Paul Kocyla (@movax on Hackaday.io) just assembled the new Silver baby-EmDrive cavity today and has some questions:
New Cavity Assembled
Got the endplate piston from Jo today. Here´s the assembled cavity.
I got a question for the microwave professionals: There is a small gap between the endplate piston and the cavity walls. What will this mean for the wave propagation?
The piston might touch the cavity on one side. Should I better isolate the cavity wall from the piston, or should it somehow contact the cavity on all sides?
The question is which mode he like to drive.
There are big differences between the fields and currents through the gap for different mode shapes!
Was already discussed here:
http://forum.nasaspaceflight.com/index.php?topic=38203.msg1418675#msg1418675
http://forum.nasaspaceflight.com/index.php?topic=38203.msg1418696#msg1418696
http://forum.nasaspaceflight.com/index.php?topic=38203.msg1418939#msg1418939
I know, that's why I asked him which mode he wants to excite, but he doesn't know. He specifically answered last weeek:
We want to permutate all possible parameters of the EMdrive, which means many positions of the small endplate and a wide frequency spectrum 23-25 GHz. The tests will be run automatically. So there is no specific mode planned
But at such a small size, several modes could overlap near the same frequency, for example TE013, TE114 and TM113.
BTW his antenna is a 1/4 lambda stub of 24 GHz, located near the small end.
I work in the K-band (18–26,5 GHz) with conical cavities some years till now! With a silver plated cavity the resonance bandwidth is to small for overlapping more than 2..3 modes and even this is only random or a tuning problem!
(VNA backed!)
Tell him the can contact me in germany if he like to do so. (first time via PM here)
Tell him the can contact me in germany if he like to do so. (first time via PM here)
Thanks for him! Paul will contact you soon
Anyone else keep having great ideas and insight (mostly while daydreaming and dreaming) only to forget what it was? I dream of photons and copper cans every night.
Anyone else keep having great ideas and insight (mostly while daydreaming and dreaming) only to forget what it was? I dream of photons and copper cans every night.
This is very common: I have books by famous scientists like Poincare, Duhem and others, as well as articles written by mathematician's, physicists, and inventors that some of the best ideas (their aha!) moments often come during dreams. Many of them kept a notebook by their bed to write down their ideas as soon as awake, in order not to forget them. Our unconscious mind keeps thinking about problems while we are asleep.
In vacuum? On an airplane? No way. That's essentially a pressure vessel, no way they'd let that on a plane - way too dangerous. Free-flying in a vacuum requires a spaceflight.
The NASA drop tube that I have indicated operates in vacuum condition.
For the plane and its parabolic trajectory I have suggested the use of a small vacuum chamber around the test device (I agree... nothing afraid me
). But I understand that even if the plane can flight with this test set up, it is impossible to insure that the test device will not hurt the walls of the vacuum chamber. So we forget this idea ...
Remains the possibility of a test within the vacuum drop tube. Now, are 5.3 seconds of free fall time sufficient to measure a thrust variation ? This is an open question.
(video snip)
Can you set up a second camera watching the frustum and rig while the first looks at the paper? Not perfect, but the first thing I'd think of with the camera only recording the laser moving is that you might be physically manipulating the rig. Given that the lights are going to be off, I realize that this would be difficult. Maybe some form of thermal camera? Then again I can understand just wanting the verify that the thing is giving some kind of detectable result before fiddling with it more.
I have a suggestion that might Kill three birds with one stone rfmwguy.
Take your camera and shoot the backside of the graph paper. Easier for your camera to see the red dot without blossoming out from sensitivity to the red light.
You can see the device and the paper in one view if it's set up right.
On the front of the paper run two strips of electrical tape up and down separated by a small gap maybe 1/4 inch. It will help define the movement. Like a vertical bar graph display and make your lines heavy horizontally when you do the graph paper.
One other thing, twist the power leads together and the heater leads together, you'll reduce noise and cancel AC effects the leads may carry.
I also suggested twisting the leads, but I'm not sure the insulation on the red wire is actually 4000V rated. If not, don't do it, it may breakdown through to the other wires. I'm not sure that terminal block is good for 4000V either. Humidity may cause it to arc to ground.
Todd
Have to confess, I did a test firing this AM. No arcs on terminal. Humidity was low. Will measure that on Tuesday. Yes, I'm avoiding anything next to hv insulation. Proper wire for this is silicone insulated...like on oscilloscope test lead, only heavier guage. Could not locate easily.
