Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1803700 times)

Offline Mulletron

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I support "Resonant Cavity Thruster" as well.

Challenge your preconceptions, or they will challenge you. - Velik

Offline deltaMass

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"Resonant" is a bit odd. On the one hand, all cavities are resonant in principle, rendering the name tautologous. On the other hand, some people may feel that running off resonance has advantages of some sort.

Unfortunately, "Cavity Drive" makes one think of an urgent trip to the dentist.  ???

I'd vote for Propellantless Microwave Drive (PMD).
« Last Edit: 07/22/2015 06:15 PM by deltaMass »

Offline rfmwguy

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"Resonant" is a bit odd. On the one hand, all cavities are resonant in principle. On the other hand, some people may feel that running off resonance has advantages of some sort.

Unfortunately, "Cavity Drive" makes one think of an urgent trip to the dentist.  ???
Electromagnetic Thruster is Cannae's patent, QV Thruster is White, EM Drive is SPR...Electromagnetic Drive or Reactor seems safe, perhaps a little better than Thruster since we're not 100% sure its pushing rather than pulling.

Offline Mulletron

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Phonons or photons. From sound to X-rays and beyond....the frequency band is not the most fundamental thing here. Why should we be hamstrung to microwaves only, when optics and sound are equally mature and fertile.

The issue is...whether or not a cavity resonator (be it a pillbox or the frustum of a cone or some other configuration) can be useful as a propulsion device; and if so can it be useful for spaceflight.
« Last Edit: 07/22/2015 06:34 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

Online Rodal

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Propellantless Electromagnetic Drive ?

Seems to satisfy all the above constraints...

Offline mwvp

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Something very interesting and important occurs as the cutoff is closely approached. The group velocity decrease exponentially.

Cut-off is a concept that ... does not apply to tapered waveguides, as it has been remarked and shown in several peer-reviewed papers I have pointed out in the paper I wrote about cut-off frequencies of the truncated cone used for the EM Drive (which I attach below).
...
One can safely reduce the small diameters of the EM Drives used by Shawyer, NASA and Yang to only 20% of its tested value without reaching cut-off per se.  Now, whether it is better or worse to have such a longer cone remains to be explored

Thank you very much. Looks like its got some very useful stuff. I just glanced through it, I'll look at it in detail later. What I'd like to see, in some other similar papers also, is the effect on Q as the cavity length is extended and dia. reduced beyond the arbitrary, non-applicable "cutoff".

I was reading that it was better to terminate a cavity; leaving an open is not so much radiation loss but reactance, or evanescence that will cause losses, Q reduction.

So in addition to having field data on cavity, Q and complex impedance vs. frequency would be interesting also. In my thinking frustrum motion causes Doppler sidebands to occur in stale cavity energy, and these sideband will be dispersed, and I think the region around and the geometry of the frustrum at the short end will be significant. If not in frequency-selective attenuation of reflections due to dissipation, than by phase-shifting the E & H fields and changing the power factor.

Something else to consider, along the lines of dielectric/waveguide-defect ghost modes:

Attenuation in Rectangular Waveguides with Finite Conductivity Walls
Kim Ho YEAP1, Choy Yoong THAM 2, Ghassan YASSIN 3, Kee Choon YEONG4

"We have examined the validity of our model by carrying
out measurements on the loss arising from the fundamental
TE10 mode near the cutoff frequency. We also found good
agreement...our method gives higher losses, which we
attribute to the coupling between modes as a result of
dispersion.
...
ment with the PPM and experimental results for the case of
the dominant TE10 mode. An important consequence of this
work is the demonstration that the loss computed for de-
generate modes propagating simultaneously is not simply
additive. In other words, the combined loss of two co-ex-
isting modes is higher than adding the losses of two modes
propagating independently. This can be explained by the
mode coupling effects, which is significant when the phase
constants of two propagating modes are different yet very
close."

Offline mwvp

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Propellantless Electromagnetic Drive ?

Seems to satisfy all the above constraints...

+1. Otherwise "dispersive" should qualify cavity.

Online Rodal

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Something very interesting and important occurs as the cutoff is closely approached. The group velocity decrease exponentially.

Cut-off is a concept that ... does not apply to tapered waveguides, as it has been remarked and shown in several peer-reviewed papers I have pointed out in the paper I wrote about cut-off frequencies of the truncated cone used for the EM Drive (which I attach below).
...
One can safely reduce the small diameters of the EM Drives used by Shawyer, NASA and Yang to only 20% of its tested value without reaching cut-off per se.  Now, whether it is better or worse to have such a longer cone remains to be explored

Thank you very much. Looks like its got some very useful stuff. I just glanced through it, I'll look at it in detail later. What I'd like to see, in some other similar papers also, is the effect on Q as the cavity length is extended and dia. reduced beyond the arbitrary, non-applicable "cutoff"....
Excellent idea.

