Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1798911 times)

Offline phaseshift

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Returning to Randall/Sundrum for a moment. It’s been pointed out over and over again that the EMDrive, as it is proposed to operate, violates CoM - no disagreement by me there.  IF it does actually produce thrust then the answer must be 'outside the box’  (pun intended). In the interview video, that was posted several days ago with Randall and Sundrum, Sundrum briefly talks about how CoM can be violated (in appearance).  Their theory, which has nothing to do with the EM drive, says that there is another 3 dimensional space called the Planck brane, sometimes it’s called the Gravity brane, or Strong brane, that exists in parallel to our 3-space brane (the Tev brane) and they are joined by a finite dimension that is very short. The distance between the Gravity brane and our Tev brane is the reason that gravity is such a comparatively weak force. Sundrum says in the interview that energy, and mass, could move into this dimension (or possibly other dimensions), where we can not directly measure it and thus energy/momentum seems to disappear. By-the-way the Randall-Sundrum Model is the first theory to come from string theory that is testable and will be tested at CERN this summer (2015); it's being taken very seriously. 

IF they are right - what does the energy/mass do when it moves into this finite dimension? Remember at the end of this dimension is the Planck brane.  The dimension is very much like a cavity.  Two things come to my mind:

1. Is it possible that the ‘thrust’ is pushing off the internals of this dimension?  Sound familiar? I think this is close to what Dr. White is suggesting - though he says ‘Quantum Vacuum’. By internals I mean whatever resides in the dimension - who knows what that could be.

2. Our Universe may have begun with an inflationary period where all the dimensions grew at rates far beyond the speed of light.  Why didn’t this 4th dimension inflate as well? What is keeping it the size that it is? Can its size be changed? (the other dimensions changed size, and still are).  If Randall/Sundrum are correct then any change in size of this 4th dimension will change the local gravitational force.  Is there something about the specific frequencies and shape of the EM drive frustum that allow some very small amount of energy to enter this 4th dimension? Can this energy change the length of the dimension and thus the strength of gravity? What would be the magnitude of the change in gravity if the dimension increased by 10%, or doubled?  Dr. White is using an interferometer to measure changes in the shape of space-time within the frustum by aiming a laser through a window on each side. While the results are super borderline above noise it might show a blue shifting of the laser which would indicate a lower gravitational force - a red shift would indicate a larger gravitational force.  If the 4th dimension were to increase in length gravity would be weaker, space would not be as curved, and there would be a blue shift in the laser.

One might argue that we should have seen the affects of this before now.  Maybe we have, but the affects are so small, that they have gone unnoticed, or we have assigned them a ‘constant’ - just like we have recently done with the cosmological constant - just to make the equations produce the right results.
« Last Edit: 05/29/2015 06:34 PM by phaseshift »
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Offline frobnicat

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"Macroscopic and Direct Light Propulsion of Bulk Graphene Material"
http://arxiv.org/ftp/arxiv/papers/1505/1505.04254.pdf
My question here is what do the CoM (conservation of mass) and CoE (conservation of energy) people think about this force on the graphene?  Obviously it is much larger than that of just light.  Do we still have a violation here?  What is interesting is it is being observed in matter.  Whats to stop them from using a mirror behind a ship and reflecting the laser to propel the ship?  It might not be the right thing to do but  we could even shove a graphene sponge in the narrow end of the cavity and let that magnetron go.  Well I diverge but my question is regarding the CoM and CoE argument.

