Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1879758 times)

Offline mwvp

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You've provoked me to attempt to clarify and express my own vague notions. Apologies.

There is a fundamental difference between light bouncing around in an  emdrive and the astronaut in the space station.

Agreed...

Light does not obey conservation of momentum under specific conditions.

It is, however counter-intuitively

This has been practically demonstrated:
Optical diametric drive acceleration through action–reaction symmetry breaking
http://www.nature.com/nphys/journal/v9/n12/full/nphys2777.html

That involves nonlinear materials; waveguides, in our power-regime and consistent with Maxwell are linear

Take a look at the equation for radiation pressure.

F=hf/c
...
If that equation holds true, F=hf/c, then slowing light down INCREASES the force of radiation pressure.  That is completely non-intuitive for me.  It makes no sense whatsoever.  Slower should be less force, right?

If you consider Force is the consequence of change in momentum, momentum the product of mass and velocity, and those depend on the characteristics of the propagation medium.

Power=1/2 Capacitance x Voltage^2, and P=1/2 Inductance x Current^2. And V=1/C LC^.5. In a waveguide, you have the causal E and H fields, and the resultant D and B flux densities, and Vg. Its obvious to me, that physical materials with dipole densities are capable of becoming polarized and storing far more energy than free space, and they will have the same palpable forces one feels with magnets or piezoelectric crystals, much greater than free space and have much greater propagation delays. In the case of the hollow metallic waveguide, the geometry determines the inductance and capacitance. That's all intuitive to me, when I follow the energy as a first principle and consider propagation velocity as a consequence.

Key: Radiation pressure varies inversely with the speed of light.

I'm still perplexed by this, and I wish to know more.

Well, there again, I'm thinking energy density, and first-principles: Epsilon-r and Mu-r of the medium, and that wave propagation velocity as a consequence and not a cause.


What's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.

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


This explains the tapered waveguide emdrive.  At the big end the radiation pressure is close to hf/c0.  At the little end, the light is much slower, approaching zero, so the radiation pressure is radically larger.  The imbalance in forces makes the ship go.

Ieeeee...think not.

Putting these together gives you the guts of Mr. Shawyer's emdrive theory, ignoring the bits around general relativity.

What!?!? Why, that's where the strangeness, beauty and magic happen!

  The net force is the large radiation pressure from the slow moving light in the near-cutoff or dielectric little end minus the small radiation pressure from the free space propagating big end

Net force? Really? I considered that initially too. A very crude analogy is to consider a photon-gas in a balloon. A plasma balloon would want to be a Spheromak, but consider a soap bubble. Its round; minimum energy configuration. How to make it a cone? Lets say its a viscous, UV curing polymer bubble and you hit an annular ring at top with some UV to thicken it, blow more air in. Now its a conical bubble. What is the gas pressure gradient? Is it moving? No (helium notwithstanding). However, the narrow top skin that was UV-hardened is now under higher tension to hold the shape, more than the naturally relaxed round bottom. The gas pressure is homogeneous, but not the skin tension.

Somewhat similarly in the frustrum waveguide, The TM013 shows stronger fields near the apex than the bottom. EM energy in free space tries to relax homogeneously, but impinges on the frustrum, induces currents and force, is reflected and concentrated or dispersed according to the geometry. The tensioned frustrum creates the inhomogeneous environment, and the EM energy relaxes to an inhomogeneous equilibrium standing wave.

I know the waveguide geometry defines the inductance and capacitance, and tend to think that the E and H fields would be homogeneous but the D and B flux densities are concentrated according to the frustrum geometry and consequent complex impedance, but I'm not certain.

What I'm sure of is uniform energy relaxation in the structure (CoE) at equilibrium.

...
What am I missing?

Several things;

If it works, this is how I think it will:

The vacuum and the speed of light are special, counter-intuitive absolute inertial frames (relativity).
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1400486#msg1400486
http://arxiv.org/abs/0708.3519

The Sagnac effect; Doppler-induced AM modulation of the standing wave, superposition of sum & difference frequencies
https://en.wikipedia.org/wiki/Sagnac_effect

The frustrum as:
1. a rotor, and its enclosed free space with its absolute frames as a stator
2. a sideband filter, selectively attenuating and reinforcing the sum/difference Sagnac interference frequencies

In the static case, EM energy reaches a force balance equilibrium with the frustrum; no change in EM mode/momentum

In the frustrum-perturbed case, Doppler-shift induced Sagnac interference modulation of the standing waves results in AM modulation of the EM modes, a traveling wave of changing momentum, reacting against the frustrum to boost forward acceleration, and retard reverse acceleration.

