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JP2011050051

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DESCRIPTION JP2011050051
A thermoacoustic device using carbon nanotubes is provided. A thermoacoustic device (10)
includes at least one first electrode (142), at least one second electrode (144) disposed at a
predetermined distance from the first electrode, and a sound wave generator (14) including a
carbon nanotube structure. , A substrate 185, and a plurality of fins 188 thermally connected to
the substrate. The sound wave generator 14 is electrically connected to the first electrode 142
and the second electrode 144, and the substrate 185 is the first electrode 142, the second
electrode 144, and the sound wave generator 14. Support. [Selected figure] Figure 1
Thermoacoustic apparatus equipped with a heat dissipation element
[0001]
The present invention relates to a thermoacoustic device, and more particularly to a
thermoacoustic device provided with a heat dissipation device.
[0002]
In general, an acoustic device comprises a signal device and a sound generator.
The signaling device transmits a signal to the sound generator (e.g. a speaker). The speaker can
convert an electrical signal to sound as an electroacoustic transducer.
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[0003]
According to the principle of operation, speakers are classified into various types such as
dynamic speakers, magnetic speakers, electrostatic speakers, and piezoelectric speakers. The
various types of speakers all produce mechanical sound by means of mechanical vibration, that
is, they realize electro-mechanical force-sound conversion. Here, dynamic speakers are widely
used.
[0004]
Referring to FIG. 12, a conventional dynamic speaker 500 includes a voice coil 502, a magnet
504, and a cone 506. The voice coil 502 is disposed between the magnets 504 as a conductive
component. When a current is supplied to the voice coil 502, the cone 506 is vibrated by the
interaction of the electromagnetic field of the voice coil 502 and the magnetic field of the magnet
504 to continuously generate pressure fluctuation of air, thereby generating a sound wave. it
can. However, the dynamic speaker 500 relies on the action of the magnetic field.
[0005]
Thermoacoustic phenomenon is a phenomenon in which sound and heat are related, and there
are two aspects, energy conversion and energy transport. Transferring the signal to the
thermoacoustic device generates heat in the thermoacoustic device and propagates to the
surrounding media. Sound waves can be generated due to the thermal expansion and pressure
waves generated by the transmitted heat.
[0006]
H.D.Arnold、I.B.Crandall, “The thermophone as a
precision source of sound”, Phys. 1917, 10, 22-38, Shoushan
Fanet al. “Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers”, Nano
Letters, 2008, Vol. 8 (12), p. 4539-4545 Kaili Jiang, Qunqing Li, Shoushan Fan, "Spinning
continuous carbon nanotube yarns", Nature, Volume 419, p. 801
05-05-2019
2
[0007]
Non-Patent Document 1 discloses a thermophone manufactured by a thermoacoustic
phenomenon. Thermoacoustic phenomenon is a phenomenon in which sound and heat are
related, and there are two aspects, energy conversion and energy transport. Transferring the
signal to the thermoacoustic device generates heat in the thermoacoustic device and propagates
to the surrounding media. Sound waves can be generated by thermal expansion and pressure
waves generated by the transmitted heat. Here, a platinum piece having a thickness of 7 × 10 <5> cm is used as a thermoacoustic component. However, for a platinum piece having a thickness
of 7 × 10 <-5> cm, the heat capacity per unit area is 2 × 10 <-4> J / cm <2> · K. Since the heat
capacity per unit area of platinum pieces is very high, there is a problem that the sound is very
weak when the thermophone using platinum pieces is used outdoors.
[0008]
In order to solve the above-mentioned problem, a thermoacoustic device using a carbon
nanotube film is disclosed in Patent Document 2. Since the carbon nanotube film has a large
specific surface area and a low heat capacity per unit area, when using the carbon nanotube film
as a sound wave generator, the thermoacoustic device can generate sound waves in a wide
frequency response range. it can.
[0009]
Since carbon nanotube films are very thin and flexible, they are generally placed on the surface
of a support to prevent damage to the carbon nanotube films. However, when the thermoacoustic
apparatus is operated, the heat generated by the carbon nanotube film is absorbed by the
support, and there is a problem that the support becomes hot.
