JP5113002B2 - Electroacoustic transducer - Google Patents

Description

  The present invention relates to an electroacoustic transducer, and more particularly to a device that converts an electrical signal into an acoustic signal using electrowetting.

  A typical example of an electroacoustic transducer is a speaker. As the speaker, an electrodynamic type is widely used. An electrodynamic type speaker causes a voice current to flow through a voice coil disposed in a magnetic field of a permanent magnet, and uses a Lorentz force acting on the current in the magnetic field to vibrate the voice coil and the vibration plate coupled thereto. (For example, refer to Patent Document 1).

  Although not as popular as the electrodynamic type, there is also an electrostatic type speaker that uses an electrostatic force acting between the electrodes. An electrostatic speaker is configured to vibrate electrodes by applying a voltage corresponding to an audio signal between the electrodes (see, for example, Patent Document 2).

  In addition, there is a piezoelectric speaker using the electrostrictive effect of a piezoelectric element. A piezoelectric speaker applies a voltage corresponding to an audio signal to a piezoelectric element to cause stretching vibration (see, for example, Patent Document 3).

Although not an electroacoustic transducer, an electrowetting device has emerged as a device that converts electrical signals into mechanical behavior. An electrowetting device places a droplet on a set of electrodes, changes the contact angle by adjusting the surface tension of the solid-liquid interface with the voltage applied to the electrodes, and changes the shape of the droplet (For example, refer to Patent Document 4).
Japanese Patent Laying-Open No. 2008-177692 (paragraph number 0018, FIGS. 1 and 2) JP 2008-118513 A (paragraph number 0010-0013, FIGS. 1 and 2) JP 2008-92518 (paragraph number 0024-0025, FIG. 1-3) Japanese Patent Laying-Open No. 2005-185090 (paragraph number 0033, FIG. 1)

An electrodynamic loudspeaker is suitable for obtaining a large amplitude acoustic vibration, but a magnetic circuit, a voice coil, and the like are indispensable. Therefore, the electrodynamic loudspeaker has a complicated structure with a large number of parts and is not suitable for downsizing and thinning.
In contrast, electrostatic loudspeakers are suitable for downsizing and thinning, but they are structured to vibrate the thin film supported by tension, making it difficult to ensure stability in manufacturing and use, and between the electrodes. Since the electrostatic force rapidly decreases as the electrode interval increases, a very high voltage is required to increase the vibration amplitude.

A piezoelectric speaker is also suitable for downsizing and thinning, but it is difficult to obtain a large amplitude because the expansion ratio of the piezoelectric element is small, and it is disadvantageous in terms of sound quality because it uses the resonance of the piezoelectric element.
Although the electrowetting device is suitable for miniaturization and thinning, the volume velocity of the droplet deformed by the electric signal becomes 0 as a whole, and therefore, the sound is not effective except for the wavelength close to the droplet size. For this reason, it cannot be used as it is as a speaker.

  Accordingly, an object of the present invention is to realize an electroacoustic transducer that is suitable for downsizing and thinning and that can easily obtain acoustic vibrations of large amplitude.

  The invention according to claim 1 as means for solving the problem includes a holding means for holding a droplet in a state where the surface is divided into at least two, and the droplet is vibrated by electrowetting based on an electric signal. It is an electroacoustic transducer characterized by comprising a driving means for deforming it.

  The invention according to claim 2 as means for solving the problem is that the holding means has a support plate that supports the droplets, and faces the support plate so that the droplets are partially exposed from the holes. 2. The apparatus according to claim 1, further comprising: a counter plate sandwiched in a state, wherein the driving unit includes a pair of electrodes in contact with the droplet and a driving source that applies an electric signal to the pair of electrodes. It is an electroacoustic transducer as described in (1).

  The invention according to claim 3 as means for solving the problem is the electroacoustic transducer according to claim 2, wherein the support plate and the counter plate also serve as the one set of electrodes. .

  The invention according to claim 4 as means for solving the problem is that the support plate also serves as one electrode of the set of electrodes, and the one electrode on the side in contact with the droplet is The electroacoustic transducer according to claim 2, comprising the other insulated electrode.

  The invention according to claim 5 as means for solving the problem is characterized in that the support plate and the counter plate each have one electrode and the other electrode of the set of electrodes. Item 3. The electroacoustic transducer according to Item 2.

