Applying Wireless Power Transfer on Charging Portable Devices

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devices (e.g. cell phones, microbots and laptops) using wireless power transfer concept .... Power beaming using laser diodes has advantages like high ability to ...
Applying Wireless Power Transfer on Charging Portable Devices Marwan F. Abdel Razik, Heba Tallah O. Silem, Omnia A. M. Akl, Yasmeen M. Abd Alradi, Mohammed E. Elbtity, Yousef Atef, Amjad A. Mohammed, Ziad Elmasry 

Abstract— Due to crucial requirements of electrical power and noticeably increasing amount of the electronic devices day after day, this paper discusses the application of charging portable devices (e.g. cell phones, microbots and laptops) using wireless power transfer concept. The paper navigates through different techniques that are used to transfer power wirelessly and comes up with the suitable one for this application. In order to be more applicable and handy for users and to improve the transmitted power and the distance of transmission, some modifications are suggested on the chosen technique. The paper took into consideration the mobility of the devices to be charged. The other contribution of this paper is adding a controllability for delivering power to specific devices rather that others using authentication technique. Index Terms— wireless power transfer, wireless power transmission, authorization, control, DNP

I. INTRODUCTION

W

ireless Power Transmission (WPT) is defined as an efficient way to transmit electrical power from one place to another without using wires or any substances between transmitter and receiver [1]. WPT is not a new concept, since James Maxwell was the first one who has given the first theory of transferring power through electromagnetic radiation [2]. In 1893, Tesla proved Maxwell's theory and demonstrated the Illumination of vacuum bulbs and transported energy to it without wires through vacuum using electromagnetic waves  Marwan F. Abdel Razik is a SCADA engineer and a M.Sc. student at Cairo University, Giza, Egypt (e-mail: [email protected]). Heba Tallah O. Silem is a trainer engineer in Egyptian engineers syndicate and a M.Sc. student at Portsaid University, PortSaid, Egypt. Omnia A. M. Akl is a teacher assistant at Arab Academy for Science and Technology and Maritime Transport. She is also a M.Sc. student at Alexandria University, Alexandria, Egypt (e-mail: [email protected]). Yasmeen M. Abd Alradi is an undergraduate student at South Valley University, Qena, Egypt. Mohammed E. Elbtity is an undergraduate student at Al-Azhar University, Cairo, Egypt, (e-mail: [email protected]). Yousef Atef is a graduate student at Alexandria University, Alexandria, Egypt. Amjad A. Mohammed is an assistant researcher at Ain-Shams University, Cairo, Egypt. Ziad Elmasry is an undergraduate student at Alexandria University, Alexandria, Egypt.

[3]. In 1918, Henrick Hertz focused his efforts on (WPT) and experimentally validated the findings in principles [2]. William C. Brown was the first one who proposed the use of microwave energy for power transmission. He demonstrated in 1964 a microwave-powered model helicopter that received all the power needed for flight from a microwave beam at 2.45 GHz [3]. In 1983 in Japan, the first world's MPT experiments in the ionosphere called the MINIX (Microwave Ionoshpere Nonlinear Interaction Experiments) rocket have been demonstrated. Similarly, in 1987 in Canada, the first world's fuel free airplane powered by microwave energy from the ground was reported, and the system is called SHARP (Stationary High-Altitude Relay Platform). In 2004 Japan proposed wireless charging of electric motor vehicles by microwave power transmitting [3]. The Wireless power transmission is required in cases where instantaneous or continuous energy transfer is needed, but interconnecting wires are inconvenient, dangerous, or impossible [4]. So, why wireless power transfer is important? The development of electronic devices such as laptops, cell phones, and other mobile electronics has generated a great need for technologies that can wirelessly transfer enough power over medium range distances (approximately 0.5m to 5m). Although the fields of microwave transmission involve some forms of wireless power transmission and have been researched for decades, mid-range wireless power transfer (that can energize home and office electronics) is a relatively new field with significant potential. Wireless Power Transmission is typically considered using one of several methods: inductive coupling, microwaves, and lasers. They will be explained in details later in the paper. II. METHODS OF WPT The three common methods used to transfer power wirelessly find continuous developments over decades until today. The inductive coupling was the first technique used for WPT [2]. The idea is very likely to be as the idea of power transformers without the steel core. The inductive coupling is intended to transmit power for short distances; this is why it is called nearfield or mid-range. Due to the large loss of power and low efficiency of this technique, a modification is performed based on a resonance frequency between the transmitter and receiver

