Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JP2014200114 Abstract: PROBLEM TO BE SOLVED: To reduce variation in sound pressure in frequency characteristics of sound pressure. SOLUTION: A sound generator comprises a film 3 serving as a support plate, a frame member 5 provided on the outer peripheral portion of the film 3, and a piezoelectric element 1 provided on the film 3 in the frame of the frame member 5. And the resin layer 20 provided on the film 3 in the frame of the frame member 5, and the resin layer 20 has the air bubbles 8. The air bubble 8 makes it possible to reduce peaks and dips in the frequency characteristic of the sound pressure while suppressing a drop in the sound pressure, thereby generating high-quality sound. [Selected figure] Figure 1B Acoustic generator, acoustic generator and electronic device [0001] The present invention relates to a sound generator, a sound generator and an electronic device. [0002] Piezoelectric speakers are conventionally known as small-sized, low-current-driven acoustic devices that use a piezoelectric body as an electroacoustic transducer, and are used, for example, as acoustic generators to be incorporated into small electronic devices such as mobile computing devices. It is done. [0003] 11-05-2019 1 In general, an acoustic generator using a piezoelectric body as an electroacoustic transducer has a structure in which a piezoelectric element in which an electrode of a silver thin film or the like is formed on the piezoelectric body is attached to a metal diaphragm. Such an acoustic generator generates a shape distortion in the piezoelectric element by applying an alternating voltage to the piezoelectric element, and generates a sound by transmitting the shape distortion of the piezoelectric element to a metal diaphragm to vibrate. [0004] However, since an acoustic generator having a structure in which a piezoelectric element is attached to a metal diaphragm is such that area bending vibration is generated by restraining a piezoelectric element that spreads and vibrates with a metal plate whose area does not change. It has been difficult to provide sound pressure characteristics with low conversion efficiency, small size, and low resonance frequency. [0005] In order to solve such problems, the applicant has proposed a sound generator using a resin film as a diaphragm instead of a metal diaphragm (see, for example, Patent Document 1). [0006] In this sound generator, a bimorph-type laminated piezoelectric element is sandwiched between a pair of resin films in the thickness direction, and the resin film is fixed to a frame member in a tensioned state. Thereby, the sound conversion efficiency is improved, and high sound pressure can be generated. [0007] JP, 2010-177867, A [0008] However, the above-mentioned sound generator has variations in sound pressure in frequency 11-05-2019 2 characteristics of sound pressure, and in order to further improve the sound quality, it is necessary to reduce the variations in sound pressure. [0009] The present invention is made in view of the above, and an object of the present invention is to provide an acoustic generator, an acoustic generator, and an electronic device that can reduce variation in sound pressure in frequency characteristics of sound pressure. [0010] The sound generator according to the present invention comprises a film, a frame member provided on an outer peripheral portion of the film, a piezoelectric element provided on the film in the frame of the frame member, and a frame in the frame member. And a resin layer provided on the film, wherein the resin layer has bubbles. [0011] According to one aspect of the sound generator according to the present invention, it is possible to reduce the variation in sound pressure in the frequency characteristic of sound pressure. [0012] FIG. 1A is a plan view showing a first embodiment of a sound generator. FIG. 1B is a cross-sectional view showing a first embodiment of a sound generator. FIG. 2 is a partial cross-sectional view for explaining a first example of an effective placement method of air bubbles in the resin layer of the sound generator of the first embodiment. FIG. 3 is a partial cross-sectional view for explaining a second example of the effective arrangement method of air bubbles in the resin layer of the sound generator of the first embodiment. FIG. 4 is a partial cross-sectional view for explaining a third example of the effective arrangement 11-05-2019 3 method of air bubbles in the resin layer of the sound generator of the first embodiment. FIG. 5 is a partial cross-sectional view for explaining a fourth example of the effective arrangement method of the air bubbles in the resin layer of the sound generator of the first embodiment. FIG. 6 is a cross-sectional view schematically showing the sound generator of the second embodiment. FIG. 7 is a view schematically showing the electronic device of the third embodiment. FIG. 8 is a graph showing an example of the frequency characteristic of sound pressure. FIG. 9 is a graph showing an example of the frequency characteristic of sound pressure. FIG. 10 is a graph showing an example of the frequency characteristic of sound pressure. FIG. 11 is a graph showing an example of sound pressure frequency characteristics. [0013] Hereinafter, embodiments of a sound generator, a sound generator and an electronic device according to the present invention will be described in detail based on the drawings. Note that this embodiment does not limit the present invention. And