  The invention according to claim 6 as means for solving the problem is characterized in that at least one of the pair of electrodes is in contact with the droplet through a water repellent layer. It is an electroacoustic transducer of description.

  The invention according to claim 7 as means for solving the problem is characterized in that at least one of the pair of electrodes is in contact with the droplet through an insulating layer. This is an electroacoustic transducer.

  The invention according to claim 8 as means for solving the problem is the electroacoustic transducer according to claim 2, wherein the support plate, the counter plate, and the set of electrodes are flat plates. is there.

The invention according to claim 9 as means for solving the problem is the electroacoustic transducer according to claim 8, wherein the flat plate is flexible.
The invention according to claim 10 as means for solving the problems is characterized in that the support plate, the counter plate, and the set of electrodes are non-flat plates. It is.

The invention according to claim 11 as means for solving the problem is the electroacoustic transducer according to claim 10, wherein the non-flat plate is non-flexible.
The invention according to claim 12 as means for solving the problems is characterized in that the droplet, the support plate, the counter plate, and the set of electrodes are transparent. It is an acoustic converter.

  The invention according to claim 13 as means for solving the problem is the electroacoustic transducer according to claim 1, wherein the electric signal is an AC voltage biased in a DC direction.

The invention according to claim 14 as means for solving the problem is the electroacoustic transducer according to claim 13, wherein the DC bias is larger than the AC voltage.
The invention according to claim 15 as means for solving the problem is the electroacoustic transducer according to claim 13, wherein the AC voltage is derived from an audio signal.

The invention according to claim 16 as means for solving the problem is the electroacoustic transducer according to claim 1, wherein the droplet is a water droplet.
The invention according to claim 17 as means for solving the problem is the electroacoustic transducer according to claim 1, wherein the droplet is a droplet of an electrolytic solution.

The invention according to claim 18 as means for solving the problem is the electroacoustic transducer according to claim 1, wherein the droplet is an ionic liquid droplet.
The invention according to claim 19 as means for solving the problem is the electroacoustic transducer according to claim 1, wherein the droplets are a plurality of independent droplets.

The invention according to claim 20 as means for solving the problem is the electroacoustic transducer according to claim 19, wherein the plurality of droplets are arranged in an array.
The invention according to claim 21 as means for solving the problem is the electroacoustic transducer according to claim 20, wherein the array is a one-dimensional array.

  The invention according to claim 22 as means for solving the problem is the electroacoustic transducer according to claim 20, wherein the array is a two-dimensional array.

  According to the first aspect of the present invention, the electroacoustic transducer includes a holding unit that holds a droplet in a state where the surface is divided into at least two surfaces, and the droplet is vibrated by electrowetting based on an electric signal. Therefore, it is possible to realize an electroacoustic transducer that is suitable for downsizing and thinning and can easily obtain a large amplitude acoustic vibration.

  According to the invention of claim 2, the holding means includes a support plate that supports the droplets, and a counter plate that faces the support plate and sandwiches the droplets with the droplets partially exposed from the holes. And the drive means has a set of electrodes in contact with the droplets and a drive source for applying an electric signal to the set of electrodes. An electroacoustic transducer that can be easily obtained can be realized.

According to the invention which concerns on Claim 3, since the said support plate and the said opposing board serve as said 1 set of electrodes, the components for electroacoustic transducer structure can be decreased.
According to the invention of claim 4, the support plate also serves as one electrode of the set of electrodes, and the other electrode insulated from the one electrode on the side in contact with the droplet. Therefore, the electrodes can be concentrated on the support plate side.

  According to the invention according to claim 5, since the support plate and the counter plate have one electrode and the other electrode of the set of electrodes, respectively, the support and driving of the droplet are appropriately shared. be able to.

According to the invention of claim 6, since at least one of the one set of electrodes contacts the droplet through the water repellent layer, it is possible to appropriately perform electrowetting.
According to the invention of claim 7, since at least one of the pair of electrodes contacts the droplet through the insulating layer, electrolysis of the droplet can be prevented, and electrowetting Can be performed stably.

According to the invention which concerns on Claim 8, since the said support plate, the said opposing plate, and said 1 set of electrode are flat plates, a flat-shaped electroacoustic transducer can be obtained.
According to the invention of claim 9, since the flat plate is flexible, diversification of the surface shape is easy.

