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#2560
by
graybeardsyseng
on 03 Nov, 2017 15:32
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The antenna excites the TE01x modes and is very simple to construct. It was designed and impedance matched in FEKO before it was constructed. There are a number of different antennas that will work for TE01x modes, but few that are as easy to build.
Jamie -
Roger all that - I think its likely a great antenna and of course construction ease or difficulty is a major factor. I was concerned more with how to analyze it and what patterns you would get. I am glad FEKO supports analysis of it - as I said I don't know FEKO very well nor have access to it. Does it provide the self resonance frequency as an output? That is what I was most interested in based on you concern over the SRF being very close to your frustum resonance.
I think your build is outstanding and can hardly wait for powered flight . . . err . . . tests. heh heh .
Herman
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#2561
by
Peter Lauwer
on 03 Nov, 2017 15:45
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Jamie - are you using a loop antenna? Sorry but I have forgotten.
If so it can likely be analyzed as a single coil inductor - probably treated as a helical transmission line since typically above 1Ghz lumped components must usually be addressed as transmission lines. In any case it should be relatively simple to move the self resonance frequency (SRF) with a bit of capacitance (treat this as an open circuit transmission line).
If you are using a 1/4 lambda spike or wheel antenna that is somewhat different.
Herman
graybeardsyseng
Herman, check out this
https://forum.nasaspaceflight.com/index.php?topic=42978.msg1698864#msg1698864
if I'm not wrong the above is the antenna Jamie is currently using
I'm not sure if that is the loop Jamie is using. He did a lot of different testing with different styles. Although he should be using a
Loop antenna that couples to the magnetic field. like the loop in EagleWorks test frustum. (see attached)
It should have both ends of the loop coupled to the coax feed.
https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm
This is a very nice site for referencing loop antennas.
My Very Best,
Shell
Very useful site, Shell. Thanks!
Only, at the frequency ranges we use, a 1/10 WL circumference of the loop is not reachable, I think.
Say 2.5 GHz => 12 cm WL => 12 mm loop circ => 3.8 mm diameter loop. So, for practical dimensions we are more in the 1/4 WL range.
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#2562
by
SteveD
on 03 Nov, 2017 16:34
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Is there a workshop/conference concerning the EM drive going on shortly? I remember Jamie was trying to finish in time to present.
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#2563
by
Monomorphic
on 03 Nov, 2017 16:36
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Roger all that - I think its likely a great antenna and of course construction ease or difficulty is a major factor. I was concerned more with how to analyze it and what patterns you would get. I am glad FEKO supports analysis of it - as I said I don't know FEKO very well nor have access to it. Does it provide the self resonance frequency as an output? That is what I was most interested in based on you concern over the SRF being very close to your frustum resonance.
I've had thoughts of modifying the design to be more like a closed loop as follows. This would still allow it to be impedance matched using the current z-axis tuning system.
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#2564
by
Monomorphic
on 03 Nov, 2017 16:43
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Is there a workshop/conference concerning the EM drive going on shortly? I remember Jamie was trying to finish in time to present.
The conference has been going on the last three days, including today. I decided a couple of weeks ago to back out of this workshop to give me more time to solve a critical problem that was obscuring the data with ~5uN of noise. That ended up being natural convection from the walls of the enclosure as well as the on-board electronics. I've continued to work on the problem, having good results with lots of insulation and additional heat sinks. Heidi Fearn said I can present at the next conference instead. I was told that will be some time later in 2018 again in Estes Park, CO.
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#2565
by
X_RaY
on 03 Nov, 2017 19:56
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MaxFEM
Description
MaxFEM is an open source software to solve electromagnetic problems in a numerical way by using the finite element method. The package brings together under a single interface different modules or applications that can address problems in electrostatics, direct current, magnetostatics, transient magnetics and eddy currents, in two and/or three dimensions and in cartesian and/or cylindrical coordinates.
The user can make internal changes to adapt to his/her needs both the interface and the contained calculus programs. Moreover, thanks to the modular structure of the interface is the possibility of incorporating other problems (eg, thermal coupled electromagnetic). Under the GPL license, anyone can include your own application and redistribute the software.
