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1 Implementation of Wireless Charger for Mobile Phone 2 Based on Solar Energy 3 4 Running Head: Implementation of Wireless Charger for Mobile Based Solar 5 6 Talit Jumphoo1, Peerapong Uthansakul1* and Hoi-Shun Lui2 7 8 1 School of Telecommunication Engineering, Suranaree University of Technology 9 10 Muang, Nakhon Ratchasima, Thailand 30000 2 School of Information Technology and Electrical Engineering, The University of 11 Queensland 12 Brisbane St Lucia, QLD, 4072, Australia 13 Email: [email protected], [email protected], [email protected] 14 *Corresponding Author 15 16 Abstract 17 Recently, the technology that can promise to energize devices without wire 18 connection has been in attention of researchers around the world. Moreover, 19 if this technology can merge the ability to harvest energy from the 20 environment, then it can provide the long-life battery for many important 21 applications and permit deploying self-energized devices. This paper presents 22 the use of a solar energy to charge mobile phone with wireless connection. 23 The design and implementation of proposed system have been undertaken. 24 The measured results indicate that the proposed system can be used as the 25 wireless charger powered by solar energy. The prototype sourced by solar 26 energy has been tested outdoor from 10:00-17:00 for 3 days. The results show 27 that the light intensity plays a main role on the charging time of the wireless 28 charger. 29 30 Keyword: wireless charger, solar energy, transformer, Magnetic flux 31 32 Introduction 33 Self-energized devices can be powered by different kinds of energy, including 34 radio frequency, solar, thermal, and vibration. In addition, a single device can be 35 energized from multiple ambient energy sources (G. Park, 2005; Ferro Solutions 36 2004). Radio frequency (RF) devices utilize electromagnetic radiation emitted by 37 radio devices, such as wireless radio networks. As the most commonly used 38 frequencies are well known, the devices have an antenna and circuitry tuned to 39 maximize energy harvesting at these frequencies. Unfortunately, typical electric 40 field strengths are weak (unless located close to sources), which severely limits 41 the quantity of energy that can be harvested, e.g., to approximately two orders of 42 magnitude less than indoor solar and thermoelectric devices. Active systems 43 attempt to overcome this limit by broadcasting RF energy, as is done currently for 44 RFID tags used in commercial (J.A. Paradiso and T. Starner, 2007). 45 Thermoelectric devices consume energy developed from temperature differences 46 via the Seebeck effect, i.e., a temperature difference at the junction of two metals 47 or semiconductors causes current to flow across the junction. The power density 48 of thermoelectric increases with the temperature difference increasing their 49 attractiveness in applications such as sun/shade installations, compressors, and 50 hot/cold/air/water/refrigerant flows. Vibration sources extract energy from 51 ambient vibrations. As power usually scales with the cube of vibration frequency 52 and the square of vibration amplitude, these devices have the most value in 53 applications with high frequency, high-amplitude vibrations. Thus, potentially 54 promising vibration sources could include compressors, motors, pumps, blowers, 55 and, perhaps to a lesser extent, fans and ducts. All vibration-harvesting systems 56 contain mechanical elements that vibrate, typically a spring-mass assembly with 57 its natural frequency close to those of the vibration source to maximize energetic 58 coupling between the vibration source and the harvesting system. Several 59 different ways exist to translate the vibrating elements into electric energy, 60 including piezoelectric (S. Tigunta et al., 2013; A. Boonruang et al., 2012), 61 capacitive, and inductive systems (S. Roundy, 2003). 62 Solar energized devices use photovoltaic (PV) (S. Phungsripheng et al., 2013) 63 cells to convert incident light into electricity. As such, they leverage the extensive 64 investments made and progress achieved in increasing the efficiency and reducing 65 the cost of PV for building- and utility-scale power. Solar devices can produce 66 energy from both outdoor and indoor light sources, although outdoor insolation 67 levels yield approximately two to three orders of magnitude more electricity per 68 unit area than indoor electric light sources (J.A. Paradiso and T. Starner, 2007; S. 69 Roundy; 2003). Relative to other sources, solar devices can achieve high energy 70 densities when used in direct sun, but will not function in areas without light (e.g., 71 highly shaded areas, ducts). Applications to date include contact and motion 72 sensors for building applications (C. Park and P. Chou, 2004) as well as 73 calculators, PDAs, and wristwatches. While a wide variety of harvesting 74 modalities are now feasible, solar energy harvesting through photo-voltaic 75 conversion provides the highest power density, which makes it the modality of 76 choice to power an embedded system that consumes several mW using a 77 reasonably small harvesting module. 