Author Topic: Couple of Questions, and a Theory  (Read 1074 times)

Offline Akya2120

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Couple of Questions, and a Theory
« on: 02/19/2017 09:02 AM »
How much research has been done on the geometry of the frustrum? I know commonly 17 (IIRC) has been chosen, and I'm sure there is a reason. Has anyone considered using the golden triangle? Meaning a side angle of 36. It would just seem natural to me that the ideal shape would match a recurring pattern we find all over our existence. I could make the same argument for the ratio of the small and large side, as well as the distance between ends. I would very much so like to model the fields in these supposed golden conic sections, but alas I am not there yet.

A consideration for making these more energy efficient. Rather than using a magnetron, why not create an LC circuit and essentially use the capacitor as the emitter of this high frequency light. That way the driving circuit can strike resonance and we only have to do a little work to maintain the signal. Certainly it would require more electronics than a magnetron, but that's not too complicated. I would imagine plate capacitors would be better at generating RF than typical shelf bought capacitors. Also, the plates could be segmented to help the capacitors act as an antenna.

Offline ThinkerX

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Re: Couple of Questions, and a Theory
« Reply #1 on: 02/20/2017 06:53 AM »
Your comment probably belongs in the current EM Drive thread.  Still...

1 - Multiple 'half cone angles' have been considered for the EM Drive's frustum. Along with flat ends, curved ends, and flared sides. 

2 - I believe the LC circuit concept has been brought up before.  Currently poster and experimentalist 'Monomorphic' is testing an EM drive design that does not employ a magnetron.

Offline abuzuzu

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Re: Couple of Questions, and a Theory
« Reply #2 on: 03/03/2017 11:31 PM »
Akya2120

First off it seems you are new here welcome.  I have been lurking here for years.  I have learned a lot reading the comments.

I will start out telling you I am an old experienced analog, RF and microwave design engineer.  Excuse me in advance if I sound like an old professor.  Truth is I was a professor of electrical engineering specializing in electronics design and electro-magnetic theory for part of my career.

It turns out you can make a very strong argument that a resonant cavity is an LC circuit.

Imagine a parallel connected LC circuit.  Reduce the number of turns in the inductor until you have a single U shaped turn orientated horizontally.  Reduce the capacitor plates until you have nothing left but the capacitance from one terminal end of the inductor to the other terminal end of the inductor. Essentially your LC circuit considered of a single, horizontally oriented, U shaped wire.   Now put a large number of these U shaped wired in parallel with each other roataing about an axis line that passes perpendicularly though the wire end point terminals.   You will have a resonant cavity shaped like a pillbox

People who have studied waveguide theory will have multiple objections with the over simplified image I painted above but for my purposes the point I wish to make is that there is a progression of electrically resonant structures starting with conventional point-like ( much smaller than the wavelength) LC circuits. to distributed, transmission line resonant circuits with discrete L or C loading, to pure transmission line resonant circuits to infinite numbers of transmission line structures connected together as to define a solid surface- a cavity resonator.

You can certainly can describe and perhaps build an LC circuit that is equivalent to a conventional cavity.  A EM thruster cavity is a bit tricky because in order to generate thrust the propagation velocity of the contained EM-wave needs to be faster at one end of the cavity and slower at the other end of the cavity.  In principal it seems to me you might be able to determine an equivalent LC circuit and as lumped constant LC networks have reflections off the boundaries and variable propagation velocities you might even - in theory- be able to generate thrust.  This would be a great EE Electro-magnetics PhD project topic.

The reason no one- or almost no one attempts LC EM thrusters is that resonant cavity resistive loses are hundreds to thousands of times smaller than LC resonator losses.  Also just because you can derive an LC equivalent circuit for a cavity does not mean you can actually build the equivalent circuit.   You will find the required LC parameters will be vastly too small, or vastly too large to actually construct the circuit.