Behavior is characterized as negative inertial impedance or ratcheting. Mechanical vibration is expected according to the mass of the device and the spring tension of a load cell.

It isn't an absolute velocimeter; The frustrum power coupling probe/loop supplies EM energy in the inertial frame of the frustrum, but due to the high-Q of the cavity, most energy is stale.

Alas, that I could do the math.

Or perhaps its just taken me a couple months to abandon common sense and delude myself with wishful-thinking;
https://en.wikipedia.org/wiki/Pathological_science#N-rays
« Last Edit: 07/22/2015 10:28 AM by mwvp »

Offline arc

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There is a fundamental difference between light bouncing around in an  emdrive and the astronaut in the space station.  It took me a while to grok this, but I think I can explain it now.

grok... been a while since i've heard that... good on you

Ok... Im thinking on this because you have tied in concepts that originated a while ago (years) and have bubbled to the surface through Warptech and Notsosureofit.  Somewhere in this the combinational factors of cavity-shape, E-field, B(H)-field, Q-concentrator(field_density_factor) elements work to invoke warptechs g_mimic and consequently/inherently a time dependent transitive localised distortion.

« Last Edit: 07/22/2015 09:52 PM by arc »

Offline deltaMass

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F=hf/c
Force = Planck length times frequency divided by the speed of light.
It's a bad idea to write down physics equations in which the units do not match on either side.
It's also a bad idea to misrepresent Planck's constant as "Planck length".
But the worst idea of all is to post such stuff on a public forum.
It guarantees that people will not take seriously anything you say about physics ever again.

Offline ElizabethGreene

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It's a bad idea to write down physics equations in which the units do not match on either side.  It's also a bad idea to misrepresent Planck's constant as "Planck length".
Fixed.  Again. 

Quote
But the worst idea of all is to post such stuff on a public forum.
It guarantees that people will not take seriously anything you say about physics ever again
I'll repeat it, in case I haven't been clear in disclaiming this already.  I should not be taken seriously.  I am seeking enlightenment, not providing it.

Offline SeeShells

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FWIW, I admire the meepers doing what I cannot do, burn through iterations and generate 3D models. I vote for both us builders, meepers and theoretical types keep doing what we are doing...trying to help in our own way.

p.s. NSF-1701 exoskeleton needed some strengthening today. Just got that completed. I'll post a pic in a minute.
That is the truth. Reminds me of my CFO who had her masters in business and was an EE too boot. We were working on a deadline project and all hands  on deck were called to make it so. She asked if she could help. Sure, I said, we need some holes drilled here in this aluminum. Handed her the drill and made sure she found the marks to simply drill some holes. I thought it was very nice of her to offer her help. Twenty minutes later I looked over and she was still drilling the same hole, red faced and sweating. I walked over and said please take a break. She said geez this aluminum is hard to drill I never thought it was so hard. Looking at the drill I said, you have it going the wrong way.

True story and it's the same here.

Shell

Offline Notsosureofit

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In the comparison of a Sagnac resonator to a frustum resonator, the "area" is spacial-temporal for the frustum, as opposed to spacial-spacial for the Sagnac.  A symmetric cavity corresponds to a zero-area Sagnac.  They are both subject to gravity-wave distortion.
« Last Edit: 07/22/2015 01:01 PM by Notsosureofit »

Offline deltaMass

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It's a bad idea to write down physics equations in which the units do not match on either side.  It's also a bad idea to misrepresent Planck's constant as "Planck length".
Fixed.  Again. 

Quote
But the worst idea of all is to post such stuff on a public forum.
It guarantees that people will not take seriously anything you say about physics ever again
I'll repeat it, in case I haven't been clear in disclaiming this already.  I should not be taken seriously.  I am seeking enlightenment, not providing it.
OK, now using Planck's constant. But do you also understand that the units are wrong, and that what you have written is like saying 2 apples = 3 pears?