78 This paper focuses on using solar cell energy in providing an alternative power 79 source to charge mobile phone devices. Previous works in this field can be found 80 in (T. Voigt, H. Ritter, and J. Schiller, 2003; A. Kansal and M. Srivastava, 2003; 81 A. Kansal, D. Potter, and M. Srivastava, 2004). A solar harvesting augmented 82 high-end embedded system was described by T. Voigt et al. (2003), in which a 83 switch matrix was used to power individual system components from either the 84 solar panel or the battery. Harvesting aware protocols have also been proposed for 85 data routing (A. Kansal and M. Srivastava, 2003), and distributed performance 86 scaling (A. Kansal, D. Potter, and M. Srivastava, 2004). Apart from solar energy, 87 this paper also presents the wireless channel for power charging by converting the 88 solar energy into wireless signal in which the mobile phone can be charged 89 without wire connection. The motivation of this wireless charger is as follows. 90 Through the years, technology has allowed the cellular phone to shrink not only 91 the size of the ICs, but also the batteries. New combinations of materials have 92 made possible the ability to produce batteries that not only are smaller and last 93 longer, but also can be recharged easily. However, as technology has advanced 94 and made our phones smaller and easier to use, we still have one of the original 95 problems: we must plug the phone into the wall in order to recharge the battery. 96 Most people accept this as something that will never change, so they might as 97 well accept it and carry around either extra batteries with them or a charger. Either 98 way, it is just something extra to weigh a person down. There has been research 99 done in the area of shrinking the charger in order to make it easier to carry with 100 the phone. Most people do not realize that there is an abundance of energy all 101 around us at all times. We are being bombarded with energy waves every second 102 of the day. Radio and television towers, satellites orbiting earth, and even the 103 cellular phone antennas are constantly transmitting energy. If it could be possible 104 to gather the energy and store it, we could potentially use it to power other 105 circuits. In the case of the cellular phone, this power could be used to recharge a 106 battery that is constantly being depleted. The potential exists for cellular phones, 107 and even more complicated devices - i.e. pocket organizers, person digital 108 assistants (PDAs), and even notebook computers - to become completely wireless. 109 The concept needs an efficient antenna along with a circuit capable of converting 110 alternating-current (AC) voltage to direct-current (DC) voltage. The efficiency of 111 an antenna, as being discussed here, is related to the shape and impedance of the 112 antenna and the impedance of the circuit. The details of proposed wireless charger 113 is described in the next section including transmitting and receiving circuits. 114 Then, the experimental setup, measured results and discussion are presented 115 respectively. 116 Components of Proposed Wireless Charger 117 Transmitting Circuit 118 In general, there are many kinds of circuit that can convert the DC power 119 energized by solar cells into another form. In this paper, the concept of 120 transformer has been adopted and modified by using only air medium instead of 121 iron. This is like the induction theory from the basic principle of electromagnetic 122 dilemma. When the current flows into a coil, the magnetic flux will be generated 123 and radiate in the perpendicular plane at the center of coil. This magnetic flux 124 depends on the intensity of current as well as the number of coils. The formula of 125 magnetic field can be expressed in (1). B= 126 μo nI 2a 127 where μo = 4π × 10−7 H/m 128 From Faraday law, the relationship between electromotive force and magnetic 129 flux can be given by (2). 130 ε= − N∆∅ ∆t (1) (2) 131 where ε is the electromotive force, ∆∅ is the changing of magnetic flux, ∆t is the 132 interval time of magnetic flux changing and N is the number of coil. 133 The original concept of Faraday's iron ring apparatus requires the iron to be the 134 medium for magnetic flux to flow across two coils. This concept has been 135 modified by replacing air medium instead of iron ring. It can be obviously 136 realized that the efficiency of air-core transformer is lower than iron but this can 137 make the charger be wireless of mobile phone. 