each form illustrated below as an embodiment can be combined suitably in the range which does not contradict the shape and size of each member which constitute a sound generator. [0014] (1) First Embodiment [Structure of Sound Generator] First, a sound generator according to a first embodiment of the present invention will be described based on FIGS. 1A and 1B. FIG. 1A is a plan view of the first embodiment of the sound generator, and FIG. 1B is a cross-sectional view taken along the line A-A 'of FIG. 1A. In FIG. 1A, the position of the piezoelectric element 1 which is covered by the resin layer 20 and can not be seen in the + Z direction is indicated by a broken line. Moreover, in FIG. 1B, in order to facilitate understanding, the thickness direction (Z-axis direction) of the laminated piezoelectric element 1 is shown enlarged. Moreover, in FIG. 1A and 1B, illustration of the bubble 8 in resin 20 is abbreviate ¦ omitted. 11-05-2019 4 [0015] The sound generator of the first embodiment shown in FIGS. 1A and 1B includes a film 3, a frame member 5 provided on the outer peripheral portion of the film 3, and a piezoelectric element provided on the film 3 in the frame of the frame member 5. 1 and the resin layer 20 provided on the film 3 in the frame of the frame member 5. [0016] The frame member 5 is constituted by a pair of frame members 5a and 5b, and as shown in FIG. 1B, the film 3 is held by holding the outer peripheral portion of the film 3 with the frame members 5a and 5b under tension. Is fixed to the frame member 5, and the laminated piezoelectric element 1 is disposed on the upper surface of the film 3. [0017] Among them, the piezoelectric element 1 is formed in a plate shape and the upper and lower main surfaces are formed in a square shape, a rectangular shape or a polygonal shape. The piezoelectric element 1 is a laminate 13 in which four piezoelectric layers 7 (7a, 7b, 7c, 7d) and three internal electrode layers 9 (9a, 9b, 9c) are alternately stacked. Including surface electrode layers 15a and 15b formed on the upper and lower surfaces of the laminate 13 and first to third external electrodes provided at the end of the laminate 13 in the longitudinal direction (Y-axis direction) There is. [0018] The first external electrode 17 is disposed at the end of the laminate 13 in the -Y direction, and is connected to the surface electrode layers 15a and 15b and the internal electrode layer 9b. A second external electrode 18 and a third external electrode (not shown) are disposed at an end in the + Y direction of the laminate 13 at an interval in the X-axis direction. The second outer electrode 18 is connected to the inner electrode layer 9a, and the third outer electrode (not shown) is connected to the inner electrode 9c. The piezoelectric layer 7 is polarized in the direction indicated by the arrow in FIG. 1B, so that when the piezoelectric layers 7a and 7b 11-05-2019 5 contract, the piezoelectric layers 7c and 7d extend, and the piezoelectric layer 7a, When 7b extends, a voltage is applied to the first external electrode 17, the second external electrode 18, and the third external electrode so that the piezoelectric layers 7c and 7d contract. As described above, the piezoelectric element 1 is a bimorph type piezoelectric element, and when an electric signal is input, the piezoelectric element 1 bends and vibrates in the Z axis direction so that the amplitude changes in the Y axis direction. [0019] The upper and lower end portions of the second external electrode 18 are extended to the upper and lower surfaces of the laminated body 13 to form folded external electrodes 18 a, and these folded external electrodes 18 a are formed on the surface of the laminated body 13. The surface electrode layers 15a and 15b are extended at a predetermined distance so as not to contact the surface electrode layers 15a and 15b. Similarly, upper and lower end portions of a third external electrode (not shown) are extended to the upper and lower surfaces of the laminate 13 to form respective folded external electrodes (not shown), and these folded external electrodes are formed. (Not shown) is extended at a predetermined distance from the surface electrode layers 15a and 15b so as not to contact the surface electrode layers 15a and 15b formed on the surface of the laminate 13. [0020] The four layers of the piezoelectric layer 7 and the three layers of the internal electrode layer 9 were formed by firing simultaneously in the laminated state, and the surface electrode layers 15 a and 15 b were formed into the laminated body 13. After that, it is formed by applying and baking a conductor paste. [0021] In the piezoelectric element 1, the main surface on the film 3 side and the film 3 are bonded by the adhesive layer 21. The thickness of the adhesive layer 21 is desirably 20 μm or less, and more desirably 10 μm or less. When the thickness of the adhesive layer 21 is 20 μm or less, the vibration of the laminate 13 is easily transmitted to the film 3. 