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JP2012205198

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DESCRIPTION JP2012205198
An object of the present invention is to provide a thermoacoustic device which is excellent in
high-speed reactivity and small in harmonic distortion. According to the present invention, there
is provided a thermoacoustic device comprising a pair of electrodes and a CNT film connected
between the two electrodes and composed of a plurality of independent long carbon nanotube
molecules. , It is characterized in that it is electrically connected between both electrodes alone. It
is preferable that the CNT film is formed in a stripe shape. It is preferable to further include a
heat dissipation CNT film provided in the slit of the CNT film formed in a stripe shape. [Selected
figure] Figure 1
Thermoacoustic device
[0001]
The present invention relates to thermoacoustic devices.
[0002]
As a device for generating a sound wave, a sound wave generator using mechanical vibration
such as an electrodynamic conversion device including a magnet and a coil, a capacitor
conversion device, a conversion device using a piezoelectric material, etc. is widely used.
In recent years, unlike these sound wave generators, development of a sound wave generator
(thermoacoustic apparatus) using a thermoacoustic effect that does not perform mechanical
05-05-2019
1
vibration at all has been advanced.
[0003]
This thermoacoustic apparatus usually comprises a heat insulating layer and a heat generating
body layer provided on the surface of the heat insulating layer. In the thermoacoustic device
having such a structure, the heat generation of the heat generating layer by applying a voltage or
the like causes a temperature change of the air layer on the surface of the heat generating layer,
and the sound changes due to the air density due to the temperature change. It is configured to
occur. Since such a thermoacoustic apparatus does not involve mechanical vibration, it has the
advantages of a wide frequency band, being less susceptible to the influence of the surrounding
environment, and relatively easy to miniaturize.
[0004]
In this thermoacoustic apparatus, carbon nanotubes (hereinafter, also referred to as "CNTs") are
used as a heating element for forming a heating element layer in order to enhance the generation
efficiency of sound waves. It has been proposed to use (see JP 2010-93805 A and JP 2009268108 A). According to this thermoacoustic apparatus, since CNTs having a small heat capacity
and a large specific surface area are used as a heating element, high-speed temperature change
corresponding to an electric signal or the like is possible, and sound waves can be favorably
generated. It is assumed. However, even a thermoacoustic apparatus using CNT as a heating
element as described above is not sufficient in high-speed reactivity, and has high harmonic
distortion, so there is room for improvement for practical use.
[0005]
JP, 2010-93805, A JP, 2009-268108, A
[0006]
The present invention has been made based on the above-described circumstances, and an object
of the present invention is to provide a thermoacoustic device which is excellent in high-speed
reactivity and in which harmonic distortion is small.
[0007]
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As a result of intensive investigations, the inventors of the present invention have found that
when CNTs are used as a heating element, contact resistance occurs at the portion where CNT
molecules are connected, and heat generation at this contact portion increases the nonuniformity
of the heat generation state. It has been found that the reaction and the occurrence of harmonic
distortion are affected, and the present invention has been completed.
That is, the presence of a large number of linkages between the molecules increases the heat
capacity and lowers the high-speed reactivity, and the heat generation of the linkages reduces the
transient response and tends to generate harmonic distortion. The present invention has been
accomplished by finding out and improving this point.
[0008]
The invention made to solve the above-mentioned problems is a thermoacoustic device
comprising: a pair of electrodes; and a CNT film which connects the two electrodes and which is
composed of a plurality of independent long carbon nanotube molecules. A nanotube molecule is
characterized in that it is electrically connected between the two electrodes alone.
[0009]
In the thermoacoustic device, each CNT molecule alone is electrically connected between the two
electrodes, and the CNT film has no connection portion between the CNT molecules.
Therefore, according to the said thermoacoustic apparatus, the heat capacity of a CNT film |
membrane becomes small and it is excellent in high-speed reactivity.
