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Comment by jfoutz | Hacker News Reader

> power is not transmitted via electromagnetic radiation, but via oscillating magnetic fields

I don't think you can have one without the other, can you?

That's probably true. I admittedly am pretty bad with basic EM physics. Would love someone to explain this to me like I'm five.

A varying magnetic field produces an electrical field.

A varying electrical field produces a magnetic field.

Therefore if you produce either a varying electrical field or a varying magnetic field, you will generate the other, which will then propagate out; this is EM radiation.

I only did a quick read of the paper, but this looks like they are generating a standing wave (think like a guitar string, where the amplitude of motion is fixed at any point along the string) with a wavelength much larger than the size of the room; this lets them capture the electrical field in capacitors in the center of the room while still having a moving magnetic field throughout the room, thus effectively separating the two, which allows for a moving magnetic field (which the receivers can convert to an electric field) without having a high-magnitude electrical field in the free space of the room.

Seems to me more like they used the big copper tube in the center of the room and the aluminum walls of the room itself to guide the current flow. It's as if the copper tube and the room are a big conductor through which electricity flows (actually oscillates) - this changing electric field in the conductor creates a magnetic field in the space around it, i.e., the room. So the electric field is contained and guided through the conducting walls of the room, while the magnetic field permeates the space in the room itself.

Yes, the walls and ceiling conducting are important to this (otherwise there would be a large induced electric field outside the room).

There are capacitive elements in the pole which is important for allowing it to be resonant at a wavelength much larger than the room (the wavelength used is over 200 meters).

The very long wavelength means that, in theory, one cuold design a room with less of the perimeter conductive (a wire mesh would certainly work; they suggest that doors and windows, or even conductive panels that are connected could work).

There are electric and magnetic fields. While you can't have one without the other, one always dominates when those fields propagate. Also, the effects vary depending on distance from the generating source.[1]

This article apparently says that they have made a practical way to transfer magnetic energy to inductors (coils) well beyond the near field range.[2] They do this by creating quasistatic magnetic fields within a specific space. The coils within that space react to the magnetic fields the way coils in a circuit would.

[1] https://en.wikipedia.org/wiki/Near_and_far_field [2] https://en.wikipedia.org/wiki/Inductor

[3] https://en.wikipedia.org/wiki/Magnetoquasistatic_field

I think you can. Using electricity, you can induce a magnetic field (Electromagnets) and vise versa, using magnets you can create electricity.

Like the other commentor though, I'm not very strong with my physics knowledge, so I can't answer for certain, but I'll be reading about it at the gym tonight I think.

Can you read while running on treadmill or something? That's an extraordinary multitask if you can!

No, I use the recumbent bike machine.

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