Acoustic transducers, acoustic equipment and ultrasonic oscillators

Abstract

To increase a sound voltage level per driving voltage, and being driven at the flat sound voltage level in a wide frequency band.SOLUTION: An acoustic transducer comprises: a vibration part having a diaphragm and a vibrator that is arranged onto the diaphragm to drive the diaphragm; a frame part that is arranged so as to enclose the vibration part; and a connection part that connects the vibration part with the frame part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an acoustic transducer, an acoustic device, and an ultrasonic oscillator. [Background technology]

[0002] In recent years, development of audio equipment such as earphones has been progressing for applications such as listening to music and watching videos, and video conferencing. The speaker drivers used in audio equipment, which are the sound generating means, are realized using, for example, MEMS (Micro Electro Mechanical Systems) technology. For example, piezoelectrically driven MEMS, which utilizes the contraction of piezoelectric films such as PZT (Lead Zirconate Titanate), which are easily miniaturized, due to the application of voltage, are often selected for speaker drivers. Such speaker drivers are required to be able to output a sound pressure level of 100 dB or more at 1 kHz with a low voltage (<10 V), and to maintain a flat sound pressure level across a wide frequency band.

[0003] Patent Document 1 discloses a piezoelectrically driven MEMS speaker driver that is a square piezoelectric MEMS in which a PZT film is formed on a silicon layer, with slits formed in two pairs of diagonal directions of the square, and is equipped with a cantilever structure in which only one side of a triangle is fixed. Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional speaker drivers using piezoelectrically driven MEMS, the goal is to improve the sound pressure level per voltage by thinning the silicon thickness of the MEMS part, improving the ease of driving the speaker surface, and increasing the volume velocity (amplitude displacement). However, this method poses the problem that resonance on the speaker surface occurs in the driving frequency band due to the silicon thickness of the MEMS part, making it impossible to achieve the flat sound pressure level required along with low-voltage driving.

[0005] The present invention has been made in view of the above, and has as its object to increase the sound pressure level per drive voltage and to drive at a flat sound pressure level over a wide frequency band. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present invention provides a sound generating device comprising: a vibration section including a vibration plate and a vibrating body arranged on the vibration plate to drive the vibration plate; a frame section arranged to surround the vibration section; and a connecting section connecting the vibration section and the frame section. The diaphragm is rectangular and has a plurality of notches in an area other than the center of the diaphragm, and the vibrator is formed between two adjacent notches of the plurality of notches and contacts the diaphragm at sides other than the four corners of the rectangle. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, it is possible to increase the sound pressure level per drive voltage and drive the piezoelectric element at a flat sound pressure level over a wide frequency band. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing the configuration of an acoustic transducer according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along the line AA' in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along the line BB' in FIG. [Figure 4] FIG. 4 is a plan view showing the configuration of a conventional acoustic transducer. [Figure 5] FIG. 5 is a diagram schematically illustrating the operation of the conventional acoustic transducer shown in FIG. [Figure 6] FIG. 6 is a diagram showing an example of peaks of sound pressure levels of the conventional acoustic transducer shown in FIG. [Figure 7] FIG. 7 is a diagram illustrating the operation of the acoustic transducer. [Figure 8] FIG. 8 is a diagram showing an example of peaks of the sound pressure level of an acoustic transducer. [Figure 9] FIG. 9 is a diagram illustrating a first modified example of the first embodiment. [Figure 10]FIG. 10 is a diagram illustrating a second modified example of the first embodiment. [Figure 11] FIG. 11 is a plan view showing the configuration of an acoustic transducer according to the second embodiment. [Figure 12] FIG. 12 is a diagram illustrating a first modified example of the second embodiment. [Figure 13] FIG. 13 is a plan view showing the configuration of an acoustic transducer according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an acoustic transducer, an acoustic device, and an ultrasonic oscillator will be described in detail with reference to the accompanying drawings.

[0010] (First embodiment) Fig. 1 is a plan view showing the configuration of an acoustic transducer 1 according to a first embodiment. As shown in Fig. 1, the acoustic transducer 1 is a piezoelectrically driven MEMS (Micro Electro Mechanical Systems) speaker driver. The acoustic transducer 1 includes a vibrating section 2, an outer fixed frame section 3 which is a frame section provided on the outside of the vibrating section 2 so as to surround the vibrating section 2, and an elastic member 4 which is a connecting section which elastically connects the vibrating section 2 and the outer fixed frame section 3.

