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JP2017536016

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DESCRIPTION JP2017536016
Abstract The materials used for acoustic transducer membranes require very specific properties
and require many trade-offs in any practical system. Graphene and graphene related materials
are a newly discovered type of material with several excellent properties that offer the potential
to significantly contribute to the performance of many acoustic conversion systems. Thus, we
have established graphene oxide based transducers as the basis of ribbon microphones and
diaphragm loudspeakers using low cost manufacturing and processing techniques.
Method and apparatus for graphene oxide based acoustic transducer
[0001]
Cross-Reference to Related Applications This patent application also claims priority to US
Provisional Patent Application No. 62 / 060,043, entitled "Method and Apparatus for Graphene
Oxide-Based Acoustic Transducer," filed October 6, 2014. The entire contents of which are
incorporated herein by reference.
[0002]
The present invention relates to acoustic transducers, and more particularly to graphene oxide
based acoustic transducers.
[0003]
A microphone (also known as a mic or mike) is an acousto-electrical converter or sensor that
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converts sound in a medium (typically air) into an electrical signal.
Microphones are used in many applications such as telephones, game consoles, hearing aids,
loudspeakers, movie and video production, live and recording audio technology, two-way radios,
radios and television broadcasts, and also in computers, voice recordings, voices It is used for
recognition, voice over IP (VoIP) and also for non-acoustic purposes (e.g. ultrasound or knock
sensors).
[0004]
At present, many microphones use electromagnetic induction (dynamic microphone), capacitance
change (condenser microphone), or piezoelectric (piezoelectric microphone) to generate an
electrical signal from air pressure fluctuation.
Also, the microphone must generally be used in conjunction with a preamplifier before the signal
can be amplified with an audio power amplifier for use and / or recording.
[0005]
Dynamic microphones operate via electromagnetic induction, are robust, relatively inexpensive,
and are moisture resistant. This, combined with the potentially high gain before feedback, makes
it ideal for use on the stage. The most common dynamic microphone today is the moving coil
microphone, which utilizes a small movable induction coil located in the magnetic field of a
permanent magnet attached to the diaphragm. When the diaphragm vibrates under acoustical
stimulation, the coil moves in the magnetic field and generates a variable current in the coil by
electromagnetic induction. A single dynamic membrane does not respond linearly to all audio
frequencies, so some dynamic microphones use multiple membranes for different parts of the
speech spectrum and were obtained Combine the signals. It is difficult to combine multiple
signals correctly, and the design to do this tends to be expensive. Some other designs, on the
other hand, are more specifically directed to individual parts of the speech spectrum.
[0006]
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Ribbon microphones use thin, usually corrugated, metallic ribbons suspended in a magnetic field.
The ribbon is electrically connected to the output of the microphone and vibration of the ribbon
in the magnetic field generates an electrical signal. Ribbon microphones are similar to moving
coil microphones in that both microphones generate sound by magnetic induction. However, the
basic ribbon microphone detects sound in a bi-directional pattern. This is because ribbons that
are open both back and forth for sound generation respond to pressure gradients rather than
sound pressure.
[0007]
Ribbon microphones were previously delicate and expensive, but due to the materials currently
used, some of the current ribbon microphones are very durable and are also suitable for outdoor
use ( It was previously limited to the studio environment). Ribbon microphones are highly valued
for their ability to capture high frequency details as compared to condenser microphones that
sound subjectively "aggressive" or "weak" at the upper end of the frequency spectrum. The
ribbon microphones are used in pairs by their bi-directional pickup pattern to generate a
Blumlein Pair recording array. Ribbon microphones can also be configured by surrounding
various portions of the ribbon with an acoustic trap or baffle, in addition to the standard two-way
pick-up pattern, which allows for cardioid, hypercardioid, omnidirectional , And allow for variable
polarity patterns. However, these configurations are less common.
[0008]
A loudspeaker (also known as a speaker or loudspeaker) produces sound in response to an
electrical signal input. The most common speakers in use today are dynamic speakers that
operate on the same basic principle as dynamic microphones, but contrary to dynamic
microphones, they produce sound from electrical signals. When an AC electroacoustic signal
input is applied through a coil of wire suspended in a circular gap between the voice coil and the
permanent magnet pole, the induction law of Faraday causes the coil to move back and forth
quickly, which The paper cone attached to the coil is moved back and forth to push air to
generate sound waves.
[0009]
In order to properly reproduce a wide range of frequencies, many loudspeaker systems use more
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than one loudspeaker, in particular for higher sound pressure levels or maximum accuracy.