Multiplatform software
Two programming languages have been used to the codification of MaxFEM:
Python: to develop the graphical interface.
Fortran: to develop the calculus codes.
Besides, the fact of using Python gives MaxFEM the property of being multiplatform:
Windows
Linux
Mac OS
http://www.usc.es/en/proxectos/maxfem/installers.htmlJust trying to get it working...
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#2566
by
rq3
on 04 Nov, 2017 00:22
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Jamie - are you using a loop antenna? Sorry but I have forgotten.
If so it can likely be analyzed as a single coil inductor - probably treated as a helical transmission line since typically above 1Ghz lumped components must usually be addressed as transmission lines. In any case it should be relatively simple to move the self resonance frequency (SRF) with a bit of capacitance (treat this as an open circuit transmission line).
If you are using a 1/4 lambda spike or wheel antenna that is somewhat different.
It's a simple antenna design. The polish group is also using the same design. It had the same coupling as a standard loop in FEKO.
A "loop" antenna can be either capacitively (voltage) coupled to it's ground plane (open loop), or magnetically (current) coupled to its voltage source (closed loop). Either is valid, depending upon the mode(s) you wish to excite. Since no-one knows which is "right", both/all/any methods are valid/invalid. Pick one. If the result does not meet your hypothesis, pick another. That's experimentation.
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#2567
by
john smith 19
on 04 Nov, 2017 10:16
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Maybe I'm totally off target but ... what if one modulates the signal injected into the cavity? I mean ... using different waveforms
Was this already experimented?
Not intentionally (not with the intention to achieve an express purpose) to my knowledge, except that magnetrons by their nature already contain amplitude, frequency and phase modulation
Dr. Rodal,
I go back to a time I learned the basics of electronics with tubes, transistors where the new wonder toy IC's were stuff of dreams. The magnetron is nothing but a tube that self excites to produce microwaves. This isn't rocket science but tube science. Tubes are still around and still are used in the semiconductor industry where signal splatter and jitter have to be tightly controlled.
This is the one of the first articles I ran across that reinforced what I knew of tubes and what caused issues. http://lea.hamradio.si/~s57uuu/mischam/magnetr/
I was able to build a thermally stabilized water cooled current and voltage controlled supply locked into Fo by the use of a waveguide > antenna this gave me a very stable signal with no AM jitters and side lobes.
It's not entirely true that a magnetron is nasty noisy and unusable as a RF device it's just tougher to do than a lower wattage SS device.
During the late 70's Ratheon and JPL did a lot of work on Satellite Solar Power stations. They needed a lot of Kw sized microwave sources to transmit the power to Earth and found that oven magnetrons could be phase locked. IIRC they shut down the heater when oscillation was self sustaining.
The work was written up in a series of reports on the NASA NTRS web site with JPL as the centre.
Wheather they are stable enough, or phase shiftable enough, for this task is another matter.
I had thought this was common knowledge and I rarely check this thread.
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#2568
by
aero
on 04 Nov, 2017 16:09
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I respect Greg Egan, and I am familiar with the quoted paper. In this case the statement - quoting
"If the cavity contains a standing wave, then the fields will have a harmonic time dependence of the form sin(ωt) or cos(ωt), and over one complete cycle of the mode, a period of 2π/ω, all the fields will return to their origin values. So at each point in the interior of the cavity, we will have:
∫cycle (∂Si / ∂t) dt = Si(t0+2π/ω) – Si(t0) = 0
So, averaged over a complete cycle in the same way, each component of the net force on the wall will sum to zero."
does not agree in the general case with the paper
arXiv:0807.1310v5 [physics.class-ph] 21 Nov 2008
The Lorentz Force and the Radiation Pressure of Light
Tony Rothman∗ and Stephen Boughn†
You either linked the wrong paper or completely misunderstood the paper. The paper is dealing with a single electron, not a closed cavity. Eagan's result and that paper are consistent. Trying to say otherwise is making a very similar mistake to what the paper is pointing out about the "Freshman argument," applying basic results without going through the full details.