Further, according to the thermoacoustic device, since the decrease in transient response due to
the heat generation from the connection portion of the CNT molecules is suppressed, the
occurrence of harmonic distortion is reduced. Furthermore, according to the thermoacoustic
device, the mechanical strength of the CNT film is high because the CNT film does not have a
linking part between molecules.
[0010]
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It is preferable that the CNT film is formed in a stripe shape. According to the thermoacoustic
apparatus, by forming the CNT film in a stripe shape, the heat dissipation property of this film is
further enhanced. As a result, the high-speed reactivity can be further enhanced and the
occurrence of harmonic distortion can be further reduced. .
[0011]
It is preferable to further include a heat dissipation CNT film provided in the slit of the CNT film
formed in a stripe shape. According to the thermoacoustic device, the heat dissipation CNT film is
alternately disposed in proximity to the CNT film, thereby further enhancing the heat dissipation
of the CNT film, and further improving the high-speed reactivity and the ability to reduce
harmonic distortion. It can be demonstrated.
[0012]
It is preferable to further include a heat insulating layer laminated on the back surface of the
CNT film. According to the thermoacoustic device, by covering the back surface of the CNT film
with the heat insulating layer, it is possible to suppress the flow of heat generated to the back
surface side, and enhance the ability to generate sound waves such as high-speed reactivity. .
[0013]
It is good to further have a heat dissipation layer laminated on the back of the above-mentioned
heat insulation layer. According to the thermoacoustic apparatus, by further providing the heat
dissipation layer on the back surface of the heat insulating layer, the heat dissipation property of
the CNT film is further enhanced, and as a result, it is intended to further improve the high-speed
reactivity and reduce the generation of harmonic distortion. it can.
[0014]
As described above, the thermoacoustic device of the present invention is excellent in high-speed
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reactivity because each CNT molecule alone is electrically connected between both electrodes
and there is no connection portion between CNT molecules in the CNT film. And harmonic
distortion is small. Therefore, the thermoacoustic apparatus of the present invention can be
suitably used as a speaker, particularly as an ultrasonic speaker or the like.
[0015]
They are a typical perspective view (a) and a typical side view (b) of a thermoacoustic device
concerning a first embodiment of the present invention. It is a typical sectional view of the
thermoacoustic device concerning a second embodiment of the present invention. It is a
schematic plan view of the thermoacoustic apparatus which concerns on 3rd embodiment of this
invention. It is a schematic plan view of the thermoacoustic apparatus which concerns on other
embodiment of this invention. It is a schematic diagram which shows the method to form the
CNT film | membrane of a comparative example. It is a SEM photograph which shows the method
to form the CNT film | membrane of a comparative example. It is a schematic diagram showing
the apparatus used for evaluation of the Example. In a reference example, it is a table and a
graph which show resistance value and change rate of a CNT film at the time of changing
temperature of a CNT film. In a reference example, it is a table and a graph which show
resistance value and change rate of a CNT film at the time of maintaining temperature of a CNT
film at 120 ° C.
[0016]
First Embodiment Hereinafter, embodiments of the thermoacoustic apparatus of the present
invention will be described in detail as first to third embodiments and other embodiments. The
thermoacoustic apparatus 1 of FIG. 1 includes a substrate 2, a pair of spacers 3, a CNT film 4,
and a pair of electrodes 5.
[0017]
The substrate 2 fixes the arrangement state of the CNT film 4 and the like, and protects the back
surface and the like of the CNT film 4.
[0018]
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The substrate 2 is a rectangular plate in plan view.
The size of the substrate 2 is not particularly limited, and can be appropriately set according to
the application of the thermoacoustic device 1 or the like, and for example, the longitudinal and
lateral lengths are 1 mm to 10 cm, and the thickness is about 0.1 mm to 5 mm It is.
[0019]
The material of the substrate 2 is not particularly limited as long as it has a certain strength, and
metal materials such as iron and aluminum, non-metal materials such as glass and synthetic
resin, and the like can be used. The substrate 2 may or may not have flexibility. In addition, when
the board | substrate 2 has a softness | flexibility, the said thermoacoustic apparatus can extend
the range of a use as a flexible apparatus.
