17-11-2012, 01:04 PM
WIRELESS CHARGING OF HANDHELDS USING RADIO FREQUENCY FROM NON-CONVENTIONAL ENERGY RESOURCES
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ABSTRACT:
Sustainable development will require replacement of older technologies and increased use of both renewable energy and wireless technology. What if there was a way we could harvest the energy that is being transmitted and use it as a source of power for handhelds? And also that to from Non-conventional energy source like solar power. This paper deals with a system that enables you to charge your handhelds wirelessly form zero pollutant solar energy.
A system that to be presented will be using a receiving antenna and charge pump technology to charge a handheld’s battery without wires. The base station which is a transmitter of power is powered from solar energy. The solar energy which is trapped is transmitted as radio frequency from the base station. At the receiving end we contain antenna that is tuned to transmitted frequency and a charge pump to charge up the battery of Handhelds.
INTRODUCTION
Global warming from greenhouse gases, mainly CO2, is one of today’s most important environmental issues. Electricity production is often a source of CO2 emissions, for instance when fossil fuel is combusted in power plants. So Non-conventional energy source like solar power solves this problem. At present use of hand held also increased and power consumed by these devices also increased rapidly. However, as technology has advanced and made our phones smaller and easier to use, we still have one of the original problems: we must plug the phone into the wall in order to recharge the battery. Most people accept this as something that will never change, so they might as well accept it and carry around either
extra batteries with them or a charger. Either way, it’s just something extra to weigh a person down. There has been research done in the area of shrinking the charger in order to make it easier to carry with the phone. One study in particular went on to find the lower limit of charger size. But as small as the charger becomes, it still needs to be plugged in to a wall outlet. How can something are called “wireless” when the object in question is required to be plugged in, even though periodically?
SYSTEM OVERVIEW
The system to be presented here is presented with two modules. In the first module we see about solar powered base station which transmit power wirelessly and in the second module we see energy harvesting and charge pump circuitry. In solar power powered base station is where you trap the solar energy and you transmit the solar power. It consists of solar array, Battery backup system, Power regulator, Base station equipments and a Transmitting antenna.
At the receiving end we have energy harvesting and charge pump circuitry where the transmitted power is harvested and using the charge pump the voltage level is raised and is used to charge the hand held
SOLAR POWERED BASE STATION
Solar powered base station is where the solar energy is trapped and transmitted. The main components of it are solar arrays, Power regulation system, Battery backup System base station equipments with Antenna.
The various components of the Solar Powered Base Station are shown in the block diagram and the purpose and the usage of each component are explained in detail below
ANTENNA
For this paper, the monopole antenna was the antenna of choice because of its relative ease of use. A monopole antenna basically consists of a piece of copper wire with one end connected to the circuit, and the other left open. Probably the best reason for using an antenna such as this is that it fits nicely into the chosen stands. The wire is attached to the circuit and then wound once around the inside of the case; making sure that it does not touch any other part of the circuit or itself. Another good quality of this type of antenna is that its operating frequency range is fairly large. For this research, this is helpful because precise tuning of the antenna is not required.
THE CHARGE PUMP
At this point, it is necessary to explain what exactly a charge pump is, and how it works. A charge pump is a circuit that when given an input in AC is able to output a DC voltage typically larger than a simple rectifier would generate. It can be thought of as a AC to DC converter that both rectifies the AC signal and elevates the DC level.
NUMBER OF STAGES
The number of stages, as shown in Figure .2, in the system has the greatest effect on the output voltage. The capacitance, both in the stages and at the end of the circuit, affects the speed of the transient response and the stability of the output signal. The number of stages is essentially directly proportional to the amount of voltage obtained at the output of the system. Generally, the voltage of the output increases as the number of stages increases. This is due to how the voltage doubler works as explained earlier.
SIMULATION
The Simulation started first is to keep all stages the same value. This is the simplest. The other way is to vary the stage capacitance between stages based on the charge in the circuit. The first schematic shown in Figure .5. is a seven stage design with all the stage capacitors being the same value.
Simulations were begun starting with four stages of voltage doublers that all had the same stage capacitance. The simulations were run from 4 stages to 9 stages. In the previous research, the capacitance for the stages was 1nF. This is where the simulations were started. The input is a power source, which is setup to model the RF source used in testing.
Simulation Results
Focusing on the Agilent HSMS-2820 Schottky diode, simulations were begun starting with four stages of voltage doublers that all had the same stage capacitance. The simulations were run from 4 stages to 9 stages. The input is a power source, which is setup to model the RF source used in testing. The only value of output capacitance used for these results is 15nF. According to the simulations, the rise time for the circuit is under 2 milli-seconds. A sample of the simulation result can be seen in Figure .6.
CONCLUSION
In this paper, we submit a first step towards a goal that would have profound ramifications on the cellular phone industry and the portable electronic device industry as a whole. Simulation results show that while we were not completely successful at achieving our overall goal of having the charging circuit in a stand be able to charge the battery of a cellular phone while it was within the phone using a wireless RF source, we have completed the goal of being able to charge the battery while the phone is in its stand. Circumventing the proprietary circuitry in the charging path will allow future adaptation of the wireless RF energy harvesting concept produced by this research.