[0011] The elastic members 4 are, for example, elastic springs, and are provided at the ends of the four sides of the square-shaped vibrating section 2.

[0012] The vibration unit 2 includes a square vibration plate 6 and a piezoelectric driver 7 disposed on the vibration plate 6 to drive the vibration plate 6. The piezoelectric driver 7 is an example of a vibrating body having a piezoelectric film formed thereon. The vibration plate 6 is made of silicon. The piezoelectric driver 7 is disposed over almost the entire area of ​​the vibration plate 6.

[0013] When a voltage is applied to the piezoelectric driver 7 along the surface direction, which is the XY plane, the piezoelectric film of the piezoelectric driver 7 contracts in the in-plane direction, and the piezoelectric driver 7 deforms in the surface direction as a unimorph with the diaphragm 6. When the voltage applied to the piezoelectric driver 7 is changed over time, the surface of the diaphragm 6 vibrates, generating pressure waves in the surrounding air, which are perceived by humans as sound.

[0014] The input voltage waveform is obtained by converting the waveform of the sound to be reproduced into a voltage, and sound is reproduced by inputting this voltage waveform to the piezoelectric driver 7.

[0015] 2 is a cross-sectional view taken along line AA' in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB' in FIG.

[0016] The piezoelectric driving section 7 has a structure in which a piezoelectric material 9 is sandwiched between an upper electrode 8 and a lower electrode 10. The diaphragm 6 is bonded to a support layer 12 and supported thereon.

[0017] When viewed from the outer fixed frame 3, the acoustic transducer 1 has a structure comprising an elastic member 4 between the outer fixed frame 3 and the vibrating unit 2, and the vibrating unit 2. For this reason, the resonance modes in the planar direction are two modes: a mode in which the vibration displacements of the vibrating unit 2 and the elastic member 4 are aligned, and an anti-resonance mode in which the vibration displacements of the vibrating unit 2 and the elastic member 4 are reversed by 180 degrees.

[0018] As shown in Fig. 3, the elastic member 4 may be formed of a diaphragm 6 made of silicon. In this case, the spring constant of the elastic member 4 can be changed by changing the thickness of the diaphragm 6 made of silicon or the dimensions of the elastic member 4, thereby enabling the design of a desired resonance / anti-resonance. The thickness of the elastic member is preferably in the range of 5 to 40 µm in order to ensure a sufficient sound pressure level.

[0019] As shown in FIG. 3, the elastic member 4 is formed of a diaphragm 6 made of silicon, but this is not limited to this, and the elastic member 4 can also be formed of a separate material from the diaphragm 6.

[0020] In this case, materials that can be used to form the elastic member 4 include materials that can be used in MEMS devices, such as Si, SiC, and epoxy-based materials, as well as materials that can be used in 3D printers, such as ABS resin, PLA resin, ASA resin, PP resin, PC resin, nylon resin, acrylic resin, PETG, and thermoplastic polyurethane. From the perspective of ease of manufacture, it is preferable that the elastic member 4 be formed from the same material as the diaphragm 6.

[0021] Here, the peak of the sound pressure level will be described.

[0022] First, the peak of the sound pressure level in a conventional acoustic transducer will be described, with reference to Fig. 4, which is a plan view showing the configuration of a conventional acoustic transducer.

[0023] As shown in Figure 4, a conventional acoustic transducer includes a square silicon diaphragm 26 and a piezoelectric driver 27 disposed on the diaphragm 26 to drive the diaphragm 26. When a voltage is applied in the planar direction of the piezoelectric driver 27, which is the XY plane, the piezoelectric film of the piezoelectric driver 27 contracts in the in-plane direction. Then, as a unimorph with the diaphragm 26, the piezoelectric driver 27 deforms in the planar direction. When the voltage applied to the piezoelectric driver 27 is changed over time, the diaphragm 26 acquires a velocity in the planar direction, generating pressure waves in the surrounding air that are perceived by humans as sound.