Individual loudspeakers are used to reproduce different frequency ranges. These loudspeakers
are typically subwoofers (for very low frequencies), woofers (for low frequencies), mid-range
speakers (for intermediate frequencies), tweeters (for high frequencies) and also the maximum
audio frequency It may be a supertweeter optimized for
[0010]
As with the microphones, ribbon speakers using thin metal film ribbons suspended in a magnetic
field provide very good high frequency response due to the small mass of the ribbons, and thus
are used in tweeters and super tweeters It was easy. The extension of the ribbon (although not
strictly a true ribbon speaker) is a planar magnetic speaker using a conductor printed or
embedded on a flat (flat) diaphragm, and the current flowing in the coil is a magnetic field When
interacting and properly designed, a membrane that moves without bending or wrinkling is
obtained, and the majority of the membrane surface that receives the driving force reduces
resonance problems in the coil drive flat diaphragm.
[0011]
The market for loudspeakers and microphones has expanded significantly over the past decade,
with portable multimedia players, portable gaming systems, smartphones, etc., significantly
exceeding the amount of use in the home. In 2013, global audio visual headphones market sales
were estimated to be about 300 million sets, about $ 8 billion. The latest trend in microphone
headphones is expected to account for nearly 20% of worldwide shipments and grow to 40% in
2017. At the same time, in portable applications, low-cost headphones, such as the earbud "ear
bud", have taken a significant share of the market to traditional over-ear and on-ear headphones .
This is primarily due to marketing and branding strategies of companies such as BeatsTM,
SkullCandyTM. Thus, nowadays, premium audio visual (AV) devices dominate the market where
AV devices have hitherto been the only necessary accessories.
[0012]
Therefore, it would be beneficial to leverage the technical capabilities gained by the ribbon
microphones currently used primarily in recording studios to the wider international market for
AV devices. Similarly, it would be beneficial to leverage the ribbon and / or planar loudspeaker
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design to this wider AV international market. It would be further beneficial to establish new
materials that improve the mechanical strength of ribbon microphones and loudspeakers, and to
reduce the material and implementation costs of such microphones and loudspeakers.
[0013]
Other aspects and features of the present invention will become apparent to those ordinarily
skilled in the art upon review of the following description of specific embodiments of the
invention in conjunction with the accompanying drawings.
[0014]
The object of the present invention is to address the limitations of the prior art for acoustic
transducers, and more particularly to provide a graphene oxide based acoustic transducer.
[0015]
According to one embodiment of the present invention, there is provided a method of forming an
acoustic transducer comprising: depositing and treating a graphene containing material from
solution to form a graphene containing film; Heat treating to adjust the electrical properties of
the material.
[0016]
According to one embodiment of the present invention, there is provided a method of forming an
acoustic transducer comprising: manufacturing a first predetermined portion of a MEMS acoustic
transducer using a silicon based MEMS manufacturing process; Producing the second
predetermined portion of the transducer by deposition and processing of the graphene
containing material.
[0017]
According to one embodiment of the present invention, an acoustic transducer element
comprising at least a graphene containing material is provided.
[0018]
Other aspects and features of the present invention will become apparent to those ordinarily
skilled in the art upon review of the following description of specific embodiments of the
invention in conjunction with the accompanying drawings.
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[0019]
Embodiments of the invention will now be described, by way of example only, with reference to
the accompanying drawings, in which:
[0020]
1 is a scanning electron micrograph and an optical micrograph showing the layered
nanostructure of graphene oxide paper made according to an embodiment of the present
invention and its structure after thermal reduction.
FIG. 5 schematically illustrates the production of oxidized graphene ribbons according to an
embodiment of the present invention.
7 is an image showing an aluminum coated graphene oxide ribbon manufactured and used in
accordance with an embodiment of the present invention.
Fig. 5 is an image showing a mechanical testing device for measuring the strength and modulus
of a material of a ribbon manufactured according to an embodiment of the present invention.
FIG. 5 shows stress-strain curves of oxidized graphene ribbons, aluminum coated graphene oxide
ribbons, and aluminum ribbons according to embodiments of the present invention.
FIG. 7 is an image of a ribbon microphone motor with attached an oxidized graphene ribbon
reduced by an aluminum coating crimped according to an embodiment of the present invention.
FIG.
FIG. 7 is a plot of sensitivity versus frequency of oxidized graphene ribbons according to
embodiments of the present invention.
7 is an image showing an exemplary loudspeaker for headphones, in accordance with an
embodiment of the present invention. FIG. 6 shows experimental results comparing flat GO
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diaphragm loudspeakers with prior art molded mylar diaphragms. Fig. 6 shows experimental
results comparing flat GO diaphragm loudspeakers with prior art flat mylar diaphragms. FIG. 6
shows experimental results comparing flat GO diaphragm loudspeakers with prior art flat mylar
diaphragms and molded mylar diaphragms.
[0021]
The present invention relates to acoustic transducers, and more particularly to graphene oxide
based acoustic transducers.
