Electrostatic speaker

Abstract

To provide an electrostatic speaker which can be implemented without using a piezo electric element.SOLUTION: The electrostatic speaker comprises: a case; a fixed interdigital electrode part fixed to the case and including a plurality of interdigitals; a movable interdigital electrode part including a plurality of interdigitals engaged with the respective interdigitals of the fixed interdigital electrode part via a space; a vibration film connected to the movable interdigital electrode part; and a board connected to the fixed interdigital electrode part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to electrostatic speakers. [Background technology]

[0002] Conventional MEMS speakers mainly use a method of driving a diaphragm with a piezoelectric element, such as the MEMS acoustic transducer disclosed in Patent Document 1.

[0003] The MEMS acoustic transducer in Patent Document 1 includes a substrate, a vibrating membrane formed within the substrate, and a bending actuator applied to the vibrating membrane. The vibrating membrane includes at least one integrated permanent magnet and is electromechanically controllable. The bending actuator can be piezoelectrically controlled separately from the vibrating membrane. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 178000 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional structures using piezoelectric elements directly drive the diaphragm, which tends to generate unnecessary distortion vibrations. Furthermore, attaching the piezoelectric element increases the weight of the entire vibrating section, reducing amplitude. Furthermore, the need to attach the piezoelectric element during the manufacturing process complicates the process.

[0006] Therefore, an object of the present disclosure is to provide an electrostatic speaker that can be realized without using a piezoelectric element. [Means for solving the problem]

[0007] The electrostatic speaker of the present disclosure includes a case, a fixed comb electrode portion, a movable comb electrode portion, a diaphragm, and a substrate.

[0008] The fixed comb-teeth electrode portion is fixed to the case and includes a plurality of comb teeth. The movable comb-teeth electrode portion includes a plurality of comb teeth that mesh with the respective comb teeth of the fixed comb-teeth electrode portion via gaps. The vibration membrane is connected to the movable comb-teeth electrode portion. The substrate is connected to the fixed comb-teeth electrode portion. [Effects of the Invention]

[0009] The electrostatic speaker of the present disclosure can be realized without using a piezoelectric element. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of an electrode assembly of an electrostatic speaker according to a first embodiment. [Figure 2] FIG. 2 is a plan view of the electrode assembly of the electrostatic speaker according to the first embodiment. [Figure 3] 1 is a cross-sectional view of an electrode assembly of an electrostatic speaker according to a first embodiment. [Figure 4] 1 is a cross-sectional view of an electrode assembly of an electrostatic speaker according to a first embodiment. [Figure 5] 4A and 4B are diagrams illustrating the operating principle of the movable comb electrode portion. [Figure 6] FIG. 10 is a perspective view of an electrode assembly of an electrostatic speaker according to a second embodiment. [Figure 7] FIG. 10 is a cross-sectional view of an electrode assembly of an electrostatic speaker according to a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view of an electrode assembly of an electrostatic speaker according to a first modification. [Figure 9] FIG. 10 is a cross-sectional view of an electrostatic speaker according to a second modification. [Figure 10] FIG. 10 is a cross-sectional view of an electrostatic speaker according to a third modification. [Figure 11] FIG. 10 is a cross-sectional view of an electrostatic speaker according to a fourth modification. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. Note that components having the same functions are assigned the same numbers, and redundant explanations will be omitted. [Example]

