-
#700
by
aero
on 19 Aug, 2015 00:10
-
Everything is the same. I also checked the Poynting vector plots, the stress plots, and the force plots. All identical to the antenna near the small base. I also have plots of the fields in other directions showing the antenna is at the small base.
Yea - the log files confirm the antenna was the same. Re-checking resonance now.
-
#701
by
SeeShells
on 19 Aug, 2015 00:46
-
Well that sucks.
As we say out West... Yeeiup.
From what I understand meep stops at the surface boundary of the walls with Maxwell. A Senior Physics student majoring in high energy physics mentioned it to me about the limits of meep, never verified it though, although it makes sense.
Calling //ElizabethGreen. What did you find out when you said you thought you were seeing evanescent waves out the top of the frustum and were waiting for some equipment to arrive and check. Any news yet?
Ok, poo on the Yang-Shell 6 degree sides. It means I'm modifying and running with the Crazy-Eddie-Drive build with the ceramic plates. So I need to push a little harder.
Shell
PS: The new anti-vibration platforms seem to be working, still need to let it set another day.
-
#702
by
Prunesquallor
on 19 Aug, 2015 01:03
-
It is way, way too early to start jumping to conclusions. Anyone who does is not being fair. Until open and replicated experimental data is available, it's all noise as far as I'm concerned. As matters stand, there is nothing that is open and replicated.
The ironclad test is a space test. This cannot readily be fooled with artifacts. What's required for that is twin units in reasonably close proximity, one powered and one not, and in all other respects identical.
I know I'm a broken record, but IMHO there are many more uncontrollable factors in low earth orbit than in the lab, considering the minscule power available for the thruster on a cubesat.
-
#703
by
Prunesquallor
on 19 Aug, 2015 01:12
-
The new version of the baby-EmDrive, 3D-printed and silver-plated has been received by the folks at hackaday.io!
Db = 29.64 mm
Ds = 16.12 mm
L = 21.87mm
+ cylindrical neck for tuning = 5mm
Antenna placement near the small base = 5.5 mm below cylindrical neck
Excitation frequency between 24 an 25 GHz.
Several modes predicted and very close from each others (TE013, TE114 and TM113) according to TT's spreadsheet.
Flat ends plates to begin with, but spherical ends are doable too.
Shot glass to the stars!
-
#704
by
Rodal
on 19 Aug, 2015 01:36
-
Well that sucks.
...From what I understand meep stops at the surface boundary of the walls with Maxwell. A Senior Physics student majoring in high energy physics mentioned it to me about the limits of meep, never verified it though, although it makes sense. ...
The reason why Meep is an open source code is for users to write their own code to introduce whatever equations they want to use for the walls, etc. Many papers I have seen where Meep is used, it is not used as a black box but the researchers write the new parts of the code necessary for their research. Similarly, Wolfram Mathematica out of the box cannot post-process Meep data to calculate the Poynting vector, stress tensor, etc. I had to write code in Wolfram Mathematica to be able to ouput the stress, I had to write code to make the vector plots, etc..
Therefore open codes that enable the user to write their own code do not have limitations, as anything that can be analyzed certainly can be coded (as proved by von Neumann). If there is an equation that expresses quantum tunneling as a function of the wall thickness, material, and the surrounding electromagnetic fields, that equation can in principle be coded into Meep (or into Wolfram Mathematica, or into C). At that point, the question is rather what code is more expedient to program. Rather the statement has to be qualified to read instead "out of the box, Meep..."
-
#705
by
SeeShells
on 19 Aug, 2015 02:11
-
Well that sucks.
...From what I understand meep stops at the surface boundary of the walls with Maxwell. A Senior Physics student majoring in high energy physics mentioned it to me about the limits of meep, never verified it though, although it makes sense. ...