Spark plug wire from your local auto parts store. You can even get it shielded.
In vacuum? On an airplane? No way. That's essentially a pressure vessel, no way they'd let that on a plane - way too dangerous. Free-flying in a vacuum requires a spaceflight.
The NASA drop tube that I have indicated operates in vacuum condition.
For the plane and its parabolic trajectory I have suggested the use of a small vacuum chamber around the test device (I agree... nothing afraid me ). But I understand that even if the plane can flight with this test set up, it is impossible to insure that the test device will not hurt the walls of the vacuum chamber. So we forget this idea ...
Remains the possibility of a test within the vacuum drop tube. Now, are 5.3 seconds of free fall time sufficient to measure a thrust variation ? This is an open question.
Hadn't thought about a drop tube. That's a really interesting idea. If you could build a device with a few mm/s
2 accel I'm sure you could detect that reliably!
http://www.nasa.gov/audience/foreducators/k-4/features/F_Drop_Everything.htmlNot vacuum though
There was a coupling loop on an EW pic behind the HDPE. It was abt 3.5 cm from edge, which is where mine is.
If you mean this internal picture, the loop was near the 280 mm big base:
I have gone over and checked all the data posted at NSF by Paul March and I fully agree: the NASA Eagleworks copper truncated cone has an antenna mounted on the frustum sidewall approximately 15% of the frustum’s 9.00” length, (~1.35” or 3.43cm), up from the Big Base of the cavity as shown in the image in your post and as shown in their AIAA Brady et.al report.
This is very crucial because NASA's test (which in my opinion are the most trustworthy tests) have been run with the antenna near the Big End.
Thus NASA's tests are in agreement with the Meep computer runs, post-processed with Wolfram Mathematica ( http://forum.nasaspaceflight.com/index.php?topic=38203.msg1418516#msg1418516 ) to analyze the stress tensor and forces that show that it is only when the antenna is located near the Big End that the there is an imbalance of forces pointing towards the small end that cannot be overcome by the reactions from the forces on the side-walls. When the antenna is placed near the small end, the forces from the side wall can overcome the force towards the big end and result in no net force on the truncated cone.
I look forward to RFMWGUY's test with the magnetron at the small end to see what he finds
Doc, can yuo give me the url of paul march's folder again? Thanks...
aero and Dr. Rodel. These are the dims you need to use. Let me know if it's an issue.
Shell
Mod the image.
Doc, nevermind. I found the original EW pic showing the drive antenna on the small end.
This is where I suspect Mr. March was going. Also he had a top-mounted 100 kW Magnetron on a concept drawing.
Its a year after your other pic.
Correction, the drive antenna was in front of the dielectric. Strange looking HDPE, almost looks infused with graphene
Doc, nevermind. I found the original EW pic showing the drive antenna on the small end.
This is where I suspect Mr. March was going. Also he had a top-mounted 100 kW Magnetron on a concept drawing.
Its a year after your other pic.
Correction, the drive antenna was in front of the dielectric. Strange looking HDPE, almost looks infused with graphene
I had forgotten about that design. If my memory serves me correctly, he wrote that they got bad thrust results with that design.
At the time of the discussion we were not running Meep and hence the issue of the antenna location did not come up.
Perhaps the reason why they got bad results has everything to do with the fact that the antenna was at the small end
In vacuum? On an airplane? No way. That's essentially a pressure vessel, no way they'd let that on a plane - way too dangerous. Free-flying in a vacuum requires a spaceflight.
The NASA drop tube that I have indicated operates in vacuum condition.
For the plane and its parabolic trajectory I have suggested the use of a small vacuum chamber around the test device (I agree... nothing afraid me ). But I understand that even if the plane can flight with this test set up, it is impossible to insure that the test device will not hurt the walls of the vacuum chamber. So we forget this idea ...
Remains the possibility of a test within the vacuum drop tube. Now, are 5.3 seconds of free fall time sufficient to measure a thrust variation ? This is an open question.
It's not so much the drop that worries me as the effect on the device of the stop at the end.
Doc, nevermind. I found the original EW pic showing the drive antenna on the small end.
This is where I suspect Mr. March was going. Also he had a top-mounted 100 kW Magnetron on a concept drawing.
Its a year after your other pic.
