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#700 by aero on 16 Feb, 2015 16:11
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@TMEubanks
Regarding your question:Quotewhat is the mesh size in these plots? I think the rule of thumb is < lambda / 40, which is a little less than 4 mm.
We can get a handle on that by looking at the image properties, knowing that meep computes a data point for each pixel of the image, and that the general dimensions of the vacuum chamber are 30" x 36". The image pixel dimensions are 3612 x 4354. That converts to about 0.23 mm/pixel which is spacial resolution. (The boundry layer adds some overhead.) It is a rough order of magnitude higher resolution than required by the fields, but considering that the 0.002" gaps at the attachment points of the base plates and cone body is only 0.0508 mm I need to run at very high resolution or those gaps won't be resolved. Even so, I am now using 5.5 times the design gap size in order that it will be resolved and allow RF energy to escape via the gap in the model. I'm only slightly concerned about this because the forces detected by meep get larger as the gap size gets smaller. If it were the other way around then it would be a bigger concern.
Of course in the real world, RF energy can escape via gaps at much smaller sizes or so I think.
@Rodal
Meep can compute in one, two or three dimensions, x - x,y - x,y,z Cartesian and cylindrical.
Meep advertises a built-in method to utilize symmetry of the model but the vacuum chamber/EM thruster model is not symmetric. And in any case there seems to be a problem in reconstructing the output files correctly for the magnetic fields when mirror symmetry is utilized. Dr. Dominic, whom I might call my meep mentor, avoids using symmetry in his models, hence so do I. -
#701 by Reactionless on 16 Feb, 2015 16:12
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Have any tests been done reversing the drive?
http://nextbigfuture.com/2015/02/update-on-emdrive-work-at-nasa.htmlQuoteThey have now confirmed that there is a thrust signature in a hard vacuum (~5.0x10^-6 Torr) in both the forward direction, (approx. +50 micro-Newton (uN) with 50W at 1,937.115 MHz), and the reversed direction, (up to -16uN with a failing RF amp), when the thruster is rotated 180 degrees on the torque pendulum.
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#702 by Rodal on 16 Feb, 2015 16:13
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.....
Yes, and they have done it (reversing the drive) under hard vacuum.
Have any tests been done reversing the drive? -
#703 by Star One on 16 Feb, 2015 16:15
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.....
Yes, and they have done it (reversing the drive) under hard vacuum.
Have any tests been done reversing the drive?
Which seems to be a rather significant point. -
#704 by Reactionless on 16 Feb, 2015 16:19
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Which seems to be a rather significant point.
If it was only an interaction with the vacuum chamber or pendulum, would the thrust direction being reversed on reversing the drive be something that was expected as well, or is this a strike against the chamber/pendulum interaction explanation?
They also observed a reversal of thrust under different modes, even when they kept the orientation the same. -
#705 by TMEubanks on 16 Feb, 2015 16:20
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Quote
They have now confirmed that there is a thrust signature in a hard vacuum (~5.0x10^-6 Torr) in both the forward direction, (approx. +50 micro-Newton (uN) with 50W at 1,937.115 MHz), and the reversed direction, (up to -16uN with a failing RF amp), when the thruster is rotated 180 degrees on the torque pendulum.
This needs to be redone.
+50 and -16 is evidence of systematic errors. It is simply not good enough to say (or imply), well, if we could redo it properly, it would be +- 50. That needs to be demonstrated (or not). -
#706 by Star One on 16 Feb, 2015 16:23
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Quote
They have now confirmed that there is a thrust signature in a hard vacuum (~5.0x10^-6 Torr) in both the forward direction, (approx. +50 micro-Newton (uN) with 50W at 1,937.115 MHz), and the reversed direction, (up to -16uN with a failing RF amp), when the thruster is rotated 180 degrees on the torque pendulum.
This needs to be redone.
+50 and -16 is evidence of systematic errors. It is simply not good enough to say (or imply), well, if we could redo it properly, it would be +- 50. That needs to be demonstrated (or not).
Give them a chance. Your enthusiasm is good but time is the best response here. Anyway Star Drive may if he is able to answer more specifically.
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#707 by Star-Drive on 16 Feb, 2015 17:32
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Quote
They have now confirmed that there is a thrust signature in a hard vacuum (~5.0x10^-6 Torr) in both the forward direction, (approx. +50 micro-Newton (uN) with 50W at 1,937.115 MHz), and the reversed direction, (up to -16uN with a failing RF amp), when the thruster is rotated 180 degrees on the torque pendulum.