I read this, nice research, nice find, still struggling to understand how the sample, when levitated, can neutralize the charge build-up that would occur though. There is no CoM or CoE argument against this find, this is no fundamentally different from a beamed ablative propulsion scheme. The injected energy is used to expel particles of mass>0, therefore it is to be expected that the thrust/power ratio is
1/ Bigger than that of a photon rocket if power counts only the imparted energy
2/ Lower than that of a photon rocket if power counts imparted energy + mass equivalent energy of expelled particles

This is not propellantless, the floated device loses mass. The exotic aspect is that the expelled mass is electrons, but this is sooner or later (rather sooner) to be paid back as the devices builds up charge and it gets more and more difficult to release electrons against this growing voltage. For continuous operation it has to be replenished in electrons. Recycling the ejected electrons would cancel any net thrust, like a traditional rocket that would try to swallow back its exhaust. So this needs a source of "free" electrons, if possible harvested at low velocity relative to system. This is not unlike a jet engine that needs to swallow ambient mass and uses power to accelerate it and expel it faster backward, everything is ok as far as CoM and CoE is concerned, that can't be used as an apparent free energy generator, unlike an EM drive thrusting continuously (constant thrust for constant power) at constant velocity (no acceleration) above a certain velocity.

Offline Rodal

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Returning to Randall/Sundrum for a moment. It’s been pointed out over and over again that the EMDrive, as it is proposed to operate, violates CoM - no disagreement there.  ...
Sorry, but to clarify, there are lots of explanations for the EM Drive and I don't know of any author that has proposed EM Drive thrust while simultaneously claiming violation of Conservation of Momentum.  These are a few explanations that come to mind:

Shawyer
Prof. Yang
Dr. White QVF MHD model
Paul March QVF and Woodward Mach Effect "two sides of the same coin"
Dr. White and March 5-Dimensional Brane near our Universe
Notsosureofit
Dr. McCulloch
Todd "WarpTech"
van Tiggelen "magneto chiral" interaction

and so on and on

All of these authors claim that momentum is conserved, by different means.

I am not aware of any author claiming that the EM Drive has thrust and that it violates conservation of momentum.  All of the theories can and have been criticized as non-viable, for different reasons (other than conservation of momentum).  For example, you can criticize Dr. White's theory on the basis that you may state that the Quantum Vacuum is frame-less, immutable and non-degradable.  You can criticize Dr. McCulloch's theory because of his assumption that photons accelerate in an EM Drive to the point of producing Unruh radiation. And you may criticize Shawyer's arguments on the basis that he assumes a discontinuous pair of waveguides instead of a cavity, and that his thrust-reaction free body diagram leads to one waveguide having negative mass and performing negative virtual work. You can criticize van Tiggelen's magneto chiral interaction with the QV as being way too small to justify the EM Drive thrust claims.   But one cannot criticize them by saying (as Sean Carroll appears to do in his latest blog) that they didn't consider conservation of momentum, which they all did.
« Last Edit: 05/29/2015 05:36 PM by Rodal »

Offline WarpTech

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When you state:  <<Optimize their integral force equation for the correct representation for D, E and B, H, i.e., NOT standing waves>>

are you proposing to only consider the evanescent wave terms and to ignore the standing wave terms in the analysis? (since the standing wave terms perfectly cancel out when averaged over an integer number of time periods)

Or do you see any interaction/coupling between the standing wave terms and the evanescent wave terms so that both have to be considered in the analysis?
....


The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Minor point, but the standing waves lose energy to the electrons in the copper, which in turn, radiate at SHORTER wavelengths.  IR has shorter wavelengths than microwave.

True for the IR, but scattering of microwave photons by the metal will down-grade them to lower energy, longer wavelengths, which can then be attenuated.

Offline WarpTech

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The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Todd, although I understood the general lines of the mechanism you're describing, I'm a bit confused about the frequency shifting.
Initially you said that the shape of the cavity was the reason for the attenuation of the waves, where now you seem to put the wavelength shift to thermal causes?

Furthermore, doesn't the heat have a negative impact on the Q ? with a higher Q, you can store more energy in the standing waves, but more energy means more heat... At some point they must equalize eachother, no?

That would also mean that Shawyer's projections of having Q's running into the millions will probably never materialize?
Unless there are other ways to achieve attenuation without the thermo effects?

