WO2014163261A1

WO2014163261A1 - Piezoelectric speaker

Info

Publication number: WO2014163261A1
Application number: PCT/KR2013/008673
Authority: WO
Inventors: 윤지선; 조정호; 백종후; 정영훈; 남중희
Original assignee: 한국세라믹기술원
Priority date: 2013-04-01
Filing date: 2013-09-27
Publication date: 2014-10-09
Also published as: KR20140119474A; KR101517523B1

Abstract

A piezoelectric speaker according to the present invention comprises: a piezoelectric layer; a piezoelectric element having electrodes formed on both sides of the piezoelectric layer; and a vibration member that is attached to a side of the piezoelectric element and that is made of cellulose. According to the mode for carrying out the invention, opposite-phase vibration of a frame can be absorbed by the cellulose vibration member. Therefore, a conventional distorted sound effect caused by opposite-phase vibration of a frame can be reduced. In addition, cellulose has a piezoelectric character, thereby providing, when needed, a complementary piezoelectric effect to the piezoelectric layer by applying voltage to the vibration member having a piezoelectric character, and amplifying a vibration.

Description

Piezoelectric speaker

The present invention relates to a piezoelectric speaker, and more particularly to a piezoelectric speaker with improved acoustic characteristics.

In general, a piezoelectric element refers to an element having a characteristic of changing electrical energy and mechanical energy from each other, and a piezoelectric speaker is an acoustic component that generates sound in a desired frequency band by acoustically converting the mechanical movement of the piezoelectric element. It is a representative product.

Such piezoelectric speakers are thinner, lighter, and consume less power than voice coil motor (VCM) type speakers, and are being actively applied to portable terminals. Conventional piezoelectric speakers include a piezoelectric speaker of a method in which a piezoelectric body is attached to an upper portion of a metal diaphragm, and a film type piezoelectric speaker made of a piezoelectric material such as PVDF (Polyvinylidene Fluoride) in the form of a film.

Among these, the piezoelectric speaker using the metal diaphragm has a structure in which a piezoelectric body is attached to the upper portion of the metal diaphragm, as shown in Korean Patent Laid-Open Publication No. 10-2001-0030510. Since such a piezoelectric speaker is made of a metal diaphragm, there is a problem that the output sound pressure level is low and it is difficult to reproduce sound in a low frequency band. In addition, unnecessary resonance or anti-vibration is generated from the frame supporting the diaphragm, which causes a high total harmonic distortion (THD) problem.

The film-type piezoelectric speaker is in the form of a piezoelectric vibrating plate including a piezoelectric film and electrodes formed on the upper and lower portions of the piezoelectric film, as in Korean Patent Registration No. 10-1159734, and the piezoelectric film vibrates by an electrical signal, and outputs it as sound. do. Such a film-type piezoelectric speaker has a disadvantage in that the piezoelectric constant of the piezoelectric film is not large so that displacement is small, so that the film-type piezoelectric speaker must be manufactured in a large area to compensate for this. In addition, the film-type piezoelectric speaker also has a disadvantage in that it has a lower output sound pressure level and total harmonic distortion (THD) in the low frequency region than the voice coil motor (VCM) type speaker. Has a limit.

The present invention provides a piezoelectric speaker with improved acoustic characteristics.

In addition, the present invention provides a piezoelectric speaker of a hybrid type that can improve the output sound pressure in the low frequency region, and can reduce the distortion of sound due to semi-vibration of the frame.

A piezoelectric speaker according to the present invention includes a piezoelectric element having a piezoelectric layer and electrodes formed on both surfaces of the piezoelectric layer; And a vibrating member attached to one side of the piezoelectric element and including cellulose.

The piezoelectric layer includes at least one of PZT, PMN-PT, PZN-PT, PIN-PT, PYN-PT, PVDF, PVDF-TrFE, BNT (BaNiTiO3), and BZT-BCT.