138 For the transmitting circuit, this paper uses a transistor to be an electronic 139 amplifier to connect with feedback loop as illustrated in Figure 1. The point 1 of 140 Figure 1 is the frequency filter which is designed by RC circuit. The resistance 141 and capacitance form the action of phase-shifted oscillator in order for positive 142 feedback. When the electric source is input at the amplifying circuit, the noise in 143 electronic circuit will make the oscillator work. After that, the LC circuit has been 144 selected to tune the operating frequency as shown in point 2 of Figure 1. The 145 inductance and capacitance will store the electric power at frequency resonant. At 146 this point, the current flows into coil and the inductive electromagnetic field will 147 be transferred to receiver via air medium. The last part of transmitting circuit is 148 low pass filter as seen in point 3 of Figure 1. The inductance 𝑋𝐿 is low and the 149 capacitance 𝑋𝐶 is high. Then, the low frequency signals can easily pass the 150 inductive coil in which the output of system is high. In turn, the higher frequency 151 signals hardly pass through the filter. 152 In the RC design, the capacitor is set to 470 pF and resistance is 15kΩ. It is used 153 to control the interval time between charge and discharge process. For the tuning 154 filter, the capacitor is set to 100 nF. The transistor BD139 is selected to amplify 155 signals. The capacitor of matching the coil impedance is set to 4.7 nF in which the 156 complex value of capacitor and coil will be cancelled to each other. 157 Figure 2 depicts the assembly of wireless charger for (left) inside and (right) 158 outside. It can be clearly seen that the overall circuit and coil is so thin and small 159 that all assembly can be easily installed. The box of wireless charger can be 160 modified to fit with any mobile layouts. 161 Receiving Circuit 162 In the receiving circuit, the first part is the receiving coil reacting the power 163 transfer from transmitter as seen in point 1 of Figure 3. This current will be fed to 164 the rectifier in order to convert from AC to DC. The rectifier is shown in point 2 165 of Figure 3. Finally, the voltage regulator will be used to control the constant level 166 of output at 5V as shown in point 3 of Figure 3. This regulator is very important 167 because it is the safety checker for mobile phone. In case that the output voltage is 168 not stable, the variation of voltage will make the life time of battery shorter. 169 Moreover, it might cause the mobile phone broken. As seen in Figure 3, the 170 matching part use the capacitor of 4.7 nF. The diode 1N4148 is used to perform 171 the AC to DC conversion. IC LM7805 is performed as the regulator to control the 172 constant output of 5V. 173 Figure 4 shows the assembly of mobile phone for (left) inside and (right) outside. 174 It is clearly seen that the circuit and coil is so thin and small that can be placed 175 inside the case of mobile phone. The modified mobile phone can be used normally 176 in all functions. 177 Magnetic Transferring Coil 178 One of the most important part of wireless charger is the magnetic transferring 179 coil. This paper chooses the flat spiral coil inductor because it save the space by 180 spreading a number of coils over one flat plane as shown in Figure 5. This is very 181 practical because it can be used to install on the back case of mobile phone. In this 182 paper, the area of back case is 5.8cm x 1.1cm. Therefore, the selection of copper 183 wire has to be take this area into account. That is the reason why this paper 184 chooses the copper number 22 which is suitable for this back case. 185 All components of wireless charger for mobile phone can be illustrated in Figure 186 6 and the photography of real prototype is presented in Figure 7. As seen in Figure 187 7, the dimension of solar cell is small and convenient to install on any rooftop. 188 Actually, there are many products of solar cell in commercial. This paper employs 189 the popular product on the shelf which its efficiency is typical. Please note that the 190 higher voltage and current can be achieved if the size and quality of solar cell is 191 extended. 192 Experimental Results and Discussion 193 Three experiments have been carried out in order to investigate the performance 194 of proposed system. The first experiment is to investigate the change of current 195 and voltage from solar energy throughout daytime. This experiment will let the 196 researcher realize the suitable time period and the gap in one day of using solar 197 energy. The second experiment is to compare between using proposed system as 198 wireless charger and using conventional charger as wire charger. The results will 199 let us know the acceptable delay when using wireless charger. For the last 200 experiment, the relationship between voltage and distance between charger and 201 mobile phone is illustrated. The results will guide the design of proper space for 202 holding the mobile. 