I believe that if the frustum were perfectly conductive, with no thermal losses at all, there would be no thrust. The reason being, the lowest frequency injected is still above the cut-off of the small end. So the attenuation would be minimal, but when there is thermal dissipation there is scattering of the microwaves that cause them to lose energy and shift to lower frequency and stretch to longer wavelengths that are strongly attenuated toward the front.  Higher Q means more available energy in this bandwidth of evanescent waves.

As I said, I am learning. I don't have all the answers and I tend to think out-loud. These discussions help me a lot but please take them with a grain of salt, until I publish a paper! :)

Thanks!

Offline aero

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Would be nice if Aero could modify his model to include copper loss in the waveguide. I'm still looking at old thread 2 posts. It would also be nice if Aero could post his .ctl file. Thanks.

My existing control files, written is Scheme, are not well diciplined or focused. With multiple options built in and Scheme's prohibition  against reusing variable names, the code is pretty bad. I use variable names that were meaningful to me at the time I coded them but on revisiting earlier control files I have a hard time figuring out what I intended by particular variables. So I don't think my existing control files would be useful except as something for a serious programmer to laugh at.

Maybe I could make and post a single purpose control file using constants with no options. Then a user could program the constants into variables choosing names as he/she saw fit, and add options at will.
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Offline phaseshift

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Returning to Randall/Sundrum for a moment. It’s been pointed out over and over again that the EMDrive, as it is proposed to operate, violates CoM - no disagreement there.  ...
Sorry, but to clarify, yes there is disagreement.  There are lots of explanations for the EM Drive and I don't know of any author that has proposed EM Drive thrust while simultaneously claiming violation of Conservation of Momentum. 

I'll change what I wrote above - I meant "no disagreement by me" :)
« Last Edit: 05/29/2015 05:35 PM by phaseshift »
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Offline Rodal

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The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Todd, although I understood the general lines of the mechanism you're describing, I'm a bit confused about the frequency shifting.
Initially you said that the shape of the cavity was the reason for the attenuation of the waves, where now you seem to put the wavelength shift to thermal causes?

Furthermore, doesn't the heat have a negative impact on the Q ? with a higher Q, you can store more energy in the standing waves, but more energy means more heat... At some point they must equalize eachother, no?

That would also mean that Shawyer's projections of having Q's running into the millions will probably never materialize?
Unless there are other ways to achieve attenuation without the thermo effects?

I believe that if the frustum were perfectly conductive, with no thermal losses at all, there would be no thrust. The reason being, the lowest frequency injected is still above the cut-off of the small end. So the attenuation would be minimal, but when there is thermal dissipation there is scattering of the microwaves that cause them to lose energy and shift to lower frequency and stretch to longer wavelengths that are strongly attenuated toward the front.  Higher Q means more available energy in this bandwidth of evanescent waves.

As I said, I am learning. I don't have all the answers and I tend to think out-loud. These discussions help me a lot but please take them with a grain of salt, until I publish a paper! :)

Thanks!

But now you appear to not be considering the paper by Zeng and Fan.  Please recall that Zeng and Fan derive attenuation (and phase) coefficients that are not due to resistive losses or dielectric losses leading to heating.

No, instead they derive attenuation (and phase) coefficients purely due to the geometrical shape;

alpha + j beta = - (1/E) dE/dr

where "d" is the partial derivative, and E represents the Electric field in the TE or TM modes.

They express this attenuation as Hankel functions purely due to geometry, attenuation due to evanescent waves, due to the change in the Electric field in the longitudinal direction.

The attenuation considered by Zeng and Fan is due to modes reaching cut-off in the truncated cone as one approaches the small end of the truncated cone.  As this happens, it appears that there could be an exchange from standing waves to evanescent waves.

