WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 11. INTRODUCTION1.1 Electromagnetic SpectrumFig.1.1. Electromagnetic SpectrumTo start with, to know what a spectrum is: when white light is shone through a prism itis separated out into all the colors of the rainbow; this is the visible spectrum. So white light isa mixture of all colors. Black is NOT a color; it is what you get when all the light is takenaway. Some physicists pretend that light consists of tiny particles which they call photons.They travel at the speed of light (what a surprise). The speed of light is about 300,000,000meters per second. When they hit something they might bounce off, go right through or getabsorbed. What happens depends a bit on how much energy they have. If they bounce offsomething and then go into your eye you will "see" the thing they have bounced off. Somethings like glass and Perspex will let them go through; these materials are transparent.Black objects absorb the photons so you should not be able to see black things: youwill have to think about this one. These poor old physicists get a little bit confused when theytry to explain why some photons go through a leaf, some are reflected, and some areabsorbed. They say that it is because they have different amounts of energy. Other physicistspretend that light is made of waves. These physicists measure the length of the waves and thishelps them to explain what happens when light hits leaves. The light with the longest
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 2wavelength (red) is absorbed by the green stuff (chlorophyll) in the leaves. So is the light withthe shortest wavelength (blue). In between these two colors there is green light, this is allowedto pass right through or is reflected. (Indigo and violet have shorter wavelengths than bluelight.)Well it is easy to explain some of the properties of light by pretending that it is madeof tiny particles called photons and it is easy to explain other properties of light by pretendingthat it is some kind of wave. The visible spectrum is just one small part of the electromagneticspectrum. These electromagnetic waves are made up of to two parts. The first part is anelectric field. The second part is a magnetic field. So that is why they are calledelectromagnetic waves. The two fields are at right angles to each other.The "electromagnetic spectrum" of an object has a different meaning, and is insteadthe characteristic distribution of electromagnetic radiation emitted or absorbed by thatparticular object. The electromagnetic spectrum extends from below the low frequencies usedfor modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometres down toa fraction of the size of an atom. The limit for long wavelengths is the size ofthe universe itself, while it is thought that the short wavelength limit is in the vicinity ofthe Planck length, although in principle the spectrum is infinite and continuous.Most parts of the electromagnetic spectrum are used in science for spectroscopic andother probing interactions, as ways to study and characterize matter. In addition, radiationfrom various parts of the spectrum has found many other uses for communications andmanufacturingThe types of electromagnetic radiation are broadly classified into the followingclasses:1. Gamma radiation2. X-ray radiation3. Ultraviolet radiation4. Visible radiation5. Infrared radiation6. Microwave radiation7. Radio waves
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 3This classification goes in the increasing order of wavelength, which is characteristicof the type of radiation. While, in general, the classification scheme is accurate, in realitythere is often some overlap between neighbouring types of electromagnetic energy. Forexample, SLF radio waves at 60 Hz may be received and studied by astronomers, or may beducted along wires as electric power, although the latter is, in the strict sense, notelectromagnetic radiation at all.The distinction between X-rays and gamma rays is partly based on sources: thephotons generated from nuclear decay or other nuclear and sub nuclear/particle process, arealways termed gamma rays, whereas X-rays are generated by electronic transitions involvinghighly energetic inner atomic electrons. In general, nuclear transitions are much moreenergetic than electronic transitions, so gamma-rays are more energetic than X-rays, butexceptions exist. By analogy to electronic transitions, muonic atom transitions are also said toproduce X-rays, even though their energy may exceed 6 mega electron volts(0.96 pJ), whereas there are many (77 known to be less than 10 keV (1.6 fJ)) low-energynuclear