Leap Wireless power transmission technology WiTricity light of current communications possibilities September 2008 No. 91
text. Nai Tong
Massachusetts Institute of Technology (MIT) research team in November 2006 launched a code-named WiTricity (Wireless Electricity) research project, trying to amplify a distance of several meters at each other's systems to send power wirelessly technology. Recently, MIT team made public their results, has been proficient to approach wireless transmission way through two meters appearance the 60-watt light bulb in the initial objectives.
Figure 1 MIT WiTricity
research team designed their utensil. Photo left for the power of the transmitter, the receiver in the right light lamp is installed on the lights.
the comprehension of wireless transmission power is the opener to the magnetic field coupled resonators (Magnetically Coupled Resonator), is shown in Figure 1 left and right ends of the coil device. The two resonators are a pair of 5.25 with a 6 mm copper wire coated ring, with the inductor-capacitor (LC) specifics of the coil antenna, the LC resonant frequency of 9.90MHz.
WiTricity a wide range of application places. Such as assorted domestic purposes or for military intention machines, electric vehicles, portable devices, medicinal instruments, sensors,
Lacoste Arin Patent Trainers, electric blankets or heating function of the appliance, and so with both possible.
Figure 2 pictures of the fortress Tesla
In fact, wireless power transmission (Wireless Power Transmission) or wireless power transmission (Wireless Energy Transfer) is yet a very old research. Early in the 19th centenary, Thomas Edison (Thomas Edison) and Nicola. Tesla (Nikola Tesla) to have spent enormous time and energy research includes wireless transmission, containing the various long distance power transmission technology. As early as 1891 Tesla attempted to demonstrate its feasibility, in 1904 the construction of the Tesla Power Tower (Telsa Tower) (Figure 2), attempt to achieve long-distance power transmission. Although this arrange failed, but later still Tesla effect (Telsa Effect) (Figure 3) to commemorate this term had tried to transmit power wirelessly transmit the avant-garde engineers.
the electromagnetic transmission of electric power is not feasible
a few meters to tens of meters distance transmission of data, is the most popular wireless network technology. It has been marveled why also not properly take advantage of these low and fashionable wireless network to transmit electricity. But in fact the wireless network to transmit electricity is not possible,
New Lacoste Trainers High Top, because the electromagnetic waves is not appropriate to transferring energy or electricity. The radio receiver, case in point, the bottom station radio broadcasting stations to dozens or hundreds of kilowatts (kW) high-power radio transmitter toward the direction of the marking 360 degrees, but compared with the transmitter power, the receiver can receive only be used little to describe the energy transfer efficiency is low.
Figure 3 Tesla effect was designed to test the system architecture chart
use of arrow antennas or laser focus in the same instruction so that eruption of electromagnetic waves is a viable reach in theory, in fact, it was also proposed track in 1968 solar power (Solar Power Station) the notion of offering to carry a big solar power satellite system, the usage of microwave transmission to globe motifs. However, deserving to the satellite's transmitter must stop emulating the receiver, so the actual applications are too many limitations.
The MIT method is chosen resonance. Resonance is a very prevalent phenomenon in ecology, and diversity. Musical instruments are acoustic resonance, child wag, mechanical resonance, electromagnetic resonance, nuclear magnetic resonance gas. Here are some common characteristics of resonance, that is, energy exchange will happen in the same frequency between two objects, and the frequency is not incongruous with the energy transfer between two objects. Such as acoustic resonance, assuming a hundred in the room, placed the glass, the digit of individual liquid into a little another, so that each wine has its assorted fixed frequencies. When the opera musician has a loud sound when practicing, instead of the same intonation, which is the vibration frequency of the same glass, there will be a strong resonance, but other frequencies are different glasses nothing will happen.
the use of the MIT way but electromagnetic resonance. Specifically, the use of so-called Evanescent Tail can be watched as a fast decay of electromagnetic fields with distance.
Figure 4 shows a simple example, that body of two-dimensional disc with high dielectric (Dielectric Disk) the use of resonance. Proximity in the mid field region is not scatter to far areas. And the outer areas are prevailed by electromagnetic waves. Electromagnetic energy loss is too large, not suitable for energy transfer media.