Conical waveguides with a small cone angle and low value of longitudinal wavenumber kr appear to have the most attenuation, according to Zeng and Fan.
« Last Edit: 05/29/2015 08:47 PM by Rodal »

Offline dustinthewind

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"Macroscopic and Direct Light Propulsion of Bulk Graphene Material"
http://arxiv.org/ftp/arxiv/papers/1505/1505.04254.pdf
My question here is what do the CoM (conservation of mass) and CoE (conservation of energy) people think about this force on the graphene?  Obviously it is much larger than that of just light.  Do we still have a violation here?  What is interesting is it is being observed in matter.  Whats to stop them from using a mirror behind a ship and reflecting the laser to propel the ship?  It might not be the right thing to do but  we could even shove a graphene sponge in the narrow end of the cavity and let that magnetron go.  Well I diverge but my question is regarding the CoM and CoE argument.

I read this, nice research, nice find, still struggling to understand how the sample, when levitated, can neutralize the charge build-up that would occur though. There is no CoM or CoE argument against this find, this is no fundamentally different from a beamed ablative propulsion scheme. The injected energy is used to expel particles of mass>0, therefore it is to be expected that the thrust/power ratio is
1/ Bigger than that of a photon rocket if power counts only the imparted energy
2/ Lower than that of a photon rocket if power counts imparted energy + mass equivalent energy of expelled particles

This is not propellantless, the floated device loses mass. The exotic aspect is that the expelled mass is electrons, but this is sooner or later (rather sooner) to be paid back as the devices builds up charge and it gets more and more difficult to release electrons against this growing voltage. For continuous operation it has to be replenished in electrons. Recycling the ejected electrons would cancel any net thrust, like a traditional rocket that would try to swallow back its exhaust. So this needs a source of "free" electrons, if possible harvested at low velocity relative to system. This is not unlike a jet engine that needs to swallow ambient mass and uses power to accelerate it and expel it faster backward, everything is ok as far as CoM and CoE is concerned, that can't be used as an apparent free energy generator, unlike an EM drive thrusting continuously (constant thrust for constant power) at constant velocity (no acceleration) above a certain velocity.

I am embarrassed as I meant to type CoM for conservation of momentum and not mass.  Also the way I understood it, there is no loss of electrons.  You kick off an electron and the graphene sponge immediately becomes charged and is immediately attracted to the electron.  I didn't see anything about supplying current to the graphene in the vacuum tube.  This attraction of the electron to the graphene should give more force than just the light striking a surface.  I saw some arguments earlier way back that suggested if we got over a certain force per power input that maybe we would have a perpetual motion device on our hands.  The idea is taking a really light ship with a laser and mounting it pointing in the direction of the ship such that the light strikes in the direction the ship wants to go.  photons coming out of the laser don't provide much force but the light striking the gaphene provide more force than simply light so we have again propellantless propulsion but with force much greater than that of photons. 

Offline MyronQG

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Returning to Randall/Sundrum for a moment. It’s been pointed out over and over again that the EMDrive, as it is proposed to operate, violates CoM - no disagreement by me there.  IF it does actually produce thrust then the answer must be 'outside the box’  (pun intended). In the interview video, that was posted several days ago with Randall and Sundrum, Sundrum briefly talks about how CoM can be violated (in appearance).  Their theory, which has nothing to do with the EM drive, says that there is another 3 dimensional space called the Planck brane, sometimes it’s called the Gravity brane, or Strong brane, exists in parallel to our 3-space brane (the Tev brane) and they are joined by a finite dimension that is very short. The distance between the Gravity brane and our Tev brane is the reason that gravity is such a comparatively weak force. Sundrum says in the interview that energy, and mass, could move into this dimension (or possibly other dimensions), where we can not directly measure it and thus energy/momentum seems to disappear. By-the-way the Randall-Sundrum Model is the first theory to come from string theory that is testable and will be tested at CERN this summer (2015); it's being taken very seriously. 

