Electroacoustic transducer

Abstract

Provided is an electro-acoustic transducer in which a plurality of vibrators are disposed on a vibration plate, the electro-acoustic transducer being capable of reducing power consumption while suppressing a reduction in sound pressure in a high-pitch region. A piezoelectric vibrator includes a vibrating plate and a vibrator group composed of a plurality of piezoelectric vibrators disposed on one surface of the vibrating plate, the plurality of piezoelectric vibrators each belong to any one of a first group to an n-th group, upper limit frequencies of frequency bands of input signals input to the piezoelectric vibrators are different for each group, and when the upper limit frequencies in each group are set to f1-fn, the upper limit frequencies of the piezoelectric vibrators are set to f1-fn, the upper limit frequencies of the piezoelectric vibrators are set to f1-fn, and the upper limit frequencies of the piezoelectric vibrators are set to f1-fn. The upper limit frequency gradually decreases from the upper limit frequency f1 in the first group toward the upper limit frequency fn in the n-th group.

Description

Technical Field

[0001] The invention relates to an electroacoustic converter. Background Art

[0002] When a thin image display device such as a liquid crystal display or an organic EL display is used as an image display device and an audio generating device that reproduces audio together with an image, a speaker that is an acoustic device for generating audio is required.

[0003] Here, conventional speaker shapes are generally funnel-shaped so-called cones, spherical domes, etc. However, if these speakers are built into the above-mentioned thin image display device, the thinness and lightness, which are advantages of the thin image display device, may be impaired.

[0004] In such a thin image display device, a structure is conceivable in which an exciter (vibrator) is attached to a display panel and the display panel is vibrated as a vibration plate to reproduce audio.

[0005] For example, Patent Document 1 describes a display speaker including a display panel, a vibrator, and one or more vibrating weights, wherein the vibrator is bonded to the display panel surface, and the vibrating weight is coupled to the vibrator.

[0006] In addition, as a thin vibrator, Patent Document 2 describes a laminated piezoelectric element, which is formed by laminating a plurality of piezoelectric films formed by sandwiching a piezoelectric body layer between two thin-film electrodes, the piezoelectric films being polarized in the thickness direction, and the polarization directions of adjacent piezoelectric films being opposite. Patent Document 2 describes that the laminated piezoelectric element is attached to a vibration plate to be used as an electroacoustic transducer for reproducing audio.

[0007] Previous technical literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2021-090167

[0010] Patent Document 2: International Publication No. 2020 / 095812 Summary of the invention

[0011] Technical issues to be solved by the invention

[0012] It can be considered that the output of the piezoelectric vibrator (piezoelectric vibrator) described in Patent Document 2 is relatively small, so when using a large vibration plate such as a large-size display panel, multiple piezoelectric vibrators are pasted to the vibration plate and the same signal is input to the multiple piezoelectric vibrators to ensure output.

[0013] However, according to the research conducted by the present inventors, it has been found that when a plurality of vibrators are arranged on a diaphragm to form an electroacoustic transducer, the sound pressure in the high-frequency range does not increase but tends to decrease.

[0014] Furthermore, when a plurality of vibrators are used, power needs to be supplied to each vibrator, which causes a problem in that power consumption increases.

[0015] The present invention aims to solve the problems of the prior art and to provide an electroacoustic transducer having a plurality of vibrators arranged on a vibration plate, wherein a drop in sound pressure in a high-frequency region can be suppressed and power consumption can be reduced.

[0016] Means for solving technical problems

[0017] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0018] [1] An electroacoustic transducer comprising a vibration plate and a vibrator group consisting of a plurality of piezoelectric vibrators arranged on one surface of the vibration plate,

[0019] The plurality of piezoelectric vibrators each belong to any one of the first to nth groups,

[0020] The upper limit frequency of the frequency band of the input signal to the piezoelectric vibrator is different for each group.

[0021] In each group, the upper limit frequency is set to f1~f n When the upper limit frequency increases from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n And gradually becomes lower.

[0022] [2] The electroacoustic converter according to [1], wherein:

[0023] When the number of piezoelectric vibrators belonging to each group is N1 to N n When the number of piezoelectric vibrators in the first group N1 is increased to the number of piezoelectric vibrators in the nth group N n The number of piezoelectric vibrators in each group satisfies N1≤N2≤N3≤…≤N n .

[0024] [3] The electroacoustic converter according to [1] or [2], wherein:

[0025] The upper limit frequency f1 in the first group is 15 kHz or more.

[0026] [4] The electroacoustic converter according to any one of [1] to [3], comprising two vibrator groups,

[0027] The two vibrator groups are arranged symmetrically with respect to the center line of the diaphragm in the left-right direction.

[0028] [5] The electroacoustic converter according to any one of [1] to [4], wherein:

[0029] The piezoelectric vibrator includes a piezoelectric film including a piezoelectric layer and electrode layers provided on both surfaces of the piezoelectric layer.

[0030] [6] The electroacoustic converter according to [5], wherein:

[0031] The piezoelectric layer is composed of a polymer composite piezoelectric body in which piezoelectric particles are contained in a matrix composed of a polymer material.

[0032] [7] The electroacoustic converter according to [5] or [6], wherein:

[0033] The piezoelectric vibrator is formed by stacking a plurality of piezoelectric films by folding the piezoelectric film one or more times.

[0034] [8] The electroacoustic converter according to any one of [1] to [7], wherein:

[0035] The outer peripheries of two adjacent piezoelectric vibrators are parallel to each other, and the interval between the outer peripheries is 40 mm or less.

[0036] [9] The electroacoustic converter according to any one of [1] to [8], wherein:

[0037] The vibration plate is bent in the arrangement direction of the plurality of piezoelectric vibrators of the vibrator group.

[0038]

[10] The electroacoustic converter according to [9], wherein:

[0039] When the distance between the piezoelectric vibrator located at the center of the vibration plate in the arrangement direction of the plurality of piezoelectric vibrators and the viewing position is L1, and the distance between the outer piezoelectric vibrator and the viewing position is L2, the range of L1×0.9<L2<L1×1.1 is satisfied.

[0040]

[11] The electroacoustic converter according to any one of [1] to

[10] , wherein:

[0041] When the distance between the piezoelectric vibrator on the center side of the vibration plate in the arrangement direction of the piezoelectric vibrators and the viewing position is set to L1, and the distance between the outer piezoelectric vibrator and the viewing position is set to L2, the input timing of the input signal to the outer piezoelectric vibrator is advanced by time t = (L2-L1) / c compared to the input timing of the input signal to the piezoelectric vibrator on the center side.

[0042] Here, c (m / s) is the speed of sound.

[0043] Effects of the Invention

[0044] According to the present invention, it is possible to provide an electroacoustic transducer including a plurality of vibrators arranged on a vibration plate, wherein a drop in sound pressure in a high-frequency region can be suppressed and power consumption can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a diagram schematically showing an example of the electroacoustic transducer of the present invention.

[0046] Figure 2 Yes means Figure 1 A block diagram of an example of a circuit included in the electroacoustic transducer shown.

[0047] Figure 3 1 is a graph showing the relationship between frequency and normalized sound pressure and a diagram showing the frequency band of each piezoelectric vibrator.

[0048] Figure 4 1 is a graph showing the relationship between frequency and normalized sound pressure and a diagram showing the frequency band of each piezoelectric vibrator.

[0049] Figure 5 This is a graph showing the ideal relationship between sound pressure and frequency in a structure having a plurality of piezoelectric vibrators.

[0050] Figure 6 This is a graph showing the relationship between actual sound pressure and frequency in a structure having a plurality of piezoelectric vibrators.

[0051] Figure 7 This is a diagram for explaining the power consumption of the piezoelectric vibrator.

[0052] Figure 8 This is a diagram for explaining power consumption when the upper limit frequency is 10 kHz.

[0053] Fig. 9 This is a diagram for explaining power consumption when the upper limit frequency is 4 kHz.

[0054] Fig.10 This is a diagram for explaining an example of a piezoelectric film included in a piezoelectric vibrator included in the electroacoustic transducer of the present invention.

[0055] Fig.11 It is a perspective view schematically showing an example of a piezoelectric vibrator included in the electroacoustic transducer of the present invention.

[0056] Fig.12 This is a diagram schematically showing an example of a piezoelectric vibrator included in the electroacoustic transducer of the present invention.

[0057] Fig.13 This is a diagram schematically showing another example of the piezoelectric vibrator included in the electroacoustic transducer of the present invention.

[0058] Fig.14This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0059] Fig.15 This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0060] Fig.16 This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0061] Fig.17 This is a diagram schematically showing another example of the electroacoustic transducer of the present invention.

[0062] Fig.18 This is a block diagram showing another example of the circuit included in the electroacoustic transducer of the present invention.

[0063] Fig.19 This is a block diagram showing another example of the circuit included in the electroacoustic transducer of the present invention.

[0064] Fig. 20 It is a diagram for explaining the path difference.

[0065] Fig.21 This is a diagram schematically showing another example of the electroacoustic transducer of the present invention.

[0066] Fig. 22 This is a diagram schematically showing another example of the electroacoustic transducer of the present invention. DETAILED DESCRIPTION

[0067] Hereinafter, the electroacoustic transducer of the present invention will be described in detail based on the preferred embodiments shown in the drawings.

[0068] The description of the constituent elements described below is made based on typical embodiments of the present invention, but the present invention is not limited to these embodiments.

[0069] In addition, in this specification, the numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0070] In this specification, the terms "same", "identical" and the like include a range of errors generally allowed in the technical field.

[0071] <<First embodiment>>

[0072] [Electroacoustic Converter]

[0073] The electroacoustic converter of the present invention is an electroacoustic converter as follows:

[0074] A vibrator group including a vibrator plate and a plurality of piezoelectric vibrators arranged on one surface of the vibrator plate.

[0075] The plurality of piezoelectric vibrators belong to any one of the first group to the nth group, respectively.

[0076] The upper limit frequency of the frequency band of the input signal to the piezoelectric vibrator is different for each group.

[0077] Set the upper limit frequency in each group to f1~f n When the upper limit frequency moves from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n Gradually getting lower.

[0078] Figure 1 Detailed Description of the Invention A side view schematically showing an example of the electroacoustic transducer of the present invention is shown in FIG.

[0079] Figure 1 The electroacoustic transducer 100 shown includes a vibration plate 102 and a plurality of piezoelectric vibrators ( 50 a to 50 j ) arranged on one surface of the vibration plate 102 .

[0080] The piezoelectric vibrators (50a to 50j) are driven by applying voltage using an external power source. When the piezoelectric vibrators are driven, the piezoelectric vibrators expand and contract in the surface direction, causing the vibration plate to which the piezoelectric vibrators are attached to bend, resulting in the vibration plate vibrating to generate sound. The vibration plate vibrates according to the magnitude and waveform of the driving voltage applied to the piezoelectric vibrators, and generates sound corresponding to the driving voltage applied to the piezoelectric vibrators.

[0081] That is, the piezoelectric vibrator functions as a so-called exciter.

[0082] exist Figure 1 In the example shown, five piezoelectric vibrators 50a to 50e are arranged in the right area in the left-right direction of the vibration plate 102. The five piezoelectric vibrators 50a to 50e are arranged in the vertical direction in the figure. The five piezoelectric vibrators 50a to 50e are the vibrator group 60R in the present invention. In the piezoelectric vibrators 50a to 50e included in one vibrator group 60R, basically the same signal is input except that the vibration in the high-frequency region is appropriately cut.

[0083] In addition, in the figure, five piezoelectric vibrators 50f to 50j are arranged in the left area in the left-right direction of the vibration plate 102. The five piezoelectric vibrators 50f to 50j are arranged in the vertical direction in the figure. The five piezoelectric vibrators 50f to 50j are the vibrator group 60L in the present invention. In the piezoelectric vibrators 50f to 50j included in one vibrator group 60L, basically the same signal is input except that the vibration in the high-frequency region is appropriately cut.

[0084] Right now, Figure 1 The electroacoustic transducer 100 shown has two transducer groups, and the two transducer groups are arranged symmetrically with respect to the center line of the diaphragm 102 in the left-right direction.

[0085] The signals input to the piezoelectric vibrators 50a to 50e of the vibrator group 60R and the signals input to the piezoelectric vibrators 50f to 50j of the vibrator group 60L may be the same or different. For example, the right channel signal of the stereo audio is input to the piezoelectric vibrators 50a to 50e of the vibrator group 60R, and the left channel signal is input to the piezoelectric vibrators 50f to 50j of the vibrator group 60L.

[0086] The transducer group 60R and the transducer group 60L basically have the same structure except that they are arranged at different positions and input signals. Therefore, in the following description, the transducer group 60R will be described.

[0087] Furthermore, the structures of the piezoelectric vibrators may be the same or different. The piezoelectric vibrators will be described in detail later.

[0088] exist Figure 1 In the electroacoustic converter 100 shown in the figure, the plurality of piezoelectric vibrators of the vibrator group 60R belong to any one of the three groups, namely, the first group to the third group. Figure 1 In the example shown, in the figure, the piezoelectric vibrator 50c arranged in the center in the up-down direction belongs to the first group G1, the piezoelectric vibrator 50b arranged on the upper side of the piezoelectric vibrator 50c and the piezoelectric vibrator 50d arranged on the lower side of the piezoelectric vibrator 50c belong to the second group G2, and the piezoelectric vibrator 50a arranged on the upper side of the piezoelectric vibrator 50b and the piezoelectric vibrator 50e arranged on the lower side of the piezoelectric vibrator 50d belong to the third group G3.

[0089] Input signals having different upper limit frequencies of frequency bands are input to the piezoelectric vibrators in groups.

[0090] Figure 2 A diagram schematically showing a block diagram of a circuit for inputting an input signal to each piezoelectric vibrator of the electroacoustic transducer 100 is shown.

[0091] Figure 2 The circuit 120 shown includes a distributor 124 for distributing an input signal input from the outside to each group, three low-pass filters 125G1 to 125G3 for filtering the distributed signals, three amplifiers 126G1 to 126G3, and piezoelectric vibrators 50a to 50e.

[0092] exist Figure 2 In the circuit shown, an input signal input from the outside passes through a distributor and then passes through an amplifier to be input to the piezoelectric vibrator.