This needs to be redone.
+50 and -16 is evidence of systematic errors. It is simply not good enough to say (or imply), well, if we could redo it properly, it would be +- 50. That needs to be demonstrated (or not).
Give them a chance. Your enthusiasm is good but time is the best response here. Anyway Star Drive may if he is able to answer more specifically.
Folks:
The copper frustum reversed thrust data was started just before our second EMPower Model-1165 RF amp started dying due to internal corona discharges around its RF output line created when its internal pressure had leaked down from 760 Torr on the Friday afternoon just before the MLK Holiday here in the USA. This data shot was obtained about an hour after the vacuum pumps were turned on Friday evening. When I cam back on the following Tuesday with the vacuum pumps going all weekend, I tried the same test, but the amp would just turn on and drawn the right dc current, but would only deliver about 25 milli-watts of RF no matter what the input level was. Why? Because the RF was just creating a nice blue glow in the amplifier...
We should have the repaired RF amps back in the lab by Wednesday morning and the reverse thrust testing is where I'll be picking up again at that time.
Best, Paul M. -
#708 by TMEubanks on 16 Feb, 2015 19:23
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Excellent news! Good luck.
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#709 by Mulletron on 16 Feb, 2015 19:53
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How hard would it be to put the 1165 inside a more vacuum resilient container?
http://www.empowerrf.com/pdfs/1165.pdf
Notice the paper says max altitude 50K feet!
It is operating beyond specs in that vacuum.....why they keep dying!
We gotta figure this out, pronto! -
#710 by frobnicat on 16 Feb, 2015 20:41
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Well, you can calculate it, or you can try and devise better experiments (e.g., the same test in a fiberglass chamber). In the end, I suspect it will take a test in space to really be sure, but that's expensive, so it is entirely proper to make it jump through all kinds of hoops here on the ground first. (And, note, it is quite possible that it will either be rejected or just fade away in the process.)
Marshall, how about these methods proposed by Mulletron to test whether the EM Drive thrust is due to evanescent wave interaction:I can think of 3 ways to test the evanescent wave theory.
1) Is the measured thrust the same with the chamber door open and closed?
2) Is the thrust still there when the test article is rolled out of the chamber. Not sure if 2 is possible.....
3) Change the conditions near the resonant cavity; like wrap the thing in thick foam and then wrap all that with foil, see what the thrust does.
...
As for 3) : how about putting aluminium plates fixed to the chamber (not on the balance arm) very close to the frustum at its rest position, an inch or so from the small and/or big end. If the thrust is due to coupling of leaked radiation between moving frustum and nearby fixed parts (chamber rest frame) this could show a strong correlation. This should be relatively easy to do and wouldn't modify the weight on balance or other dynamic parameters of experiment.
Maybe Aero you could tell from simulation what kind of influence on apparent thrust would be expected from putting such shield very close to frustum ?
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#711 by birchoff on 16 Feb, 2015 20:43
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...
Have any tests been done reversing the drive?
Both the test run that was reported on in Brady et al and the test run that Star-Drive talked about have included running the drive in a reverse orientation. -
#712 by Mulletron on 16 Feb, 2015 20:56
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Plugged in some numbers to come up with the near field reactive and near field radiating using 2ghz and largest dimension of frustum 280mm.
Near field reactive: .024m
Near field radiating: .261m
But there is a problem with this near field scenario. This is for antennas. The frustum isn't an antenna. The outer surface is also grounded through the coax cable at a minimum. Thus this type of evanescent wave interaction is not an option.
References:
https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10112.html
http://en.wikipedia.org/wiki/Near_and_far_field#Near-field_characteristics
Another possible method of evanescent wave production by TIRF is an option however, which is an optical phenomenon associated with boundary conditions of two different refractive indexes. I remain unconvinced that this applies to Emdrive solely because the air/copper/air boundary does not fit this scenario. Copper is a conductor, thus any evanescent E field component will completely vanish. Here's info from an expert over at Polywell:
http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=2949&start=270#p118973QuoteYes, evanescent waves are propagating waves. They propagate in the direction of the interface, so their momentum is parallel to the boundary. It is just their amplitude that decays exponentially away from the interface layer.