[0020]
The pair of spacers 3 is a rectangular plate in plan view. The spacers 3 are stacked parallel to
each other on the opposite end edges of the surface of the substrate 2. The pair of spacers 3
separates the substrate 2 from the CNT film 4 and thermally insulates the CNT film 4 from the
substrate 2.
[0021]
The size of the spacer 3 is not particularly limited, and can be appropriately set according to the
size of the substrate 2 etc. For example, the length is about the same as the length of one side of
the substrate 2 and the width is about 1 mm to 1 cm The thickness is about 0.05 mm to 3 mm.
[0022]
The material of the spacer 3 is also not particularly limited, and metals, metal oxides, other
inorganic substances, synthetic resins, etc. can be used, but in order to enhance the thermal
insulation properties of the CNT film 4, glass, silicon, synthetic resins Materials with low thermal
conductivity such as are preferred.
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In addition, when the spacer 3 is formed from electroconductive materials, such as a metal, the
spacer 3 can also be functioned as an electrode. In addition, an adhesive or a pressure sensitive
adhesive can be used as the spacer 3, and in this case, the CNT film 4 can be easily fixed during
manufacture.
[0023]
The CNT film 4 is bridged between the two spacers 3. Further, the pair of electrodes 5 has a strip
shape, and is superimposed on the surface of the pair of spacers 3 so as to sandwich the end of
the CNT film 4. That is, the CNT film 4 connects the two electrodes 5.
[0024]
The CNT film 4 is composed of a plurality of independent long CNT molecules 6. Each CNT
molecule 6 is electrically connected between the two electrodes 5 alone. Specifically, each CNT
molecule 6 is disposed substantially perpendicular to the opposing direction of both electrodes 5,
that is, to both electrodes 5. In the thermoacoustic device 1, since the CNT molecules 6 are
arranged as described above, there is no contact portion between the ends of the CNT molecules
6 or a portion in which the CNT molecules 6 randomly overlap. Therefore, according to the said
thermoacoustic apparatus 1, the heat capacity of the CNT film | membrane 4 becomes small, and
it is excellent in high-speed reactivity.
[0025]
In addition, since the CNT film 4 does not have a connection portion between the CNT molecules
6 as described above, in the thermoacoustic device 1, the decrease in transient response due to
heat generation from the connection portion between the CNT molecules 6 is suppressed. It is
done. Therefore, according to the thermoacoustic device 1, the occurrence of harmonic distortion
is reduced. Furthermore, according to the thermoacoustic device 1, the mechanical strength of
the CNT film 4 is high because there is no connection portion between the CNT molecules 6 in
the CNT film 4 as described above.
[0026]
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The lower limit of the opposing direction length of the two electrodes 5 of the CNT film 4 is
preferably 1 mm, more preferably 1.5 mm, and particularly preferably 2 mm. On the other hand,
the upper limit of the length of the CNT film 4 is preferably 10 mm, more preferably 6 mm. The
length of the CNT film 4 is the length of each independent CNT molecule forming the CNT film 4.
If the length of the CNT film 4 is less than the above lower limit, conversion of the generated heat
to sound waves may be difficult. Conversely, if the length of the CNT film 4 exceeds the above
upper limit, production of such CNT molecules becomes difficult.
[0027]
The lower limit of the average thickness of the CNT film 4 is preferably 0.05 μm, and more
preferably 0.1 μm. On the other hand, the upper limit of the average thickness of the CNT film 4
is preferably 100 μm, and more preferably 20 μm. If the average thickness of the CNT film 4 is
less than the above lower limit, formation of such a thin film may be difficult. Conversely, when
the average thickness of the CNT film 4 exceeds the upper limit, the heat dissipation of the CNT
film 4 may be reduced, and the high-speed reactivity and the ability to suppress harmonic
distortion may be reduced.
