

[0022] [3] According to the driver unit described in [1] or [2], wherein,

[0023] On the side of the perforated plate opposite to the piezoelectric film, there is a sound-absorbing layer made of porous components configured to cover the through holes.

[0024] [4] The driver unit according to any one of [1] to [3], wherein,

[0025] The boundary line of the curved portion of the piezoelectric film is circular.

[0026] [5] The driver unit according to any one of [1] to [4] has a series resistor,

[0027] The series resistor is connected between the electrode layer of the piezoelectric film and the signal source that drives the piezoelectric film.

[0028] [6] A type of over-ear headphone, comprising:

[0029] The driver unit described in any one of [1] to [5];

[0030] Housing, having an opening and accommodating the drive unit; and

[0031] Ear pads are positioned on the opening side of the housing.

[0032] [7] The headphones according to [6], wherein,

[0033] The second air chamber, defined by the drive unit and the housing, is connected to the outside.

[0034] [8] The headphones according to [6] or [7], wherein,

[0035] A housing is disposed on the concave side of the piezoelectric film of the actuator unit.

[0036] [9] The headphones according to [6] have a protective ring,

[0037] The protective ring is configured to contact the ear pad between the driver unit and the ear pad.

[0038] The protective ring has an opening that extends through the surface perpendicular to the ear pad.

[0039] When viewed from a direction perpendicular to the surface in contact with the ear pad, the protective ring contacts more than 30% of the total area of ​​the ear pad.

[0040] The minimum distance between the protective ring and the piezoelectric film of the driver unit is 0.3 mm or more.

[0041] Invention Effects

[0042] According to the present invention, a driver unit and a headset can be provided, wherein the driver unit has a piezoelectric film having a pre-formed curved portion, and frequency characteristics can be improved when the driver unit is adapted to a headset. Attached Figure Description

[0043] Figure 1 This is a cross-sectional view conceptually illustrating an example of a headset of the present invention having the driver unit of the present invention.

[0044] Figure 2 yes Figure 1 The exploded perspective view of the driver unit shown.

[0045] Figure 3 yes Figure 1A three-dimensional view of the piezoelectric thin film of the driver unit shown.

[0046] Figure 4 yes Figure 3 A cross-sectional view of a piezoelectric thin film.

[0047] Figure 5 yes Figure 3 A top view of a piezoelectric thin film.

[0048] Figure 6 This is a top view that conceptually illustrates another example of a piezoelectric thin film.

[0049] Figure 7 This is a diagram illustrating the function of the driver unit of the present invention.

[0050] Figure 8 This is a diagram conceptually illustrating another example of a headset of the present invention having the driver unit of the present invention.

[0051] Figure 9 This is a diagram that conceptually illustrates another example of the driver unit of the present invention.

[0052] Figure 10 This is a cross-sectional view used to illustrate an example of the structure of a piezoelectric thin film.

[0053] Figure 11 This is a conceptual diagram illustrating an example of a method for fabricating piezoelectric thin films.

[0054] Figure 12 This is a conceptual diagram illustrating an example of a method for fabricating piezoelectric thin films.

[0055] Figure 13 This is a conceptual diagram illustrating an example of a method for fabricating piezoelectric thin films.

[0056] Figure 14 This is a block diagram that conceptually illustrates an example of the circuitry that drives the driver unit.

[0057] Figure 15 It is a graph showing the relationship between frequency and sound pressure.

[0058] Figure 16 It is a graph showing the relationship between frequency and sound pressure.

[0059] Figure 17 It is a graph showing the relationship between frequency and sound pressure.

[0060] Figure 18 It is a graph showing the relationship between frequency and sound pressure.

[0061] Figure 19 This is a conceptual diagram used to illustrate the function of a headset with a driver unit that has a comparative example.

[0062] Figure 20 This is a diagram that conceptually illustrates another example of the piezoelectric thin film possessed by the actuator unit of the present invention.

[0063] Figure 21 yes Figure 20 A partially enlarged sectional view.

[0064] Figure 22 This is a cross-sectional view conceptually illustrating another example of a headset of the present invention having the driver unit of the present invention.

[0065] Figure 23 This is a conceptual illustration of an example of the headset of the present invention being pressed onto an artificial ear.

[0066] Figure 24 This is a conceptual illustration of another example of the present invention's headset being pressed onto an artificial ear.

[0067] Figure 25 It is a diagram used to illustrate the area ratio of the contact between the protective ring and the ear pad.

[0068] Figure 26 This is a cross-sectional view conceptually illustrating another example of a headset of the present invention having the driver unit of the present invention.

[0069] Figure 27 It is a graph showing the relationship between frequency and sound pressure.

[0070] Figure 28 It is a graph showing the relationship between frequency and sound pressure.

[0071] Figure 29 It is a graph showing the relationship between frequency and sound pressure. Detailed Implementation

[0072] Hereinafter, the driver unit and headphones of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0073] The following description of the constituent elements is based on a representative embodiment of the present invention, but the present invention is not limited to this embodiment.

[0074] In addition, in this specification, the numerical range indicated by “~” refers to the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0075] [Driver unit and headphones]

[0076] The actuator unit of the present invention comprises: a piezoelectric thin film having a piezoelectric body layer and an electrode layer, the piezoelectric body layer being composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix comprising a polymer material, the electrode layer being disposed on both sides of the piezoelectric body layer; and a perforated plate having at least one through hole, the piezoelectric thin film having a curved portion, the curved portion being shaped to protrude toward one of the main surfaces and be recessed toward the other main surface, the perforated plate being stacked on the concave side of the curved portion of the piezoelectric thin film, the through hole communicating with the outside of a first air chamber defined by the concave side of the piezoelectric thin film and the perforated plate.

[0077] The headphones of the present invention have:

[0078] The aforementioned driver unit;

[0079] Housing, with an opening accommodating the driver unit; and

[0080] Ear pads are positioned on the side of the driver unit opposite to the housing.

[0081] <Driver Unit>

[0082] Figure 1 This is a cross-sectional view of an example of a headset of the present invention having an example of the driver unit of the present invention.

[0083] Figure 1 The headset 200 shown includes: a driver unit 100, a housing 202, ear pads 204, and ear pad locking components 206.

[0084] Figure 2 An exploded perspective view of the driver unit 100 is shown.

[0085] like Figure 1 and Figure 2 As shown, the driver unit 100 includes: a holding member 106, a piezoelectric film 10, a perforated plate 102, a holding member 108, a porous member 104, and a fastening member 110.

[0086] The piezoelectric film 10 has a piezoelectric body layer and an electrode layer. The piezoelectric body layer is composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material. The electrode layer is disposed on both sides of the piezoelectric body layer. The piezoelectric film also has a curved portion 10a, which is shaped to protrude toward one of the main surfaces and be recessed toward the other main surface.

[0087] The details of each layer constituting the piezoelectric thin film 10 will be described in detail later.

[0088] Figure 3 The figure shows a perspective view of the piezoelectric thin film 10. Figure 4 The figure shows a cross-sectional view of the piezoelectric thin film 10. Figure 5 The image shows a top view of the piezoelectric film 10. A top view is a view taken from a direction perpendicular to the main surface of the flat portion (the area where the curved portion 10a is not formed) of the piezoelectric film 10. Figure 4 The diagram is viewed from the direction of arrow b. Furthermore, in this invention, the main surface refers to the largest surface of the sheet-like object.

[0089] exist Figures 3-5 In the example shown, the piezoelectric film 10 has a generally circular shape when viewed from above, with a (convex) curved portion 10a formed at its approximately central portion with a diameter Ds and a height H, protruding towards one of the main surfaces. Furthermore, when viewed from the main surface opposite to the side of the main surface where the curved portion 10a protrudes, the curved portion 10a appears recessed. That is, the piezoelectric film 10 can also be described as a film with a recessed portion.

[0090] Furthermore, in Figures 3-5 In the example shown, the shape of the curved portion 10a when viewed from above is approximately circular. That is, the shape formed by the boundary line of the curved portion 10a is circular. Furthermore, in Figures 3-5 In the example shown, the curved portion 10a is shaped as a part of a sphere (roughly spherical).

[0091] Furthermore, the shape of the curved portion 10a is not particularly limited, but is preferably part of a sphere or a part of an ellipsoid of revolution. Also, the shape of the curved portion when viewed from above is not particularly limited, and can be, for example... Figure 6 The shape shown is roughly elliptical.

[0092] Furthermore, the shape of the curved portion when viewed from a cross-section perpendicular to the main surface of the piezoelectric film is as follows: Figure 4 As shown, it is preferred that the entire section bends, but this is not a limitation; a portion may also have a flat section. For example, the top of the bend may be flat.

[0093] Furthermore, when the curved portion 10a, viewed from a section perpendicular to the main surface of the piezoelectric film 10, is defined as an arc, and the straight line connecting the two endpoints of the arc is defined as a chord, the angle θ formed by the main surface of the retaining member 106 and the chord does not need to be a right angle (90°). For example, when the chord length is 60 mm and the distance from the midpoint of the arc to the midpoint of the chord, i.e., the arc height, is 5 mm, the case where the angle formed by the tangent at the two endpoints of the arc and the chord is equal to the inscribed angle of the arc is called the tangent-chord theorem, and the inscribed angle in this case is 18.9°. That is, if the angle θ formed by the main surface of the retaining member 106 and the chord is 18.9° or greater, interference between the curved portion 10a of the piezoelectric film 10 and the retaining member 106 can be avoided.

[0094] If a voltage is applied to the electrode layer (electrode pair) of the piezoelectric layer holding the piezoelectric film 10, the piezoelectric layer is driven to stretch and contract according to the applied voltage. At this time, in the bending portion 10a, the stretching and contraction in the surface direction is converted into vibration in the direction perpendicular to the surface, and the electrical signal is converted into vibration (sound).

[0095] The diameter Ds and height H of the curved portion 10a of the piezoelectric film 10 are not particularly limited, and can be appropriately set according to the size of the housing and ear pads of the headset 200 to which the driver unit 100 is assembled. From the viewpoint of improving the sound pressure level in the audible range, the diameter Ds of the curved portion 10a is preferably 30mm to 80mm, more preferably 40mm to 70mm, and even more preferably 50mm to 60mm. Furthermore, the height H of the curved portion 10a is preferably 1mm to 10mm, more preferably 2mm to 7mm, and even more preferably 3mm to 5mm. In addition, regarding the abnormal deformation of the curved portion 10a described later, a smaller diameter Ds is less likely to occur, but the driver unit 100 of the present invention can appropriately suppress the abnormal deformation of the curved portion 10a. Therefore, from the viewpoint of improving the sound pressure level in the audible range, it is preferable to set the diameter Ds within the above range.

[0096] Furthermore, from the viewpoint of effectively converting the planar expansion and contraction of the piezoelectric film under applied voltage into vibration in a direction perpendicular to the plane to increase sound pressure, the ratio H / Ds of the diameter Ds to the height H of the bent portion 10a preferably satisfies 0 < H / Ds ≤ 0.15. The upper limit of H / Ds is preferably 0.1 or less, more preferably 0.075 or less, and even more preferably 0.05 or less. The lower limit is preferably 0.003 or more, more preferably 0.005 or more.

[0097] A perforated plate 102 is stacked on the concave side of the curved portion 10a of the piezoelectric film 10. In the example shown, the perforated plate 102 is in direct contact with the concave side of the piezoelectric film 10.

[0098] A perforated plate 102 is disposed on the concave side of the curved portion 10a of the piezoelectric film 10, and defines a first air chamber 101 enclosed between the perforated plate 102 and the concave surface.

[0099] One or more through holes 102a are formed approximately at the center of the perforated plate 102, which communicate the first air chamber 101 with the outside. In the example shown, 13 through holes 102a are arranged alternately. Furthermore, the shape of the opening cross section of each through hole 102a is approximately circular.

[0100] The number and size of the through holes 102a formed in the perforated plate 102 are not particularly limited. Furthermore, in the example shown, all the through holes 102a have the same diameter, but this is not a limitation; through holes 102a with different diameters may also be present. Moreover, the ratio of the total area of ​​the through holes 102a to the area of ​​the vibration region of the piezoelectric film 10, i.e., to the area of ​​the curved portion 10a viewed from above, is preferably 3% to 70%. This will be explained in detail later.

[0101] The configuration of the through hole 102a is not particularly limited as long as it can connect the first air chamber 101 to the outside. Furthermore, when there are multiple through holes 102a, the configuration pattern of the multiple through holes 102a is also not particularly limited.

