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Omnidirectional resonant inductive wireless power?

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BigBad

Thu Oct 24 2013, 12:54PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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OK, let's look at this from a sphere at the 'far field'; really good idea.

The thing is that the dipole moment vector doesn't have to rotate in a circle around the sphere; it can take arbitrarily shaped closed loops.

Imagine if you have a hundred phases, and the angles of the coils are arranged around a loop, but the angles of the coils wobble up and down above and through the horizontal, even reaching the vertical, and then coming back again before closing the loop. As the phase spins around the field will cover every angle of the sphere, so the receiver will be excited whatever angle it's at; it won't be exactly lined up, but it will be within the right angle to cut the flux and absorb the energy at some point of the cycle.

Uspring

Thu Oct 24 2013, 01:54PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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BigBad wrote:

The thing is that the dipole moment vector doesn't have to rotate in a circle around the sphere; it can take arbitrarily shaped closed loops.

It can be an ellipse but not more than that. Here's the proof:
The dipole moment of each of the solenoids is

Xi * Ai * cos(w*t+Pi)

where the X's are the vectors pointing along the axes of the solenoids, i.e. the directions of each dipole moment. Ai are the amplitudes and Pi the phases. The i's are indices.

This can be written as the real part of

Xi * Ai * e^(j*w*t+j*Pi)

which is the same as

Xi * Ai * e^(j*Pi) * e^(j*w*t)

You can factor out the term e^(j*w*t) because it does not depend on i. The term in front of it

Xi * Ai * e^(j*Pi)

can be summed up over all i's and the sum is a vector with a real and imaginary part, e.g.

Vreal + j*Vim

The summed result is then

(Vreal + j*Vim) * e^(j*w*t)

The real part of this is the total dipole moment

Vreal * cos(w*t) - Vim * sin(w*t)

This is a vector drawing out ellipses in space and could be achieved by 2 solenoids oriented along Vreal and Vim.

BigBad

Thu Oct 24 2013, 02:15PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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That's actually pretty damn cool.

So you have to use slightly different frequencies for the three different axes, which also helps with the coupling issue, since they won't correlate. That WILL work, you won't get ellipses, you'll get Lissajous figures which fill space just fine.

Uspring

Thu Oct 24 2013, 02:37PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Yes, that will have a resemblance to phased array radar beacons roaming in all directions.

Ash Small

Thu Oct 24 2013, 06:02PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Copy and paste didn't work too well with this quote, but the full formulae, etc. are here:

"One other observation is worth mentioning. As long as the frequency
ratio !1=!2 is a rational number, the curveâ€”no matter
how complexâ€”will eventually repeat itself, causing the motion
to be periodic.2 But if !1=!2 is irrational, the point P will never
retrace its own path, resulting in a non-periodic motion. However,
as time progresses the curve will gradually fill the rectangle
bounded by the lines x D a; y D b (fig. 72)."

twist2b

Tue Nov 05 2013, 08:12PM

Registered Member #2086 Joined: Tue Apr 21 2009, 02:33AM
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You should also look into as the "antenna" using fractals. It's used in the receiver to pickup multiple bands of frequencies. The problem with making a omnidirectional resonance is that it reduces the strength...

This website helps a lot in understanding directivity and field strength. Antennas in towers used for cell phones are actually setup in a very simple "fractal" system so that they are effectively omnidirectional to an extent.

BigBad

Tue Nov 12 2013, 05:14PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

Oh yeah, while I remember, there's one other way to get omni power that I found.

If you use two orthogonal coils with 90 degree phasing at the transmitter, and you have two orthogonal coils at the receiver, it's physically impossible for them to be at 90 degrees to each other over the whole cycle.

radiotech

Mon Nov 25 2013, 03:21AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

What about the use of Helmholtz coils that give a uniform field in a given space? Then
at any point in that space, that field could excite your resonant circuit.

BigBad

Tue Nov 26 2013, 10:36PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Not sure whether that works as well as you'd expect, IRC when I modelled it before, if you put the two coils together rather than separate you end up with 4 times the field at the same point in space because the inductance is a square law on the number of turns.

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