transitions (e.g., the 7.6 eV (1.22 aJ) nuclear transition of thorium-229), and, despitebeing one million-fold less energetic than some muonic X-rays, the emitted photons are stillcalled gamma rays due to their nuclear origin.The convention that EM radiation that is known to come from the nucleus, is alwayscalled "gamma ray" radiation is the only convention that is universally respected, however.Many astronomical gamma sources (such as gamma ray bursts) are known to be too energetic(in both intensity and wavelength) to be of nuclear origin. Quite often, in high energy physicsand in medical radiotherapy, very high energy EMR (in the >10 MeV region) which is ofhigher energy than any nuclear gamma ray, is not referred to as either X-ray or gamma-ray,but instead by the generic term of "high energy photons."The region of the spectrum in which a particular observed electromagnetic radiationfalls, is reference frame-dependent (due to the Doppler shift for light), so EM radiation thatone observer would say is in one region of the spectrum could appear to an observer movingat a substantial fraction of the speed of light with respect to the first to be in another part ofthe spectrum. For example, consider the cosmic microwave background. It was produced,when matter and radiation decoupled, by the de-excitation of hydrogen atoms to the groundstate. These photons were from Lyman series transitions, putting them in the ultraviolet (UV)
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 4part of the electromagnetic spectrum. Now this radiation has undergone enoughcosmological red shift to put it into the microwave region of the spectrum for observersmoving slowly (compared to the speed of light) with respect to the cosmos.1.2 Microwave RegionMicrowave wavelengths range from approximately one millimeter (the thickness of apencil lead) to thirty centimeters (about twelve inches). In a microwave oven, the radio wavesgenerated are tuned to frequencies that can be absorbed by the food. The food absorbs theenergy and gets warmer. The dish holding the food doesnt absorb a significant amount ofenergy and stays much cooler. Microwaves are emitted from the Earth, from objects such ascars and planes, and from the atmosphere. These microwaves can be detected to giveinformation, such as the temperature of the object that emitted the microwaves.Microwaves have wavelengths that can be measured in centimeters! The longermicrowaves, those closer to a foot in length, are the waves which heat our food in amicrowave oven. Microwaves are good for transmitting information from one place toanother because microwave energy can penetrate haze, light rain and snow, clouds, andsmoke. Shorter microwaves are used in remote sensing. These microwaves are used forclouds and smoke, these waves are good for viewing the Earth from space Microwave wavesare used in the communication industry and in the kitchen as a way to cook foods. Microwaveradiation is still associated with energy levels that are usually considered harmless except forpeople with pace makers.Fig.1.2 Microwave region of electromagnetic spectrumHere we are going to use the S band of the Microwave Spectrum.
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 5Table 1.2 Microwave spectrumDesignation Frequency rangeL Band 1 to 2 GHzS Band 2 to 4 GHzC Band 4 to 8 GHzX Band 8 to 12 GHzKu Band 12 to 18 GHzK Band 18 to 26 GHzKa Band 26 to 40 GHzQ Band 30 to 50 GHzU Band 40 to 60 GHz
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 62. TRANSMITTER SECTIONThe transmitter section consists of two parts. They are: Magnetron Slotted waveguide antenna2.1 MagnetronFig.2.1 MagnetronMagnetron is the combination of a simple diode vacuum tube with built in cavityresonators and an extremely powerful permanent magnet. The typical magnet consists of acircular anode into which has been machined with an even number of resonant cavities. Thediameter of each cavity is equal to a one-half wavelength at the desired operating frequency.The anode is usually made of copper and is connected to a high-voltage positive directcurrent. In the center of the anode, called the interaction chamber, is a circular cathode.The magnetic fields of the moving electrons interact with the strong field supplied bythe magnet. The result is that the path for the electron flow from the cathode is not directlyto the anode, but instead is curved. By properly adjusting the anode voltage and the strengthof the magnetic field, the electrons can be made to bend that they rarely reach the anodeand cause current flow. The path becomes circular loops. Eventually, the electrons do reachthe anode and cause current flow. By adjusting the dc anode voltage and the strength of the