Offline Rodal

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...

What's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.

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

...
Cut-off is a concept that applies to constant section waveguides.  It 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).

As shown by several authors, and latest by Zeng and Fan (often quoted by Todd "WarpTech") in a tapered waveguide all modes run continuously from a travelling wave region  through a transition to an evanescent wave region and the value of the attenuation increases as the cone vertex is approached.

I have also shown this in detail for the EM Drive for several geometries: there is no such thing as cut-off unless you approach a small end of zero dimensions (which is impractical).  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 (as the whole issue of whether the EM Drive force is real or an experimental artifact also remains to be proven).  But that the cut-off concept does not apply is well confirmed by now.  In a tapered waveguide modes do not get cut-off, instead the modes persist, with a larger diameter region where the wave is a travelling wave to a transition region to a region near the apex where the wave becomes evanescent.
« Last Edit: 07/22/2015 02:11 PM by Rodal »

Offline Ricvil

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upon reflection light undergoes a 180 degree phase change on metal surfaces

Yes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.
With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".
This is a example of superposition  principle to model boundary conditions.



Know anything about increased skin depth and attenuation with evanescent modes? I read somewhere bends in the waveguide cause increased RF penetration and loss, and evanescent modes came to mind. Googled around for it briefly but didn't find anything. That would help explain selective sideband attenuation, but the big end, rather than the small end (with the low cutoff) is what's been observed to get hot.

If the antenna is close of big base then I have a possible explanation.
The antenna is a pertubation on the shape of the cavity, and the tappered conical cavity has many modes very close each other at some frequencys. This is a scenario of a "ghost mode" rising.
In waveguides, a ghost mode is a localized resonance of very high Q which concentrates very high EM fields in a region of few lambdas. If the length of the cavity is greater than  the extension of the ghost mode region ( in the case near the big base), then the small base  will not feel the strong field of the ghost mode.
The magnetron can amplify the strenght of ghost mode too.
Then the big base is hot because the proximity of the ghost mode, and the small base not.

Offline Rodal

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upon reflection light undergoes a 180 degree phase change on metal surfaces

Yes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.
With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".
This is a example of superposition  principle to model boundary conditions.



Know anything about increased skin depth and attenuation with evanescent modes? I read somewhere bends in the waveguide cause increased RF penetration and loss, and evanescent modes came to mind. Googled around for it briefly but didn't find anything. That would help explain selective sideband attenuation, but the big end, rather than the small end (with the low cutoff) is what's been observed to get hot.

If the antenna is close of big base then I have a possible explanation.
The antenna is a pertubation on the shape of the cavity, and the tappered conical cavity has many modes very close each other at some frequencys. This is a scenario of a "ghost mode" rising.
In waveguides, a ghost mode is a localized resonance of very high Q which concentrates very high EM fields in a region of few lambdas. If the length of the cavity is greater than  the extension of the ghost mode region ( in the case near the big base), then the small base  will not feel the strong field of the ghost mode.
The magnetron can amplify the strenght of ghost mode too.
Then the big base is hot because the proximity of the ghost mode, and the small base not.

Very interesting observation.

Let's couple this observation with the fact that tapered waveguides (ref.: my previous post) do not have sharp cut-off frequencies, but that modes that would be sharply cut-off instead transition from a travelling wave region through an evanescent wave region at the small end.

I imagine that the RF feed (whether located near the big end or the small end,  but particularly near the small end) might also affect this transition (for better or for worse).

An antenna near the big end may amplify the participation of a ghost mode, particularly a ghost mode that would naively be discounted as cut-off (it is not sharply cut-off if the cross section is tapered) when using cut-off frequency formulas based on constant cross-section waveguides.
« Last Edit: 07/22/2015 02:33 PM by Rodal »

Offline rfmwguy

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Thought experiment alert -

I won't give the links out to the youtube videos, because the filmakers are idiots, but suffice it to say magnetrons are dangerous and powerful. Most of the videos involve an open-ended can or cone that radiates the EM at objects; exploding a boom-box is one of them.