11-05-2019 6 [0022] As an adhesive for forming the adhesive layer 21, known materials such as epoxy resin, silicon resin, polyester resin and the like can be used. As a method of curing the resin used for the adhesive, any method such as heat curing, photo curing or anaerobic curing may be used. [0023] Furthermore, in the sound generator of the first embodiment, the resin is filled inside the frame member 5 a so that the piezoelectric element 1 is embedded, and the resin layer 20 is formed. [0024] For the resin layer 20, epoxy resin, acrylic resin, silicon resin, rubber, etc. can be adopted. Further, the resin layer 20 is preferably applied in a state of completely covering the piezoelectric element 1 from the viewpoint of suppressing peaks and dips, but it is not necessary to completely cover the piezoelectric element 1. Furthermore, the region of the film 3 not covered by the piezoelectric element 1 is also covered by the resin layer 20. The resin layer 20 does not necessarily have to cover the entire film 3. In some cases, the resin layer 20 may be provided to cover a part of the film 3. The thickness of the resin layer 20 is set to, for example, about 0.1 mm to 1 mm. [0025] Thus, in the acoustic generator of the first embodiment, the resonance phenomenon can be appropriately damped by providing the resin layer 20. By such a damping effect, it is possible to suppress a resonance phenomenon and to suppress a peak or a dip in a frequency characteristic of sound pressure which is generated due to the resonance phenomenon. As a result, it becomes possible to flatten the frequency characteristic of sound pressure. [0026] 11-05-2019 7 As the piezoelectric layer 7, existing piezoelectric ceramics such as lead-free piezoelectric materials such as lead zirconate (PZ), lead zirconate titanate (PZT), Bi layer compounds, tungsten bronze structure compounds, etc. can be used. . The thickness of the piezoelectric layer 7 is set to 10 to 100 μm from the viewpoint of low voltage drive. [0027] The internal electrode layer 9 can be formed using various existing conductor materials, but it is desirable to include a metal component consisting of silver and palladium and a material component constituting the piezoelectric layer 7. Further, by incorporating the ceramic component that constitutes the piezoelectric layer 7 in the internal electrode layer 9, it is possible to reduce the stress due to the thermal expansion difference between the piezoelectric layer 7 and the internal electrode layer 9. The internal electrode layer 9 may not contain a metal component consisting of silver and palladium, and may not contain a material component constituting the piezoelectric layer 7. [0028] The surface electrode layers 15a and 15b and the first to third external electrodes can be formed using various existing conductor materials, but it is desirable that the metal component made of silver contain a glass component. By thus containing the glass component, strong adhesion can be obtained between the piezoelectric layer 7 and the internal electrode layer 9 and the surface electrode layer 15 and the first to third external electrodes. [0029] The frame member 5 has a rectangular shape, and as shown in FIG. 1B, the frame member 5 is configured by bonding two rectangular frame-shaped frame members 5a and 5b. The outer peripheral portion of the film 3 is sandwiched between the frame members 5a and 5b, and the film 3 is fixed in a tensioned state. The thickness of the frame members 5a and 5b is, for example, about 100 to 1000 μm, and the length of one side of the inside of the frame is, for example, about 20 mm to 200 mm. The material of the frame members 5a and 5b may be any material that is less likely to be deformed than the resin layer 20. For example, hard resin, plastic, engineering plastic, ceramics, etc. can be used. For example, stainless steel can be suitably used. . 11-05-2019 8 The material, thickness, and the like of the frame members 5a and 5b are not particularly limited. Further, the shape of the frame member 5 is not limited to a rectangular shape, and for example, a part or all of the inner peripheral part or the outer peripheral part may be elliptical, or the inner peripheral part or the outer peripheral part may be rhombus Good. [0030] The film 3 is fixed to the frame members 5a and 5b in a state in which the film 3 is tensioned in the surface direction by sandwiching the outer peripheral part of the film 3 between the frame members 5a and 5b, and the film 3 serves as a diaphragm Plays. The thickness of the film 3 is, for example, 10 to 200 μm, and the film 3 is made of, for example, a resin such as polyethylene, polyimide, polypropylene or polystyrene, or a paper made of pulp, fibers or the like. Peaks and dips can be suppressed by using these materials. [0031] [Air Bubbles of Resin Layer] Subsequently, air bubbles in the resin layer 20 which the sound generator of the first embodiment of the present embodiment has will be described. The resin layer 20 of the first embodiment has air bubbles 8 as shown in FIGS. The size of the air bubble 8 (maximum value of the distance between two points located on the surface) is preferably, for example, about 20 to 150 μm. Moreover, although a spherical shape is mentioned as a representative example of the shape of the bubble 8, you may be another shape. In addition, about the ratio which the bubble 8 occupies to the resin layer 20, it demonstrates in full detail in the Example using FIGS. 8-11. [0032] As described above, by providing the air bubbles 8 in the resin layer 20, the sound quality of the sound generated from the sound generator can be improved. The reason why this effect can be obtained can be estimated as follows, though it can not be specified clearly. When air bubbles (voids) are present in the resin layer 20, stress generated by the vibration of the vibrator constituted by the film 3 integrated with the piezoelectric element 1 and the resin layer 20 is concentrated in the vicinity of the air bubbles 8. As a result, the local strain in the