[0012] The structure of the electrode assembly, which is an assembly obtained by removing the case from the electrostatic speaker of Example 1, will be described below with reference to Figures 1 to 4. As shown in Figure 1, the explanation will be given assuming that the direction in which the multiple comb-teeth electrodes of the fixed comb-teeth electrode portion 102 of the electrode assembly 10 of this example are aligned is the +x / -x direction, the direction in which the comb teeth of each comb-teeth electrode extend is the +y / -y direction, and the movable direction of the movable comb-teeth electrode portion 103 is the +z / -z direction. The electrode assembly 10 of this embodiment includes a rectangular frame 101, a fixed comb-teeth electrode section 102 fixed to the frame 101 and including a plurality of comb teeth extending from each of two opposing inner sides of the frame 101, a movable comb-teeth electrode section 103 including a plurality of comb teeth that mesh with each of the comb teeth of the fixed comb-teeth electrode section 102 via gaps, a vibration membrane 104 disposed near the center of the inner side of the frame 101, with the movable comb-teeth electrode section 103 connected to each of its two sides and positioned so as not to contact the fixed comb-teeth electrode section 102, a substrate 105 connected to the fixed comb-teeth electrode section 102 via the frame 101 (see FIGS. 3 and 4), and a spring 106 connecting the frame 101 and the vibration membrane 104. The electrode assembly 10 is fixed to a case (not shown). The movable comb-teeth electrode section 103 is movable in the +z / -z directions between predetermined positions by a drive mechanism (not shown). The substrate 105 includes a circuit for boosting an input signal and a bias voltage circuit for positioning the movable comb electrode portion 103 at a predetermined position by a drive mechanism (not shown).

[0013] 5 shows the operating principle of the movable comb-tooth electrode unit 103. As shown in the figure, after the movable comb-tooth electrode unit 103 is stably positioned at a predetermined position using a bias voltage, a Coulomb force is generated between the fixed comb-tooth electrode unit 102 and the movable comb-tooth electrode unit 103 in response to an input signal, displacing the position of the movable comb-tooth electrode unit 103 in the +z / -z direction and driving the vibrating membrane 104 in conjunction with the movable comb-tooth electrode unit 103.

[0014] As shown in FIGS. 1 and 2, it is preferable to connect the movable comb-tooth electrode portion 103 and the vibration membrane 104 in a direction (+y / -y direction in the example of the figures) perpendicular to the direction of movement of the movable comb-tooth electrode portion 103 (+z / -z direction), as this simplifies the process and contributes to a thinner design. The movable comb-tooth electrode portion 103 is generally made thinner than the vibration membrane 104, but this is not limited to this. For example, the movable comb-tooth electrode portion 103 and the vibration membrane 104 may be integrated, and the movable comb-tooth electrode portion 103 and the vibration membrane 104 may have the same thickness. Furthermore, the thickness of the movable comb-tooth electrode portion 103 may be made thicker than the vibration membrane 104 for design purposes. [Example]

[0015] The structure of the electrode assembly, which is an assembly obtained by removing the case from the electrostatic speaker of Example 2, will be described below with reference to Figures 6 and 7. As shown in Figure 6, electrode assembly 20 of this example includes thin, disk-shaped diaphragm 201, cylindrical movable connecting part 202, square plate-shaped fixed connecting part 203 with circular hole 203a at its center, annular movable comb electrode part 204 with a comb-tooth pattern formed thereon, cylindrical shaft 205 formed at the center of movable comb electrode part 204, annular fixed comb electrode part 206 with a comb-tooth pattern formed thereon, square plate-shaped frame 207 with fixed comb electrode part 206 at its center and with circular hole 207a at the center of fixed comb electrode part 206 (corresponding to the hole portion of the annular shape), and square plate-shaped substrate 208 with circular hole 208a at its center.

[0016] The movable direction of the movable comb electrode portion 204 is the +z / -z direction, and in the following description, the +z direction will be referred to as the upward direction or simply "up", and the -z direction will be referred to as the downward direction or simply "down".

[0017] In the figure, the details of the comb tooth pattern of the movable comb tooth electrode portion 204 and the details of the comb tooth pattern of the fixed comb tooth electrode portion 206 are omitted, but in reality, the comb tooth patterns are formed in the hatched areas in the figure. As in Example 1, each comb tooth of the fixed comb tooth electrode portion 206 and each comb tooth of the movable comb tooth electrode portion 204 are formed to mesh with each other via a gap.

[0018] Hereinafter, the electrode assembly 20 will be described by dividing it into a portion fixed to the case (fixed portion) and a portion movable relative to the case (movable portion).

[0019] <Fixed part> The fixed portion includes the peripheral portion of the vibration membrane 201 , the fixed connection portion 203 , the fixed comb-teeth electrode portion 206 , the frame 207 , and the substrate 208 .