[0024] Fig. 5 is a diagram schematically illustrating the operation of the conventional acoustic transducer shown in Fig. 4, and Fig. 6 is a diagram illustrating an example of a peak in the sound pressure level of the conventional acoustic transducer shown in Fig. 4. In this case, m1 corresponds to the total mass of piezoelectric driver 27 and diaphragm 26 in the region where piezoelectric driver 27 is provided along the z axis (from the front to the back of the page) in Fig. 4, and k1 corresponds to the spring constant of piezoelectric driver 27 in Fig. 4. In other words, mass m1 is the mass of the inner region of piezoelectric driver 27, excluding diaphragm 26 in the region outside piezoelectric driver 27. The frequency ω of the primary resonance at this time is expressed by the following equation, and at this frequency the amplitude of diaphragm 6 becomes maximum, resulting in a peak in the sound pressure level.

[0025]

number

[0026] Therefore, when a conventional acoustic transducer has a cantilever structure, a resonance mode in which the piezoelectric driving part 27 vibrates in the plane direction may exist in the operating frequency band (20 to 30 kHz band) as shown in Fig. 5. When there is resonance in which the piezoelectric driving part 27 vibrates in the plane direction, as shown in Fig. 6, it is known that the surface velocity of the acoustic transducer also peaks at that frequency, and the frequency response of the sound pressure level also has a peak.

[0027] Therefore, when a conventional acoustic transducer has a cantilever structure, if there is a sound pressure level peak in the frequency band in which the acoustic transducer is used, it is necessary to drive the acoustic transducer in a frequency band that avoids the resonance frequency, or to modulate the original input signal, which poses a problem of reducing the reproducibility of the sound that the acoustic transducer can reproduce.

[0028] Next, a description will be given of the peak sound pressure level in the acoustic transducer 1 of this embodiment. Here, Fig. 7 is a diagram schematically showing the operation of the acoustic transducer 1, and Fig. 8 is a diagram showing an example of the peak sound pressure level of the acoustic transducer 1.

[0029] In this case, m1 corresponds to the total mass of the piezoelectric driver 7 in Fig. 1 and the diaphragm 6 in the region where the piezoelectric driver 7 is provided along the z axis of Fig. 4 (from the front to the back of the page), m2 corresponds to the total mass of the support layer 12 in Fig. 2 and the diaphragm 6 in the region where the support layer 12 is provided, k1 represents the spring constant of the diaphragm 6 in Fig. 1, and k2 represents the composite spring constant of the four elastic springs 4 in Fig. 1. In other words, mass m1 is the mass of the inner region that does not include the diaphragm 6 in the region outside the piezoelectric driver 7. Mass m2 is the mass of the outer region that does not include the diaphragm 6 in the region inside the vibrating body 7.

[0030] As shown in FIG. 7, if the left-right direction is the x-axis, and in the acoustic transducer 1, the right end position of the diaphragm 6 of mass m2 is set to x2 and the right end position of the diaphragm 6 is set to x1, the equation of motion is as follows:

[0031]

number

[0032] When the eigenvalues ​​of the above simultaneous equations are solved, the result is as follows:

[0033]

number

[0034] Here, the eigenvalue has two solutions, and therefore it can be seen that the structure of acoustic transducer 1 has two resonance points. Furthermore, in this solution, large and small eigenvalues ​​have different phases during vibration; with small eigenvalues, mass m2 and vibrating membrane mass m1 vibrate in phase, while with large eigenvalues, the respective masses vibrate with a phase difference of 180 degrees. When there is a 180-degree phase difference, the volume velocity can be reduced, thereby suppressing the peak sound pressure level. Furthermore, when they are in phase, the peak displacement during driving becomes larger.

[0035] On the other hand, it is known that the power spectrum for the vibration frequency of a speaker is proportional to the fourth power of the frequency in the low frequency range below resonance, is independent of frequency in the mid frequency range, and is inversely proportional to the square of the frequency in the high frequency range sufficiently higher than the resonance frequency.For this reason, by using the above formula to design eigenvalues ​​that are in phase with the low frequency range where radiation efficiency falls, and by designing eigenvalues ​​that are 180 degrees out of phase with the high frequency range where radiation efficiency falls, a structure with flat characteristics with small sound pressure level peaks can be achieved.

