Patent ID: 12245513

DESCRIPTION OF EMBODIMENTS

Example 1

Hereinafter, a sound pressure-electrical signal conversion device1according to an example of the present invention will be described in detail with reference toFIGS.1to3.

As illustrated inFIG.1, the sound pressure-electrical signal conversion device1is a device in which a polymer sheet2is sandwiched between a pair of electrodes10spreading in a sheet shape and facing each other. The polymer sheet2is a dielectric film and insulates the electrodes10from each other. That is, it is not necessary to provide another insulating layer. As the polymer sheet2, a dielectric film is used. That is, dielectric polarization is generated with respect to an external electric field while the electrodes10are electrically insulated from each other. In particular, the polymer sheet2is preferably thin in order of μm, and the polymer sheet2is made thin, whereby a distance between the electrodes10can be shortened and a drive voltage can be further reduced.

Additionally, the dielectric film is particularly preferably an electret film. The electret film is a dielectric as described above, traps negative charges in an internal negative charge layer, induces positive charges inversely proportional to a distance from the negative charge layer on both main surfaces, and charges the positive charges on the surfaces of the main surfaces. Additionally, the dielectric film may be a piezoelectric conversion film that has a discontinuous structure in a thickness direction by having pores or being formed of materials having different hardness and that also have a piezoelectric conversion effect.

As the electret film, for example, a fluorine-based polymer can be suitably used. Additionally, stretchability may be imparted to the electret film by using a porous fluorine-based polymer membrane or the like.

Referring also toFIG.2, the electrode10includes an insulating flexible substrate11and conductive fibers13having one end fixed to the flexible substrate11. For the flexible substrate11, for example, a woven fabric or a fiber mesh can be used. Additionally, any other material may be used as long as the material is a sheet-shaped body having flexible and insulating properties and having a plurality of through-holes14penetrating both main surfaces, and for example, the material can be paper having a plurality of through-holes14or a resin sheet having a plurality of through-holes14.

The conductive fibers13are, for example, fibers such as silver-plated fibers or carbon fibers that are conductive by contact between fibers. Additionally, in order to fix one end to the flexible substrate11, it is also preferable to use short fibers. Here, fixing one end does not necessarily mean fixing only one end of both ends. It is sufficient if a part of the conductive fibers13is fixed to the flexible substrate11and a part of the conductive fibers13on a side of the polymer sheet2is fixed so as to be movable. Additionally, both the ends may be fixed so that an intermediate part of the conductive fibers13can be vibrated, and a metal mesh or the like can also be used. Furthermore, the conductive fibers13are arranged at a density so that the conductive fibers13comes in contact with each other to form electrical conduction in a direction along the inside of a plane on the flexible substrate11.

A pressure sensitive adhesive12can be used to fix the conductive fibers13to the flexible substrate11. As illustrated in the drawing, the pressure sensitive adhesive12is preferably arranged in a mesh shape so that at least a part of the through-hole14of the flexible substrate11is exposed. As the pressure sensitive adhesive12, various pressure sensitive adhesives such as an acrylic pressure sensitive adhesive and a urethane pressure sensitive adhesive can be used. Note that other fixing methods such as fixing using an adhesive and fixing by embedment can also be used without using the pressure sensitive adhesive12.

According to the sound pressure-electrical signal conversion device1as described above, an electrical signal is given to the electrodes10, whereby the conductive fibers13can be vibrated to generate sound pressure. That is, the sound pressure-electrical signal conversion device1can be used as a speaker. Additionally, the conductive fibers13are vibrated by receiving the sound pressure, whereby the pair of electrodes10can be caused to output an electrical signal. That is, the sound pressure-electrical signal conversion device1can be used as a microphone.

In particular, as illustrated inFIG.3, in a case where the sound pressure-electrical signal conversion device1is used as a speaker, when an electrical signal is input to the electrode10, the conductive fibers13facing each other with the polymer sheet2that is the dielectric film interposed therebetween obtain an attractive force or a repulsive force and vibrate. Sound pressure generated by the vibration propagates to the outside of the electrode10through a plurality of holes of the pressure sensitive adhesive12arranged in a mesh shape and a plurality of holes penetrating both main surfaces of the flexible substrate11(see arrows). Note that the pressure sensitive adhesive12does not necessarily require a hole, and the sound pressure can be propagated even if the pressure sensitive adhesive12is passed through.

