Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1797945 times)

Offline VAXHeadroom

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This is probably easily debunked, but it does pertain to Conservation of Momentum.

Couple days ago, I was at a lake.  Glass calm, no waves, no current.

I loaded myself into a canoe for a little spin.  Got out into the water. Drifted to a complete or near complete halt.  Then...

while remaining seated AND hands holding on tight to the side of the canoe, I 'threw' my torso forward.  I never actually left the seat.  But the canoe did move in that direction.  I then straightened myself up (slowly) and repeated the process a few times.  Each time, the canoe would shoot forward (ok move forward at less than paddle speed) for about two yards or so...but there was never any corresponding 'back motion' when I straightened.

So...violation of CoM or something else?  And could what I was doing be used as an analogy for whatever is going on with the EM Drive?

No violation.  F=MA If A is different in the two different directions, force is also different.  CoE is also conserved since more energy was expended to accelerate your mass in one direction than the other.  You were asymmetrically converting energy into force.
(somebody here is probably going to bite my head of for some boneheaded error :) )
Emory Stagmer
  Executive Producer, Public Speaker UnTied Music - www.untiedmusic.com

Offline deltaMass

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Yes this is the same person. He has many interests and you can see some of them on his personal web page that will reconcile what you found about him: http://johncostella.webs.com
There I find:
PhD thesis : Single-particle electrodynamics

And Shawyer states "This inquiry showed that he was not an electrodynamics expert"

Offline aero

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@Traveler

Quote
Frustum big diameter        m   0.2314000
Frustum small diameter   m   0.1257000
Frustum centre length   m   0.1386000

and asked him for the resonate frequency. He sent me the following:

External Rf                   Hz   3,900,300,000

I would prefer not to make an assumption, so I will ask. "Are those internal dimensions?" And, "Are the end plates flat or curved?"
Retired, working interesting problems

Offline deltaMass

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I am grateful to Costella for pointing out that not only does Shawyer not understand Newton's laws (or if he does, is unable to communicate them clearly), but also seems incapable of correctly drawing force vectors at the sidewall. This in Shawyer's mind gave a finite net thrust, based purely on the summation of his incorrect reflected force vectors over the complete surface of the frustum. A childish error unworthy of even a junior reliability engineer, one might say?

Are you seriously considering Roger Shawyer predicted the forces produced by his EmDrive using… arrows on a drawing, instead of equations?
Yes, seriously. Like several other people noticed. But don't go putting words in people's mouths. There is no "instead of" as you state. There is instead "in addition to". To quote from the attached PDF:

What’s wrong in Shawyer’s paper

Now we get to the point that a number of people have already made, but perhaps not confidently enough. Look at the arrows that Shawyer labels ‘Fs1’ and ‘Fs2’ on his Figure 2.4. These are sup-posed to be the forces that the particle imparts to the wall of the conical part of his contraption.
But hang on a minute! When a particle bounces elastically off a wall, doesn’t the wall feel a force that is perpendicular to the wall? Of course it does: if you remember your high school physics, you subtract the initial momentum vector from the final momentum vector, and the resultant force points into the wall.

etc...

Offline kml


My understanding is you need to insert the antenna at the internal diameter point where the effective guide wavelength is equal to the actual guide wavelength and the antenna should be a 1/4 wave stub at the effective guide wavelength.

In my EMDrive Calc, the lower left chart shows a red vertical line where that condition is satisfied.

You generally want a TE feedpoint to be 1/4 guided wave away from one of the shorted ends.  This is so the reflections off that end are in phase with the probe.    The ideal length of the probe will probably be much shorter than you would use for a non-enclosed waveguide as you don't want too much coupling to pull power out of the resonator.    In my rectangular waveguide resonator I started with the standard 1/8 wave probe which resulted in a TE101 Q of 35.   Incrementally shortening it increased Q until I stopped at about 1/20 wave and TE101 Q=400.  Increasing the length to TE102 further increased the Q from 400 to 1600.   I have a separate monitor probe which is off center and about half the length of the feed probe.  It pulls out about 10% of the power in it's current location.   I suspect moving it to a side wall will dramatically reduce that and increase Q further.

 I don't know if any of that translates to tapered cylinders but be prepared to try different lengths and positions.

Offline deltaMass

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While I'm happily cruising along in debunk mode, I might as well toss out the fact that photon momentum goes as the phase velocity and not as the group velocity. This renders the purported thrust mechanism of "differential group velocity" incorrect.
https://en.wikipedia.org/wiki/EmDrive#Theory

Offline flux_capacitor

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@deltamass:


Sometimes when you want anybody to understand quickly the basis of a theory, instead of using complicated equations, you simplify the concepts with what is know as popularization, through drawings and analogies. Those drawings and analogies are only that: approximations. And because they are only approximations, sometimes they are well found and clever, sometimes they are more or less misleading. Shawyer, in the drawing you refer to, was just trying to show the force imbalance exerted on the two end plates. The drawing was not good enough since it didn't show the forces on the walls. It wasn't the drawing upon which Shawyer built his theory! But what Costella did, was to throw the baby out with the bath water, on the sole basis of a not so clever popularization drawing. When I read that "refutation paper" at that time, I thought it was incredible being so rude (slandering Shawyer as a fraud) while at the same time never bothering to go into the maths. Costella's paper was very poor from both a human and a scientific viewpoint, and for that reason I think it was a shame that paper was so widely publicized. Gred Egan's work on frustum resonant cavities was much better for example.