[0102] Viewed from above, the perforated plate 102 has insertion holes 102b near its ends for inserting through the fastening member 110 (described later). The number and arrangement of the insertion holes 102b in the perforated plate 102 can be set to match the number and arrangement of the threaded holes 106a in the retaining member 106. In the example shown, there are a total of eight insertion holes 102b at predetermined intervals in the circumferential direction. However, the number and arrangement of the insertion holes 102b are not limited to this. Furthermore, the perforated plate 102 can be configured such that it does not have insertion holes 102b, and its outer diameter does not overlap with the position of the threaded holes 106a in the retaining member 106, and it is held only by the retaining member 106 and the retaining member 108.

[0103] There is no particular limitation on the thickness of the perforated plate 102. From the viewpoint of miniaturization and weight reduction of the driver unit 100, it is preferably 0.1 mm to 5 mm, more preferably 0.2 mm to 3 mm, and even more preferably 0.3 mm to 1 mm.

[0104] As a perforated plate 102, it is possible to utilize various plate-shaped materials (sheets, films).

[0105] As an example, the perforated plate 102 can include resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins; foam plastics made of expanded polystyrene, expanded polystyrene, and expanded polyethylene; plywood, corkboard, leather such as cowhide; various types of paperboard such as carbon paper and Japanese paper; various corrugated cardboard materials made by laminating other paperboards onto one or both sides of corrugated paperboard; and thin-film metals made of various metals such as stainless steel, aluminum, copper, and nickel, as well as various alloys. Furthermore, the perforated plate 102 can be a composite material formed by laminating thin films made of these materials, and can also undergo various surface treatments such as aluminum anodizing.

[0106] Holding member 106 and holding member 108 are components used to hold the piezoelectric film 10 and the perforated plate 102 in a stacked state. Holding member 106 and holding member 108 are annular (ring-shaped) plate components. Holding member 106 is disposed on the piezoelectric film 10 side and holding member 108 is disposed on the perforated plate 102 side, clamping the piezoelectric film 10 and the perforated plate 102, and holding them in a stacked state.

[0107] The opening of the retaining member 106 has a diameter larger than the diameter of the curved portion 10a of the piezoelectric film 10 when viewed from above, and has a size for the curved portion to be inserted through the protrusion 10a. The retaining member 106 abuts against at least a portion of the edge of the piezoelectric film 10.

[0108] Viewed from above, the retaining member 106 has a threaded hole 106a near its end for engaging with the fastening member 110 described later. The number and arrangement of the threaded holes 106a in the retaining member 106 can be appropriately set. In the example shown, there are a total of eight threaded holes 106a provided at predetermined intervals in the circumferential direction. However, the number and arrangement of the threaded holes 106a are not limited to this.

[0109] The opening of the retaining member 108 is sized to not block the through hole 102a of the perforated plate 102. Furthermore, viewed from above, the retaining member 108 has an insertion hole 108a near its end for inserting the fastening member 110, which will be described later. The number and arrangement of the insertion holes 108a in the retaining member 108 can be set to match the number and arrangement of the threaded holes 106a in the retaining member 106. In the example shown, a total of eight insertion holes 108a are provided at predetermined intervals in the circumferential direction. However, the number and arrangement of the insertion holes 108a are not limited to this.

[0110] like Figure 1 As shown, a screw serving as a fastening member 110 is inserted from the retaining member 108 side into the insertion hole 108a of the retaining member 108 and the insertion hole 102b of the perforated plate, and screwed into the threaded hole 106a of the retaining member 106, thereby retaining the piezoelectric film 10 and the perforated plate 102 by the retaining member 106 and the retaining member 108.

[0111] Furthermore, in the illustrated example, the retaining members 106 and 108 are generally circular in top view, and their openings are also generally circular. However, this is not a limitation; various shapes can be used as long as they can properly clamp the piezoelectric film 10 and the perforated plate 102. Moreover, the retaining members 106 and 108 do not have to be the same shape. For example, the retaining members 106 and 108 may have different opening diameters or different thicknesses.

[0112] The thickness of the retaining member 106 and the retaining member 108 is preferably 0.3 mm to 5 mm, more preferably 0.5 mm to 3 mm, and even more preferably 1 mm to 2 mm.

[0113] The same material as the material used to form the retaining member 106 and retaining member 108 can be used.

[0114] In the example shown, the retaining member 106 and retaining member 108 are structured to be fixed by the fastening member (screw) 110 while the piezoelectric film 10 and the perforated plate 102 are clamped, but this is not a limitation. Various known methods can be used to fix the retaining member 106 and retaining member 108, such as using bolts and nuts, or using fixing clamps. Furthermore, the retaining member 108 on the perforated plate 102 side may be omitted, and the perforated plate 102 itself may serve as the retaining member. That is, the perforated plate 102 and the retaining member 108 may also be formed integrally.

[0115] A porous component 104 is disposed on the surface of the perforated plate 102 opposite to the piezoelectric film 10 to cover the through holes 102a. In the example shown, the perforated plate 102 has a plurality of through holes 102a, and therefore the porous component 104 is configured to cover the plurality of through holes 102a. The porous component 104 corresponds to the sound-absorbing layer in this invention.

[0116] The porous component 104 has multiple small holes or pores formed inside, making it a component capable of communicating with gas. The porous component 104 acts as an airflow resistance between the first air chamber 101 and the second air chamber, which are connected through the through hole 102a of the perforated plate 102, and functions as a pressure regulating valve. This will be described in detail later.

[0117] There are no particular limitations on the porous component 104, and known porous components can be appropriately utilized. For example, various known porous components can be used, such as foams, foaming materials (e.g., foamed polyurethane foam (e.g., CALMFLEX F manufactured by INOAC CORPORATION, polyurethane foam manufactured by HIKARI CO.,LTD.), flexible polyurethane foam, ceramic particle sintering materials, phenolic foam, melamine foam, polyamide foam, etc.). Furthermore, nonwoven or woven fabrics can also be used as porous components. As a nonwoven fabric, various known nonwoven fabrics can be used, such as nonwoven sound-absorbing materials (microfiber nonwoven fabrics (e.g., Thinsulate from 3M Company), polyester nonwoven fabrics (e.g., White Qion from Tokyo Bouon Co., Ltd., QonPET from Bridgestone KBG Co., Ltd., Micromat from Softplene Industrial Co., Ltd., and these products are also provided in a double-layer structure of high-density thin-surface nonwoven fabric and low-density back-side nonwoven fabric), and plastic nonwoven fabrics such as acrylic fiber nonwoven fabrics, natural fiber nonwoven fabrics such as wool and felt, metal nonwoven fabrics, and glass nonwoven fabrics, etc.), and other materials containing tiny air particles (glass wool, rock wool, nanofiber sound-absorbing materials (silica nanofibers, acrylic nanofibers (e.g., XAI from Mitsubishi Chemical Corporation)) etc.

[0118] Furthermore, multiple layers of porous components (non-woven fabric, woven fabric) with different airflow resistances can be stacked. Additionally, at least two types of porous components, non-woven fabrics, and woven fabrics can be stacked together.

[0119] The thickness of the porous component (non-woven fabric, woven fabric) is not particularly limited, as long as it is set to a thickness that allows the outflow and inflow rates of the gas (air) from the first air chamber 101 to be in a desired state, depending on the type of porous component (non-woven fabric, woven fabric). The thickness of the porous component (non-woven fabric, woven fabric) is preferably 1 mm to 50 mm, more preferably 3 mm to 30 mm, and even more preferably 5 mm to 20 mm.

[0120] Furthermore, in the example shown in the figure, the porous component 104 is configured to be disposed on the side of the perforated plate 102 opposite to the piezoelectric film 10, but it is not limited to this. The porous component (non-woven fabric, woven fabric) may also be disposed in the through hole 102a of the perforated plate 102.

[0121] The driver unit 100 having the structure described above is assembled into the headphones 200.

[0122] <Headphones>

[0123] The headphones 200 have a headband (not shown) and a pair of housings disposed at both ends of the headband, and can be connected to an audio device (music player, smartphone, etc., not shown) via wired or wireless connection.

[0124] Figure 1 This is a conceptual cross-sectional view of a portion of a headset, comprising: a housing 202 forming the outer shell of the headset; a driver unit 100 housed within the housing 202; ear pads 204 disposed on the side of the driver unit 100 opposite to the side of the housing 202; and ear pad locking members 206 for locking the ear pads 204 to the housing 202.

[0125] When a user wears the headphones 200, the housing 202 has an opening on the side that becomes the user's ear, and the driver unit 100 is disposed within the housing 202 in such a way that at least a portion of the opening is blocked.

[0126] The shape of the housing 202 can be set to be the same as that of the housing of conventionally known headphones, such as a shape that is roughly cylindrical with a bottom, roughly spherical, or a part of a roughly elliptical body.

[0127] exist Figure 1 In the example shown, the actuator unit 100 is configured such that the piezoelectric film 10 side faces the opening of the housing 202, and the porous component 104 side faces the interior (bottom) of the housing 202. In other words, the housing 202 is disposed on the concave side of the piezoelectric film 10.

[0128] like Figure 1 As shown, a second air chamber 201 is formed in the headphones, defined by the perforated plate 102 and the housing 202 of the driver unit 100. The second air chamber 201 communicates with the first air chamber 101 via a through hole 102a and a porous component 104. Furthermore, in Figure 1 In the example shown, the housing 202 has a through hole 202a on the bottom surface, and the second air chamber 201 communicates with the outside.

[0129] In addition, Figure 1 In the example shown, the housing 202 has a through hole 202a on its bottom surface, thereby connecting the second air chamber 201 to the outside, but this is not a limitation. For example, the through hole may also be located on the side surface of the housing 202. Alternatively, a gap may be provided between the housing 202 and the driver unit 100, thereby connecting the second air chamber 201 to the outside. Furthermore, the housing 202 may not have a through hole 202a. That is, the headphones may be designed as a completely closed type.

[0130] Furthermore, in Figure 1 In the example shown, the porous component 104 fills a portion of the second air chamber 201, but it is not limited to this; the porous component 104 may also fill the entire area of ​​the second air chamber 201. Furthermore, the porous component 104 may be divided into multiple parts and disposed within the second air chamber 201.

[0131] The ear pad 204 is a cushioned, slightly circular (donut-shaped) component used to cover the user's ears when the user wears the headphones 200. The ear pad 204 is disposed on the opening side of the housing 202, i.e., on the driver unit 100 side. Furthermore, in the example shown, the ear pad 204 is locked to the ear pad locking member 206 and is fixed to the housing 202 or the driver unit 100 by the ear pad locking member 206.

[0132] There are no particular limitations on the use of ear pad 204, and it is possible to make appropriate use of previously known ear pad 204.

[0133] In addition, although the illustration is omitted, the headset 200 may further include components that are known in conventional headsets 200, such as circuitry for driving the driver unit 100 and a cover for protecting the driver unit 100.

[0134] Next, the function of the headset 200 equipped with the driver unit 100 of the present invention having this structure will be explained.

[0135] As described above, the inventors have studied the use of a piezoelectric thin film in a driver unit for headphones. This piezoelectric thin film comprises: a piezoelectric layer containing a polymer composite piezoelectric material, wherein the polymer composite piezoelectric material is formed by dispersing piezoelectric particles in a matrix composed of a polymer material; and electrode layers disposed on both sides of the piezoelectric layer. When used as a driver unit for headphones, small size and lightweight are required to enable mounting in headphones and to produce high-quality sound over a wide frequency range. Therefore, the inventors believe that utilizing the piezoelectric thin film itself as a diaphragm, and having a structure that allows for mounting in headphones and achieves a wide frequency range, is suitable for piezoelectric thin films with protrusions (bent portions), the protrusions being formed into a convex shape protruding towards a main surface.

[0136] In headphones, there is a known method that makes the internal air chamber (within the shell) substantially sealed by sealing the ear against the ear pads, thus increasing the sound pressure in the low-frequency range.

[0137] However, according to the inventors' research, the following problem has been discovered: In the structure of assembling a driver unit into a headphone, the driver unit has a piezoelectric film with a curved portion formed into a convex shape that protrudes toward a main surface. If the ear is made to fit tightly against the ear pads so that the shell is in a basically sealed state, resonance caused by standing waves will occur in the shell, especially in the high frequency range, causing deviations in frequency characteristics (also known as fluctuations in frequency characteristics, peaks, notches, etc.), thus making it impossible to obtain a flat frequency characteristic.

[0138] In contrast, in the headphone 200 with the driver unit 100 of the present invention, the driver unit 100 has a perforated plate 102 with a through hole 102a on the concave side of the curved portion 10a of the piezoelectric film 10, and more preferably has a sound-absorbing layer made of a porous material on its back side, thereby suppressing resonance in the housing 202 and suppressing frequency characteristic deviations (frequency characteristic fluctuations, peaks and notches) in the high frequency range, thereby obtaining a flat frequency characteristic.