Located between the piezoelectric element and the vibration member to bond between the piezoelectric element and the vibration member, and includes an adhesive layer having elasticity.

The adhesive layer may include at least one of an epoxy silicone resin and an acrylic oligomer.

It is installed so as to surround at least the vibration member, and includes a frame for supporting the vibration member.

According to the embodiment of the present invention, the anti-vibration of the frame can be absorbed by using cellulose, which is flexible as a vibration member attached to one side of the piezoelectric element and has high elasticity. Therefore, the distortion of sound due to the semi-vibration of the frame can be reduced as in the prior art.

In addition, since cellulose has a piezoelectric characteristic, the magnitude of the vibration can be adjusted while vibrating the vibrating member itself by applying a voltage to the vibrating member having the piezoelectric characteristic and adjusting the magnitude of the voltage as necessary. The vibration generated by the vibration member itself complements the piezoelectric properties of the piezoelectric layer and amplifies the vibration. As a result, the sound pressure generated from the piezoelectric element and the sound pressure generated from the vibrating member are added, so that the sound pressure is improved compared with the conventional art, and in particular, the sound pressure is improved in the low frequency region, so that the output sound pressure can be evenly improved from the low frequency to the high frequency region. have.

In addition, when using a diaphragm made of metal as in the related art, a human-friendly piezoelectric speaker can be manufactured without causing a problem such as an artificial ringing.

1 is a cross-sectional view showing a piezoelectric speaker according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments of the present invention make the disclosure of the present invention complete and the scope of the invention to those skilled in the art. It is provided to inform you completely. Like numbers refer to like elements in the figures.

Referring to FIG. 1, a piezoelectric speaker according to an exemplary embodiment of the present invention may include a piezoelectric element 100, a vibration member 200 attached to one side of the piezoelectric element 100, and a frame for supporting the vibration member 200. 400, a cap 600 positioned above the piezoelectric element 100 and the vibrating member 200 to cover the piezoelectric element 100 and the vibrating member 200.

The piezoelectric element 100 includes a piezoelectric layer 110, a first electrode 120a formed on one surface of the piezoelectric layer 110, for example, an upper surface thereof, and a second electrode 120b on the other surface of the piezoelectric layer 110, for example, a lower surface thereof. do.

The piezoelectric layer 110 is a means having a piezoelectric characteristic by polarizing in the thickness direction, and is formed in the form of a film that is substantially rectangular in this embodiment. The shape of the piezoelectric layer 110 may be variously changed without being limited to the exemplary embodiment provided that the piezoelectric characteristics that may be applied to the piezoelectric speaker are formed. In addition, the piezoelectric layer 110 may be formed in various structures in which a single layer or multiple layers of thin films are stacked. The piezoelectric layer 110 may be attached to the vibration member 200 in a symmetrical or asymmetrical structure. The piezoelectric layer 110 is not only polycrystalline ceramics such as lead zirconate titanate (PZT) but also lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT), and lead indium (PIN-PT). single crystal piezoelectric materials such as niobate-lead titanate (PN-PT), lead ytterbium niobate-lead titanate (PYN-PT), flexible piezoelectric polymer materials such as polyvinylidene fluoride (VDF) and polyvinyledenedifluoride-tetrafluoroethylene (PVDF-TrFE), BaNiTiO ₃ ), And at least one of barium zirconate titanate-barium calcium titanate (BZT-BCT) in the form of a thin film or film.

The first and

second electrodes

120a and 120b are formed above and below the piezoelectric layer 110, respectively, to apply an electrical signal, that is, a voltage, to the piezoelectric layer 110. The first and

second electrodes

120a and 120b are formed of a conductive material, for example, using carbon nanotubes (CNT), Ag, carbon (C) powder, or a metal paste such as Al, or polyaniline. ), Polyphosphothiophene (polythiophene), PEDOT (poly (3,4-ethylene-dioxythiophene), polypyrrole, PPV (polyphenylenevinylene), and the like, by using at least one or more of a conductive polymer and derivatives thereof and organic conductors Can be. The first and

second electrodes

120a and 120b may be manufactured in various polygonal shapes, such as a quadrangle and a fan.

