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JP2018514980

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DESCRIPTION JP2018514980
Abstract The present disclosure provides systems, methods and apparatus for ultrasound
microphones and ultrasound acoustic radios. In one aspect, a system includes a transmitter and a
receiver. The receiver comprises a membrane. The membrane comprises a single layer or
multiple layers of two dimensional material. The receiver is operative to receive sound waves in a
frequency range, the frequency range being an ultrasound frequency range. [Selected figure]
Figure 1A
Ultrasonic microphone and ultrasonic acoustic radio
[0001]
This application is related to US Provisional Patent Application No. 62 / 133,804, filed Mar. 16,
2015, and US Provisional Patent Application No. 62 / 143,565, filed Apr. 6, 2015. Priority is
claimed, and all of these patents are incorporated herein by reference. This application is a
related application of US Patent Application No. 14 / 737,903, filed June 12, 2015, which is
incorporated herein by reference.
[0002]
STATEMENT OF GOVERNMENT SUPPORT This invention was awarded by Contract No. DE-AC
02-05 CH 11231 awarded by the US Department of Energy, Grant No. N00014-09-1066
awarded by the Naval Research Office, and by the National Science Foundation It was made with
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Government support under Grant No. EEC-083819. The government has certain rights in the
invention.
[0003]
TECHNICAL FIELD The present disclosure relates generally to devices capable of transmitting
and receiving sound waves, and more particularly to devices capable of transmitting and
receiving ultrasound.
[0004]
Modern wireless communications are based on the generation and reception of electromagnetic
(EM) waves over a wide frequency range from Hz to THz, resulting in large bandwidth resources.
However, EM communication has various disadvantages including high attenuation coefficient of
conductive material and antenna size. On the other hand, animals have effectively used acoustic
waves for short-range communication for millions of years. Acoustic wave based communication
can overcome some of the problems of EM.
[0005]
For example, acoustic waves have been studied as underwater communication by submarines
because they propagate well in conductive materials. Marine mammals such as whales and
dolphins are known to communicate effectively via acoustic waves. In terrestrial acoustic
communication, the audible or acoustic band (i.e., about 20 kHz to 20 Hz, human-audible sounds)
is often occupied by human speech while the subsonic band is in motion. May be disturbed by
vehicles and building construction.
[0006]
The ultrasound band has a wide frequency span and is often free of disturbances but is seldom
used for high data rate communication purposes. The ultrasound band is a frequency higher than
the upper limit of the human listening range, and generally taken higher than about 20 kHz. One
significant reason that the ultrasound band is seldom used is that there is no wide bandwidth
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ultrasound generator and receiver. Conventional piezoelectric based transducers operate at only
one resonant frequency and can not be used in communications where a wider bandwidth is
required to embed an information stream.
[0007]
Described herein are wideband ultrasonic acoustic radios equipped with graphene based
electrostatic acoustic wave generators and receivers. Acoustic transducers exhibit a very good
flat frequency response over the human audible range (i.e. about 20 Hz to 20 kHz) as well as the
ultrasound range (i.e. up to at least 0.5 MHz). We succeeded in recording the sound of bats of
frequency sweep ultrasonic bat. Amplitude modulated information transmission at 0.3 MHz has
been demonstrated. Ultrasonic acoustic radio pairs also provide a novel distance measurement
method using interference between acoustic and electromagnetic signals.
[0008]
One innovative aspect of the subject matter described in this disclosure can be implemented in a
system that includes a transmitter and a receiver. The receiver comprises a membrane, which
comprises one or more layers of two-dimensional material. The receiver is operative to receive
sound waves in a frequency range, which is an ultrasound frequency range.
[0009]
In some embodiments, the film comprises a graphene film. In some embodiments, the receiver
further includes a first electrode proximate to the first side of the membrane and circuitry
associated with the first electrode. The circuit operates to measure the rate of oscillation of the
membrane, which is caused by the acoustic wave.
[0010]
Another innovative aspect of the subject matter described in the present disclosure is
implemented in a method that includes generating an acoustic wave having a frequency using a
transmitter and receiving the acoustic wave using a receiver. be able to. The frequency of the
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sound waves is in the ultrasonic frequency range. The receiver comprises a membrane, which
comprises one or more layers of two-dimensional material.
[0011]
In some embodiments, the film comprises a graphene film. In some embodiments, the transmitter
comprises a second membrane, which comprises one or more layers of two-dimensional material.
In some embodiments, the receiver further includes a first electrode proximate to the first side of
the membrane and circuitry associated with the first electrode. The circuit operates to measure
the rate of oscillation of the membrane, which is caused by the acoustic wave.
[0012]
Another innovative aspect of the subject matter described in the present disclosure is a
membrane comprising a monolayer or layers of a two-dimensional material, a first electrode
proximate to the first side of the membrane, and a first It can be implemented in an apparatus
that includes the circuitry associated with the electrodes. The circuit operates to measure the rate
of oscillation of the membrane, which is caused by the acoustic wave.
[0013]
In some embodiments, the device further comprises a frame supporting the membrane. The
frame includes a substantially circular open area that defines a substantially circular portion of
the membrane. In some embodiments, the circuit includes a resistor and an amplifier. The
membrane is connected to a voltage source. The first electrode is connected to the negative input
of the amplifier. The positive input of the amplifier is connected to ground. A resistor is
connected to the negative input of the amplifier and the output of the amplifier.
[0014]
The details of one or more embodiments of the subject matter described herein are set forth in
the accompanying drawings and the description below. Other features, aspects, and advantages
will be apparent from the detailed description, the drawings, and the claims. It should be noted
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that the relative dimensions of the following figures may not be drawn to scale.
[0015]
FIG. 1 is an example of a schematic cross-sectional view of a graphene electrostatic broadband
receiver (ie, a graphene microphone). FIG. 6 illustrates an example of a graphene film suspended
in a frame. FIG. 1 is an example of a schematic cross-sectional view of an electrostatic drive
graphene speaker. FIG. 2 shows an example of a stack of different two-dimensional materials.
FIG. 2 shows an example of a stack of different two-dimensional materials. FIG. 7 is an example of
a schematic diagram of a graphene microphone at various stages in a manufacturing process.
FIG. 7 is an example of a schematic diagram of a graphene microphone at various stages in a
manufacturing process. FIG. 7 is an example of a schematic diagram of a graphene microphone at
various stages in a manufacturing process. FIG. 7 is an example of a schematic diagram of a
graphene microphone at various stages in a manufacturing process. FIG. 7 is an example of a
schematic diagram of a graphene microphone at various stages in a manufacturing process. FIG.