called a resonator [5]. By using this technique, more power is delivered to the receiver since little energy is dissipated by the surrounding off-resonant devices [5]. So, obstacles may interrupt the beam of transmission without a relative effect on efficiency. However, the transferring distance is limited and in case of multi-receivers, a separating distance between the receivers must be considered in order to neglect the effect of mutual inductance between the receiving coils on the resonant coupling interaction and hence the resonance frequency [6] which adds more complications in the design of the system in addition to the difficulty of considering moving receivers by this technique. Inductive coupling is suitable for just two objects that are relatively close to each other (e.g., chargeable toothbrushes or medical equipment) [2]. Some suggested modifications to increase the efficiency of this technique are by modifying the shape of the coil [7] or using silver-plated coils (hence increasing the Q-factor of coils) [5] and a resonance frequency tracking systems with variable capacitance for auto-tuning [6]. A work in [8] extended a previous analysis of coupled magnetic resonance to transfer maximum possible power for nearly any distance or orientation as long as the receiver is within the working range of the transmitter. The second technique used for WPT is transmitting microwave energy where the electric power is transmitted at a frequency of microwave range to get the capability of travelling further distances [8]. This technique is used in two types of applications; energy harvesting and electromagnetic power reception. The first type is applied for receiving milliwatts from microwave transmitters or even from sources of noise and radio stations. It is applied successfully in Radio-Frequency Identification (RFID) passive tags [2] [9]. The other type is what of concern; the EM power reception is applied for transmitting tens of watts for reasonable distances suitable for this application [10]. The advantages of this technique are; it does not require a specific position for the receiver relative to the transmitter, hence the receiver is free to move within the circle range of the transmission. The efficiency of microwave power transmission is much greater than other techniques (coupling and lasers). It is about 54% [8]. The drawbacks of this technique are the interference that may occur between the transmitted energy and data transmitted at a neighboring frequency. However, some efforts are exerted to preserve a specific bandwidth for WPT. Another drawback is that the large size and weight of the transmitter and receiver antennas [2]. However, some researches included circular patch antennas and microstrip implementation to make the antenna in a compact size that makes it possibly be used in mobile applications [11]. However, Safety of microwave power transmission has not been proven yet. The third way of WPT is the optical beam power transmission using a collimated beam of laser; this is accepted as a possible method for long distance transmission [12]. The transmission of power wirelessly using quasi-optical electromagnetic waves is not new, it is back to 1895 [12], in 2009 the laser power transmission successfully used to power the space elevator sponsored by NASA [2]. The optical power system is used to transfer tens of watts over tens of meters safely and efficiently, while safety and efficiency are proportional. The optical beam source is laser

diodes which convert the electrical power to optical power, then the electrical power is retrieved by photovoltaic diode on the other side [12]. The maximum amount of exposure for a human to be safe from the laser beam is measured by the power density (the amount of optical power radiated per unit area), while the allowable wavelength of the laser beam for safe power beaming system is between 1200nm to 1400nm. Power beaming using laser diodes has advantages like high ability to increase the beam intensity that is directed to the receiver using collimation, it is easy to control the direction of energy propagation therefore it is easier to direct power to a load and authenticate [12]. Also it has a smaller size of receiver and transmitter than microwave power system [2]. Power transmission using laser beam seems to be an efficient way. However, there are some parameters that may affect system efficiency and drop it to the range of 10% to 20% [2] like absorption or scattering of photons because of air particles, rain, fog and smoke, distortion of wave due to wind and temperature that affects the refraction index of air [12], power conversions within the system from electrical power to optical power and vice versa [2] and the largest effect is that of distance which affects the beam collimation, but it depends on the mode structure of the laser diode, where single mode laser has been used for wireless power transfer out to 1km. As with any power system, heat affects system components where laser diodes and photovoltaic are sensitive to heat. However, cooling system, and heat sinks can be used to reduce the thermal heat at the transmitter and receiver [12]. Table 1 summarizes the comparison of the three techniques. TABLE 1 SUMMARY OF COMPARISON Technique