If you look at your own result you will find not coincidentally that you got 2 times a photon rocket. This is from not including the reaction of the antenna, and probably a factor of 2 that I think is likely related to how you inserted gamma which you admitted was arbitrary, and I think isn't quite correct.
I don't really feel like delving into any more details of your math right now since Maxwell's equations quite clearly will not produce a force consistent with a working emDrive.
I don't want a big argument here but this is the right paper -
https://arxiv.org/pdf/0807.1310.pdf Perhaps you might check section 4 in which the authors move beyond the introductory electron case. And as for the for the value of force that I calculated being the same as a photon rocket, the factor of two notwithstanding, that is quite understandable as my approach in this case basically considered only the 100 Watt power loss. That detail may be hidden, but it is embedded.
But the pertinent question is asked earlier in my original post, please address this question:
"Does the preferential heating of the big end of the frustum imply that the internal reflection coefficient is lower at the big end?"
If the answer is "Yes," then I haven't seen any math by anyone that addresses the existing situation within the EM drive frustum.
If the answer is "No" then I'm finished.
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#2569
by
meberbs
on 04 Nov, 2017 18:08
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I don't want a big argument here but this is the right paper - https://arxiv.org/pdf/0807.1310.pdf
Perhaps you might check section 4 in which the authors move beyond the introductory electron case.
First, you previously directly referenced the earlier sections which I stated are irrelevant. You are now changing your argument by referencing the later section 4, discussing a different situation. You should be explicitly admitting that you are changing your argument and admitting that your previous line of argument was wrong. **
Second, section 4 is a bit more relevant, but it still is in support of Egan's work, demonstrating the way charges currents and fields interact on the surface of a conductor to produce the forces. Egan doesn't go to that level, because he is using more generic results that apply for a general case and not just a straight on reflection.
And as for the for the value of force that I calculated being the same as a photon rocket, the factor of two notwithstanding, that is quite understandable as my approach in this case basically considered only the 100 Watt power loss. That detail may be hidden, but it is embedded.
I am not sure what you are trying to say here. It seems clear that your formulation depends on multiple unstated assumptions that in the end are equivalent to calculating the force that would be produced if a laser reflected off of a mirror. This basically happens by effectively assuming all of the photons start travelling uniformly in one direction but ignoring the force generated when they are emitted, and ignoring the momentum transfer when they get absorbed.
But the pertinent question is asked earlier in my original post, please address this question:
"Does the preferential heating of the big end of the frustum imply that the internal reflection coefficient is lower at the big end?"
If the answer is "Yes," then I haven't seen any math by anyone that addresses the existing situation within the EM drive frustum.
If the answer is "No" then I'm finished.
The answer is that your model is extremely simplified, so you have to define what you mean by "internal reflection coefficient." Photons aren't just being reflected back and forth perpendicularly, but are bouncing in all directions. Reflection coefficient is in general dependent on incident angle, but when all points of the cavity have overlapping photons moving in multiple directions this starts to be undefinable. To deal with this, you just look at the fields as a whole, and calculate the forces exerted by these fields on the walls, and the losses in the walls from the induced currents based on the material properties. Egan did this, and it is also part of all of the FEKO and other simulations that have been done on here.
**I am being a bit more direct (and therefore harsher sounding) than I would like, however this kind of goalpost moving is disturbingly common on this section of the forum, and the directness of what you just did makes this a good example. I hope that you can set an example for others here by owning your mistake.
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#2570
by
spupeng7
on 04 Nov, 2017 23:20
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All,
The link is to some 'word salad' and a tentative equation which I have concocted in a sincere attempt to demystify some of my ravings on this forum. It proposes a mechanism by which the asymmetric distribution of charges within the emdrive frustum can act to accelerate it relative to the outside universe, without breaking conservation laws or inventing new interactions.
http://vixra.org/abs/1711.0115Comments most welcome.
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#2571
by
aero
on 04 Nov, 2017 23:26
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I don't see any movement of the "Goal Posts." Where did I reference anything from the article more specifically than the whole article? Except in my latest post where I pointed you to section 4, and of course earlier, equation 2.4.