[0093] The distributor 124 performs processing for distributing an input signal from the outside. In the example shown in the figure, the piezoelectric vibrators 50a to 50e are divided into three groups, so the distributor 124 distributes the input signal from the outside into three groups.

[0094] Here, in the present invention, three low-pass filters 125G1 to 125G3 are provided at the rear stage of the distributor 124 so that the upper limit frequencies of the frequency bands of the input signals respectively input to the piezoelectric vibrators 50a to 50e divided into three groups become frequencies different for each group, and low-pass filtering processing is performed respectively.

[0095] For example, Figure 3 As shown in the lower part of , when an input signal with an upper limit frequency f1 of 20 kHz is input to the piezoelectric vibrator 50c belonging to the first group G1, an input signal with an upper limit frequency f2 of 10 kHz is input to the piezoelectric vibrators 50b and 50d belonging to the second group G2, and an input signal with an upper limit frequency f3 of 4 kHz is input to the piezoelectric vibrators 50a and 50e belonging to the third group G3, the low-pass filter 125G1 performs low-pass filtering on the allocated input signals in such a way that the upper limit frequency f1 becomes 20 kHz. Thus, the piezoelectric vibrator 50c belonging to the first group G1 is allocated an input signal with an upper limit frequency f1 of 20 kHz. The low-pass filter 125G2 performs low-pass filtering on the allocated input signals in such a way that the upper limit frequency f2 becomes 10 kHz. Thus, the piezoelectric vibrators 50b and 50d belonging to the second group G2 are allocated an input signal with an upper limit frequency f2 of 10 kHz. The low-pass filter 125G3 performs low-pass filtering on the allocated input signal so that the upper limit frequency f3 becomes 4 kHz. Thus, the piezoelectric vibrators 50a and 50e belonging to the third group G3 are allocated the input signal whose upper limit frequency f3 is 4 kHz.

[0096] That is, when the upper limit frequencies in the respective groups are set to f1 to f3, the upper limit frequencies gradually decrease from the upper limit frequency f1 in the first group toward the upper limit frequency f3 in the third group.

[0097] Input signals having different upper limit frequencies that are branched by the distributor 124 and the low-pass filters and subjected to low-pass filtering are amplified by the amplifiers 126G1 to 126G3 and supplied to the piezoelectric vibrators.

[0098] exist Figure 2 In the example shown, the input signal amplified by the amplifier 126G1 is supplied to the piezoelectric vibrator 50c belonging to the first group G1. Furthermore, the input signal amplified by the amplifier 126G2 is supplied to the piezoelectric vibrator 50b and the piezoelectric vibrator 50d belonging to the second group G2. Furthermore, the input signal amplified by the amplifier 126G3 is supplied to the piezoelectric vibrator 50a and the piezoelectric vibrator 50e belonging to the third group G3.

[0099] As the amplifiers 126G1 to 126G3 , various known amplifiers used in electroacoustic transducers can be used as appropriate.

[0100] Each piezoelectric vibrator is driven by an input signal amplified by each amplifier. When each piezoelectric vibrator is driven, the piezoelectric vibrator expands and contracts in the plane direction, bending the vibration plate to which the piezoelectric vibrator is attached, and as a result, the vibration plate vibrates to generate sound.

[0101] In this case, in the electroacoustic converter of the present invention, by inputting input signals having different upper limit frequencies in groups, it is possible to suppress a drop in sound pressure in a high-frequency region and reduce power consumption.

[0102] In this regard, the results of the examples and comparative examples described later are used. Figure 3 and Figure 4 Provide explanation.

[0103] exist Figure 3 and Figure 4 In FIG. 1 , the upper graph is a graph showing the relationship between frequency and normalized sound pressure, and the lower graph is a graph showing the frequency band of an input signal input to each piezoelectric vibrator.

[0104] Figure 4 As shown in the lower part of FIG. 8 , there is a conventional example in which an input signal having the same upper limit frequency is input to all piezoelectric vibrators, and the upper graph shows the frequency characteristics (relationship between frequency and sound pressure) in this case.

[0105] And, in Figure 5 FIG. 4 shows a graph showing the ideal (without phase interference) frequency characteristics when three or five piezoelectric vibrators are driven based on the measured values ​​of the frequency characteristics when one piezoelectric element is driven. Figure 6 Graphs showing frequency characteristics when one, three, or five piezoelectric vibrators are actually driven are shown in FIG.

[0106] like Figure 5 As shown in the figure, in an ideal case without phase interference, the sound pressure when three piezoelectric vibrators are driven should be about 3 times (+10 dB) higher than that when one piezoelectric vibrator is driven in a wide frequency range of 100 to 20 kHz. Also, the sound pressure when five piezoelectric vibrators are driven should be about 5 times (+14 dB) higher than that when one piezoelectric vibrator is driven in a wide frequency range of 100 to 20 kHz.

[0107] However, in reality, due to phase interference, Figure 6 As shown, even if the number of piezoelectric elements is increased, the sound pressure does not increase in a high frequency region, but may decrease instead.

[0108] like Figure 6As shown in FIG. 1 , in the frequency band below 4 kHz, the sound pressure increases as the number of piezoelectric vibrators increases. However, in the high frequency region exceeding 4 kHz, the sound pressure does not increase even if the number of piezoelectric vibrators increases, but may decrease instead.

[0109] Therefore, if Figure 4 As shown in the upper graph, when the input signal having the same upper limit frequency is input to all five piezoelectric vibrators, the sound pressure is significantly lowered in a high-frequency region.

[0110] In this way, when the electroacoustic converter is configured as a structure in which a plurality of piezoelectric vibrators are arranged on a vibration plate, phase interference can be considered as the reason why the sound pressure in the high-frequency region is reduced instead of increased. In the above-mentioned electroacoustic converter, the vibration plate vibrates in the region where each piezoelectric vibrator is arranged to generate sound, so each piezoelectric vibrator has a difference in path length relative to a certain viewing position. Therefore, phase interference caused by the positive phase component and the reverse phase component due to the path difference, that is, mutual cancellation of sound waves, occurs, and the sound pressure does not increase.

[0111] At this time, in the bass region, since the wavelength of the sound wave is long, even if there is a slight path difference, mutual cancellation is unlikely to occur, and the sound pressure does not decrease, but is increased by the additive effect.

[0112] On the other hand, in the high-frequency region, since the wavelength of the sound wave is short, mutual cancellation occurs due to a slight path difference, and as a result, the addition effect does not work, and not only does the sound pressure not increase, but sometimes the sound pressure decreases when there are multiple piezoelectric vibrators relative to one piezoelectric vibrator. The reason for this decrease when there are multiple piezoelectric vibrators is the ratio of the individual that transmits the positive phase component to the individual that transmits the reverse phase component relative to the viewing position, the performance variation of each individual, etc.

[0113] Furthermore, if the piezoelectric vibrators are driven by input signals of the same frequency band, the power consumption of the piezoelectric vibrators becomes the same, so the total power consumption of the vibrator group becomes several times (5 times in the example shown) the power consumption of one piezoelectric vibrator. For example, if the power consumption of one piezoelectric vibrator is 15W, the total power consumption of the vibrator group is 75W.

[0114] In contrast, in the electroacoustic converter of the present invention, input signals with different upper limit frequencies are input in groups. Figure 3 and Figure 6 Provide explanation.

[0115] from Figure 6 It can be seen that in the frequency band of 10kHz to 20kHz, the sound pressure is highest when one piezoelectric vibrator is driven. Figure 3As shown in the lower part of , one piezoelectric vibrator 50 c belongs to the first group G1 , and an input signal having a frequency band with an upper limit frequency of 20 kHz or more is input to the piezoelectric vibrator 50 c .

[0116] Next, from Figure 6 It can be seen that in the frequency band of 4kHz to 10kHz, the sound pressure is highest when the three piezoelectric vibrators are driven. Figure 3 As shown in the lower part of , the two piezoelectric vibrators 50b and 50d belong to the second group G2, and together with the piezoelectric vibrator 50c of the first group, an input signal including a frequency band below 10 kHz is input to the three piezoelectric vibrators.

[0117] Next, from Figure 6 It can be seen that in the frequency band below 4kHz, the sound pressure is highest when 5 piezoelectric vibrators are driven. Figure 3 As shown in the lower part of , the two piezoelectric vibrators 50a and 50e belong to the third group G3, and together with the piezoelectric vibrator 50c of the first group and the piezoelectric vibrators 50b and 50d of the second group G2, an input signal including a frequency band below 4 kHz is input to the five piezoelectric vibrators.

[0118] By thus making the upper limit frequency of the input signal to each group of piezoelectric vibrators different in each frequency band so that the number of piezoelectric vibrators driven is the number with the highest sound pressure, it is possible to suppress a significant drop in sound pressure in a high-frequency region.

[0119] Moreover, if Figure 3 As shown in the lower right part of , by making the upper limit frequency of the input signal to each group of piezoelectric vibrators different, the power consumption of the piezoelectric vibrators in the second and third groups can be lower than that of the piezoelectric vibrators in the first group. Figure 7 to Figure 9 Provide explanation.

[0120] Figure 7 The left graph of is a graph schematically showing the relationship between frequency and impedance in a piezoelectric vibrator. As shown in the graph, the higher the frequency is in the frequency band up to 20kHz, the lower the impedance characteristic of the piezoelectric vibrator is. Regarding the power consumption of a piezoelectric vibrator with such an impedance characteristic, if the voltage is set constant, the power consumption when a 1kHz sine wave is input is set to 1, and the power consumption for each frequency is standardized, the result is as follows Figure 7 As shown in the diagram on the right side of , the higher the frequency, the higher the power consumption. For example, when a 0 to 20 kHz input signal is input to the piezoelectric vibrator, Figure 7 The value obtained by integrating the right graph of (the area indicated by gray in the figure) is the power consumption of the piezoelectric vibrator. If the frequency is 1 kHz and the normalized power consumption is 1, the area is about 180 grids.

[0121] As an example, when a 20 to 20 kHz input signal is input to the piezoelectric vibrator, and a voltage is applied so that the power consumption becomes 15 W, the power consumption per grid becomes 0.083 W.

[0122] Since the input signal with the upper limit frequency of 10kHz is input to the piezoelectric vibrator of the second group G2, Figure 8 As shown, its power consumption is 45 grids and is about 4W.

[0123] Since the input signal with the upper limit frequency of 4kHz is input to the piezoelectric vibrator of the third group G3, Fig. 9 As shown, its power consumption is 8 grids and is about 1W.

[0124] Therefore, the total power consumption of the transducer group 60R is 15W+4W×2+1W×2=25W.

[0125] In this way, the power consumption of the piezoelectric vibrator which lowers the upper limit frequency of the input signal can be significantly reduced. Therefore, the power consumption of the vibrator group can be significantly reduced.

[0126] Here, in the above example, one vibrator group has five piezoelectric vibrators, but the present invention is not limited thereto. One vibrator group may have 2 to 4 piezoelectric vibrators, or may have 6 or more piezoelectric vibrators.

[0127] Furthermore, in the above example, the plurality of piezoelectric vibrators are divided into three groups, but the present invention is not limited thereto and the plurality of piezoelectric vibrators may be divided into two groups or four or more groups. When the plurality of piezoelectric vibrators are divided into n groups, the upper limit frequencies of the first to nth groups are set to f1 to f2. n When the upper limit frequency moves from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n Gradually getting lower.

[0128] Furthermore, in the above example, the upper limit frequency of the input signal to the piezoelectric vibrator of the first group G1 is set to 20 kHz, the upper limit frequency of the input signal to the piezoelectric vibrator of the second group G2 is set to 10 kHz, and the upper limit frequency of the input signal to the piezoelectric vibrator of the third group G3 is set to 4 kHz, but the present invention is not limited thereto. The upper limit frequency of the input signal to each group can be appropriately set according to the structure of the electroacoustic converter, the characteristics of the piezoelectric vibrator, the required specifications of the product, etc.

[0129] Furthermore, from the viewpoint of a practical audible range, the upper limit frequency of the input signal input to the piezoelectric vibrator belonging to the first group having the highest upper limit frequency is preferably 15 kHz or more.

[0130] Furthermore, the number of piezoelectric vibrators belonging to each group is not particularly limited, but it is preferred that the number of piezoelectric vibrators be reduced as the upper limit frequency is higher. n When the number of piezoelectric vibrators in the first group N1 is increased to the number of piezoelectric vibrators in the nth group N n The number of piezoelectric vibrators in each group preferably satisfies N1≤N2≤N3≤…≤N n By reducing the number of piezoelectric vibrators in a group with a higher upper limit frequency, it is possible to more appropriately suppress a drop in sound pressure due to phase interference in a high frequency region and to more appropriately reduce power consumption.

[0131] And, in Figure 1 In the example shown, in one vibrator group, a plurality of piezoelectric vibrators are arranged in the vertical direction, but the present invention is not limited to this. Fig.17 As shown, a plurality of piezoelectric vibrators may be arranged in the left-right direction, or may be arranged two-dimensionally in the up-down direction and the left-right direction.

[0132] exist Fig.17 In the example shown, five piezoelectric vibrators 50a to 50e are arranged in the right area in the left-right direction of the vibration plate 102. The five piezoelectric vibrators 50a to 50e are arranged in the left-right direction in the figure. The five piezoelectric vibrators 50a to 50e are the vibrator group 60R in the present invention. In the piezoelectric vibrators 50a to 50e included in one vibrator group 60R, basically the same signal is input except that the vibration in the high-frequency region is appropriately cut.

[0133] In addition, in the figure, five piezoelectric vibrators 50f to 50j are arranged in the left area in the left-right direction of the vibration plate 102. The five piezoelectric vibrators 50f to 50j are arranged in the left-right direction in the figure. The five piezoelectric vibrators 50f to 50j are the vibrator group 60L in the present invention. In the piezoelectric vibrators 50f to 50j included in one vibrator group 60L, basically the same signal is input except that the vibration in the high-frequency region is appropriately cut.

[0134] Right now, Fig.17 The electroacoustic transducer 100 b shown has two transducer groups, and the two transducer groups are arranged symmetrically with respect to the center line of the diaphragm 102 in the left-right direction.

[0135] The signals input to the piezoelectric vibrators 50a to 50e of the vibrator group 60R and the signals input to the piezoelectric vibrators 50f to 50j of the vibrator group 60L may be the same or different. For example, the right channel signal of the stereo audio is input to the piezoelectric vibrators 50a to 50e of the vibrator group 60R, and the left channel signal is input to the piezoelectric vibrators 50f to 50j of the vibrator group 60L.