Figure 4 high dielectric body vibration of the electromagnetic field 2-D disk
I used to evaluate the energy loss of QR. QR larger, that the smaller the energy loss. Assuming QR = 1,992, meaning a wheel time of vibration, electromagnetic energy 1 / 1992 to electromagnetic radiation. If fully constituted only by the electromagnetic waves of objects, the thing in a phase of time, all the energy will disappear. Taking into list the nature of materials readily available, use about 100M ~ 1GHz down the resonance frequency for wireless power transmission ought be the most feasible. To 1GHz, the rate of this frequency dielectric (Dielectric Permittivity) the real part of the large, very small imaginary part of a lot of the material can be used as transmitter and receiver, such as titanium dioxide (TiO2) (Table 1). Table 1
lofty dielectric matter
Material / Material
rate than the dielectric loss dielectric Im (ε) / εTiO2
9610-3BaTi4O9
3710-4LiTaO3
Dielectric
4010-4 imaginary parts of the real part of the percentage, to cry for the The smaller the percentage, of lesson, the smaller the energy loss.
energy transfer efficiency for the system design to take advantage of electronic key
magnetic resonance theory for energy transmission, transmission efficiency, the telling transmission distance, obstacles for the transfer of energy, especially essential For the human body have adverse effects, etc., are required to elaborate the experiments and appraisal.
MIT's transmission system, a transmitter and receiver installed on the resonance of their body, and the transmitter into energy. When began resonance transmitter and receiver, the transmitter of the energy ebb, the gradual accumulation of the receiver. Until the transmitter side of the energy is tired, the resonance also will be stopped. The energy can be used to drive mechanism or to charge the power cell.
mandate to improve the efficiency of energy transfer, MIT team used the Strong coupling region is a let κ / Γ value is much larger than one cause. Simple words, κ and Γ is to make sure the key parameters of energy transfer efficiency. Specifically, κ quantified bond strength, Γ is the absorption of electromagnetic radiation caused by the system or the ratio of the size of the quantity of energy loss. In short, κ / Γ is much larger than a combination of the establishment of strong regional, energy transfer rate is much higher than the rate of loss, in other words, the energy transfer efficiency is relatively high.
κ calculation formula can be secondhand coupled mode theory (Coupled-Mode Theory, CMT) to obtain approach. Q value of the combined model theory close to ω/2Γ.
κ value greater the higher bond strength, the higher the energy interchange. Energy loss to that Γ is small and that a large Q value. Q value and inversely proportional to Γ.
then see by displacement distance. κ / Γ 1 namely the MIT crew is many larger than the tentative focus, and guide to mighty coupling zone namely apt achieve high stamina transfer efficiency of the physical basis. κ / Γ is not only a feature of transmission efficiency, which itself is a function of the distance. When 2 objects resonate with distance gradually, the fusion of weaker degree. Based on the test shows namely while κ / Γ is less than 1, the energy wastage ambition chance very massive (Figure 5).
Figure 5 κ value and the distance between
If the consideration of the practical application of
location, during system design have to spend a lot of exertion, primarily in the transmitter the size and fashion, to make the best considering.
Second, look at the practical application of the barrier. This point can be used to solve Maxwell equations have value. Using the coupled mode theory can also be approximate.
the data calculation, even if the transmitter or the receiver closer to the wall of the body such as vibration, Q value is only a little less, that the energy loss is not too magnificent. Even if the transmitter buried in the middle of the walls, Q value is only depressed by about half.
in real life context, Dielectric barrier than the real value of maximum small. For sample, cement is about 4.5, 1.2 to 5 wood, quartz cup is 4, the consequent loss of the dielectric is very small. But there are exceptions, the water is clear example. When the transmitter is very close to water, the resonance Q value to fall to about one-third the customary value. But even so, on the practical point of view is merely befitting.
wireless power systems have minimal impact on human health effects in humans
can be said that it can enter the wireless power technology level of practical application. Because the experiment directly to the alive to lead to ethical problems, so use MIT team leader in his office responsible for collating the robot to simulate the human body of books. In this experiment, MIT team is still based on high dielectric body as a disk to mail the receiver. Transmitter placed in the dome of the chief position, the receiver mounted on the robot, the robot will push back and forth. The room is a cube, beds, wall and ceilings are the same material. The shape of the transmitter output, less resilient limitations, the transmitter will not consider the internal energy loss, focusing on the energy loss at the receiving end.
