The homotenna (homopolar motor + antenna).

[gravityblock]

The latest thread on homopolar motors made me think about some old concepts again, one of them being the "homotenna" idea.

I had this new idea and thought it was worth sharing at the very least.

The concept is simple, you have a coil wrapped around a ferrite core. This would be your rotor. Then both ends of this coil are connected to rings sliding against brushes leading to your exterior circuit. One lead of this circuit is electromagnetically shielded.
The circuit is then energized with HF AC, the high frequency being crucial and somewhere between 10kHz-1Mhz so the shield can do its job shielding the electromagnetic field.

The theory behind it is also simple. We already know that the external circuit in a homopolar motor causes the torque on the disk/magnet assembly. However if the below concept were to be energized with DC current both external wires would cause an equal but opposite torque on the rotor assembly leading to no motion. But if we were to replace the PM with an EM and fed it with HF AC current through the stationary leads AND we can shield one lead completely so its EM field becomes invisble to the rotor then a net torque could arise. Since both the current in the coil and the current going through the external circuit lead are the same and synchronized, this should lead to a torque acting only in one direction on the rotor. And since there's no coil part going from rim to center, there should be no induced back emf.

The key here is the shielding of the field of one lead and making it disappear to the rotating magnet. This is much more efficient than the antenna idea as currents can be higher and frequency lower.

Broli,

I think the best way (possibly the only way) to shield the field of one lead is to have it rotate with the disk/magnet.  The lead which is rotating will become invisible to the rotor and a net torque will arise from the stationary lead.  Below is a quote on a homopolar experiment found under the heading of "Flux management by differential shielding on this page".  On the same page of the differential shielding there is another experiment under the heading of "Rotating magnet assembly on circular path about a fixed centre point".  I had an idea very similar to this, but instead of using a diametrical current it would use a radial current and the nylon shaft would be replaced with a conductive shaft while using only one plate instead of two.  I don't see why we can't combine the shielding of one lead by having it rotate with the disk/magnet or electromagnet on a circular path about a fixed center point as I described above along with a few other modifications to produce a generator with no induced back emf.  I'm attaching a photo of the rotating magnet assembly to this post.

It seems that although there can be no flux inside the shield, it is concentrated at each end and produces the same emf in the conductor being shielded as would be produced without it. It would require a shield of 'infinite' length to prevent this phenomenon. This is yet another example of an immutable corollary of the laws of electromagnetic induction!

Gravock

[gravityblock]

Here's a video explanation for those who may be a little lost in my last post in regards to the two magnets connected by a shaft which rotates on a pivot bolt and a circular track.  In this video, the two magnets are connected by the shaft with opposite poles facing each other.  The force acting on each magnet is in the same direction, so both magnets will either move forward or backwards on the conductive tracks depending on the polarity of the current.  However, if the two magnets are connected to the shaft with like poles facing each other, then one magnet will want to move forwards while the other magnet wants to move backwards when the conductive tracks are energized.  By placing a pivot bolt through the middle of the shaft, then the two magnets will run on the circular track with a net rotation which is either CW or CCW depending on the polarity of the current.

Gravock

[gravityblock]

Broli,

Do you think the rotating wire piece being pushed away from the magnet is nothing more than the centrifugal force?  The centrifugal force definitely needs to be ruled out, so I'll be devising an experiment to check for this.  I have two axially magnetized magnets 2" dia. and 3/8 in. thick.

Gravock

According to Faraday himself on page 136 in a publication titled, "Experimental researches in electricity / by Michael Faraday", the outward force acting on the rotating wire piece could not be from a centrifugal force.  If the outward force was due to the centrifugal force, then the distance between the rotating wire piece and magnet would not increase as the speed of revolution decreases (see the snapshot of page 136 below).  In conclusion, the centrifugal force is ruled out by Michael Faraday as being responsible for the outward force acting on the rotating wire piece.  How in the world has this gone unnoticed for nearly 200 years? 

Gravock

[broli]

It's interesting indeed as centripetal force was the first thing that came to mind as well.

[gravityblock]

Revolving Aluminum Cylinder (video).  See snapshot below for a quick description of the video and for the frontal view of the second part of the video.

Gravock