[0139] Furthermore, it is known that the following problem sometimes occurs in the assembly of a driver unit into a headphone: the driver unit has a piezoelectric film with a convex curved portion formed protruding toward a main surface side; the curved portion of the piezoelectric film deforms from the formed shape (hereinafter also referred to as abnormal deformation), resulting in a decrease in sound quality. Specifically, as... Figure 19 As shown, in the conventional headphones 1000, when worn on the ears, if the ear pads 204 are pressed against the user's ears (U... Figure 19 In the case of the ear pad 204 (as indicated by arrow X), the ear pad 204 deforms, thereby ensuring proper airtightness of the air chamber surrounded by the ear U, the ear pad 204, and the actuator unit (piezoelectric film 10). At this time, due to the reduction in the volume of the air chamber, the air pressure inside the ear-side air chamber increases. A pressure difference is then created between the air chamber on the ear side (convex side) and the air chamber on the housing side (concave side) of the piezoelectric film 10. However, in the case of a soft piezoelectric film, even a relatively small pressure difference can cause abnormal deformation of the formed curved portion. If this curved portion deforms abnormally, such as... Figure 16 As shown in the comparison between the solid and dashed lines in the graph, it can be seen that changes in frequency response lead to a decrease in sound quality. It is evident that sound pressure level drops, especially in the low-frequency range.

[0140] Furthermore, when the headphones are removed, there is sometimes a pressure difference between the ear pad side of the piezoelectric film 10 and the opposite side (the housing 202 side), which can cause abnormal deformation of the bending part.

[0141] In contrast, the headphones 200 having the driver unit 100 of the present invention, such as Figure 7As shown, when wearing the headphones 200, if the ear pads 204 are pressed against the user's ears (U), Figure 7 (In the middle, arrow X), the ear pad 204 deforms, thereby ensuring that the air chamber surrounded by the ear U, ear pad 204, and actuator unit 100 (piezoelectric film 10) has proper airtightness. Because the volume of this air chamber decreases, the air pressure inside the air chamber increases. At this time, the first air chamber 101 and the second air chamber on the concave side of the piezoelectric film 10 are separated by a perforated plate 102. Preferably, the back side of the perforated plate 102 is covered by a porous component 104, thus preventing the air in the first air chamber 101 from being instantly discharged into the second air chamber (…). Figure 7 As a result, the pressure rise in the ear-side air chamber can be suppressed, preventing the piezoelectric film from bending and deforming. During this period, the air in the ear-side air chamber surrounded by the ear pad 204, the ear U, and the actuator unit 100 (piezoelectric film 10) also passes through the ear pad 204 (…). Figure 7 In the middle, arrow Z) or through the gap between the ear pad 204 and the ear U, the air pressure in the air chamber gradually decreases. Thus, by maintaining a pressure balance between the convex side of the piezoelectric film 10 on the ear pad 204 side and the concave side on the opposite side (the housing 202 side), abnormal deformation of the bent portion 10a can be prevented. Therefore, as Figure 15 As shown by the solid and dashed lines in the curve graph, this also helps prevent changes in frequency characteristics from causing a decrease in sound quality. For example... Figure 15 As shown, a flat frequency response can be achieved from the low frequency range to the high frequency range. Furthermore, in Figure 7 For illustrative purposes, the illustrations of retaining member 106, retaining member 108, and fastening member 110 are omitted.

[0142] Furthermore, when the headphones 200 are removed, it is possible to prevent the difference in air pressure between the ear pad 204 side of the piezoelectric film 10 and the opposite side (the housing 202 side), thereby preventing deformation of the bent portion 10a.

[0143] As described above, the headphone 200 having the driver unit 100 of the present invention has a perforated plate 102 with a through hole 102a and a porous component 104 disposed on the concave side of the piezoelectric film 10 with the bend 10a, which reduces the pressure change in the first air chamber 101 on the concave side when wearing or removing the headphone 200, thereby also preventing abnormal deformation of the bend 10a.

[0144] Furthermore, as a preferred embodiment, the driver unit 100 of the present invention has a sound-absorbing layer composed of a porous component 104 on the back side of the perforated plate 102 (the side opposite to the piezoelectric film 10). In the headphones 200 having such a driver unit 100, the structure of the piezoelectric film 10 on the concave side (back side) having a sound-absorbing layer composed of the perforated plate 102 and the porous component 104 on its back side is a so-called composite sound-absorbing structure. By selecting the aperture ratio of the perforated plate 102, the thickness of the sound-absorbing layer on the back side, and the material, a wide range of sound absorption characteristics can be achieved, allowing for arbitrary selection of porous sound absorption, plate vibration sound absorption, and resonant sound absorption features. Therefore, standing waves generated within the housing can be suppressed, and fluctuations and peak / notch waves in the frequency response can be improved to obtain a flat frequency response.

[0145] Here, in Figure 1 In the example shown, the actuator unit 100 is configured such that the piezoelectric film 10 side faces the opening of the housing 202, and the porous component 104 side faces the interior (bottom) of the housing 202, with the housing 202 disposed on the concave side of the piezoelectric film 10, but it is not limited to this configuration. Figure 8 As shown in the headset 200b, the driver unit 100 can be configured such that the piezoelectric film 10 side faces the interior of the housing 202 and the porous component 104 side faces the opening of the housing 202. In other words, it can also be configured such that the housing 202 is positioned on the convex side of the piezoelectric film 10.

[0146] exist Figure 8 In the case of the structure of the headset 200b shown, resonance caused by standing waves in the housing 202 can also be suppressed, and deviations in the high-frequency response can be suppressed, thereby obtaining a flat frequency response.

[0147] Furthermore, in Figure 1 In the example shown, the driver unit 100 is configured to have a porous component 104, which is arranged to cover the through holes 102a of the perforated plate 102, but is not limited to this, such as Figure 9 The driver unit 100b shown may also be a structure without the porous component 104. Figure 9 The driver unit 100b shown does not have the porous component 104, but has the same characteristics as... Figure 1 The driver unit 100 shown has the same structure.

[0148] As described above, the combination of the perforated plate 102 and the porous component 104 constitutes a so-called composite sound-absorbing structure. By selecting the aperture ratio of the perforated plate 102, the thickness of the sound-absorbing layer on the back side, and the material, a wide range of sound absorption characteristics can be achieved, allowing for arbitrary selection of porous sound absorption, plate vibration sound absorption, and resonant sound absorption features. Therefore, it is possible to suppress standing waves generated within the housing, improve frequency response fluctuations and peak / notch waves, and obtain a flat frequency response. On the other hand, the perforated plate 102 alone can achieve sound absorption characteristics with both plate vibration and resonant features, thus having a certain effect on suppressing the generation of standing waves within the housing.

[0149] From the viewpoint of obtaining flat frequency characteristics by improving the fluctuations, peaks, and notch waves in the frequency characteristics in the high-frequency region, the ratio of the total area of ​​the through hole 102a to the area of ​​the vibration region of the piezoelectric film 10, i.e. the area of ​​the curved portion 10a when viewed from above, is preferably 3% to 70%, more preferably 25% to 65%, and even more preferably 40% to 60%.

[0150] Furthermore, from the viewpoint of obtaining flat frequency characteristics by improving frequency fluctuations, peaks, and notch waves in the high-frequency region, the diameter (equivalent circle diameter) of each through hole 102a of the perforated plate 102 is preferably 0.01 mm to 10 mm, more preferably 0.1 mm to 6 mm, and even more preferably 0.5 mm to 4 mm.

[0151] Even in a driver unit 100b that does not have a porous component 104, a flat frequency response can be obtained by appropriately setting the total area and diameter of the through holes 102a of the perforated plate 102, thereby improving fluctuations, peaks, and notch waves in the frequency response.

[0152] <Piezoelectric Thin Film>

[0153] Next, the layer structure of the piezoelectric thin film 10 will be described.

[0154] The piezoelectric thin film 10 has a piezoelectric body layer and an electrode layer. The piezoelectric body layer is composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material. The electrode layers are disposed on both sides of the piezoelectric body layer. When a voltage is applied to the electrode layers (electrode pairs) that hold the piezoelectric body layer, the piezoelectric body layer expands and contracts according to the applied voltage. As a result, the piezoelectric thin film 10 (piezoelectric body layer 20) contracts in the thickness direction. At the same time, due to Poisson's ratio, the piezoelectric thin film 10 also expands and contracts in the planar direction. Thus, the piezoelectric thin film 10 can exhibit piezoelectric properties.

[0155] exist Figure 10 The enlarged view shows a portion of the piezoelectric thin film 10.

[0156] Figure 10The piezoelectric thin film 10 shown includes: a piezoelectric layer 20, which is a sheet-like material with piezoelectric properties; a first electrode layer 24, stacked on one side of the piezoelectric layer 20; a first protective layer 28, stacked on the side of the first electrode layer 24 opposite to the piezoelectric layer 20; a second electrode layer 26, stacked on the other side of the piezoelectric layer 20; and a second protective layer 30, stacked on the side of the second electrode layer 26 opposite to the piezoelectric layer 20. That is, the piezoelectric thin film 10 has the following structure: the piezoelectric layer 20 is sandwiched between electrode layers, and a protective layer is stacked on the surface of the electrode layers that is not in contact with the piezoelectric layer.

[0157] In this invention, such as Figure 10 As schematically shown, the piezoelectric layer 20 is a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing polymer material.

[0158] The material used for the matrix 34 (matrix also serving as adhesive) of the polymer composite piezoelectric body constituting the piezoelectric layer 20 is preferably a polymer material that has viscoelasticity at room temperature. Furthermore, in this specification, "room temperature" refers to a temperature range of approximately 0 to 50°C.

[0159] The polymer composite piezoelectric (piezoelectric layer 20) preferably has the following requirements.

[0160] (i) flexibility

[0161] For example, when held in a portable manner, such as a newspaper or magazine, with a slow, bending motion similar to that of a document, it is subjected to relatively slow but significant bending deformation at a frequency of several Hz from the outside. In this case, there is a concern that if the polymer composite piezoelectric material is rigid, a correspondingly large bending stress will be generated, leading to cracking at the interface between the polymer matrix and the piezoelectric particles, ultimately resulting in failure. Therefore, the polymer composite piezoelectric material is required to have appropriate flexibility. Furthermore, if the strain energy can be diffused outward as heat, the stress can be relaxed. Therefore, the polymer composite piezoelectric material is required to have a moderately large loss tangent.

[0162] (ii) Sound quality

[0163] The loudspeaker vibrates piezoelectric particles in the 20Hz–20kHz audio frequency band, and the vibrational energy causes the entire polymer composite piezoelectric film (piezoelectric film) to vibrate as a whole, thereby reproducing sound. Therefore, to improve the efficiency of vibrational energy transfer, the polymer composite piezoelectric material needs to have appropriate stiffness. Furthermore, if the loudspeaker's frequency response is smooth, the change in sound quality when the lowest resonant frequency changes with curvature is also reduced. Therefore, the polymer composite piezoelectric material needs to have a sufficiently large loss tangent.

[0164] In summary, the polymer composite piezoelectric material is required to exhibit rigidity for vibrations in the 20Hz–20kHz range, while exhibiting flexibility for vibrations below a few Hz. Furthermore, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large relative to vibrations at all frequencies below 20kHz.

[0165] Typically, polymeric solids exhibit viscoelastic relaxation mechanisms. With increasing temperature or decreasing frequency, large-scale molecular motion is observed as a decrease (relaxation) in the stored elastic modulus (Young's modulus) or a maximum loss of elastic modulus (absorption). Among these, relaxation caused by the micro-Brownian motion of molecular chains through amorphous regions is called principal dispersion, and very large relaxation phenomena can be observed. The temperature at which this principal dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most clearly manifested.

[0166] In the polymer composite piezoelectric (piezoelectric layer 20), by using a polymer material with a glass transition point at room temperature—in other words, a polymer material that is viscoelastic at room temperature—in the matrix, a polymer composite piezoelectric material that exhibits rigidity for vibrations in the range of 20 Hz to 20 kHz and flexibility for slow vibrations below a few Hz is achieved. In particular, to appropriately express this characteristic, it is preferable to use a polymer material with a glass transition point at room temperature (0–50°C) within a frequency of 1 Hz in the matrix of the polymer composite piezoelectric.

[0167] As a viscoelastic polymer material at room temperature, various known materials can be used. Preferably, the polymer material has a maximum loss tangent Tanδ of 0.5 or higher at a frequency of 1 Hz based on dynamic viscoelasticity testing at room temperature (0–50°C).

