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Wireless energy transfer and resonant coupling? Answered

I am getting a bit sick and tired of frying expensive parts, entire coils and sitting in stinking smoke for hours, so time to gather some new ideas from you guys ;)

Problem as short as possible:
I am working on wireless energy transmission.
Not with the usualy distances we know from charging pads or electric toothbrushes though, I am aiming for 30cm and more of distance here.
After endless hours wasted on testing different coil designs I think I got that one nailed quite good but the thing is that I seem to be unable to keep resonance under load.
The coils require a very tiny window for the right operating frequency in the 40kHz range or for the other design in the 150kHz region.
When the frequency shifts more than 3 or 4kHz from the resonant point the efficiency drops to useless.
Since this entire thing is planned to be as simple as possible so everyone can do it I would like to prevent complicated electronics.
The few I need so far are done through ready to use modules.
Of course a microcontroller would be the most obvious choice here but that does not fit in as I like "old school" for this one.

Two ways I considered so far with more or less success:
a) Fixed frequency feed and limited output power.
This works actually quite well but only allows for tiny power levels like charging a mobile phone or tablet if you have some time.
Problem however is that load changes affect the frequency and without a link back to the sender the efficiency goes down and not enough energy reaches the receiver for usage.
b) ZVS driven coil.
So far this approach gives the best output power but also uses huge amounts of juice.
Good to make a fancy glass stand for your TV and supply the power through a hidden receiver in the base of the TV but since there is no limit or link between sender and receiver it is full power only.

Is there a really simple way to provide a limited amount of power together with automatic resonance keping?
Next one might be a bit tricky:
Is there a simple way to increase the harmonic frequencies?
As we know every simple oscillator also creates and reacts to the corresponding harmonic frequencies.
On the sender's side I would like to be able to not just feed the primary frequency but also one of the harmonic frequencies with a similar power level.
Again without a microcontroller or extensive electronics where possible.


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4 years ago

I am pretty sure you know all this but:

To extract energy from a radio signal you need a resonant cct. ie a capacitor and a suitable inductance. The resonant frequency of the coil/inductor will be 1/2pi sqr LC


How much you extract depends on several things:

The amount of energy beamed at you, ie you will get more if the signal is directional.

The stability of the frequency.

The match between your resonant cct (often called a tank cct) and the receiving circuit.

So you need to best match the load to the effective impedance of the tank cct to get maximum energy transfer.

Despite what Tesla is reputed to have done this is actually really hard over any real distance.

Higher frequency will be more effective and of course with his Tesla coil machine he was generating vast levels of radiated energy.

As with almost all transmitter/receiver technology the theory will only take you so far, after that it becomes something of an art and fine tuning to get the max output is often done by trial and error.


Answer 4 years ago

Extracting energy from the harmonics may not be as effective as you think as the energy content drops off rapidly as you move away from the centre Freq. However to get at that energy your going to have to have a wider bandwidth at your receiver, now your into areas where widening the band width makes the receiver less effecient - swings and roundabouts.


Answer 4 years ago

It is not so much about extracting energy but more a matter of using a multiple coil design.
The harmonics I plan to use on an additional coil to test the effects on the resulting magnetic field and its direction.
Biggest problem is not to be able to suck enough energy out of the receiver but to find a feasable balance between energy going into the sender and available energy at the receiver.
Considering that an omnidirectional system could feed multiple devices while a more directional field is great to power a single device at greater distance.

Not really taking into account the fact that a lot of energy would be radiated and cause other problems LOL


Answer 4 years ago

Not going the traditional route of engeneering here ;)
Until I manage to get it working good enough for a new Instructable I just say: coil design makes all the difference here ;)