According to the invention concerning Claim 10, since the said support plate, the said opposing plate, and said 1 set of electrode are non-plates, a non-plate-shaped electroacoustic transducer can be obtained.
According to the eleventh aspect of the present invention, the non-flat plate is non-flexible, so that it is easy to maintain the surface shape.

According to the twelfth aspect of the invention, since the droplet, the support plate, the counter plate, and the set of electrodes are transparent, a transparent electroacoustic transducer can be obtained.
According to the invention of claim 13, since the electric signal is an AC voltage biased in a DC manner, an acoustic vibration having the same frequency as the frequency of the AC voltage can be obtained.

According to the invention of claim 14, since the DC bias is larger than the AC voltage, the ratio of the second harmonic component can be reduced.
According to the fifteenth aspect of the invention, since the AC voltage is derived from an audio signal, audio vibration can be obtained.

According to the invention of claim 16, since the droplet is a water droplet, procurement is easy.
According to the invention of claim 17, since the droplet is a droplet of an electrolytic solution, the properties of the droplet can be easily adjusted.

According to the invention of claim 18, since the droplet is an ionic liquid droplet, a nonvolatile droplet can be obtained.
According to the nineteenth aspect of the invention, since the droplets are a plurality of independent droplets, a plurality of acoustic generation sources can be provided.

According to the twentieth aspect, since the plurality of droplets are arranged in an array, sound can be increased by output synthesis.
According to the invention of claim 21, since the array is a one-dimensional array, sound output synthesis can be performed one-dimensionally.

  According to the invention of claim 22, since the array is a two-dimensional array, sound output synthesis can be performed two-dimensionally.

The best mode for carrying out the invention will be described below in detail with reference to the drawings. The present invention is not limited to the best mode for carrying out the invention.
FIG. 1 schematically shows the configuration of the electroacoustic transducer 1. The electroacoustic transducer 1 is an example of the best mode for carrying out the invention. An example of the best mode for carrying out the invention relating to the electroacoustic transducer is shown by the configuration of this device.

  As shown in FIG. 1, the electroacoustic transducer 1 has a configuration in which a droplet 10 is sandwiched between a pair of electrodes 12 and 14 and an electric signal is applied from the drive unit 16 to the electrodes 12 and 14. The facing distance between the electrodes 12 and 14 is fixed. The electrical signal applied from the drive unit 16 to the electrodes 12 and 14 is a voltage.

  The electrode 12 is in contact with the droplet 10 through the insulating layer 122, and the electrode 14 is in contact with the droplet 10 with a part of the droplet 10 being exposed from the through hole 142. As a result, the surface of the droplet 10 is divided into a portion exposed from the through hole 142 and a portion sandwiched between the electrodes 12 and 14.

The surface of the insulating layer 122 has water repellency. The water repellency is imparted by a surface water-repellent treatment or a water-repellent layer formed on the surface. Thus, the insulating layer 122 also serves as a water repellent layer.
The electrodes 12, 14 also have water repellency. Similarly to the electrode 12, the electrode 14 may be brought into contact with the droplet 10 through an insulating layer (water repellent layer). Alternatively, the electrode 12 may be brought into direct contact with the droplet 10 without using the insulating layer 122.

  The configuration of the electroacoustic transducer 1 is basically the same as that of an existing electrowetting device, but a through hole 142 is provided in the electrode 14 so that a part of the droplet 10 is exposed to the outside. The configuration is different from the existing one.

  The droplet 10 is an example of a droplet in the present invention. For example, water is used as the liquid forming the droplet 10. Water is preferable in terms of easy procurement. The liquid may be an electrolytic solution. The electrolytic solution is preferable in that the properties of the droplets can be adjusted by selecting the electrolyte. As the electrolytic solution, for example, a NaCl solution or a KCl solution is used.

  The liquid may also be a room temperature molten salt or ionic liquid. The ionic liquid is preferable in that it is nonvolatile. As the ionic liquid, for example, a pyridine-based, alicyclic amine-based, aliphatic amine-based cation or fluorine-based anion is used.

  The electrodes 12 and 14 are an example of support means in the present invention. This support means is also used as an electrode. The electrode 12 is an example of a support plate in the present invention. The electrode 14 is an example of a counter plate in the present invention. The through hole 142 is an example of a hole in the present invention.

  The electrodes 12, 14 and the drive unit 16 are an example of drive means in the present invention. The electrodes 12 and 14 are also an example of a set of electrodes in the present invention. The electrode 12 is an example of one electrode in the present invention. The electrode 14 is an example of the other electrode in the present invention. The drive unit 16 is an example of a drive source in the present invention.