The reason why Meep is an open source code is for users to write their own code to introduce whatever equations they want to use for the walls, etc. Many papers I have seen where Meep is used, it is not used as a black box but the researchers write the new parts of the code necessary for their research. Similarly, Wolfram Mathematica out of the box cannot post-process Meep data to calculate the Poynting vector, stress tensor, etc. I had to write code in Wolfram Mathematica to be able to ouput the stress, I had to write code to make the vector plots, etc..
Therefore open codes that enable the user to write their own code do not have limitations, as anything that can be analyzed certainly can be coded (as proved by von Neumann). If there is an equation that expresses quantum tunneling as a function of the wall thickness, material, and the surrounding electromagnetic fields, that equation can in principle be coded into Meep (or into Wolfram Mathematica, or into C). At that point, the question is rather what code is more expedient to program. Rather the statement has to be qualified to read instead "out of the box, Meep..."
Stand corrected so I'll make it so... "out of the box, Meep..."
-
#706
by
aero
on 19 Aug, 2015 02:23
-
That is exactly right, just about. (because I don't know any better, but maybe ...)
Here is a nice paper on electron tunnelling. I have found those same equations (same form) describing evanescent waves propagating through a wave guide below cutoff frequency. I like this paper because ISU is my school.
http://tuttle.merc.iastate.edu/ee439/topics/tunneling.pdfI have made the effort to code the final equation up in Maxima and got an answer that I didn't like. Maybe an understanding of the physics, barriers and the cavity energies would help to get an answer with assurance, an understanding that is beyond me. It would be nice to know if Q needs to be greater than 10
50, because such an answer would rule out tunnelling based on current knowledge.
-
#707
by
deltaMass
on 19 Aug, 2015 02:35
-
Here is an EM Drive test that we can all do in a bathtub (no, a hot tub is not required) without having to worry about dangerous magnetrons, or getting electrocuted.
EM Drive 2D simulation by Grzegorz Maj using water as a medium (not the first time that a physics problems with waves has been analyzed using water as an analog) "the Water Drive"
Droplets falling on the Water Drive are used to create waves inside the Water Drive.
Notice that it moves towards the big base.
https://www.youtube.com/watch?t=77&v=VEacNk2uFaM
Suggestion: try other shapes (squares, circles, trombone, etc.).
That's most unscientific. The intrinsic x-y momentum of the driving source is not examined and not controlled for. The least one could do to be honest here is to flip the shape around so that now the small end faces right.
-
#708
by
deltaMass
on 19 Aug, 2015 02:38
-
It is way, way too early to start jumping to conclusions. Anyone who does is not being fair. Until open and replicated experimental data is available, it's all noise as far as I'm concerned. As matters stand, there is nothing that is open and replicated.
The ironclad test is a space test. This cannot readily be fooled with artifacts. What's required for that is twin units in reasonably close proximity, one powered and one not, and in all other respects identical.
I know I'm a broken record, but IMHO there are many more uncontrollable favors in low earth orbit than in the lab, considering the minscule power available for the thruster on a cubesat.
I'm surprised that you think the protocol I described is that flawed. Obviously, as well, you'd want to repeat the experiment with the other one powered and the original (powered) one now unpowered.
-
#709
by
wallofwolfstreet
on 19 Aug, 2015 04:29
-
Something that I've been thinking about a bit recently: where are Shawyer's previous emdrive builds, and is there any sort of avenue there for an independent replication?
Correct me if I'm wrong, but Shawyer constructed at least three different emdrives and their attendant testing platforms over the last 15 years (the feasibility rig, the demonstrator and the flight thruster) as well as a possible yet unconfirmed superconducting design. Surely these rigs still exist, as I can see no reason why he would have dismantled them. Given that this is the case, perhaps one of the simplest avenues for an independent replication (i.e. an independent body works with the exact same device and determines whether or not they can get the exact same (within error margin) force measurement) would simply be for him to supply his prebuilt emdrives to one of the many replicators clamoring for a drive?