[0010]
A thermoacoustic device according to the present invention comprises at least one first electrode,
at least one second electrode disposed at a predetermined distance from the first electrode, a
sound wave generator including a carbon nanotube structure, a substrate, And a plurality of fins
thermally connected to the substrate, wherein the sound wave generator is electrically connected
to the first electrode and the second electrode, and the substrate is the first electrode and the
second electrode. And the sound generator.
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[0011]
The sound wave generator is suspended facing one surface of the substrate so as to be separated
by a predetermined distance.
[0012]
Compared with the prior art, by installing the heat dissipation element in the thermoacoustic
apparatus of the present invention, the heat generated from the acoustic wave generator is
released to lower the temperature of the region facing the acoustic wave generator of the
thermoacoustic apparatus. The thermal acoustic device can be prevented from being damaged
and the lifetime of the thermal acoustic device can be extended.
[0013]
It is a schematic diagram of the thermoacoustic apparatus in Example 1 of this invention.
It is sectional drawing of the thermoacoustic apparatus in Example 1 along line | wire II-II of FIG.
It is a SEM photograph of the carbon nanotube film of the present invention.
It is a schematic diagram of the carbon nanotube segment of this invention. It is a schematic
diagram of the thermoacoustic apparatus provided with the fan in Example 1 of this invention. It
is a schematic diagram of the thermoacoustic apparatus in Example 2 of this invention. FIG. 7 is a
cross-sectional view of the thermoacoustic device in Example 2 along the line VII-VII in FIG. 6; It
is a schematic diagram of the thermoacoustic apparatus in Example 3 of this invention. It is
sectional drawing of the thermoacoustic apparatus in Example 3 along line IX-IX of FIG. FIG. 10
is an enlarged view of the heat pipe shown in FIG. 9; It is a schematic diagram of the
thermoacoustic apparatus in Example 3 of this invention. It is a schematic diagram of the
conventional speaker.
[0014]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
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[0015]
Example 1 Referring to FIGS. 1 and 2, a thermoacoustic device 10 according to the present
invention comprises a signal input device 12, a sound wave generator 14, a first electrode 142, a
second electrode 144, and two supports. 16 and a heat dissipation element 18.
The sound wave generator 14 is supported by the two supports 16 and spaced apart from the
heat dissipation element 18 by a predetermined distance. The signal input device 12 is
electrically connected to the sound wave generator 14 by the first electrode 142 and the second
electrode 144.
[0016]
The heat dissipating element 18 includes a substrate 185 and a plurality of fins 188. The
substrate 185 is flat and has a first surface 184 and a second surface 186. The substrate 185 is
made of a material (e.g., copper or aluminum) having a low far-infrared absorptivity and excellent
thermal conductivity. The dimensions of the substrate 185 may be the same as or larger than the
sound generator 14. In the present embodiment, the substrate 185 is a sheet made of copper and
has a thickness of 1 mm to 5 mm.
[0017]
The plurality of fins 188 are disposed on the second surface 186 of the substrate 185. The
plurality of fins 188 may be made of a heat conductive material such as gold, silver, copper, iron,
or aluminum. In the present embodiment, the fin 188 is a sheet made of copper and has a
thickness of 0.5 mm to 1 mm. The plurality of fins 188 may be fixed to the second surface 186
of the substrate 185 by solder or screws. Alternatively, the plurality of fins 188 and the substrate
185 may be integrally formed. The plurality of fins 188 can release the heat absorbed by the
substrate 185 to the surrounding medium, thereby reducing the temperature of the substrate
185.
[0018]
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Further, referring to FIG. 5, the heat dissipation element 18 may include a fan 19. The fan 19 is
associated with the fins 188 by clips or engagement elements (not shown). By the wind
generated by the operation of the fan 19, the fins 188 can be blown to enhance the heat
radiation efficiency of the fins 188.