I think too that Shawyer does not have the good theory to explain the thrust produced by the EmDrive. But don't think the man once began to wrote some incomplete arrows on a tablecloth before thinking about calculations or experiments. That's completely an upside-down reasoning.

Offline flux_capacitor

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While I'm happily cruising along in debunk mode, I might as well toss out the fact that photon momentum goes as the phase velocity and not as the group velocity. This renders the purported thrust mechanism of "differential group velocity" incorrect.
https://en.wikipedia.org/wiki/EmDrive#Theory

I used to found exactly the opposite searching that information, so we should ask someone specialized in microwaves to clarify this phase velocity vs group velocity thing. Perhaps we should open a good specialized microwave engineering text book IRL (please, no Wikipedia for such specialized stuff) and search about that.

What I found is: it is group velocity (not phase velocity) which contributes to the radiation pressure at the end plates. The group velocity (sometimes referred to as the guide velocity) carries the energy and momentum of the EM wave along a waveguide. The equations for group velocity are well defined and show that the velocity decreases as the guide dimensions decrease until cut off where propagation stops.

But I'm not an expert, so any expert should clarify :)
« Last Edit: 06/17/2015 09:15 PM by flux_capacitor »

Offline deltaMass

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@deltamass:


Sometimes when you want anybody to understand quickly the basis of a theory, instead of using complicated equations, you simplify the concepts with what is know as popularization, through drawings and analogies. Those drawings and analogies are only that: approximations. And because they are only approximations, sometimes they are well found and clever, sometimes they are more or less misleading. Shawyer, in the drawing you refer to, was just trying to show the force imbalance exerted on the two end plates. The drawing was not good enough since it didn't show the forces on the walls. It wasn't the drawing upon which Shawyer built his theory! But what Costella did, was to throw the baby out with the bath water, on the sole basis of a not so clever popularization drawing. When I read that "refutation paper" at that time, I thought it was incredible being so rude (slandering Shawyer as a fraud) while at the same time never bothering to go into the maths. Costella's paper was very poor from both a human and a scientific viewpoint, and for that reason I think it was a shame that paper was so widely publicized. Gred Egan's work on frustum resonant cavities was much better for example.

I think too that Shawyer does not have the good theory to explain the thrust produced by the EmDrive. But don't think the man once began to wrote some incomplete arrows on a tablecloth before thinking about calculations or experiments. That's completely an upside-down reasoning.
I agree with you that Shawyer "does not have a good theory". And I also think that by no means should Shawyer be singled out in this respect. That's because I don't think anybody has a good theory :)

Online Rodal

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While I'm happily cruising along in debunk mode, I might as well toss out the fact that photon momentum goes as the phase velocity and not as the group velocity. This renders the purported thrust mechanism of "differential group velocity" incorrect.
https://en.wikipedia.org/wiki/EmDrive#Theory
Not so fast moving along...

The group velocity of  a simple plane wave is:

vg=∂ω/∂k=∂E/∂p=p/m=v

which is exactly the velocity of the particle.

If a wave packet is localized, the group velocity measures how the "center of mass" of this packet is moving



The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this deep-water case, the phase velocity is twice the group velocity. The red dot [the phase velocity] overtakes two green dots [the group velocity] when moving from the left to the right of the figure.
« Last Edit: 06/17/2015 09:54 PM by Rodal »

Offline flux_capacitor

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So Rodal, which carries information and momentum: the phase or the group velocity?

Offline rfmwguy

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@deltamass:
(..)
I agree with you that Shawyer "does not have a good theory". And I also think that by no means should Shawyer be singled out in this respect. That's because I don't think anybody has a good theory :)

I'm workin' on it, I'm working on it! ;) Just procrastinating on slapping together (shiver) formulas after years of abstinence...I know, I swore off them, went to Formulas Anonymous meetings and everything...

Seriously, have not studied it long enough to spew out anything with scientific formulae...but I will eventually, IF I see something other than Null results on my project. If its there, it'll be discected and exposed eventually. Boom!