[0036] As described above, the resonant mode vibration frequency of the acoustic transducer 1 of this embodiment is lower than the resonant mode frequency obtained when the end of the vibrating part 2 is fixed, and the anti-resonant mode is higher. When the vibration of the surface of the acoustic transducer 1 is converted into a sound pressure level, the higher the frequency, the higher the conversion efficiency. Therefore, by being able to change the resonant mode to a lower frequency band, it is possible to reduce the sound pressure level peak. Furthermore, in the anti-resonant mode, the in-plane velocities of the vibrating part 2 and the elastic member 4 are in opposite directions, so the increase in volume velocity (amplitude displacement) is smaller than the normal peak. Therefore, it is possible to reduce the peak in the sound pressure level.

[0037] As shown in the example of the sound pressure level peak of the acoustic transducer 1 in Fig. 8, the arrow P1 indicates the sound pressure level peak due to the resonance mode, and the arrow P2 indicates the part where the flat characteristic is achieved due to the anti-resonance mode. As shown in Fig. 8, the acoustic transducer 1 has a small sound pressure level peak and a flat characteristic.

[0038] As described above, according to this embodiment, the acoustic transducer 1 has a structure in which an elastic member 4 is provided on the outer periphery of the vibrating part 2 on which the piezoelectric film is formed, and the elastic member 4 is connected to an outer fixed frame part 3 provided further outside the outer periphery of the vibrating part 2, thereby increasing the sound pressure level per driving voltage and enabling driving at a flat sound pressure level over a wide frequency band.

[0039] The configuration of the vibration section 2 is not limited to the configuration shown in Fig. 1. For example, in order to increase the driving speed of the vibration section 2, a cavity may be provided in the diaphragm 6.

[0040] [First Modification] FIG. 9 is a diagram illustrating a first modified example of the first embodiment.

[0041] The first modified example shown in Fig. 9 differs from the embodiment shown in Fig. 1 in that piezoelectric drive units 7 are not arranged at the four corners of the diaphragm 6. This improves the bending elasticity of the diaphragm 6 and reduces the reduction in sound pressure level that would otherwise occur due to the rigidity of the piezoelectric drive units 7 arranged at the four corners of the diaphragm 6. In addition, in the first modified example shown in Fig. 9, notches 60 are formed at the four corners of the diaphragm 6.

[0042] The notches 60 formed at the four corners of the vibration plate 6 may be square-shaped notches 60 adjacent to the piezoelectric driving unit 7 as shown in Figure 9(a), or may be L-shaped notches 60 adjacent to the piezoelectric driving unit 7 as shown in Figure 9(b).

[0043] This can reduce the reduction in sound pressure level caused by the rigidity of the four corners of the diaphragm 6, which would otherwise be due to an improvement in the bending elasticity of the diaphragm 6.

[0044] [Second Modification] FIG. 10 is a diagram illustrating a second modified example of the first embodiment.

[0045] In a second modified example shown in Fig. 10, a plurality of notches 60 are provided, each with a different longitudinal direction orientation compared to the embodiment shown in Fig. 1. Specifically, in the modified example shown in Fig. 10, the angle θ between the longitudinal direction orientation of each of the plurality of notches 60 and the side of the diaphragm 6 is other than 90 degrees. In the second modified example, the length of the notches 60 is increased without reducing the area of ​​the central part of the diaphragm 6, so that the sound pressure level does not decrease.

[0046] (Second embodiment) Next, a second embodiment will be described.

[0047] The second embodiment differs from the first embodiment in the configuration of the elastic member 4. In the following description of the second embodiment, the description of the same parts as in the first embodiment will be omitted, and only the parts that differ from the first embodiment will be described.

[0048] Fig. 11 is a plan view showing the configuration of an acoustic transducer 1 according to a second embodiment. In the acoustic transducer 1 according to the first embodiment, the elastic members 4 are provided at the ends of the four sides of the square-shaped vibration section 2, but this is not limited to this. As shown in Fig. 11, in the acoustic transducer 1 according to the second embodiment, in addition to the ends of the four sides of the square-shaped vibration section 2, the elastic members 4 are also provided near the center of each side.

[0049] Increasing the number of elastic members 4 of the same size in this way has the effect of increasing the resonance frequency of the anti-resonance mode, thereby increasing the degree of freedom in design.

[0050] [First Modification] FIG. 12 is a diagram illustrating a first modified example of the second embodiment.

[0051] In the first modified example shown in FIG. 12, two elastic members 4 are added to each of the four sides of the square-shaped vibration section 2 of the second embodiment shown in FIG.