I will compute the effect on theoretical Q and report back when I have a chance.  Basically I will assume the same skin depth formula applies all over the cavity, calculated the standard way, and the effect on Q should emerge from the ratio of the volume integral of the squared magnitude of the magnetic field to its surface integral. (The ratio of the average electromagnetic energy density to the average dissipated power in the wall -times 2 divided by the skin depth-).
« Last Edit: 07/22/2015 07:19 PM by Rodal »

Offline flux_capacitor

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"Resonant" is a bit odd. On the one hand, all cavities are resonant in principle, rendering the name tautologous.
There is an entry on Wikipedia as cavity resonator within the article about resonators, and there is a dedicated article microwave cavity (/RF cavity).
Unfortunately, "Cavity Drive" makes one think of an urgent trip to the dentist.  ???
You made my day with this one :D

Propellantless Electromagnetic Drive ?

Seems to satisfy all the above constraints...

I don't think it fits. "Propellantless Electromagnetic Drive" seems way too vague. This term is so general that it could apply to any propellantless propulsion based on electromagnetic fields: Woodward's Mach-Lorentz Thruster (MLT) and Mach-Effect Thruster (MET), White's Q-Thruster, Serrano's Field Propulsion Thruster, Podkletnov's Gravity-Impulse Generator… and the other fringe stuff like Searl's disks, EM ash can covers, toilet seats and whatnot.

We're dealing with microwave cavities here. So I would largely prefer the more specific resonant cavity thruster, dropping RF and microwave since cavities could maybe operate at different frequencies.

Otherwise "dispersive" should qualify cavity.
Very precise for scientists, but I'm afraid it would be incomprehensible for the layman.
« Last Edit: 07/22/2015 07:35 PM by flux_capacitor »

Offline deltaMass

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The Frustumator?

Offline deltaMass

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It seems to me that a key characteristic is the asymmetry. This is not a feature of any other drive of which I'm aware, save Cannae.

Offline leomillert

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Asymmetric dispersive drive (ADD)?

Offline deltaMass

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Asymmetric Cavity Thruster (ACT)

(Cannae's is only asymmetric on the inside)
« Last Edit: 07/22/2015 07:54 PM by deltaMass »

Offline DrBagelBites

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Perhaps a poll would be in order?

Offline leomillert

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To all those proposing to use Thruster in the name, I reiterate what rfmwguy said:

Electromagnetic Drive or Reactor seems safe, perhaps a little better than Thruster since we're not 100% sure its pushing rather than pulling.

Offline SeeShells

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Propellantless Mass System?

Offline Hauerg

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ACD
Asymmetric Cavity Drive


Offline rfmwguy

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DIYer head's up. Copper flashing seems to be a cost-effect solution for frustum walls if you are not using mesh. As I was looking around for supplies, found this: http://www.acehardware.com/product/index.jsp?productId=1290779&KPID=984489&kpid=984489&pla=pla_984489

A 10ft roll seems to be the smallest length. I'd recommend the 14 inch for frustum heights to 11 inches. I can say from experience that .021 thickness will not be self-supporting and an exoskeleton will be needed. When I switched to a magnetron, the 1/8 in square copper supports were not ideal. I'd move to 1/4 in copper struts or possibly tubing.

Top and bottom plates on nsf-1701 were 1/2 oz copper clad pc board, again too flimsy for a 750g magnetron. Try the next size up. Solid copper plates would weigh too much, I stick with the pcb stuff, just make sure there are plated thru-holes or plenty of bolts to connect the 2 ground planes.

Any metal above ground potential will be subject to plasma discharge, so "mind the gaps" ;)

p.s. Bonus points for anyone who knows that phrase...

Offline SeeShells

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Something very interesting and important occurs as the cutoff is closely approached. The group velocity decrease exponentially.

Cut-off is a concept that ... does not apply to tapered waveguides, as it has been remarked and shown in several peer-reviewed papers I have pointed out in the paper I wrote about cut-off frequencies of the truncated cone used for the EM Drive (which I attach below).


Something else to consider, along the lines of dielectric/waveguide-defect ghost modes:

Attenuation in Rectangular Waveguides with Finite Conductivity Walls
Kim Ho YEAP1, Choy Yoong THAM 2, Ghassan YASSIN 3, Kee Choon YEONG4

ment with the PPM and experimental results for the case of
the dominant TE10 mode. An important consequence of this
work is the demonstration that the loss computed for de-
generate modes propagating simultaneously is not simply
additive. In other words, the combined loss of two co-ex-
isting modes is higher than adding the losses of two modes
propagating independently. This can be explained by the
mode coupling effects, which is significant when the phase
constants of two propagating modes are different yet very
close."


This so rings a bell, I was just mentioning this to someone today. I couldn't agree more.
 
snip...
"Well anyway I want to squeeze the traveling resonate modes down into the small end of the cavity as far as I can exciting ghost modes and evanescent waves because  maxwell equations dealing with normal waveform degradation is quite set in how it works, but maxwell stumbles in evanescent and ghost mode calculations (not so much ghost but it becomes very hard to calculate interactions) and they both have extraordinary pumped up Q energy of spin and momentum within them.

Had my second cuppa and toast and off to the shop...again."
end snip.

Funny how things work out isn't it?

Shell



Offline X_RaY

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ACD
Asymmetric Cavity Drive

This debate is actually not really helpful.  :-\ The one who explains the physics correctly will give it a name in his paper, or do it democratically, but let's go back to science right now ::)

This for example:
ghost modes in imperfect waveguides
http://bayes.wustl.edu/etj/articles/ghost.modes.pdf
« Last Edit: 07/22/2015 08:32 PM by X_RaY »

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