[0136] exist Fig.17 In the electroacoustic converter 100b shown in FIG. Figure 1 Similar to the example shown, input signals having different upper limit frequencies of the frequency band are input to the piezoelectric vibrators in the vibrator group for each group.

[0137] Furthermore, in one vibrator group, it is preferred that outer circumferences of two adjacently arranged piezoelectric vibrators are parallel to each other.

[0138] Furthermore, there is no particular restriction on the interval between adjacent piezoelectric vibrators, but the smaller the interval between the piezoelectric vibrators, the smaller the path difference. Therefore, from the perspective of suppressing phase interference, it is better to make the piezoelectric vibrators as close to each other as possible, preferably less than 40 mm, more preferably less than 20 mm, further preferably less than 10 mm, and particularly preferably less than 5 mm. In addition, if the interval between adjacent piezoelectric vibrators is made close, the frequency at which phase interference occurs moves to the high-frequency side. Therefore, the upper limit frequency of the input signal input to each group of piezoelectric vibrators can be appropriately adjusted accordingly.

[0139] On the other hand, depending on the material of the vibration plate, if the piezoelectric vibrators are placed too close to each other, crosstalk and other adverse effects may occur. Therefore, it is preferable to place the piezoelectric vibrators as close as possible according to the material of the vibration plate.

[0140] And, in Figure 1 The electroacoustic transducer 100 shown has a structure including two transducer groups, but the present invention is not limited thereto. The electroacoustic transducer of the present invention may have a structure including one transducer group or may have a structure including three or more transducer groups.

[0141] And, in Figure 1 In the electroacoustic converter 100 shown, the two vibrator groups are arranged symmetrically with respect to the center line of the left-right direction of the vibration plate, but the present invention is not limited thereto, and the arrangement of each vibrator group can be appropriately set according to the performance required in the electroacoustic converter. In addition, the vertical direction and the left-right direction of the vibration plate (electroacoustic converter) can be determined by taking the vertical direction as the vertical direction and the horizontal direction as the left-right direction in the state in which the electroacoustic converter is set for use. In addition, when the vibration plate is an image display panel, the vertical direction and the left-right direction can be set according to the image displayed on the image display panel.

[0142] And, in Figure 2 In the example of the circuit shown, a low-pass filter is provided for changing the upper frequency limit of the input signal corresponding to each group after distribution by the distributor, but the present invention is not limited thereto, and the same processing can be performed by a channel distributor, a DSP (digital signal processor), etc. instead of the distributor. Furthermore, the distribution of the input signal and the low-pass filtering processing can be performed by a single channel distributor, a DSP, etc.

[0143] Furthermore, when the input signal is a digital audio signal, the digital signal can be directly allocated and low-pass filtered before the signal is placed in the amplifier after DA conversion and converted into an analog signal. Alternatively, the signal can be allocated and converted into an analog signal after initial DA conversion and low-pass filtered through an analog low-pass filter before being placed in the amplifier.

[0144] And, in Figure 2 In the circuit example shown, after the distribution by the distributor, amplification by the amplifier is performed for each group, but the present invention is not limited to this.

[0145] Fig.18 2 is a block diagram showing another example of the circuit included in the electroacoustic transducer of the present invention.

[0146] Fig.18 The circuit 120b shown includes: an amplifier 126 for amplifying an input signal input from the outside; a channel distributor 127 for distributing the amplified signal to each group and performing filtering processing for each group; and piezoelectric vibrators 50a to 50e.

[0147] exist Fig.18 In the circuit shown, an input signal input from the outside passes through an amplifier 126 and then passes through a channel distributor 127 to be input to the piezoelectric vibrator.

[0148] The channel distributor 127 distributes the input signal amplified by the amplifier 126. In the example shown in the figure, the piezoelectric vibrators 50a to 50e are divided into three groups, so the channel distributor 127 distributes the input signal into three groups.

[0149] The channel distributor 127 performs low-pass filtering processing with different cutoff frequencies on the three distributed input signals, and supplies input signals with different upper limit frequencies to each of the piezoelectric vibrators 50a to 50e divided into three groups.

[0150] For example, with Figure 3, when an input signal having an upper limit frequency f1 of 20 kHz is input to the piezoelectric vibrator 50c belonging to the first group G1, an input signal having an upper limit frequency f2 of 10 kHz is input to the piezoelectric vibrators 50b and 50d belonging to the second group G2, and an input signal having an upper limit frequency f3 of 4 kHz is input to the piezoelectric vibrators 50a and 50e belonging to the third group G3, the channel distributor 127 performs low-pass filtering on the input signal supplied to the piezoelectric vibrator 50c belonging to the first group G1 among the input signals distributed so that the cutoff frequency fc1 becomes 20 kHz. Furthermore, the channel distributor 127 performs low-pass filtering on the input signal supplied to the piezoelectric vibrators 50b and 50d belonging to the second group G2 among the input signals distributed so that the cutoff frequency f C2 Furthermore, the channel distributor 127 performs low-pass filtering on the input signals supplied to the piezoelectric vibrators 50a and 50e belonging to the third group G3 among the distributed input signals so that the cutoff frequency fc3 becomes 4 kHz.

[0151] Input signals having different upper limit frequencies distributed by the channel distributor 127 and subjected to low-pass filtering are supplied to the piezoelectric vibrators.

[0152] Each piezoelectric vibrator is driven by an input signal having a different upper limit frequency. When each piezoelectric vibrator is driven, the piezoelectric vibrator expands and contracts in the plane direction, bending the vibration plate to which the piezoelectric vibrator is attached, and as a result, the vibration plate vibrates to generate sound.

[0153] In this case, in the electroacoustic converter of the present invention, by inputting input signals having different upper limit frequencies in groups, it is possible to suppress a drop in sound pressure in a high-frequency region and reduce power consumption.

[0154] Fig.19 A block diagram showing another example of the circuit included in the electroacoustic transducer of the present invention is shown.

[0155] Fig.19 The circuit 120c shown has: an amplifier 128 that amplifies an input signal input from the outside and has a function as a distributor for distributing the input signal to each group; low-pass filters 125G1 to 125G3 that filter the distributed signals; and piezoelectric vibrators 50a to 50e.

[0156] exist Fig.19 In the circuit shown, an input signal input from the outside passes through an amplifier 128 and then passes through low-pass filters 125G1 to 125G3 to be input to the piezoelectric vibrator.

[0157] The amplifier 128 performs processing of amplifying an input signal input from the outside and distributing the amplified input signal. In the example shown in the figure, the piezoelectric vibrators 50a to 50e are divided into three groups, so the amplifier 128 distributes the input signal into three groups.

[0158] The three divided input signals are supplied to low-pass filters 125G1 to 125G3 , respectively.

[0159] The low-pass filters 125G1 to 125G3 perform low-pass filtering processes having different cutoff frequencies.

[0160] For example, with Figure 3 In the same manner as in the example shown in the lower part of FIG. 1 , when an input signal having an upper limit frequency f1 of 20 kHz is input to the piezoelectric vibrator 50c belonging to the first group G1, an input signal having an upper limit frequency f2 of 10 kHz is input to the piezoelectric vibrators 50b and 50d belonging to the second group G2, and an input signal having an upper limit frequency f3 of 4 kHz is input to the piezoelectric vibrators 50a and 50e belonging to the third group G3, the low-pass filter 125G1 performs low-pass filtering processing on the input signal supplied to the piezoelectric vibrator 50c belonging to the first group G1 among the amplified and distributed input signals so that the cutoff frequency fc1 becomes 20 kHz. Furthermore, the low-pass filter 125G2 performs low-pass filtering processing on the input signal supplied to the piezoelectric vibrators 50b and 50d belonging to the second group G2 among the distributed input signals so that the cutoff frequency fc2 becomes 10 kHz. Furthermore, the low-pass filter 125G3 performs low-pass filtering processing on the input signals supplied to the piezoelectric vibrators 50a and 50e belonging to the third group G3 among the distributed input signals so that the cutoff frequency fc3 becomes 4 kHz.

[0161] Input signals having different upper limit frequencies subjected to low-pass filtering by the low-pass filters 125G1 to G3 are supplied to the piezoelectric vibrators.

[0162] Each piezoelectric vibrator is driven by an input signal having a different upper limit frequency. When each piezoelectric vibrator is driven, the piezoelectric vibrator expands and contracts in the plane direction, bending the vibration plate to which the piezoelectric vibrator is attached, and as a result, the vibration plate vibrates to generate sound.

[0163] In this case, in the electroacoustic converter of the present invention, by inputting input signals having different upper limit frequencies in groups, it is possible to suppress a drop in sound pressure in a high-frequency region and reduce power consumption.

[0164] In addition, in Figure 1 As in the example shown, in the case of a configuration in which there are two transducer groups, a right channel signal of stereo audio is input to one transducer group, and a left channel signal is input to the other transducer group, Fig.18The circuit 120b shown includes an amplifier 126 and Fig.19 The amplifier 128 included in the circuit 120c shown may be a stereo amplifier that separately amplifies the right channel and left channel signals included in the stereo audio (signal).

[0165] and, Fig.19 The amplifier 128 included in the circuit 120c shown is a stereo amplifier that respectively amplifies the right channel and left channel signals contained in the stereo audio (signal), and can be set to a structure in which the right channel signal is distributed into multiple groups according to the number of groups, and the left channel signal is distributed into multiple groups according to the number of groups.

[0166] Or, in Fig.18 In the example shown, the following structure can be used: the channel distributor 127 distributes the stereo audio (signal) to each group, performs filtering processing on each group, and distributes it to the right channel and the left channel. Fig.19 In the example shown, the following configuration may be adopted: the low-pass filters 125G1 to 125G3 filter the stereo audio (signal) and distribute the resultant to the right channel and the left channel.

[0167] And, with Figure 2 Compared with the structure in which an amplifier is provided on the downstream side of the distributor (the part having the distribution function) as in the example shown in FIG. Fig.18 and Fig.19 As in the example shown in the figure, the structure having an amplifier on the upstream side of the distributor (the part having the distribution function) can reduce the number of amplifiers, which is advantageous from the perspective of cost reduction. This is also the case in a structure in which the upper limit frequencies of input signals to the plurality of piezoelectric vibrators included in one vibrator group are not set to be different.

[0168] Hereinafter, the constituent elements of the electroacoustic transducer of the present invention will be described.

[0169] <Vibration plate>

[0170] Preferably, the vibration plate 102 is a flexible member. In the present invention, flexibility has the same meaning as flexibility in general, indicating the ability to bend and bend, and specifically, the ability to bend and stretch without being destroyed or damaged.

[0171] The vibration plate 102 is not limited as long as it is preferably flexible, and various sheet-shaped objects (plate-shaped objects, films) can be used.

[0172] As an example, there are shown 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, foamed plastics made of expanded polystyrene, expanded styrene and expanded polyethylene, plywood, cork board, leather such as cowhide, carbon sheet, various paperboards such as Japanese paper, and various corrugated paper materials formed by pasting other paperboards on one or both sides of corrugated paperboard, etc. In addition, a laminated board formed by pasting a plurality of these may be used.

[0173] Furthermore, as long as the vibration plate 102 has flexibility, display devices such as organic electroluminescent (OLED (Organic Light Emitting Diode)) displays, liquid crystal displays, micro LED (Light Emitting Diode) displays, and inorganic electroluminescent displays, as well as projector screens, can be preferably used.

[0174] In addition, in the electroacoustic transducer 100 , it is preferable that the electrode layer of the piezoelectric vibrator 50 and the vibration plate 102 are not electrically connected.

[0175] If the electrode layer of the piezoelectric vibrator 50 is electrically connected to the vibration plate 102 , a short circuit or other failure may occur. Therefore, by adopting a structure in which the electrode layer of the piezoelectric vibrator 50 and the vibration plate 102 are not electrically connected, the risk of failure can be reduced.

[0176] <Piezoelectric vibrator>

[0177] A piezoelectric vibrator is a piezoelectric actuator that converts electrical energy into mechanical energy.

[0178] As piezoelectric vibrators, for example, PZT (lead zirconate titanate), PLZT (lanthanum-doped lead zirconate titanate), barium titanate, zinc oxide, BFBT (solid solution of bismuth ferrite and barium titanate), and vibrators using ceramic piezoelectrics such as the Piezoelectric element shown in Patent Document 1, PVDF (polyvinylidene fluoride), etc. are exemplified.

[0179] (Piezoelectric film)

[0180] The piezoelectric vibrator preferably includes a piezoelectric film including a piezoelectric layer having piezoelectricity and electrode layers provided on both surfaces of the piezoelectric layer.

[0181] Fig.10 An example of a piezoelectric film is shown in FIG.

[0182] like Fig.10As shown, the piezoelectric film 10 has a piezoelectric layer 20, a first electrode layer 24 stacked on one surface of the piezoelectric layer 20, a first protective layer 28 stacked on the first electrode layer 24, a second electrode layer 26 stacked on the other surface of the piezoelectric layer 20, and a second protective layer 30 stacked on the second electrode layer 26.

[0183] As the piezoelectric layer 20 , various known piezoelectric layers can be used.

[0184] In the piezoelectric film 10, as Fig.10 As schematically shown in FIG. 1 , the piezoelectric layer 20 is preferably a polymer composite piezoelectric body including piezoelectric particles 36 in a matrix 34 composed of a polymer material.

[0185] A polymer material having viscoelasticity at room temperature is preferably used as the material of the matrix 34 (matrix and binder) of the polymer composite piezoelectric body constituting the piezoelectric layer 20. In this specification, "room temperature" refers to a temperature range of about 0 to 50°C.

[0186] Here, the polymer composite piezoelectric body (piezoelectric layer 20) preferably meets the following requirements.