So I suppose I am aiming this question more or less to TheTraveller: Has Shawyer ever expressed any interest in having his previously built and tested rigs be subjected to external examination by an independent authority? While that may have been impossible before, surely the recent and growing media exposure will have interested a few reputable academics in doing such independent testing. If not, maybe you, as the liaison of this forum to Shawyer, could ask him if he is interested in such a thing?
-
#710
by
deltaMass
on 19 Aug, 2015 04:53
-
You theorise as if this were about science. Shawyer runs a company. If he were to do as you suggest, he would have no control over the situation. Thus if a null result were found - or yet, a null result fabricated - he is powerless to act.
-
#711
by
ThinkerX
on 19 Aug, 2015 07:17
-
Ok...latest thing I have been wondering (as per earlier conversation with Doctor Rodal)
Would an 'electromagnetic Dean Drive' actually move itself (and attached spacecraft) in space? Aka high earth orbit or interplanetary space. (Because 'electromagnetic Dean Drive' is what Rodal has mentioned more than once.)
The reduced thrust in a vacuum bothers me here. As Shell says, giant red flag. Also wonder how much of a vacuum for these tests as compared with very high orbit or interplanetary space.
Another red flag is Shawyer electing to focus on EM Drive uses for within an atmosphere. From a straightforward engineering perspective, he knows the capabilities of these devices better than anybody - maybe. He must have a great deal of unreleased test data.
Starting to suspect that a fully depressurized EM Drive in high orbit/interplanetary space would either
1) not move the spacecraft; OR
2) have a performance comparable to a photon rocket. Best case might be thrust a few dozen times that of a photon rocket for unclear reasons.
Still wondering if a pressurized EM Drive in high orbit / interplanetary space would produce thrust comparable to tests in atmosphere. Question becomes - pressurized with what?
-
#712
by
Chrochne
on 19 Aug, 2015 08:18
-
-
#713
by
SeeShells
on 19 Aug, 2015 08:49
-
Ok...latest thing I have been wondering (as per earlier conversation with Doctor Rodal)
Would an 'electromagnetic Dean Drive' actually move itself (and attached spacecraft) in space? Aka high earth orbit or interplanetary space. (Because 'electromagnetic Dean Drive' is what Rodal has mentioned more than once.)
The reduced thrust in a vacuum bothers me here. As Shell says, giant red flag. Also wonder how much of a vacuum for these tests as compared with very high orbit or interplanetary space.
Another red flag is Shawyer electing to focus on EM Drive uses for within an atmosphere. From a straightforward engineering perspective, he knows the capabilities of these devices better than anybody - maybe. He must have a great deal of unreleased test data.
Starting to suspect that a fully depressurized EM Drive in high orbit/interplanetary space would either
1) not move the spacecraft; OR
2) have a performance comparable to a photon rocket. Best case might be thrust a few dozen times that of a photon rocket for unclear reasons.
Still wondering if a pressurized EM Drive in high orbit / interplanetary space would produce thrust comparable to tests in atmosphere. Question becomes - pressurized with what?
Ya know ThinkerX we all are wondering if it would work in the vacuum of space, away from gravitational influence. Catch here, if we have a hard time making this work here on the ground in a controlled environment, it's not ready for space. Yet.
Find out why the reduced thrust in vacuum, correct for it if you can, use it to an advantage if you can. Get stable thrusts time and time again, picking it apart bit by bit, little by little, little steps at a time, logging all the data. Building your theories, your data.
I'm reminded of the time of the Wright brothers and all those who thought they had human flight down with their contraptions and weird gizmos, they crashed, failed or died trying. Then the Wright bros did it right, built scale models, built (I think one of the very first) wind tunnels to test the models in and little by little bit by bit, logging it all ... flew and changed our world. Over a hundred years latter that basic science still rings true.
Patience Grasshopper, this isn't MacGyver (the old TV show) where with a piece of chewing gum, a bobby pin, a used battery from a personal vibrator and foobiedustballs builds a interstellar rocket. This dang thing needs to be nitpicked apart bit by bit.
Ok, back to bed, perchance to dream.