Online Rodal

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So Rodal, which carries information and momentum: the phase or the group velocity?
In most cases, it is the group velocity that carries information and energy
« Last Edit: 06/17/2015 09:30 PM by Rodal »

Offline deltaMass

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http://www.quora.com/Is-there-a-relationship-between-refractive-index-and-radiation-pressure

Quote
The new experiment confirms, to a  precision of about 0.05%, that the momentum associated with  electromagnetic radiation increases directly with the refractive index  of the medium into which it passes, discriminating substantially in favour of the phase velocity ratio and against the group velocity ratio

Offline WarpTech

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... If the frustum were replaced by a cylinder, this phase interference would not happen. The frustum is a nice conical-section representation of a spherically symmetric gravitational field, that only exists over a very narrow bandwidth. :)
Todd

What about two cylindrical resonators that are at a set distance and close together but out of phase?  Doesn't this re-introduce the  phase shifted asymmetrical attenuation?

If I had software like COMSOL, I could answer that. It's not so easy to do by hand and I find that;

D x dB/dt + dD/dt x B = 0,

with every other scenario I've tried. I think the DC cone idea I posted this morning is uniquely possible due to the axial symmetry and radial asymmetry of the cone shape.
Todd


Offline flux_capacitor

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So Rodal, which carries information and momentum: the phase or the group velocity?
In most cases, it is the group velocity that carries information and energy

Ok thanks, that confirm what I thought, as the phase velocity in certain conditions can sometimes exceed the speed of light, but the group velocity can never exceed c.
« Last Edit: 06/17/2015 09:35 PM by flux_capacitor »

Online Rodal

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http://www.quora.com/Is-there-a-relationship-between-refractive-index-and-radiation-pressure

Quote
The new experiment confirms, to a  precision of about 0.05%, that the momentum associated with  electromagnetic radiation increases directly with the refractive index  of the medium into which it passes, discriminating substantially in favour of the phase velocity ratio and against the group velocity ratio

See this that addresses this conundrum:  http://arxiv.org/ftp/physics/papers/0607/0607094.pdf

(much easier than for me having to type it)

The phase velocity is E/p while the group velocity is ∂E/∂p

Unfortunately quantum mechanics means characteristics of both wave and particle so the question is ill-posed.  In  situations that we can intuitively relate to the group velocity is associated with momentum since the group velocity  is associated with the particle, but in other situations (absorptive media) the wave plays a more important role
« Last Edit: 06/17/2015 09:55 PM by Rodal »

Offline deltaMass

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"So even if it resonates, it won't push. QED"
http://physics.stackexchange.com/questions/130662/emdrive-cavity-modes

Some maths, probably similar to Egan.

Online dustinthewind

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... If the frustum were replaced by a cylinder, this phase interference would not happen. The frustum is a nice conical-section representation of a spherically symmetric gravitational field, that only exists over a very narrow bandwidth. :)
Todd

What about two cylindrical resonators that are at a set distance and close together but out of phase?  Doesn't this re-introduce the  phase shifted asymmetrical attenuation?

If I had software like COMSOL, I could answer that. It's not so easy to do by hand and I find that;

D x dB/dt + dD/dt x B = 0,

with every other scenario I've tried. I think the DC cone idea I posted this morning is uniquely possible due to the axial symmetry and radial asymmetry of the cone shape.
Todd

I was saying that because the evanescent waves (or the currents) in the two cavities walls being out of phase by pi/2 and 1/4 lambda apart interact.  One cavities evanescent waves appear to be working against the other so it is attenuated at one end.  The other is constructively interfering and working with its partner cavity evanescent waves (due to time retardation).  As a result energy is attenuated from one cavity and transported (tunneled) to the other creating a non-standing wave as a result.  It appears to be asymmetric attenuation in one cavity and asymmetric amplification in the other but with opposite wall orientation w.r.t. each cavity.  Hopefully I am not too far off in this but I think I am right.   
« Last Edit: 06/17/2015 10:44 PM by dustinthewind »

Online Rodal

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http://www.quora.com/Is-there-a-relationship-between-refractive-index-and-radiation-pressure

Quote
The new experiment confirms, to a  precision of about 0.05%, that the momentum associated with  electromagnetic radiation increases directly with the refractive index  of the medium into which it passes, discriminating substantially in favour of the phase velocity ratio and against the group velocity ratio

See this that addresses this conundrum:  http://arxiv.org/ftp/physics/papers/0607/0607094.pdf

(much easier than for me having to type it)

The phase velocity is E/p while the group velocity is ∂E/∂p

Unfortunately quantum mechanics means characteristics of both wave and particle so the question is ill-posed.  In  situations that we can intuitively relate to the group velocity is associated with momentum since the group velocity  is associated with the particle, but in other situations (absorptive media) the wave plays a more important role

So, perhaps we can put it this charitable way:  Shawyer's ad-hoc approximation is closer to the truth for the case in which there is no dielectric insert inside the cavity (in which case the photons may behave more like particles with a group velocity vg for reflective boundary conditions) and it is further away from the truth for the case of the cavity containing a dielectric insert (since the momentum associated with  electromagnetic radiation increases directly with the refractive index  of the medium into which it passes through)
« Last Edit: 06/17/2015 10:50 PM by Rodal »

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