[0022]
The following description provides exemplary embodiment (s) only and is not intended to limit
the scope, applicability, and configuration of the present disclosure.
Rather, the description of the exemplary embodiment (s) below will provide those skilled in the
art with a description that enables the exemplary embodiments. It will be understood that various
changes may be made in the function and arrangement of elements without departing from the
spirit and scope as set forth in the appended claims.
[0023]
The term "portable electronic device" (PED), as used herein and throughout the present
disclosure, is for use in communications and other applications that require energy for batteries
or other independent forms of electrical power. Refers to a wireless device. This includes devices
such as cell phones, smart phones, personal digital assistants (PDAs), portable computers, pagers,
portable multimedia players, portable game consoles, laptop computers, tablet computers, and
electronic readers, etc. It is not limited to these.
[0024]
The term "fixed electronic device" (FED), as used herein and throughout the present disclosure,
refers to wireless and / or wired for communications and other applications that require a
connection to a fixed interface to obtain power. Point to a device. This includes, but is not limited
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to, laptop computers, personal computers, computer servers, kiosks, game consoles, digital set
top boxes, analog set top boxes, internet enabled devices, internet enabled televisions, and
multimedia players.
[0025]
An "acoustic transducer", as used herein and throughout the present disclosure, converts an
electrical signal into an acoustic signal propagated into the medium and / or converts an acoustic
signal propagating into the medium into an electrical signal , Component, device, or system,
within a component, device, or element. Such acoustic transducers may include, but are not
limited to, microphones and loudspeakers (PEDs, FEDs, wearable devices, and other devices, such
as forming part of headphones).
[0026]
As used herein, the term "user" is used to monitor, obtain, store, transmit and process, without
limitation, the biometric data locally or remotely to the user. And can refer to an individual or
group of individuals that can be analyzed, but is not limited to these. Users may, for example,
through dashboards, web services, websites, software plug-ins, software applications, graphical
user interfaces, by means of contracts with their service providers, third party providers,
companies, social networks, social media etc. Get electronic content. Users include, but are not
limited to, private individuals, employees of organizations and / or businesses, members of
community organizations, members of charitable organizations, men, women, children, teenagers,
and animals. The user may further include, in its broadest sense, software systems,
mechanical systems, robotic systems, android systems, etc., characterized by incorporating
acoustic transducers, but is not limited thereto.
[0027]
The term "wearable device" or "wearable sensor" relates to a small electronic device, an electronic
device, an electronic component, and an electronic transducer worn by a user at a site including
under clothing, inside clothing, and on clothing. These are part of a wider range of general types
of wearable technologies, including "wearable computers". "Wearable computer", in contrast, is
intended for general or special purpose information technology and media development. These
wearable devices and / or wearable sensors and / or transducers may be smartphones, smart
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watches, electronic textiles, smart shirts, smart shirts, activity trackers, smart glasses, smart
headgear, sensors, navigation systems, alarm systems, medical examinations And a diagnostic
device, but is not limited thereto.
[0028]
1. Graphene Graphene, a single layer of carbon atoms arranged in a hexagonal crystal lattice,
was first discovered in 2004 by A. Geim and K. Novoselov. The discovery of this stable twodimensional material has led to the study of its electrical properties. Unlike the other carbon
crystal structures, diamond and graphite (insulator and conductor, respectively), the electrical
properties of graphene can be tuned by an electric field. This property, which is found in silicon,
which is an important foundation element of the modern technological age, brings the prospect
of faster, cheaper and more efficient electronics technology using graphene, and also with
graphene It led to the important research of the basic characteristics of the related materials.
Measurement of the mechanical properties of graphene shows that the intrinsic strength of
graphene is 130,000 MPa, which is the highest strength of the materials measured so far and
more than 25 times stronger than the strongest steel The It was reported that the Young's
modulus, which is a measure of stiffness, was 1TPa. Due to the stiffness and low density of
graphene, the speed of sound in graphene is ˜20,000 m / s, which is the fastest among known
materials.
[0029]
1.1 Graphene Materials Due to the high strength and low mass of graphene materials, graphene
materials are suitable to solve some of the problems with aluminum ribbons used in ribbon
transducers and also other transducer films It is also possible to use in The butterfly (Zhou)
realized an earbud electrostatic speaker with excellent acoustic performance, using a 35-layer,
3.5 mm diameter graphene film. While this example demonstrates the performance achievable
using pure graphene films, its method of manufacture requires high temperature chemical vapor
deposition techniques, and high purity nickel sacrificial films, especially given large consumer
use. Not cost effective.