The vibration member 200 is a means for acoustically converting a mechanical signal generated by an electrical signal applied to the piezoelectric element 100, and is attached to the lower portion of the piezoelectric element 100 by the first adhesive layer 300. It has a thicker thickness than the piezoelectric element 100 and is made of a flexible and highly elastic material. In an embodiment of the present invention, a bio-based cellulose (Cellulose) is used as the vibration member 200 in the form of a thin film or a film. Cellulose has piezo-electric characteristics, has high elastic modulus, is lightweight, is easy to process in large areas, and has excellent acoustic impedance. In addition, the cellulose may be methyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate, nitro cellulose, cellulose sulfate, hydroxypropyl cellulose. It is preferable to use cellulose containing at least one selected from various cellulose derivatives such as cellulose, preferably cellulose containing at least one selected from carboxymethyl cellulose and hydroxypropyl cellulose. good. In addition, the weight average molecular weight of the cellulose is preferably tens of thousands to hundreds of thousands, preferably 50,000 to 250,000, and at this time, if the weight average molecular weight is less than 50,000, there may be a problem of manufacturing a vibrating member including cellulose. If it exceeds 250,000, there may be a problem in realizing the anti-vibration absorption and piezoelectric characteristics of the vibration member including cellulose, it is preferable to use cellulose having the weight average molecular weight.

The vibration member 200 vibrates according to the vibration of the piezoelectric element 100, more specifically, the vibration of the piezoelectric layer 110, and the negative pressure generated from the piezoelectric element 100 and the cellulose vibration member 200. Sound pressure generated in the) is added, and the sound pressure is improved. As described above, since cellulose has a piezoelectric characteristic, when a voltage is applied to the vibrating member 200, the cellulose vibrates itself. Accordingly, by applying power to the vibrating member 200 as necessary, by vibrating the vibrating member 200 by itself, and controlling the magnitude of the vibration by adjusting the size of the voltage, the piezoelectric characteristics of the piezoelectric element 100 is supplemented or amplified Therefore, the output sound pressure in the low frequency region is improved.

On the other hand, due to the vibration of the piezoelectric element 100 and the vibration member 200, semi-vibration is generated in the frame 400 supporting the vibration member 200, the semi-vibration of the frame 400 is a problem that distorts sound Generates. However, since the vibration member 200 of the present invention is flexible and uses cellulose having high elasticity, the vibration member 200 can absorb the anti-vibration of the frame 400, and thus the sound distortion is compared with the conventional one. Can be reduced.

In addition, the characteristics of the cellulose (Cellulose) vibration member 200 can evenly improve the output sound pressure from the low frequency to high frequency region, when using a diaphragm made of metal as in the prior art, does not cause problems such as artificial ringing Therefore, a human-friendly piezoelectric speaker can be manufactured.

The first adhesive layer 300 is applied between the piezoelectric element 100 and the vibration member 200 to bond the vibration member 200 to the lower portion of the piezoelectric element 100. The first adhesive layer 300 is effective to use a material having a high modulus of elasticity, and in the exemplary embodiment of the present invention, at least one or more of an epoxy silicone resin and an acrylic oligomer are used. Since the first adhesive layer 300 made of a high elastic material is positioned between the piezoelectric element 100 and the vibration member 200, the vibration of the piezoelectric layer 100 may be uniformly transmitted to the vibration member 200, Anti-vibration from the frame 400 is absorbed to reduce negative distortion.