vicinity of the bubble 8 becomes large, a part of the vibrational energy is absorbed by the bubble 8, and the Q value at the resonance of the vibration system decreases. As a result, it is possible to reduce 11-05-2019 9 peaks and dips in the frequency characteristics of sound pressure that are caused due to resonance. As a result, the frequency characteristic of the sound pressure becomes flatter, and the sound quality of the sound generated by the sound generator is improved. Furthermore, since the sound quality can be improved without increasing the thickness of the resin layer 20, it is also possible to avoid a decrease in the overall sound pressure. And since peaks and dips caused by all the resonance modes can be reduced by the bubbles 8 contained in the resin layer 20, the sound quality is improved over the entire frequency band where the sound pressure can be obtained by the bending and bending vibration of the vibrator. be able to. [0033] As described above, according to the sound generator of the first embodiment, the variation in sound pressure in the frequency characteristic of sound pressure can be reduced, and the sound quality can be improved. Next, an effective arrangement method of the air bubbles 8 in the resin layer 20 will be described with reference to FIGS. [0034] FIG. 2 is a partial cross-sectional view for explaining a first example of an effective arrangement method of the air bubbles 8 in the resin layer 20 of the sound generator of the first embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary between the frame member 5a and the resin layer 20. [0035] In the example shown in FIG. 2, at least a part of the air bubbles 8 in the resin layer 20 is provided in contact with the boundary between the frame member 5 a and the resin layer 20. The boundary between the frame member 5a and the resin layer 20 is a portion where rigidity changes in the sound generator, and therefore, a portion where stress concentrates when the sound generator vibrates. By providing the air bubble 8 in the portion where the stress is concentrated, the effect of the air bubble 8 absorbing vibration energy can be enhanced, so that the sound quality of the sound generated from the sound generator can be effectively improved. As described above, in the example illustrated in FIG. 2, at least a part of the air bubbles 8 in the resin layer 20 is provided so as to be in contact with the part where the rigidity changes in the sound generator. The sound quality of the sound can be effectively improved. 11-05-2019 10 [0036] Further, in the example shown in FIG. 2, the air bubbles 8 arranged to be in contact with the boundary between the frame member 5 a and the resin layer 20 are not completely spherical, but are in the direction contacting with the boundary between the frame member 5 a and the resin layer 20 (frame It is desirable to have a shape that extends in a direction parallel to the boundary between the member 5a and the resin layer 20). That is, the air bubbles 8 arranged to be in contact with the boundary between the frame member 5a and the resin layer 20 have a long shape in the direction along the boundary between the frame member 5a and the resin layer 20 (the frame member 5a and It is desirable that the length in the direction along the boundary with the resin layer 20 be larger than the length in the direction perpendicular to the boundary between the frame member 5 a and the resin layer 20. Thereby, the area in which the air bubble 8 contacts the boundary between the frame member 5a and the resin layer 20 can be increased, so the effect of absorbing the vibration energy is enhanced, and the sound quality of the sound generated from the sound generator is improved. Can be improved. In the present specification, when the sound generator is viewed in plan, it is viewed in plan from the thickness direction of the resin layer 20 (Z-axis direction). [0037] FIG. 3 is a partial cross-sectional view for explaining a second example of the effective arrangement method of the air bubbles 8 in the resin layer 20 of the acoustic generator of the first embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary between the piezoelectric element 1 and the resin layer 20. [0038] In the example shown in FIG. 3, at least a part of the air bubbles 8 in the resin layer 20 is provided in contact with the boundary between the piezoelectric element 1 and the resin layer 20. The boundary between the piezoelectric element 1 and the resin layer 20 is a portion where the rigidity changes in the sound generator. Therefore, by providing at least a part of the air bubbles 8 in the resin layer 20 in contact with the boundary between the piezoelectric element 1 and the resin layer 20, as in the first example described above, the sound generated from the acoustic 11-05-2019 11 generator Sound quality can be effectively improved. [0039] Further, in the example shown in FIG. 3, the bubbles 8 arranged to be in contact with the boundary between the piezoelectric element 1 and the resin layer 20 are not completely spherical, but expand in the direction in contact with the boundary between the piezoelectric element 1 and the resin layer 20 It is desirable to have a shape like this. That is, the bubbles 8 arranged to be in contact with the boundary between the piezoelectric element 1 and the resin layer 20 have a long shape in the direction along the boundary between the piezoelectric element 1 and the resin layer 20 (the piezoelectric element 1 and the resin layer 20) It is desirable that