  In FIG. 1, the voltage applied from the driving unit 16 to the electrodes 12 and 14 is zero. For this reason, the interfacial tension of the liquid droplet 10 at the solid-liquid interface between the electrodes 12 and 14 is maximum, whereby the upper surface of the liquid droplet 10 protrudes outward from the through-hole 142 of the electrode 14, and the electrodes 12 and 14. The part sandwiched between them is in a state of overhanging in the horizontal direction.

  Hereinafter, the surface of the droplet 10 exposed from the through hole 142 is referred to as an upper surface, and the surface sandwiched between the electrodes 12 and 14 is referred to as a side surface. The application of voltage from the drive unit 16 to the electrodes 12 and 14 is simply referred to as voltage application, and the interfacial tension of the droplet 10 at the solid-liquid interface between the electrodes 12 and 14 is simply referred to as interfacial tension.

  FIG. 2 shows a state when a voltage is applied to the electrodes 12 and 14. As shown in FIG. 2, the droplet 10 spreads between the electrodes 12 and 14 in the horizontal direction due to a decrease in interfacial tension (and contact angle) corresponding to the applied voltage. At this time, since the volume of the droplet 10 does not change, the upper surface of the droplet 10 sinks by the amount spread in the horizontal direction.

  By alternately switching the applied voltage, the droplet 10 is alternately switched between the state of FIG. 1 and the state of FIG. As a result, the upper surface of the droplet 10 reciprocates in the vertical direction, and the side surface reciprocates in the horizontal direction. That is, the upper surface of the droplet 10 vibrates in the vertical direction, and the side surface vibrates in the horizontal direction.

  Since the upper surface and the side surface of the droplet 10 are in contact with separate gas phases separated by the electrodes 14, they have a significant volume velocity for each gas phase. Therefore, sound can be generated from the upper surface and the side surface of the droplet 10. The frequency and amplitude of the sound are determined by the frequency and amplitude of the applied voltage regardless of the droplet size.

  The contact angle of electrowetting is expressed by the following Young-Lippmann equation.

here,
θ: Contact angle γ: Interfacial tension (s, l, g, solid phase, liquid phase, gas phase, respectively)
ε ₀ : dielectric constant of vacuum ε _r : relative permittivity V: voltage
d: Thickness of the insulating layer (in the case of an electrode without an insulating layer, the thickness of the electric double layer)
It is.

  Since the contact angle θ is determined by the square of the voltage V according to the above formula, when the voltage V is an AC voltage, the frequency of the acoustic vibration is twice the frequency of the voltage V. Therefore, in order to obtain an acoustic vibration having the same frequency as the frequency of the voltage V, the voltage V is set to an AC voltage biased in a DC manner. At that time, the direct current bias is made larger than the amplitude of the alternating voltage so that the ratio of the double frequency (second harmonic) component becomes small.

  If the AC voltage is a voice-derived signal, acoustic vibration corresponding to the voice can be obtained. Thereby, the electroacoustic transducer 1 becomes a speaker. In this speaker, since the liquid itself becomes a sound generation source, there is no room for resonance to occur when the vibration plate is vibrated, and good sound quality can be obtained.

  In addition, since the vibration amplitude of the liquid droplet is not limited by the operation of the solid, vibration with a large amplitude can be easily obtained even if the size is smaller than that of the conventional speaker. Moreover, since the mechanical part is composed of a droplet and a pair of electrodes, it is very easy to make the speaker small and thin.

  Since the sound generated from the upper surface of the droplet 10 and the sound generated from the side surface are in opposite phases, only one of the sounds is used. For example, when only the sound generated from the upper surface of the droplet 10 is used, a sound insulating or absorbing member 18 is provided between the electrodes 12 and 14 as shown in FIG. Sound insulation or sound absorption.

  Alternatively, the spread of the electrodes 12 and 14 in the horizontal direction may be made larger than ½ of the acoustic wavelength in the use band to reduce the acoustic effect generated from the side surface of the droplet 10. The same applies hereinafter.

  The electrode 14 may be provided on the same side as the electrode 12 as shown in FIG. However, the electrode 14 is provided insulated from the electrode 12. At this time, the plate member 140 having the through-hole 142 functions not as an electrode but as an opposing plate that sandwiches the droplet 10 with the electrode 12. The plate member 140 is an example of a counter plate in the present invention.