Shell
-
#714
by
OttO
on 19 Aug, 2015 08:55
-
An interesting article about measurement of resonant modes
[EDIT] and position of antenna.
Dielectric square resonator investigated with microwave experimentshttp://www.researchgate.net/profile/Barbara_Dietz/publication/263736539_Investigation_of_a_Dielectric_Square_Resonator_with_Microwave_Experiments
/links/547485350cf2778985abe4a0.pdf
"gives an overview of the number of modes with a given symmetry that were unambiguously identi fied for the diff erent positions of the excitation antenna"
-
#715
by
RERT
on 19 Aug, 2015 09:55
-
Dr.Rodal -
I've thought about the problem of the side wall forces, and nothing occurs to me to to explain why they might reliably net to zero, even in the light of your comments. That they net to zero may be the case, but it is not obvious: unless I'm mistaken you yourself were asking for meep data at the walls to calculate forces some number of thousand posts ago. The answer wasn't obvious to you then and it isn't obvious to me now.
Please can you give a straightforward answer as to what your argument is? Please don't bother to repeat or approximate another sequence of astoundingly condescending and arrogant questions. Throughout this discussion, right or wrong, I've tried to remain civil, constructive and adult. I'd be very grateful if you could do the same, and just respond quickly and to the point.
Thanks in advance,
R.
-
#716
by
graybeardsyseng
on 19 Aug, 2015 11:22
-
...
On the top of my rotary table but under all the equipment will be a thin copper layer that will serve as my reference ground plane. Everything will be grounded to this high frequency ground reference plane.
...
Anybody who has ever designed and debugged a high frequency pcb knows the value of a solid copper ground plane.
So yes ground loops can be a problem but not if using a large area solid copper ground plane with additional high frequency decoupling capacitors and ferrite donuts.
At 2.4 GHz ferrite donuts are not needed. Instead an air core inductor inline with each power lead that is not at ground potential is all that is needed. Filter caps on either side of the inductor are used to prevent voltage sag from current transients. They are a high impedance path to RF. But since the inductor only needs to be a few nH. caps are not needed.
The fustrum is your ground plane. No thin copper sheet is needed. Any conductors going to this ersatz ground plane will be many wavelengths long. So it is impossible to make this copper sheet a ground at RF.
The biggest problem with driving a fustrum from a coax feed is matching the loop inside the cavity. It is virtually impossible to make the loop exactly the right length so it will almost never be a 50 Ohms resistive load at the frequency used. It will always be capacitive because of the adjacent cavity walls. So a large part of the RF sent into the cavity will just get reflected back on the shield. Ferrites are only useful up to VHF frequencies so putting ferrite donuts on the coax will have no effect. Maybe coiling the coax will help but a lot of RF will still get radiated because of the mismatch. Matching networks can be used but in that case the return wave is just dissipated in the matching network.
Quite right - there is a very significant difference between power grounding and RF grounding. At the appoximately 12cm wavelengths most folks are working with (2.45 Ghz or thereabout) any ground lead longer than about 6cm is also a pretty decent radiator. Google RF grounding - there is wealth of info about it. Power and safety ground are also very important.
Just a comment from those using loop antennas. Loop antennas are magnetic antenna and work differently from antennas like dipoles and monopoles. The common circumference for loop antennas is on the order of 1 lambda not lambda/2. A half wavelength circmumference will have a VERY high input impedance and will be hard to couple. A full wavelength loop will be significantly closer to 50 ohms, although wavelength variations due to excited mode and geometry of the cavity will also have significant effects. I will try to model up some example loops and patterns later today/tonight when I have access to the software.
Herman
I thought a 1/10 wave loop or even a simulating square loop would work well and aero and imbfan have tried to model it in meep, although it's a very tough nut to crack in the meep software.
I would love to see your models.
