Concentrating the Earth’s Magnetic Field for Harvesting

Well you certainly aren't the first to think of this (there is quite a bit on the subject on the internet).

a number of them have also indicated that the relative "local" weakness of the earth's magnetic field as measured at any given point on the planet's surface makes such harvesting operations impractical.

Correct. This is THE main problem as the magnetic field of the earth is so small. A refrigerator magnet produces a magnetic field of about 0.1T, that's 100,000uT compared to the mean magnetic field of the earth at 45uT (2200 times smaller). This means you need an enormous area to get any useful power out. 100m long 'antenna' are not going to be enough even for small amounts of power.

How did You calculate your magnetic field strength and antenna magnet field figures as they seem unrealistically high (leading to your false conclusion of a potential 10MW generation).

Lets get some perspective. Here is a good real world example for you - the height of the support tower alone of a 2.5MW wind turbine is about 100m. Do you think two lengths of 100m iron are going to produce the same power as 4 of these wind turbines?

http://www.wind-energy-the-facts.org/index-18.html

Sorry, no free lunch here.

G.A.

Yeah, I forgot the 0.01 m^3 multiplier, and was trying to make a big impression of how much energy was stored in a small volume. Actually, I was initially drawing my optimism from the size of the H field in the gap, and the corresponding large currents that could be induced in a superconductive coil. These inductive currents, then, could flow through a diode into a capacitor where the upper ceiling on power output would be limited only by whatever upper limit on "refresh frequency" the superconductor naturally imposed.

Rather than say all this, I did a much too hasty calculation of magnetic energy just before making my first post, and made a glaring error which may prejudice readers against the general idea. This error, however, does not obviate the idea. The maximum possible power output would still seem to be Energy*Frequency. I arbitrarily chose 100Hz to yield 10MW, which sounded impressive, but I could just have just as easily [though perhaps not ;)] had the Energy figure correct (1000J) and chosen 10,000Hz as my refresh frequency, yielding, again 10MW.

What upper limits on refresh frequency there may actually be I can't begin to say with any assurance, although with different direction surface currents flowing on the inside and outside of a superconductive coil (at least in the open circuit condition) I suspect they have to do with AC field penetration into the interior of the coil which at some point, breaks down the effective separation between the inside and outside surface currents flowing in a magnetically immersed superconductive coil.

What seems clear to me is that I am not positioned to bring this idea any further myself. I have no academic contacts, and my history of mental illness and corresponding lack of work history makes me easy to disregard (even though I graduated cum laude in EE) ...and perhaps justify-ably so.

As for the simulation, not only do I not trust a "proper" simulation's match with "the World," I also mistrust my ability to do a proper simulation! Hence my request for help in verification. One thing is, as a given antenna length with gap width gathers a fixed amount of flux from the surrounding volume, I chose an antenna cross-sectional area of 0.01 m^2 (11 cm circular diameter), which bumps up the B and H field magnitudes by a factor of 100. This (11cm diameter) seemed like a decent size (to me) for a matching superconductive coil.

Anyway, you corrected a glaring error in my post, and did it with a kind tone which I deeply appreciate.

Godspeed.

Welcome to CR4

Enjoy!!

What happens to your antennae when you discharge the energy? Shouldn't you get a reaction similar but opposed to what happened when it got charged?

It looks like you would end up with a large EM transmitter!

Even if you use superconductors to obtain large currents, they have a very low voltage capacity. This makes them very difficult to pump up to a usable voltage. We don't have yet a powerful and efficient uV to V up converter. Maybe one day but not in the next 10 years.

You will have more chances success with solar winds and very large (100 Km) antennas.

marcot wrote: "Even if you use superconductors to obtain large currents, they have a very low voltage capacity."

I'm going into a somewhat winded discussion of this, as I am in part hammering out the reasoning for myself. Thanks for bearing with my wordiness... I believe the low voltages you refer to are covered in the book:

Bernoulli potential in superconductors: how the electrostatic field helps to Understand Superconductivity

As I browsed this book, whenever a steady-state superconductive current diverges from a straight path, patches of extra charge concentrations (or charge deficits) build up voltages, which exist external to the superconductor, and which internally, apply themselves only to the accelerations of charge which accompany the divergence from a straight path. Flux linkages are not changing in steady-state, so no conventionally inductive voltages are present.

These steady-state voltages are likely indeed small, and our design template being discussed does make use of them in the transition from the energetically "spent" open circuit condition to the short circuit condition, or the "current refresh" portion of the repeatable energy off-loading cycle. These small voltages, when applied across the near negligible resistance and inductance of the external circuit's short circuit, quickly refresh the original short circuit current.

Under transient coil conditions, however, (like when the short-circuit current is suddenly interrupted and directed into a charged capacitor) the actual magnitudes of currents and associated flux linkages are changing, so more conventionally large inductive voltages are capable of being supported by the superconductor.

As I see it, the superconductive coil in this configuration may properly be thought of as two inductive coils - one for the inner surface and one for the outer surface. In "spent" open circuit conditions (external circuit current reduced to zero), the magnitude of the inner surface current and the (opposed in direction) outer surface current is equal, with small Bernoulli's voltages built up at the ends of the coil where the outer surface current suddenly reverses direction to "become" the inner surface current.

In the short circuit condition, the inner surface current is zero, and all the external surface current flows in the external circuit as "short-circuit" current. Then as the circuit is opened through a diode to the voltage of a charge capacitor, the external surface current begins decreasing and the internal surface current begins increasing (in the opposite direction) -and as they do, the external circuit current being dumped into the capacitor heads toward zero as energy is off-loaded into the cap - finally reaching zero as the internal surface current magnitude matches the external surface current magnitude. Basically just Kirchoff's (sp?) current law as applied at the termination point of the superconducting coil.

On the questions relating to this amounting to a large EM transmitting antenna - I think all receiving and transmitting antennas are actually in dialog, both with each other and with the surrounding environment, should that environment change. And while the power for this antenna coil comes from elsewhere, its operation may have both local environmental effects, while also being in dialog with whatever far-away magnetic current loops (in the earth, sun, or intervening space) are providing power for its operation.

what if you used the moon as your anntenas ancore point? Tuned the antenna to the frequency of the moons orbit and the earths rotation as to attenuates most inductive noise do to stray magnetic fields and solar flare magnetic interfearence. As to the problem of power transmission at the end of the arrey useing a (tesla coil) modulate that frequecy into a HF carrier wave, Then useing tuned receivers tethered to hub points across the globe where it could be harnessed and filterd with super conductor RCL tank cercuits.