More interesting is the plasma that is created at sharp edges on non-grounded metallic objects. The visual on the plasma "waves" inside exposed lightbulbs was strange...just before the filaments arc'd and burnt.

Multiply the potential for plasma arcs by several fold in a closed cavity, and you can surmise there is significant energy there. How that Energy potential translated into kinetic energy is my conundrum. One thing to keep in mind is that particulates in the air, including water droplets, can become excited and thrown in a certain direction...so here's the thought experiment...

The small and large plates are basically mirrors, reflecting radiation back and forth for X (?) cycles before being lost as heat. Concave end plates would create more of a focus. Lets say some EM gets reflected out of this TE or TM reflecting "column" and strikes the frustum sides...possibly imparting momentum. In which direction you ask? Towards the small end, along the taper. A vector force if you will, as the end plate reflections would balance out with CoM.

So, do we have a Maser-like device that allows some energy to escape the column and strike the frustum before its lost...maybe, maybe not. I still have not rationalized "mass-less" EM imparting kinetic energy beyond a photo rocket. That is unless it is picking up particulates in the air and firing them off...

(tilt)

Offline SeeShells

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@SeeShell -
Your .png and .csv files data is/are up have been uploaded here:

https://drive.google.com/folderview?id=0B1XizxEfB23tfm04QWNVVVVvT3gtcVAzRUp6T1BCLVpoV0EyeVVKR2ZxQkp2a3NKcUNPMU0&usp=sharing

I uploaded my meep data request file/form to hopefully explain what the data is, although it needs more English and fewer Scheme statements. The inside big end is at row 15 and small end at row 216 of the csv files, and the total run meep time t = 13.054 (6527 timesteps).
Thanks, interesting but not quite what we were looking to do. I'm still working out the antenna shape and placement and getting feedback like I said I was going to do on launching a Te mode. What I found out is a answer from a wonderful source that mretty much just lurks here.

Of course doing it isn't as easy as it seemed to be and I'm not sure you can do it in a meep model.
 
Quote from a email:
 "Your test setup looks great. If you use a 1/4 probe on the big end or little end you will launch a TM mode. If you use a 1/10 wave loop you will excite a TE mode at either top or bottom. I believe If you launch from the big end the net force will be toward the small end or vice versa launching from the small end as the reflected wave will be reduced by Q losses and will be smaller in magnitude than the launched wave.  A loop on the side wall will excite either mode depending on orientation wrt the frustum z axis. All walls on the frustum look like a conductive ground plane. For low power testing ,with the sweeper , the sample port I would use a probe 1/4 wavelength from the side wall, variable probe depth for the needed coupling to put the SA sampler in its optimum resolution range. If you use a loop you should place it at a low impedance point or H plane max node. <End Quote>

After hours of reading and several emails to people who are beyond my skills in antennas I would agree with this.

Shell

Offline SeeShells

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...

What's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.

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

...
Cut-off is a concept that applies to constant section waveguides.  It 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).

As shown by several authors, and latest by Zeng and Fan (often quoted by Todd "WarpTech") in a tapered waveguide all modes run continuously from a travelling wave region  through a transition to an evanescent wave region and the value of the attenuation increases as the cone vertex is approached.

I have also shown this in detail for the EM Drive for several geometries: there is no such thing as cut-off unless you approach a small end of zero dimensions (which is impractical).  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 (as the whole issue of whether the EM Drive force is real or an experimental artifact also remains to be proven).  But that the cut-off concept does not apply is well confirmed by now.  In a tapered waveguide modes do not get cut-off, instead the modes persist, with a larger diameter region where the wave is a travelling wave to a transition region to a region near the apex where the wave becomes evanescent.
Dr. Rodal,
To make this work with the 1/2 centerline 6.1 degree angle of my cavity I need to rerun your numbers and spreadsheet it. Can you help here?
Shell

Offline Carl G

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Reminder.

You need to ensure your posts are useful, correctly formatted, on topic and related to space flight, or they will be trimmed to stop the thread turning into a mess.