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 7magnetic field, the electron path is made circular. In making their circular passes in theinteraction chamber, electrons excite the resonant cavities into oscillation. A magnetron,therefore, is an oscillator, not an amplifier. A takeoff loop in one cavity provides the output.Magnetrons are capable if developing extremely high levels of microwave power..When operated in a pulse mode, magnetron can generate several megawatts of power in themicrowave region. Pulsed magnetrons are commonly used in radar systems. Continuous-wavemagnetrons are also used and can generate hundreds and even thousands of watts of power.2.2 Slotted Waveguide AntennaThe slotted waveguide is used in an omni-directional role. It is the simplest ways toget a real 10dB gain over 360 degrees of beam width. The Slotted waveguide antenna isa Horizontally Polarized type Antenna, light in weight and weather proof.3 Tuning screws areplaced for tweaking the SWR and can be used to adjust the centre frequency downwards from2320MHz nominal to about 2300 MHz .This antenna is available for different frequencies.This antenna, called a slotted waveguide, is a very low loss transmission line. It allowspropagating signals to a number of smaller antennas (slots). The signal is coupled into thewaveguide with a simple coaxial probe, and as it travels along the guide, it traverses the slots.Each of these slots allows a little of the energy to radiate. The slots are in a linear arraypattern. The waveguide antenna transmits almost all of its energy at the horizon, usuallyexactly where we want it to go. Its exceptional directivity in the elevation plane gives it quitehigh power gain. Additionally, unlike vertical collinear antennas, the slotted waveguidetransmits its energy using horizontal polarization, the best type for distance transmission.Fig 2.2 Slotted waveguide antenna
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 83. RECEIVER SECTIONThe basic addition to the mobile phone is going to be the rectenna. A rectenna is arectifying antenna, a special type of antenna that is used to directly convert microwaveenergy into DC electricity. Its elements are usually arranged in a mesh pattern, giving it adistinct appearance from most antennae. A simple rectenna can be constructed from aSchottky diode placed between antenna dipoles. The diode rectifies the current induced in theantenna by the microwaves. Rectenna are highly efficient at converting microwave energy toelectricity. Some experimentation has been done with inverse rectenna, converting electricityinto microwave energy, but efficiencies are much lower--only in the area of 1%. With theadvent of nanotechnology and MEMS the size of these devices can be brought down tomolecular level. It has been theorized that similar devices, scaled down to the proportionsused in nanotechnology, could be used to convert light into electricity at much greaterefficiencies than what is currently possible with solar cells. This type of device is called anoptical rectenna. Theoretically, high efficiencies can be maintained as the device shrinks, butexperiments funded by the United States National Renewable energy Laboratory have so faronly obtained roughly 1% efficiency while using infrared light. Another important part of ourreceiver circuitry is a simple sensor. This is simply used to identify when the mobile phoneuser is talking. As our main objective is to charge the mobile phone with the transmittedmicrowave after rectifying it by the rectenna, the sensor plays an important role. The wholesetup looks something like this.Fig 3.1.Block Diagram
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 93.1 Sensor CircuitThe sensor circuitry is a simple circuit, which detects if the mobile phone receives anymessage signal. This is required, as the phone has to be charged as long as the user is talking.Thus a simple F to V converter would serve our purpose. In India the operating frequency ofthe mobile phone operators is generally 900MHz or 1800MHz for the GSM system formobile communication. Thus the usage of simple F to V converters would act as switches totrigger the rectenna circuit to on.A simple yet powerful F to V converter is LM2907. Using LM2907 would greatlyserve our purpose. It acts as a switch for triggering the rectenna circuitry. The general blockdiagram for the LM2907 is given below.Fig 3.2.LM2907Fig 3.3.LM2907 ICThus on the reception of the signal the sensor circuitry directs the rectenna circuit to ONand the mobile phone begins to charge using the microwave power.