That is, in the sound pressure-electrical signal conversion device1, the polymer sheet2sandwiched between the pair of electrodes10is not used as a diaphragm, but the conductive fibers13that are a part of the electrodes10are used as vibrators. Since a part of the conductive fibers13is fixed to the flexible substrate11and the other parts thereof are movable, the conductive fibers13individually function as vibrators and are responsible for forming sound pressure.

Additionally, while the electrodes10facing each other with the polymer sheet2interposed therebetween are insulated from each other, a distance between the electrodes10can be made close to the thickness of the polymer sheet2. Accordingly, high sound pressure can be obtained even if the drive voltage is low. In particular, the conductive fibers13are preferably fixed to one main surface of the flexible substrate11and arranged so as to face the polymer sheet2. This can bring the conductive fibers13in close proximity to the polymer sheet2and as a result, can bring the conductive fibers13in closest proximity to the electrodes10facing each other. As a result, the drive voltage can be further reduced.

Additionally, when the polymer sheet2is an electret film, charging such that a surface voltage is, for example, −200 V or more can be obtained, and it is not necessary to apply a bias voltage.

Furthermore, since the sound pressure-electrical signal conversion device1includes a flexible material, the sound pressure-electrical signal conversion device1can be three-dimensionally deformed, for example, bent or twisted. Additionally, the sound pressure-electrical signal conversion device1may include a stretchable material and be made stretchable. In addition, as described above, since the conductive fibers13are individually used as vibrators, even if the sound pressure-electrical signal conversion device1is three-dimensionally deformed, there is no change in a state in which each of the conductive fibers13is fixed to the flexible substrate11, and frequency characteristics are not substantially changed. That is, the sound pressure-electrical signal conversion device1is excellent in operational stability against deformation.

Note that as illustrated inFIG.4, even in a case where a polymer sheet2′ is obtained using a material having no stretchability, while a plurality of polymer sheets2′ is partially overlapped with each other and is made slidable, insulation between the electrodes10is maintained, whereby the sound pressure-electrical signal conversion device1can be made stretchable.

Additionally, even if the sound pressure-electrical signal conversion device1is used as a microphone, it is not necessary to apply a bias voltage for a reason similar to the reason described above, and a large electrical signal can be obtained even at low sound pressure. In this case, the conductive fibers13are responsible for converting sound pressure into an electrical signal.

Note that the conductive fibers13may be fibers in which a conductive film is provided on a surface of a needle-shaped body whose rigidity is controlled. A frequency band is controlled by the rigidity, whereby it is possible to easily obtain the sound pressure-electrical signal conversion device1having frequency characteristics suitable for an application.

Additionally, the conductive fibers13may be arranged on only one of the pair of electrodes10. That is, the other electrode may include a thin film or the like. In this case, the conductive fibers13arranged on one electrode10are vibrated, whereby the sound pressure-electrical signal conversion device1can be used as a speaker or a microphone similar to the speaker or the microphone described above.

[Speaker Manufacturing Test]

Next, with reference toFIGS.5to8, description will be given regarding a result of study on sound pressure characteristics and the like in a case where a plurality of sound pressure-electrical signal conversion devices1was actually manufactured and used as speakers.

As illustrated inFIG.5, when sound pressure was measured by changing the film thickness of the polymer sheet2, it was found that in the case of the polymer sheet2having thinner film thickness, higher sound pressure is obtained. Additionally, it was also found that the thickness of the polymer sheet2is made thin to order of whereby high sound pressure is obtained, which is preferable. That is, it was reconfirmed that according to the sound pressure-electrical signal conversion device1described above, since the distance between the electrodes10can be shortened, high sound pressure can be obtained even at a low drive voltage.

FIG.6illustrates photographs of one electrode10as viewed from a face side to which the conductive fibers13are fixed. In particular, while the upper photograph illustrates the electrode10before being extended, the lower photograph illustrates the electrode10extended by tension being applied in the left-right direction of a paper surface. Additionally, positions of the left and right ends of each photograph before the extension corresponded to positions of the left and right ends of each photograph after the extension. In this example, an extension rate exceeded approximately 50% (150% in terms of length).

FIG.7illustrates changes in the sound pressure when the sound pressure-electrical signal conversion device1was extended, similarly to a case where the electrode10was extended as described above. As illustrated in the drawing, the larger the extension rate, the larger the sound pressure. This is considered to be because the opening of the through-hole14of the flexible substrate11of the electrode10was enlarged by the extension, and the propagation of the sound pressure to the outside of the electrode10was improved. Additionally, this is also considered to be because the thickness of the polymer sheet2was reduced by the extension and the distance between the electrodes10was shortened.