[0028]
The CNT film 4 preferably has a single-layer structure in which CNT molecules are disposed
substantially in parallel in a planar manner. With the single-layer structure, the surface area of
the CNT film 4 is expanded. As a result, the heat capacity of the CNT film 4 is reduced, and the
high-speed reactivity of the thermoacoustic device 1 can be further enhanced.
[0029]
The lower limit of the impedance of the CNT film 4 is preferably 1 Ω, more preferably 5 Ω. On
the other hand, the upper limit of this impedance is preferably 1,000 Ω, more preferably 100 Ω.
If the impedance of the CNT film 4 is less than the above lower limit, a current easily flows and
there is a possibility that it may be ignited and burnt. On the other hand, if this impedance
exceeds the above-mentioned upper limit, the current does not flow easily and it is difficult to
generate heat and it does not generate sound, and a high voltage is required to flow the current.
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[0030]
As CNT molecules constituting the CNT film 4, either single-walled single-walled nanotubes
(SWNTs) or multi-walled multi-walled nanotubes (MWNTs) can be used, but MWNTs are
preferred in terms of conductivity and heat capacity. Preferably, MWNTs having a diameter of
1.5 nm or more and 100 nm or less are more preferable.
[0031]
The CNT molecules are in an unspun state in which individual molecules are independent.
By using such independent CNT molecules, the uniformity of the CNT film 4 is enhanced and the
surface area is expanded, so that the temperature change rate of the CNT film 4 is fast, and the
high-speed reactivity can be further enhanced.
[0032]
The CNTs (molecules) can be produced by a known method, and can be produced by, for
example, a CVD method, an arc method, a laser ablation method, a DIPS method, a CoMoCAT
method or the like. Among these, it is preferable to use iron as a catalyst and a substrate and to
manufacture by a CVD method using ethylene gas from the viewpoint that CNTs (MWNT) of a
desired size can be efficiently obtained. In this case, on a substrate such as a quartz glass
substrate or a silicon substrate with an oxide film, an iron or nickel thin film serving as a catalyst
can be formed, and crystals of CNT molecules of a desired length can be obtained.
[0033]
The material of the pair of electrodes 5 is not particularly limited as long as it has conductivity.
For example, a conductive adhesive containing silver particles can be used. The pair of electrodes
5 is energized to generate heat in the CNT film 4.
[0034]
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In the thermoacoustic device 1, the CNT film 4 generates heat by applying an alternating signal
voltage to the pair of electrodes 5. This heat generation causes a temperature change of the air
layer on the surface of the CNT film 4, and a sound wave is generated due to the air density due
to the temperature change. In the thermoacoustic device 1, each CNT molecule 6 alone is
electrically connected between the two electrodes 5. Therefore, the thermoacoustic device 1 is
excellent in high-speed reactivity and has small harmonic distortion. Therefore, the
thermoacoustic device 1 can be suitably used as a speaker, in particular, an ultrasonic speaker or
the like.
[0035]
(Manufacturing method) The said thermoacoustic apparatus 1 can be suitably manufactured, for
example with the following method. An adhesive is laminated on both surface edges of the
substrate 2 to form a pair of spacers 3. The CNT molecules are bridged between the spacers 3 to
form a CNT film 4. Specifically, for example, the CNT film 4 is obtained by peeling off the abovedescribed vertically aligned CNT molecules from the substrate on which iron or nickel is
deposited as a catalyst, and fixing the CNT molecules between the adhesive as the spacer 3. Can
be formed. Then, a pair of electrodes 5 can be formed by laminating a conductive adhesive on
both end edges (spacer 3) of the CNT film 4, and the thermoacoustic device 1 can be obtained.
[0036]
In the above process, after separating vertically oriented CNT molecules from the iron substrate,
a solvent such as isopropyl alcohol is sprayed or dipped in a bundle of CNTs composed of a
plurality of CNT molecules, for example. And those dried may be used as a CNT film. Through
such a process, the bundle of CNTs shrinks. Such a bundle of shrunk CNTs has a small change
with time in resistance in a high temperature environment, and by using it as a CNT film, the
high-speed reactivity of the obtained thermoacoustic device and the ability to suppress the
generation of harmonic distortion are further improved. Do.