7 is an example of a schematic diagram of a graphene microphone at various stages in a
manufacturing process. FIG. 7 is an example of a schematic diagram of a graphene microphone at
various stages in a manufacturing process. FIG. 7 is an example of a schematic diagram of a
graphene microphone at various stages in a manufacturing process. FIG. 7 is an example of a
schematic diagram of a graphene microphone at various stages in a manufacturing process. FIG.
2 shows an example of the working principle of a graphene microphone and associated circuitry
for signal extraction. FIG. 2 shows an example of the working principle of a graphene
microphone and associated circuitry for signal extraction. 7 shows the frequency response of
graphene microphones in different configurations. 7 shows the frequency response of graphene
microphones in different configurations. 7 shows the frequency response of graphene
microphones in different configurations. Fig. 1 shows a schematic view of an ultrasound
transceiver (i.e. an ultrasound acoustic radio). FIG. 7 is an example of a flow diagram illustrating
the method of using the ultrasound transceiver. FIG. 7 illustrates an example of the performance
of an ultrasound transmitting and receiving device. FIG. 7 illustrates an example of the
performance of an ultrasound transmitting and receiving device. FIG. 7 illustrates an example of
the performance of an ultrasound transmitting and receiving device. FIG. 1 is an example of a
schematic illustration of a distance measuring device that can exploit the interference of acoustic
and electromagnetic (EM) signals with signals obtained from such devices. FIG. 1 is an example of
a schematic illustration of a distance measuring device that can exploit the interference of
acoustic and electromagnetic (EM) signals with signals obtained from such devices. FIG. 6
illustrates an example of the operation of a conventional microphone.
FIG. 7 illustrates an example of the operation of a graphene microphone.
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[0016]
Reference will now be made in detail to some specific embodiments of the present invention,
including the best mode contemplated by the inventors for carrying out the invention. These
particular embodiments are illustrated in the accompanying drawings. While the invention will
be described in connection with these particular embodiments, it will be understood that it is not
intended to limit the invention to the described embodiments. On the contrary, it is intended to
cover alternatives, modifications, and equivalents as may be included within the spirit and scope
of the invention as defined by the appended claims.
[0017]
In the following detailed description, numerous specific details are set forth in order to provide a
thorough understanding of the present invention. Certain exemplary embodiments of the present
invention may be practiced without some or all of these specific details. In other instances, well
known process operations have not been described in detail so as not to unnecessarily obscure
the present invention.
[0018]
Various techniques and features of the present invention are sometimes described in the singular
for clarity. However, it should be noted that some embodiments include multiple iterations of a
technology or multiple instantiations of a mechanism, unless otherwise stated.
[0019]
Introduction The ultra-low mass and high mechanical strength of graphene makes it attractive
for sound conversion applications. In the past, electrostatically driven graphene diaphragm
loudspeakers have been demonstrated that have an equalized frequency response throughout the
human audible range (i.e., about 20 Hz to 20 kHz). The maximum high frequency cutoff of the
loudspeaker was not determined, and the measurement was limited to 20 kHz by the available
detection equipment, but as shown below, the graphene speaker works at least to 0.5 MHz.
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Graphene allows air damping to be dominant over the mass and spring constant of the
diaphragm itself over a wide frequency range. In principle, the very good mechanical properties
of graphene and the favorable coupling (coupling) with air and other media make it possible,
both in sound generation and reception, which is a central requirement of ultrasonic acoustic
radios Broadband transducers can be made available. The term "radio" as used in this application
is a system that includes a transmitter and a receiver.
[0020]
In a conventional acoustic receiver (i.e., a microphone), the movement of the suspension
diaphragm is induced by acoustic pressure-induced air pressure fluctuations, which movement is
then via Faraday induction (using magnets and coils), i.e. capacitive Into electrical signals. The
areal mass density of the diaphragm sets an upper limit on the frequency response of the
microphone. In the human auditory system, the diaphragm (tympanic membrane) is relatively
thick (approximately 100 μm), flat FR is limited to approximately 2 kHz, and maximum
detection is limited to approximately 20 kHz. In bats, the tympanic membrane is thinner, which
allows the bats to hear echoes of reflected echolocation up to about 200 kHz.
[0021]
The diaphragms of high performance commercial microphones can be designed to provide a flat
frequency response from the audible range to approximately 140 kHz. In microphones, thinning
and reducing the weight of the diaphragm allows more faithful tracking of sound vibrations at
high frequencies, which usually requires a smaller suspension area to obtain structural integrity.
If the diaphragm is small, the low frequency response will necessarily be sacrificed, also due to
the coupling inefficiency, mainly due to the high effective stiffness of the diaphragm (which
reduces the response vibration amplitude). Smaller diaphragms also increase detection (i.e.
electronic conversion) problems. A broadband microphone with an equalized frequency response
that covers both the audible and ultrasonic regions is technically very difficult.
[0022]
The successful design, construction and operation of an ultrasonic acoustic radio are described
herein. One component of an ultrasonic acoustic radio is a capacitively coupled mechanically
vibrating graphene diaphragm-based receiver (ie, a graphene microphone), which can be paired
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with a graphene-based acoustic transmitter . Graphene microphones have a well-equalized
frequency response (within a 10 dB variation of a perfectly flat band response) covering at least
20 Hz to 0.5 MHz (limited by the characterization instrument) and a wild echoing bat And have
sufficient sensitivity to record. This efficient graphene ultrasound transmitter / receiver radio
system successfully encodes, propagates, and decodes wireless signals. The same ultrasound
acoustic radio can be used to accurately measure distance using the interference between
ultrasound and electromagnetic waves.
[0023]
Apparatus, Systems, and Methods FIG. 1A shows an example of a schematic cross-sectional view
of a graphene microphone 150. The graphene microphone 150 includes a graphene film 155
suspended in a frame 157 (see top view from below, see FIG. 1B) approximately midway between
the two electrodes 160 and 165. Two spacers 170 and 175 separate the graphene film 155 from
the electrodes 160 and 165 respectively. In some embodiments, the spacing between the
graphene film 155 and each of the electrodes 160 and 165 is about 50 microns to 1 millimeter
(mm), or about 150 microns.