[0030]
In embodiments of the present invention, another method is provided for producing large
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amounts of films from precursor materials that can be made cheaper. This method allows the
production of large scale films of larger dimensions and complex forms while maintaining the
benefits of pure graphene. One of the simplest precursors used in these fabrication methods
according to embodiments of the present invention is graphene oxide (GO). Graphene oxide (GO)
is an oxidized form of graphene that contains up to 40% by weight oxygen. GO can be produced
by exfoliating and oxidizing graphene flakes (typically 10 μm to 20 μm in size) made from bulk
graphite using strong acid and ultrasonic agitation. The oxygen groups applied on the face of the
flake provide a surface charge, which allows easy dispersion in polar solvents (eg water), but GO
is an insulator, typical of square GO films The resistance value is about 10 MΩ · m. However, GO
maintains most of the high strength of the hexagonal graphene lattice by covalent carbon
bonding in the plane. Even so, the mechanical properties of the individual flakes of GO are not as
high in strength as pure graphene. This is because oxidation induced defects reduce the number
of carbon covalent bonds in the material.
[0031]
GO has an excellent ability to self assemble into a layered film called "GO paper" ("Preparation
and characterization of graphene oxide paper" by Dikin et al. ("Preparation and Characterization
of Graphene Oxide Paper" "), Nature magazine, 448, p. 457). GO paper provides a flexible and
durable material whose physical dimensions and thickness can be easily changed. Referring to
FIG. 1, a first image 100 is shown by a scanning electron microscopic photomicrograph of the
layer structure of GO paper. The mechanical strength of the GO paper is due to the combination
of the mechanical properties of the GO flakes themselves and the mechanical properties of
interlayer hydrogen bonding between the stacked flakes. The properties of the GO paper can be
further tuned by "adhering" the sheet with various molecules, such as poly (vinyl alcohol). Among
the techniques for forming GO paper sheets are, in particular, techniques for forming an aqueous
suspension of GO on an inorganic filter by vacuum filtration or on a suitable substrate by
deposition and passive evaporation.
[0032]
GO paper is highly insulating due to the high oxygen content of the material, but oxygen can be
removed by a process known as reduction. Among the techniques for the production of reduced
GO (rGO) paper, particularly simple is the thermal reduction by exposing the GO paper to high
temperatures. For example, at temperatures above 270 ° C. most of the oxygen is removed. The
second image 150 of FIG. 1 shows a photomicrograph of a cross section of rGO paper film.
Heating to higher temperatures in an inert atmosphere further removes oxygen. Alternatively,
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chemical reduction, for example, with a strong reducing agent (eg, hydrazine or hydroiodic acid)
can produce a reduced, low oxygen content GO membrane. The resistivity of the rGO film
depends on the reduction method, but the resistivity of the rGO film can be as low as 30 μΩ · m.
[0033]
1.2 Applications of Ribbon Transducers To test GO and rGO paper membranes as acoustic
transducer materials, we have optimized a ribbon microphone with the advantage of high
strength and low mass being the best test platform Adopted as. The ribbon microphone is one of
the oldest voice technologies used today and is a gracefully simple system. In this system, a light
weight conductive ribbon is suspended in a magnetic field such that movement of the ribbon in
the magnetic field due to pressure gradients from the acoustic wave induces an electrical current.
The speed of this system, and hence the high frequency response, is mass controlled by the
weight of the ribbon. Since the ribbon itself has low resistance, the output impedance of the
ribbon microphone is generally determined by the resistance value of the ribbon reflected via the
step-up transformer at the output of the microphone.
[0034]
Materials conveniently used in ribbon transducers should have very low mass and very high
conductivity. As a result, ribbons have heretofore been constructed of high purity aluminum.
Also, although aluminum is low density (2.7 g / cm <2>), the ribbon must still be very thin, which
causes problems with mechanical integrity. Although the strength of aluminum is relatively high
and the ultimate strength is 60 ΜΡa, there is a trade-off between mechanical strength and mass,
so in fact the aluminum ribbon is very fragile and careful in handling and installation is
necessary. Thus, ribbon microphone applications have been limited by the fragile nature of the
very thin aluminum used in many models of these transducers.
[0035]
In addition to the problem of breakage, aluminum is highly ductile and plastic deformation can
occur if high sound pressure levels are present. The deformation of the ribbon results in a
permanent change of the resonant frequency of the ribbon assembly and a weakening of the
aluminum material. Thus, damaged ribbons require replacement or readjustment, and this
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periodic maintenance can significantly increase the cost of ownership of the ribbon microphone.
Therefore, we use graphene materials (e.g. GO paper film and rGO paper film) commonly used in
ribbon transducers to overcome these drawbacks, due to their high strength and low mass. It
proved to be more suitable than materials such as
[0036]
2. Design and manufacture of oxidized graphene ribbons In the following description of
embodiments of the invention for GO paper ribbon acoustic transducers, the ribbon materials of
the prototype remain as similar in size and thickness to commercially available aluminum
ribbons as possible It is formed to be. Thus, these materials can be judged by mass and
mechanical properties. The first material was an aluminum coated GO ribbon. A very thin
aluminum coating was applied without significant increase in mass to make the insulating GO
conductive. The second material was a thermally reduced rGO ribbon with a thin aluminum
coating on both sides to enhance conductivity.
