Wireless Transmission of Electricity
Transmitting electricity wirelessly is a new and attractive technology that is turning heads. The purpose of the project is to determine whether this technology would be practical for consumer use without causing any major interferences and maintaining adequate efficiency.
Wireless electricity is not a new technology, but recent advancements in electronics have made the possibility for implementation into the market more likely. It was found that using resonance within the circuitry of the coils yielded higher efficiency and farther distance. Resonance tunes the system to a specific operating frequency, but much like in mechanical resonance with music, electronic resonance creates harmonic frequencies as well. The hypothesis of my experiment was that transmitting electricity will be practical at short distances, but will cause noticeable interferences with RF receivers at the harmonic frequencies. After creating and improving upon my coil designs, I tested my coils using a radio receiver that measured the intensity of the signal in dBμ. Improving the Q of my inductors allowed for me to operate on a smaller bandwidth to achieve more accurate results. I took my inductors to an open space to eliminate as much background noise as possible. I then measured the intensity at thirty-degree intervals around my transmitter, increasing the distance as I went.
The data collected seems to show that, even with a very voltage application, transmitting electricity wirelessly would greatly interfere with consumer products that can operate within the harmonic frequencies of the transmitter. Considering the power transfer needed for higher voltage application is much higher than the power in my experiment, wireless electricity might overpower consumers’ radio stations.
I live in a small Indiana town called Greentown. I attend Eastern High School and am currently a senior with a great deal of interests, but mostly enjoy physics. I spend a lot of time learning because I am fascinated with knowing things because knowing is one of the most powerful things we have. I struggled in the early years of high school determining what career I was most suited for, but I knew I either wanted to go into medicine as a doctor or become an engineer of some sort. Then I participated in science fair at my high school which ultimately decided my where my career would go. Science fair changed my outlook and made me realize that I am much more interested in engineering because of the endless possibilities and challenges that it provides. Engineering allows you to think of whatever your mind can imagine. Nikola Tesla, considered the innovator of wireless electricity, created an impression on me because of his wild thinking, planning to ionize the atmosphere to allow anyone in any location to receive power. Although the idea was radical, the journey he took to try to actualize his dream led him to other great discoveries along the way, which is the beauty in science and engineering. I plan to attend college to get a degree in energy engineering and hopefully someday become an innovator myself.
Is wireless electricity practical for consumer use without causing interferences with other consumer products operating at similar frequencies? I hypothesized that transmitting electricity will be practical at short distances, but will cause noticeable interferences with RF receivers at the harmonic frequencies.
A group of researchers working out of MIT released an article about using resonance as a means for more efficient and farther distance wireless power transfer using relatively low frequencies. Many other types of wireless power transfer systems could be made, but most require either a laser, or the use of dangerous, ionizing, and high frequency electromagnetic waves that aren’t quite safe. Using resonance, power can be transferred at frequencies that are very close to the frequencies broadcasted from radio stations. Many studies have been done to prove that, at least with low power applications, the radio waves used today that are non-ionizing do not seem to cause any adverse health effects. This makes transmitting wireless electricity by using resonance and low frequencies a very appealing technology for not only industries, but for consumers as well. The technology itself is very much like radio but slightly different.
The research shaped my project by creating the link between the power transmission and radio stations using similar technology to test whether such a technology would interfere with consumer products.
1. ) The receiving antenna made from 14 AWG copper wire will be formed into a rectangular coil.
2. ) Measure the coil's diameter, inductance and resistance.
3. ) Find the resonant frequency of the coil and match the required capacitance needed for resonance.
4. ) The frequency will be achieved by using the function generator to power the primary coil with a frequency of 2.8MHz and voltage of 12V.
5. ) The wave function from the function generator will be a sine wave.
6. ) Determine whether the system transfers power by attaching the LED to the receiving coil and observe if the LED lights up.
7. ) If it works, attach the secondary coil to the oscilloscope.
8. ) Record voltage from the oscilloscope with the two coils as close as they can be measuring the distance they are apart.
9. ) Increase distance by half a centimeter recording the voltage for each distance until there is no voltage. Indicate the distance that the LED does not light up anymore.