[0024]
In some embodiments, the graphene film 155 is a single layer graphene film (ie, a single layer of
graphene). In some embodiments, the graphene film 155 is a multilayer graphene film. For
example, in some embodiments, the graphene film 155 includes one or more layers of graphene.
In some embodiments, graphene film 155 is about 0.34 nanometers (nm) (i.e., the thickness of a
monolayer of graphene) to 1 micron thick, or about 20 nm thick. Graphene microphones with
thinner graphene films allow the microphones to respond to higher frequency sound waves.
[0025]
The frame 157 can enable handling of the graphene film during the manufacturing process of
the graphene microphone 150. In addition, the frame 157 can suspend part of the graphene film
155, that is, not to be in contact with other materials. In this manner, the graphene film 155 can
be suspended on the frame 157 to form a graphene diaphragm, which is a sheet of semi-flexible
material locked at its periphery. In some embodiments, frame 157 is a disc of material that
defines a substantially circular open area, typically at the center of the disc. That is, in some
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embodiments, the frame 157 is similar to a metal washer, which is a thin sheet of material
(typically a disc with through holes (typically circular and in the center) State). In some
embodiments, frame 157 is attached to one side of graphene film 155. In some embodiments, the
frame has a thickness of about 20 microns to 200 microns, or about 50 microns. In some
embodiments, the frame has an outer diameter of about 500 microns to 6 centimeters (cm), or
about 10 mm. The open area defined by the frame can have a diameter of about 100 microns to
5 cm, or about 8 mm.
[0026]
In some embodiments, the frame includes other configurations. For example, the frame can
define an open area having a rectangular, square or oval shape, and the frame material is
designed to suspend the graphene film in this open area.
[0027]
In some embodiments, frame 157 is a non-conductive material. For example, in some
embodiments, frame 157 comprises a polymer or a ceramic. For example, in some embodiments,
frame 157 is polyimide. Many different materials can be used for the frame, as long as the
material supports the graphene film 155 and has sufficient mechanical strength to allow the
incorporation of the frame 157 into the graphene microphone 150.
[0028]
In some embodiments, the graphene film 155 is in electrical contact with a terminal (not shown).
In some embodiments, the terminals are metal wires. For example, in some embodiments, the
terminal is a gold wire having a thickness of about 10 microns to 30 microns, or about 20
microns. In some embodiments, other material and terminals of other dimensions are used. In
some embodiments, a portion of graphene film 155 is disposed between spacers 170 and 175. In
some embodiments, the electrical contact between the terminal and the graphene film 155 is in
the region between the graphene film 155 and the spacer 170 or the spacer 175. In some
embodiments, the terminals do not contact the graphene film 155 in the open area defined by
the spacers 170 and 175, whereby the graphene film 155 vibrates in response to the acoustic
wave without interference of the terminals with vibration. It is possible to
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[0029]
In some embodiments, spacers 170 and 175 are each a disc of material that defines a
substantially circular open area, typically at the center of the disc. That is, in some embodiments,
spacers 170 and 175 are each similar to a metal washer. In some embodiments, spacers 170 and
175 include non-conductive materials. In some embodiments, spacers 170 and 175 comprise a
polymer or a ceramic. In some embodiments, spacers 170 and 175 are each about 50 microns to
1 mm, or about 150 microns in thickness. As the spacers 170 and 175 become thicker, the
graphene film will be further away from the electrodes 160 and 165, and the microphone will
respond to the sound a weaker signal (eg, lower signal to noise ratio) Will generate. In some
embodiments, spacers 170 and 175 are each sufficiently thick to prevent graphene films from
contacting electrodes 160 and 165.
[0030]
In some embodiments, the electrodes 160 and 165 include small holes or openings 167 so that
sound can cause the graphene film 155 in the graphene microphone 150 to vibrate. The small
holes 167 are through holes in the electrodes 160 and 165. The small holes 167 may have any
cross section. For example, in some embodiments, the perforations 167 have a square cross
section. In some embodiments, the perforations 167 have a circular cross section. In some
embodiments, pores 167 have dimensions of about 10 microns to 500 microns, or 150 microns.
For example, if the perforations 167 have a square cross section, the sides of the perforations
may be about 10 microns to 500 microns, and if the perforations 167 have a circular cross
section, the diameter of the perforations is about 10 It can be micron to 500 micron. In some
embodiments, the electrodes have a thickness of about 50 microns to 1000 microns, or about
300 microns.
[0031]
The electrodes 160 and 165 can be materials that can conduct electricity. In some embodiments,
electrodes 160 and 165 are doped silicon electrodes. In some embodiments, an oxide layer 180
or other insulating layer is deposited or formed on the electrodes 160 and 165 to prevent the
graphene film 155 from shorting to the electrodes 160 and 165. In some embodiments, oxide
layer 180 has a thickness of about 400 nm to 600 nm, or about 500 nm. In some embodiments,
the oxide layer is a SiO 2 layer.
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[0032]
In some embodiments, layer 180 is a conductive material when electrodes 160 and 165 are not
conductive. For example, in some embodiments, electrodes 160 and 165 comprise a polymer,
ceramic, or semiconductor coated with a layer of conductive material 180. In some embodiments,
the layer of conductive material 180 comprises a metal such as, for example, copper, aluminum,
silver, or gold. For example, in some embodiments, electrodes 160 and 165 comprise silicon and
the layer of conductive material 180 comprises gold. In some embodiments, the layer of
conductive material 180 has a thickness of about 10 nm to 30 nm, or about 20 nm.
[0033]
In some embodiments, the graphene microphone 150 includes an acoustic cavity 185. Without
the acoustic cavity 185, the sound pressure on the front and back of the graphene film 155 tends
to cancel out at low frequencies, which may result in a reduced response of the graphene
microphone 150. The acoustic cavity 185 may allow the graphene microphone 150 to sense
frequencies below about 200 Hz. In some embodiments, acoustic cavity 185 serves to isolate or
partially isolate the sides of graphene film 155 proximate to second electrode 165 from acoustic
waves.
[0034]
For example, the acoustic cavity 185 is about 1 cm wide (eg, wide enough to join the side or back
of the second electrode 165), and a distance of about 5 cm from the graphene film 155 to the
back wall of the acoustic cavity 185 It can be determined. The acoustic cavity 185 should be
large enough so that the air between the graphene film 155 and the acoustic cavity 185 is not
excessively compressed during operation of the graphene microphone 150, if the air is
excessively compressed: The performance of the graphene microphone 150 will be degraded.
