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Implementation of Wireless Charger for Mobile Phone
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Based on Solar Energy
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Running Head: Implementation of Wireless Charger for Mobile Based Solar
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Talit Jumphoo1, Peerapong Uthansakul1* and Hoi-Shun Lui2
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School of Telecommunication Engineering, Suranaree University of Technology
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Muang, Nakhon Ratchasima, Thailand 30000
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School of Information Technology and Electrical Engineering, The University of
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Queensland
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Brisbane St Lucia, QLD, 4072, Australia
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Email: [email protected], [email protected], [email protected]
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*Corresponding Author
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Abstract
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Recently, the technology that can promise to energize devices without wire
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connection has been in attention of researchers around the world. Moreover,
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if this technology can merge the ability to harvest energy from the
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environment, then it can provide the long-life battery for many important
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applications and permit deploying self-energized devices. This paper presents
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the use of a solar energy to charge mobile phone with wireless connection.
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The design and implementation of proposed system have been undertaken.
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The measured results indicate that the proposed system can be used as the
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wireless charger powered by solar energy. The prototype sourced by solar
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energy has been tested outdoor from 10:00-17:00 for 3 days. The results show
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that the light intensity plays a main role on the charging time of the wireless
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charger.
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Keyword: wireless charger, solar energy, transformer, Magnetic flux
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Introduction
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Self-energized devices can be powered by different kinds of energy, including
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radio frequency, solar, thermal, and vibration. In addition, a single device can be
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energized from multiple ambient energy sources (G. Park, 2005; Ferro Solutions
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2004). Radio frequency (RF) devices utilize electromagnetic radiation emitted by
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radio devices, such as wireless radio networks. As the most commonly used
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frequencies are well known, the devices have an antenna and circuitry tuned to
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maximize energy harvesting at these frequencies. Unfortunately, typical electric
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field strengths are weak (unless located close to sources), which severely limits
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the quantity of energy that can be harvested, e.g., to approximately two orders of
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magnitude less than indoor solar and thermoelectric devices. Active systems
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attempt to overcome this limit by broadcasting RF energy, as is done currently for
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RFID tags used in commercial (J.A. Paradiso and T. Starner, 2007).
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Thermoelectric devices consume energy developed from temperature differences
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via the Seebeck effect, i.e., a temperature difference at the junction of two metals
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or semiconductors causes current to flow across the junction. The power density
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of thermoelectric increases with the temperature difference increasing their
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attractiveness in applications such as sun/shade installations, compressors, and
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hot/cold/air/water/refrigerant flows. Vibration sources extract energy from
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ambient vibrations. As power usually scales with the cube of vibration frequency
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and the square of vibration amplitude, these devices have the most value in
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applications with high frequency, high-amplitude vibrations. Thus, potentially
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promising vibration sources could include compressors, motors, pumps, blowers,
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and, perhaps to a lesser extent, fans and ducts. All vibration-harvesting systems
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contain mechanical elements that vibrate, typically a spring-mass assembly with
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its natural frequency close to those of the vibration source to maximize energetic
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coupling between the vibration source and the harvesting system. Several
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different ways exist to translate the vibrating elements into electric energy,
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including piezoelectric (S. Tigunta et al., 2013; A. Boonruang et al., 2012),
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capacitive, and inductive systems (S. Roundy, 2003).
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Solar energized devices use photovoltaic (PV) (S. Phungsripheng et al., 2013)
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cells to convert incident light into electricity. As such, they leverage the extensive
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investments made and progress achieved in increasing the efficiency and reducing
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the cost of PV for building- and utility-scale power. Solar devices can produce
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energy from both outdoor and indoor light sources, although outdoor insolation
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levels yield approximately two to three orders of magnitude more electricity per
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unit area than indoor electric light sources (J.A. Paradiso and T. Starner, 2007; S.
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Roundy; 2003). Relative to other sources, solar devices can achieve high energy
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densities when used in direct sun, but will not function in areas without light (e.g.,
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highly shaded areas, ducts). Applications to date include contact and motion
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sensors for building applications (C. Park and P. Chou, 2004) as well as
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calculators, PDAs, and wristwatches. While a wide variety of harvesting
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modalities are now feasible, solar energy harvesting through photo-voltaic
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conversion provides the highest power density, which makes it the modality of
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choice to power an embedded system that consumes several mW using a
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reasonably small harvesting module.