[0019]
The two supports 16 are disposed on the first surface 184 of the substrate 185 and are used to
support the thermoacoustic generator 14. The two supports 16 are attached to the first surface
184 with a thermally insulating adhesive or screw. The support 16 is made of a heat insulating
material or a heat insulating material. For example, the support 16 is made of a hard material
such as diamond, glass, quartz, or a flexible material such as plastic or resin. If the area of the
thermoacoustic generator 14 is large, the number of supports 16 can be increased. In the present
embodiment, the support 16 is a strip-like structure made of quartz. Here, the direction from one
support 16 to another support 16 is defined as the longitudinal direction L of the thermoacoustic
generator 14, and the direction perpendicular to the longitudinal direction L is the
thermoacoustic generation. It is defined as the width direction W of the vessel 14 (see FIG. 1).
The length of one of the supports 16 is the same as or longer than the width of the
thermoacoustic generator 14.
[0020]
The sound wave generator 14 is suspended by the support 16 opposite to the first surface 184
of the substrate 185 in parallel to the first surface 184 of the substrate 185. The sound wave
generator 14 includes a carbon nanotube structure. The carbon nanotube structure has a large
specific surface area (eg, 100 m <2> / g or more). The heat capacity per unit volume of the
carbon nanotube structure is 0 (not including 0) to 2 × 10 <-4> J / cm <2> · K, but preferably 0
(not including 0) It is -1.7 * 10 <-6> J / cm <2> * K, and it is 1.7 * 10 <-6> J / cm <2> * K in a
present Example. A plurality of carbon nanotubes are uniformly dispersed in the carbon
nanotube structure. The plurality of carbon nanotubes are connected by intermolecular force. In
the carbon nanotube structure, the plurality of carbon nanotubes are arranged in an oriented
manner or not oriented. The carbon nanotube structures are classified into two types of nonoriented carbon nanotube structures and oriented carbon nanotube structures according to the
arrangement of the plurality of carbon nanotubes. In the non-oriented carbon nanotube structure
in this embodiment, the carbon nanotubes are arranged or entangled along different directions.
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In the oriented carbon nanotube structure, the plurality of carbon nanotubes are arranged along
the same direction. Alternatively, in the oriented carbon nanotube structure, when the oriented
carbon nanotube structure is divided into two or more regions, a plurality of carbon nanotubes in
each region are arranged along the same direction. In this case, the alignment directions of
carbon nanotubes in different regions are different. The carbon nanotube is a single-walled
carbon nanotube, a double-walled carbon nanotube, or a multi-walled carbon nanotube. When
the carbon nanotube is a single-walled carbon nanotube, the diameter is set to 0.5 nm to 50 nm,
and when the carbon nanotube is a double-walled carbon nanotube, the diameter is set to 1 nm
to 50 nm, and the carbon nanotube is a multilayer carbon In the case of nanotubes, the diameter
is set to 1.5 nm to 50 nm.
[0021]
The carbon nanotube structure is formed in the shape of a free-standing thin film. Here, a selfsupporting structure is a form which can utilize the said carbon nanotube structure
independently, without using a support material. That is, it means that the carbon nanotube
structure can be suspended by supporting the carbon nanotube structure from opposite sides
without changing the structure of the carbon nanotube structure. The carbon nanotube structure
is flat and has a thickness of 0.5 nm to 1 mm. The heat capacity per unit volume of the carbon
nanotube structure increases as the specific surface area of the carbon nanotube structure
decreases. The larger the heat capacity per unit volume of the carbon nanotube structure, the
lower the sound pressure of the thermoacoustic device.
[0022]
The carbon nanotube structure includes at least one carbon nanotube film 143a shown in FIG.
The carbon nanotube film is a drawn carbon nanotube film. The carbon nanotube film 143a is
obtained by drawing from a super-aligned carbon nanotube array (see Non-Patent Document 3).