the length in the direction along the boundary with the resin layer 20 be larger than the length in the direction perpendicular to the boundary between the piezoelectric element 1 and the resin layer 20). As a result, the area in which the air bubble 8 contacts the boundary between the piezoelectric element 1 and the resin layer 20 can be increased, so the effect of absorbing the vibration energy is enhanced, and the sound quality of the sound generated from the sound generator Can be effectively improved. [0040] FIG. 4 is a partial cross-sectional view for explaining a third example of the effective arrangement method of the air bubbles 8 in the resin layer 20 of the sound generator of the first embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary between the film 3 and the resin layer 20. [0041] In the example shown in FIG. 4, at least a part of the air bubbles 8 in the resin layer 20 is provided in contact with the boundary between the film 3 and the resin layer 20. The boundary between the film 3 and the resin layer 20 is a portion where the rigidity changes in the sound generator. Therefore, by providing at least a part of the air bubbles 8 in the resin layer 20 in contact with the boundary between the film 3 and the resin layer 20, as in the first and second examples described above, from the acoustic generator The sound quality of the generated sound can be effectively improved. 11-05-2019 12 [0042] Further, in the example shown in FIG. 4, the air bubbles 8 disposed so as to be in contact with the boundary between the film 3 and the resin layer 20 are not completely spherical, but in the direction contacting with the boundary between the film 3 and the resin layer 20 It is desirable that the shape is expanded in a direction parallel to the boundary with the resin layer 20). That is, when viewed from a direction parallel to the boundary between the film 3 and the resin layer 20, the air bubbles 8 arranged to be in contact with the boundary between the film 3 and the resin layer 20 are at the boundary between the film 3 and the resin layer 20 It is desirable that the shape along the direction is long (the length along the boundary between the film 3 and the resin layer 20 is larger than the length perpendicular to the boundary between the film 3 and the resin layer 20). . As a result, the area in which the air bubble 8 contacts the boundary between the film 3 and the resin layer 20 can be increased, so the effect of absorbing the vibration energy of the air bubble 8 is enhanced, and the sound quality of the sound generated from the sound generator is effective. Can be improved. [0043] FIG. 5 is a partial cross-sectional view for explaining a fourth example of the effective arrangement method of the air bubbles 8 in the resin layer 20 of the sound generator of the first embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary between the film 3 and the resin layer 20. [0044] In the example shown in FIG. 5, the air bubbles 8 in the resin layer 20 are arranged so as to be unevenly distributed in the vicinity of the boundary between the film 3 and the resin layer 20 in the thickness direction of the resin layer 20. Further, the bubbles 8 in the resin layer 20 are arranged to be distributed more as they approach the interface between the film 3 and the resin layer 20. That is, the number of air bubbles 8 is arranged to increase as the interface between the film 3 and the resin layer 20 is approached. By arranging the air bubbles 8 in this manner, the sound quality of the sound generated from the sound generator can be effectively improved. The reason why this effect is obtained is estimated as follows. That is, since the boundary between the film 3 and the resin layer 20 is a portion where the rigidity changes in the sound generator, when the sound generator vibrates, the 11-05-2019 13 portion near the boundary with the film 3 in the resin layer 20 is resin The strain (deformation) becomes larger than that of the portion of the layer 20 which is far from the boundary with the film 3. Therefore, it is effective by arranging so as to be localized near the boundary between the film 3 and the resin layer 20, or arranging so that the number of the air bubbles 8 increases toward the interface between the film 3 and the resin layer 20. The vibration energy can be absorbed by the air bubbles 8. As a result, the Q value at the resonance of the vibration system can be reduced, and peaks and dips in the frequency characteristics of the sound pressure generated due to the resonance can be reduced, and a more flat frequency characteristic of the sound pressure can be obtained. it can. [0045] [Production method] An example of the production method of the sound generator of the present invention will be described. [0046] First, the piezoelectric element 1 is prepared. First, a binder, a dispersant, a plasticizer, and a solvent are kneaded with powder of a piezoelectric material to prepare a slurry. As a piezoelectric material, any of lead-based and nonlead-based can be used. [0047] Next, the above-mentioned slurry is formed into a sheet to obtain a green sheet. Then, an internal electrode paste is printed on the green sheet to form an internal electrode pattern, three green sheets on which the electrode pattern is formed are stacked, and a green sheet on which the electrode pattern is not printed is stacked. Then, a laminated molded body is produced. [0048] Next, the laminate molded body is degreased and fired, and cut into a predetermined size, whereby the