IF they are right - what does the energy/mass do when it moves into this finite dimension? Remember at the end of this dimension is the Planck brane.  The dimension is very much like a cavity.  Two things come to my mind:

1. Is it possible that the ‘thrust’ is pushing off the internals of this dimension?  Sound familiar? I think this is close to what Dr. White is suggesting - though he says ‘Quantum Vacuum’. By internals I mean whatever resides in the dimension - who knows what that could be.

2. Our Universe may have begun with an inflationary period where all the dimensions grew at rates far beyond the speed of light.  Why didn’t this 4th dimension inflate as well? What is keeping it the size that it is? Can its size be changed? (the other dimensions changed size, and still are).  If Randall/Sundrum are correct than any change in size of this 4th dimension will change the local gravitational force.  Is there something about the specific frequencies and shape of the EM drive frustum that allow some very small amount of energy to enter this 4th dimension? Can this energy change the size of the dimension and thus the strength of gravity? What would be the magnitude of the change in gravity if the dimension increased by 10%, or doubled?  Dr. White is using an interferometer to measure changes in the shape of space-time within the frustum by aiming a laser through a window on each side. While the results are super borderline above noise it might show a blue shifting of the laser which would indicate a lower gravitational force - a red shift would indicate a larger gravitational force.  If the 4th dimension were to increase in length gravity would be weaker, space would not be as curved, and there would be a blue shift in the laser.

One might argue that we should have seen the affects of this before now.  Maybe we have, but the affects are so small, that they have gone unnoticed, or we have assigned them a ‘constant’ - just like we have recently done with the cosmological constant - just to make the equations produce the right results.

Agreed. If the EMDrive does work, it violates CoM in our 4D-spacetime but not necessarily in a hypothetical {branes + bulk} 5D-spacetime.

Offline Rodal

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Agreed. If the EMDrive does work, it violates CoM in our 4D-spacetime but not necessarily in a hypothetical {branes + bulk} 5D-spacetime.
That's also Dr. White's and Paul March's 5D brane conjecture.

Offline X_RaY

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When you state:  <<Optimize their integral force equation for the correct representation for D, E and B, H, i.e., NOT standing waves>>

are you proposing to only consider the evanescent wave terms and to ignore the standing wave terms in the analysis? (since the standing wave terms perfectly cancel out when averaged over an integer number of time periods)

Or do you see any interaction/coupling between the standing wave terms and the evanescent wave terms so that both have to be considered in the analysis?
....


The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Minor point, but the standing waves lose energy to the electrons in the copper, which in turn, radiate at SHORTER wavelengths.  IR has shorter wavelengths than microwave.

Hello, if you dońt want to use standing waves/resonance inside the cavity you have to use a other shape/length of the cone or a pump frequency  far away from some eigenresonance value. ???
If you do something like that the   Zin=~l1l and the Q goes to zero means the energy would be reflected! If you try to tune this situation away with a waveguide-tuner or somthing else you create a other circuit with effektive LCR(cavity)+LCR(tuner) which is in resonance.
Or may be i missed some aspekt in my mind what is usefull to generate some trust with a cavity out of resonance?

Offline Notsosureofit

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When you state:  <<Optimize their integral force equation for the correct representation for D, E and B, H, i.e., NOT standing waves>>

are you proposing to only consider the evanescent wave terms and to ignore the standing wave terms in the analysis? (since the standing wave terms perfectly cancel out when averaged over an integer number of time periods)

Or do you see any interaction/coupling between the standing wave terms and the evanescent wave terms so that both have to be considered in the analysis?
....


The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Minor point, but the standing waves lose energy to the electrons in the copper, which in turn, radiate at SHORTER wavelengths.  IR has shorter wavelengths than microwave.

True for the IR, but scattering of microwave photons by the metal will down-grade them to lower energy, longer wavelengths, which can then be attenuated.

Mmmm, as an old (very old) radar guy, I can think of no instance where a metal like copper will do that.  You need at least a non-linear material on the surface.  Didn't we discuss this in Thread 1 ?