In the single carbon nanotube film, a plurality of carbon nanotubes are connected end to end
along the same direction. That is, the single carbon nanotube film 143a includes a plurality of
carbon nanotubes whose ends in the longitudinal direction are connected by an intermolecular
force. Referring to FIGS. 3 and 4, the single carbon nanotube film 143a includes a plurality of
carbon nanotube segments 143b. The plurality of carbon nanotube segments 143b are
connected end to end by intermolecular force along the length direction. Each carbon nanotube
segment 143b includes a plurality of carbon nanotubes 145 connected by intermolecular force in
parallel to each other. The lengths of the plurality of carbon nanotubes 145 are the same in the
single carbon nanotube segment 143b. Toughness and mechanical strength of the carbon
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nanotube film 143a can be enhanced by immersing the carbon nanotube film 143a in an organic
solvent. Since the heat capacity per unit area of the carbon nanotube film immersed in the
organic solvent is low, the thermoacoustic effect can be enhanced. The carbon nanotube film
143a has a width of 100 μm to 10 cm and a thickness of 0.5 nm to 100 μm.
[0023]
The carbon nanotube structure may include a plurality of stacked carbon nanotube films. In this
case, the adjacent carbon nanotube films are bonded by an intermolecular force. The carbon
nanotubes in the adjacent carbon nanotube film cross each other at an angle of 0 ° to 90 °.
When the carbon nanotubes in the adjacent carbon nanotube film intersect at an angle of 0 ° or
more, a plurality of micro holes are formed in the carbon nanotube structure. Alternatively, the
plurality of carbon nanotube films may be juxtaposed without gaps.
[0024]
The method for producing a carbon nanotube film includes a first step of providing the superaligned carbon nanotube array, and a second step of stretching at least one carbon nanotube film
from the carbon nanotube array using a tool such as tweezers. And.
[0025]
Since the sound wave generator 14 of the present embodiment includes the drawn carbon
nanotube film, the carbon nanotube film is stretched along the direction perpendicular to the
carbon nanotubes in the carbon nanotube film to obtain approximately 200% to 300%. A
deformation rate can be produced.
After stretching the carbon nanotube film, the light transmittance of the carbon nanotube film
can be increased to 80% to 90%. At the same time, the sound density of the sound generator 14
does not change. The acoustic wave generator 14 using the carbon nanotube film can also
generate an acoustic wave by the carbon nanotube film even if it is damaged or ruptured.
[0026]
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The first electrode 142 and the second electrode 144 are electrically connected to the sound
wave generator 14 respectively. The first electrode 142 is supported by the one support 16 and
fixed to the sound wave generator 14. The second electrode 144 is supported by another support
16 and fixed to the sound wave generator 14. The first electrode 142 and the second electrode
144 are made of any conductive material of metal, conductive adhesive, carbon nanotube, and
ITO. In the present embodiment, the first electrode 142 and the second electrode 144 are formed
by printing a conductive silver paste.
[0027]
Furthermore, since the carbon nanotube structure used for the sound wave generator 14 has
adhesiveness, the sound wave generator 14 can be directly adhered to the first electrode 142
and the second electrode 144. Alternatively, the first electrode 142 and the second electrode 144
may be bonded to the sound wave generator 14 respectively by a conductive adhesive.
[0028]
Further, the first electrode 142 and the second electrode 144 are electrically connected to the
signal input device 12 by a wire 149. The signal from the signaling device can be transferred to
the sound generator 14. The signal input device 12 is any one of an electrical signal device, a
direct current pulse signal device, an alternating current device, and an electromagnetic wave
signal device (for example, an optical signal device, a laser). The signal transferred from the
signal input device 12 to the sound wave generator 14 is, for example, an electromagnetic wave
(for example, an optical signal), an electric signal (for example, alternating current, direct current
pulse signal, audio electric signal) or a mixed signal thereof. It is. The signal is received by the
sound generator 14 and emitted as heat. Since the carbon nanotube structure of the sound wave
generator 14 includes a plurality of carbon nanotubes and the heat capacity of a unit area is
small, the pressure wave can be generated in the surrounding medium by the temperature wave
generated by the sound wave generator 14 . When a signal (e.g., an electrical signal) is
transferred to the carbon nanotube structure of the sound wave generator 14, heat is generated
in the carbon nanotube structure by the signal strength and / or the signal. The diffusion of the
temperature wave thermally expands the surrounding air to produce a sound. The principle of
generating this sound is largely different from the principle of generating sound by the pressure
wave generated by the mechanical vibration of the diaphragm in the conventional speaker. If the
input signal is an electrical signal, the thermoacoustic device 10 operates according to an electrothermal-sound conversion scheme.