[0052] When manufacturing the acoustic transducer 1, which is a piezoelectric-driven MEMS speaker driver, taking into consideration transportability and other factors, the greater the combined spring elastic modulus of the multiple elastic members 4, the easier it will be to manufacture without breaking them. However, if the combined spring elastic modulus of the multiple elastic members 4 becomes larger, the resonant frequency of the resonant mode will shift to a higher frequency.

[0053] (Third embodiment) Next, a third embodiment will be described.

[0054] In the third embodiment, the shape of the elastic member 4 is different from that of the first and second embodiments. In the following description of the third embodiment, the description of the same parts as those in the first and second embodiments will be omitted, and only the parts that differ from the first and second embodiments will be described.

[0055] Fig. 13 is a plan view showing the configuration of an acoustic transducer according to a third embodiment. While the elastic member 4 in the first and second embodiments has a rectangular shape, as shown in Fig. 13, the elastic member 4 in this embodiment has a meandering shape.

[0056] By making the shape of the elastic member 4 meandering in this way, the spring constant of the elastic member 4, which is an elastic spring, can be reduced, and the anti-resonance mode can be shifted to a lower frequency, thereby increasing design freedom.

[0057] The acoustic transducer 1 according to each embodiment can be applied to various types of acoustic devices such as speakers, earphones, electronic devices, portable electronic devices, etc. Furthermore, the acoustic transducer 1 according to each embodiment can also be applied to an ultrasonic oscillator that generates ultrasonic waves by vibration of the acoustic transducer 1.

[0058] The present invention has been described above in terms of preferred embodiments thereof. While the present invention has been described herein with reference to specific examples, it is apparent that various modifications and changes can be made to these examples without departing from the broad spirit and scope of the present invention as defined in the appended claims. In other words, the details of the examples and the accompanying drawings should not be construed as limiting the present invention. [Explanation of symbols]

[0059] 1 acoustic transducer 2 Vibration unit 3 Frame 4 Connection 6 diaphragm 7 Vibration body 60 notch [Prior art documents] [Patent documents]

[0060] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0178000

Claims

1. a vibration unit including a vibration plate and a vibrator disposed on the vibration plate to drive the vibration plate; a frame portion disposed to surround the vibration portion; a connecting portion that connects the vibration portion and the frame portion; Equipped with The diaphragm is rectangular and has a plurality of notches in an area other than the center of the diaphragm, the vibrator is formed between two adjacent notches among the plurality of notches and is in contact with the diaphragm at sides other than the four corners of the rectangle; An acoustic transducer characterized by:

2. the connecting portion elastically connects the vibrating portion and the frame portion, and separates the vibration resonance of the vibrating portion into resonance and anti-resonance.

2. The acoustic transducer according to claim 1.

3. The anti-resonance reduces the peak in the sound pressure level because the increase in amplitude displacement is smaller than the normal peak due to the in-plane velocity of the vibrating part and the connecting part being in opposite directions, and the resonance occurs in a low frequency range, reducing the peak in the sound pressure level.

3. The acoustic transducer according to claim 2.

4. The connecting portion is a rectangular elastic member.

4. The acoustic transducer according to claim 1, wherein the acoustic transducer is a piezoelectric element.

5. The connecting portion is an elastic member having a meander structure.

4. The acoustic transducer according to claim 1, wherein the acoustic transducer is a piezoelectric element.

6. The connection portions are provided at the ends of four sides of the square-shaped vibrating portion.

6. An acoustic transducer according to claim 1, wherein the acoustic transducer is a piezoelectric element.

7. The connection portions are provided at the ends of four sides of the square-shaped vibration portion and between the ends of the four sides of the vibration portion.

6. An acoustic transducer according to claim 1, wherein the acoustic transducer is a piezoelectric element.

8. The connection portion realizes two modes: a resonance mode in which the vibration displacements of the connection portion and the vibration portion are aligned, and an anti-resonance mode in which the vibration displacements of the connection portion and the vibration portion are reversed by 180 degrees.

8. An acoustic transducer according to claim 1, wherein the acoustic transducer is a piezoelectric element.

9. An acoustic transducer comprising: an acoustic transducer according to any one of claims 1 to 8; An audio device characterized by:

10. An acoustic transducer comprising: an acoustic transducer according to any one of claims 1 to 8; An ultrasonic oscillator characterized by:

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