Offline Rodal

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...
Dr. Rodal,
To make this work with the 1/2 centerline 6.1 degree angle of my cavity I need to rerun your numbers and spreadsheet it. Can you help here?
Shell
What are the parameters of what you would like to have calculated:

Big Diameter =  meters
SmallDiameter = meters
Axial Length measured perpendicular to ends =  meters
Ends=   Flat or Spherical
Excitation Frequency =   GHz

Offline SeeShells

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...
Dr. Rodal,
To make this work with the 1/2 centerline 6.1 degree angle of my cavity I need to rerun your numbers and spreadsheet it. Can you help here?
Shell
What are the parameters of what you would like to have calculated:

Big Diameter =  meters
SmallDiameter = meters
Axial Length measured perpendicular to ends =  meters
Ends=   Flat or Spherical
Excitation Frequency =   GHz

Thank You...

Big Diameter =  .201 meters
SmallDiameter = .1492 meters
Axial Length measured perpendicular to ends = .24 meters
Ends= Flat
Excitation Frequency = 2.45  GHz

Offline Rodal

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Wikipedia has changed the title of the article from EM Drive to https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster


Perhaps we should change the title of this thread as well, in the upcoming thread 4 to  RF resonant cavity thruster -  related to space flight applications ?

or Microwave cavity thruster -  related to space flight applications ?

keeping up with Wikipedia, in a more descriptive name that is not tied (as the name "EM Drive" is) to the commercial enterprise of Roger Shawyer?

Feedback?

PS: I don't like the use of acronyms like "RF" or "EM"
« Last Edit: 07/22/2015 04:20 PM by Rodal »

Online WarpTech

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...

What's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.

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

...
Cut-off is a concept that applies to constant section waveguides.  It 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).

As shown by several authors, and latest by Zeng and Fan (often quoted by Todd "WarpTech") in a tapered waveguide all modes run continuously from a travelling wave region  through a transition to an evanescent wave region and the value of the attenuation increases as the cone vertex is approached.

I have also shown this in detail for the EM Drive for several geometries: there is no such thing as cut-off unless you approach a small end of zero dimensions (which is impractical).  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 (as the whole issue of whether the EM Drive force is real or an experimental artifact also remains to be proven).  But that the cut-off concept does not apply is well confirmed by now.  In a tapered waveguide modes do not get cut-off, instead the modes persist, with a larger diameter region where the wave is a travelling wave to a transition region to a region near the apex where the wave becomes evanescent.

However.... in a tapered waveguide, the group and phase velocity are NOT constant. Regardless if there is no cut-off per-se, the wave is either accelerating toward the big end, or being attenuated toward the small end. The velocity in the "z" direction is not constant, which is all he was referring to and that is absolutely correct.

What I have now is a Thrust-to-power ratio that reduces to 1/c for no waveguide, or 1/v_phase for a straight waveguide, but something radically different for a tapered waveguide that Zeng and Fan write about. There is nothing inconsistent between what was said here about group velocity going to zero, and what Zeng and Fan wrote.  Point is, don't nit-pick the English language.
Todd

Offline SeeShells

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Wikipedia has changed the title of the article from EM Drive to https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster


Perhaps we should change the title of this thread as well, in the upcoming thread 4 to  RF resonant cavity thruster -  related to space flight applications ?

or Microwave cavity thruster -  related to space flight applications ?

keeping up with Wikipedia, in a more descriptive name that is not tied (as the name "EM Drive" is) to the commercial enterprise of Roger Shawyer?

Feedback?

PS: I don't like the use of acronyms like "RF" or "EM"
Neither do I.

I have the title of my gofundme as ElectroMagnetic Reaction Drive for that very reason but it would be weird to rename this that wouldn't it?

I bow to the other powers here and must get out into the shop building.

Shell

Offline rfmwguy

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Wikipedia has changed the title of the article from EM Drive to https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster


Perhaps we should change the title of this thread as well, in the upcoming thread 4 to  RF resonant cavity thruster -  related to space flight applications ?

or Microwave cavity thruster -  related to space flight applications ?

keeping up with Wikipedia, in a more descriptive name that is not tied (as the name "EM Drive" is) to the commercial enterprise of Roger Shawyer?

Feedback?

PS: I don't like the use of acronyms like "RF" or "EM"
Good plan, I'd change it over to resonant cavity thruster. RF is typically up to 1-3 GHz (depending on who you ask) and MW acronym takes over from there. There's my 2 cents

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