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[0029]
When the thermoacoustic device 10 is activated, the substrate 185 is heated by the heat
generated by the carbon nanotube structure of the acoustic wave generator 14. Since the heat
transmitted to the substrate 185 can be dissipated by the plurality of fins 188 disposed on the
substrate 185, the substrate 185 of the thermoacoustic device 10 can be operated even if the
thermoacoustic device 10 is operated for a long time. Temperature is not too high, and the user
can directly hold the substrate 185 of the thermoacoustic device 10 by hand.
[0030]
Example 2 Referring to FIGS. 6 and 7, a thermoacoustic device 20 according to the present
invention includes a sound wave generator 24, a plurality of first electrodes 242, a plurality of
second electrodes 244, a heat dissipation element 28, and a signal. And an input device (not
shown). The sound wave generator 24 is installed on the heat dissipating element 28 by the first
electrode 242 and the second electrode 244.
[0031]
The heat dissipation element 28 includes a substrate 285 and a plurality of fins 288. The
substrate 285 is flat and has a first surface 284 and a second surface 286. The substrate 285 is
made of a hard material such as diamond, glass or quartz. In the present embodiment, the
substrate 185 is a sheet made of ceramic and has a thickness of 1 mm to 5 mm.
[0032]
Referring to FIG. 6, the plurality of fins 288 are disposed on the second surface 286 of the
substrate 285. The plurality of fins 288 may be made of a heat conductive material such as gold,
silver, copper, iron, or aluminum. In the present embodiment, the fin 288 is a sheet made of
copper and has a thickness of 0.5 mm to 1 mm. The plurality of fins 188 may be secured to the
second surface 286 of the substrate 285 with solder or screws. The plurality of fins 288 can
release the heat absorbed by the substrate 285 to the surrounding medium, thereby reducing the
temperature of the substrate 285.
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[0033]
The first electrode 242 and the second electrode 244 are alternately disposed on the first surface
284 of the substrate 285 in parallel. The first electrode 242 and the second electrode 244 are
fixed with an adhesive or a screw.
[0034]
The sound wave generator 24 is electrically connected to the first electrode 242 and the second
electrode 244. The sound wave generator 24 is suspended opposite to the first surface 284 of
the substrate 285 in parallel to the first surface 284 of the substrate 285. The sound wave
generator 24 is the same as the sound wave generator 14 of the first embodiment.
[0035]
The signal input device is electrically connected to the first electrode 242 and the second
electrode 244. The signal from the signal input device is transferred to the sound wave generator
24 by the first electrode 242 and the second electrode 244. Since the plurality of first electrodes
242 and the plurality of second electrodes 244 are alternately arranged in parallel, the resistance
of the sound generator 24 is reduced, and the voltage applied to the sound generator 24 is
reduced. It can be done. Furthermore, referring to FIG. 5, the fan of the first embodiment can be
assembled to the heat dissipation element 28.
[0036]
Further, referring to FIG. 6, a heat reflective layer 25 may be provided on the first surface 284 of
the substrate 285 in order to reduce the temperature of the substrate 285 efficiently. The
plurality of first electrodes 242 and the plurality of second electrodes 244 are respectively
disposed on the heat reflection layer 25. The heat reflecting layer 25 is made of white metal, a
metal compound, an alloy, or a composite material. For example, the heat reflecting layer 25 is
made of any one of chromium, titanium, aluminum, silver, gold, zinc and zinc-aluminum alloy.