[0035]
In some embodiments, the graphene microphone 150 may not include the electrode 160 and the
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spacer 170. In some embodiments, graphene microphone 150 may perform better (eg, better
frequency response) if graphene microphone 150 includes electrode 160 and spacer 170. For
example, the electrode 160 can serve to reduce the tension of the graphene film 155 such that
the graphene microphone 150 responds to lower frequency sound.
[0036]
In some embodiments, the frequency response of the graphene microphone is in the ultrasonic
frequency range. In some embodiments, the frequency response of the graphene microphone
includes an audible frequency range (e.g., about 20 Hz to 20 kHz) and an ultrasonic frequency
range. In some embodiments, the frequency response of the graphene microphone is about 20
kHz to 10 GHz, about 200 kHz to 10 GHz, about 20 kHz to 10 MHz, or about 200 kHz to 10
MHz.
[0037]
FIG. 1C is an example of a schematic cross-sectional view of an electrostatically driven graphene
loudspeaker (EDGS) 100. Embodiments of graphene loudspeakers are described in US patent
application Ser. No. 14 / 737,903.
[0038]
The loudspeaker 100 comprises a graphene film 105 suspended at a frame 107 approximately
halfway between the two electrodes 110 and 115. In some embodiments, the graphene film 105
suspended at the frame 107 can be similar to the graphene film 155 suspended at the frame 157
shown in FIG. 1B. In some embodiments, the distance between the graphene film 105 and each of
the electrodes 110 and 115 is about 50 microns to 1 mm, or about 150 microns.
[0039]
In some embodiments, the graphene film 105 is a single layer graphene film (ie, a single layer of
graphene). In some embodiments, the graphene film 105 is a multilayer graphene film. For
example, the graphene film 105 can include about 1 to 100 layers of graphene. In some
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embodiments, the graphene film 105 has a thickness of about 20 nm to 40 nm, or about 30 nm.
[0040]
The frame 107 allows part of the graphene film 105 to be suspended, ie, not to be in contact
with other materials. Thus, by suspending the graphene film 105 on the frame 107, a graphene
diaphragm can be formed, and the diaphragm is a sheet of a semi-flexible material locked at the
periphery thereof. In some embodiments, frame 107 is a disc of material that defines a
substantially circular open area, typically at the center of the disc. That is, in some embodiments,
the frame is similar to a metal washer, which is a thin plate (typically disc-shaped) of material
with through holes (typically circular and in the center) ). In some embodiments, the frame has a
thickness of about 120 microns to 360 microns, or about 240 microns. In some embodiments,
the frame has an outer diameter of about 7 mm to 21 mm, or about 14 mm. The open area
defined by the frame can have a diameter of about 3 mm to 11 mm, or about 7 mm.
[0041]
In some embodiments, the frame can include other configurations. For example, the frame can
define an open area having a rectangular, square or oval shape, and the frame material is
designed to suspend the graphene film in this open area.
[0042]
In some embodiments, the graphene film 105 is attached approximately halfway along the
thickness of the frame 107. For example, when the frame 107 is about 240 microns thick, the
graphene film 105 can be attached to the frame 107 such that a frame of about 120 microns
extends from each side of the graphene film. In some embodiments, the graphene film is offset
from the midpoint along the thickness of the frame.
[0043]
In some embodiments, the frame 107 is a polymer, metal or semiconductor material. As long as
the material supports the graphene film 105 and has sufficient mechanical strength to allow the
04-05-2019
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frame 107 to be incorporated into the microphone 100, many different materials can be used for
the frame.
[0044]
In some embodiments, the frame 107 includes two parts, the graphene film 105 is attached to
one part of the frame, and the other part of the frame is stacked on top of the graphene film to
form a structure The graphene film is sandwiched between the two parts. For example, a
graphene film can be suspended on a frame by aligning and attaching two metal washer-shaped
parts to both sides of the graphene film.
[0045]
In some embodiments, the graphene film 105 is in electrical contact with a terminal (not shown).
In some embodiments, the terminals are metal wires. For example, in some embodiments, the
terminal is a gold wire having a thickness of about 10 microns to 30 microns, or about 20
microns. Other materials and terminals of other dimensions can be used in some embodiments.
[0046]
Electrodes 110 and 115 function to activate graphene film 105. In some embodiments, the
electrodes 110 and 115 include small holes 117 so that sound can be output from the
loudspeaker 100. The small holes 117 are through holes in the electrodes 110 and 115. The
small holes 117 may have any cross section. For example, in some embodiments, the perforations
117 have a square cross section. In some embodiments, the pores 117 have dimensions of about
200 microns to 300 microns, or 250 microns. For example, if the perforations 117 have a square
cross section, the sides of the perforations may be about 200 microns to 300 microns, and if the
perforations 117 have a circular cross section, the diameter of the perforations may be about
200. It can be micron to 300 micron. In some embodiments, the electrodes are about 425
microns to about 625 microns thick, or about 525 microns thick.
[0047]
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In some embodiments, one of the electrodes 110 or 115 includes a small hole so that sound can
be emitted from the loudspeaker 100. In some embodiments, the other electrode defines an open
area and does not necessarily include the stoma. The open area can allow the graphene film to
move, ie, the open area allows air / gas to enter and exit between the electrode and the
membrane, which can prevent movement of the membrane There is sex.
[0048]
Electrodes 110 and 115 can be materials that can conduct electricity. In some embodiments,
electrodes 110 and 115 are doped silicon electrodes. In some embodiments, an oxide layer 120
or other insulating layer is deposited or formed on the electrodes 110 and 115 to short the
graphene film 105 to the electrodes 110 and 115 with large drive amplitude when the
loudspeaker is operating. To prevent. In some embodiments, oxide layer 120 has a thickness of
about 400 nm to 600 nm, or about 500 nm. In some embodiments, the oxide layer is a SiO 2
layer.
[0049]
In some embodiments, layer 120 is a conductive material when electrodes 110 and 115 are not
conductive. For example, in some embodiments, electrodes 110 and 115 comprise a polymer,
ceramic, or semiconductor coated with a layer of conductive material 120. In some embodiments,
the layer of conductive material 120 comprises a metal such as, for example, copper, aluminum,
silver, or gold. For example, in some embodiments, electrodes 110 and 115 comprise silicon and
the layer of conductive material 120 comprises gold. In some embodiments, the layer of
conductive material 120 has a thickness of about 10 nm to 30 nm, or about 20 nm.