[0168] Therefore, when a polymer composite piezoelectric is slowly bent by an external force, the stress concentration at the interface between the polymer matrix and the piezoelectric particles in the part of maximum bending moment is relaxed, and high flexibility can be expected.

[0169] Furthermore, the viscoelastic polymer material at room temperature preferably has a stored elastic modulus (E') at a frequency of 1 Hz obtained based on dynamic viscoelasticity measurement that is 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0170] Therefore, it is possible to reduce the bending moment generated when the polymer composite piezoelectric is slowly bent by external force, while maintaining rigidity for acoustic vibrations in the range of 20Hz to 20kHz.

[0171] Furthermore, among viscoelastic polymer materials at room temperature, those with a relative permittivity of 10 or higher at 25°C are preferred. Consequently, when a voltage is applied to the polymer composite piezoelectric, a higher electric field is applied to the piezoelectric particles in the matrix, thus allowing for a larger deformation.

[0172] However, on the other hand, if good moisture resistance is to be ensured, it is also preferable that the dielectric constant of the polymer material is less than 10 at 25°C.

[0173] Examples of viscoelastic polymers that meet these conditions at room temperature include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Furthermore, commercially available products such as HYBRAR5127 (manufactured by KURARAY CO.,LTD) can also be appropriately used as such polymers. Among these, materials containing cyanoethyl groups are preferred, and cyanoethylated PVA is particularly preferred.

[0174] As a viscoelastic polymer material at room temperature, a polymer material having a cyanoethyl component is preferred, and cyanoethylated PVA is particularly preferred. That is, in this invention, the piezoelectric layer 20 preferably uses a polymer material having a cyanoethyl component as the matrix 34, and cyanoethylated PVA is particularly preferred.

[0175] In the following description, the aforementioned polymeric materials, represented by cyanoethylated PVA, will also be collectively referred to as "polymeric materials that have viscoelasticity at room temperature".

[0176] In addition, these viscoelastic polymers at room temperature can be used in combination (mixed) with only one type.

[0177] The matrix 34, which uses these viscoelastic polymers at room temperature, can be used in combination with a variety of polymers as needed.

[0178] That is, viscoelastic materials such as cyanoethylated PVA can be added to the matrix 34 for the purpose of adjusting dielectric or mechanical properties, or other dielectric polymer materials can be added as needed.

[0179] Examples of polymeric materials that can be added include fluorinated polymers such as polyvinylidene fluoride, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer; vinylidene cyanide-vinyl acetate copolymer; cyanoethyl cellulose; cyanoethyl hydroxysucrose; cyanoethyl hydroxycellulose; cyanoethyl hydroxypulllan; cyanoethyl methacrylate; cyanoethyl cyanoacrylate; cyanoethyl hydroxyethyl cellulose; cyanoethyl linear starch; cyanoethyl hydroxypropyl cellulose; cyanoethyl dihydroxypropyl cellulose; cyanoethyl hydroxypropyl linear starch; cyanoethyl polyacrylamide; cyanoethyl ethyl polyacrylate; cyanoethyl pullulan; cyanoethyl polyhydroxymethylene; cyanoethyl glycidyl pullulan; cyanoethyl sucrose; and cyanoethyl sorbitol, as well as synthetic rubbers such as nitrile rubber or chloroprene rubber.

[0180] Among them, polymers containing cyanoethyl groups are preferred.

[0181] In addition, in the matrix 34 of the piezoelectric layer 20, these dielectric polymer materials are not limited to one type, but can be added in multiple ways.

[0182] In addition, in order to adjust the glass transition point Tg, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene and isobutene, as well as thermosetting resins such as phenolic resin, urea-formaldehyde resin, melamine resin, alkyd resin and mica can be added to the matrix 34 in addition to dielectric polymer materials.

[0183] Furthermore, to improve adhesion, tackifiers such as rosin esters, rosin, terpenes, terpene phenols, and petroleum resins can be added.

[0184] There is no particular limitation on the amount of materials other than viscoelastic polymers such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20, but it is preferable to add materials of 30% by mass or less, based on their proportion in the matrix 34.

[0185] Therefore, the properties of the added polymer material can be expressed without damaging the viscoelastic relaxation mechanism in the matrix 34, thus achieving preferred results in terms of high dielectric constant, improved heat resistance, and improved adhesion with the piezoelectric particles 36 and the electrode layer.

[0186] The piezoelectric layer 20 is a layer composed of a polymer composite piezoelectric material containing piezoelectric particles 36 in the substrate 34. The piezoelectric particles 36 are dispersed in the substrate 34. Preferably, the piezoelectric particles 36 are uniformly (or substantially uniformly) dispersed in the substrate 34.

[0187] The piezoelectric particle 36 is a particle composed of ceramic particles with perovskite or wurtzite crystal structures.

[0188] Examples of ceramic particles constituting piezoelectric particles 36 include lead zirconate titanate (PZT), lanthanum lead zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0189] The particle size of the piezoelectric particles 36 is not limited, and can be appropriately selected according to the size and application of the piezoelectric film 10. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm.

[0190] By setting the particle size of the piezoelectric particles 36 within this range, optimal results can be obtained in the piezoelectric film 10, which can take into account both high voltage characteristics and flexibility.

[0191] In addition, the piezoelectric particles 36 in the piezoelectric layer 20 can be uniformly and regularly dispersed in the substrate 34, and can also be irregularly dispersed in the substrate 34 as long as they are uniformly dispersed.

[0192] In the piezoelectric thin film 10, the ratio of the substrate 34 to the piezoelectric particles 36 in the piezoelectric layer 20 is not limited, and can be appropriately set according to the size and thickness of the piezoelectric thin film 10 in the surface direction, its application, and the required characteristics.

[0193] The volume fraction of piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore, it is even more preferably set to 50 to 80%.

[0194] By setting the ratio of the substrate 34 to the piezoelectric particles 36 within the above-mentioned range, an optimal result can be obtained that combines high voltage characteristics and flexibility.

[0195] In the piezoelectric film 10, the thickness of the piezoelectric layer 20 is not particularly limited, and can be appropriately set according to the required characteristics of the piezoelectric film 10.

[0196] The thicker the piezoelectric layer 20, the more advantageous it is in terms of rigidity, such as the stiffness of the sheet, but the voltage (potential difference) required to make the piezoelectric film 10 expand and contract by the same amount becomes larger.

[0197] The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm.

[0198] By setting the thickness of the piezoelectric layer 20 within the aforementioned range, a preferred result can be obtained while ensuring rigidity and appropriate flexibility.

[0199] Furthermore, the piezoelectric layer 20 is preferably polarized in the thickness direction. When a voltage is applied to the electrode layer (electrode pair) holding the piezoelectric layer 20, the piezoelectric particles 36 in the piezoelectric layer 20 stretch and contract along the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to Poisson's ratio, the piezoelectric film 10 also stretches and contracts in the planar direction. Thus, the piezoelectric film 10 can exhibit piezoelectric properties.

[0200] like Figure 10 As shown, the piezoelectric thin film 10 has the following structure: a first electrode layer 24 is provided on one side of this piezoelectric layer 20, and a first protective layer 28 is provided thereon; a second electrode layer 26 is provided on the other side of the piezoelectric layer 20, and a second protective layer 30 is provided thereon. Here, the first electrode layer 24 and the second electrode layer 26 form an electrode pair.

[0201] That is, the piezoelectric thin film 10 has the following structure: the two sides of the piezoelectric body layer 20 are sandwiched by an electrode pair, namely the first electrode layer 24 and the second electrode layer 26, and the laminate is sandwiched by the first protective layer 28 and the second protective layer 30.

[0202] Thus, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts according to the applied voltage.

[0203] Furthermore, the first and second electrodes in the electrode layer and protective layer are added for the convenience of explaining the piezoelectric thin film 10. Therefore, the first and second electrodes in this invention have no technical significance and are irrelevant to actual use.

[0204] In this invention, in addition to these layers, the piezoelectric film 10 may also have, for example, an adhesive layer for bonding the electrode layer and the piezoelectric body layer 20 and an adhesive layer for bonding the electrode layer and the protective layer.

[0205] The adhesive can be either a bonding agent or a binder. Furthermore, the adhesive can appropriately be the same material as the polymer material (i.e., the substrate 34) from which the piezoelectric particles 36 are removed from the piezoelectric layer 20. Additionally, an adhesive layer can be present on both sides of the first electrode layer 24 and the second electrode layer 26, or it can be present only on one side of the first electrode layer 24 and the second electrode layer 26.

[0206] In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the first electrode layer 24 and the second electrode layer 26, while also imparting appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20, composed of the substrate 34 and piezoelectric particles 36, exhibits excellent flexibility for slow bending deformation; however, depending on the application, there may be insufficient rigidity or mechanical strength. To compensate for this deficiency, the first protective layer 28 and the second protective layer 30 are provided in the piezoelectric film 10.

[0207] The first protective layer 28 and the second protective layer 30 are identical in structure only in their placement. Therefore, in the following description, when it is not necessary to distinguish between the first protective layer 28 and the second protective layer 30, the two components will be collectively referred to as protective layers.

[0208] There are no limitations on the protective layer; various sheet-like materials can be used. For example, various resin films are preferred.

[0209] Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins can be appropriately utilized due to their excellent mechanical properties and heat resistance.

[0210] There is no limitation on the thickness of the protective layer. Furthermore, the thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same, but they can also be different.

[0211] If the rigidity of the protective layer is too high, it will not only restrict the expansion and contraction of the piezoelectric layer 20, but also impair its flexibility. Therefore, except in cases where mechanical strength or good operability as a sheet is required, a thinner protective layer is more advantageous.

[0212] In the piezoelectric film 10, as long as the thickness of the protective layer is less than twice the thickness of the piezoelectric layer 20, an optimal result can be obtained in terms of balancing rigidity and appropriate flexibility.

[0213] For example, when the thickness of the piezoelectric layer 20 is 50 μm and the protective layer is made of PET, the thickness of the protective layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0214] In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric body layer 20 and the first protective layer 28, and a second electrode layer 26 is formed between the piezoelectric body layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided for applying a voltage to the piezoelectric body layer 20 (piezoelectric film 10).

[0215] The first electrode layer 24 and the second electrode layer 26 are basically the same except for their positions. Therefore, in the following description, when it is not necessary to distinguish between the first electrode layer 24 and the second electrode layer 26, the two components will be collectively referred to as electrode layers.

[0216] In this invention, the material used to form the electrode layer is not limited, and various conductors can be used. Specifically, examples include metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, their alloys, laminates and composites of these metals and alloys, and indium tin oxide. Alternatively, conductive polymers such as PEDOT / PPS (polyvinyl dioxythiophene-polystyrene sulfonic acid) can also be used. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferred as electrode layers. From the viewpoints of conductivity, cost, and flexibility, copper is more preferred.

[0217] Furthermore, there are no restrictions on the method of forming the electrode layer. Various known methods can be used, such as vacuum evaporation and sputtering vapor deposition (vacuum film formation), film formation by coating, and methods of bonding foils formed from the above materials.

[0218] In particular, considering reasons such as ensuring the flexibility of the piezoelectric thin film 10, thin films of copper or aluminum, etc., deposited by vacuum evaporation, are preferably used as the electrode layer. Among them, copper thin films deposited by vacuum evaporation are particularly preferred.

[0219] There is no limitation on the thickness of the electrode layers. Furthermore, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same, but they can also be different.

[0220] Similar to the aforementioned protective layer, if the electrode layer is too rigid, it will not only restrict the expansion and contraction of the piezoelectric layer 20, but also impair its flexibility. Therefore, within a range where the resistance does not become excessively high, a thinner electrode layer is more advantageous.

[0221] In the piezoelectric film 10, if the product of the electrode layer thickness and Young's modulus is less than the product of the protective layer thickness and Young's modulus, the flexibility will not be seriously impaired, and therefore it is preferred.

[0222] For example, in the case of a combination where the protective layer is PET (Young's modulus: about 6.2 GPa) and the electrode layer is made of copper (Young's modulus: about 130 GPa), if the thickness of the protective layer is 25 μm, then the thickness of the electrode layer is preferably 1.2 μm or less, more preferably 0.3 μm or less, and preferably 0.1 μm or less.

[0223] As described above, the piezoelectric film 10 has the following structure: a piezoelectric layer 20 formed by dispersing piezoelectric particles 36 in a matrix 34 containing a polymer material and sandwiched between a first electrode layer 24 and a second electrode layer 26, and further, the laminate is sandwiched between a first protective layer 28 and a second protective layer 30.