[0037]
2.1 Synthesis of GO Paper Synthesis of GO and rGO paper membranes was initiated from the
suspension of single layer GO flakes in water. The steps of a simple evaporation method
employed in the ribbon reported in the present invention are shown in FIG. Step 210-Preparation
of suspension of GO flakes in water Step 220-Coating polymer substrate with GO suspension,
drying the film in the drying step to evaporate water, self-organizing GO flakes Step 230Carefully peel off the GO membrane from the polymer substrate,-Step 240-Cut the GO membrane
into strips,-Step 250-(Optional) GO ribbon to produce the rGO ribbon Place in an oven at 280 °
C. Step 260- Crimp the GO (or rGO) ribbon.
[0038]
The final GO film thickness can be controlled by the amount of GO deposited. Since the
conductivity of the ribbon is an important factor of ribbon transducer sensitivity, 100 nm of
aluminum was deposited on each ribbon by electron beam evaporation to make the GO ribbon
conductive and to enhance the conductivity of the rGO ribbon. . Although other methods
(including the more common plasma sputtering) can be used for aluminum deposition, deposition
is a relatively gentle process, and the thickness can be controlled with greater precision.
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Optionally, other high conductivity materials (e.g. including other metals such as gold or silver)
can be deposited. However, in this experiment, aluminum was selected in consideration of the
tradeoff between aluminum mass and conductivity. The ribbon was pressed in a wave form for
several hours to form a crimp. FIG. 3 shows a photograph of a crimped ribbon used during the
experiment.
[0039]
3. Experimental Results Comparative measurements of physical, mechanical and acoustic
properties of GO and rGO ribbons were made and contrasted with conventional aluminum
ribbons according to the prior art. Each ribbon was also used in a microphone to drive a system
with current to demonstrate a functioning speaker. The three types of ribbons showed significant
differences in strength, plasticity and conductivity. The power level differences were also
significant, but the relative frequency responses of the different ribbons were consistent.
[0040]
3.1 Physical Properties The physical properties of three ribbons compared: the aluminum ribbon
of the prior art and the GO ribbon / rGO ribbon according to an embodiment of the invention are
summarized in Table 1. The rGO ribbon was the lightest material, the lowest density (1.25 g / cm
<3>) with a weight of 0.74 mg, and the thickness was 3 μm, comparable to the aluminum
ribbon. The GO ribbon had a thickness of 5 μm, was heavier (1.81 mg), and was equivalent to
the density of the aluminum ribbon (2.2 g / cm <3>). The resistance value of the ribbon was the
most significant difference. The resistivity of the GO ribbon was measured to be 15.5 μΩ · m,
which was considerably higher than the pure aluminum ribbon of 0.054 μΩ · m. However, for
the rGO ribbon, depositing 100 nm of aluminum on both sides reduced the resistance of the
sample to 1.75 μΩ · m.
[0041]
3.2 Mechanical test The tensile strength test can measure the force required to pull a thin ribbon
to break and the elasticity of the sample. From these tests, it is possible to determine the strength
of the material as well as a measure of the Young's modulus, the slope of the strain curve, and
the stiffness of the material. The strength of GO produced by the simple vapor deposition method
was measured using the setup shown in FIG. 4 and was an elongation of 3.5% at 130 MPa, as is
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apparent from FIG. A 2.5 μm pure aluminum ribbon piece obtained from a commercially
available ribbon microphone was also measured using this setup. The graph in FIG. 5 shows
stress-strain curves for both aluminum and GO samples as well as rGO samples. The aluminum
sample has a very narrow area of elastic elongation (area I) and, due to the malleability of this
material, is in a wider area of plastic deformation (area II). Mechanical tests show that the GO
material is stronger than aluminum, withstands significantly more force, and is free of
deformation and subsequent detuning. The rGO sample has a strength of 20 MPa and is much
weaker than the other materials but does not deform before breaking.
[0042]
3.3 Microphone Measurement As shown in FIG. 6, the ribbon was placed in the assembly with a
5 mm gap between two 30 mm neodymium bar magnets. The drooping length of each ribbon
was 36 mm. The resonant frequency test was performed by driving the ribbon with a low
frequency AC current and measuring the increase in potential across the ribbon. The resonant
frequency was less than 20 Hz for all ribbons. Prior to testing, wire mesh blast shields were
placed on both sides of the motor assembly.