  The electrodes 12 and 14 may be provided on the support plate 120 and the counter plate 140, respectively, as shown in FIG. In this way, the electrodes 12 and 14 can be configured specifically for droplet driving, and the support plate 120 and the counter plate 140 can be configured specifically for droplet holding.

  The sound generator for a speaker can have a unit structure of the structure shown in FIGS. 1 to 5 and an aggregate of a plurality of units. As a result, the volume increases, and a speaker with a sufficient volume can be obtained. Within the assembly, the plurality of droplets are individually independent. The electrodes may be common to the entire assembly or may be separate for each unit or units.

  The assembly of unit structures can be a one-dimensional array or a two-dimensional array as required. At this time, if the electrodes, the support plate, and the like are made of a flexible material, a speaker that can be easily adapted to various shapes can be obtained. In addition, you may comprise the speaker of various shapes with the non-flexible material shape | molded previously. A transparent speaker can be obtained if the electrodes, the support plate, etc. and the droplets are made of a transparent material.

It is a figure which shows the typical structure of the electroacoustic transducer of an example of the best form for implementing invention. It is a figure which shows the operation state of the electroacoustic transducer of an example of the best form for implementing invention. It is a figure which shows the typical structure of the electroacoustic transducer of an example of the best form for implementing invention. It is a figure which shows the operation state of the electroacoustic transducer of an example of the best form for implementing invention. It is a figure which shows the typical structure of the electroacoustic transducer of an example of the best form for implementing invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Electroacoustic transducer 10: Droplet 12,14: Electrode 16: Drive part 18: Sound insulation or sound absorption member 120: Support plate 122: Insulating layer 140: Opposite plate 142: Through-hole

Claims (22)

Holding means for holding the droplet in a state where the surface is divided into at least two parts,
An electroacoustic transducer comprising driving means for vibrating the droplets by electrowetting based on an electric signal. The holding means is
A support plate for supporting the droplets;
A counter plate that faces the support plate and sandwiches the droplet in a state where the droplet is partially exposed from the hole;
The driving means includes
A set of electrodes in contact with the droplet;
The electroacoustic transducer according to claim 1, further comprising a drive source that applies an electrical signal to the set of electrodes. The electroacoustic transducer according to claim 2, wherein the support plate and the counter plate also serve as the one set of electrodes. 3. The support plate according to claim 2, wherein the support plate also serves as one electrode of the pair of electrodes and has the other electrode insulated from the one electrode on a side in contact with the droplet. The electroacoustic transducer described. The electroacoustic transducer according to claim 2, wherein the support plate and the counter plate each have one electrode and the other electrode of the set of electrodes. The electroacoustic transducer according to claim 2, wherein at least one of the pair of electrodes is in contact with the droplet through a water repellent layer. The electroacoustic transducer according to claim 2, wherein at least one of the pair of electrodes is in contact with the droplet through an insulating layer. The electroacoustic transducer according to claim 2, wherein the support plate, the counter plate, and the set of electrodes are flat plates. The electroacoustic transducer according to claim 8, wherein the flat plate is flexible. The electroacoustic transducer according to claim 2, wherein the support plate, the counter plate, and the set of electrodes are non-flat plates. The electroacoustic transducer according to claim 10, wherein the non-flat plate is inflexible. The electroacoustic transducer according to claim 2, wherein the droplet, the support plate, the counter plate, and the set of electrodes are transparent. The electroacoustic transducer according to claim 1, wherein the electrical signal is an AC voltage biased in a DC manner. The electroacoustic transducer according to claim 13, wherein the DC bias is larger than the AC voltage. The electroacoustic transducer according to claim 13, wherein the AC voltage is derived from an audio signal. The electroacoustic transducer according to claim 1, wherein the droplet is a water droplet. The electroacoustic transducer according to claim 1, wherein the droplet is a droplet of an electrolytic solution. The electroacoustic transducer according to claim 1, wherein the droplet is an ionic liquid droplet. The electroacoustic transducer according to claim 1, wherein the droplets are a plurality of independent droplets. The electroacoustic transducer according to claim 19, wherein the plurality of droplets are arranged in an array. The electroacoustic transducer according to claim 20, wherein the array is a one-dimensional array. The electroacoustic transducer according to claim 20, wherein the array is a two-dimensional array.

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