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Here is the spectrum or the input loading and output (everything is 50 ohms). The generator sweeps from 1MHz to 6MHz linearly so it starts at 1MHz and is 0.5MHz/div. So the action is at 3.15MHz.
Placing a hand directly behind the coils has almost no effect so the pickup coils are acting as good rear shields.
Aluminum foil placed between the coils (grounded) only drops the output voltage about 1/2 so magnetic fields can't be ruled out.
Putting a hand in front of the transmitting coil widens the the bandwidth and lowers the output voltage while a hand placed in front of the receiving coil narrows the bandwidth and increases the output voltage (~10 - 20%).
So voltage is falling a bit faster than the 1/d^2 function.
If I placed the coils very near (1/2 inch) I got the dual hump thing:
The phase angle between the input and output voltage is very low:
This was at a distance of 7R (21 inches) and the signal generator was set to 20.0Vp-p (7.07Vrms 50 ohm). I am only getting 456uW out but I suspect the transmitting coil's power factor is very low.
Not sure what it all means. Just typing notes before I forget them )
Great work Steve!! I have not had a chance to "think" about any of this yet 0:)
Cheers,
Terry
UPDATE:
I looked at the input power:
I have 270mW going in!
Into a 1 ohm resistor I get 3.6mW out and the open load is 1.04V
The the efficiency does not seem good in this very low power test...
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Maybe I didn't make it clear, but I only used the signal generator and square wave for tuning. To do the actual experiment I switched over to my HF transmitter, which does drive the system at its true resonance.
Sorry steve, you were pretty much clear, I'm just flimsy
Since I just couldn't resistthrowing something in this thread I had to lash something up in 15 minutes as soon as I got time.
What I wanted to see is how would ''true'' magnetically coupled system workat some ghetto scale.
I ran a simple royer oscillator at 1,2Mhz built out of two IRFZ44's. I needed to use really small pullup resistors wich dissipated lots of power.
There is no voltages higher than 50V anywhere in the circuit so it's sure that electric field doesn't play much of a role.
I could light a small 24V bulb connected to a coil of wire from some 2cm. Adding a resonant capacitor in parallel indeed had a major effect on impedance and output power.
Putting a good conductive plane under the coil has a small benefit since it reflects some of field back. Putting aluminium or copper foil between coils completely kills out the transmission.
24V 5W bulb without
And with approximately resonant capacitor in paralell, same exposure. But still this obivously won't work too well except for most point-blank power transfer
Mosfet gate voltage. 33ohm resistors turn them on in less than 100ns but dissipate over 4W to do that. The entire fully loaded circuit consumes about 6W...
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Wireless energy again
)