[0037]
Second Embodiment The thermoacoustic device 11 of FIG. 2 includes a CNT film 4, a pair of
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electrodes 5, a heat insulation layer 7, and a heat dissipation layer 8. The CNT film 4 and the pair
of electrodes 5 are the same as those provided in the thermoacoustic apparatus 1 of FIG.
[0038]
The heat insulating layer 7 is laminated on the back surface of the CNT film 4. According to the
thermoacoustic device 11, the back surface of the CNT film 4 is covered with the heat insulating
layer 7, thereby suppressing the flow of the generated heat to the back surface side and
enhancing the sound wave generation capability such as high-speed reactivity. be able to.
[0039]
The material for forming the heat insulating layer 7 is not particularly limited as long as it has
heat insulating properties, but in order to exert excellent heat insulating properties, it is
preferable to use a porous material. In order to prevent current from flowing to the heat
insulating layer 7 side, it is preferable to use a material having electrical insulation.
[0040]
Such materials include, for example, glass, zeolite, alumina, silica, ceramics, other metal oxides,
engineering plastics, carbon materials (carbon, silicon carbide, titanium carbide, etc.), nitrogen
materials (silicon nitride, etc.), and surfaces The porous metal etc. which were coat | covered with
insulating materials, such as an oxide, can be mentioned.
[0041]
As the above-mentioned silica, for example, a silica airgel obtained by drying a hydrated gel
obtained from a mixed reaction of tetramethyl orthosilicate (TMOS), aqueous ammonia and
ethanol using supercritical drying is preferable.
This silica airgel can exhibit particularly excellent thermal insulation.
[0042]
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11
The above engineering plastics include polyimide (PI), polyphenylene sulfide (PPS), polyether
imide (PEI), polyetheretherketone (PEEK), fluorine resin, etc., and the heat resistance temperature
is 150 ° C. or higher, preferably 200 ° C. The above resins are preferred.
[0043]
The thermal conductivity of the material forming the heat insulating layer 7 at 25 ° C. is
preferably 0.1 W / mK or less, more preferably 0.06 W / mK or less, and particularly preferably
0.03 W / mK or less.
The thermal conductivity can be measured by the flash method described in JIS-R1611 (2010).
[0044]
The lower limit of the porosity of the heat insulating layer 7 is preferably 50% by volume, more
preferably 80% by volume, and still more preferably 90% by volume. When the heat insulation
layer 7 has such a porosity, heat insulation performance can be exhibited effectively. In addition,
in order to suppress the fall of intensity | strength, 99 volume% is preferable and, as for the
upper limit of the porosity of the heat insulation layer 7, 97 volume% is more preferable. The
porosity can be calculated by the Archimedes method.
[0045]
Moreover, as a minimum of the average diameter of the hole of the heat insulation layer 7, 5 nm
is preferable and 10 nm is more preferable. On the other hand, as an upper limit of the mean
diameter of the hole of heat insulation layer 7, 1,000 nm is preferred and 200 nm is more
preferred. When the average diameter of the holes is less than 5 nm, sufficient heat insulation
may not be exhibited. Conversely, if the average diameter of the holes exceeds 1,000 nm, the
strength may be reduced.
[0046]
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The average thickness of the heat insulating layer 7 can be, for example, 0.1 mm or more and 3
mm or less. If the average thickness of the heat insulating layer 7 is less than the above lower
limit, the heat insulation and the strength may be reduced. On the contrary, when the average
thickness of the heat insulation layer 7 exceeds the above-mentioned upper limit, there is a
possibility that the heat dissipation of the heat insulation layer 7 may fall.
[0047]
The heat dissipation layer 8 is laminated on the back surface of the heat insulating layer 7.