[0187] (i) Flexibility

[0188] For example, when it is held in a lightly bent state like a newspaper or magazine for carrying, it is constantly subjected to relatively slow and large bending deformation of less than several Hz from the outside. At this time, if the polymer composite piezoelectric body is hard, a correspondingly large bending stress will be generated, and cracks will be generated at the interface between the polymer matrix and the piezoelectric particles, which may result in damage. Therefore, the polymer composite piezoelectric body is required to have moderate softness. In addition, if the strain energy can be diffused to the outside as heat, the stress can be relieved. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0189] (ii) Sound quality

[0190] The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz. Through the vibration energy, the entire polymer composite piezoelectric body (piezoelectric film) vibrates as a whole, thereby reproducing the sound. Therefore, in order to improve the transmission efficiency of vibration energy, the polymer composite piezoelectric body is required to have a moderate hardness. In addition, if the frequency characteristics of the speaker are smooth, the change in sound quality when the lowest resonance frequency changes with the change of curvature also becomes smaller. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0191] In summary, the polymer composite piezoelectric body is required to exhibit a hard action for vibrations of 20 Hz to 20 kHz, and a soft action for vibrations of several Hz or less. In addition, the polymer composite piezoelectric body is required to have a moderately large loss tangent for vibrations of all frequencies below 20 kHz.

[0192] Moreover, when used as a piezoelectric vibrator, it is preferred to simply adjust the spring constant by stacking according to the rigidity (hardness, toughness, spring constant) of the target material (vibration plate) to which it is attached. In this case, the thinner the bonding layer between the piezoelectric vibrator and the vibration plate, the higher the energy conversion efficiency can be.

[0193] Generally, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximization (absorption) in the loss modulus. Among them, the relaxation caused by the micro-Brownian motion of the molecular chain in the amorphous region is called the main dispersion, and a very large relaxation phenomenon can be observed. The temperature that causes this main dispersion is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most prominently manifested.

[0194] In the polymer composite piezoelectric body (piezoelectric body layer 20), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature in the matrix, a polymer composite piezoelectric body that exhibits a hard action for a vibration of 20 Hz to 20 kHz and a soft action for a slow vibration of several Hz or less is realized. In particular, from the perspective of appropriately showing the performance, it is preferred to use a polymer material having a glass transition point at room temperature, i.e., 0 to 50° C., at a frequency of 1 Hz in the matrix of the polymer composite piezoelectric body.

[0195] As the polymer material having viscoelasticity at room temperature, various known polymer materials can be used, but preferably a polymer material having a maximum value of a loss tangent Tanδ of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, i.e., 0 to 50°C. is used.

[0196] Thus, when the polymer composite piezoelectric body is slowly bent by an external force, stress concentration at the interface between the polymer matrix and the piezoelectric particles in the maximum bending moment portion is alleviated, and high flexibility can be expected.

[0197] Furthermore, for a polymer material having viscoelasticity at room temperature, the storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0198] This can reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can also exhibit a strong action against acoustic vibrations of 20 Hz to 20 kHz.

[0199] Furthermore, it is more preferable that the relative dielectric constant of the polymer material having viscoelasticity at room temperature is 10 or more at 25° C. Thus, when voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the matrix, and thus a larger deformation amount can be expected.

[0200] However, on the other hand, in consideration of ensuring good moisture resistance, etc., it is also preferable that the relative dielectric constant of the polymer material be 10 or less at 25°C.

[0201] Examples of polymer materials having viscoelasticity at room temperature that satisfy such conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. In addition, commercial products such as HYBRAR5127 (manufactured by KURARAY CO., LTD.) can also be preferably used as these polymer materials. Among them, materials having cyanoethyl groups are preferably used as polymer materials, and cyanoethylated PVA is particularly preferably used.

[0202] As the polymer material having viscoelasticity at room temperature, a polymer material having a cyanoethyl group is preferably used, and cyanoethylated PVA is particularly preferably used. That is, in the present invention, in the piezoelectric layer 20, a polymer material having a cyanoethyl group is preferably used as the matrix 34, and cyanoethylated PVA is particularly preferably used.

[0203] In the following description, the above-mentioned polymer materials represented by cyanoethylated PVA are also collectively referred to as "polymer materials having viscoelasticity at room temperature".

[0204] These polymer materials having viscoelasticity at room temperature may be used alone or in combination (mixed) of two or more.

[0205] The matrix 34 made of such a polymer material having viscoelasticity at room temperature may use a plurality of polymer materials in combination as necessary.

[0206] That is, in addition to the viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 34 as needed for the purpose of adjusting dielectric properties and mechanical properties.

[0207] As dielectric polymer materials that can be added, for example, fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, polyvinylidene fluoride-trifluoroethylene copolymers, and polyvinylidene fluoride-tetrafluoroethylene copolymers, vinylidene cyanide-vinyl acetate copolymers, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl pullulan, cyanoethyl sucrose, and cyanoethyl sorbitol, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified.

[0208] Among them, it is preferable to use a polymer material having a cyanoethyl group.

[0209] Furthermore, in the matrix 34 of the piezoelectric layer 20 , these dielectric polymer materials are not limited to one kind, and multiple kinds may be added.

[0210] Furthermore, in addition to the dielectric polymer material, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene and isobutylene, and thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica may be added to the matrix 34 for the purpose of adjusting the glass transition point Tg.

[0211] Furthermore, for the purpose of improving adhesiveness, a tackifier such as rosin ester, rosin, terpenes, terpene phenols, and petroleum resin may be added.

[0212] The amount of material other than the polymer material having viscoelasticity such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20 is not particularly limited, but is preferably 30% by mass or less in terms of the ratio in the matrix 34 .

[0213] In this way, the characteristics of the added polymer material can be manifested without damaging the viscoelastic relaxation mechanism in the matrix 34, so preferred results can be obtained from the perspectives of high dielectric constant, improved heat resistance, and improved adhesion with the piezoelectric particles 36 and the electrode layer.

[0214] The piezoelectric layer 20 is a layer composed of a polymer composite piezoelectric body including piezoelectric particles 36 in a matrix 34. The piezoelectric particles 36 are dispersed in the matrix 34. It is preferable that the piezoelectric particles 36 are dispersed in the matrix 34 uniformly (substantially uniformly).

[0215] The piezoelectric particles 36 are composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0216] Ceramic particles constituting the piezoelectric particles 36 include, for example, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0217] The particle size of the piezoelectric particles 36 is not limited and may be appropriately selected according to the size of the piezoelectric film 10 and the purpose of the piezoelectric vibrator (laminated piezoelectric element) 50. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm.

[0218] By setting the particle size of the piezoelectric particles 36 within this range, a preferable result can be obtained from the viewpoint that the piezoelectric film 10 can achieve both high piezoelectric characteristics and flexibility.

[0219] The piezoelectric particles 36 in the piezoelectric layer 20 may be uniformly and regularly dispersed in the matrix 34 , or may be irregularly dispersed in the matrix 34 as long as they are uniformly dispersed.

[0220] In the piezoelectric film 10, the quantitative ratio of the matrix 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 film 10 in the surface direction, the purpose of the piezoelectric film 10, and the properties required in the piezoelectric film 10.

[0221] The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore, further preferably 50 to 80%.

[0222] By setting the amount ratio of the matrix 34 to the piezoelectric particles 36 within the above range, a preferable result can be obtained from the viewpoint of being able to achieve both high piezoelectric characteristics and flexibility.

[0223] In the piezoelectric film 10 , the thickness of the piezoelectric layer 20 is not particularly limited and may be appropriately set depending on the application of the piezoelectric film 10 , the number of stacked layers of the piezoelectric film 10 in the piezoelectric vibrator 50 , the characteristics required of the piezoelectric film 10 , and the like.

[0224] The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as the strength of the sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount becomes larger.

[0225] 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.

[0226] By setting the thickness of the piezoelectric layer 20 within the above range, a preferable result can be obtained from the viewpoints of ensuring both rigidity and appropriate flexibility.

[0227] Furthermore, the piezoelectric layer 20 is preferably subjected to polarization processing (polling) in the thickness direction.

[0228] In the piezoelectric film 10 , the piezoelectric layer 20 is not limited to the polymer composite piezoelectric body including the piezoelectric particles 36 in the matrix 34 made of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA as described above.

[0229] That is, in the piezoelectric film 10 , the piezoelectric layer can utilize various known piezoelectric layers.

[0230] As an example, it is also possible to utilize a polymer composite piezoelectric body that contains the same piezoelectric particles 36 in a matrix containing dielectric polymer materials such as the above-mentioned polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, a piezoelectric layer composed of polyvinylidene fluoride, a piezoelectric layer composed of a fluororesin other than polyvinylidene fluoride, and a piezoelectric layer formed by stacking a film composed of poly-L-lactic acid and a film composed of poly-D-lactic acid, etc.

[0231] However, as described above, from the perspectives of being able to exhibit hard action for vibrations of 20 Hz to 20 kHz and soft action for slow vibrations below several Hz, and being able to obtain excellent acoustic properties and excellent flexibility, it is preferred to utilize the above-mentioned polymer composite piezoelectric body containing piezoelectric particles 36 in a polymer matrix 34 composed of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA.

[0232] like Fig.10 As shown, the piezoelectric film 10 has the following structure: a first electrode layer 24 is provided on one side of the piezoelectric layer 20, a first protective layer 28 is provided thereon, and 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. The first electrode layer 24 and the second electrode layer 26 form an electrode pair.

[0233] That is, the piezoelectric film 10 has a structure in which both surfaces of the piezoelectric body layer 20 are sandwiched between the first electrode layer 24 and the second electrode layer 26 , which are an electrode pair, and the stacked body is sandwiched between the first protective layer 28 and the second protective layer 30 .

[0234] In this manner, in the piezoelectric film 10 , a region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts in accordance with an applied voltage.

[0235] In the present invention, the piezoelectric film 10 may have, in addition to these layers, 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.

[0236] The adhesive may be a binder or an adhesive. Furthermore, the adhesive may preferably be made of the same material as the polymer material, that is, the matrix 34, from which the piezoelectric particles 36 are removed from the piezoelectric layer 20. In addition, the adhesive layer may be provided on both the first electrode layer 24 side and the second electrode layer 26 side, or may be provided on only one of the first electrode layer 24 side and the second electrode layer 26 side.

[0237] 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, and play a role in giving appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20 composed of the matrix 34 and the piezoelectric particles 36 shows very excellent flexibility for slow bending deformation, but on the other hand, there is a case where the rigidity or mechanical strength is insufficient depending on the application. The piezoelectric film 10 is provided with the first protective layer 28 and the second protective layer 30 to compensate for this deficiency.

[0238] The first protective layer 28 and the second protective layer 30 are not limited, and various sheet-like materials can be used. As an example, various resin films are preferably exemplified.

[0239] 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 are preferably used due to their excellent mechanical properties and heat resistance.

[0240] The thickness of the first protective layer 28 and the second protective layer 30 is not limited. Furthermore, the thickness of the first protective layer 28 and the second protective layer 30 is basically the same, but may be different.

[0241] If the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only the expansion and contraction of the piezoelectric layer 20 is restricted, but also the flexibility is impaired. Therefore, except for the case where mechanical strength or good handling as a sheet is required, the thinner the first protective layer 28 and the second protective layer 30 are, the more advantageous it is.

[0242] In the piezoelectric film 10 , when the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20 , a preferable result can be obtained from the viewpoints of ensuring both rigidity and appropriate flexibility.

[0243] For example, when the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made of PET, the thickness of the first protective layer 28 and the second protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 25 μm or less.

[0244] In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is formed between the piezoelectric layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10).

[0245] In the present invention, the materials for forming the first electrode layer 24 and the second electrode layer 26 are not limited, and various conductors can be used. Specifically, 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 are exemplified. Alternatively, conductive polymers such as PEDOT / PPS (polyethylene dioxythiophene-polystyrene sulfonic acid) are also exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the first electrode layer 24 and the second electrode layer 26. Among them, copper is more preferred from the viewpoints of conductivity, cost, flexibility, etc.

[0246] Furthermore, the method for forming the first electrode layer 24 and the second electrode layer 26 is not limited, and various known methods such as vapor deposition methods (vacuum film forming methods) such as vacuum evaporation and sputtering, film formation by plating, and methods of pasting foils formed of the above materials can be used.

[0247] Among them, thin films of copper, aluminum, etc. formed by vacuum deposition are preferably used as the first electrode layer 24 and the second electrode layer 26 because flexibility of the piezoelectric film 10 can be ensured. Among them, thin films of copper formed by vacuum deposition are particularly preferably used.

[0248] The thickness of the first electrode layer 24 and the second electrode layer 26 is not limited. Furthermore, the thickness of the first electrode layer 24 and the second electrode layer 26 is substantially the same, but may be different.

[0249] Among them, similar to the first protective layer 28 and the second protective layer 30, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, not only the expansion and contraction of the piezoelectric layer 20 is restricted, but also the flexibility is impaired. Therefore, as long as the resistance does not become too high, the thinner the first electrode layer 24 and the second electrode layer 26 are, the more advantageous it is.

[0250] In the piezoelectric film 10 , if the product of the thickness and Young's modulus of the first electrode layer 24 and the second electrode layer 26 is lower than the product of the thickness and Young's modulus of the first protective layer 28 and the second protective layer 30 , flexibility is not seriously impaired, which is preferred.

[0251] For example, in the case of a combination in which the first protective layer 28 and the second protective layer 30 are PET (Young's modulus: approximately 6.2 GPa) and the first electrode layer 24 and the second electrode layer 26 are composed of copper (Young's modulus: approximately 130 GPa), if the thickness of the first protective layer 28 and the second protective layer 30 is 25 μm, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and preferably 0.1 μm or less.

[0252] As described above, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 in which the piezoelectric particles 36 are dispersed in the matrix 34 made of a polymer material is sandwiched between the first electrode layer 24 and the second electrode layer 26 , and the stacked body is further sandwiched between the first protective layer 28 and the second protective layer 30 .

[0253] Such a piezoelectric film 10 preferably has a local value of loss tangent (Tan δ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement at room temperature, and more preferably has a local value of 0.1 or more at room temperature.

[0254] Thus, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from being generated at the interface between the polymer matrix and the piezoelectric particles.

[0255] In the piezoelectric film 10 , the storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 10 to 30 GPa at 0° C. and 1 to 10 GPa at 50° C. The conditions are the same as those for the piezoelectric layer 20 .

[0256] Thus, the piezoelectric film 10 can have a large frequency dispersion in the storage elastic modulus (E') at room temperature, that is, it can exhibit a hard action for vibrations of 20 Hz to 20 kHz and exhibit a soft action for vibrations of several Hz or less.

[0257] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10 and the piezoelectric layer 20 may be measured by a known method. For example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nano Technology Inc. may be used for measurement.