[0043]
The measured sensitivity of 100 Hz to 20 kH (24 octave moving average) of the test ribbon is
shown in FIG. Data below 100 Hz were removed from the plot results as they were unreliable due
to the setup used. As apparent from FIG. 7, the relative frequency response of all the ribbons is
almost identical, and it can be said that the transformer frequency response is dominant. The
aluminum ribbon has a mid band sensitivity of about 2 mV / Pa. The sensitivities of the rGO
ribbons are comparable but slightly reduced to about 1 mV / Pa. The sensitivity of the GO ribbon
was much lower than the other two ribbons, and was about 0.1 mV / Pa. This is considered to be
due to the high resistance of the ribbon. From these measurements and results, as well as
previously published graphene conductivity data, we have optimized the material to enhance
graphene oxide based ribbons that are more sensitive than pure aluminum ribbons. Show that it
can be produced while maintaining the mechanical properties of the
[0044]
4. Diaphragm Loudspeakers Like ribbon microphones, diaphragm loudspeakers require low
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inertia and high speed response for good frequency response. Also in the case of diaphragms, it
is expedient for the total mass to be small. Wideband features, such as human perception for
acoustical transients, require a wide frequency response of the diaphragm, which requires a
lightweight, rigid damping structure. At the same time, within the diaphragm, a phenomenon
called "speaker break up" ("speaker break up") degrades the quality of sound generation. This
phenomenon is caused by mechanical resonance in the diaphragm (due to standing acoustic
waves propagating to the diaphragm itself). These can be suppressed by increasing the
mechanical resonance frequency, which is favored by high sound velocity diaphragm materials.
[0045]
The figure of merit (FOM) taking into account the above factors is given by equation (1) which is
the ratio of the speed of sound in the material divided by the density of the material. Because the
speed of sound in the material is given by equation (2), combining these yields equation (3).
Where Vs is the speed of sound, E is the Young's modulus, and ρ is the mass density of the
material.
[0046]
See Table 2. Table 2 shows the material properties of the general material range and the FOM
obtained for these general materials. From these results it can be seen that beryllium has the
highest FOM (and thus, a much higher FOM than the second CVD diamond). According to the
material properties of graphite, FOM of the graphite diaphragm will be 6.5-9.5 · m <4> / kgs. It is
expected that the FOM of graphene oxide is similar and can produce a loudspeaker diaphragm
without "speaker break up" yet having a small total mass.
[0047]
Referring to FIG. 8, a first light micrograph 800 and a second light micrograph 850 of the rGO
diaphragm are shown. The rGO diaphragm is formed by producing a shaped diaphragm (by the
design shown in schematic 860) by "crimping" the rGO membrane. Such shaping may be useful,
for example, in the implementation of loudspeakers such as tweeter loudspeakers (for higher
power, larger diaphragms have a narrow radiation pattern). "Clamping" can be accomplished by a
number of means. These include the use of solidification molds (solid molds) in which the rGO
material is placed and pressure is applied, high humidity conditions, application of steam or
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vapors before or during the crimping process, to aid crimping. Including but not limited to the
application of mechanical pressure with a flexible mold or other means having a similar effect.
[0048]
Referring now to FIGS. 9A-9B, respectively, the frequency response of the flat GO diaphragm is
shown as compared to prior art Mylar-based loudspeakers and flat mylar loudspeakers. An ideal
frequency response for a loudspeaker in comparison would be a passband with a flat frequency
response of about 20 Hz to 10 kHz. Referring now to FIG. 9C, harmonic distortion of prior art
paper and Mylar loudspeakers is shown as compared to harmonic distortion of GO diaphragms.
These measurements are obtained by incorporating diaphragm loudspeakers into headphones
and measuring their performance with a test dummy head having a high sensitivity microphone
in the ear channel.
[0049]
Overall, the GO diaphragm can produce better sound quality as compared to the Mylar
diaphragm. This is due to having an overall lower distortion level, and a flatter frequency
response and higher SPL (sound pressure level). This is due to the reduced low frequency
performance of these initial GO diaphragms compared to the Mylar diaphragms, thus improving
the harmonic distortion of these GO diaphragms to produce better sound. However, in
comparison to prior art molded standard mylar molded diaphragms, GO diaphragms do not
perform as well and are inferior to the lower distortion of molded mylar diaphragms. However, as
apparent from the comparison between the flat mylar diaphragm and the formed mylar
diaphragm, it is expected that the distortion is reduced by forming the GO film into the
acoustically formed diaphragm having the dust cone and the groove shown in FIG. Be done.
[0050]
5. Comment As is apparent from the above results, the main advantages of graphene ribbon
based microphone ribbons according to embodiments of the present invention over pure
aluminum ribbons are lighter weight, higher strength and reduced plastic deformation It is Both
the coated GO ribbon and the coated rGO ribbon have an effective density lower than that of
aluminum. The mass of the rGO ribbon was 33% less than the mass of the aluminum ribbon.