10.) Voltage, current, frequency and wavelength need to be determined by the oscilloscope and formulas. Record findings.
11.) The coil will then be taken to an area that would require around eighty meters of free space with little to no electronic or physical interferences that would disrupt the antenna.
12.) Place a high sensitivity RF receiver 1 meter away from the transmitter at intervals of 30 degrees. Measure the interference and dBμ measurement at each harmonic frequency. Repeat at 2, 4, 6, 8, 12, 15, 18, 22, 26, 32, 38, 44, 52 and 60 meters away from the transmitter.
13.) Repeat steps 4 through 14 using a square wave function.
14.) Repeat steps 4 through 14 using a triangle wave function.
The data collected was graphed using a radar plot to show the intesity of interference at thirty degree intervals around the transmitter with respect to the distance from the transmitter. The graphs are in the Google Documents below. The radar plots show that, at one meter (blue cirlce), the intensity of the interference with the RF receiver has the largest colored circle, which corresponds to the greatest amount of interference. The sine wave at the operating frequency of 3180 kHz averaged 97.83 dBµ at one meter, decreasing to an average of 25.67 dBµ at six meters. The background of the surrounding area used for testing had an average background intensity of 24.54 dBµ, meaning that data near that intensity could be background interference instead of interference from the transmitter. The intensity of near fields should falloff at the inverse of the distance cubed, so the largest falloff of intensity should between one and two meters. Most graphs followed this trend well, except for the sine wave at the operating frequency, which led me to graph the falloff of the intensity with respect to distance.
Sine Wave Graphs
Square Wave Graphs
Triangle Wave Graphs
The falloff data was analyzed using Vernier Logger Pro to determine the the correlation between the expected falloff and the actual falloff. The correlation between the actual results and the theoretical results at the operating frequency was 66.54% which is relatively low. At the sixth harmonic of 19415 kHz, the correlation is 99.86%. This data made me realize that the operating frequency was powerful enough to surpass my RF receiver's maximum intensity measurement capabilities. I feel that more sophisticated equipment would have been able to prove that the falloff was correct.
The quality factor (Q) of the transmitter determines the bandwidth, and mostly contributes to the efficieny of the system. The first constructed coil had a low Q, which also had less interference because the energy is being transmitted at more thant the points of resonance. After recontructing the coil to increase the Q, the interference was greater but more defined as shown in the graphs contained in the documents below.
Graphs of Q
The RF receiver was overpowered by a small voltage source of 10 volts from the function generator, which is far less power than what is required for transmitting power for a farther distance.
The collected data shows that many different factors will need to be taken into account in order to create a practical system for wireless power. The transferred power was very noticeable on a RF receiver at multiple frequencies other than the operating frequency. The voltage and current supplied to the transmitter is much less than what would be needed to power even a small electronic device, but the interferences are still intense enough to easily overpower a radio station within the same frequency. The interferences with a system that operates using much more power would be much greater and further from the transmitter. The operating frequency of 3.18 MHz created interference with an intensity averaging 97.8 dBμ, while the fifth harmonic had an intensity averaging 79.7 dBμ at one meter around the transmitter. The intensity at each harmonic frequency decreased quickly when the distance between the receiver and transmitter increased. Potential sources of error could have came from the lack of good equipment for measurement and analysis. The function generator gradually sweeps through the different frequencies over time, so certain measurements were likely recorded at a frequency that would be higher than if there was no sweeping. The receiver used to measure the data also had one limitation that was realized after analyzing the data, which showed that the intensity being transmitted was slightly more than the receiver is able to measure. A better-designed system with greater processes for the coil construction would likely get rid of some of the harmonics that were found to be intrusive. Designing the coils to have a much sharper point of resonance will also make the interference at one very specific frequency for a higher Q. Considering the low voltage used in the experiment compared to the voltage required for many applications of the technology is much less, it will be far more difficult at higher power sources to truly have practical wireless power without causing problems with some existing devices. Wireless power transfer is an engineering challenge that will take time to achieve.
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Mark Kady-Electrical Engineer
Mark Pollard-Electrical Engineer