The frame 400 is attached to surround the vibration member 200 at least by the second adhesive layer 500 to support the vibration member 200. The frame 400 is made of plastic or aluminum including polybutylene terephthalate (PBT), polyacetal (POM), polycarbonate (PC), etc. to minimize the anti-vibration when the vibration member 200 vibrates. It is preferable to be made of any one or more of them. In the case of the frame 400 according to the embodiment, the area corresponding to the lower side of the vibrating member 200, that is, the lower portion of the frame 400 is closed, but is not limited thereto and may have a shape in which the lower portion is opened.

Here, the second adhesive layer 500 may use at least one of the same material as that of the first adhesive layer 300 described above, that is, an epoxy silicone resin and an acrylic oligomer.

Cap 600 is to protect the piezoelectric speaker, is installed to be connected to the frame 400 on the upper side of the piezoelectric element 100, covers the vibration member 200, the piezoelectric element 100, a plurality of sound on the front And a hole 610. The shape of the sound hole 610 may be variously changed into a circle, an ellipse, a polygon, or the like.

Hereinafter, a method of manufacturing a piezoelectric speaker according to an exemplary embodiment of the present invention will be briefly described with reference to FIG. 1.

First, the piezoelectric element 100 including the piezoelectric layer 110 and the first and

second electrodes

120a and 120b is manufactured. For this purpose, at least one of PZT, PMN-PT, PZN-PT, PIN-PT, PYN-PT, PVDF, PVDF-TrFE, BNT (BaNiTiO3), and BZT-BCT is manufactured in the form of a thin film or film. The piezoelectric layer 110 is manufactured. Then, a carbon paste such as carbon nanotubes (CNT), Ag, carbon (C) powder or Al is applied to the upper and lower portions of the manufactured piezoelectric layer 110, or polyaniline, polythiophene, PEDOT (poly ( 3,4-ethylene-dioxythiophene)), polypyrrole, polyphenylenevinylene (PPV), or the like, and at least one of a conductive polymer, a derivative thereof, and an organic conductor are coated to form the first and

second electrodes

120a and 120b.

When the piezoelectric element 100 is manufactured, an adhesive material including at least one of a high elastic modulus material such as an epoxy silicone resin and an acrylic oligomer may be formed under the piezoelectric element 100 or may vibrate. The first adhesive layer 300 is formed by coating the upper portion of the member 200.

In addition, cellulose may be manufactured in a thin film or film form to provide a vibrating member 200, and the vibrating member 200 may be disposed below the piezoelectric element 100 using the first adhesive layer 300. Attach and dry. In this case, the first adhesive layer 300 is an adhesive material including at least one of a material having a high modulus of elasticity, such as an epoxy silicone resin and an acrylic oligomer.

Subsequently, the vibration member 200 is fixed to the frame 400 using the second adhesive layer 500 made of a high elastic adhesive material, and a cap 600 having a plurality of sound holes 610 is provided on the front surface thereof. The vibration member 200 and the piezoelectric element 100 are covered.

When the piezoelectric speaker is manufactured by the above-described method, a voltage is applied to the piezoelectric layer 110 through the first and

second electrodes

120a and 120b. At this time, the piezoelectric layer 110 is polarized by the applied voltage, thereby contracting or extending, and thus vibration is generated in the piezoelectric layer 110. The vibration of the piezoelectric layer 110 is transmitted to the vibration member 200, thus causing the vibration member 200 to vibrate, and the sound pressure generated from the piezoelectric layer 110 and the sound pressure generated from the vibration member 200 are added. Sound pressure is improved.

Meanwhile, semi-vibration is generated in the frame 400 by vibrating the piezoelectric layer 110 and the vibrating member 200. The vibrating member 200 made of cellulose has excellent elastic force and high internal loss characteristics. The anti-vibration of the frame 400 is absorbed by the vibration member 200. Therefore, it is possible to reduce the sound distortion caused by the semi-vibration of the frame 400.