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This paper focuses on using solar cell energy in providing an alternative power
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source to charge mobile phone devices. Previous works in this field can be found
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in (T. Voigt, H. Ritter, and J. Schiller, 2003; A. Kansal and M. Srivastava, 2003;
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A. Kansal, D. Potter, and M. Srivastava, 2004). A solar harvesting augmented
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high-end embedded system was described by T. Voigt et al. (2003), in which a
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switch matrix was used to power individual system components from either the
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solar panel or the battery. Harvesting aware protocols have also been proposed for
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data routing (A. Kansal and M. Srivastava, 2003), and distributed performance
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scaling (A. Kansal, D. Potter, and M. Srivastava, 2004). Apart from solar energy,
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this paper also presents the wireless channel for power charging by converting the
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solar energy into wireless signal in which the mobile phone can be charged
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without wire connection. The motivation of this wireless charger is as follows.
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Through the years, technology has allowed the cellular phone to shrink not only
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the size of the ICs, but also the batteries. New combinations of materials have
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made possible the ability to produce batteries that not only are smaller and last
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longer, but also can be recharged easily. However, as technology has advanced
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and made our phones smaller and easier to use, we still have one of the original
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problems: we must plug the phone into the wall in order to recharge the battery.
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Most people accept this as something that will never change, so they might as
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well accept it and carry around either extra batteries with them or a charger. Either
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way, it is just something extra to weigh a person down. There has been research
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done in the area of shrinking the charger in order to make it easier to carry with
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the phone. Most people do not realize that there is an abundance of energy all
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around us at all times. We are being bombarded with energy waves every second
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of the day. Radio and television towers, satellites orbiting earth, and even the
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cellular phone antennas are constantly transmitting energy. If it could be possible
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to gather the energy and store it, we could potentially use it to power other
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circuits. In the case of the cellular phone, this power could be used to recharge a
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battery that is constantly being depleted. The potential exists for cellular phones,
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and even more complicated devices - i.e. pocket organizers, person digital
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assistants (PDAs), and even notebook computers - to become completely wireless.
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The concept needs an efficient antenna along with a circuit capable of converting
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alternating-current (AC) voltage to direct-current (DC) voltage. The efficiency of
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an antenna, as being discussed here, is related to the shape and impedance of the
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antenna and the impedance of the circuit. The details of proposed wireless charger
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is described in the next section including transmitting and receiving circuits.
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Then, the experimental setup, measured results and discussion are presented
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respectively.
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Components of Proposed Wireless Charger
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Transmitting Circuit
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In general, there are many kinds of circuit that can convert the DC power
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energized by solar cells into another form. In this paper, the concept of
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transformer has been adopted and modified by using only air medium instead of
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iron. This is like the induction theory from the basic principle of electromagnetic
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dilemma. When the current flows into a coil, the magnetic flux will be generated
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and radiate in the perpendicular plane at the center of coil. This magnetic flux
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depends on the intensity of current as well as the number of coils. The formula of
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magnetic field can be expressed in (1).
B=
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μo nI
2a
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where μo = 4π × 10−7 H/m
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From Faraday law, the relationship between electromotive force and magnetic
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flux can be given by (2).
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ε= −
N∆∅
∆t
(1)
(2)
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where ε is the electromotive force, ∆∅ is the changing of magnetic flux, ∆t is the
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interval time of magnetic flux changing and N is the number of coil.
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The original concept of Faraday's iron ring apparatus requires the iron to be the
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medium for magnetic flux to flow across two coils. This concept has been
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modified by replacing air medium instead of iron ring. It can be obviously
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realized that the efficiency of air-core transformer is lower than iron but this can
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make the charger be wireless of mobile phone.
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For the transmitting circuit, this paper uses a transistor to be an electronic
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amplifier to connect with feedback loop as illustrated in Figure 1. The point 1 of
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Figure 1 is the frequency filter which is designed by RC circuit. The resistance
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and capacitance form the action of phase-shifted oscillator in order for positive
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feedback. When the electric source is input at the amplifying circuit, the noise in
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electronic circuit will make the oscillator work. After that, the LC circuit has been
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selected to tune the operating frequency as shown in point 2 of Figure 1. The
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inductance and capacitance will store the electric power at frequency resonant. At
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this point, the current flows into coil and the inductive electromagnetic field will
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be transferred to receiver via air medium. The last part of transmitting circuit is
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low pass filter as seen in point 3 of Figure 1. The inductance 𝑋𝐿 is low and the
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capacitance 𝑋𝐶 is high. Then, the low frequency signals can easily pass the
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inductive coil in which the output of system is high. In turn, the higher frequency
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signals hardly pass through the filter.
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In the RC design, the capacitor is set to 470 pF and resistance is 15kΩ. It is used
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to control the interval time between charge and discharge process. For the tuning
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filter, the capacitor is set to 100 nF. The transistor BD139 is selected to amplify
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signals. The capacitor of matching the coil impedance is set to 4.7 nF in which the
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complex value of capacitor and coil will be cancelled to each other.