[0258] As an example of the measurement conditions, the following are respectively illustrated: the measurement frequency is 0.1Hz~20Hz (0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz and 20Hz), the measurement temperature is -50~150°C, the heating rate is 2°C / minute (in a nitrogen atmosphere), the sample size is 40mm×10mm (including the clamping plate area), and the chuck spacing is 20mm.

[0259] In the laminated piezoelectric element 50 , a driving source for applying a driving voltage for expanding and contracting the piezoelectric film 10 , that is, supplying driving power (input signal), is connected to the first electrode layer 24 and the second electrode layer 26 of each piezoelectric film 10 .

[0260] The example of the circuit of the driving source is as described above.

[0261] The method of extracting electrodes from the first electrode layer 24 and the second electrode layer 26 is not limited, and various well-known methods can be used.

[0262] As an example, a method of connecting a conductor such as copper foil to the first electrode layer 24 and the second electrode layer 26 to lead out the electrodes to the outside, and a method of forming through holes in the first protective layer 28 and the second protective layer 30 by laser or the like and filling the through holes with a conductive material to lead out the electrodes to the outside are illustrated.

[0263] Preferred methods for extracting electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

[0264] (Stacked piezoelectric element)

[0265] The above-mentioned piezoelectric film can be used as a piezoelectric vibrator in the form of a stacked piezoelectric element in which a plurality of piezoelectric films are stacked by folding the piezoelectric film one or more times.

[0266] Fig.11 It is a perspective view schematically showing an example of a stacked piezoelectric element as a piezoelectric vibrator. Fig.12 Is has Fig.11 A side view of an electroacoustic transducer of a stacked piezoelectric element is shown.

[0267] Fig.12 The electroacoustic converter 100 shown includes a laminated piezoelectric element (piezoelectric vibrator) 50, a vibration plate 102, and an adhesive layer 104 disposed between the laminated piezoelectric element 50 and the vibration plate 102. The laminated piezoelectric element 50 and the vibration plate 102 are adhered to each other via the adhesive layer 104. The vibration plate 102 is as described above.

[0268] exist Fig.11 and Fig.12In the example shown, the stacked piezoelectric element 50 is formed by stacking three layers of piezoelectric films 10 by folding a single rectangular strip of piezoelectric film 10 twice in one direction. Fig.12 and the following Fig.13 In the figure, the protective layer is omitted.

[0269] like Fig.12 As shown, a driving source is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 constituting the stacked piezoelectric element 50. The stacked piezoelectric element 50 (piezoelectric film 10) is driven as a piezoelectric body by applying a voltage (input signal) to the first electrode layer 24 and the second electrode layer 26, so that the piezoelectric layer 20 expands and contracts. If the stacked piezoelectric element 50 is driven, the stacked piezoelectric element 50 expands and contracts in the surface direction, causing the vibration plate 102 to which the stacked piezoelectric element 50 is attached to bend, and as a result, the vibration plate 102 vibrates in the thickness direction to generate sound. The vibration plate 102 vibrates according to the magnitude of the driving voltage applied to the stacked piezoelectric element 50, and the electroacoustic converter 100 generates sound corresponding to the applied driving voltage.

[0270] exist Fig.11 and Fig.12 In the example shown, the stacked piezoelectric element 50 has a stacked portion where three piezoelectric films 10 are stacked in a plan view and a protrusion protruding outward from the stacked portion in a planar direction. That is, the stacked piezoelectric element 50 is provided with the protrusion in such a manner that when one piezoelectric film 10 is folded back twice, Fig.11 In the embodiment, in the two layers starting from the layer on the lower surface side, the lengths in the folding direction are made to be approximately the same, the length of the piezoelectric film 10 of the layer on the uppermost surface side is made longer than the piezoelectric films 10 of other layers, and one end in the folding direction does not overlap with the piezoelectric films 10 of other layers.

[0271] In addition, Fig.11 In the example shown, the stacked piezoelectric element 50 is configured as a stacked piezoelectric element formed by folding the piezoelectric film 10 twice and stacking three layers of piezoelectric films 10, but is not limited to this. The stacked piezoelectric element may be a stacked piezoelectric element formed by stacking two layers of piezoelectric films, or may be a stacked piezoelectric element formed by stacking four or more layers of piezoelectric films.

[0272] The adjacent layers of the piezoelectric film 10 in the stacked portion are bonded together by an adhesive layer 19 .

[0273] As the adhesive layer 19 for bonding the piezoelectric films together, various known adhesive layers can be used as long as they can bond the adjacent piezoelectric films 10. As the adhesive layer 19, the same material as the adhesive layer for bonding the vibration plate and the laminated piezoelectric element described later can be used.

[0274] In the present invention, the laminated portion refers to the portion in a plan view, that is, Fig.11In the case of a stacked piezoelectric element, when viewed from above (or below), the piezoelectric film overlaps two or more layers. Fig.11 and Fig.12 In the example shown, a region where three layers of the piezoelectric film 10 are stacked is a stacked portion.

[0275] On the other hand, the protruding portion refers to a region that protrudes from the laminated portion in the surface direction and does not overlap with other layers in a plan view. Fig.11 and Fig.12 In the example shown, the right end of the uppermost layer in the figure is a protruding portion.

[0276] like Fig.11 As shown in FIG. 1 , the protruding portion is provided with a lead 40 and a lead 42 for connecting the first electrode layer 24 and the second electrode layer 26 (hereinafter, also collectively referred to as electrode layers) to an external electrode. Fig.12 As shown, when the piezoelectric film 10 has a protective layer (the first protective layer 28 and the second protective layer 30), a through hole is formed in the protective layer (the first protective layer 28 and the second protective layer 30) in the region of the protruding portion to expose the electrode layer, and a connecting portion is provided to be electrically connected to the wire 40 and the wire 42. The method for forming the through hole is not limited, and it can be performed by a known method such as laser processing, dissolution removal using a solvent, and mechanical processing such as mechanical grinding according to the material forming the protective layer.

[0277] The connection portion is filled with a known conductive material such as a conductive metal paste such as a silver paste, a conductive carbon paste, and a conductive nano-ink, and is connected to a lead wire connected to an external power source.

[0278] In addition, the method for connecting the electrode layer and the lead wire in the protruding portion is not limited, and various known methods can be used.

[0279] The stacked piezoelectric element 50 is driven by applying a voltage to the electrode layer using an external power source via a connection portion provided at the protruding portion. When the stacked piezoelectric element 50 is driven, the stacked piezoelectric element 50 expands and contracts in the surface direction, bending the vibration plate to which the stacked piezoelectric element 50 is attached, and as a result, the vibration plate vibrates to generate sound. The vibration plate vibrates according to the magnitude of the driving voltage applied to the stacked piezoelectric element 50, and generates sound corresponding to the driving voltage applied to the stacked piezoelectric element 50.

[0280] Here, in Fig.11 In the illustrated example, the laminated piezoelectric element has a structure in which the piezoelectric film 10 is folded back and laminated, but the present invention is not limited to this.

[0281] Fig.13 This is a diagram showing another example of the structure of the laminated piezoelectric element included in the electroacoustic transducer of the present invention.

[0282] Fig.13 The stacked piezoelectric element shown is formed by stacking three layers of single-sheet piezoelectric films 10. The piezoelectric films 10 are bonded to each other via an adhesive layer 19. A driving source for applying a driving voltage is connected to each piezoelectric film 10. Fig.13 In order to simplify the drawings, the first protective layer and the second protective layer are omitted. However, as a preferred embodiment, Fig.13 In the illustrated multilayer piezoelectric element, all the piezoelectric films 10 have both the first protective layer and the second protective layer.

[0283] In addition, the stacked piezoelectric element is not limited to this, and a piezoelectric film with a protective layer and a piezoelectric film without a protective layer may coexist. Moreover, in the case where the piezoelectric film has a protective layer, the piezoelectric film may have only the first protective layer or only the second protective layer. As an example, if Fig.13 The stacked piezoelectric element with a three-layer structure shown can be structured as follows: the top piezoelectric film in the figure only has the second protective layer on the second electrode layer 26, the middle piezoelectric film has no protective layer, and the bottom piezoelectric film only has the first protective layer on the first electrode layer 24.

[0284] As a preferred method, Fig.13 The stacked piezoelectric element shown has a structure in which the polarization directions ( Fig.13 Multiple layers (three layers in the example shown) of piezoelectric films 10 are stacked in opposite directions (in the direction indicated by the arrows in the figure), and adjacent piezoelectric films 10 are adhered together using an adhesive layer 19.

[0285] Alternatively, the stacked piezoelectric element may have a structure in which a plurality of piezoelectric films 10 are stacked so that the polarization directions of adjacent piezoelectric films 10 are the same.

[0286] In the piezoelectric film 10, the polarity of the voltage applied to the piezoelectric layer 20 corresponds to the polarization direction. Therefore, the polarity of the applied voltage is in the polarization direction indicated by the arrow, and the polarity of the electrode layer on the side indicated by the arrow (downstream side of the arrow) and the polarity of the electrode layer on the opposite side (upstream side of the arrow) are consistent in all piezoelectric films 10.

[0287] In the example shown in the figure, the electrode on the side indicated by the arrow indicating the polarization direction is set as the first electrode layer 24, and the electrode on the opposite side is set as the second electrode layer 26. In all piezoelectric films 10, the polarity of the first electrode layer 24 and the second electrode layer 26 are made the same.

[0288] Therefore, if Fig.13As shown, in a stacked piezoelectric element in which the polarization directions of the piezoelectric layers 20 of adjacent piezoelectric films 10 are opposite to each other, in adjacent piezoelectric films 10, the first electrode layers 24 are opposed to each other on one surface, and the second electrode layers 26 are opposed to each other on the other surface. Fig.13 In the stacked piezoelectric element shown, even if the electrode layers of adjacent piezoelectric films 10 are in contact with each other, there is no concern that a short circuit will occur.

[0289] In order to expand and contract the stacked piezoelectric element with good energy conversion efficiency, it is preferable to make the adhesive layer 19 thin so that the adhesive layer 19 does not hinder the expansion and contraction of the piezoelectric layer 20. In contrast, in the case where there is no concern about short circuit even if the electrode layers of adjacent piezoelectric films 10 are in contact with each other, Fig.13 The laminated piezoelectric element shown may not have the adhesive layer 19. As a preferred embodiment, even if the adhesive layer 19 is present, the adhesive layer 19 can be made extremely thin as long as the required adhesive force is obtained. Therefore, the laminated piezoelectric element can be expanded and contracted with high energy conversion efficiency.

[0290] In addition, in the piezoelectric film 10, the absolute amount of expansion and contraction of the piezoelectric layer 20 in the thickness direction is very small, and the expansion and contraction of the piezoelectric film 10 is substantially performed only in the surface direction. Therefore, even if the polarization directions of the stacked piezoelectric films 10 are opposite, as long as the polarity of the voltage applied to the first electrode layer 24 and the second electrode layer 26 is correct, all the piezoelectric films 10 expand and contract in the same direction.

[0291] The polarization direction of the piezoelectric film 10 may be detected by a d33 meter or the like. Alternatively, the polarization direction of the piezoelectric film 10 may be found based on the treatment conditions of the corona poling treatment described later.

[0292] and, Fig.13 The stacked piezoelectric element shown is preferably made of a long (large area) piezoelectric film, and the piezoelectric films 10 are cut out from the long piezoelectric film and stacked. In this case, all the piezoelectric films 10 constituting the stacked piezoelectric element are identical.

[0293] However, the present invention is not limited to this. That is, in the present invention, the stacked piezoelectric element can utilize various structures, for example: a structure formed by stacking piezoelectric films of different layer structures such as a piezoelectric film having a first protective layer and a second protective layer and a piezoelectric film not having a first protective layer and a second protective layer; and a structure formed by stacking piezoelectric films of different thicknesses of the piezoelectric layer 20.

[0294] and, Fig.11 and Fig.12In the stacked piezoelectric element shown, the stacked piezoelectric element can be formed by only one long piezoelectric film 10 , and only one driving source is required to apply a driving voltage, and only one electrode needs to be drawn out from the piezoelectric film 10 .

[0295] Therefore, compared with Fig.13 The stacked piezoelectric element formed by stacking a plurality of monolithic piezoelectric films 10 as shown reduces the number of components and simplifies the structure, thereby improving the reliability of the stacked piezoelectric element and achieving cost reduction.

[0296] Furthermore, the piezoelectric film 10 has a thickness direction ( Fig.12 By folding back and stacking a piezoelectric film 10 polarized in the thickness direction, the polarization direction of the piezoelectric films 10 adjacent (opposite) in the stacking direction is as follows: Fig.12 The arrow in the middle indicates the opposite direction. Therefore, in the stacked piezoelectric element formed by folding back a piezoelectric film 10, between the layers of adjacent piezoelectric films 10, the first electrode layers 24 face each other on one surface, and the second electrode layers 26 face each other on the other surface. Therefore, even if the electrode layers of adjacent piezoelectric films 10 touch each other, there is no need to worry about short circuit.

[0297] like Fig.12 In a stacked piezoelectric element in which the piezoelectric film 10 is folded back as in the illustrated stacked piezoelectric element, it is preferable that the core rod 58 is inserted into the folded back portion of the piezoelectric film 10 in contact with the piezoelectric film 10 .

[0298] The first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 are formed of a metal vapor-deposited film or the like. If the metal vapor-deposited film is bent at an acute angle, cracks (fissures) are likely to occur, which may cause disconnection of the electrode layer. Fig.12 In the stacked piezoelectric element shown, cracks and the like are likely to occur in the electrodes on the inner side of the bent portion.

[0299] On the other hand, in the laminated piezoelectric element formed by folding the piezoelectric film 10 , by inserting the core rod 58 into the folded portion of the piezoelectric film 10 , the first electrode layer 24 and the second electrode layer 26 can be prevented from being folded, and disconnection can be appropriately prevented.

[0300] <Paste layer>

[0301] The adhesive layer 104 may be a layer composed of an adhesive that has fluidity when attached and then becomes solid, or a layer composed of an adhesive that is a soft solid gel (rubbery) when attached and then remains in a gel state, or a layer composed of a material having the characteristics of both an adhesive and an adhesive. Furthermore, the adhesive layer may be formed by applying a fluid adhesive such as a liquid, or may be formed by using a sheet-like adhesive.