[0020] Fixed connection portion 203 has a predetermined length L in the direction in which movable comb-teeth electrode portion 204 can move (+z direction / -z direction). The upper edge of hole 203a in fixed connection portion 203 is adhesively fixed to the peripheral portion of the lower surface of vibration membrane 201. The lower surface of fixed connection portion 203 and the upper surface of frame 207 are adhesively fixed by adhesive layer 210. This connects fixed comb-teeth electrode portion 206 and the peripheral portion of vibration membrane 201. The lower surface of frame 207 and the upper surface of substrate 208 are adhesively fixed by adhesive layer 210.

[0021] <Movable parts> The movable portion includes the center of the vibration membrane 201 , the movable connection portion 202 , the movable comb electrode portion 204 , and the shaft 205 .

[0022] The lower surface of the central portion of vibrating membrane 201 is adhesively fixed to the upper surface of movable connecting part 202. Vibrating membrane 201 can be made of, for example, a resin material. Different materials may be laminated on vibrating membrane 201 to achieve desired acoustic characteristics. Movable connecting part 202 has a predetermined length L in the direction of movement of movable comb electrode part 204 (+z direction / -z direction). The lower surface of movable connecting part 202 and the upper surface of shaft 205 are adhesively fixed by adhesive layer 210. This connects movable comb electrode part 204 and the central portion of vibrating membrane 201.

[0023] As shown in Figure 7, the SiO2 layer 209 remains on the shaft 205, the fixed comb-tooth electrode portion 206, and the frame 207. The reason for providing the SiO2 layer 209 is to form and separate the comb-tooth electrodes by stopping the etching of Si at the SiO2 layer 209. In other words, the movable comb-tooth electrode portion 204 is formed by anisotropically etching the lower side so that the layers above the SiO2 layer 209 remain, and the fixed comb-tooth electrode portion 206 is formed by anisotropically etching the upper side so that the layers below the SiO2 layer 209 remain. Finally, the unnecessary portions of the SiO2 layer 209 are removed to separate the electrodes.

[0024] This allows the height of the comb-tooth electrodes to be controlled, but the height of the comb-tooth electrodes may also be controlled by other methods.

[0025] In this embodiment, since the electrode assembly 20 is configured as described above, the diaphragm 201 and the movable comb-teeth electrode portion 204 can be arranged on different planes separated by a distance L, and the diaphragm 201 is shaped to cover each of the comb-teeth electrodes. This allows the area of ​​the diaphragm 201 to be increased, thereby reducing the drive voltage. In addition, the area of ​​each comb-teeth electrode portion can be increased, improving the efficiency of the diaphragm driving force. Furthermore, since the electrode assembly 20 is structured so that the diaphragm 201 covers the entire sealed space, generated sound waves do not bend around in front of or behind the diaphragm 201, improving low-frequency output.

[0026] In this embodiment, the electrode assembly is disclosed that includes one comb-tooth electrode portion of each type. However, for example, the electrode assembly may be configured to include a plurality of comb-tooth electrode portions of each type.

[0027] [Variation 1] Although the above-described electrode assembly 20 uses the vibrating membrane 201, a vibrating plate having higher rigidity than the vibrating membrane 201 may be used instead of the vibrating membrane 201. In this case, as shown in Fig. 8, a vibrating plate 211 smaller than the dimensions of the hole 203a of the fixed connecting part 203 may be arranged, and a similar plate 213 may be arranged so as to surround the periphery of the vibrating plate 211, with the lower surface of the plate 213 adhesively fixed to the upper surface of the fixed connecting part 203, and the vibrating plate 211 and the plate 213 may be connected by a spring 212, thereby ensuring the mobility of the vibrating plate 211.

[0028] [Variation 2] Below, variations on the electrode assembly and case shape will be disclosed in Modifications 2-4. For example, as shown in Fig. 9, a case 31 shaped to cover the top of the electrode assembly 10 of Example 1 may be adhesively fixed to the outer edge of a substrate 105 extending outward from the electrode assembly 10, and an air chamber 32 may be formed by the case 31 and the substrate 105. A sound hole 31a may be formed in the top surface of the case 31.