The reflection coefficient is a wave phenomenon. Is it even meaningful to speak of the reflection coefficient and photons in the same breath? One is classic, the other is quantum. Yes, photons bounce or ricochet all over but from the temperature profiles, there doesn't seem to be much energy lost to the sidewalls. Sidewall heating near the big end is, IMO, due to conduction from the big end because there isn't a corresponding temperature rise near the small end and ricochetting photons wouldn't be end selective.
But the pertinent question is asked earlier in my original post, please address this question:
"Does the preferential heating of the big end of the frustum imply that the internal reflection coefficient is lower at the big end?"
Ignore my simple model and look at Paul March's post of experimental temperature data. I am asking about the reflection coefficient of the inside big end of the frustum, verses the reflection coefficient of the inside of the small end, and not addressing sidewall issues. Don't worry about being critical, I've read most of your posts, and you seem to always be critical of new ideas. But at least you talk, others don't contribute at this level at all.
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#2572
by
meberbs
on 05 Nov, 2017 00:02
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I don't see any movement of the "Goal Posts." Where did I reference anything from the article more specifically than the whole article? Except in my latest post where I pointed you to section 4, and of course earlier, equation 2.4.
You pointed to the early parts of the paper, which I pointed out was irrelevant and did not prove your point. Rather than acknowledging this, you just pointed to a different part of the paper. Changing your argument without acknowledging that your original argument was wrong is a form of moving the goalposts.
I then explained that section 4 of the paper also does not support your point, and still you make no counterargument or acknowledgment that you were wrong. Lets get this out of the way now: Are you willing to admit to being wrong? If not, please don't waste any more of anyone's time.
The reflection coefficient is a wave phenomenon. Is it even meaningful to speak of the reflection coefficient and photons in the same breath?
Yes, reflection coefficient is the chance that a specific wavelength photon incident at a specific angle will be reflected rather than absorbed.
Yes, photons bounce or ricochet all over but from the temperature profiles, there doesn't seem to be much energy lost to the sidewalls. Sidewall heating near the big end is, IMO, due to conduction from the big end because there isn't a corresponding temperature rise near the small end and ricochetting photons wouldn't be end selective.
This is science, opinions don't matter. The fact is that heating of the walls is related to local field strength.
But the pertinent question is asked earlier in my original post, please address this question:
"Does the preferential heating of the big end of the frustum imply that the internal reflection coefficient is lower at the big end?"
Read my last post again. I addressed this question. The problem is the question is kind of like asking "what flavor is the sky, sweet or sour?" The correct answer is that trying to specify a flavor for the sky is not a well defined question.
Ignore my simple model and look at Paul March's post of experimental temperature data. I am asking about the reflection coefficient of the inside big end of the frustum, verses the reflection coefficient of the inside of the small end, and not addressing sidewall issues.
The temperature data says nothing about a "reflection coefficient." It does say something about distribution of fields and field strength.
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#2573
by
aero
on 05 Nov, 2017 00:32
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@meberbs
I an not "wrong," you have read much more into my posts than I actually wrote, you wrote nothing to further the answer to my question and You probably don't even realize that you are in full attack mode.
I don't need the aggravation, so in the future please don't ever again trouble yourself to reply to any of my posts.
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#2574
by
tleach
on 05 Nov, 2017 01:28
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Well, regardless of whether the question s
Is or is not specific enough, it would seem to be the case that the EW frustum did show preferential heating of the large end plate. And, that also happens to be where Shawyer placed his YCBO and Sapphire in his most recent patent application (the rest of the cavity is silver plated if I recall). And didn't Todd's theory have something to say about a preference for which direction the waste heat was emmitted?
Have any of the other replicators metioned that particular asymmetry before?
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#2575
by
aero
on 05 Nov, 2017 02:09
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Well, regardless of whether the question s
Is or is not specific enough, it would seem to be the case that the EW frustum did show preferential heating of the large end plate. And, that also happens to be where Shawyer placed his YCBO and Sapphire in his most recent patent application (the rest of the cavity is silver plated if I recall). And didn't Todd's theory have something to say about a preference for which direction the waste heat was emmitted?