[0302] Here, in the electroacoustic transducer 100, the piezoelectric vibrator (stacked piezoelectric element) 50 is expanded and contracted, thereby bending and vibrating the vibration plate 102 to generate sound. Therefore, in the electroacoustic transducer 100, it is preferable that the expansion and contraction of the piezoelectric vibrator is directly transmitted to the vibration plate 102. If a viscous substance such as a vibration-relieving substance exists between the piezoelectric vibrator 50 and the vibration plate 102, the efficiency of transmitting the expansion and contraction energy of the piezoelectric vibrator 50 to the vibration plate 102 becomes low, and the driving efficiency of the electroacoustic transducer 100 is reduced.

[0303] Considering this point, the adhesive layer 104 for adhering the piezoelectric vibrator 50 and the vibration plate 102 is preferably an adhesive layer composed of an adhesive agent, which can obtain a solid and hard adhesive layer 104, rather than an adhesive layer composed of an adhesive agent. As a more preferred adhesive layer 104, an adhesive layer composed of a thermoplastic adhesive such as a polyester adhesive and a styrene-butadiene rubber (SBR) adhesive is specifically exemplified.

[0304] Bonding is different from adhesion and is useful when a high bonding temperature is required. In addition, thermoplastic adhesives are preferred because they have "relatively low temperature, short time and strong bonding".

[0305] The thickness of the adhesive layer 104 is not limited, and may be appropriately set according to the material of the adhesive layer 104 so as to obtain a sufficient adhesive force (adhesive force, adhesive force).

[0306] In the electroacoustic converter 100, when the adhesive layer 104 is thin, the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric vibrator 50 to the vibration plate 102 is improved, thereby improving the energy conversion efficiency. In addition, if the adhesive layer 104 is thick and has high rigidity, the expansion and contraction of the piezoelectric vibrator 50 may be restricted.

[0307] Taking this into consideration, the adhesive layer 104 is preferably thin. Specifically, the thickness of the adhesive layer 104 after adhesion is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0308] In the electroacoustic transducer 100 , the adhesive layer 104 is a layer provided as a preferred embodiment, and is not an essential component.

[0309] Therefore, the electroacoustic transducer 100 may not have the adhesive layer 104, but may use a known crimping mechanism, a fastening mechanism, a fixing mechanism, etc. to fix the vibration plate 102 and the piezoelectric vibrator 50. For example, when the piezoelectric vibrator 50 is rectangular in plan view, the electroacoustic transducer may be formed by fastening the four corners with components such as bolts and nuts, or the electroacoustic transducer may be formed by fastening the four corners and the center with components such as bolts and nuts.

[0310] However, in this case, when a driving voltage is applied from a driving source, the piezoelectric vibrator 50 expands and contracts independently of the vibration plate 102. In some cases, only the piezoelectric vibrator 50 bends, and the expansion and contraction of the piezoelectric vibrator 50 is not transmitted to the vibration plate 102. In this way, when the piezoelectric vibrator 50 expands and contracts independently of the vibration plate 102, the vibration efficiency of the vibration plate 102 caused by the piezoelectric vibrator 50 is reduced. There is a possibility that the vibration plate 102 cannot be vibrated sufficiently.

[0311] Taking this into consideration, the vibration plate 102 and the piezoelectric vibrator 50 are preferably attached to each other via the adhesive layer 104 .

[0312] Furthermore, the stacked piezoelectric element generates sound by vibrating the vibration plate 102 by causing the stacked plurality of piezoelectric films 10 to expand and contract. Therefore, the stacked piezoelectric element preferably transmits the expansion and contraction of each piezoelectric film 10 directly. If a viscous substance such as a vibration-relieving substance exists between the piezoelectric films 10, the transmission efficiency of the expansion and contraction energy of the piezoelectric films 10 becomes low, and the driving efficiency of the stacked piezoelectric element is reduced.

[0313] Taking this into consideration, the adhesive layer 19 for bonding the piezoelectric films 10 to each other is preferably an adhesive layer composed of an adhesive so as to obtain a solid and hard adhesive layer 19, rather than an adhesive layer composed of an adhesive. As a more preferred adhesive layer 19, specifically, an adhesive layer composed of a thermoplastic adhesive such as a polyester adhesive and a styrene-butadiene rubber (SBR) adhesive is preferably exemplified.

[0314] In the laminated piezoelectric element, the thickness of the adhesive layer 19 is not limited, and may be appropriately set according to the material forming the adhesive layer 19 so as to exhibit a sufficient adhesive force.

[0315] In the laminated piezoelectric element, when the adhesive layer 19 is thin, the transmission effect of the expansion and contraction energy of the piezoelectric film 10 is improved, thereby improving the energy conversion efficiency. On the other hand, when the adhesive layer 19 is thick and has high rigidity, the expansion and contraction of the piezoelectric film 10 may be restricted.

[0316] Considering this point, the adhesive layer 19 is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element, the adhesive layer 19 is preferably hard and thin. Specifically, the thickness of the adhesive layer 19 after bonding is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0317] in addition, Fig.12 and Fig.13In the stacked piezoelectric element of the example shown, the polarization directions of the adjacent piezoelectric films are opposite to each other, and there is no risk of the adjacent piezoelectric films 10 being short-circuited, so the adhesive layer 19 can be made thinner.

[0318] In the laminated piezoelectric element, if the spring constant (thickness×Young's modulus) of the adhesive layer 19 is high, the expansion and contraction of the piezoelectric film 10 may be restricted. Therefore, the spring constant of the adhesive layer 19 is preferably equal to or less than that of the piezoelectric film 10.

[0319] Specifically, it is preferred that the product of the thickness of the adhesive layer 19 and the storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is 2.0×10 6 N / m or less, 1.0×10 at 50°C 6 Below N / m.

[0320] Furthermore, the internal loss of the adhesive layer 19 at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 1.0 or less at 25° C. when the adhesive layer 19 is composed of a pressure-sensitive adhesive, and is preferably 0.1 or less at 25° C. when the adhesive layer 19 is composed of a bonding agent.

[0321] In addition, in the laminated piezoelectric element, the adhesive layer 19 is provided as a preferred embodiment and is not an essential component.

[0322] Therefore, the stacked piezoelectric element may not have the adhesive layer 19, but may be formed by stacking the piezoelectric films 10 and making them close together using a known crimping mechanism, a fastening mechanism, a fixing mechanism, etc. For example, when the piezoelectric film 10 is rectangular, the stacked piezoelectric element may be formed by fastening the four corners with bolts and nuts, or the stacked piezoelectric element may be formed by fastening the four corners and the center with bolts and nuts. Alternatively, after the piezoelectric film 10 is stacked, the stacked piezoelectric film 10 may be fixed by attaching an adhesive tape to the peripheral portion (end face) to form a stacked piezoelectric element.

[0323] However, in this case, when a driving voltage is applied from a power source, each piezoelectric film 10 expands and contracts independently, and depending on the situation, each layer of each piezoelectric film 10 bends in opposite directions to cause a gap. In this way, when each piezoelectric film 10 expands and contracts independently, the driving efficiency as a stacked piezoelectric element is reduced, and the expansion and contraction of the entire stacked piezoelectric element becomes smaller, so that the vibration plate 102 and the like abutting against it may not be able to vibrate sufficiently. In particular, when each layer of each piezoelectric film 10 bends in opposite directions to cause a gap, the driving efficiency as a stacked piezoelectric element is greatly reduced.

[0324] Taking this into consideration, the multilayer piezoelectric element preferably includes a bonding layer 19 for bonding adjacent piezoelectric films 10 together, as in the multilayer piezoelectric element shown in the figure.

[0325] Here, if Fig.12 As shown, in the case where the electroacoustic transducer 100 has a structure in which a stacked piezoelectric element is adhered to a vibration plate 102, the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 Hz and 25°C obtained based on dynamic viscoelasticity measurement is preferably 0.1 to 3 times the product of the thickness of the vibration plate 102 and the Young's modulus.

[0326] As described above, the piezoelectric film 10 of the present invention has excellent flexibility under the environment at room temperature, and the stacked piezoelectric element formed by stacking the piezoelectric films 10 also has excellent flexibility under the environment at room temperature.

[0327] On the other hand, the vibration plate 102 has a certain degree of rigidity. If a highly rigid laminated piezoelectric element is combined with such a vibration plate 102 , the vibration plate 102 becomes rigid and difficult to bend, which is disadvantageous in terms of the flexibility of the electroacoustic transducer 100 .

[0328] In contrast, in the present invention, the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 Hz and 25° C. obtained based on dynamic viscoelasticity measurement is preferably three times the product of the thickness of the vibration plate 102 and the Young's modulus. That is, the spring constant of the stacked piezoelectric element is preferably three times or less than that of the vibration plate 102 for slow movements.

[0329] With such a structure, the electroacoustic transducer 100 can exhibit soft motion with respect to slow motion caused by external forces such as bending and curling, that is, it can exhibit good flexibility with respect to slow motion.

[0330] In the electroacoustic transducer 100, the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity measurement is preferably less than 2 times the product of the thickness of the vibration plate 102 and the Young's modulus, further preferably less than 1 times, and particularly preferably less than 0.3 times.

[0331] On the other hand, taking into account the materials used in the stacked piezoelectric element and the preferred structure of the stacked piezoelectric element, the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity measurement is preferably greater than 0.1 times the product of the thickness of the vibration plate 102 and the Young's modulus.

[0332] In the electroacoustic converter 100, the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 kHz and 25° C. in the master curve obtained by dynamic viscoelasticity measurement is preferably 0.3 to 10 times the product of the thickness of the vibration plate 102 and the Young's modulus. That is, in the fast movement of the stacked piezoelectric element in the driven state, the spring constant is preferably 0.3 to 10 times that of the vibration plate 102.

[0333] As described above, in the electroacoustic transducer 100, the laminated piezoelectric element expands and contracts in the plane direction to vibrate the vibration plate 102, thereby generating sound. Therefore, the laminated piezoelectric element preferably has a certain degree of rigidity (hardness, toughness) relative to the vibration plate 102 at frequencies in the audio band (20 Hz to 20 kHz).

[0334] The product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 kHz and 25° C. in the master curve obtained by the dynamic viscoelasticity measurement is preferably set to 0.3 times or more, more preferably 0.5 times or more, and further preferably 1 times or more of the product of the thickness of the vibration plate 102 and the Young's modulus. That is, the spring constant of the stacked piezoelectric element is preferably 0.3 times or more, more preferably 0.5 times or more, and further preferably 1 times or more of that of the vibration plate 102 for rapid action.

[0335] Thus, in the audio frequency band, the rigidity of the laminated piezoelectric element with respect to the diaphragm 102 is sufficiently ensured, and the electroacoustic transducer 100 can output a sound of high sound pressure with high energy conversion efficiency.

[0336] On the other hand, taking into account the materials that can be used in the stacked piezoelectric element, the preferred structure of the stacked piezoelectric element, etc., the product of the thickness of the stacked piezoelectric element and the storage modulus at a frequency of 1 kHz and 25°C obtained based on dynamic viscoelasticity measurement is preferably less than 10 times the product of the thickness of the vibration plate 102 and the Young's modulus.

[0337] It is also clear from the above description that the product of the thickness of the stacked piezoelectric element (piezoelectric vibrator) and the storage modulus at a frequency of 1 Hz and 25°C obtained based on dynamic viscoelasticity measurement is not only affected by the thickness of the adhesive layer 19, but is also greatly affected by the physical properties of the adhesive layer 19, such as the storage modulus.

[0338] On the other hand, the product of the thickness of the vibration plate 102 and the Young's modulus, that is, the spring constant of the vibration plate is greatly affected not only by the thickness of the vibration plate but also by the physical properties of the vibration plate.

[0339] Therefore, in the present invention, in order to satisfy the condition that the product of the thickness of the stacked piezoelectric element and the storage modulus of the stacked piezoelectric element at a frequency of 1 Hz and 25°C obtained based on dynamic viscoelasticity measurement is 0.1 to 3 times the product of the thickness of the vibration plate 102 and the Young's modulus, the thickness and material of the adhesive layer 19 and the thickness and material of the vibration plate are important. Furthermore, in the present invention, in order to satisfy the condition that the product of the thickness of the stacked piezoelectric element and the storage modulus of the stacked piezoelectric element at a frequency of 1 kHz and 25°C is 0.3 to 10 times the product of the thickness of the vibration plate 102 and the Young's modulus, the thickness and material of the adhesive layer 19 and the thickness and material of the vibration plate 102 are also important.

[0340] That is, in the present invention, when the electroacoustic transducer has a structure of the vibration plate 102 , it is preferable to appropriately select the thickness and material of the adhesive layer 19 and the thickness and material of the vibration plate 102 so as to satisfy the above conditions.

[0341] In other words, in the present invention, the thickness and material of the adhesive layer 19 and the thickness and material of the vibration plate 102 are appropriately selected based on the characteristics of the piezoelectric film 10, etc., thereby preferably satisfying the condition that the product of the thickness of the stacked piezoelectric element and the storage modulus of the stacked piezoelectric element at a frequency of 1 Hz and 25°C obtained based on dynamic viscoelasticity measurement is 0.1 to 3 times the product of the thickness of the vibration plate 102 and the Young's modulus and / or the condition that the product of the thickness of the stacked piezoelectric element and the storage modulus of the stacked piezoelectric element at a frequency of 1 kHz and 25°C is 0.3 to 10 times the product of the thickness of the vibration plate 102 and the Young's modulus.

[0342] The above-mentioned product of the thickness and the storage elastic modulus is the same also when the single-layer piezoelectric film 10 is used as a piezoelectric vibrator instead of the laminated piezoelectric element.

[0343] <Method of producing piezoelectric film>

[0344] Below, reference Figure 14 to Figure 16 , an example of a method for manufacturing the piezoelectric film 10 is described.

[0345] First, prepare Fig.14 The sheet 11a shown in the figure has a first electrode layer 24 formed on the surface of the first protective layer 28. Fig.16 Schematically shown in FIG. 1 is a sheet-like object 11 c in which the second electrode layer 26 is formed on the surface of the second protective layer 30 .

[0346] The sheet 11a can be made by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, etc. Similarly, the sheet 11c can be made by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, etc.

[0347] Alternatively, a commercially available sheet in which a copper thin film or the like is formed on a protective layer may be used as the sheet 11 a and / or the sheet 11 c .