[0224] This piezoelectric film 10 preferably has a maximum value of the loss tangent (Tanδ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature.

[0225] Therefore, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of less than a few Hz from the outside, it can effectively diffuse the strain energy to the outside as heat, thus preventing cracking at the interface between the polymer matrix and the piezoelectric particles.

[0226] The piezoelectric thin film 10 is preferably characterized by a storage elastic modulus (E') at a frequency of 1 Hz, obtained based on dynamic viscoelasticity measurements, being 10–30 GPa at 0°C and 1–10 GPa at 50°C. Furthermore, these conditions also apply to the piezoelectric layer 20.

[0227] Therefore, the stored elastic modulus (E') of the piezoelectric film 10 at room temperature can have a large frequency dispersion. That is, it can operate relatively stiffly for vibrations in the range of 20 Hz to 20 kHz, and exhibit softness for vibrations below a few Hz.

[0228] Furthermore, the product of the thickness of the piezoelectric film 10 and the stored elastic modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 1.0 × 10⁻⁶ at 0°C. 5 ~2.0×10 6 N / m, 1.0×10 at 50℃ 5 ~1.0×10 6 N / m. Furthermore, this condition also applies to piezoelectric layer 20.

[0229] Thus, the piezoelectric film 10 can possess appropriate rigidity and mechanical strength without compromising flexibility and acoustic properties.

[0230] Furthermore, in the master curve obtained by dynamic viscoelasticity measurement, the loss tangent (Tanδ) of the piezoelectric film 10 at 25°C and 1kHz is preferably 0.05 or higher. This condition also applies to the piezoelectric layer 20.

[0231] As a result, the frequency response of the loudspeaker using the piezoelectric film 10 becomes smoother, and the amount of change in sound quality when the lowest resonant frequency f0 changes with the curvature of the loudspeaker can also be reduced.

[0232] Furthermore, in this invention, the stored elastic modulus (Young's modulus) and loss tangent of the piezoelectric thin film 10 and piezoelectric layer 20 can be measured by known methods. As an example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nano Technology Inc. can be used for measurement.

[0233] As an example of measurement conditions, the measurement frequency can be 0.1Hz to 20Hz (0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz and 20Hz), the measurement temperature can be -50 to 150℃, the heating rate can be 2℃ / min (in a nitrogen atmosphere), the sample size can be 40mm × 10mm (including the clamping area), and the distance between the clamps can be 20mm.

[0234] In the driver unit 100, an external power source (signal source) is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 to apply a driving voltage that causes the piezoelectric film 10 to expand and contract, that is, to supply driving power (driving signal).

[0235] There are no restrictions on the external power source (signal source); it can be either a DC power source or an AC power source. Furthermore, the driving voltage can be appropriately set to drive the piezoelectric film 10, depending on the thickness of the piezoelectric layer 20 and the forming material.

[0236] There are no restrictions on the method of drawing electrodes from the first electrode layer 24 and the second electrode layer 26, and various known methods can be used.

[0237] As an example, methods can be illustrated such as connecting a conductive material such as copper foil to the first electrode layer 24 and the second electrode layer 26 to lead out electrodes to the outside, and forming through holes in the first protective layer 28 and the second protective layer 30 by means of a laser, and filling the through holes with a conductive material to lead out electrodes to the outside.

[0238] Preferred electrode extraction methods include those described in Japanese Patent Application Publication No. 2014-209724 and Japanese Patent Application Publication No. 2016-015354.

[0239] As described above, the piezoelectric thin film 10 includes: a piezoelectric layer 20, which is composed of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material; and electrode layers (first electrode layer 24 and second electrode layer 26) disposed on both sides of the piezoelectric layer 20. Furthermore, the piezoelectric thin film 10 has protective layers (first protective layer 28 and second protective layer 30) disposed on each electrode layer.

[0240] If a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric thin film 10 having this piezoelectric layer 20, the piezoelectric particles 36 stretch and contract along the polarization direction according to the applied voltage. As a result, the piezoelectric thin film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to Poisson's ratio, the piezoelectric thin film 10 also stretches and contracts in the in-plane direction. This stretching and contraction is about 0.01 to 0.1%.

[0241] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the thickness stretching is very small, with a maximum of only about 0.3 μm.

[0242] In contrast, the piezoelectric film 10, i.e., the piezoelectric layer 20, has a dimension in the planar direction that is significantly larger than its thickness. Therefore, for example, if the diameter of the bent portion 10a of the piezoelectric film 10 is 10 cm, the piezoelectric film 10 (bent portion 10a) can stretch or contract by a maximum of about 0.1 mm in the planar direction by applying a voltage.

[0243] The piezoelectric film 10 generates sound through vibration in the thickness direction. That is, the actuator unit 100 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10 and generates sound corresponding to the driving voltage applied to the piezoelectric film 10.

[0244] <Methods for Manufacturing Piezoelectric Thin Films>

[0245] The following is for reference. Figures 11-13 An example of a method for manufacturing the piezoelectric thin film 10 will be described.

[0246] First, prepare Figure 11 The sheet 11a shown has a first electrode layer 24 formed on the surface of the first protective layer 28. Further, preparation is made in... Figure 13 The schematic diagram shows a sheet 11c on the surface of the second protective layer 30 on which the second electrode layer 26 is formed.

[0247] The sheet 11a can be fabricated as the first electrode layer 24 by forming a copper thin film on the surface of the first protective layer 28 through vacuum evaporation, sputtering, or plating. Similarly, the sheet 11c can be fabricated as the second electrode layer 26 by forming a copper thin film on the surface of the second protective layer 30 through vacuum evaporation, sputtering, or plating.

[0248] Alternatively, commercially available sheets with a copper film or the like formed on a protective layer can be used as sheet 11a and / or sheet 11c.

[0249] Flakes 11a and 11c can be of the same kind of substance or different kinds of substance.

[0250] Additionally, when the protective layer is very thin and has poor operability, a protective layer with a separator (pseudo-support) can be used as needed. Furthermore, PET or similar materials with a thickness of 25–100 μm can be used as the separator. The separator can be removed after hot-pressing the electrode layer and the protective layer.

[0251] Next, as Figure 12 As shown, after coating the first electrode layer 24 of the sheet 11a with a coating material (coating composition) to form a piezoelectric layer 20, the coating material is cured to form the piezoelectric layer 20. Thus, a piezoelectric laminate 11b is made by stacking the sheet 11a and the piezoelectric layer 20.

[0252] The piezoelectric layer 20 can be formed using various methods, depending on the material used to form the piezoelectric layer 20.

[0253] As an example, firstly, the above-mentioned cyanoethylated PVA and other polymer materials are dissolved in an organic solvent, and then piezoelectric particles such as PZT particles are added and stirred to prepare a coating.

[0254] There are no restrictions on organic solvents; various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.

[0255] After preparing the sheet 11a and the coating, the coating is cast onto the sheet 11a, allowing the organic solvent to evaporate and the sheet to dry. Thus, as... Figure 12 As shown, a piezoelectric stack 11b is formed by having a first electrode layer 24 on the first protective layer 28 and a piezoelectric layer 20 stacked on the first electrode layer 24.

[0256] There are no restrictions on the casting method of the coating; all known methods (coating devices) can be used, such as rod coaters, slidecoats, and doctor knives.

[0257] Alternatively, if the polymer material is a heat-melting substance, a melt containing piezoelectric particles 36 can be created by heating and melting the polymer material, and then processed through extrusion molding, etc. Figure 11 The sheet 11a shown is extruded in sheet form and cooled, thereby producing a sheet-like material. Figure 12 The piezoelectric laminate 11b shown.

[0258] In addition, as mentioned above, in the piezoelectric layer 20, in addition to viscoelastic polymeric materials at room temperature, polymeric piezoelectric materials such as PVDF can also be added to the matrix 34.

[0259] When adding these polymeric piezoelectric materials to the substrate 34, the desired polymeric piezoelectric material can be dissolved in the aforementioned coating. Alternatively, the desired polymeric piezoelectric material can be added to a heated and melted polymeric material that is viscoelastic at room temperature, and then heated and melted.

[0260] After the piezoelectric layer 20 is formed, a calendering process can be performed as needed. The calendering process can be performed once or multiple times.

[0261] As is well known, calendering refers to the process of heating the surface to be processed by a hot press or heated rollers while pressing it to achieve flattening and other effects.

[0262] Next, the piezoelectric layer 20 of the piezoelectric layer stack 11b is subjected to a polarization treatment. The polarization treatment of the piezoelectric layer 20 can be performed before the calendering process, but it is preferred to perform it after the calendering process.

[0263] There are no limitations on the method for polarizing the piezoelectric layer 20, and known methods can be used. For example, electric field polarization and corona polarization can be exemplified by directly applying a DC electric field to the object to be polarized. Alternatively, when performing electric field polarization, a second electrode layer 26 can be formed before the polarization treatment, and the electric field polarization treatment can be performed using the first electrode layer 24 and the second electrode layer 26.

[0264] Furthermore, in the piezoelectric thin film 10 of the present invention, the polarization treatment is not performed along the surface direction of the piezoelectric layer 20, but along the thickness direction.

[0265] Next, as Figure 13 As shown, on the piezoelectric layer 20 side of the piezoelectric laminate 11b that has undergone polarization treatment, a pre-prepared sheet 11c is laminated with the second electrode layer 26 facing the piezoelectric layer 20.

[0266] Furthermore, using a hot press device and heating rollers, the laminate is held between the first protective layer 28 and the second protective layer 30 and hot-pressed to bond the piezoelectric laminate 11b to the sheet 11c, thereby producing a product as shown in the image. Figure 10 The piezoelectric thin film 10 shown.

[0267] Alternatively, an adhesive can be used to bond the piezoelectric laminate 11b to the sheet 11c, and preferably further crimping is performed to create the piezoelectric film 10. The same material as the substrate of the piezoelectric layer 20 can be used as the adhesive in this case.

[0268] Next, in the molding process, the piezoelectric film 10 is heated and compressed to form a curved portion 10a that protrudes to one main surface side and is recessed to the other main surface side of the piezoelectric film 10.

[0269] There are no particular limitations on the method of heat compression molding, and various known resin film processing methods can be used. As an example, a molding apparatus is used to heat compress and mold the piezoelectric film 10. This molding apparatus has a mold with a shape corresponding to the shape of the curved portion 10a to be molded, thereby enabling the curved portion 10a of the desired shape to be molded.

[0270] Alternatively, the piezoelectric film 10 can be manufactured using sliced ​​sheets 11a and 11c, or it can be manufactured using a roll-to-roll process.

[0271] The piezoelectric films produced can also be cut into desired shapes for various applications.

[0272] The piezoelectric thin film 10 produced in this way is not polarized along the plane direction, but along the thickness direction, and a large piezoelectric property can be obtained even without stretching after polarization treatment. Therefore, the piezoelectric property of the piezoelectric thin film 10 does not have in-plane anisotropy, and when a driving voltage is applied, it will stretch and contract isotropically in all directions along the plane direction.

[0273] Furthermore, the piezoelectric thin film 10 included in the actuator unit 100 can be not only the type described above, where the piezoelectric layer 20 is sandwiched between the first electrode layer 24 and the second electrode layer 26, and sandwiched between the first protective layer 28 and the second protective layer 30, but also... Figure 10The structure shown is a single piezoelectric film 10, but multiple piezoelectric films 10 can also be used. A structure with multiple piezoelectric films 10 is preferred because it can stably maintain the shape with the curved portion 10a when the size of the piezoelectric film 10 is increased. The structure with multiple piezoelectric films 10 can be formed by laminating an adhesive layer. From the perspective of adhesion, an adhesive layer is preferred as the adhesive layer. Specifically, thermoplastic polyester-based hot-melt materials can be used as the material forming the adhesive layer. The thickness of the adhesive layer is preferably 5 to 50 μm, more preferably 10 to 30 μm.

[0274] When stacking multiple piezoelectric films 10, firstly, multiple piezoelectric films 10 cut to a specified size are prepared, and then the piezoelectric films 10 are glued together using a hot melt adhesive or the like. In this case, it is preferable that the electrode leads of each piezoelectric film 10 do not contact each other. For example, if the piezoelectric film 10 has a structure with raised islands protruding in the planar direction for electrode leads, it is preferable to stack each piezoelectric film 10 in such a way that these raised islands do not overlap.

[0275] Next, the laminate of multiple piezoelectric films 10 is heated and compressed to form a curved section.

[0276] Then, electrodes are led out from the electrode layers of each piezoelectric film. For example, if each piezoelectric film has a structure with raised islands, through holes can be made in the protective layer of the raised islands by laser processing or the like, and conductive material can be filled into the through holes to lead out the electrodes.

