Obsessed by the improvements of StarTrek and the fourth millennium, while feeling restricted by the limits of today's technology or that boring second law of thermodynamics? Just let your imagination flow - you needn't be Scotty to beam your thoughts in here!
By greatjay
I was reading a post by someone back in 2005 and some responses doubting the possibility of electric current flowing say for example from a phone charger to a phone. This is a revolutionary concept that researchers have already started working on and I have done some research on this and it is possible.

When two coils have electromagnetic fields with the same resonant frequency(product of induction of the coils and the capacitance plates attached to each end),current can flow from on coil to another or even from one coil to many coils. This is way different than radio ways, and as such reduces fears of people getting electricuted by the current. The current only flows between these mediums with electromagnetic forces around the coils and same frequency. In november 2007, some experiments were carried out by some researchers but they could only achieve electric transfers between devices about 7 feet apart. At least we know that the possiblity exists but we now need to improve on this technology to be able to leave your cell phone at home and still charge it a block away. This would mean a completely wireless world.

Please share your thoughts on this and lets improve our world.
By zanesjoy
Transmission of energy without wires or wireless transmission of electric power load on the power supply is switched on without each other wireless. Wireless communication is useful in cases where the wires between them are difficult, dangerous or even impossible. The problem with the wireless transmission is different from the wireless communications such as radio.
By krylon
The general idea is to use two helical resonators (coils). It will work at frequencies from 150kHz up to 10MHz or more. Lower frequencies need bigger coils, but the driver is probably simpler. The coils radiate electromagnetic waves too, but inefficiently, so you should chose a frequency that does not interfere. The diameter can be 150mm - 500mm, and the number of turns will self resonate. Use the first link to calculate the resonant frequency. The coils should be symmetrical and identical, and made from thicker wire to reduce resistance due to skin effect (1 or 2mm diameter), or copper tube up to 6mm. Use a former so the coils stay in shape, though this will have some effect on the resonance, as will metal benches, bench tops and the floor.

The signal is a sine wave adjusted to the resonant frequency. It can be coupled in and out using a second coil (inductive link) of a few turns, though finding the exact number of link turns to match the load to the source impedance will be more efficient. Ideally there could be two leds in parallel but reverse to work on both half cycles. Use ultra bright leds as they are much brighter for a given power.

The signal/power source.
Initially use a function generator for a sine-wave signal. With 50 ohm output impedance and the voltage set to a little below the maximum (say 14.14V p-p) the voltage when loaded with a 50 ohms resistor is half, and so 7.07V p-p. Divided by 2.818 to get rms voltage, it is 2.5V RMS. WIth 2.5V and 50 ohms the power is V^2/R = 125mW. This should light the leds, but not sure of the range - maybe 0.5m or more. A power up to 1W will give greater range. The range is not likely to be more than about 1/10 wavelength.

A 1W RF amplifier is shown in the first link. It will need a stable sine wave driving source of about 20-100mW to drive it. You can scale the values of L and C for other frequencies. An amateur radio low power transmitter may suit, at least for ideas. These are transmitters up to about 1W. The second to fourth links show examples. The crystal controlled types are not readily tunable to suit the coil resonance. The third link shows an adjustable type, that is useful for a few percent of frequency change, and the fourth link shows a type that would suit if you can figure out the Cyrillic chars.

You will need experience to adapt and make these radio circuits. If you get hold of the ARRL handbook it may help.

An altogether different approach is to use a current mode op-amp like the LT1206. This has about 20Vp-p with a 50 ohm load, so 1W, and will operate up to 15 or 20MHz at this level using +/-15V with current rating up to several hundred mA. This will need a suitable oscillator to drive it - perhaps a VFO circuit for radio amateurs
By Dncan85
If you have two coils that are supposed to be identical, it is difficult to wind them to be exactly the same because you might miscount the number of turns.

So, you wind one of the coils with slightly too many turns and start removing turns until you get maximum output.

One refinement to this is to have a small capacitor and put it across the coil each time you test it. If the capacitor makes the received signal worse, you can remove another turn. If it makes the signal better, you have already passed the resonance point.

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