# Is it possible to induce few volts IMPULS over 10 m distance?

I'm currently learning about electromagnetism at college, so this question is on mine mind for a few weeks.

If we have on one side: 9 V battery, DC-DC converter to few kilovolts, capacitor, button, and small dimensions inductor L1 (no more than 5 cm diameter).

And on the other side at distance of 10 meters secondary inductor L2, simillar dimensions as primary, but thinner wire and more turns. In schematic DC-DC converter is missing.

MAIN QUESTION: Is it possible to induce for example 3 V short impuls on the secondary inductor when we press button?

I tried to calculate it with Lenz law, but i didn't succeed, :/

Sub-Questions:

1. Does induced signal duration depends on resistance in series with capacitor?
2. If we have instead of inductor, resonat circuit, is it practically possible that signal last for a few seconds?

Thank you for your answers.

## 1 Answer

Is it possible to induce for example 3 V short impuls on the secondary inductor when we press button?

Hopefully this should help: - It's all about dumping as much current as you can into the transmit coil and, with your circuit you probably want to rethink the 1000 mF capacitor on the transmit side; it will have significant ESR and restrict current significantly.

It might be better if you concentrated on making both coils resonant at the same frequency - not only does this vastly increase the current into the transmit coil but it makes the receive coil more sensitive by the Q-factor.

So, will you get 3 volts with a 10 metre gap - not you won't easily - just do the math following my equation and you will see that it's likely you will need hundreds (if not thousands) of amps flowing in the transmit coil to achieve volts at the receive coil. Much beyond the transmit coil the flux density falls as a cube law with distance.

However, you might receive 3 mV that you can amplify up to 3 volts.

If we have instead of inductor, resonat circuit, is it practically possible that signal last for a few seconds?

The better the tuning (higher Q) the longer the signal will last.

The higher the frequency the higher the induced voltage will be because of rate of change of flux BUT the harder it is to dump the intial current into the transmit coil due to reactance. I would recommend wiring you transmit coil from high quality litz wire and making the diameter as large as you can.

• Thank you sir, i understand. But how to determine current in a first coil? How can i calculate inductance resistance Xl=2*PifL, if i don't have frequency of signal? Thank you again. – fender_cro Dec 31 '16 at 1:46
• The tuning capacitance causes resonance with the inductor. therefore you do have frequency – Andy aka Dec 31 '16 at 10:23
• Ok, basicly i need to study oscillator...Many tnx., happy new year :) – fender_cro Dec 31 '16 at 20:11
• Happy new year to you. The formula for the resonant frequency is $F = \dfrac{1}{2\pi\sqrt{LC}}$ – Andy aka Dec 31 '16 at 23:35