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 103.2 RectennaA rectifying antenna rectifies received microwaves into DC current. A rectennacomprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitterand converting it into electric power. A simple rectenna can be constructed from a Schottkydiode placed between antenna dipoles as shown in Fig.3.4. The diode rectifies the currentinduced in the antenna by the microwaves. Rectenna are highly efficient at convertingmicrowave energy to electricity. In laboratory environments, efficiencies above 90% havebeen observed with regularity. In future rectennas will be used to generate large-scale powerfrom microwave beams delivered from orbiting GPS satellites.Fig 3.4.RectificationFig 3.5 Rectenna Array
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 113.4 Process of RectificationStudies on various microwave power rectifier configurations show that a bridgeconfiguration is better than a single diode one. But the dimensions and the cost of that kind ofsolution do not meet our objective. This study consists in designing and simulating a singlediode power rectifier in “hybrid technology” with improved sensitivity at low power levels.We achieved good matching between simulation results and measurements thanks to theoptimization of the packaging of the Schottky diode.Microwave energy transmitted from space to earth apparently has the potential toprovide environmentally clean electric power on a very large scale. The key to improvetransmission efficiency is the rectifying circuit. The aim of this study is to make a low costpower rectifier for low and high power levels at a frequency of 2.45GHz with good efficiencyof rectifying operation. The objective also is to increase the detection sensitivity at low powerlevels of power.Different configurations can be used to convert the electromagnetic waves into DCsignal. The study done showed that the use of a bridge is better than a single diode, but thepurpose of this study is to achieve a low cost microwave rectifier with single Schottky diodefor low and high power levels that has a good performance.This study is divided on two kinds of technologies. The first is the hybrid technologyand the second is the monolithic one.The goal of this investigation is the development of a hybrid microwave rectifier withsingle Schottky diode. The first study of this circuit is based on the optimization of therectifier in order to have a good matching of the input impedance at the desired frequency2.45 GHz. Besides the aim of the second study is the increasing of the detection sensitivity atlow levels of power. The efficiency of Schottky diode microwave rectifying circuit is foundto be greater than 90%.3.3 Brief introduction of Schottky Barrier Diode:A Schottky barrier diode is different from a common P/N silicon diode. The commondiode is formed by connecting a P type semiconductor with an N type semiconductor, this isconnecting between a semiconductor and another semiconductor; however, a Schottky barrier
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 12diode is formed by connecting a metal with a semiconductor. When the metal contacts thesemiconductor, there will be a layer of potential barrier (Schottky barrier) formed on thecontact surface of them, which shows a characteristic of rectification. The material of thesemiconductor usually is a semiconductor of n-type (occasionally p-type), and the material ofmetal generally is chosen from different metals such as molybdenum, chromium, platinumand tungsten. Sputtering technique connects the metal and the semiconductor.A Schottky barrier diode is a majority carrier device, while a common diode is aminority carrier device. When a common PN diode is turned from electric connecting tocircuit breakage, the redundant minority carrier on the contact surface should be removed toresult in time delay. The Schottky barrier diode itself has no minority carrier, it can quicklyturn from electric connecting to circuit breakage, its speed is much faster than a common P/Ndiode, so its reverse recovery time Tr is very short and shorter than 10 ns. And the forwardvoltage bias of the Schottky barrier diode is under 0.6V or so, lower than that (about 1.1V) ofthe common PN diode. So, The Schottky barrier diode is a comparatively ideal diode, such asfor a 1 ampere limited current PN interface.Below is the comparison of power consumption between a common diode and aSchottky barrier diode:P=0.6*1=0.6WP=1.1*1=1.1WIt appears that the standards of efficiency differ widely. Besides, the PIV of the Schottkybarrier diode is generally far smaller than that of the PN diode; on the basis of the same unit,the PIV of the Schottky barrier diode is probably 50V while the PIV of the PN diode may beas high as 150V. Another advantage of the Schottky barrier diode is a very low noise indexthat is very important for a communication receiver; its working scope may reach 20GHz.
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 134. ADVANTAGES1) Charging of mobile phone is done wirelessly2) We can saving time for charging mobiles3) Wastage of power is less4) Better than witricity as the distance the witricity can cover is about 20meters whereas in this technology we are using base station for transmissionthat can cover more area5) Mobile get charged as we make call even during long journeyFig.4.1.Mobile charging during journey
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 145. DISADVANTAGES1) Radiation problems may occur2) Network traffic may cause problems in charging3) Charging depends on network coverage4) Rate of charging may be of minute range
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 156. APPLICATIONSAs the topics name itself this technology is used for“Wireless charging of mobile phones”.Fig.6.1.Mobile getting charged from mobile tower
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 167. CONCLUSIONThus this paper successfully demonstrates a novel method of using the power ofmicrowave to charge mobile phones without use of wired chargers. It provides greatadvantage to mobile phone users to carry their phones anywhere even if the place is devoid offacilities for charging. It has effect on human beings similar to that from cell phones atpresent. The use of rectenna and sensor in mobile phone could provide new dimension in therevolution of mobile power.
WIRELESS MOBILE PHONE CHARGINGDept. Of ECE, SIST 178. REFERENCES1. Theodore.S.Rappaport , “Wireless Communications Principles and Practice”2. www.seminarprojects.com3. www.seminarsonly.com4. www.wikipedia.org