[0277] Each piezoelectric film has two electrode layers connected to an external power source (signal source). However, in order to make each piezoelectric film operate in the same phase, the wiring is connected by applying an AC signal of appropriate polarity according to the polarization direction of each piezoelectric layer.

[0278] <Preferred Embodiment of the Driver Unit>

[0279] In a driver unit equipped with a piezoelectric film 10, when the sound pressure level in the high-frequency range is higher than that in the low-frequency range, by adding a series resistor to the input signal, the voltage applied to the piezoelectric film 10 in the high-frequency range can be reduced, thus gradually lowering the sound pressure level in the high-frequency range and flattening the frequency response. As a result, the sound pressure level in the high-frequency range is higher than that in the low-frequency range, making the masked low-frequency range easier to hear.

[0280] Specifically, such as Figure 14 As shown in the block diagram, a resistor 222 is connected between the signal source 220 and the piezoelectric film 10.

[0281] Although the signal source 220 is connected to headphones, it is any known player. Furthermore, the resistor 222 is disposed, for example, inside the headphones (within the housing) and connected midway to the wiring connected to the electrode layer of the piezoelectric film 10.

[0282] In a piezoelectric thin film, the structure in which the piezoelectric layer, acting as a dielectric, is sandwiched between electrodes is similar to that of a capacitor, and can be represented by an equivalent circuit consisting of an electrostatic capacitance, an equivalent series inductance, and an equivalent series resistance connected in series. Here, within the audible range (20Hz–20kHz) of the piezoelectric thin film, the equivalent series inductance is inactive; therefore, the piezoelectric thin film 10 can be represented by an equivalent circuit consisting of an electrostatic capacitance C and an equivalent series resistance ESR connected in series.

[0283] In this equivalent circuit, the capacitive reactance Xc = 1 / (2π×f×C) caused by the electrostatic capacitance C is inversely proportional to the frequency f of the power supply. Therefore, as the frequency increases, the capacitive reactance Xc decreases. This capacitive reactance Xc is the ratio of voltage to current when driving the piezoelectric layer.

[0284] For simplicity, if we consider the impedance Z of the piezoelectric film as merely the capacitive reactance Xc, assuming that the impedance Z is 8000Ω at a frequency f of 100Hz, and considering a 200Ω resistor connected in series with the piezoelectric film, and applying an operating voltage of 10Vrms, then as shown in Table 1 below, the voltage Vrms1 applied to the piezoelectric film is approximately 9.8V, and the voltage Vrms2 related to the resistor is approximately 0.2V. Next, at a frequency f of 1000Hz, the impedance Z of the piezoelectric film becomes 800Ω, therefore the voltage Vrms1 applied to the piezoelectric film becomes 8.0V, and the voltage Vrms2 related to the resistor becomes 2.0V. Finally, at a frequency f of 10000Hz, the impedance Z of the piezoelectric film becomes 80Ω, therefore the voltage Vrms1 applied to the piezoelectric film becomes approximately 2.9V, and the voltage Vrms2 related to the resistor becomes approximately 7.1V. Furthermore, at a frequency f of 20000Hz, the impedance Z of the piezoelectric film becomes 40Ω, so the voltage Vrms1 applied to the piezoelectric film becomes approximately 1.7V, and the voltage Vrms2 related to the resistor becomes approximately 8.3V.

[0285] Furthermore, Table 1 shows the results of calculating the change in sound pressure based on the voltage ratio.

[0286] [Table 1]

[0287]

[0288] Therefore, if a resistor is connected in series with the piezoelectric film, the higher the frequency of the applied voltage (signal), the lower the voltage applied to the piezoelectric film. Since the piezoelectric film is voltage-driven, a higher frequency and a lower voltage result in a higher frequency range and a greater reduction in sound pressure level compared to the case without a resistor. Thus, in a driver unit equipped with a piezoelectric film, when the sound pressure level in the high-frequency range is higher than that in the low-frequency range, connecting a resistor in series with the piezoelectric film reduces the voltage applied to the piezoelectric film in the high-frequency range, allowing for a smoother reduction in sound pressure level in the high-frequency range and a flatter frequency response.

[0289] The resistance value for connection to the piezoelectric film can be appropriately set according to the area, frequency characteristics, driving voltage, impedance, etc. of the piezoelectric film. When the actuator unit (the curved part of the piezoelectric film) is Φ6cm in size, the series resistance value is preferably 100 to 1000Ω, more preferably 200 to 700Ω, and even more preferably 300 to 500Ω.

[0290] The structure of connecting a resistor in series between a piezoelectric film and a signal source, when combined with a driver unit having the above structure, can achieve a flatter frequency response. This driver unit includes a piezoelectric film with a curved portion and a perforated plate stacked on the concave side of the curved portion. A first air chamber defined by the concave surface of the piezoelectric film and the perforated plate communicates with the outside through a through-hole formed in the perforated plate. However, the structure of connecting a resistor in series between the piezoelectric film and the signal source is not limited to the combination of the above structure with a driver unit. When combined with a driver unit (electroacoustic transducer) having a piezoelectric film, the aforementioned effect of flattening the frequency response can be achieved. The piezoelectric film has a piezoelectric body layer and an electrode layer. The piezoelectric body layer is composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material. The electrode layer is disposed on both sides of the piezoelectric body layer.

[0291] In the example described above, the piezoelectric film 10 of the driver unit is configured to have a first electrode layer 24 and a first protective layer 28 on one side of the piezoelectric layer 20, and a second electrode layer 26 and a second protective layer 30 on the other side, but is not limited to this configuration.

[0292] Figure 20 The diagram illustrates another example of the piezoelectric thin film in the actuator unit of the present invention.

[0293] Figure 20 The piezoelectric film 40 shown has a structure in which a reinforcing sheet 42 is stacked on the piezoelectric film 10. The laminate (piezoelectric film 40) formed by stacking the piezoelectric film 10 and the reinforcing sheet 42 has a curved portion 40a that is shaped to protrude toward one main surface side and recess toward the other main surface side.

[0294] exist Figure 21 The image shows a partially enlarged cross-sectional view of the piezoelectric thin film 40. Figure 21 The piezoelectric film 40 shown includes: a piezoelectric layer 20, which is a sheet-like material with piezoelectric properties; a first electrode layer 24, stacked on one side of the piezoelectric layer 20; a first protective layer 28, stacked on the side of the first electrode layer 24 opposite to the piezoelectric layer 20; a second electrode layer 26, stacked on the other side of the piezoelectric layer 20; a second protective layer 30, stacked on the side of the second electrode layer 26 opposite to the piezoelectric layer 20; a reinforcing sheet 40, stacked on the side of the second protective layer 30 opposite to the piezoelectric layer 20; and an adhesive layer 44, which adhesively bonds the second protective layer 30 and the reinforcing sheet 40. Furthermore, the piezoelectric layer 20, the first electrode layer 24, the first protective layer 28, the second electrode layer 26, and the second protective layer 30 have... Figure 10 The example shown has the same structure, so its description is omitted. Furthermore, adhesive layer 44 can also be a weakly adhesive layer that can be easily peeled off.

[0295] The reinforcing sheet 42 is a sheet-like component, and various resin films are preferably exemplified as an example. The resin film used for the reinforcing sheet 42 can be the same resin film used in the aforementioned protective layer. Furthermore, non-woven fabrics and woven fabrics can also be used as the reinforcing sheet 42. Examples of non-woven fabrics and woven fabrics used in the aforementioned porous components can be exemplified as the non-woven fabric. Additionally, paper and Japanese paper can be used as non-woven fabrics, and cold-weather yarn can be used as woven fabrics.

[0296] The piezoelectric film 40 has a reinforcing sheet 42, and by integrally forming the curved portion 40a, abnormal deformation of the curved portion 40a can be better suppressed when wearing or removing the headphones, which are equipped with a driver unit having the piezoelectric film 40. Furthermore, in addition to wearing the headphones, when subjected to impacts such as drops, or when a user touches the curved portion 40a of the piezoelectric film 40, the curved portion 40a is less prone to abnormal deformation due to the reinforcing sheet 42. This also improves manufacturability during manufacturing.

[0297] Furthermore, if the bent part is abnormally deformed, even if it returns to its original shape, deformation marks will remain, which may lead to poor appearance or affect sound performance. However, because the piezoelectric film 40 has a reinforcing sheet 42, deformation marks are not easily left behind.

[0298] Furthermore, this effect based on the reinforcing plate 42 can also be achieved in driver units that do not have perforated plates.

[0299] The thickness of the reinforcing sheet 42 also depends on the thickness of the protective layer, the material of the reinforcing sheet 42, etc., but from the viewpoint of suppressing abnormal deformation of the bent portion 40a, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. On the other hand, if the reinforcing sheet 42 is too thick, the vibration of the piezoelectric film 40 may be suppressed, resulting in a decrease in sound pressure. Therefore, the thickness of the reinforcing sheet 42 is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less.

[0300] Here, if the thickness of the protective layer is sufficiently thick without affecting the sound pressure level, it is possible to better suppress the abnormal deformation of the bending portion 40a when wearing or removing the headphones, and it is also possible to suppress abnormal deformation of the bending portion 40a when subjected to impact or touched. On the other hand, as described above, it is necessary to lead the electrode outward from the electrode layer of the piezoelectric film. From a manufacturing point of view, it is preferable to lead the electrode outward after the bending portion is formed. Furthermore, from a manufacturing point of view, it is preferable to lead the electrode outward by forming a through hole in the protective layer using a laser or the like, and filling the through hole with a conductive material. When forming the through hole in the protective layer using a laser or the like, it is necessary to make the protective layer relatively thin from the viewpoints of manufacturing efficiency and the quality stability of the through hole. In this case, the thickness of the protective layer is preferably 1 μm to 10 μm, more preferably 3 μm to 6 μm.

[0301] Thus, when it is necessary to make the protective layer thinner, the deformation of the bent portion 40a can be better suppressed by the piezoelectric film 40 having a reinforcing sheet 42.

[0302] When the piezoelectric film 40 has a reinforcing sheet 42, when forming a through hole in the protective layer using a laser or the like, for example, after forming a bent portion 40a on the piezoelectric film 40 with the reinforcing sheet 42, at the edge portion further outward than the bent portion 40a (see reference) Figure 5 In symbol 10c), a portion of the reinforcing sheet 42 is lifted (peeled off), and a through hole is formed by laser processing of the protective layer. After the through hole is filled with a conductive material, a lead wire made of metal foil such as Cu is bonded to the conductive material, thereby enabling the electrode to be led out to the outside. In addition, during the drying process of the conductive material, good adhesion is formed between the conductive material and the lead wire.

[0303] Therefore, in order to peel off the reinforcing sheet 42, it is preferable to use a weak adhesive layer in the adhesive bonding between the reinforcing sheet 42 and the protective layer.

[0304] In addition, Figure 20In the example shown, the reinforcing sheet 42 is configured to be disposed on the convex side of the piezoelectric film 40, but it is not limited to this and can also be disposed on the concave side. Alternatively, the reinforcing sheet 42 can be disposed on both sides of the piezoelectric film 40.

[0305] In this invention, the headphones preferably have a protective ring disposed between the driver unit and the ear pad, in contact with the ear pad. The protective ring has an opening that extends through the ear pad in a direction perpendicular to the surface in contact with it. When viewed from the direction perpendicular to the surface in contact with the ear pad, the protective ring contacts an area of ​​at least 30% of the total area of ​​the ear pad, and the shortest distance between the protective ring and the piezoelectric film of the driver unit is at least 0.3 mm. Figure 22 This structure will be explained.

[0306] Figure 22 This is a cross-sectional view conceptually illustrating another example of the headphones of the present invention. Figure 22 The headset 230 shown includes: a housing 202 forming the outer shell; a driver unit 100 housed within the housing 202; ear pads 204 disposed on the side of the driver unit 100 opposite to the side of the housing 202; and a protective ring 232 disposed between the ear pads 204 and the driver unit 100. Additionally, Figure 22 In the example shown, the housing 202, the driver unit 100, and the ear pad 204 have the same Figure 1 The examples shown have the same structure, therefore their explanation is omitted. And, in Figure 22 Although the illustration of the ear pad locking component is omitted, in the text... Figure 22 The headset 230 shown may also have an ear pad locking component.

[0307] The protective ring 232 is a ring-shaped plate component with an opening. The protective ring 232 is configured to contact the ear pad 204 to prevent the ear pad 204 from deforming towards the driver unit 100 and contacting the piezoelectric film 10 (bent portion 10a) when the user wears the headphones 230. Regarding this, using... Figure 23 and Figure 24 Please provide an explanation.