[0348] The sheet-shaped object 11 a and the sheet-shaped object 11 c may have the same structure or different structures.

[0349] In addition, when the protective layer is very thin and has poor handling properties, a protective layer with a separator (pseudo-support) can be used as needed. In addition, as a separator, PET with a thickness of 25 to 100 μm can be used. The separator can be removed after the electrode layer and the protective layer are thermocompressed.

[0350] Then, if Fig.15 As shown, a coating material (coating composition) to be the piezoelectric layer 20 is applied onto the first electrode layer 24 of the sheet 11a and then cured to form the piezoelectric layer 20. Thus, a laminate 11b in which the sheet 11a and the piezoelectric layer 20 are laminated is produced.

[0351] The piezoelectric layer 20 can be formed by various methods depending on the material forming the piezoelectric layer 20 .

[0352] As an example, first, the polymer material such as the cyanoethylated PVA described above is dissolved in an organic solvent, and then the piezoelectric particles 36 such as PZT particles are added and stirred to prepare a coating material.

[0353] The organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.

[0354] After preparing the sheet 11a and preparing the coating, the coating is cast (coated) on the sheet 11a, and the organic solvent is evaporated and dried. Fig.15 As shown in FIG. 1 , a stacked body 11 b is produced in which a first electrode layer 24 is provided on a first protective layer 28 and a piezoelectric layer 20 is stacked on the first electrode layer 24 .

[0355] The coating material is not particularly limited in its casting method, and any known method (coating device) such as a bar coater, a slide coater, or a doctor knife can be used.

[0356] Alternatively, if the polymer material is a heat-meltable substance, a melt can be prepared by heating and melting the polymer material and adding the piezoelectric particles 36 thereto, and then extruding the melt to obtain a melt. Fig.10 The sheet 11a shown in FIG. 1 is extruded into a sheet and cooled to produce a sheet such as Fig.11 The stacked body 11b is shown.

[0357] As described above, in the piezoelectric layer 20 , a polymer piezoelectric material such as PVDF (polyvinylidene fluoride) may be added to the matrix 34 in addition to the polymer material having viscoelasticity at room temperature.

[0358] When adding these polymer piezoelectric materials to the matrix 34, the polymer piezoelectric materials added to the coating material may be dissolved or added to a polymer material having viscoelasticity at room temperature that has been heated and melted and then heated and melted.

[0359] After forming the piezoelectric layer 20, a calendering treatment may be performed as needed. The calendering treatment may be performed once or multiple times. As is well known, the calendering treatment refers to a treatment such as flattening by pressing while heating the treated surface with a hot press or a heated roller.

[0360] In addition, the rolling process can be performed after the polarization process described later. However, if the rolling process is performed after the polarization process, the piezoelectric particles 36 pressed in by pressing rotate, and there is a possibility that the effect of the polarization process is reduced. Considering this point, the rolling process is preferably performed before the polarization process.

[0361] Next, the piezoelectric layer 20 of the stacked body 11b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24 is polarized. The polarization of the piezoelectric layer 20 may be performed before the rolling process, but is preferably performed after the rolling process.

[0362] The method of polarization treatment of the piezoelectric layer 20 is not limited, and a known method can be used. For example, electric field polarization in which a DC electric field is directly applied to an object to be polarized is exemplified. In addition, when electric field polarization is performed, the second electrode layer 26 can be formed before the polarization treatment, and the first electrode layer 24 and the second electrode layer 26 can be used to perform the electric field polarization treatment.

[0363] Furthermore, in the piezoelectric film 10 of the present invention, it is preferable that the polarization treatment be performed in the thickness direction rather than in the surface direction of the piezoelectric layer 20 .

[0364] Then, if Fig.16 As shown in FIG. 1 , a sheet-like object 11 c prepared in advance is stacked on the piezoelectric layer 20 side of the polarized laminate 11 b so that the second electrode layer 26 faces the piezoelectric layer 20 .

[0365] Furthermore, the laminate is heat-pressed and bonded by using a heat press device and a heating roller to sandwich the first protective layer 28 and the second protective layer 30, and the laminate 11b and the sheet 11c are attached to each other, thereby producing a laminate as shown in FIG. Fig.10 The piezoelectric film 10.

[0366] Alternatively, the piezoelectric film 10 may be produced by bonding the laminate 11 b and the sheet 11 c together using an adhesive and preferably further bonding them by pressure bonding.

[0367] Such a piezoelectric film 10 can be manufactured using a slice-shaped sheet 11 a and a sheet 11 c or the like, or can be manufactured by a roll-to-roll process.

[0368] The manufactured piezoelectric film can also be cut into desired shapes according to various applications.

[0369] The piezoelectric film 10 manufactured in this way is polarized only in the thickness direction rather than in the plane direction, and even if no stretching treatment is performed after the polarization treatment, high piezoelectric properties can be obtained. Therefore, the piezoelectric film 10 does not have in-plane anisotropy in terms of piezoelectric properties, and when a driving voltage is applied, it expands and contracts isotropically in all directions in the plane direction.

[0370] <<Second embodiment>>

[0371] Here, the electroacoustic converter may be the following electroacoustic converter:

[0372] A vibrator group including a vibrator plate and a plurality of piezoelectric vibrators arranged on one surface of the vibrator plate.

[0373] The vibration plate is bent in the arrangement direction of the plurality of piezoelectric vibrators of the vibrator group.

[0374] Furthermore, the electroacoustic converter is preferably as follows:

[0375] If the interval between adjacent piezoelectric vibrators of a plurality of piezoelectric vibrators is set to d, the distance between the piezoelectric vibrator located on the center side relative to the center position of the vibration plate in the arrangement direction of the piezoelectric vibrators and the viewing and listening position is set to L1, and the distance between the outer piezoelectric vibrator and the viewing and listening position is set to L2, then the range of L1×0.9<L2<L1×1.1 is satisfied.

[0376] First, use Fig. 20 The path difference is explained. Fig. 20 In FIG. 1 , only two piezoelectric vibrators are shown for the sake of explanation, but the same is true for a case where three or more piezoelectric vibrators are provided.

[0377] like Fig. 20 As shown in FIG. 1 , when piezoelectric vibrators (50k, 50l) are arranged on a flat vibration plate 102, the distance from the vibration plate 102 (electroacoustic transducer) to the viewing position P separated by a predetermined distance becomes a distance different from the piezoelectric vibrator. If the interval between the piezoelectric vibrator 50k and the piezoelectric vibrator 50l is d, and the angle formed by the line segment connecting the piezoelectric vibrator 50l on the side away from the viewing position P and the viewing position P and the vibration plate 102 is θ, the path difference b is expressed by b=d×cosθ.

[0378] At wavelengths where the path difference b is an odd multiple of half the wavelength, phase interference occurs between the acoustic wave emitted by the piezoelectric vibrator 50k and the acoustic wave emitted by the piezoelectric vibrator 501, resulting in mutual cancellation. Therefore, even if the number of piezoelectric vibrators is increased, the sound pressure does not increase, but may decrease.

[0379] According to the formula for the path difference b, by reducing the interval d between the piezoelectric vibrators, the path difference b can be reduced and the point sound source can be brought closer. However, there is a physical limit to bringing the piezoelectric vibrators closer together.

[0380] In contrast, Fig.21 The electroacoustic converter 100c shown in the figure has a vibration plate 102b and a vibrator group composed of a plurality of piezoelectric vibrators (50k, 50l) arranged on one surface of the vibration plate 102b. The vibration plate 102b is curved in the arrangement direction of the plurality of piezoelectric vibrators (50k, 50l), that is, in the vertical direction in the figure. In addition, the vibration plate 102b is curved in a manner concave toward the viewing position P. In addition, Fig.21 In the figure, only two piezoelectric vibrators are shown for the sake of explanation, but three or more piezoelectric vibrators may be provided.

[0381] By bending the vibration plate 102b in this way, the difference in distance from each piezoelectric vibrator (50k, 50l) to the viewing position P, i.e., the path difference, is reduced, thereby suppressing the occurrence of phase interference regardless of the wavelength. Therefore, in a structure having a plurality of piezoelectric vibrators, the sound pressure does not decrease, and the sound pressure can be increased by the additive effect.

[0382] Here, the viewing position P refers to the position of the user assumed when using the electroacoustic transducer, and is basically located on the horizontal center line of the display when the viewer is a single person. For example, when the electroacoustic transducer is used in combination with a display, the optimal viewing distance is set according to the size of the display, so the viewing position P can be set according to the viewing distance.

[0383] Alternatively, the structure may be as follows: the electroacoustic transducer (or a display incorporating the electroacoustic transducer) includes a driving device capable of changing the bending state (radius of curvature) of the vibration plate 102b and a sensor such as a human sensor for measuring the distance to the user, whereby the position of the user (audio-visual position P) is determined by the sensor, and the bending state (radius of curvature) of the vibration plate 102b is changed according to the determined audio-visual position.

[0384] Here, when one person is listening, the viewing position on the front center line is basically preferred, but if it deviates from the center line, the offset can be detected by the sensor, so it can be set to an asymmetric curve on the left and right to reduce the path difference b (so that L1 and L2 described later meet the following range).

[0385] Furthermore, a configuration may be adopted in which a user can arbitrarily set the bending state (curvature radius) of the vibration plate 102b.

[0386] Furthermore, the curvature radius R of the curved vibration plate 102 b may be set so that the distances from the piezoelectric vibrators ( 50 k , 50 l ) to the viewing position P become substantially the same.

[0387] Specifically, if Fig.21 As shown, if the distance from the center position of the vibration plate to the piezoelectric vibrator 50k on the center side and the viewing position in the arrangement direction of the plurality of piezoelectric vibrators is set to L1, and the distance from the piezoelectric vibrator 501 on the outer side than the piezoelectric vibrator 50k on the center side and the viewing position is set to L2, it is preferred to satisfy the range of L1×0.9<L2<L1×1.1.

[0388] By changing the curvature of the vibration plate 102b, the distances (L1, L2) from each piezoelectric vibrator (50k, 50l) to the viewing position P can be within the above range, that is, substantially the same. By reducing the difference between the distances L1 and L2, that is, the path difference, the phase interference can be suppressed regardless of the wavelength.

[0389] In addition, Fig.21 In the example shown, a structure having two piezoelectric vibrators is described; however, in the case of having three or more piezoelectric vibrators, the distances L2 from the piezoelectric vibrators located on the most central side to the viewing position preferably satisfy the above range, relative to the distance L1 from the piezoelectric vibrator to the viewing position.

[0390] <<Third embodiment>>

[0391] Here, the electroacoustic converter may be the following electroacoustic converter:

[0392] A vibrator group including a vibrator plate and a plurality of piezoelectric vibrators arranged on one surface of the vibrator plate.

[0393] If the interval between adjacent piezoelectric vibrators of a plurality of piezoelectric vibrators is set to d, the distance from the center position of the vibration plate to the piezoelectric vibrator on the center side and the viewing position in the arrangement direction of the piezoelectric vibrators is set to L1, and the distance from the outer piezoelectric vibrator to the viewing position is set to L2, then compared with the input timing of the input signal to the piezoelectric vibrator on the center side, the input timing of the input signal to the outer piezoelectric vibrator is advanced by time t = (L2-L1) / c.

[0394] Here, c (m / s) is the speed of sound.

[0395] As described above, when piezoelectric vibrators (50k, 501) are arranged on a flat vibration plate 102, the distance from the vibration plate 102 (electroacoustic transducer) to the viewing position P separated by a predetermined distance becomes a different distance for the piezoelectric vibrators, and a path difference b=d×cosθ is generated.

[0396] Basically, the same signal is input to each piezoelectric vibrator (50k, 50l) included in the same vibrator group. However, when each piezoelectric vibrator is driven at the same time, due to the presence of the path difference b, for example, the time until the sound wave emitted by the piezoelectric vibrator 50k and the sound wave emitted by the piezoelectric vibrator 50l reach the viewing position P is different. In this case, as described above, at a wavelength where the path difference b is an odd multiple of half the wavelength, the phase interference of the sound wave emitted by the piezoelectric vibrator 50k and the sound wave emitted by the piezoelectric vibrator 50l occurs, resulting in mutual cancellation. Therefore, even if the number of piezoelectric vibrators is increased, the sound pressure does not increase, but may decrease instead.

[0397] In contrast, the input timing of the input signal to the piezoelectric vibrator 501 which is at a longer distance from the viewing position P is set earlier than the input timing of the input signal to the piezoelectric vibrator 50k which is at a shorter distance from the viewing position P, so that the timing when the sound wave emitted by the piezoelectric vibrator 501 arrives at the viewing position P is approximately the same as the timing when the sound wave emitted by the piezoelectric vibrator 50k arrives at the viewing position P.

[0398] Specifically, if the distance from the piezoelectric vibrator 50k to the viewing position P is set to L1, the distance from the piezoelectric vibrator 50l to the viewing position P is set to L2, and the speed of sound is set to c (m / s), then by advancing the input time of the signal to the piezoelectric vibrator 50l by time t = (L2-L1) / c, the time when the sound wave emitted by the piezoelectric vibrator 50l arrives at the viewing position P can be made to be approximately the same as the time when the sound wave emitted by the piezoelectric vibrator 50k arrives at the viewing position P.

[0399] Thus, in a structure in which a plurality of piezoelectric vibrators are arranged on a vibration plate, the occurrence of phase interference can be suppressed regardless of the wavelength, so that the sound pressure does not decrease and the sound pressure can be increased by the additive effect.

[0400] In addition, the processing of inputting timing of the pressing electric vibrator shift signal may be performed using DPS or the like.

[0401] Here, in Fig. 22 In the example shown, two piezoelectric vibrators are described. However, when the vibrator group has more than three piezoelectric vibrators, the piezoelectric vibrator that is shortest in distance to the viewing position P, i.e., the piezoelectric vibrator on the center side of the vibration plate, is used as a reference. According to the path difference between the distance between each piezoelectric vibrator and the viewing position P relative to the reference piezoelectric vibrator, the input moment of the signal to each piezoelectric vibrator can be set to time t.