Have any of the other replicators metioned that particular asymmetry before?
And regardless of the details of how the energy of the RF is actually converted to waste heat, doesn't the simple fact that it is converted to waste heat mean that it is not reflected back into the frustum? Waves or photons, the answer must be yes.
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#2576
by
meberbs
on 05 Nov, 2017 02:45
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@meberbs
I an not "wrong," you have read much more into my posts than I actually wrote, you wrote nothing to further the answer to my question and You probably don't even realize that you are in full attack mode.
If you are not wrong, why did you not answer any of my objections to your statements?
I did answer your question, you just apparently don't like that the answer was not just a "yes" or "no."
I am not attacking, I am trying to respond to your misunderstandings. If you want to call what I did an attack, then your posts are an attack on Egan when you accuse him of making freshman level mistakes whithout actually pointing out anything actually wrong with what he did, and an attack on science when you try to use a paper arguing that radiation pressure should be calculated with rigorous analysis to support your non-rigorous analysis.
How about we agree not to use the word "attack" and instead have a friendly discussion which is what I thought we were doing?
I don't need the aggravation, so in the future please don't ever again trouble yourself to reply to any of my posts.
As long as people post wrong information I will respond with corrections so that those here interested in learning something can do so.
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#2577
by
Star One
on 05 Nov, 2017 15:11
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This thread seems to have slowed down and quite a few regulars appear to have disappeared most recently The Traveller? Also does the Reddit get much updating does anyone know, as the last time I looked it seemed fairly moribund?
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#2578
by
LowerAtmosphere
on 05 Nov, 2017 15:46
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This thread seems to have slowed down and quite a few regulars appear to have disappeared most recently The Traveller? Also does the Reddit get much updating does anyone know, as the last time I looked it seemed fairly moribund?
As with navigating any sea there will always be doldrums. Most are awaiting test data or new discoveries on the theoretical front. I am keeping an eye about net polarization in vortices and the influence of harmonic frequencies on radiation and group behaviour across discontinuities in metallic lattices. I believe most behaviour of any closed cavity can be directly explained by the boundaries permitting or blocking certain frequencies which in turn will change the evolution of the charge/momentum along the wall. The old posts from Hyperplanck (a user who seems to have gotten completely engrossed in publishing an omnibus work on string theory last I heard) really should have gotten more traction. It's all about the phonons and interaction between walls via different layers of both free and bound electrons, in short.
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#2579
by
WarpTech
on 05 Nov, 2017 17:56
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Well, regardless of whether the question s
Is or is not specific enough, it would seem to be the case that the EW frustum did show preferential heating of the large end plate. And, that also happens to be where Shawyer placed his YCBO and Sapphire in his most recent patent application (the rest of the cavity is silver plated if I recall). And didn't Todd's theory have something to say about a preference for which direction the waste heat was emmitted?
Have any of the other replicators metioned that particular asymmetry before?
Yes, but in my model the "reflection coefficient" is irrelevant because, when the MW cavity is charged to a steady state maximum energy, the EM field will exert pressure on all sides. Unless, the small end is below cut-off, in which case the momentum in that direction will be imparted to the side walls. Either way, the power losses to the copper are directly proportional to the force exerted by the field. If the whole frustum is made of copper, then the forces should balance and cancel out.
However, my "theory" is that; IF there is a higher power dissipation at one end vs the other end, then there will be a NET flow of energy & momentum in that direction and the frustum should move the other way. On the other hand, without a dielectric or dissimilar metals, there is no reason (other than geometry) why the power dissipation would be different at one end vs the other. I've suggested using a different metal for the big end plate. Something with higher losses, like nickel or steel. Or, something with lower losses like silver or superconductor, depending on which way you want it to thrust.
Regarding the force, my "guess" is that it will be less than a photon rocket operating at the available power inside the frustum, i.e., < Q*P
in/c, and will not thrust in steady state. It must be pulsed, which lowers the average thrust.