So in this context, evanescent waves "hug" the boundary. The propagate parallel to the boundary. They do not radiate away from the boundary. Their amplitude falls exponentially with distance, unlike radiating waves which fall off with inverse square. The above quote from Polywell matches any check of the literature online.
I am willing to play devil's advocate for a second and accept that evanescent waves do appear on the outer surface of the conical frustum.
Quoting the oracle, http://en.wikipedia.org/wiki/Evanescent_waveQuoteThey are formed at the boundary between two media with different wave motion properties, and are most intense within one third of a wavelength from the surface of formation.
The 1/3 wavelength figure also appears in other references. Evanescent fields would be most intense within .05m or ~2 inches from the conical frustum. Any structure within that range is subject to scrutiny.
We know, as was recent reported that this kind of evanescent wave can impart momentum and spin on particles in the following manner.QuoteMomentum and spin represent fundamental dynamic properties of quantum particles and fields. In particular, propagating optical waves (photons) carry momentum and longitudinal spin determined by the wave vector and circular polarization, respectively. Here we show that exactly the opposite can be the case for evanescent optical waves. A single evanescent wave possesses a spin component, which is independent of the polarization and is orthogonal to the wave vector. Furthermore, such a wave carries a momentum component, which is determined by the circular polarization and is also orthogonal to the wave vector.
Thus for this type of evanescent wave to be applicable to Emdrive, there would have to be circularly polarized wave in use. The Emdrive is excited by linearly polarized plane waves. If it were excited by circularly polarized radiation, the momentum vector imparted on any particle nearby would be orthogonal to the direction of measured thrust. Under vacuum testing, these particles were removed. Thus this evanescent wave hypothesis does not hold.
http://www.nature.com/ncomms/2014/140306/ncomms4300/full/ncomms4300.html
http://arxiv.org/ftp/arxiv/papers/1308/1308.0547.pdf
Now that I'm done playing devil's advocate, these are the only ways I can find in the literature to "tunnel" radiation out of a waveguide. You have to run it at cutoff and use metamaterials. None of these conditions fit Emdrive.
http://personal.us.es/marques/2005-PhysRevB_72_075116.pdf
http://people.ee.duke.edu/~cummer/reprints/074_Liu08_PRL_EMTunnelingMeasurements.pdf
A final method of producing evanescent waves is to operate the waveguide at or below cutoff. Given the .159 meter diameter of the small end, cutoff is 1886.79mhz. Any frequency lower than this would go evanescent inside the cavity. The lowest frequency in which a certain mode can propagate is the cutoff frequency of that mode. Evanescent modes are modes below the cutoff frequency. They cannot propagate down the waveguide for any distance, dying away exponentially. The only test that got close to cutoff was the TE012 test at 1880.4 from Brady et al, but this does not count as the frustum was loaded with PE, which displaced the E and H fields, changing the resonant frequency. So this does not count as running the device below cutoff, as it wouldn't resonate anyway if it were in cutoff.QuoteShawyer's statement, "The small end diameters are set just above the cut-off diameter corresponding to the mode and frequency of the design."
http://forum.nasaspaceflight.com/index.php?topic=29276.msg1275094#msg1275094
Lastly it is well known from studying evanescent wave coupling and resonant inductive coupling that evanescent modes will NOT couple to another medium unless the other medium is resonant at that exact mode. So this mode of interaction is not a possibility.
http://en.wikipedia.org/wiki/Evanescent_wave#Evanescent-wave_coupling
http://en.wikipedia.org/wiki/Resonant_inductive_coupling
http://en.wikipedia.org/wiki/Wireless_power
I think this definitively puts evanescent wave theories to bed.
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#713 by Rodal on 16 Feb, 2015 20:57
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To be thorough, if "the drive" means the pillbox-shaped cavity that's correct, if the "the drive" means the truncated cone (frustum), no:...
Have any tests been done reversing the drive?
Both the test run that was reported on in Brady et al and the test run that Star-Drive talked about have included running the drive in a reverse orientation.
Only the Cannae pillbox cavity was reported to run in a reversed configuration in the Brady et.al. report ( http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf ), on test runs 1B and 2B, as reported in the text, and summarized in Table 1. Cannae Testing: Summary of Results and Conclusions and illustrated on Figure 11. Cannae Test Article on Torsion Pendulum (thrust to the right, a.k.a. reverse orientation).