[0308] Figure 23 This diagram shows a state in which a headset 200 without a protective ring 232 is pressed onto an artificial ear (measuring device) M and a load is applied from above. Figure 24 This diagram shows the state in which a headset 230 with a protective ring 232 is pressed onto an artificial ear (measuring device) M and a load is applied from above.

[0309] like Figure 23As shown, when the headphones 200 do not have a protective ring 232, depending on the shape, size, and material of the ear pads 204, the positional relationship between the ear pads 204 and the driver unit 100 (piezoelectric film 10), and the pressure applied to the headphones 200, the ear pads 204 may deform towards the driver unit 100, causing them to come into contact with the curved portion 10a of the piezoelectric film 10, thereby causing the curved portion 10a to deform. If the curved portion 10a deforms, the sound quality will be reduced.

[0310] In contrast, such as Figure 24 As shown, the headphone 230 has a protective ring 232, which prevents the ear pads 204 from deforming towards the driver unit 100 even when pressure is applied to the headphone 200, thus preventing contact with the piezoelectric diaphragm 10 (bent portion 10a). By preventing the ear pads 204 from contacting the piezoelectric diaphragm 10 (bent portion 10a), abnormal deformation of the bent portion 10a of the piezoelectric diaphragm 10 can be prevented, and the sound quality degradation associated with the deformation of the bent portion 10a can be prevented. Furthermore, by preventing the ear pads 204 from deforming towards the driver unit 100, the ear pads 204 are effectively flattened over a larger area, thereby improving the airtightness of the space formed by the user's ear and the ear pads 204, and further improving the sound pressure level in the mid-low frequency range.

[0311] Furthermore, this effect based on the protective ring 232 can also be achieved in headphones with driver units that do not have perforated plates.

[0312] exist Figure 22 In the example shown, one side of the protective ring 232 contacts the ear pad 204, and the other side contacts the driver unit 100 (holding member 106). However, the invention is not limited to this; a spacer or similar element may be provided between the other side of the protective ring 232 and the driver unit 100 (holding member 106), or the holding member 106 may also serve as a spacer. By providing a spacer or allowing the holding member 106 to function as a spacer, the distance between the protective ring 232 and the piezoelectric film 10, i.e., the distance between the ear pad 204 and the piezoelectric film 10, can be appropriately adjusted. Furthermore, the protective ring 232 and the holding member 106 can also be an integrated component. Figure 22 Although omitted, the locking component 206 can have the function of the protective ring 232, or it can be a component that is further integrated with the retaining component 106.

[0313] Furthermore, when viewed from a direction perpendicular to the surface in contact with the ear pad 204, the protective ring 232 preferably contacts an area of ​​at least 30% of the total area of ​​the ear pad. (Use) Figure 25 This point needs clarification.

[0314] Figure 25The ear pad 204 and the protective ring 232 are viewed from a direction perpendicular to the surface where the protective ring 232 contacts the ear pad 204 (viewed from the left and right sides). Figure 22 (The image is shown.)

[0315] exist Figure 25 In the diagram, the area indicated by the upper right shaded line is the ear pad 204, and the area where the upper left and upper right shaded lines overlap is the area where the ear pad 204 contacts the protective ring 232. Specifically, the ratio of the area where the upper left and upper right shaded lines overlap (the area where the protective ring 232 contacts the ear pad 204) to the area indicated by the upper right shaded line (the total area of ​​the ear pad 204) is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more.

[0316] Therefore, when the user wears the headphones 230, it can prevent the ear pads 204 from deforming toward the driver unit 100, prevent the ear pads 204 from contacting the piezoelectric film 10, and prevent the curved portion 10a of the piezoelectric film 10 from deforming abnormally.

[0317] Furthermore, the shortest distance t between the protective ring 232 and the piezoelectric film 10 of the driver unit 100 (reference) Figure 22 (Enlarged view) Preferably, the diameter is 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. Furthermore, the shortest distance t between the protective ring 232 and the piezoelectric film 10 is the distance of the piezoelectric film 10 when it is not driven.

[0318] Therefore, even when the piezoelectric film 10 is driven to vibrate, contact with the protective ring 232 can be prevented. Furthermore, when the user wears the headphones 230, the ear pads 204 can be prevented from deforming towards the driver unit 100 and contacting the piezoelectric film 10, and the curved portion 10a of the piezoelectric film 10 can be prevented from deforming abnormally.

[0319] Furthermore, the inner diameter (diameter of the opening) of the protective ring 232 can be larger than, smaller than, or approximately the same as the inner diameter of the ear pad 204. Preferably, the inner diameter of the protective ring 232 is approximately -10mm to +10mm relative to the inner diameter of the ear pad 204.

[0320] Furthermore, the thickness of the protective ring 232 is not particularly limited, but from the viewpoints of preventing the protective ring 232 from deforming when the ear pad 204 is pressed and miniaturizing the headphone 232, it is preferably 0.5mm to 10mm, more preferably 1mm to 7mm, and even more preferably 2mm to 5mm.

[0321] Furthermore, a grille can be installed at the opening of the protective ring, or a protective ring with an integrated grille can be used. Figure 26This is a cross-sectional view conceptually illustrating another example of the headphones of the present invention. Figure 26 The headset shown has a protective ring 233 instead of a protective ring 232, and in addition, has the same... Figure 22 The headphones shown have the same structure.

[0322] The central portion of the protective ring 233, directly below the central hole of the ear pad 204, has a grid-like area with multiple holes. This prevents physical contact with the piezoelectric film 10, such as with fingers, from causing abnormal deformation, while simultaneously allowing sound to be transmitted to the ear.

[0323] The contact surface between the protective ring 233 and the ear pad 204 is preferably flat, but to ensure that the minimum distance t between the protective ring 233 and the piezoelectric film 10 is 0.3 mm or more, such as Figure 26 As shown, the central section (grille section) can be bent as needed.

[0324] The driver unit and headphones of the present invention have been described in detail above. However, the present invention is not limited to the above examples. Various improvements or modifications can be made without departing from the spirit of the present invention.

[0325] Example

[0326] The following are specific embodiments of the present invention to provide a more detailed description. However, the present invention is not limited to these embodiments; the materials, quantities, proportions, processing content, processing order, etc., shown in the following embodiments can be appropriately modified without departing from the spirit of the invention.

[0327] [Example 1]

[0328] <Fabrication of Piezoelectric Thin Films>

[0329] Through the above Figures 11-13 The method shown in the figure was used to fabricate a piezoelectric thin film.

[0330] First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following composition ratio. Then, PZT particles were added to the solution as piezoelectric particles at the following composition ratio, and the mixture was stirred with a propeller mixer (2000 rpm) to prepare a coating for forming a piezoelectric layer.

[0331] ·PZT particles···········300 parts by mass

[0332] ·Cyanoethylated PVA··········30 parts by weight

[0333] ·DMF·············70 parts by weight

[0334] In addition, the PZT particles are made by sintering commercially available PZT raw material powder at 1000-1200℃, followed by crushing and grading the powder to achieve an average particle size of 2μm.

[0335] On the other hand, sheets 11a and 11b were prepared by vacuum evaporating a copper film with a thickness of 0.1 μm onto a PET film with a thickness of 4 μm. That is, in this example, the first electrode layer and the second electrode layer are copper vapor-deposited films with a thickness of 0.3 μm, and the first protective layer and the second protective layer are PET films with a thickness of 4 μm. In addition, in order to obtain good operability during the process, a material with a 50 μm thick separator (pseudo-support PET) was used on the PET film. After the sheet 11c was heat-pressed, the separators of each protective layer were removed.

[0336] On the first electrode layer (copper vapor-deposited thin film) of sheet 11a, a pre-prepared coating for forming a piezoelectric layer was applied using a doctor blade coater. Furthermore, the coating was applied in a manner that ensured a film thickness of 50 μm after drying.

[0337] Next, the object obtained by coating the sheet with the coating material is heated and dried on a hot plate at 120°C to evaporate the DMF. Thus, a piezoelectric laminate 11b is produced, which has a copper first electrode layer on a PET first protective layer and a piezoelectric layer (polymer composite piezoelectric layer) with a thickness of 50 μm on it.

[0338] The fabricated piezoelectric layer was polarized in the thickness direction.

[0339] On a piezoelectric laminate that has undergone polarization treatment, a sheet 11c on which a copper thin film has been deposited on a PET film is laminated with the second electrode layer (copper thin film side) facing the piezoelectric layer.

[0340] Next, using a laminating apparatus, the piezoelectric laminate and the sheet-like material are hot-pressed together at 120°C, thereby adhesively bonding the piezoelectric layer and the second electrode layer to create a product as shown. Figure 10 The piezoelectric thin film shown.

[0341] Next, using a mold with a shape corresponding to the shape of the curved portion 10a to be formed, and employing a hot pressing device (ASONE Corporation AH-2003), the fabricated piezoelectric film is formed into the shape shown in the figure using a heat compression molding method. Figure 1The shape shown has a curved portion 10a. The curved portion 10a is shaped as a part of a sphere. Furthermore, when viewed from a direction perpendicular to the main surface of the piezoelectric film, the curved portion 10a is circular with a diameter of 60 mm and a height of 5 mm.

[0342] Then, a diameter of 64mm is cut out with the curved part 10a as the center.

[0343] As described above, a piezoelectric thin film 10 with a curved portion was fabricated.

[0344] <Factory of Driver Unit>

[0345] A copper plate with a thickness of 100 μm was prepared as the perforated plate. The copper plate was cut into pieces with a diameter of 86 mm, and 13 through holes with a diameter of 4 mm were formed in an alternating pattern in approximately the center (see reference). Figure 2 The total area of ​​the through holes is 6% of the area of ​​the vibration region (bending portion) of the piezoelectric film. Furthermore, eight insertion holes are provided at equal intervals along the circumference near the ends.

[0346] A 3mm thick acrylic sheet is cut into two rings with an outer diameter of 86mm and an inner diameter of 60mm, serving as two retaining components. Near the end of one retaining component, eight insertion holes are provided at equal intervals along the circumference. Near the end of the other retaining component, eight threaded holes are provided at equal intervals along the circumference.

[0347] The structure is as follows: a retaining member with a threaded hole, a piezoelectric film, a perforated plate, and a retaining member with an insertion hole are stacked sequentially. From the retaining member side with the perforated plate, a screw, serving as a fastening member, is inserted through the insertion hole and screwed into the threaded hole of the retaining member on the piezoelectric film side. The piezoelectric film and the perforated plate are held together by the two retaining members. Additionally, a perforated plate is stacked on the concave side of the curved portion of the piezoelectric film.

[0348] As a porous component, 15mm thick polyurethane foam (UBTK manufactured by Bridgestone Corporation) was cut into 60mm diameter pieces. This porous component was then placed on the retaining component side of a perforated plate to create the actuator unit. The porous component was then glued to the perforated plate using adhesive. At this point, care was taken to ensure the adhesive did not clog the through holes.

[0349] [Comparative Example 1]

[0350] The driver unit was fabricated in the same manner as in Example 1, except that it did not have a perforated plate and porous components.

[0351] [evaluate]

[0352] The driver unit of the manufactured embodiment and comparative example was housed in a housing, and an ear pad was disposed on the opening side of the housing to create a test unit simulating a headset.

[0353] At the opening of the housing, the actuator unit is arranged with the concave surface of the curved portion facing the housing side. An ear pad is arranged on the side of the actuator unit opposite to the housing, serving as a test unit. At this time, it is assumed that there is a gap between the actuator unit and the housing, and a second air chamber defined by the actuator unit and the housing is connected to the outside structure.

[0354] The ear pad side of the fabricated test unit was placed unloaded on a headset testing artificial ear (TYPE2015E manufactured by Akoh Co., Ltd.). A sinusoidal sweep signal with a frequency of 20Hz to 20kHz and an applied voltage of 10Vpp was input to the piezoelectric film, and the sound pressure level was measured. Next, with the test unit pressed against the headset testing artificial ear at a pressure of 200g, a sinusoidal sweep signal with a frequency of 20Hz to 20kHz and an applied voltage of 10Vpp was input to the piezoelectric film, and the sound pressure level was measured.

[0355] The frequency characteristics of Example 1 and Comparative Example 1 are shown in graphs respectively. Figure 15 , Figure 16 .

[0356] like Figure 16 As shown, in Comparative Example 1, the sound pressure level in the high-frequency range produces a peak-notch effect, resulting in fluctuations in the frequency response.