203 For the first experiment, the prototype shown in Figure 7 has been tested outdoor 204 for 3 days. In each day, the measurement starts on 10:00 and stops on 17:00. 205 Within 1 hour, the data has been recorded 10 times and the averaging values is the 206 representative value for that interval. The results in Table 1 show that the 207 maximum current and voltage can be achieved at the time of 13:00-14:00. This is 208 because at that time the sunlight strongly provides the maximum light intensity. 209 However, the current gap between minimum and maximum is 75.3 mA which is 210 very high. It means that this charger cannot be used for all daytime. This is the 211 limit of wireless charger to be energized by solar cell. 212 In the second experiment, the results in Table 2 reveal that the charging time of 213 conventional charger consume 1.38 minutes to charge 1% of battery while it takes 214 7.24 minutes for wireless charger. This is about 5.2 times longer by wireless 215 charger. This delay is the expense of more convenient devices which is not 216 required wire connection any more. 217 For the last experiment, the relationship of voltage and distance between wireless 218 charger and mobile phone is investigated. The measurement is undertaken at 219 11:00. The results help researcher to design the tradeoff between power 220 degradation and the thickness of case in practice. As seen in Figure 8, the 221 minimum distance is limited to 4.5 cm because the voltage will be dropped below 222 5 V in which it cannot utilize for charging battery. 223 Conclusion 224 This paper suggests the use of a solar energy in mobile phone devices in 225 cooperating with wireless charging technology. The results of this paper indicate 226 that it is possible to use solar energy to supply mobile phone batteries with the 227 necessary power. Also the prototype prove that the implementation is simple and 228 it can be done easily for public use. Although the charging time of wireless 229 charger is longer by 5.2 times, but there is no need to pay the cost of electricity. 230 This can be a free energy source for devices in daily use. 231 References 232 G. Park (2005) Overview of Energy Harvesting Systems (for Low- 233 PowerElectronics). the First Los Alamos National Laboratory Engineering 234 Institute Workshop: Energy Harvesting. p 1-11. 235 236 237 238 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. 240 Pengpat (2013) Effects of BZT Addition on Physical and Electrical 241 Properties of Calcium Phosphate Bioglass. Suranaree Journal of Science and 242 Technology., 20(3):197-203 243 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 246 Technology., 19(4):251-257. 247 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. 250 S. Phungsripheng, S. Sanorpim, T. Wasanapiarnpong (2013) Effect of nitrogen 251 doping on photovoltaic property of lead lanthanum zirconate titanate 252 ferroelectric ceramics. Suranaree Journal of Science and Technology., 20 253 (2):109-116. 254 C. Park and P. Chou (2004) Power utility maximization for multiple-supply 255 systems by a load-matching switch. Proc. ACM/IEEE International 256 Symposium on Low Power Electronics and Design. pp. 168–173. 257 T. Voigt, H. Ritter, and J. Schiller (2003) Utilizing solar power in wireless sensor 258 networks. Proc. IEEE Conference on Local Computer Networks. p 1-5. 259 A. Kansal and M. Srivastava (2003) An environmental energy harvesting 260 framework for sensor networks. Proc. ACM International Symposium on 261 Low Power Electronics and Design, pp. 481–486. 262 A. Kansal, D. Potter, and M. Srivastava (2004) Performance aware tasking for 263 enrironmentally powered sensor networks. Proc. ACM International 264 Conference on Measurement and Modeling of Computer Systems, pp.223– 265 234. 266 267 268 269 Figure 1. Transmitting Circuit 270 271 272 Figure 2. Assembly of wireless charger (left) inside and (right) outside 273 274 Figure 3. Receiving Circuit 275 276 277 278 279 Figure 4. Assembly of mobile phone (left) inside and (right) outside 280 281 Figure 5. Flat spiral coil 282 283 284 285 Figure 6. All components of wireless charger for mobile phone. 286 287 288 289 Figure 7. Photography of proposed wireless charger. 290 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 0 291 292 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 9.60 293 294 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 295 296 297 298 299 300 301 Figure 8. Voltage versus distance between wireless charger and mobile phone energized by solar cell at 11:00.