The Brady et.al. paper does not report a single test with the truncated cone (frustum) run in the reverse configuration.
The first instance in which the truncated cone was reported to have been run in a reverse configuration is the recent disclosure by Paul March, under hard vacuum. -
#714 by birchoff on 16 Feb, 2015 21:33
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To be thorough, if "the drive" means the pillbox-shaped cavity that's correct, if the "the drive" means the truncated cone (frustum), no:...
Have any tests been done reversing the drive?
Both the test run that was reported on in Brady et al and the test run that Star-Drive talked about have included running the drive in a reverse orientation.
Only the Cannae pillbox cavity was reported to run in a reversed configuration in the Brady et.al. report ( http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf ), on test runs 1B and 2B, as reported in the text, and summarized in Table 1. Cannae Testing: Summary of Results and Conclusions and illustrated on Figure 11. Cannae Test Article on Torsion Pendulum (thrust to the right, a.k.a. reverse orientation).
The Brady et.al. paper does not report a single test with the truncated cone (frustum) run in the reverse configuration.
The first instance in which the truncated cone was reported to have been run in a reverse configuration is the recent disclosure by Paul March, under hard vacuum.
Thanks for setting me straight on that. I believe I did get the pill box and frustum results mixed up in my memory. -
#715 by birchoff on 16 Feb, 2015 21:38
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Aside from re running the reverse orientation tests. Are there any other tests that Eagleworks needs to run. I am aware that they need to get to a certain performance level before then can hand off for replication attempt. But for the life of me the only other test case I can think of wanting results for is
* Re Run frustum reverse orientation in Hard vacuum
* Run forward and reverse orientation of frustum in a null configuration -
#716 by Star One on 16 Feb, 2015 21:44
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Aside from re running the reverse orientation tests. Are there any other tests that Eagleworks needs to run. I am aware that they need to get to a certain performance level before then can hand off for replication attempt. But for the life of me the only other test case I can think of wanting results for is
* Re Run frustum reverse orientation in Hard vacuum
* Run forward and reverse orientation of frustum in a null configuration
If it is handed off for a replication attempt, is this to be done in more than one other location, in other words are multiple teams to attempt this or just one? -
#717 by birchoff on 16 Feb, 2015 21:55
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Aside from re running the reverse orientation tests. Are there any other tests that Eagleworks needs to run. I am aware that they need to get to a certain performance level before then can hand off for replication attempt. But for the life of me the only other test case I can think of wanting results for is
* Re Run frustum reverse orientation in Hard vacuum
* Run forward and reverse orientation of frustum in a null configuration
If it is handed off for a replication attempt, is this to be done in more than one other location, in other words are multiple teams to attempt this or just one?
My understanding is given what was said in the conclusion of the Brady et al paper is that they want to create a testable unit to be used by Glen Research Center and JPL and Johns Hopkins. However, I believe of the two NASA centers only Glen has signed on. No clue on whether or not Johns Hopkins has also signed on. Which is the reason they need to get the thrust levels up because the Balance at Glen has a much higher floor of detectable thrust. -
#718 by Rodal on 16 Feb, 2015 22:34
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How hard would it be to put the 1165 inside a more vacuum resilient container?
This appears to be a great finding, Mulletron, thanks for pointing it out. If the Amp that Eagleworks has been using is not rated for the hard vacuum (5*10^(-4) Torr) in their tests, do you have a best suggestion on how they should proceed?
http://www.empowerrf.com/pdfs/1165.pdf
Notice the paper says max altitude 50K feet!
It is operating beyond specs in that vacuum.....why they keep dying!
We gotta figure this out, pronto! -
#719 by Mulletron on 16 Feb, 2015 22:38
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Nope, sealing things up like that is beyond my expertise. No clue how to help. Anyone?How hard would it be to put the 1165 inside a more vacuum resilient container?
This appears to be a great finding, Mulletron, thanks for pointing it out. If the Amp that Eagleworks has been using is not rated for the hard vacuum (5*10^(-4) Torr) in their tests, do you have a best suggestion on how they should proceed?
http://www.empowerrf.com/pdfs/1165.pdf
Notice the paper says max altitude 50K feet!
It is operating beyond specs in that vacuum.....why they keep dying!
We gotta figure this out, pronto!
So why does it have to be inside the chamber again? Can't rf be piped in somehow?