Although the GO ribbon is 66% greater in mass than the aluminum ribbon, the GO ribbon tested
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was twice as thick as the aluminum ribbon.
[0051]
Thus, with appropriate optimization of graphene oxide, it is possible to make thinner samples.
The mechanical strength of GO means that it can easily support the ribbon with half thickness
and half weight of aluminum. It is also possible to increase the strength by manipulating the
nature of the interlayer bond with a polymer binder.
[0052]
The anomalous resistance of 100 nm aluminum deposited on the surface of the GO may be
because the deposited aluminum may delaminate and cause cracking and discontinuities in the
aluminum layer. The peeling of the aluminum layer on the GO has no corrective action and will
make it difficult to install the ribbon more than once. However, alternative fabrication techniques,
process flow, metallization etc may be able to improve the mechanical / electrical properties of
the GO / rGO films. Metallization includes, but is not limited to, metallization to the desired
profile after separation and / or shaping of the ribbon.
[0053]
The mechanical strength of the rGO ribbon is lower than other materials. Adjustment of the
reduction regime used is expected to produce rGO films that have higher yield strength and
lower resistance than GO. What is needed for higher strength and higher conductivity rGO films
would be to add low mass aluminum to the already low mass rGO ribbon.
[0054]
For both rGO and GO, the microphone sensitivity is dominated by the ribbon resistance.
Modifications to the ribbon design, formation of graphene oxide films, reduction of graphene
oxide, etc. will reduce resistance. It will also be apparent that other aspects of the formation of
GO and rGO films will result in lower resistance ribbons and / or diaphragms.
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[0055]
Ribbon microphones and diaphragm loudspeakers according to embodiments of the present
invention allow higher frequencies (e.g., frequencies higher than 20 kHz to 30 kHz, 80 kHz, 100
kHz, which is the general hearing range of human beings) and low frequency ultrasound region.
It will be appreciated that ribbon microphones and / or diaphragm loudspeakers operating at
frequencies above are also possible. Such microphones and loudspeakers can be non-contact
sensors, motion sensors, flow measurements, nondestructive testing, ultrasound ranging,
ultrasound identification, human medicine, veterinary medicine, biomedical applications, material
processing, and sonochemistry. Can be used for applications including, but not limited to.
[0056]
It will be apparent to those skilled in the art that ribbon microphones and diaphragm
loudspeakers according to embodiments of the present invention may be used in a wide range of
electronic devices, including PEDs, FEDs (field emission displays), and wearable devices.
[0057]
It will be apparent to those skilled in the art that other processing and manufacturing techniques,
such as chemical reduction, pressure and temperature reduction may also be used to form an
acoustic transducer element according to embodiments of the present invention.
[0058]
Further, it will also be apparent to those skilled in the art that, optionally, other graphene
containing compounds can be used as precursors by other processes and reduction techniques to
produce graphene rich films.
Similarly, it will also be apparent to those skilled in the art that, optionally, graphene can be used
directly, such as by graphene loading into a polymer matrix.
Such a polymer matrix may, for example, comprise an epoxy resin, which results in a reinforced
GO membrane with increased Young's modulus and reduced mass density.
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[0059]
It will be apparent to those skilled in the art that optionally, GO and / or rGO films, and / or other
graphene based films may be used in combination with other materials in the formation of ribbon
films.
[0060]
It will be apparent to those skilled in the art that optionally rGO films in the form of ribbons and
/ or diaphragms can form part of a microelectromechanical system according to embodiments of
the present invention.
In this case, the GO film is low temperature deposited and processed to form rGO oxide, which is
adapted to the process of MEMS structure (adapted to CMOS silicon circuits) to enable
fabrication of post CMOS of MEMS structure. Thus, MEMS cantilevers of silicon or other
materials are replaced with rGO based films. Optionally, such MEMS devices may use rGO in
combination with materials such as thin silicon carbide (SiC), silicon nitride, or silicon oxide
structural layers. The rGO film can be deposited during the MEMS fabrication sequence and can
be patterned, for example, during subsequent intermediate processing steps or through the final
release step of the MEMS.
[0061]
It will be apparent to those skilled in the art that graphene films can optionally be enhanced by
the dispersion of other conductive elements, including, for example, carbon nanotubes, multiwalled carbon nanotubes, and other fullerenes.
[0062]
Optionally, the GO and / or rGO ribbons and / or diaphragms may be laterally crimped or
longitudinally crimped, or longitudinally crimped in a first predetermined area. It will be clear to
the person skilled in the art that it may be crimped laterally in a second predetermined area (for
example, "Ribbon microphone and ribbon microphone unit" by Akino et al. ("Ribbon"). See U.S.
Pat. No. 8,275,157 entitled "Microphone and Ribbon Microphone Unit")).