laminate 13 can be obtained. The laminate 13 has its outer peripheral portion 11-05-2019 14 processed as necessary, and the paste of the surface electrode layers 15a and 15b is printed on both principal surfaces in the lamination direction of the laminate 13 and then, the longitudinal direction of the laminate 13 (Y-axis direction) The first to third external electrodes are printed on the both end faces of b) and the electrodes are baked at a predetermined temperature. Thus, the piezoelectric element 1 shown in FIGS. 1A and 1B can be obtained. [0049] Next, in order to impart piezoelectricity to the piezoelectric element 1, a direct current voltage is applied through the first to third external electrodes to polarize the piezoelectric layer 7 of the piezoelectric element 1. This polarization is performed by applying a DC voltage so as to be in the direction indicated by the arrow in FIG. 1B. [0050] Next, a film 3 to be a support is prepared, and the outer peripheral portion of the film 3 is sandwiched between the frame members 5a and 5b, and the film 3 is fixed in a tensioned state. After that, an adhesive is applied to the film 3 and the surface electrode 15a side of the piezoelectric element 1 is pressed against the film 3. Thereafter, the adhesive is cured by irradiating heat or ultraviolet light. Then, after the resin before curing is poured into the inside of the frame member 5a and the air bubbles 8 are formed in a predetermined place, the resin is cured to form the resin layer 20. In this way, the first form of the sound generator can be obtained. [0051] Various methods can be used as a method of forming the air bubbles 8 in the resin layer 20. For example, a method may be used in which a resin before curing is poured into the inside of the frame member 5a after the hollow resin spheres are disposed in desired locations. Alternatively, a method may be used in which hollow resin spheres (cured or semi-cured) are mixed in the resin before curing. In this case, for example, a resin containing hollow resin spheres is applied to a desired place and dried, and then a resin not containing hollow resin spheres is poured and cured to obtain the desired resin layer 20. It is possible to place the air bubbles 8 selectively in places. Also, prepare a plurality of uncured resins having different amounts of hollow resin spheres mixed (density of resin spheres in the resin), and order from the ones with many mixed resin 11-05-2019 15 spheres (high density of resin spheres in resin) After coating and drying on a film, bubbles 8 can be disposed as shown in FIG. 5 by pouring and curing an uncured resin not containing hollow resin spheres. Thus, by using the hollow resin spheres prepared in advance, it becomes easy to arrange the cells having the desired shape and size at the desired positions. [0052] Alternatively, the resin before curing may be poured into the inside of the frame member 5a, and gas may be injected into a desired location in the resin to form the air bubbles 8, and then the resin may be cured. For example, the tip of a thin tube is applied to the interface between the frame member 5a and the resin, and gas is intermittently injected through the tube while moving the tip of the tube along the interface between the frame member 5a and the resin. By forming 8 and thereafter curing the resin, as shown in FIG. 2, the air bubbles 8 can be arranged to be in contact with the boundary between the frame member 5 a and the resin layer 20. Similarly, the tip of the tube is brought into contact with the interface between the piezoelectric element 1 and the resin, and gas is intermittently injected through the tube while moving the tip of the tube along the interface between the piezoelectric element 1 and the resin. By forming 8 and thereafter curing the resin, as shown in FIG. 3, the air bubbles 8 can be arranged to be in contact with the boundary between the piezoelectric element 1 and the resin layer 20. And similarly, the tip of the tube is brought into contact with the interface between the film 3 and the resin, and while the tip of the tube is moved along the interface between the film 3 and the resin, gas is intermittently injected through the tube. By forming the air bubbles 8 by this, and then curing the resin, the air bubbles 8 can be arranged to be in contact with the boundary between the film 3 and the resin layer 20 as shown in FIG. [0053] For example, by using the method as described above, it is possible to arrange the air bubble 8 at a desired position in the resin layer 20 as illustrated in FIGS. 2 to 5. In addition, the method of arrange ¦ positioning the bubble 8 in the resin layer 20 is not limited to the method mentioned above, You may use another method. [0054] Moreover, although the case where the bimorph-type piezoelectric element 1 was provided in 11-05-2019 16 one main surface of the film 3 was shown in FIG. 1B, it is not restricted to this. For example, the same effect can be obtained by using a unimorph-type piezoelectric element in which a plate made of metal or the like is attached to one main surface of the piezoelectric element that vibrates in the plane direction instead of the bimorph-type piezoelectric element. Can. In addition, piezoelectric elements that vibrate in a stretching direction in the plane direction may be provided on both sides of the film 3, and unimorph type or bimorph type piezoelectric elements may be provided on both sides of the film 3. [0055] Moreover, although the example in which the resin layer 20 was provided