Offline aero

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"Macroscopic and Direct Light Propulsion of Bulk Graphene Material"
http://arxiv.org/ftp/arxiv/papers/1505/1505.04254.pdf

As I understood it, there is no directionality of the electron emission, rather it is omnidirectional with the metal container neutralizing the electrons which are emitted in the undesired directions. Therefore, the stimulating lasers can be carried onboard the ship as an integral part of the engine.

You would still have a charge buildup in free space but a grounded engine should work wonderfully well in a vacuum chamber or anywhere connected to an electrical ground.

I don't know how well it would work using a sacrificial metal such as magnesium to provide the electrons. That works well for corrosion protection on ships, plumbing, vehicles and other things prone to rusting.
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Offline rfmwguy

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I'm just gonna leave this here...

"Macroscopic and Direct Light Propulsion of Bulk Graphene Material"
http://arxiv.org/ftp/arxiv/papers/1505/1505.04254.pdf


Quote
The force generated from such a process/mechanism is much
larger than the force generated directly from the conventional light pressure, which is
much smaller than the force required to propel the samples.

Quote
The mechanism behind this novel phenomenon is believed to be an
efficient light-induced ejected electron emission process, following an Auger-like path
due to both the unique band structure of graphene and its macroscopic morphology of
this unique material.

This article is showing that for certain types of materials, light can impart more force to the material, than it would if it were simply used to as a photon rocket to push the same material. The difference is the Auger Effect, where the incoming light causes a population inversion in the material, that then causes electrons to be ejected from the material, greatly increasing the force by many orders of magnitude. Perhaps a similar effect can be obtained asymmetrically in a cavity?

Thank you for posting it!

Todd

My question here is what do the CoM (conservation of Edit:momentum) and CoE (conservation of energy) people think about this force on the graphene?  Obviously it is much larger than that of just light.  Do we still have a violation here?  What is interesting is it is being observed in matter.  Whats to stop them from using a mirror behind a ship and reflecting the laser to propel the ship?  It might not be the right thing to do but  we could even shove a graphene sponge in the narrow end of the cavity and let that magnetron go.  Well I diverge but my question is regarding the CoM and CoE argument.

Todd suggested it best, photons entering material, stimulating a high release of electrons. Photons "igniting the fuel" (graphene/carbon black) is how I interpreted it.

Offline WarpTech

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The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Todd, although I understood the general lines of the mechanism you're describing, I'm a bit confused about the frequency shifting.
Initially you said that the shape of the cavity was the reason for the attenuation of the waves, where now you seem to put the wavelength shift to thermal causes?

Furthermore, doesn't the heat have a negative impact on the Q ? with a higher Q, you can store more energy in the standing waves, but more energy means more heat... At some point they must equalize eachother, no?

That would also mean that Shawyer's projections of having Q's running into the millions will probably never materialize?
Unless there are other ways to achieve attenuation without the thermo effects?

I believe that if the frustum were perfectly conductive, with no thermal losses at all, there would be no thrust. The reason being, the lowest frequency injected is still above the cut-off of the small end. So the attenuation would be minimal, but when there is thermal dissipation there is scattering of the microwaves that cause them to lose energy and shift to lower frequency and stretch to longer wavelengths that are strongly attenuated toward the front.  Higher Q means more available energy in this bandwidth of evanescent waves.

As I said, I am learning. I don't have all the answers and I tend to think out-loud. These discussions help me a lot but please take them with a grain of salt, until I publish a paper! :)

Thanks!

But now you appear to not be considering the paper by Zeng and Fan.  Please recall that Zeng and Fan derive attenuation (and phase) coefficients that are not due to resistive losses or dielectric losses leading to heating.

No, instead they derive attenuation (and phase) coefficients purely due to the geometrical shape;

alpha + j beta = - (1/E) dE/dr

where "d" is the partial derivative, and E represents the Electric field in the TE or TM modes.