[0050]
In some embodiments, the graphene microphone 100 includes an acoustic cavity 130. The
acoustic cavity 130 may improve the low frequency performance of the graphene loudspeaker
100. In some embodiments, acoustic cavity 130 of graphene loudspeaker 100 is similar to
acoustic cavity 185 of graphene microphone 150.
[0051]
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In some embodiments, the graphene microphone has the same configuration as the graphene
loudspeaker 100. In some embodiments, the graphene loudspeaker has a similar configuration to
the graphene microphone 150.
[0052]
In some embodiments, graphene microphones and graphene loudspeakers can include twodimensional materials other than graphene. A two-dimensional material is a material comprising
or consisting of a monolayer of atoms of a molecule. For example, in some embodiments, the
microphone and / or loudspeaker include a single layer of two-dimensional material (ie, a single
layer) or multiple layers of two-dimensional material (ie, a plurality of single layers). In some
embodiments, the two-dimensional material comprises a conductive material. For example, in
some embodiments, the microphone and / or loudspeaker comprises a single layer or multiple
layers of hexagonal boron nitride (hBN) or molybdenum disulfide (MoS2), wherein the hBN or
MoS2 is a thin carbon layer or layer A thin metal layer is disposed thereon to render the hBN or
MoS2 layer conductive.
[0053]
In some embodiments, the microphones and / or loudspeakers comprise stacks or stacks of
different two-dimensional materials. For example, the microphone and / or loudspeaker can
include one or more monolayers of hBN 191 stacked or arranged in one or more monolayers of
graphene 192, as shown in FIG. 1D. As another example, the microphone and / or loudspeaker
may include one or more monolayers of graphene 193, and as shown in FIG. 1Ee, one or more
layers of hBN 194 and 195 may be graphene Are stacked or arranged on each side of one or
more monolayers of A structure comprising one or more monolayers of graphene 193, wherein
one or more layers of hBN 194 and 195 are laminated or disposed on each side of one or more
monolayers of graphene, disposed on the electrode Even in the absence of the insulating layer, it
is possible to prevent the graphene 193 from shorting to the electrode.
[0054]
In some embodiments, the graphene microphone is manufactured from a multilayer graphene
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film suspended halfway between two perforated electrodes. External acoustic waves can then be
transmitted through the electrodes to displace the graphene film, thereby altering the
capacitance between the graphene film and the electrodes, causing charge redistribution and
current flow.
[0055]
2A-2I are examples of schematic views of graphene microphones at various stages in the
manufacturing process. For example, the graphene microphones used in the experiments
described below were manufactured using this method. The graphene film used in the graphene
microphone was a multilayer graphene film having a thickness of about 20 nm and a diameter of
about 7 mm. First, 1 cm <2> pieces of 25 μm thick nickel foil were electrochemically polished,
rinsed with DI (deionized) water and loaded into a 25 mm diameter quartz tube furnace (FIG. 2A).
After hydrogen annealing, graphene layers were grown by chemical vapor deposition at 1050 °
C. with parallel flows of 50 sccm methane and 50 sccm hydrogen. The growth chamber pressure
was controlled at 1 Torr. The growth lasted 15 minutes and the methane flow rate was increased
to 200 sccm in the last 2 minutes to improve stitching between the graphene particles. The foil
was then quenched to suppress graphene growth (FIG. 2B). After removal, a layer of polymethyl
methacrylate (PMMA) was spin coated on nickel foil (Figure 2C) and oxygen plasma (1 minute at
100 W) was used to etch away the graphene film on the opposite side of the foil ( Figure 2D). A
circular opening with a diameter of 8 mm was created with a disk cutter on adhesive Kapton tape
acting as a support frame. The support frame was then attached to the PMMA layer on nickel foil
(FIG. 2E). The nickel foil was then etched off in 0.1 g mL sodium peroxide solution (FIG. 2F).
Compared to iron chloride solution, the etch rate is much slower (typically an overnight etch was
required to remove 25 μm thick nickel) and the resulting graphene film is amorphous It was
clean without carbon. Thereafter, the exposed area (not covered by the support frame) of the
PMMA layer was dissolved in acetone and the graphene film supported by the frame was washed
twice with isopropanol and dried in air (FIG. 2G). PMMA between the support frame and the
graphene acts as a buffer and improves the yield to approximately 100% (process without PMMA
has a typical yield of -30%). In some cases, the graphene film was approximately 20 nm thick or
60 monolayers of graphene as measured by light transmission. A 25 μm diameter gold wire was
attached to the edge of the graphene film to obtain electrical contact (FIG. 2H).
Finally, approximately 150 μm thick spacers were attached to both sides of the frame, followed
by deep reactive etching (DRIE) to obtain a perforated electrode made of silicon wafer. The rigid
electrode was also wired by a gold wire attached by silver paste (FIG. 2I). The surface of the
electrode facing the graphene film was coated with a conductive metal layer (20 nm sputtered
gold) to allow ohmic contact between the gold wire and the electrode. This gold coating is used to
04-05-2019
17
eliminate contact barriers that can block the flow of current during microphone operation, as the
voltage change on the graphene film is very small. It should be noted that in loudspeaker
applications this metal coating is not necessary as a large voltage is applied.
[0056]
In some embodiments, the steps of the above-described method for producing a graphene
microphone can be used to produce a graphene loudspeaker. Other methods may be used to
manufacture graphene microphones or graphene loudspeakers.
[0057]
In some embodiments, a waveguide or Helmholtz acoustic cavity is attached to the graphene
microphone. The waveguide or Helmholtz acoustic cavity can modify the frequency response of
the graphene microphone in the low frequency region by altering the attenuation or generating /
eliminating interference.
[0058]
3A and 3B show an example of the working principle for a graphene microphone and associated
circuitry for signal extraction. In the embodiment shown in FIG. 3A, a large resistor R (e.g., 10
megohms) is used to convert current to voltage. A large resistor R restricts the flow of current
and causes the graphene film to operate in a constant charge mode, which converts the film
displacement into a voltage signal. This is the way in which conventional microphones operate.
However, this circuit can be problematic at high frequencies due to parasitic capacitance in the
transmission line.