[0357] And, as Figure 16 As shown by the dashed line, when the test unit is pressed against the coupler under load, the sound pressure level in the low-frequency range is lower than that in the mid-to-high-frequency range. After the test, the piezoelectric film was observed to have deformed shape at the bend. This can be attributed to the pressure difference between the coupler side and the opposite side of the piezoelectric film when the test unit is pressed against the coupler, causing deformation of the bend and thus altering the frequency response.

[0358] In comparison, it can be seen that Figure 15 The illustrated embodiment 1 achieves a flat frequency response with essentially unchanged sound pressure across a wide frequency band from the low to the high frequency range. Furthermore, it is observed that the frequency response exhibits minimal change regardless of the applied load. Following the experiment, observation of the piezoelectric film revealed no deformation at the bending points.

[0359] [Example 2]

[0360] A series resistor (360Ω) was connected to the wiring connected to the electrode layer of the piezoelectric film. Otherwise, the driver unit was fabricated in the same manner as in Example 1.

[0361] The ear pad side of the fabricated test unit was placed on the artificial ear for testing headphones (TYPE2015E manufactured by Akoh Co., Ltd.) without load. A sinusoidal sweep signal with a frequency of 20Hz to 20kHz and a voltage of 10Vpp was input to the piezoelectric film, and the sound pressure was measured.

[0362] The results of the frequency characteristics under no-load conditions in Examples 1 and 2 are shown below. Figure 17 .

[0363] like Figure 17 As shown, in the case where there is no resistor between the piezoelectric film and the signal source (Example 1), the sound pressure in the frequency band above 1.0 kHz is slightly higher than that in the frequency band below 1.0 kHz; while in Example 2, where a series resistor is connected between the piezoelectric film and the signal source, the sound pressure in the frequency band above 1.0 kHz can be reduced, thereby making the frequency response flatter.

[0364] [Examples 2B to 2D]

[0365] As Examples 2B to 2D, the resistance values ​​of the series resistor in Example 2 were set to 100Ω, 200Ω, and 400Ω, respectively. Otherwise, the test unit was fabricated in the same manner as in Example 2, and the frequency characteristics were measured.

[0366] The results are shown in Figure 18 middle.

[0367] like Figure 18 As shown, when there is no resistor between the piezoelectric film and the signal source, the sound pressure level in the frequency band above 1.0 kHz is slightly higher than that in the frequency band below 1.0 kHz. However, by connecting a series resistor between the piezoelectric film and the signal source, the sound pressure level in the frequency band above 1.0 kHz can be reduced, thus making the frequency response flatter. Furthermore, it can be seen that by adjusting the value of the connected resistor, the reduction in sound pressure level in the frequency band above 1.0 kHz can be adjusted without affecting the sound pressure level in the frequency band below 1.0 kHz.

[0368] [Example 3]

[0369] In Example 1, during the fabrication of the piezoelectric thin film, after lamination of the sheet 11c (see reference) Figure 13 One of the 50μm thick PET separators was not removed, and a bent portion 40a was formed. This separator is used as a reinforcing sheet 42. The bent portion 40a is configured such that the side of the reinforcing sheet 42 is convex. The shape of the bent portion 40a is configured to be a part of a sphere. Furthermore, when viewed from a direction perpendicular to the main surface of the piezoelectric film, the shape of the bent portion 40a is circular, with a diameter of 60mm and a height of 5mm.

[0370] Then, cut it into a size of 70mm in diameter with the curved part 40a as the center.

[0371] As described above, a piezoelectric film 40 with a PET film thickness of 50 μm and a bending portion 40a was fabricated as the reinforcing sheet 42.

[0372] The actuator unit was fabricated using the piezoelectric thin film 40 in the same manner as in Example 1.

[0373] [Example 4]

[0374] As the reinforcing sheet 42, a PET separator with a thickness of 25 μm was used. In addition, a piezoelectric film 40 was fabricated in the same manner as in Example 3, and an actuator unit was fabricated.

[0375] [Example 5]

[0376] The reinforcing sheet 42 uses a 15 μm thick nonwoven fabric (Japanese paper), and the piezoelectric film 40 is fabricated in the following manner. Otherwise, the piezoelectric film 40 is fabricated in the same manner as in Example 3, and the actuator unit is fabricated.

[0377] In the fabrication of the piezoelectric film, after laminating the sheet 11c, two separators are removed. A 15μm thick nonwoven fabric (Japanese paper) is then glued onto a protective layer on one side, followed by forming the bending section 40a to create the piezoelectric film. A 12μm thick hot-melt sheet is used in the gluing of the nonwoven fabric (Japanese paper).

[0378] [Example 6]

[0379] The reinforcing sheet 42 was made of a 40 μm thick nonwoven fabric (Japanese paper). Otherwise, the piezoelectric film 40 was made in the same manner as in Example 5, and the actuator unit was also made.

[0380] [Example 7]

[0381] The reinforcing sheet 42 was made of a 50 μm thick fabric (cold yarn). In addition, the piezoelectric film 40 was made in the same manner as in Example 5, and the actuator unit was also made.

[0382] [Refer to Examples 1 to 5]

[0383] As for Reference Examples 1 to 5, the driver unit was fabricated in the same manner as in Examples 3 to 7, except that it did not have a perforated plate or porous components.

[0384] [evaluate]

[0385] With ear pads attached to the convex side of the curved portion of the actuator unit fabricated in Examples 1, 3-7, Comparative Examples 1, and Reference Examples 1-5, the unit was placed on a transparent acrylic plate with the ear pads facing downwards, and a load was applied from above. The state of the curved portion of the piezoelectric film was observed from below the acrylic plate under loads of 100g, 200g, 300g, 400g, 500g, and 600g. The case without deformation is designated as A, and the case with deformation is designated as C.

[0386] The results are shown in Table 2.

[0387] [Table 2]

[0388]

[0389] As shown in Table 2, compared with Example 1 without the reinforcing sheet, Examples 3-7 with the reinforcing sheet can better suppress abnormal deformation of the bending portion. Furthermore, a comparison between Comparative Example 1 and Reference Examples 1-5 also shows that the presence of the reinforcing sheet can better suppress abnormal deformation of the bending portion.

[0390] In addition, the pressure applied when wearing a typical pair of headphones is approximately 200 to 400 grams.

[0391] [Example 8]

[0392] The driver unit of Example 1 was housed in a housing, a protective ring was arranged on the opening side of the housing, and an ear pad was arranged in contact with the protective ring, thereby creating a test unit for simulating a headset.

[0393] A protective ring was made by cutting a 3mm thick acrylic sheet into a ring with an outer diameter of 74mm and an inner diameter of 40mm.

[0394] In the fabricated test unit, the shortest distance t between the protective ring and the piezoelectric film is 1 mm. Furthermore, when viewed from a direction perpendicular to the surface in contact with the ear pad, the protective ring contacts 85% of the total area of ​​the ear pad. Additionally, the ear pad has an inner diameter of approximately 32 mm, an outer diameter of approximately 72 mm, and a thickness of approximately 15 mm.

[0395] [evaluate]

[0396] First, the ear pad side of the test unit prepared in Example 1 was placed on the artificial ear for measuring headphones (TYPE2015E manufactured by Akoh Co., Ltd.). Under the conditions of pressing with loads of 200g and 500g respectively, a sinusoidal sweep signal with a frequency of 20Hz to 20kHz and a voltage of 10Vpp was input to the piezoelectric film, and the sound pressure was measured.

[0397] The frequency response is represented by a graph. Figure 27 .

[0398] like Figure 27 As shown, the sound pressure level drops significantly, especially in the low-frequency range, compared to the 200g load. This is believed to be because the ear pad deforms and comes into contact with the piezoelectric film when the test unit is pressed onto the artificial ear.

[0399] Next, the ear pad side of the test unit made in Example 8 was placed on the artificial ear for measuring headphones (TYPE2015E manufactured by Akoh Co., Ltd.), and a sinusoidal sweep signal with a frequency of 20Hz to 20kHz and a voltage of 10Vpp was input to the piezoelectric film under a load of 500g, and the sound pressure was measured.

[0400] The frequency response is represented by a graph. Figure 28 Furthermore, the results of the 200g load in Example 1 are also shown.

[0401] like Figure 28 As shown, the test unit of Example 8 with the protective ring does not experience a drop in sound pressure even when pressed against the artificial ear with a load of 500g. Furthermore, compared to the result of Example 1 with a load of 200g, Example 8 shows an increase in sound pressure in the mid-to-low frequency range. This is believed to be because the protective ring prevents deformation of the ear pad towards the driver unit, and the ear pad is effectively flattened over a larger area, thereby improving the airtightness between the artificial ear and the space within the ear pad, thus further increasing the sound pressure in the mid-to-low frequency range.

[0402] [Example 8B]

[0403] A series resistor (360Ω) was connected to the wiring connected to the electrode layer of the piezoelectric film. Otherwise, the driver unit was fabricated in the same manner as in Example 8.

[0404] The ear pad side of the fabricated test unit was placed on the artificial ear for testing headphones (TYPE2015E manufactured by Akoh Co., Ltd.) with a load of 400g. A sinusoidal sweep signal with a frequency of 20Hz to 20kHz and a voltage of 10Vpp was input to the piezoelectric film, and the sound pressure was measured.

[0405] The frequency characteristics measurement results of Examples 8 and 8B are shown below. Figure 29 .

[0406] from Figure 29 The results show that in Example 8B, where a resistor is connected in series between the piezoelectric film and the signal source, the sound pressure in the frequency band above 1.0 kHz can be reduced, thereby making the frequency response flatter.

[0407] As can be seen from the above, the present invention has significant effects.

[0408] Symbol Explanation

[0409] 10-Piezoelectric thin film, 10a-Bent portion, 10c-Edge portion, 11a, 11c-Sheet-like material, 11b-Piezoelectric laminate, 20-Piezoelectric layer, 24-First electrode layer, 26-Second electrode layer, 28-First protective layer, 30-Second protective layer, 34-Substrate, 36-Piezoelectric particle, 40-Piezoelectric thin film, 40a-Bent portion, 42-Reinforcing sheet, 44-Adhesive layer, 100, 100b-Actuator unit, 101-First air chamber, 102-Perforated plate, 102a-Through hole 102b - Insertion hole, 104 - Porous component, 106 - Retaining component, 106a - Threaded hole, 108 - Retaining component, 108a - Insertion hole, 110 - Fastening component, 200, 200b - Headphones, 201 - Second air chamber, 202 - Housing, 202a - Through hole, 204 - Ear pad, 206 - Ear pad locking component, 220 - Signal source, 222 - Resistor, 230 - Headphones, 232 - Protective ring, U - User's ear, M - Measurement device (artificial ear).

Claims

1. A driver unit, comprising: a piezoelectric film having a piezoelectric layer composed of a polymer composite piezoelectric body containing piezoelectric body particles in a matrix containing a polymer material, and an electrode layer provided on both sides of the piezoelectric layer; and a plate-shaped perforated plate having at least one through hole, the piezoelectric film has a bent portion shaped so as to protrude toward one main surface side of the piezoelectric film and be recessed toward the other main surface side of the piezoelectric film, the perforated plate is laminated on the recessed surface side of the bent portion of the piezoelectric film, the through hole communicates a first air chamber defined by the recessed surface of the piezoelectric film and the perforated plate with the outside.

2. The driver unit according to claim 1, wherein the proportion of the total area of the through hole with respect to the area of the bent portion of the piezoelectric film as viewed in plan is 3 to 70%.

3. The driver unit according to claim 1, wherein on the side of the perforated plate opposite the piezoelectric film, there is an acoustic absorption layer configured to cover the through hole, the acoustic absorption layer being composed of a porous member.

4. The driver unit according to claim 1, wherein the shape of the boundary line of the bent portion of the piezoelectric film is circular.

5. The driver unit according to claim 1, comprising a series resistor, the series resistor is connected between the electrode layer of the piezoelectric film and a signal source that drives the piezoelectric film.

6. A headphone, comprising: the driver unit according to any one of claims 1 to 5; a housing having an opening portion and accommodating the driver unit; and an ear pad configured on the opening portion side of the housing.

7. The headphone according to claim 6, wherein a second air chamber defined by the driver unit and the housing communicates with the outside.

8. The headphone according to claim 6, wherein the housing is configured on the recessed surface side of the piezoelectric film of the driver unit.

9. The headphone according to claim 6, wherein the headphone has a protective ring configured in contact with the ear pad between the driver unit and the ear pad, the protective ring has an opening portion that is perforated in a direction perpendicular to the surface of the protective ring in contact with the ear pad, when viewed in a direction perpendicular to the surface of the protective ring in contact with the ear pad, the protective ring contacts an area of 30% or more of the total area of the ear pad, the shortest distance between the protective ring and the piezoelectric film of the driver unit is 0.3 mm or more. ​ ​

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