They express this attenuation as Hankel functions purely due to geometry, attenuation due to evanescent waves, due to the change in the Electric field in the longitudinal direction.

The attenuation considered by Zeng and Fan is due to modes reaching cut-off in the truncated cone as one approaches the small end of the truncated cone.  As this happens, it appears that there could be an exchange from standing waves to evanescent waves.

Obviously, in a cylinder dE/dr (where r is the spherical radial coordinate) is zero, so in a cylinder there is no geometrical attenuation.  However, truncated cones having a small cone angle appear to have the most attenuation.

What I'm saying is, standing waves are not evanescent waves. The standing waves in TE013 mode have frequency well above the cut-off of the cavity. I do not know precisely "how" standing waves can be shifted to a longer wavelength where they can become evanescent waves, without a mechanism for those waves to lose energy, i.e, dissipation before attenuation. I'll have to go re-read Zeng and Fan again, but their derivation is for waves propagating down a tapered waveguide, not standing waves in a cavity. I do not assume that the standing waves will be attenuated, based on what I remember of their results. I am assuming that dissipation will cause the standing wave to decay to longer wavelength, where attenuation can take place. Only the evanescent waves, not the standing waves can produce thrust.

How would you consider converting the standing waves to evanescent waves? What mechanism would you choose?

Todd




Offline aero

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The standing waves in the cavity are not perfectly planer, not perfectly parallel to the flat end plates. This is, in my opinion, due to the conic shape of the frustum body. The result is that as the waves propagate into the corners they see a waveguide that gets more and more narrow so that the edges of the standing waves become evanescent waves at the ends of the cavity, in the corners. The center of the standing wave reflects from the center of the ends so resonance is maintained.

Maybe this is visable on the image posted in the last couple of pages.
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Offline deltaMass

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Quote from: Rodal
Obviously, in a cylinder dE/dr (where r is the spherical radial coordinate) is zero
Not obvious to me I'm afraid.

Offline Rodal

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How would you consider converting the standing waves to evanescent waves? What mechanism would you choose?

Todd
Physically, the only way out of this I can see for a cavity is to have losses:

1) Resistive losses

2) Dielectric losses
(not just due to the dielectric insert, but don't forget that it is not unusual to coat the interior of the EM Drive with a polymer coating to protect the copper, as was done by NASA Eagleworks).

Because, mathematically, to have a non-zero Poynting vector for a cavity either we must have:

A) sources or sinks.  We have  a source, which is the RF feed going into the cavity (for example from a magnetron), as long as it is pumping photons into the cavity.  We also have a sink:  resistive and dielectric losses.  So, this will result in a non-zero Poynting vector field, and it will be a first order effect.

or

B) a nonlinearity, such that the time variation is no longer simple harmonic but an even function of a harmonic (obviously the square of a harmonic has non-zero time average).  I don't like this explanation because it is a second order effect and therefore must lead to very small thrust effects.

__________________

Regarding Zeng and Fan, please notice that

There are 3 variables governing the spherical cone: the spherical radius r, the cone angle theta and the azimuthal angle phi. 



Phi is not a variable for a given m, so Zeng and Fan show charts of the attenuation as a function of kr and the cone angle for different modes.

Please observe that although in the text they place (undue) emphasis on the cone angle, it is only for small values of kr that the attenuation is large.  The attenuation goes to zero for large kr regardless of the cone angle.

So kr is equally (or more important) than the cone angle.

We want small kr (the wavenumber in the longitudinal direction), and small cone angle.

Take a gander at their figures 2 for different modes.

Take a look at what kr is at the bottom of the 3rd page, under Eqn 3.

Small kr means small "p".

For fixed small diameter, the bigger r2, the longer the cavity length, the bigger "p", hence the bigger kr.