[0029] [Variation 3] Furthermore, as shown in Figure 10, a case 31 shaped to cover the top of the electrode assembly 10 of Example 1 may be adhesively fixed to the outer edge of a substrate 105 extending outward from the electrode assembly 10, and an air chamber 32 may be formed by the case 31 and the substrate 105, with a sound hole 105a formed in the substrate 105.

[0030] [Variation 4] 11 , an upper case 311 shaped to cover the upper part of the electrode assembly 10 of Example 1 may be adhered and fixed to the outer edge of the substrate 105 extending outward from the electrode assembly 10, and a lower case 312 shaped to cover the lower part of the electrode assembly 10 may be adhered and fixed to the outer edge of the substrate 105, with sound hole 105a formed in the substrate 105 and sound hole 312a formed in the lower case 312. As a result, the space between the upper case 311 and the substrate 105 functions as a rear chamber 321, and the space between the lower case 312 and the substrate 105 functions as a front chamber 322.

[0031] Furthermore, if the sound holes 31a, 105a, 312a of the above-mentioned modified example 2-4 are covered with a porous sheet, the wind will not blow directly onto the comb-tooth electrode portion and the diaphragm, eliminating the risk of damage, which is preferable.

[0032] In the above-described modified example 2-4, the electrode assembly 10 of the first embodiment is exemplified, but in the above-described modified example 2-4, the electrode assembly 10 can be replaced with the electrode assembly 20.

[0033] <Effects> According to the electrostatic speaker, electrode assembly 10, electrode assembly 20, and modifications thereof of the present disclosure, the speaker is realized without using a piezoelectric element, and therefore the MEMS process can be made consistent.

[0034] Parallel plate type speakers commonly seen in conventional capacitance systems require a drive voltage of several hundred volts or more, but by adopting a comb-tooth structure and separating the drive unit from the drive plate unit, the required voltage can be reduced to several tens of volts.

Claims

1. Case and a fixed comb electrode portion fixed to the case and including a plurality of comb teeth; a movable comb-teeth electrode portion including a plurality of comb teeth that mesh with the respective comb teeth of the fixed comb-teeth electrode portion via gaps; a vibration membrane connected to the movable comb electrode portion; A substrate connected to the fixed comb-teeth electrode portion is included. Electrostatic speaker.

2. 2. An electrostatic speaker according to claim 1, The movable comb electrode portion and the vibration membrane are connected in a direction perpendicular to the movable direction of the movable comb electrode portion. Electrostatic speaker.

3. 2. An electrostatic speaker according to claim 1, a movable connection portion that connects the movable comb electrode portion and a center portion of the vibration membrane and has a predetermined length in a direction in which the movable comb electrode portion moves; a fixed connection portion that connects the fixed comb electrode portion and a peripheral portion of the vibration membrane and has a predetermined length in the direction in which the movable comb electrode portion moves; Electrostatic speaker.

4. 4. An electrostatic speaker according to claim 3, The vibrating membrane is The shape covers each comb-tooth electrode part. Electrostatic speaker.

5. 2. An electrostatic speaker according to claim 1, Each comb-tooth electrode includes multiple parts Electrostatic speaker.

6. 2. An electrostatic speaker according to claim 1, An air chamber is formed by the case and the substrate. Electrostatic speaker.

7. 7. An electrostatic speaker according to claim 6, A sound hole is formed in the case Electrostatic speaker.

8. 7. An electrostatic speaker according to claim 6, A sound hole is formed in the substrate. Electrostatic speaker.

9. 9. An electrostatic speaker according to claim 8, The case is an upper case covering an upper surface of the substrate; a lower case covering a lower surface of the substrate; a space between the upper case and the substrate functions as a rear chamber; The space between the lower case and the substrate functions as a front chamber. Electrostatic speaker.

10. 2. An electrostatic speaker according to claim 1, The substrate is A circuit for boosting an input signal and a bias voltage circuit for placing the movable comb electrode portion at a predetermined position are included. Electrostatic speaker.

11. 8. An electrostatic speaker according to claim 7, A porous sheet covering the sound hole Electrostatic speaker.

12. 9. An electrostatic speaker according to claim 8, A porous sheet covering the sound hole Electrostatic speaker.

Images