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Figure 2 depicts the assembly of wireless charger for (left) inside and (right)
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outside. It can be clearly seen that the overall circuit and coil is so thin and small
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that all assembly can be easily installed. The box of wireless charger can be
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modified to fit with any mobile layouts.
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Receiving Circuit
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In the receiving circuit, the first part is the receiving coil reacting the power
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transfer from transmitter as seen in point 1 of Figure 3. This current will be fed to
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the rectifier in order to convert from AC to DC. The rectifier is shown in point 2
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of Figure 3. Finally, the voltage regulator will be used to control the constant level
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of output at 5V as shown in point 3 of Figure 3. This regulator is very important
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because it is the safety checker for mobile phone. In case that the output voltage is
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not stable, the variation of voltage will make the life time of battery shorter.
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Moreover, it might cause the mobile phone broken. As seen in Figure 3, the
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matching part use the capacitor of 4.7 nF. The diode 1N4148 is used to perform
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the AC to DC conversion. IC LM7805 is performed as the regulator to control the
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constant output of 5V.
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Figure 4 shows the assembly of mobile phone for (left) inside and (right) outside.
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It is clearly seen that the circuit and coil is so thin and small that can be placed
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inside the case of mobile phone. The modified mobile phone can be used normally
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in all functions.
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Magnetic Transferring Coil
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One of the most important part of wireless charger is the magnetic transferring
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coil. This paper chooses the flat spiral coil inductor because it save the space by
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spreading a number of coils over one flat plane as shown in Figure 5. This is very
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practical because it can be used to install on the back case of mobile phone. In this
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paper, the area of back case is 5.8cm x 1.1cm. Therefore, the selection of copper
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wire has to be take this area into account. That is the reason why this paper
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chooses the copper number 22 which is suitable for this back case.
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All components of wireless charger for mobile phone can be illustrated in Figure
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6 and the photography of real prototype is presented in Figure 7. As seen in Figure
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7, the dimension of solar cell is small and convenient to install on any rooftop.
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Actually, there are many products of solar cell in commercial. This paper employs
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the popular product on the shelf which its efficiency is typical. Please note that the
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higher voltage and current can be achieved if the size and quality of solar cell is
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extended.
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Experimental Results and Discussion
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Three experiments have been carried out in order to investigate the performance
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of proposed system. The first experiment is to investigate the change of current
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and voltage from solar energy throughout daytime. This experiment will let the
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researcher realize the suitable time period and the gap in one day of using solar
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energy. The second experiment is to compare between using proposed system as
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wireless charger and using conventional charger as wire charger. The results will
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let us know the acceptable delay when using wireless charger. For the last
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experiment, the relationship between voltage and distance between charger and
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mobile phone is illustrated. The results will guide the design of proper space for
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holding the mobile.
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For the first experiment, the prototype shown in Figure 7 has been tested outdoor
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for 3 days. In each day, the measurement starts on 10:00 and stops on 17:00.
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Within 1 hour, the data has been recorded 10 times and the averaging values is the
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representative value for that interval. The results in Table 1 show that the
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maximum current and voltage can be achieved at the time of 13:00-14:00. This is
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because at that time the sunlight strongly provides the maximum light intensity.
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However, the current gap between minimum and maximum is 75.3 mA which is
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very high. It means that this charger cannot be used for all daytime. This is the
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limit of wireless charger to be energized by solar cell.
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In the second experiment, the results in Table 2 reveal that the charging time of
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conventional charger consume 1.38 minutes to charge 1% of battery while it takes
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7.24 minutes for wireless charger. This is about 5.2 times longer by wireless
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charger. This delay is the expense of more convenient devices which is not
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required wire connection any more.
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For the last experiment, the relationship of voltage and distance between wireless
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charger and mobile phone is investigated. The measurement is undertaken at
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11:00. The results help researcher to design the tradeoff between power
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degradation and the thickness of case in practice. As seen in Figure 8, the
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minimum distance is limited to 4.5 cm because the voltage will be dropped below
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5 V in which it cannot utilize for charging battery.
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Conclusion
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This paper suggests the use of a solar energy in mobile phone devices in
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cooperating with wireless charging technology. The results of this paper indicate
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that it is possible to use solar energy to supply mobile phone batteries with the
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necessary power. Also the prototype prove that the implementation is simple and
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it can be done easily for public use. Although the charging time of wireless
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charger is longer by 5.2 times, but there is no need to pay the cost of electricity.
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This can be a free energy source for devices in daily use.
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References
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G. Park (2005) Overview of Energy Harvesting Systems (for Low-
233
PowerElectronics). the First Los Alamos National Laboratory Engineering
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Institute Workshop: Energy Harvesting. p 1-11.