Then, by applying a voltage to the vibrating member 200 having a piezoelectric characteristic and adjusting the magnitude of the voltage, if necessary, the magnitude of the vibration can be adjusted while vibrating the vibrating member 200 itself. The vibration generated by the vibrating member 200 itself complements the piezoelectric properties of the piezoelectric layer 110 and has an effect of amplifying the vibration, thereby improving the output sound pressure in the low frequency region as compared with the conventional art. In this case, the operating voltage at which the vibration member 200 vibrates itself is lower than the operating voltage of the piezoelectric layer 110, so that the piezoelectric characteristics of the piezoelectric layer 110 may be supplemented and amplified even at a low voltage.

In addition, by the characteristics of the vibration member 200 made of cellulose (Cellulose) it is possible to evenly improve the output sound pressure from the low frequency to high frequency region, when using a diaphragm made of metal as in the prior art, problems such as artificial ringing If not, a human-friendly piezoelectric speaker can be manufactured.

The piezoelectric speaker of the present invention can be the lowest resonant frequency (F ₀ ) 300 ~ 1,000 Hz, preferably 500 ~ 900 Hz bar, not only has the effect of improving the sound pressure in the low frequency region, but also in the low frequency high frequency region It is possible to improve the output sound pressure evenly.

In addition, the piezoelectric speaker of the present invention may have a total harmony distortion (THD) of 40% or less, preferably 35% or less in a low frequency (1000 Hz or less) region, and a total harmony distortion (THD) in a high frequency (1,000 Hz or more) region. May be less than or equal to 15%, preferably less than or equal to 10%. The piezoelectric speaker of the present invention is capable of preventing and / or minimizing sound distortion.

Although described above with reference to the drawings and embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit of the invention described in the claims below. I can understand.

The present invention is a human-friendly piezoelectric speaker that improves the sound pressure evenly from the low frequency to the high frequency region, it can be widely used in mobile electronics and electrical appliances such as notebooks, portable terminals, portable audio equipment.

Claims

A piezoelectric element having a piezoelectric layer and electrodes formed on both surfaces of the piezoelectric layer; And

A vibration member attached to one side of the piezoelectric element and including cellulose;

Piezoelectric speaker comprising a.
The method according to claim 1,

The piezoelectric layer includes lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT), lead indium niobate-lead titanate (PIN-PT), and PYN-PT. piezoelectric material comprising at least one of lead ytterbium niobate-lead titanate, polyvinylidene fluoride (PVDF), polyvinyledenedifluoride-tetrafluoroethylene (PVDF-TrFE), baNiTiO 3 (BNT), and barium zirconate titanate-barium calcium titanate (BZT-BCT) speaker.
The method according to claim 1,

A piezoelectric speaker is disposed between the piezoelectric element and the vibrating member to bond the piezoelectric element and the vibrating member, and includes an adhesive layer having elasticity.
The method according to claim 3,

The adhesive layer is a piezoelectric speaker comprising at least one or more of epoxy (silicon) resin (acryl oligomer).
The method according to claim 1,

A piezoelectric speaker provided with a frame surrounding at least the vibration member, the frame supporting the vibration member.
The method according to claim 5,

The frame includes at least one selected from the group consisting of polybutylene terephthalate (PBT), polyacetal (POM), polycarbonate (PC) and aluminum (Al).
The method according to claim 1,

And the vibration member thickness is greater than the piezoelectric element thickness.
The method according to claim 2,

The piezoelectric layer is a piezoelectric speaker, characterized in that the single layer or multilayer.
The piezoelectric speaker of claim 1, wherein a minimum resonance frequency (F 0 ) is 300 to 1,000 Hz, and total harmony distortion (THD) is 40% or less.
The method of claim 1, wherein the cellulose comprises any one or more selected from methyl cellulose, carboxymethyl cellulose, cellulose acetate, nitro cellulose, cellulose sulfite and hydroxypropyl cellulose,

The cellulose is a piezoelectric speaker, characterized in that the weight average molecular weight of 50,000 ~ 250,000.