[0059]
As can be seen with the equivalent circuit model in FIG. 3A, at high frequencies, the parasitic
capacitance exhibits a small impedance, reducing the voltage drop across R. For example, even
with a parasitic capacitance of 1 pF (e.g., equivalent to about 1 cm length of RG-58 coaxial cable),
the circuit response is limited to 1/2? RC = 16 kHz. This can be acceptable in acoustic
04-05-2019
18
microphone circuits, but this does not allow detection of ultrasound signals in the range of about
20 kHz to MHz.
[0060]
To avoid the limitations of the conventional circuit of FIG. 3A, in some embodiments, a current
sensing circuit similar to that used in high speed photodiode signal detection is used. An example
of such a circuit is shown in FIG. 3B. As shown in FIG. 3B, the graphene microphone includes a
graphene film 305, an electrode 310, and an electrode 315. In some embodiments, the circuit
that converts the response of the graphene film 305 from sound to an electrical signal includes
an amplifier 325 and a resistor 320. The graphene film is connected (eg, using wires or
terminals) to a voltage source (not shown). The positive input of amplifier 325 is connected to
ground. Resistor 320 is connected to the negative input of the amplifier and the output of
amplifier 325.
[0061]
In some embodiments, electrode 310 is connected to ground. As described above with respect to
FIG. 1A, in some embodiments, the graphene microphone does not include the electrode 310.
However, in some embodiments, the graphene microphone performs better (eg, better frequency
response) if the graphene microphone includes the electrode 310.
[0062]
In some embodiments, amplifier 325 is a low noise operational amplifier. In some embodiments,
amplifier 325 has a bandwidth of about 3 mH to 9 MHz, or about 6.5 MHz. The higher
bandwidth amplifiers allow the graphene microphone to sense higher frequency sounds.
However, higher bandwidth amplifiers may have lower signal to noise ratios. In some
embodiments, amplifier 325 has low input current noise. For example, a high speed precision
Difest operational amplifier OPA 602 (Texas Instruments Inc., Dallas, Tex.) Can be used as
amplifier 325.
[0063]
04-05-2019
19
In some embodiments, resistor 320 has a resistance of about 1 megaohm to 10000 megaohms,
about 1 megaohm to 100 megaohms, or about 10 megaohms. Resistor 320 with greater
resistance will produce a signal from amplifier 325 with a higher signal to noise ratio. However,
the resistor 320 with greater resistance will reduce the bandwidth of the graphene microphone,
which may reduce the high frequency response of the graphene microphone. The resistor 320
having a large resistance may cause the circuit to be unstable.
[0064]
In some embodiments, the voltage source operates to apply a positive or negative bias voltage of
about 20 V to 1000 V, or about 30 V to 100 V, to the graphene film 305. The higher the voltage
applied to the graphene film 305, the higher the signal to noise ratio is generated from the
amplifier 325.
[0065]
The current sensing circuit shown in FIG. 3B can enable flat band circuit responses from 0 to
about 0.5 MHz. A current sensing circuit measures the velocity of the vibrating membrane (ie,
the membrane vibration being induced by the sound wave) and reduces the graphene film
tension and the graphene microphone in the overdamped region to obtain a wider frequency
response Enable operation. The operational amplifier is configured such that the microphone
electrode is directly connected to virtual ground. As a result, the parasitic capacitance in the
equivalent circuit is effectively shorted, and iout = imic and vout = Riout = Rimic can be obtained.
The output voltage is directly proportional to the microphone vibration and is not affected by
parasitic capacitance. The current sensing circuit shown in FIG. 3B also maintains consistent gain
at high frequencies. The circuit shown in FIG. 3B was used in the graphene microphone
experiments described below.
[0066]
The microphone was measured using the free field method to determine the frequency response
of the graphene microphone. Briefly, the frequency was swept over a commercial loudspeaker
and the response of the commercial microphone was measured to obtain a frequency response
FR1 (f). Then, the commercial microphone was replaced with a graphene microphone and the
04-05-2019
20
measurement was repeated to obtain FR2 (f). The frequency response of the graphene
microphone was obtained by taking the difference between the two measurements. This
differential measurement eliminates the response of the loudspeaker, coupling and drive /
amplifier circuits. Commercial microphones typically have a relatively flat frequency response
within the operating range, so this measurement can properly represent graphene microphone
performance.
[0067]
4A-4C illustrate the frequency response of graphene microphones in different configurations.
FIG. 4A shows the frequency response of a graphene microphone in the audible range (20 Hz to
20 kHz) relative to a commercial condenser microphone. Here, 0 dB corresponds to the response
of 3.3 nA / Pa generated from the graphene film. In collecting data, we adopted a computer
sound card based system with software. The graphene microphones were housed in a Faraday
cage made of copper mesh. In FIG. 4A, the data is relatively flat above 500 Hz but there is a
significant drop in response at low frequencies (approaching up to approximately 60 dB /
decade). This drop is caused by the offset before and after the graphene film described above,
and becomes significant as the increase in wavelength allows sound to be diffracted around the
microphone. Importantly, this reduction is not inherent in the graphene film itself, and proper
acoustic design can improve response.
[0068]
Improvement of the low frequency response can be easily achieved by attaching an acoustic
cavity to one side of the graphene microphone electrode. By attaching the acoustic cavity to one
side of the microphone electrode, as shown in FIG. 4B, low frequency interference is eliminated
and the graphene microphone exhibits a flat (<10 dB variation) frequency response inherent over
the entire audible range The
[0069]
Due to the low areal mass density of graphene films, graphene microphones are expected to
respond to frequencies far beyond the human hearing limit. However, measuring the frequency
response in this region of ultrasound presents some problems, mainly due to the lack of a
broadband reference microphone or loudspeaker in the region of ultrasound. As mentioned
04-05-2019
21
above, piezoelectric ultrasonic transducers operate easily in the megahertz range, but only at
resonant frequencies. A broadband electrostatic graphene loudspeaker was used as a sound wave
transmitter and an electrostatic graphene microphone was used as a receiver. By measuring the
overall response with changes in coupling between these, the response of a single transmitter /
receiver can be separated.
[0070]
FIG. 4C shows the measured frequency response of the graphene microphone. A network
analyzer was used because the frequency exceeds the limits of conventional computer sound
cards. The response appears to be relatively flat (within 10 dB) up to approximately 0.5 MHz. It
should be noted that the measured maximum frequency of the flat frequency response is only
limited by the electronic amplifier circuit and can be extended with higher bandwidth operational
amplifiers or with different detection methods such as light detection Please note that.