235
236
237
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Ferro Solutions (2004). VEH-360: Evaluation Power System Specifications.
Elsevier, NY, 605p.
J.A. Paradiso and T. Starner (2007) Energy scavenging for mobile and wireless
electronics. Pervasive Computing. 4(1):18–27.
239
S. Tigunta, N. Pisitpipathsin, S. Eitssayeam, G. Rujijanagul,T. Tunkasiri,and K.
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Pengpat (2013) Effects of BZT Addition on Physical and Electrical
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Properties of Calcium Phosphate Bioglass. Suranaree Journal of Science and
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Technology., 20(3):197-203
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A. Boonruang, Piyalak Ngernchuklin, Saengdoen Daungdaw, and Chutima
244
Eamchotchawalit (2012) Influence of Milling Method on the Electrical
245
Properties of 0.65PMN-0.35PT Ceramics. Suranaree Journal of Science and
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Technology., 19(4):251-257.
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S. Roundy (2003) Energy scavenging for wireless sensor nodes with a focus on
248
vibration-to-electricity conversion. Presentation at University of California,
249
Berkeley. http://tinyurl.com/2s8khk.
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S. Phungsripheng, S. Sanorpim, T. Wasanapiarnpong (2013) Effect of nitrogen
251
doping on photovoltaic property of lead lanthanum zirconate titanate
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ferroelectric ceramics. Suranaree Journal of Science and Technology., 20
253
(2):109-116.
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C. Park and P. Chou (2004) Power utility maximization for multiple-supply
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systems by a load-matching switch. Proc. ACM/IEEE International
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Symposium on Low Power Electronics and Design. pp. 168–173.
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T. Voigt, H. Ritter, and J. Schiller (2003) Utilizing solar power in wireless sensor
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networks. Proc. IEEE Conference on Local Computer Networks. p 1-5.
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A. Kansal and M. Srivastava (2003) An environmental energy harvesting
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framework for sensor networks. Proc. ACM International Symposium on
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Low Power Electronics and Design, pp. 481–486.
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A. Kansal, D. Potter, and M. Srivastava (2004) Performance aware tasking for
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enrironmentally powered sensor networks. Proc. ACM International
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Conference on Measurement and Modeling of Computer Systems, pp.223–
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234.
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Figure 1. Transmitting Circuit
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Figure 2. Assembly of wireless charger (left) inside and (right) outside
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Figure 3. Receiving Circuit
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Figure 4. Assembly of mobile phone (left) inside and (right) outside
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Figure 5. Flat spiral coil
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Figure 6. All components of wireless charger for mobile phone.
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Figure 7. Photography of proposed wireless charger.
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Table 1. Average currents and voltages of wireless charger.
Day1
Time
10.0
0
11.0
0
12.0
0
13.0
0
14.0
0
15.0
0
16.0
0
17.0
0
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Day2
Day3
Average
Curren
t
(mA)
108.3
Voltag
e
(V)
10.15
Curren
t
(mA)
115.0
Voltag
e
(V)
10.18
Curren
t
(mA)
122.7
Voltag
e
(V)
10.37
Curren
t
(mA)
115.1
Voltag
e
(V)
10.23
101.7
10.32
102.9
10.31
103.3
10.32
102.6
10.32
139.2
10.00
132.1
9.97
140.6
10.01
137.3
9.99
145.8
10.35
144.0
10.42
141.6
10.38
143.8
10.38
145.1
10.35
144.8
10.35
145.2
10.36
145.0
10.35
110.7
10.27
110.9
10.24
113.2
10.24
111.6
10.25
97.4
10.14
97.4
10.15
96.6
10.11
97.1
10.13
68.8
9.58
70.1
9.62
70.2
9.59
69.7
9.60
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Table 2. Comparison of charging time between wire and wireless chargers
for charging 1% battery.
Type of Charger
Wire
(minute)
Wireless
(minute)
1
1.39
7.27
2
1.35
7.13
3
1.48
7.26
4
1.42
7.39
5
1.27
7.14
6
1.42
7.28
7
1.24
7.14
8
1.43
7.21
9
1.30
7.15
10
1.43
7.22
11
1.38
7.40
12
1.32
7.27
13
1.39
7.39
14
1.37
7.20
15
1.39
7.13
16
1.23
7.16
17
1.53
7.24
18
1.49
7.14
19
1.39
7.45
20
1.44
7.14
Average
1.38
7.24
Number of Iteration
295
296
297
298
299
300
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Figure 8. Voltage versus distance between wireless charger and mobile phone
energized by solar cell at 11:00.