First, the use of electromagnetic waves transmitted power on the automaton body and found that the robot is much smaller relative to the bureau, only small part of the recipient. Using high dielectric resonance between the disk body, the robot went middle of the room, the shortest distance,
Lacoste Trainers UK, to receive the highest power, the robot waded turn of the apartment, the receiver power small. If the robot for a people to reckon the simulation, the energy sponged along humans is very small, will only outcome in a little tepid, which is the cordless field elicited in human rind surface Joule heating.
Figure 6 LC resonator using a wireless power transmission system
However, even now the temperature no matter how small, have potentially hazardous, and accordingly it must be magnetic resonance systems, such as LC resonators, preferably than the high dielectric body of the disk to achieve wireless power transmission (Figure 6). Greatest convenience of using LC coil is that the coil in the LC virtually entire the energy of the external magnetic field energy and magnetic field in the space of human life everywhere, a very small impact on the human body. For example, the use of medical magnetic resonance imaging (Magnetic Resonance Imaging, MRI) test equipment, the firing of the human body's magnetic field strength is very strong, there are other linear motors, and even the magnetic drifting bed, etc., will In the environment of human life caused by the strong magnetic field, but the fact that those magnetic fields on the human body and will not cause health concerns.
by mathematical results of magnetic resonance, the Q value of the LC resonator in the loop field radius of 30 cm, 4,000 contracts. Resonance frequency is 9MHz, converted into a wavelength of 33 meters. When the two 1.5 meter distance, the energy transfer efficiency of 90%. If the 3 meters away, distribution efficiency of 45%, κ / Γ is greater than 1.
If the LC resonator used in the room above the office simulation, assuming that the transmitter of the LC resonator with a radius of 1 meter and 3 meters away from the bed placed in a high ceiling,
Lacoste UK, joined to 10MHz AC power source. The receiver side of the resonator is 30 cm radius, Q value is around 1,000. In this circumstance, the power transmission efficiency and the rate of use of high dielectric record to the same extent, but the body's digestion of energy is almost zero, so much safer for humans.
magnetic resonance electromagnetically induced more effective
the MIT wireless power system design uses two coils, so there is a very misleading place, that is, the system using the general conviction of electromagnetic induction. Although the two systems are somewhat alike at the outset glimpse, merely the link generated by fascinating resonance in terms of efficiency a milliin due times higher than the electromagnetic induction. This is for the road back to the former can lead to resonance effects of the capacitor, a longer distance between the coils.
MIT experiment configuration is as usual: a couple of 30 cm radius of LC resonator, two meters away from every other, and configured on the receiving end of 60-watt bulb (Figure 7). First, from the Colpitts resonator using electromagnetic induction to power sent to the transmitter coil, and then by magnetic resonance, the power transmission to the receiver coil, and then re-use electromagnetic induction to provide electricity to light and shine. At 1st glance, it seems the whole system can not ascertain the capacitor, but is dispensed in the wire capacitance is in the capacitor. Experimental system the resonance frequency of approximately 10MHz, and use the solutions of Maxwell equations from the academic value of the fairly loyal. The only must further be famous that the Q value of 2,
Lacoste R75 P2 Trainers,300 pure bronze, the substantial decision of the system is 1,000. Currently leads the team that this is caused by surface oxidation. 10MHz high frequency because of skin achieve will reason wires (Skin Effect), the present is only 10 microns at the surface of skinny wires flow.
Figure 7 bottleneck and reducing the receiving coil of the experimental conditions, two meters of light tin still shine.
Another amusing answer is if either the respective situation of the coil will affect the strength of links, that is to investigate changes in the value of κ. Experiment is the use of coaxial collateral access, whether an end of the tilt of 45 degrees,
Womens Lacoste Trainers, κ values remain in the Bacheng class. If the cable axis showing the two parallel, κ value is the extent of the Qi Cheng. Therefore, the comparative rank of the point of outlook alternatively a tiny inspire, if the state to enter the utility, the chart of the system or to cost doing someone.
Principles of telegraph transportation of electric
reveal
Linear Mode