According to the thermoacoustic device 11, the heat dissipation property of the CNT film 4 is
further enhanced by further providing the heat dissipation layer 8 on the back surface of the
heat insulating layer 7, and as a result, the higher speed reactivity is improved and the
generation of harmonic distortion is reduced. Can be
[0048]
The material of the heat dissipation layer 8 is not particularly limited, and examples thereof
include metals, metal oxides, metal nitrides, resin materials in which these powders are mixed,
etc. Metals having high thermal conductivity such as copper and aluminum Is preferred. The
thickness of the heat dissipation layer 8 is not particularly limited, and is, for example, about 100
nm or more and 1 mm or less. In order to widen the surface area and enhance the heat
dissipation, an uneven shape or the like may be formed on the back surface (the surface not in
contact with the heat insulating layer 7) of the heat dissipation layer 8.
[0049]
Third Embodiment The thermoacoustic apparatus 21 of FIG. 3 includes a substrate 2, a pair of
spacers 3, a CNT film 24, a heat dissipation CNT film 9, and a pair of electrodes 25. The substrate
2 and the spacer 3 are the same as those of the thermoacoustic apparatus 1 of FIG.
[0050]
The CNT film 24 is provided between the two spacers 3 to connect the two electrodes 25. The
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CNT film 24 is formed in a stripe shape. That is, a plurality of strip-like CNT films 24 are formed
in parallel and separated. According to the thermoacoustic device 21, the CNT film 24 is formed
in a stripe shape in this manner, and the plurality of slits are provided to further enhance the
heat dissipation of the CNT film 24. As a result, the high-speed reactivity is further enhanced.
And the occurrence of harmonic distortion can be further reduced.
[0051]
The width of each of the CNT films 24 formed in the stripe shape is not particularly limited, and
is, for example, about 0.1 μm to 100 μm. The CNT film 24 is the same as the CNT film 4
provided in the thermoacoustic device 1 of FIG. 1 except that the CNT film 24 is formed in a
stripe shape.
[0052]
The heat-dissipating CNT film 9 has a strip shape, and is provided in each slit of the CNT film 24.
That is, the strip-like CNT films 24 and the strip-like heat release CNT films 9 are alternately
arranged in a plane. The adjacent CNT film 24 and the heat dissipation CNT film 9 may be in
contact with or separated from each other. Further, the heat radiation CNT film 9 is made of CNT
molecules disposed in the opposite direction of the spacer 3 in the same manner as the CNT film
24, but both ends are not in contact with the electrode 25. That is, the heat radiation CNT film 9
does not generate heat.
[0053]
The pair of electrodes 25 is stacked on the surface of each spacer 3 via both ends of the CNT film
24. However, this electrode 25 is not in contact with the heat dissipation CNT film 9. The pair of
electrodes 25 is energized to generate heat in the CNT film 24.
[0054]
According to the thermoacoustic device 21, the heat dissipation CNT films 9 are alternately
disposed in the vicinity of the CNT films 24 in this manner, whereby the heat dissipation of the
CNT films 24 is further enhanced, and the high-speed reactivity which is more excellent The
ability to reduce harmonic distortion can be exhibited.
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[0055]
<Other Embodiments> The thermoacoustic apparatus of the present invention is not limited to
the above embodiments.
For example, as in the thermoacoustic device 31 of FIG. 4A, the CNT molecules forming the CNT
film 34 may not be disposed perpendicularly to the pair of electrodes 5. Further, as in the
thermoacoustic device 41 of FIG. 4B, the CNT film 44 may be formed of CNT molecules bent on
the electrode 5. Furthermore, as in the thermoacoustic device 51 of FIG. 4C, the pair of
electrodes 55 may not be provided in parallel. Moreover, in the thermoacoustic apparatus 1 of
FIG. 1, even if there is no spacer 3, the thermoacoustic apparatus of this invention can be
comprised.
[0056]
In any of the above thermoacoustic devices, each CNT molecule alone is electrically connected
between the two electrodes, so that high-speed reactivity is excellent and occurrence of harmonic
distortion is reduced.
[0057]
Furthermore, the heat insulating material may be provided not only on the back surface of the
CNT film as a heat insulating layer, but also on the side surface or the surface side of the CNT
film.