Shell
Sorry this has taken so long to get results on modeling. Family responsibilities keep interrupting important EMDRIVE work
. Anyway I modeled several loops - all using #18gauge (very close to 1mm) copper wire, located 1/2 wavelength above "perfect" ground. All driven at 2450 Mhz. Models are all based on 24 element, 7segments per element, fed at point closest to ground plane.
Shell - I haven't gotten the tenth wavelength model working yet - keep getting geometry errors from NEC. Still working and will report as soon as possible. lambda/10 and smaller loops are 'different' - very sharp tuning and critical. Often losses in the loop material swamp the radiation resistance.
Anyway - here are the input impedances for the various cases.
one lambda loop : Z = 96.9 - j91.5 ohms
half lambda loop : Z = 553 - j87.6 ohms
two lambda loop : Z = 200 - j38 ohms
I will post far field patterns this evening. Have to go to that darn work stuff.
Herman
-
#717
by
rfmwguy
on 19 Aug, 2015 14:01
-
NSF-1701 update...all is now complete and the unit is mounted on the balance beam including oil dampener plus electrodes/cups waiting for galinstan! I't try and do a video walkound of the completed test stand tonight. Once the galinstan arrives, I'll do the test. Still have to attach laser and set up mirrors and target, but for all intents and purposes...its ready to go! Wish me luck.
-
#718
by
graybeardsyseng
on 19 Aug, 2015 15:14
-
Sorry this has taken so long to get results on modeling. Family responsibilities keep interrupting important EMDRIVE work . Anyway I modeled several loops - all using #18gauge (very close to 1mm) copper wire, located 1/2 wavelength above "perfect" ground. All driven at 2450 Mhz. Models are all based on 24 element, 7segments per element, fed at point closest to ground plane.
Shell - I haven't gotten the tenth wavelength model working yet - keep getting geometry errors from NEC. Still working and will report as soon as possible. lambda/10 and smaller loops are 'different' - very sharp tuning and critical. Often losses in the loop material swamp the radiation resistance.
Anyway - here are the input impedances for the various cases.
one lambda loop : Z = 96.9 - j91.5 ohms
half lambda loop : Z = 553 - j87.6 ohms
two lambda loop : Z = 200 - j38 ohms
I will post far field patterns this evening. Have to go to that darn work stuff.
Herman
May I ask:
1) why you used 1/2 wavelength above the ground plane and not 1/4 wave?
2) are these loop models parallel to the ground plane (same 1/2 wave spacing to the ground plane at all points of loop circumference) or orthogonal to it?
3) lambda at 2.45GHz is 122.33mm, so a 2 lambda loop is 244.67mm in circumference and 77.9mm in diameter?
Thanks so much for the information. Most appreciated.
Good Questions.
WRT
1) Old ham radio influence. We (hams) often try to mount antennas as high as possible, up to about 1/2 wavelength, in order to maximize the low angle radiation (which is generally speaking "good" for long distance communications on lower bands). I will run at 1/4 lambda high also and post results for both. (changing height above ground is very easy).
2) The plane of the loop here is normal to the surface, so orthogonal. Most diagrams (not all by any means) I have seen for driving waveguides/cavities used this orientation so I did this first. I will also run some parallel to the ground plane as well - a little harder than changing height but not too bad.
3) Yes, that is what I used.
Hope this helps,
Herman
-
#719
by
Star One
on 19 Aug, 2015 15:22
-
NSF-1701 update...all is now complete and the unit is mounted on the balance beam including oil dampener plus electrodes/cups waiting for galinstan! I't try and do a video walkound of the completed test stand tonight. Once the galinstan arrives, I'll do the test. Still have to attach laser and set up mirrors and target, but for all intents and purposes...its ready to go! Wish me luck.
I will wish you good luck.
Yea - the log files confirm the antenna was the same. Re-checking resonance now.
. Anyway I modeled several loops - all using #18gauge (very close to 1mm) copper wire, located 1/2 wavelength above "perfect" ground. All driven at 2450 Mhz. Models are all based on 24 element, 7segments per element, fed at point closest to ground plane.