[0402] Furthermore, the following structure may be adopted: the electroacoustic transducer (or a display equipped with the electroacoustic transducer) is provided with a sensor for measuring the distance to the user, such as a human sensing sensor, so that the position of the user (audio-visual position P) is determined by the sensor, and the path difference between the distance between each piezoelectric vibrator and the audio-visual position P is calculated relative to the piezoelectric vibrator serving as the reference, with the piezoelectric vibrator having the shortest distance to the audio-visual position P being used as a reference, and the input time (time t) of the signal to each piezoelectric vibrator is set.

[0403] The electroacoustic transducer of the present invention may be a combination of the above-mentioned first and second embodiments, a combination of the first and third embodiments, a combination of the second and third embodiments, or a combination of the first to third embodiments.

[0404] For example, in a structure having a vibration plate and a vibration element group composed of a plurality of piezoelectric vibration elements arranged on one surface of the vibration plate, the plurality of piezoelectric vibration elements may be configured as follows: the plurality of piezoelectric vibration elements may belong to any one of the first to nth groups, and the upper limit frequency of the frequency band of the input signal input to the piezoelectric vibration element may be different for each group, and the upper limit frequency in each group may be set to f1 to f n When the upper limit frequency moves from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n The vibration plate gradually becomes lower, and is bent in the arrangement direction of the plurality of piezoelectric vibrators of the vibrator group.

[0405] Alternatively, for example, in a structure having a vibration plate and a vibration element group consisting of a plurality of piezoelectric vibration elements arranged on one surface of the vibration plate, the plurality of piezoelectric vibration elements may be configured as follows: the plurality of piezoelectric vibration elements may belong to any one of the first to nth groups, and the upper limit frequency of the frequency band of the input signal input to the piezoelectric vibration element may be different for each group, and the upper limit frequency in each group may be set to f1 to f n When the upper limit frequency moves from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n It gradually becomes lower, and among the multiple piezoelectric vibrators in the vibrator group, when the distance from one piezoelectric vibrator to the viewing position is longer than the distance from other piezoelectric vibrators to the viewing position by a path difference (L2-L1) (m), the input timing of the input signal to other piezoelectric vibrators is advanced by a time t=(L2-L1) / c compared with the input timing of the input signal to one piezoelectric vibrator.

[0406] For example, in the second embodiment in which the vibration plate is curved, if the radius of curvature of the vibration plate is made too small, the resonance frequency of the vibration plate becomes high, which may cause the sound pressure in the bass region to become low. Therefore, in the second embodiment, the following structure can be set: after the radius of curvature of the vibration plate is set to a level that the resonance frequency of the vibration plate does not become too high, the first embodiment and / or the third embodiment can be combined to suppress the occurrence of phase interference.

[0407] Furthermore, for example, in a structure including the third embodiment, the electroacoustic transducer (or a display incorporating the electroacoustic transducer) can be configured to have a driving device capable of changing the bending state (radius of curvature) of the vibration plate, and when the radius of curvature of the vibration plate is changed, the path difference (L2-L1) of the distance between each piezoelectric vibrator and the viewing position P relative to a reference piezoelectric vibrator is calculated, and the input timing of the signal to each piezoelectric vibrator is set to time t.

[0408] Furthermore, for example, in a structure in which an electroacoustic transducer (or a display incorporating an electroacoustic transducer) has a driving device capable of changing the bending state (radius of curvature) of a vibration plate and has a sensor such as a human sensor for measuring the distance to a user, a structure is set as follows: when the sensor detects one user, phase interference is suppressed by the structure of the second embodiment (or a combination of the second embodiment with the first embodiment and / or the third embodiment). A structure may also be set as follows: when the sensor detects two or more users, the vibration plate is not bent or is bent slightly, and phase interference is suppressed by combining the first embodiment and / or the third embodiment.

[0409] Alternatively, for example, in a structure including the first embodiment, the electroacoustic transducer (or a display incorporating the electroacoustic transducer) may include a driving device capable of changing the bending state (radius of curvature) of the vibration plate, and the structure may also be such that when the radius of curvature of the vibration plate is changed, the path difference (L2-L1) of each piezoelectric vibration relative to the distance between the reference piezoelectric vibrator and the viewing position P is calculated, and the frequency at which the path difference (L2-L1) cancels each other is calculated, and the upper limit frequency of the signal input by group, that is, the cutoff frequency of the low-pass filter is changed according to the frequency. When the low-pass filter function using the DPS is used, the cutoff frequency of the low-pass filter can be changed immediately.

[0410] As mentioned above, the electroacoustic transducer of the present invention has been described in detail, but the present invention is not limited to the above-mentioned examples, and various improvements or changes can be made without departing from the scope of the present invention.

[0411] Example

[0412] Below, enumerate specific embodiment of the present invention, the present invention is described in more detail. In addition, the present invention is not limited to this embodiment, as long as do not depart from the purpose of the present invention, then can suitably change the material shown in the following embodiment, usage, ratio, processing content, processing sequence etc.

[0413] [Example 1]

[0414] [Fabrication of piezoelectric film]

[0415] Through the above Figure 14 to Figure 16 The piezoelectric film was fabricated using the method shown.

[0416] First, cyanoethylated PVA (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 at the following composition ratio as piezoelectric particles, and stirred by a propeller mixer (rotation speed 2000 rpm), thereby preparing a coating for forming a piezoelectric layer.

[0417] ·PZT particles···········300 parts by mass

[0418] ·Cyanoethylated PVA···········30 parts by mass

[0419] ·DMF··············70 parts by mass

[0420] The PZT particles used were obtained by sintering a commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the powder so as to have an average particle size of 5 μm.

[0421] On the other hand, a sheet-like product was prepared in which a copper thin film with a thickness of 0.3 μm was vacuum-deposited on a PET film with a thickness of 4 μm. That is, in this example, the first electrode layer and the second electrode layer were copper-deposited thin films with a thickness of 0.3 μm, and the first protective layer and the second protective layer were PET films with a thickness of 4 μm.

[0422] The coating material for forming the piezoelectric layer prepared in advance was applied to the first electrode layer (copper vapor-deposited film) of the sheet-like object using a slant-sheet coater. The coating material was applied so that the film thickness of the coating film after drying would be 50 μm.

[0423] Next, the object coated with the coating on the sheet was heated and dried on a hot plate at 120° C. to evaporate DMF. Thus, a laminate having a first electrode layer made of copper on a first protective layer made of PET and a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 50 μm thereon was prepared.

[0424] The produced piezoelectric layer was polarized in the thickness direction.

[0425] On the piezoelectric laminate subjected to the polarization treatment, a sheet-like product in which a copper thin film was deposited on a PET film was laminated with the second electrode layer (copper thin film side) facing the piezoelectric layer.

[0426] Next, the piezoelectric laminate and the laminate of the sheet-like object were thermally pressed together at a temperature of 120° C. using a laminating device to adhere the piezoelectric layer and the second electrode layer, thereby producing a piezoelectric film.

[0427] [Fabrication of laminated piezoelectric element]

[0428] The produced piezoelectric film was cut into a rectangular shape of 180 mm × 220 mm in plane. A piezoelectric element was produced by stacking 5 layers of piezoelectric films by folding the cut piezoelectric film 4 times in the length direction. The plane shape of the stacked part was set to 180 mm × 40 mm, and the plane shape of the protruding part was set to 180 mm × 20 mm. The stacked piezoelectric films were glued together with an adhesive layer (acrylic adhesive). An electrode lead portion was formed on the protruding part protruding from the stacked part.

[0429] Five such stacked piezoelectric elements were produced.

[0430] <Production of electroacoustic converter>

[0431] The five stacked piezoelectric elements were pasted to the vibration plate. A PET plate with a thickness of 0.5 mm and a length of 690 mm x width of 1210 mm was used as the vibration plate. The vibration plate was divided into four equal parts along the horizontal direction so that the horizontal direction of the vibration plate was consistent with the length direction of the piezoelectric element. The stacked piezoelectric elements were pasted at five intervals in the vertical direction at the center of the right end area. The intervals between the stacked piezoelectric elements (stacked parts) were set to 40 mm. The piezoelectric element and the vibration plate were pasted with an adhesive layer (acrylic adhesive).

[0432] A power amplifier (STR-DH190 manufactured by Sony Corporation) was connected to each laminated piezoelectric element of the electroacoustic transducer as an amplifier. A sine sweep signal was input to the amplifier for frequency characteristic measurement, and a pink noise signal was input to the amplifier for power consumption measurement.

[0433] Furthermore, the output (volume) of the amplifier when an input signal is input to each stacked piezoelectric element is set to a volume position where the total power consumption becomes 75 W (15 W per unit) when a pink noise signal is input to the five transducers without performing the low-pass filtering process described later.

[0434] At this time, if Figure 2 As shown in the example, five stacked piezoelectric elements are divided into three groups, and amplifiers are connected to each group. In addition, the input signal is divided into three using a line separator (LS-01J) from FX-AUDIO, and then processed using a low-pass filter with a cutoff frequency set to the upper limit frequency of each group, and input to the amplifier respectively. In addition, the cutoff attenuation slope of the low-pass filter is set to 18dB / oct.

[0435] One stacked piezoelectric element is set as the first group, and the upper limit frequency of the input signal input to the stacked piezoelectric element is set to 20kHz. In addition, the other two stacked piezoelectric elements are set as the second group, and the upper limit frequency of the input signal input to the stacked piezoelectric element is set to 10kHz. In addition, the other two stacked piezoelectric elements are set as the third group, and the upper limit frequency of the input signal input to the stacked piezoelectric element is set to 4kHz.

[0436] [Comparative Example 1]

[0437] An electroacoustic transducer was produced in the same manner as in Example 1 except that an input signal having an upper limit frequency of 20 kHz was input to all of the five laminated piezoelectric elements.

[0438] [evaluate]

[0439] The sound pressure and power consumption in the high-frequency region were evaluated for the electroacoustic transducers of the respective examples and comparative examples.

[0440] The results are shown in Figure 3 and Figure 4 .

[0441] from Figure 3 It can be seen that the example of the present invention can improve the sound pressure in the high-frequency region and significantly reduce power consumption as compared with the comparative example.

[0442] From the above, it can be seen that the effect of the present invention is obvious.

[0443] In addition, in the above-described embodiment, the upper limit frequency of the input signal is configured to be different for each group, but the present invention is not limited thereto, and the lower limit frequency can also be configured to be different for each group. For example, in addition to increasing the sound pressure in the high-frequency region by making the upper limit frequency different for each group, the sound pressure in the low-frequency region, which is prone to excessive sound pressure, can be slightly reduced by making the lower limit frequency different, and the overall flat frequency characteristics can also be approached.

[0444] Explanation of symbols

[0445] 10-piezoelectric film, 11a, 11c-sheet, 11b-piezoelectric laminate, 19-adhesive layer, 20-piezoelectric layer, 24-first electrode layer, 26-second electrode layer, 28-first protective layer, 30-second protective layer, 34-matrix, 36-piezoelectric particles, 40, 42-conducting wire, 50, 50a to 50l-piezoelectric vibrator, 58-core rod, 60R, 60L-vibrator group, 100, 100b, 100c-electroacoustic converter Converter, 102, 102b-vibration plate, 104-adhesive layer, 120, 120b, 120c-circuit, 124G1, 124G2, 124G3-distributor, 125G1, 125G2, 125G3-low pass filter, 126, 126G1, 126G2, 126G3, 128-amplifier, 127-channel distributor, G1-first group, G2-second group, G3-third group, G4-fourth group.

Claims

1. An electroacoustic converter, wherein: The electroacoustic converter includes a vibration plate and a vibrator group consisting of a plurality of piezoelectric vibrators arranged on one surface of the vibration plate. The plurality of piezoelectric vibrators each belong to any group from the first group to the nth group, The upper limit frequency of the frequency band of the input signal input to the piezoelectric vibrator is different for each group. Assume that the upper limit frequency in each group is f1~f n When the upper limit frequency increases from the upper limit frequency f1 in the first group to the upper limit frequency f in the nth group n And gradually becomes lower.

2. The electroacoustic converter according to claim 1, wherein: Assuming that the number of the piezoelectric vibrators belonging to each group is N1 to N n When the number of piezoelectric vibrators in the first group N1 is increased to the number of piezoelectric vibrators in the nth group N n The number of the piezoelectric vibrators in each group satisfies N1≤N2≤N3≤…≤N n .

3. The electroacoustic converter according to claim 1 or 2, wherein: The upper limit frequency f1 in the first group is 15 kHz or more.

4. The electroacoustic converter according to claim 1 or 2, wherein: The electroacoustic converter has two vibrator groups. The two vibrator groups are arranged symmetrically with respect to a center line of the diaphragm in the left-right direction.

5. The electroacoustic converter according to claim 1 or 2, wherein: The piezoelectric vibrator includes a piezoelectric film including a piezoelectric layer and electrode layers provided on both surfaces of the piezoelectric layer.

6. The electroacoustic converter according to claim 5, wherein: The piezoelectric layer is composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material.

7. The electroacoustic converter according to claim 5, wherein: The piezoelectric vibrator is formed by stacking the piezoelectric film in multiple layers by folding the piezoelectric film one or more times.

8. The electroacoustic converter according to claim 1, wherein: The outer peripheries of two adjacent piezoelectric vibrators are parallel to each other, and the interval between the outer peripheries is 40 mm or less.

9. The electroacoustic converter according to claim 1 or 2, wherein: The vibration plate is bent in the arrangement direction of the plurality of piezoelectric vibrators of the vibrator group.

10. The electroacoustic converter according to claim 9, wherein: When the distance between the piezoelectric vibrator located on the center side of the vibration plate in the arrangement direction of the multiple piezoelectric vibrators and the viewing and listening position is L1, and the distance between the piezoelectric vibrator located on the outside in the arrangement direction of the multiple piezoelectric vibrators and the viewing and listening position is L2, the range of L1×0.9<L2<L1×1.1 is satisfied.

11. The electroacoustic converter according to claim 1 or 2, wherein: When the distance between the piezoelectric vibrator located at the center side of the vibration plate in the arrangement direction of the plurality of piezoelectric vibrators and the viewing position is L1, and the distance between the piezoelectric vibrator located at the outer side in the arrangement direction of the plurality of piezoelectric vibrators and the viewing position is L2, the input timing of the input signal to the outer piezoelectric vibrator is advanced by a time t=(L2-L1) / c compared to the input timing of the input signal to the piezoelectric vibrator on the center side, Here, c (m / s) is the speed of sound.

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