Combining this result with the low frequency measurement (shown in FIG. 4B), the graphene
transmitter / receiver pair has an inherent equalization frequency response (20 Hz to at least 0.5
MHz) ideal for ultrasound acoustic radio operation With less than 10 dB).
[0071]
We recorded the cry of ultrasonic bats as an initial ultrasonic field test of graphene microphones.
Bats often use echolocation to travel through perfect darkness and roam for food. The frequency
of bat calls is in the range of as low as 11 kHz and as high as 212 kHz, depending on the species.
The acoustic signals of bats (bat calls) were collected locally using a graphene microphone at Del
Valle Regional Park in Livermore, California, where the bat species Western bat (parastrillus
hesperus) is commonly found. By means of the spectrogram, bat sounds consist of periodic
chirps, during which the emitted frequency is consistently decreasing at frequencies of
approximately 100 kHz to approximately 50 kHz. The duration of each chirp was about 4 ms and
the repetition period was about 50 ms. Bats are thought to use frequency sweep techniques to
identify multiple targets, improve measurement accuracy, and avoid interference from each
other. The frequency sweep or chirping of the bat represents a form of ultrasound FM radio
transmission, and the success of this recording demonstrates the effectiveness of the graphene
microphone as an ultrasound acoustic radio receiver.
[0072]
04-05-2019
22
FIG. 5A shows a schematic view of an ultrasound transceiver (ie, an ultrasound acoustic radio). As
shown in FIG. 5, the ultrasound system 500 includes a transmitter 505 and a receiver 510.
Transmitter 505 may be any of the loudspeakers described herein. For example, transmitter 505
can be a graphene loudspeaker 100 as shown in FIG. 1C. Receiver 510 may be any of the
microphones described herein. For example, receiver 510 can be a graphene microphone 150
shown in FIGS. 1A and 1B.
[0073]
FIG. 5B shows an example of a flow diagram illustrating the method of using the ultrasound
transceiver. At block 555 of method 550, a transmitter is used to generate an acoustic wave. In
some embodiments, the transmitter comprises a graphene film. In some embodiments, the sound
waves have a frequency of about 20 kHz to 10 GHz, about 200 kHz to 10 GHz, about 20 kHz to
10 MHz, or about 200 kHz to 10 MHz. For example, sound waves can be generated using
transmitter 505 shown in FIG. 5A.
[0074]
At block 560, the receiver is used to receive sound waves. In some embodiments, the receiver
comprises a graphene film. For example, sound waves may be received using receiver 510 shown
in FIG. 5A. Sound waves received at the receiver can have low power. For example, the power of
the sound waves received by the receiver may be about 1 femtowatt (ie 1 × 10 <15> watts) or
greater.
[0075]
Different frequencies can be transmitted and received using the method 550 shown in FIG. 5B.
For example, method 550 may be performed to transmit and receive a first frequency sound
wave, and then method 550 may be repeated to transmit and receive a second frequency sound
wave. In some embodiments, the first and second frequencies are both in the ultrasound
frequency range. In some embodiments, the first and second frequencies are frequency separated
from one another by at least about 50 Hz, at least about 100 Hz, at least about 1 kHz, or at least
about 10 kHz. For example, the first frequency may be about 20 kHz to 200 kHz, and the second
frequency may be about 500 MHz to 1.5 GHz.
04-05-2019
23
[0076]
In some embodiments, sound waves are used to transmit information. For example, in some
embodiments, the sound wave comprises amplitude modulation. The amplitude of the sound
wave changes in proportion to the waveform being transmitted in amplitude modulation. In some
embodiments, the sound wave comprises frequency modulation. The frequency of the sound
waves varies in proportion to the waveform being transmitted with frequency modulation. The
amplitude modulation or frequency modulation of the sound wave allows the sound wave to
contain or convey information. For example, electronic circuitry associated with transmitter 505
can change the amplitude or frequency of the sound wave to encode information in the sound
wave. Electronic circuitry associated with receiver 510 can demodulate received sound waves
and extract information.
[0077]
In some embodiments, sound waves are used to transmit power from the transmitter to the
receiver. For example, sound waves can be used to transmit power to power the device or to
charge the battery of the device. In some embodiments, the sound waves have a power of about
500 milliwatts to 5 watts or about 1 watt. The sound waves can be converted to DC power after
being received at the receiver. Charging the battery of the device with ultrasonic waves may be
advantageous compared to charging the battery of the device with electromagnetic induction,
and with ultrasonic waves the transmitter compared to electromagnetic induction. And the
receivers can be separated from each other.
[0078]
6A-6C illustrate examples of the performance of an ultrasound transceiver. FIG. 6A shows an
embodiment of an ultrasound transceiver 600 including a transmitter 605 and a receiver 610.
Transmitter 605 may be, for example, any of the graphene loudspeakers described herein. The
receiver can be, for example, any of the graphene microphones described herein.
[0079]
04-05-2019
24
In order to eliminate the possibility of the effects of EM radiation, both the transmitter and the
receiver were placed in a Faraday cage where EM communication is not possible. A 0.3 MHz
electron carrier sine wave with a 5 kHz sawtooth (90% amplitude modulation (AM)) was
modulated. The mixed signal was monitored by an oscilloscope (FIG. 6B). The electrical signal
was sent to a graphene transmitter that transmits ultrasound signals into the air. The frequency
after mixing can not be heard because it is sufficiently above the human hearing limit. FIG. 6C
shows the ultrasound signal detected by the graphene receiver and converted back to an
electrical signal. The received signal exactly duplicates the transmitted signal, and the
information is transmitted with high fidelity. It should be noted that sharp sawtooth modulation
extends the peak like a single delta function of a sine wave in the frequency domain to a much
wider peak, and the broadband characteristics of the graphene ultrasound acoustic radio have
the shape of the sawtooth (i.e. coding Note that it is essential to hold information). Narrow band
piezoelectric ultrasound transducers do not have this property.
[0080]
Another application of ultrasound transmitting and receiving devices is position detection, ie
distance measurement. The use of ultrasound for position detection is well established and it is
certainly possible to use graphene transmitters and receivers in a high directivity sonar like
reflection configuration. Here we consider the electroacoustic interference of different
embodiments.
[0081]
7A and 7B show examples of schematic illustrations of a distance measuring device 700 that can
exploit the interference between acoustic and electromagnetic (EM) signals and signals obtained
from such devices. The graphene transmitter 705 operates to transmit acoustic waves as well as
EM waves of the same frequency (EM antenna 710 is added to the graphene transmitter 705
driver electronics). A graphene receiver 725 separated by a distance L receives the acoustic
signal with the EM signal (EM receiving antenna 730 is added to the transducer electronics on
the graphene receiver 725).