Advantages

Disadvantages

Inductive coupling

 Beam can be interrupted without power loss.  Small size of system hardware.

 Low efficiency.  Short transmission distance.  Inductance between receivers affects the resonance frequency.  Difficult for moving receivers.

Microwave

 Specific position for receivers relative to transmitter is not required.  Suitable for moving receivers.  Highest efficiency amongst all types.

 Possible interference between energy and other microwave data.  Large size and weight of system hardware especially for antennas.

Laser

 Transmitted power can be increased without larger hardware or bandwidth.  Power can be easily directed to a load.  Smallest size of system hardware.

 Low efficiency.  System is affected by the environment.  Long distance affects the beam collimation.  System hardware is affected by the heat generated by the laser beam.

III. PROPOSED CONTRIBUTION A. Adding repeaters Based on the work in [8], an extension of it is mentioned here to increase not only amount of power transfer but also make it travel for further distance. This can be achieved by putting regenerative power repeaters between transmitter and receiver as shown in Fig. 1

30 seconds), when a new device enters the range of power transmission, the receiver receives the broadcast message sent from the transmitter which requests the controller to send its unique ID. When the controller sends its ID, the transmitter searches for this ID in its database, if this ID is not restricted, it sends a write command to the DO which closes the main switch allowing powering-up the device of concern. The idea of using industrial communication protocols in control is not new; it is successfully involved in many industrial fields and known as SCADA system which is an abbreviation for Supervisory Control And Data Acquisition. IV. CONCLUSION

Fig. 1. Regenerative power repeater

B. Authentication capability The second contribution discussed in this paper is adding an authentication capability to the system. Regardless of the technique used for power transmission, a transmitter should decide if a certain device is authenticated to use the service or not. There should be a closed communication channel between the transmitter and receivers using a protocol for data transfer.

Wireless power transfer finds great interest from researchers as the increasing need of electricity for portable devices with fewer wires for easy handling. The paper summarizes the steps of WPT focusing on the milestones found in the way of this technology. The use of microwave and inductive coupling concepts are the most promising approaches. However, inductive coupling approach draws the attention of most of the researchers in that field since the safety of microwaves with this amount of power is not guaranteed. The paper introduced two contributions that are considered for future work. Future papers will be published, including these contributions in details. The first one is extending the range of power transmission to reach further distances to feed more devices that have not exact positions or orientations by involving power repeaters in the system. Authorization functionality is proposed as the second contribution. This functionality allows the system to accept or reject a specific device without affecting the power transfer to other devices. It is based on a simple communication protocol between the transmitter and receivers that allows passing power to the device through a controllable switch. REFERENCES [1] Pawade, Sourabh, Tushar Nimje, and Dipti Diwase. "Goodbye Wires: Approach to Wireless Power Transmission." International journal of emerging technology and advanced engineering, ISSN: 2250-2459.

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From Fig. 2, the proposed transceiver consists of the receiving circuit (a coil in case of inductive coupling or antenna for microwave), it has two functions; it talks to the transmitter for authorization and receives the power after the authorization is done. Using an industrial communication protocol (DNP3.0, Modbus or IEC for instance) [13], the controller has a readonly register that contains a unique number and a digital-out (DO) register that is connected to the main switch which allows the received power to pass to the device. The transmitter scans for devices every specific time period (e.g.

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