10-09-2016, 04:16 PM
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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.