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I've been working lately on a new project. The project is to power a simple LED with a transferred power.

The first thing that came to my mind is "Transformers". So, I surfed the internet, I found lots of circuits that actually help in making a wirless power device.

This is the schematic:

Source 1. Source 2.

Parts:

1- Arduino

2- Two 0.02 uf capacitors

3- 2n3904 NPN transistor

enter image description here

The voltage was really small as I used the arduino to generate a 147.7 kHz square wave AC signal.

I tried changing frequency, cpacitors with the same coild. I had different results. By different results I mean different deficiency of power transfer.

My questions:

1- Is there a direct relation between them? Is there a clear mathematical equation between them?

My attempt to answer the question: Based of an internet search, I need to calculate the inductance of the wires the values of the capacitors are set based on the inductor in order to calculate the capacitor required for the frequency that you plan to use.

2- How is the LED turned on? it should be switching between forward and reverse bias so (On-OFF) because I have an AC signal output.

My attempt to answer the question: It is actually tuning on and off really quickly that I see it to be turned on all the time.

3- Are there any parameters I have to keep an eye on that will help in increasing the efficiency?

I looked for gap materials, but let's say that is fixed (air).

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    \$\begingroup\$ This will answer all your questions and includes demonstrations you can replicate: youtube.com/watch?v=r1UT4NuygmQ \$\endgroup\$ – aloishis89 May 15 '14 at 19:38
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    \$\begingroup\$ @aloishis89 If you've posted this as an answer, I've would've accepted it. Amazing, thanks! \$\endgroup\$ – Adel Bibi May 15 '14 at 22:01
  • \$\begingroup\$ I'm not sure what the StackExchange etiquette for this is, but I reposted it as an answer so it'll be easier for other people to see and find. \$\endgroup\$ – aloishis89 May 15 '14 at 22:09
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This video will answer all your questions and includes demonstrations you can replicate:

About Wireless Power Transfer

The short version is that you need quite a lot of energy to get a reasonable result since there are lots of things that cause loss. So using magnetic fields is quite inefficient. There is, however, another attempt at wireless power that uses ultrasound instead of a magnetic field. Ultrasound is a pressure wave instead of an electromagnetic wave and may be more efficient. There's a company called uBeam that is trying to commercialize that technology, however they're still in stealth mode. There are some papers on Google scholar that discuss ultrasonic energy transfer though.

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First question:

  • the voltage is ratio is equal to turns ratio
  • the efficiency is inverse proportional to the distance (gap) between coils

Second question: you already answered it.

Third question:

  • lower the gap
  • build optimum inductance coils
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  • \$\begingroup\$ Can I have more details on "optimum inductance coils"? And what is the exact relation between coupling (inductances) and efficiency? \$\endgroup\$ – Adel Bibi May 15 '14 at 9:14
  • \$\begingroup\$ @AdelBibi both coils should resonate on the same frequency (on the second depends on the capacitor). \$\endgroup\$ – Cornelius May 15 '14 at 9:20
  • \$\begingroup\$ @AdelBibi in theory, if you build a resonant circuit on an AM frequency (500 - 1600 kHz) you may get some "energy" from on-air radio stations. \$\endgroup\$ – Cornelius May 15 '14 at 9:23

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