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Abstract: Graphene-based materials have attracted much attention in recent years. Many researchers have
demonstrated prototypes using graphene-based materials, but few specific applications have appeared. Graphenebased
acoustic devices have become a popular topic. This paper describes a novel method to fabricate graphenebased
earphones by laser scribing. The earphones have been used in wireless communication systems. A wireless
communication system was built based on an ARM board. Voice from a mobile phone was transmitted to a
graphene-based earphone. The output sound had a similar wave envelope to that of the input; some differences
were introduced by the DC bias added to the driving circuit of the graphene-based earphone. The graphene-based
earphone was demonstrated to have a great potential in wireless communication.
Introduction
Graphene has attracted the attention of many
researchers in recent years. Its outstanding properties[1]
,
such as mechanical strength[2], thermal conductivity[3]
,
ultra-high mobility[4], and transparency[5] make it
attractive for use in electronic devices. Previously,
graphene was used in sound-emitting components
because of its thermal acoustic effect[6]. Conventional
speakers require mechanical moving parts to compress
air and generate sound waves; thermoacoustic speakers
work by rapid heating and cooling of a conductor that
causes expansions and contractions of the air which,
in turn, generates sound. However, because of its
zero bandgap, graphene is not suitable for low-power
electronic applications[7]. Researchers have now found
that Graphene Oxide (GO) has a bandgap of larger than
0.5 eV[8], and it can be easily reduced to graphene,
which could then be considered as a semiconductor
or a semimetal[9]. Gao et al.[10] presented a method of
laser reduction of GO to produce micro-supercapacitors
on hydrated graphite oxide films. Later, El-Kady and
Kaner[11] leveraged DVD laser scribing to improve the
performance of micro-supercapacitors.
2 Experimental
2.1 System structure
Figure 1 shows a schematic diagram of our system. The
graphene-based earphone is the receiving side of the
system. The output signal is amplified by power
amplifiers. An ARM board (Mini2440) was selected
as the control part, which controls the communication
between the user and the graphene-based earphone with
the help of the 3G module (MF210). This structure
enables the graphene-based earphone to emit users’
voices.
Our system uses an ARM9 Development Board
Mini2440, which is based on a 32-bit RISC architecture
microprocessor S3C2440 from Samsung Company. The
microprocessor has an ARM920T as its core, while
the standard macro unit and memory unit of the
chip employ 0.13m CMOS. The board measures
100 mm 100 mm. The processor’s domain frequency is set at 400 MHz, and can be increased up to
533 MHz. It is equipped with 64 MB SDRAM and
NAND Flash, and 2 MB NOR Flash with a preinstalled
BIOS. There are no setup steps or configuring
procedures to start the system. The board has low power
consumption, simple architecture, low cost, rapid
data processing, and non-volatile power down. The
Mini2440 provides rich on-chip resources. smf
supports operating system such as Linux, WinCE,
and Android. It offers such functions as physical
layer communication, device-specific applications, and
single-chip software design. In the proposed system,
as the central controller, the microprocessor S3C2440
is central. The MF210 module supports the central
processor effectively. Figure 2 shows a schematic
diagram of the Mini2440 and MF210. As noted
above, the Mini2440 development board is used to
control the monitor and the MF210 module. To achieve
communication between the two sections, the Mini2440
development board is connected with the MF210
module via a USB cable, at a rate of 115 200 bps. The
USB cable links the two parts on two USB hosts that
are provided on the board. The Mini2440 creates a
directory named /ttyUSB0 automatically when the
development board is powered on. Then the device
is mounted as a device file one /dev/ttyUSB2 in
Linux. The central processor Mini2440 controls and
monitors the MF210 module, obtaining its state and
feedback. In addition, a WCDMA sim card is inserted
into the MF210 module to guarantee that users find
the device by calling the number successfully. The
work mentioned above is supported by China Unicom
Network and the device can be connected by the
number provided by China Unicom. In order to make
sure the communication signal is sent and received
efficiently and stably, an antenna was integrated into the
MF210 module. Furthermore, the core chip of MF210
module can decode the audio and connect with external
8/16 bit binaural CODEC, so the module has a 3.5-
mm standard binaural audio interface, through which
the decoded analog voice signal is communicated to a
connected device.
2.2 Architecture of the ARM system
More recently, Tian et al.[12, 13] used laser scribing
technology to fabricate loudspeakers on a wafer. Our
group has reported on some novel acoustic devices
previously[14–20]. In this paper, a more complex acoustic application is described. With the refinement
of communication technology through the use of
microcontrollers, there are many ways to make a
telephone call. However some people, such as the
elderly, may not know how to use a phone; this can
make it difficult to call an old person. Many monitoring
systems have been built to monitor the elderly[21–24]
,
but they have been complex. If we could effectively
call old people at any time, we could make contact
with them without the need of a complex monitoring
system. With the help of an ARM development board
and a graphene-based earphone, we have come up with
a system that enables speaking to hearing-impaired
older people using a mobile phone. The ARM allows
the elderly answering a call automatically without the
need of pressing any keys. Considering that they wear
the graphene-based earphone all the time, they won’t
miss any call. The graphene-based earphone doesn’t
include vibration components and it can be ultra-thin,
so it won’t cause any uncomfortableness when it is worn
all the time. In this work, a wireless communication
system based on an ARM board was built. The
graphene-based earphone was connected to the ARM
board, so that the voice could be produced through the
graphene-based earphone. The output sound from the
graphene-based earphone showed a similar frequency
spectrogram to that of the voice input.
Software design
The software design was implemented on a Mini2440
development board. The Mini2440 software was stored
in memory to ensure speed and stability when
executed. System control employs programs written in
C and executed under Fedora (an operating system
based on the Linux kernel). The program design of
the system is diagrammed in Fig. 3. Communication is
controlled by C-language programs, whose main steps
are as follows. First, a program opens a USB serial
port device and initializes the system. It sets the bps
rate at 115 200. Second, an AT command is sent to
test the module and configure it for an analog voice
signal. Afterwards, the Mini2440 monitors the USB
port and reads the message that appear. If there is a
call, the Mini2440 answers it after two rings. Finally,
any digital voice received is decoded into analog form,
which is sent to the earphone via the binaural voice
port. A conversation is thus established.