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It will be apparent that more complex crimp patterns may be used for the ribbon and / or
diaphragm. It will be appreciated that optionally the number of crimps per unit length, and / or
the crimp height may be varied within a predetermined area of the ribbon and / or diaphragm.
Furthermore, it will also be apparent that the ribbon transducer element and the diaphragm
transducer element can be simultaneously formed in the graphene containing film by a
mechanical deformation process such as crimping.
[0063]
Optionally, GO and / or rGO ribbons and / or diaphragms may be shaped according to geometric
shapes (eg rectangular, square, circular, polygonal) or alternatively in irregular shapes It will be
apparent to one skilled in the art that it may be molded. Optionally, this design can be
determined depending on the desired frequency response or to shift or suppress resonance to
the external region of the desired resonance free operation.
[0064]
It will be apparent to those skilled in the art that optionally GO ribbons and / or rGO ribbons can
be mounted within a fixed mount or adjustable mount (e.g. "Ribbon microphone and ribbon
microphone unit according to Akino et al. See, for example, U.S. Pat. No. 8,275,156 entitled
"Ribbon Microphone and Ribbon Microphone Unit" and others known in the art.
[0065]
Thus, it will be apparent to one skilled in the art that embodiments of the present invention
provide a method of forming elements that are part of an acoustic transducer by deposition and
processing of graphene-containing materials.
Optionally, deposition and processing of the graphene containing material may be performed by
a solution based process to form an initial graphene containing film. It can then be heat treated
to obtain a graphene-containing film, which is then heat treated to adjust the film's electrical
properties.
[0066]
For those skilled in the art, embodiments of the present invention provide an acoustic transducer
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for use in a magnetic induction based loudspeaker, wherein the transducer is formed from a
process that includes deposition and processing of graphene containing material It will be clear.
[0067]
According to an embodiment of the present invention, a method of simultaneously forming a
ribbon acoustic transducer element and a diaphragm acoustic transducer element, comprising
the steps of: forming a graphene-containing film; and mechanical deformation processes
predetermined for the graphene-containing film. And providing the method.
[0068]
For those skilled in the art, embodiments of the present invention provide an acoustic transducer
in which the transducer is formed from a process including deposition and processing of
graphene-containing material, in which process a ribbon acoustic transducer element and a
diaphragm acoustic transducer element simultaneously It will be clear that it can be made.
[0069]
It will be apparent to those skilled in the art that embodiments of the present invention provide
an apparatus and method for providing a device in which a GO membrane is incorporated as part
of an acoustic transducer using MEMS elements.
Thus, a first predetermined portion of a MEMS acoustic transducer can be manufactured using a
silicon-based MEMS manufacturing process, while a second predetermined portion of the
acoustic transducer processes graphene-containing material from solution It is formed by
depositing and processing to form a graphene containing film, and then heat treating the
graphene containing film to adjust its electrical properties.
[0070]
Specific details are set forth in the above description in order to provide a thorough
understanding of the embodiments.
However, it will be understood that embodiments may be practiced without these specific details.
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For example, circuits may be shown in block diagrams in order not to obscure the embodiments
in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures
and techniques may be shown without unnecessary detail in order to avoid obscuring the
embodiments.
[0071]
It should also be noted that the embodiments may be described as a process illustrated as a
flowchart, flow diagram, data flow diagram, structure diagram, or block diagram. Although the
flowcharts may describe the operations as a sequential process, many of the operations may be
performed in parallel or simultaneously. Furthermore, reordering of the order of operations is
also possible. The process is ended when its operation is completed but may also have additional
steps not included in the figure. A process may correspond to a method, a function, a procedure,
a subroutine, a subprogram, etc. If the process corresponds to a function, the end corresponds to
the return of the function to the calling or main function.
[0072]
The foregoing disclosure of exemplary embodiments of the present invention has been presented
for purposes of illustration and description. This disclosure is not intended to be exhaustive or to
limit the invention to the precise form disclosed. Many variations and modifications of the
described embodiments will be apparent to those skilled in the art in view of the above
disclosure. The scope of the present invention is to be defined only by the appended claims and
equivalents.
[0073]
Also, in the description of the exemplary embodiments of the present invention, the detailed
description presents the method and / or process of the present invention as a particular
sequence of steps. However, the method or process should not be limited to the particular order
of steps recited, as long as the method or process is not dependent upon the particular order of
steps set forth herein. One skilled in the art will appreciate that other sequences of steps are
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possible. Therefore, the particular order of the steps set forth in the specification should not be
construed as limitations on the claims. Also, the claims directed to the methods and / or
processes of the present invention should not be limited to the practice of the steps in the order
described. Also, one of ordinary skill in the art will readily understand that the order may vary,
and still that they are within the spirit and scope of the present invention.
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