in the inner side of the frame member 5a so that the piezoelectric element 1 might be covered completely was shown in FIG. 1B, it is not limited to this. For example, the resin layer 20 may be provided only on the film 3 so as not to completely cover the piezoelectric element 1. [0056] Moreover, although the case where the shape of the part inside the frame member 5 is substantially rectangular shape was shown in FIG. 1A, it is not restricted to this. For example, the shape of the inner portion of the frame member 5 may be elliptical. [0057] (2) Second Embodiment Next, a sound generator according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing the configuration of the sound generation device 30 of the second embodiment of the present invention. In FIG. 6, only the components necessary for the description are shown, and the detailed configuration of the sound generator 10 and the general components are omitted. [0058] The sound generation device 30 is a sound generation device such as a so-called speaker, and includes, for example, a housing 31 and a sound generator 10 attached to the housing 31 as 11-05-2019 17 shown in FIG. The housing 31 has a rectangular box-like shape, and has an opening 31a on one surface. Such a housing 31 can be formed using, for example, known materials such as plastic, metal, wood and the like. In addition, the shape of the housing 31 is not limited to a box shape of a rectangular parallelepiped, and can be various shapes such as a cylindrical shape or a frustum shape, for example. [0059] The sound generator 10 is attached to the opening 31 a of the housing 31. The sound generator 10 is the sound generator of the first embodiment described above, and the description of the sound generator 10 is omitted. Since the sound generator 30 having such a configuration generates sound using the sound generator 10 that generates sound with high sound quality, sound with high sound quality can be generated. Moreover, since the sound generator 30 can resonate the sound generated from the sound generator 10 inside the housing 31, the sound pressure in the low frequency band can be increased, for example. In addition, the place where the sound generator 10 is attached can be set freely. Also, the sound generator 10 may be attached to the housing 31 via another object. [0060] (3) Third Embodiment Next, an electronic device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing the configuration of the electronic device 50 according to the third embodiment of the present invention. In FIG. 7, only the components necessary for the description are shown, and the detailed configuration of the sound generator 10 and the general components are omitted. [0061] FIG. 7 shows the case where the electronic device 50 is a mobile terminal device such as a mobile phone or a tablet terminal. As shown in FIG. 7, the electronic device 50 includes a housing 40, the sound generator 10 attached to the housing 40, and an electronic circuit 60 connected to the sound generator 10. The sound generator 10 is the sound generator of the first embodiment described above, and the description of the sound generator 10 is omitted. The electronic circuit 60 includes, for example, a controller 50a, a transmitting / receiving unit 50b, a key input unit 50c, and a microphone input unit 50d. The electronic circuit 60 is connected to the sound 11-05-2019 18 generator 10 and has a function of outputting an audio signal to the sound generator. The sound generator 10 generates a sound based on an audio signal input from the electronic circuit 60. [0062] The electronic device 50 further includes a display unit 50 e and an antenna 50 f, and these devices are attached to the housing 40. Although FIG. 7 shows a state in which all the devices including the controller 50a are housed in one housing 40, the housing form of each device is not limited. In this embodiment, at least the sound generator 10 may be attached to the housing 40 directly or through another object, and the arrangement of the other components can be freely set. [0063] The controller 50 a is a control unit of the electronic device 50. The transmitting and receiving unit 50b transmits and receives data via the antenna 50f based on the control of the controller 50a. The key input unit 50c is an input device of the electronic device 50, and receives a key input operation by the operator. The microphone input unit 50d is also an input device of the electronic device 50, and receives a voice input operation and the like by the operator. The display unit 50 e is a display output device of the electronic device 50, and outputs display information based on the control of the controller 50 a. The sound generator 10 then operates as a sound output device in the electronic device 50. The sound generator 10 is connected to the controller 50a of the electronic circuit 60, and emits a sound in response to the application of a voltage controlled by the controller 50a. [0064] Since the electronic device 50 having such a configuration generates sound using the sound generator 10 that generates sound with high sound quality, it is possible to generate sound with high sound quality. [0065] By the way, in FIG. 7, although the electronic device 50 is described as being a portable terminal device such as a smartphone, a portable telephone, a personal handy phone system (PHS), a 11-05-2019 19 personal digital assistants (PDA), etc. It may be various electronic devices having a function of emitting sound. For example, a television, a