The highest attenuation by far is reached for small kr, in other words, this means high attenuation for Lower modes are much better than high modes.  TE011 much better than TE013, because the higher the mode, the higher the kr.  This is the complete contrary of what TheTraveller is planning to do with the Flight Thruster.
« Last Edit: 05/29/2015 08:45 PM by Rodal »

Offline X_RaY

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The interaction is, as the standing waves dissipate heat in the copper, they lose energy and shift to longer wavelengths, where attenuation takes over from dissipation and imparts momentum to the copper, not heat. The standing waves provide the stored energy, but the evanescent waves do the work.

Todd, although I understood the general lines of the mechanism you're describing, I'm a bit confused about the frequency shifting.
Initially you said that the shape of the cavity was the reason for the attenuation of the waves, where now you seem to put the wavelength shift to thermal causes?

Furthermore, doesn't the heat have a negative impact on the Q ? with a higher Q, you can store more energy in the standing waves, but more energy means more heat... At some point they must equalize eachother, no?

That would also mean that Shawyer's projections of having Q's running into the millions will probably never materialize?
Unless there are other ways to achieve attenuation without the thermo effects?

I believe that if the frustum were perfectly conductive, with no thermal losses at all, there would be no thrust. The reason being, the lowest frequency injected is still above the cut-off of the small end. So the attenuation would be minimal, but when there is thermal dissipation there is scattering of the microwaves that cause them to lose energy and shift to lower frequency and stretch to longer wavelengths that are strongly attenuated toward the front.  Higher Q means more available energy in this bandwidth of evanescent waves.

As I said, I am learning. I don't have all the answers and I tend to think out-loud. These discussions help me a lot but please take them with a grain of salt, until I publish a paper! :)

Thanks!

But now you appear to not be considering the paper by Zeng and Fan.  Please recall that Zeng and Fan derive attenuation (and phase) coefficients that are not due to resistive losses or dielectric losses leading to heating.

No, instead they derive attenuation (and phase) coefficients purely due to the geometrical shape;

alpha + j beta = - (1/E) dE/dr

where "d" is the partial derivative, and E represents the Electric field in the TE or TM modes.

They express this attenuation as Hankel functions purely due to geometry, attenuation due to evanescent waves, due to the change in the Electric field in the longitudinal direction.

The attenuation considered by Zeng and Fan is due to modes reaching cut-off in the truncated cone as one approaches the small end of the truncated cone.  As this happens, it appears that there could be an exchange from standing waves to evanescent waves.

Obviously, in a cylinder dE/dr (where r is the spherical radial coordinate) is zero, so in a cylinder there is no geometrical attenuation.  However, truncated cones having a small cone angle appear to have the most attenuation.

What I'm saying is, standing waves are not evanescent waves. The standing waves in TE013 mode have frequency well above the cut-off of the cavity. I do not know precisely "how" standing waves can be shifted to a longer wavelength where they can become evanescent waves, without a mechanism for those waves to lose energy, i.e, dissipation before attenuation. I'll have to go re-read Zeng and Fan again, but their derivation is for waves propagating down a tapered waveguide, not standing waves in a cavity. I do not assume that the standing waves will be attenuated, based on what I remember of their results. I am assuming that dissipation will cause the standing wave to decay to longer wavelength, where attenuation can take place. Only the evanescent waves, not the standing waves can produce thrust.

How would you consider converting the standing waves to evanescents? What mechanism would you choose?

Todd


In this picture the TEM-waves/photons are red shifted cause of the loss factor of the cavity, lower energy leads to bigger wavelength --> larger bandwidth and therefore lower Q - what is well known.  If a given evanescent wave reaches cutoff frequency at the smaller diameter but not at the bigger the boundary conditions to resonate are not given.  What happens to the energy of these photons/field?? Would the energy of the field lose by thermal heating or trust producing ?

Is the latter option what you think is the right?
« Last Edit: 05/29/2015 07:20 PM by X_RaY »

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