FIG.8illustrates a relationship (frequency characteristics) between a frequency and the sound pressure (output) for each extension rate. As the extension rate increased from 0% to 20% and further to 50%, the sound pressure increased, but no substantial change in frequency characteristics was observed.

FIG.9illustrates a relationship (frequency characteristics) between a frequency and sound pressure according to the type of the conductive fibers13. For the conductive fibers13, three types of a silver-plated short fiber, a silver-plated twisted yarn, and a metal mesh were used. Output in a low frequency and low-pitched sound range was the highest in the metal mesh, followed by the silver-plated twisted yarn and the silver-plated short fiber, in that order. There was a tendency that as the unit weight of the conductive fibers13was increased, output in the low-pitched sound range could be increased, and as the unit weight was decreased, output in a high-pitched sound range could be increased. That is, the frequency characteristics can also be adjusted by combining and arranging a plurality of types of the conductive fibers13.

Example 2

Next, a sound pressure-electrical signal conversion device1′ according to another example of the present invention will be described in detail with reference toFIGS.10to12.

As illustrated inFIG.10, the sound pressure-electrical signal conversion device1′ is a device in which a polymer sheet2is sandwiched between a pair of electrodes10′ spreading in a sheet shape and facing each other, similarly to the sound pressure-electrical signal conversion device1described above. The polymer sheet2is a dielectric film and insulates the electrodes10′ from each other.

Here, the electrode10′ includes an insulating flexible substrate11′ and conductive fibers13having one end fixed to a flexible substrate11′. The flexible substrate11′ is impregnated or coated with a pressure sensitive adhesive, and for example, a woven fabric or a fiber mesh can be used. Here, a glass fiber net coated with the pressure sensitive adhesive was used. Then, a part of the conductive fibers13is fixed to the flexible substrate11′ with the pressure sensitive adhesive, and the other parts thereof are movable. For example, a part of the conductive fibers13arranged in a through-hole14(seeFIG.11(b)) of the flexible substrate11′ is movable.

Additionally, the electrode10′ includes a sealing sheet21for sealing the flexible substrate11′ impregnated with the pressure sensitive adhesive against the outside, and a sealing adhesive body22for sealing an end of the sealing sheet21. As the sealing sheet21, for example, a resin film having a thickness of 10 to 30 μm is suitable, and a nonwoven fabric having a thickness of 500 μm or less and the like can also be suitably used. As the sealing sheet21, a sealing sheet that can seal the pressure sensitive adhesive against the outside without inhibiting deformation required for the sound pressure-electrical signal conversion device1′ and that does not inhibit the propagation of sound pressure to the inside and outside is selected. The others are similar to Example 1.

That is, the pressure sensitive adhesive is applied to the flexible substrate11′, whereby it is no longer necessary to arrange the pressure sensitive adhesive alone in a mesh shape, and it is possible to save time and effort for manufacturing and improve the degree of freedom in terms of the type of the pressure sensitive adhesive that can be used. Additionally, the through-hole14of the flexible substrate11′ and a hole of the pressure sensitive adhesive are made to coincide with each other, and the through-hole14is not partially blocked by the pressure sensitive adhesive, which is advantageous for the propagation of the sound pressure. Furthermore, the holes of the pressure sensitive adhesive are made to follow in the deformation of the through-hole14due to the deformation of the sound pressure-electrical signal conversion device1′, and the mobility of the other parts of the conductive fibers13, a part of which is fixed to the flexible substrate11′ can be secured.

FIG.11(a)illustrates a photograph of appearance of the sound pressure-electrical signal conversion device1′ manufactured in this manner andFIG.11(b)illustrates an enlarged photograph of the sound pressure-electrical signal conversion device1′ with the sealing sheet21removed. It was observed that a number of conductive fibers13was arranged in the through-hole14of the flexible substrate11′.

FIG.12(a)illustrates a photograph of appearance of the sound pressure-electrical signal conversion device1′ is extended in a direction along the main surface andFIG.12(b)illustrates an enlarged photograph thereof. Even in a case where the sound pressure-electrical signal conversion device1′ was extended in this manner, no substantial change was observed in the frequency characteristics of the sound pressure-electrical signal conversion device1′.

Although the examples according to the present invention and modifications based on the examples have been described above, the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative examples and modifications without departing from the gist of the present invention or the appended claims.

REFERENCE SIGNS LIST

1Sound pressure-electrical signal conversion device2Polymer sheet10Electrode11Flexible substrate12Pressure sensitive adhesive13Conductive fibers14Through-hole