[0082]
The sound propagates much more slowly than the EM, so the acoustic signal received by the
graphene film of the receiver 725 will be out of phase with the EM signal of the electronic
04-05-2019
25
receiving antenna 730.
[0083]
As can be seen in FIG. 7B, when a frequency sweep is performed, the interference alternates
between constructive and destructive interference due to changes in wavelength λ.
The condition of constructive interference is Where L is the distance between the receiver and
the transmitter, λ is the wavelength of the sound wave, and n is an integer. The two closest
constructive peaks should follow the following equation: Using λ = v / f (where v is the speed of
sound and f is the frequency) we get
[0084]
The distance L is equal to the speed of sound divided by the frequency difference Δf of the two
closest constructive interference peaks. The graphene transmitter / receiver pairs were placed at
three different distances 30 mm, 45 mm and 85 mm apart. The measured frequency sweeps are
shown from top to bottom in three groups in FIG. 7B. The farther the pair is, the weaker the
signal and the smaller the frequency difference between the two constructive peaks. By fitting
the peaks, frequency differences Δf of 11.28 ± 0.08 kHz, 7.657 ± 0.003 kHz, and 4.05 ± 0.07
kHz were found respectively. Using a sound velocity of 344 m / s, this corresponds to a
measurement distance of 30.49 ± 0.22 mm, 44.92 ± 0.02 mm, and 84.94 ± 0.84 mm. In this
way, sub-mm accuracy is easily achieved using this simple electroacoustic frequency sweep
configuration.
[0085]
Electrical Modeling of Graphene Microphones A conducting vibrating graphene diaphragm forms
a variable capacitor with a fixed electrode. The capacitance is Is the vacuum dielectric constant, A
is the area of the graphene film, and x is the distance from one of the electrodes to the graphene
film. When the diaphragm is DC biased at approximately 50 V, charge is induced on the
electrode, which is described by Q = CV. Vibration of the diaphragm changes the system
capacitance and induces charge fluctuations on the electrodes, producing a current of the form:
Where u is the velocity of the membrane relative to the electrode. Thus, a graphene microphone
04-05-2019
26
can be modeled as a current source with infinite internal resistance if the current encodes a
sound wave. At the thin film limit where the graphene diaphragm vibrates with air, u is equal to
the local velocity field of air, and the amplitude U is Where p is the sound pressure level (SPL)
and Z = 400 N · s · m <-3> is the acoustic impedance of air. Thus, the amplitude of the
microphone current source is directly proportional to the loudness of the sound and independent
of the audio frequency. Using the second and third equations, it is known that the current
amplitude at 40 dB SPL (nearly soft conversation at 1 m) is 2 pA, with V = 50 V, A = 25 mm <2>,
x = 150 μm . This level of current can be reliably measured with careful signal conditioning
circuit design.
[0086]
Conventional Microphone Operation Compared to Graphene Microphone Operation A
conventional microphone measures the voltage change of the vibrating membrane. The operation
is shown in FIG. The operation of the microphone shown in FIG. 8 can be implemented using the
circuit shown in FIG. 3A. In a conventional microphone, the membrane is connected to a very
large resistor, and the charge Q is almost constant during operation. According to Gauss's law, a
charge Q results in a voltage drop between two plates. Where Q is the charge on the membrane,
d0 is the distance between the membrane and the electrode at the equilibrium position, S is the
area of the membrane, Asin (ωt) is the membrane vibrational displacement at amplitude A, ε is
the vacuum dielectric constant It is. When measuring the voltage response, it has been found that
the AC part is proportional to the amplitude A of the vibrational displacement.
[0087]
In this case, the overdamped system does not produce a flat band response. If the system is
modeled as a harmonic oscillator, then Where m is the membrane mass, ζ is the damping
coefficient, k is the spring constant, and F is the driving force applied to the membrane equal to
the sound pressure SP sin (ωt). The solution for the vibration amplitude is
[0088]
If the system becomes overdamped, then the damping term ζω becomes more dominant than
the other terms, thus A ~ω <−1>. This means that the measured voltage signal also decreases as
the frequency increases. This is the case for a conventional microphone where a relatively high
04-05-2019
27
tension film is desired, where the spring constant term k dominates and can have a flat band
response.
[0089]
As mentioned above, graphene microphones use current sensing mechanisms to support
functions in the high frequency region. FIG. 9 shows an example of the operation of a graphene
microphone. As shown in FIG. 9, the circuit actually measures the vibration velocity instead of the
displacement. The operation of the microphone shown in FIG. 9 can be implemented with the
circuit shown in FIG. 3B.
[0090]
The graphene film is held at a voltage V. The amount of charge on the graphene film is actually
changing, and a current is generated to extract vibration information. The charge on the
graphene film or fixed electrode can be calculated with the following equation using parallel
plate capacitors. The vibration amplitude is usually much smaller than the distance between the
graphene film and the electrode, and the equation can be Taylor expanded into a linear equation
at A << d0. The time variation of the charge is the measured current of the following formula. It
has been found that the amplitude of the measured current is proportional to Aω.
[0091]
Here, returning to the equation of motion, the following is obtained. Thus, an overdamped system
in which the damping term 減 衰 dominates the other terms provides a constant flow amplitude,
ie a flat band frequency response.
[0092]
Conclusions An electrostatic graphene ultrasound acoustic radio with an ideal equalized
frequency response of about 20 Hz to 0.5 MHz has been demonstrated. The receiver component
performs an independent field test when recording wild bat sounds. Amplitude and frequency
modulation communications have been demonstrated, and a novel electroacoustic distance
04-05-2019
28
measurement method has been established with an ultrasonic radio receiver with an accuracy of
less than mm.
[0093]
In the above specification of the present invention, the invention has been described with
reference to specific embodiments. However, one of ordinary skill in the art appreciates that
various modifications and changes can be made without departing from the scope of the present
invention as set forth in the claims. Accordingly, the specification and figures are to be regarded
in an illustrative rather than a restrictive sense, and all such modifications are intended to be
included within the scope of the present invention.
[0094]
150 graphene microphone 155 graphene film 157 frame 160, 165 electrode 167 small hole or
opening 170, 175 spacer 180 conductive material 185 acoustic cavity
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