05-05-2019
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[0037]
When the heat reflecting layer 25 is made of a conductive material, an insulating layer can be
further provided between the heat reflecting layer 25 and the first electrode 242 and the second
electrode 244. Thus, the heat reflecting layer 25 and the first electrode 242 and the second
electrode 244 can be kept in an insulated state.
[0038]
Third Embodiment Referring to FIGS. 8 to 11, the thermoacoustic apparatus 30 of the present
invention is different from the second embodiment in the following points. The thermoacoustic
device 30 includes a sound wave generator 34, a heat reflection layer 35, a plurality of first
electrodes 342, a plurality of second electrodes 344, a heat dissipation element 38, and a signal
input device (not shown). including. Here, the heat dissipation element 38 includes a plurality of
pipes 389. The heat dissipation element 38 includes a substrate 385 and a plurality of fins 388.
The plurality of pipes 389 are in thermal communication with the substrate 385 by the plurality
of fins 388, respectively. The substrate 385 is planar and has a first surface 384 and a second
surface 386.
[0039]
Referring to FIG. 10, the plurality of pipes 389 comprises an airtight tubular body 3896 and a
chamber 3898. The chamber 3898 is filled with a predetermined amount of fluid 3895. The fluid
3895 is any one of water, ethanol, acetone, sodium or mercury. The airtight tubular body 3896
comprises an inner wall 3894 and an outer wall 3892. The outer wall 3892 is made of a material
having excellent thermal conductivity, such as aluminum or high carbon steel. The inner wall
3894 is made of a material that has excellent thermal conductivity and does not react with the
fluid 3895. For example, the inner wall 3894 is made of copper or nickel. Furthermore, a
capillary core (not shown) can be installed on the inner wall 3894.
[0040]
Each of the pipes 389 has a first end (not shown) fixed to the substrate 385 and a second end
05-05-2019
12
opposite to the first end. The first end of the pipe 389 can be used as an evaporator and the
second end can be used as a condenser. The capillary pressure by the capillary core transfers the
fluid 3895 from the condenser to the evaporator.
[0041]
The fins 388 are assembled to the condenser of the pipe 389 by solder or screws. The fins 388
are disposed parallel to the second surface 386 of the substrate 385. The pipe 389 is installed
vertically to the fin 388.
[0042]
When the thermoacoustic device 30 is activated, it transfers a signal from the signaling device to
the sound generator 34, which makes a sound. At the same time, since the substrate 385 is
heated by the heat generated in the sound wave generator 34, the pipe 389 installed on the
substrate 385 is heated by the substrate 385, and the fluid 3895 in the pipe 389 is evaporated
to vapor. become. When the vapor penetrates the airtight tubular body 3896 and reaches the
condenser, it adheres to the capillary core and becomes a liquid. Thereby, the heat generated in
the substrate 385 can be transferred to the condenser by liquid-gas conversion of the fluid 3895.
The heat absorbed by the pipe 3896 by the plurality of fins 388 can be released to the outside of
the sound wave generator 34. Therefore, even if the user has the thermoacoustic device 30
activated for a long time, the user can not be damaged by the heat emitted from the
thermoacoustic device 30.
[0043]
DESCRIPTION OF SYMBOLS 10 thermoacoustic apparatus 12 signal input apparatus 14 sound
wave generator 142 1st electrode 143a carbon nanotube film 143b carbon nanotube segment
144 2nd electrode 145 carbon nanotube 149 wire 16 support body 18 thermal radiation
element 184 1st surface 185 board 186 2nd surface 188 Fin 19 Fan 20 Thermoacoustic Device
24 Sound Wave Generator 242 First Electrode 244 Second Electrode 28 Heat Dissipation
Element 284 First Surface 285 Substrate 286 Second Surface 288 Fin 30 Thermoacoustic Device
34 Sound Wave Generator 342 First Electrode 344 Second Electrode 38 heat dissipation element
384 first surface 385 substrate 386 second surface 388 fins 3892 outer wall 3894 inner wall
3895 fluid 3896 airtight tubular body 3898 chamber 500 dynamic speaker 502 voice Yl 504
Magnet 506 Corn
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