personal computer, and a car audio device may be various products such as a vacuum cleaner, a washing machine, a refrigerator, and a microwave oven, as a matter of course. [0066] In the present embodiment, the difference in frequency characteristics of the sound pressure between the resin layer 20 not containing the bubbles 8 and the resin layer 20 containing the bubbles 8 and the sound pressure due to the concentration of the bubbles 8 in the resin layer 20 The difference in frequency characteristics of [0067] 8 to 11 are graphs showing an example of the frequency characteristic of sound pressure. Among these, FIG. 8 indicates the frequency characteristics of the sound pressure when the volume ratio of the bubbles 8 to the entire volume of the resin layer 20 is 0%, that is, when the resin layer 20 does not include the bubbles 8. Moreover, FIG. 9 points out the frequency characteristic of the sound pressure in case the ratio of the volume of the air bubbles 8 to the volume of the entire resin layer 20 is 10%. FIG. 10 shows the frequency characteristic of the sound pressure in the case where the volume ratio of the bubbles 8 to the volume of the entire resin layer 20 is 20%. FIG. 11 indicates the frequency characteristics of the sound pressure in the case where the volume ratio of the bubbles 8 to the volume of the entire resin layer 20 is 30%. The vertical axes of the graphs shown in FIGS. 8 to 11 indicate the sound pressure, and the horizontal axes of the graphs indicate the frequency. The sound generators whose frequency characteristics of the sound pressure shown in FIGS. 8 to 11 were measured had the same configuration except for the concentration of the air bubbles 8, that is, the respective members and the dimensions and materials thereof. [0068] First, the graph shown in FIG. 8 and the graph shown in FIG. 9 are compared in order to explain 11-05-2019 20 the difference in frequency characteristics of the sound pressure depending on the presence or absence of the bubble 8. Peaks and dips located in the frequency band 210 of 700 Hz to 1 kHz, the frequency band 220 of 1.5 kHz to 2.5 kHz, and the frequency band 230 of 6 kHz to 9 kHz in FIG. 8 and the frequency band 310 of 700 Hz to 1 kHz shown in FIG. Comparing the peaks and dips respectively located in the frequency band 320 of 1.5 kHz to 2.5 kHz and the frequency band 330 of 6 kHz to 9 kHz, the peaks and dips in the graph of FIG. It can be seen that the dip is clearly smaller. In addition, a decrease in the level is also observed for a peak located near 0.4 kHz and a peak located near 5 kHz to 6 kHz. [0069] As described above, when the bubbles 8 are contained in the resin layer 20 at a volume concentration of 10%, the peaks and dips become smaller in most of the frequency bands and the flatness is improved compared to the case where the bubbles 8 are not included. It can be seen that the frequency characteristic of sound pressure is improved. [0070] Furthermore, the case where the bubbles 8 are contained at a volume concentration of 10% and the case where the bubbles 8 are contained at a volume concentration of 20% are compared. Peaks and dips located in the frequency band 310 of 700 Hz to 1 kHz and the frequency band 320 of 1.5 kHz to 2.5 kHz shown in FIG. 9 and the frequency band 410 of 700 Hz to 1 kHz shown in FIG. Comparing the peaks and dips respectively located in the 5 kHz frequency band 420, it can be seen that the peaks and dips in the graph of FIG. 10 are clearly smaller than the peaks and dips in the graph shown in FIG. [0071] As described above, when the bubbles 8 are contained in the resin layer 20 at a volume concentration of 20%, the peaks and dips become smaller and the flatness is improved as compared to the case where the bubbles 8 are contained at a volume concentration of 10%. It can be seen that the frequency characteristic of pressure is improved. [0072] 11-05-2019 21 Furthermore, the case where the bubbles 8 are contained at a volume concentration of 20% and the case where the bubbles 8 are contained at a volume concentration of 30% are compared. Peaks and dips located in the frequency band 410 of 700 Hz to 1 kHz and the frequency band 420 of 1.5 kHz to 2.5 kHz shown in FIG. 10, and the frequency band 510 of 700 Hz to 1 kHz shown in FIG. Comparing the peaks and dips respectively located in the 5 kHz frequency band 520, it can be seen that the peaks and dips in the graph of FIG. 11 are clearly smaller than the peaks and dips in the graph shown in FIG. [0073] As described above, when the bubbles 8 are contained in the resin layer 20 at a volume concentration of 30%, the peaks and dips become smaller and the flatness is improved compared to the case where the bubbles 8 are contained at a volume concentration of 20%. It can be seen that the frequency characteristic of pressure is improved. [0074] From the above results, the variation in the sound pressure in the frequency characteristic of the sound pressure can be suppressed more in the case where the bubbles 8 are included than in the case where the bubbles 8 are not included in the resin layer 20, and more It can be seen that the frequency characteristic of the sound pressure can be improved when the bubble 8 is included. This confirms the effectiveness of the present invention. [0075] 1: Piezoelectric element 3: Film 5, 5a, 5b: Frame member 8: Bubble 10: Sound generator 20: Resin layer 30: Sound generator 31, 40: Case 50: Electronic device 60: Electronic circuit 11-05-2019 22
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