By thus enclosing the CNT film with a heat insulating material or arranging the CNT film inside
the heat insulating material, the heat insulating property of the CNT film can be enhanced and
the high-speed reactivity of the thermoacoustic device can be further enhanced. .
[0058]
Hereinafter, the present invention will be described in more detail by way of examples, but the
present invention is not limited to these examples.
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[0059]
Example A substrate having a size of 60 mm in length, 60 mm in width, and 0.5 mm in thickness
was prepared.
Two double-sided tapes (spacers) were attached in parallel on the surface of the substrate at a
distance of less than 2 mm. A vertically aligned CNT (MWNT: 2 mm in length, 25 nm in average
diameter) was peeled off from the side on a substrate on which iron was deposited as a catalyst
on quartz glass as a catalyst, and pasted across the double-sided tape to form a CNT film. .
[0060]
The size of this CNT film was 2 mm in width and 50 mm in length. In the lateral direction, 2 mm
long CNT molecules are arranged. The thickness of the CNT film was 0.05 μm to 0.5 μm when
measured by SEM.
[0061]
A copper wire adhesive containing silver particles was laminated on the double-sided tape via
both ends of the CNT molecules to form a pair of electrodes, to obtain the thermoacoustic device
of the example.
[0062]
Comparative Example As shown in FIG. 5, CNTs 104 vertically oriented are drawn from the side
on a substrate 101 in which iron is deposited as a catalyst on quartz glass, and a CNT bundle 104
in which a large number of portions 103 where CNT molecules are connected is present. It
formed.
A thermoacoustic device of a comparative example was obtained by the same operation as in the
example except that this CNT bundle was used as a CNT film. FIG. 6 shows an SEM photograph of
the state in which the CNTs are pulled out of the substrate.
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[0063]
[Evaluation] The devices shown in FIG. 7 were assembled to evaluate the thermoacoustic devices
of the example and the comparative example. The input signal was Vdc = 10 V and Vp-p = 10 V.
The sound pressure in the case of using the generated thermoacoustic apparatus of the
generated example was about 1.7 times larger than that of the comparative example with respect
to the input of the sine wave of 10 kHz frequency.
[0064]
Reference Example (1) CNT bundle as CNT film, (2) shrinked CNT bundle (CNT bundle (S)), (3)
carbon fiber (CF) and (4) spun CNT as a comparison (CNT) The rate of change in resistance to
temperature change was measured. The CNT bundle of (1) is the CNT film in the above example.
The CNT bundle (S) of (2) is dried after spraying the isopropyl alcohol onto the CNT bundle of
(1). The CF of (3) is a Toraya trading card T700. The CNT spinning of (4) is the CNT film in the
above comparative example.
[0065]
In the measurement, each CNT film (CNT bundle etc.) was placed on a hot plate and temperature
was changed, and resistance at each temperature was measured using a digital multimeter. FIG. 8
shows the resistance value at each temperature and the rate of change of the resistance value.
Further, FIG. 9 shows the resistance value and the change rate of the resistance value while
holding the temperature at 120 ° C. for 20 minutes in (2) CNT bundle (S), (3) CF and (4) CNT
spinning.
[0066]
As shown in FIG. 8, it can be seen that (1) CNT bundle and (2) CNT bundle (S) have the same rate
of change in resistance at the time of temperature rise and at the time of high temperature, and
are suitable as a thermoacoustic film. Further, as shown in FIG. 9, it can be understood that the
change in resistance with time of the high temperature environment of the CNT (S) is smaller
than that of the CNT bundle and stable.
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[0067]
The thermoacoustic apparatus of the present invention can be suitably used as a speaker,
particularly as an ultrasonic speaker or the like.
[0068]
1, 11, 21, 31, 41, 51 Thermoacoustic device 2 substrate 3 spacer 4, 24, 34, 44 CNT film 5, 25,
55 electrode 6 CNT molecule 7 heat insulation layer 8 heat dissipation layer 9 heat dissipation
CNT film
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