I also point out capacitors do not generate or radiate EM energy.  You need an active device that converts applied DC power into RF power- such as a magnetron  or a transistor amplifier.  In an EM thruster there is ideally no radiated RF energy.  We do not want to build a photoic drive.  A source of RF such as a magnetron, connected to a directional antenna such as a corner reflector will generate a very small thrust from the EM radiation.  The attraction of the EM thrustor technology is that the theory hints is ought to be possible to take the same RF energy and generate orders of magnitude more thrust by containing the rf energy within an resonant cavity instead of radiating it off into space.

With respect to the golden triangle, mother nature doesn't know and does not care about ancient Greek philosophy.  Engineering structures that satisfy mother nature's requirements as described by Newton, Einstein, Mach, Woodward, Maxwell and others produce the desired effects.  Because these structures are useful they become magic to some extent in the human mind.   Other structures or constructs that are magic because they satisfy ancient human esthetics sometimes -rarely- are technically useful by coincidence.

The key thing here is that technology moves forward by understanding the details of mother natures most intimate behavior and then according to her wishes and satisfiing her requirements, not by presenting multiple random shapes and volumes and hoping for for her to smile graciously upon your latest offering.

That is why it is difficult to make experimental progress here.  The experimenter needs a solid, precise, quantitative idea of what effect he or she ( thinking of you Shell) wishes to induce and then needs the engineering and craftmanship skills to actually build a -close enough- physical copy of their detailed mental image of the device.

Ok I'm done now.

Offline LowerAtmosphere

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Re: Couple of Questions, and a Theory
« Reply #3 on: 03/04/2017 03:54 PM »
Imagine a parallel connected LC circuit.  Reduce the number of turns in the inductor until you have a single U shaped turn orientated horizontally.  Reduce the capacitor plates until you have nothing left but the capacitance from one terminal end of the inductor to the other terminal end of the inductor. Essentially your LC circuit considered of a single, horizontally oriented, U shaped wire.   Now put a large number of these U shaped wired in parallel with each other roataing about an axis line that passes perpendicularly though the wire end point terminals.   You will have a resonant cavity shaped like a pillbox
...
The attraction of the EM thrustor technology is that the theory hints is ought to be possible to take the same RF energy and generate orders of magnitude more thrust by containing the rf energy within an resonant cavity instead of radiating it off into space.

This was a very insightful and accurate post, I only object to the stack of u shaped wires depiction.

It is important for readers to note that while seeing it as a parallel circuit is correct for certain areas of the cavity, there are clear current discontinuities in the skin along the height axis.

It is actually unclear to what extent currents can propagate between the modal extrema, especially given higher energy density fields. It would be a reasonable assumption that any modal shape which covers the length of the wall, 011 perhaps, would form one circuit whereas 013, the consistently highest thrust mode so far, has clear discontinuities/asymmetries. Does this mean that the circuit analogy is short-circuited? No. Eddy currents may interact with discontinuities serving as anisotropic (remember the larger picture of the entire wall) semiconductors controlling for the individual dipole moments which arise from the circuit each modal extrema creates. The real difficulty in deciding whether to treat it as a circuit is how to depict the resonant interior of the cavity. Since the interior oscillates the walls seemingly must too. Are these oscillations harmonized over time (remember complex propagation for incident waves) and do travelling waves in the interior maintain an imbalance?

The choice between circuit and waveguide is not trivial. It is essentially a choice for the source of thrust originating from photonic propulsion (change in wavelength/optomechanics) or 'electric' propulsion (voltage and conservation of momentum). Obviously the two are tied in the 6D Hamiltonian (or insert your favorite field theory here) for the entire cavity and may be two sides of the same coin.

Many simplifications and givens exist with both waveguide and circuit models: 1) Another interpretation is through plasma physics which explicitly ties the two concepts together though confuses the overall picture even more, so I do not mention it here. 2) Shape is not discussed, though the reflective/incident angles in copper play a large role in absorption. 3) Dielectrics are not discussed. 4) Copper or an analogous metal is assumed: meta-materials so far ignored. 5) Cut-off dimensions and external fields are ignored. 5) Higher-order effects irrelevant etc etc,

The point is that the circuit model is great for the walls, but absolutely useless for the interior and the exotic effects throughout the skin. It may be more useful once the mainstream operational theory is chosen.

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