# Long range wireless power transmission

so I am trying to make something that involves long range power transmission. I need this to have small receivers 3mm-5mm wide and up to 1cm long also the transmitter can be up to 4ft wide and 2 inches tall. does anyone have any ideas? (also the range has to be 10-15ft)

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Hi Jkelly,

Welcome to the Tech Forum!

This is not a trivial endeavor, especially beyond a few millimeters. To start with, you would need to define the magnitude of power transfer you are trying to achieve, to see whether it’s realistically achievable. A cellphone transfers power to a cellular tower, but that power is measured in picowatts or less. In a perfectly lossless system, a cellphone might deliver a few milliwatts to a comparably-sized antenna receiver over a 10ft distance. Dimensions and frequency will also play a significant role, with smaller form-factors generally allowing for less power transfer. Your 3-5mm receiver severely limits this.

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I only need the power to light up a led so it does not need to transfer much power, only to transfer it a long distance.

multiple LEDs I should say. each connected to a different reciever.

There are multiple challenges here. First, each LED requires roughly 10mW to light up, which is a lot of power to transfer over that distance. Most wireless power systems use inductive coupling, as it is much more efficient. However, inductive coupling requires antennas which are of the same scale as the distance you are trying to transmit across - i.e. a 1ft diameter antenna won’t transfer much power beyond 1ft.

That leaves electromagnetic (EM) wave transmission, which can travel further, but which is far less efficient at transferring power. To transfer a reasonable amount of power over some distance, one generally needs a directional antenna, and the design of such is very technical, requiring complex calculations and is dependent upon the frequency of the transmission signal. This is the kind of subject about which electrical engineering PhD candidates write their dissertations.

Additionally, once you get into EM wave transmission (essentially radio waves), you now run into issues with the FCC. It must go through extensive lab testing to ensure it passes some stringent standards before it can be used outside of a lab environment.

This is all to say that it’s not reasonable for anyone who is not an expert in the field to consider attempting on their own. For much shorter distances where inductive coupling can be utilized (like less than around 10cm), there are many examples available, such as this and this.

The one thing we can offer which is actually capable of transferring power over the kind of distances you are talking about, are products from Powercast. They have kits and finished units for doing longer range power transmission, but they are still not of the form-factor you are specifying.

ok thank you