Correction, the drive antenna was in front of the dielectric. Strange looking HDPE, almost looks infused with graphene
I had forgotten about that design. If my memory serves me correctly, he wrote that they got bad thrust results with that design.
At the time of the discussion we were not running Meep and hence the issue of the antenna location did not come up.
Perhaps the reason why they got bad results has everything to do with the fact that the antenna was at the small end
Could not locate docs on performance related to this specific version. It just seemed it was later than shawyers loop design and only one I could confirm had a dielectric.
(Edit) also note the correct way to measure Q ...2 port.
A couple of models using SeeShell's (and Rodal's) dimensions posted earlier.
Dimensions in both cases are:
bigDiameter = 0.295(*meter*);
smallDiameter = 0.160(*meter*);
axialLength = 0.163(*meter*);
These dimensions on the model with spherical ends are exactly the same. The dimensions of the spherical ends are:
r1= 0.20114 m (*small spherical radius*)
r2= 0.370852 m (*big spherical radius*)
theta = 22.495 degrees (*half cone angle*)
These spherical segments match exactly to the conic section. Note that the axial length is the axial length of the conic section and is not the difference in the radial distance between the two spherical sections. That distance is r2 - r1 = 0.370852 m - 0.20114 m. In the meep model shown, r2 is the
inside radius of the big end spherical section while r1 is the
outside radius of the small end spherical section.
I had a blast doing the flights and would go again in a heartbeat. We had 30+ people on the plane for 4 flight days and nobody got sick.
...
Maybe if you constrained it to fly down a tube...but then the tube has to have all kinds of safety constraints (they're really picky about safety obviously!). It's a hard problem, one I'd LOVE to work on!!
Ok, I understand that it could be really difficult to get any accurate displacement measurement in vaccuum during a parabolic flight.
If you could get the device to behave that way in parabolic flight, why could you not measure the thrust of the same device in the lab? What effect are we eliminating by putting in in free fall? Why not just put it on a air bearing floor?
I agree that in principle the initial thrust can be measured on a static test bench. But I would like to measure precisely how this thrust varies when the speed of the cavity increases under its action. There is a strong rationale to think that the thrust should decrease (or the RF power consumption of the cavity increase ...) when the speed increases.
For what concern the use of a air bearing floor, I suppose that it entails to operate at ambiant pressure and that the unevitable air resistance would too much perturbate the dynamic of the experience.
In vacuum? On an airplane? No way. That's essentially a pressure vessel, no way they'd let that on a plane - way too dangerous. Free-flying in a vacuum requires a spaceflight.
I used to do some Vomit Comet runs. They would allow G-bottles of pressurized air onboard. Don't know if that's substantially different safety-wise as a small vac chamber. The bigger problem may be the roughing pumps etc.
Just to make your day, one of the most bizarre experiments that was onboard one of my flights was a live, but anesthasized pig. The ISS crews were learning how to cauterize and suture injuries in zero-g including bleeding etc. if there's anything that tops off the feeling of nausea after 30-40 parabolas, it's the smell of burning pork.
Brain is locked into loop...
I keep thinking about building the best way to have "clean" resonance patterns by using a one way material, that is "transparent" to microwaves from one side and not from the other.
It would allow the wave guides to be placed at the big or small end (needs to be tested?) and result in very clean internal patterns, even odd shaped ones like trumpet/horn shaped ones.
Technical/scientific English is often an obstacle for me, but i did manage to find a few potential interesting articles. Comprehending what's written, that's another turf...
anyway...the magical words seem to be : nonreciprocal meta-materials. I just cant picture any real material, or find where you - potentially - could buy it....
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.205101
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6565764&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F6558537%2F6565651%2F06565764.pdf%3Farnumber%3D6565764
http://people.ee.duke.edu/~cummer/ElectromagneticMetamaterials.html
Metamaterials aren't really a "material" like copper or aluminum. They are, instead, special arrangements of antennas, small resonators, conductors, and dielectrics. Combining these in clever ways can create optical properties that exist nowhere in nature. In the Phys. Rev. B abstract you linked the yellow PCB (picture C) is the metamaterial. Picture D is an array of them ready to be slid into a waveguide. These are an active exciting area of research, and time spent learning about them certainly won't be wasted. *
*Example: There are "off-the-shelf" split ring resonator and post designs for materials that exhibit negative radiation pressure. These seem _very relevant_ to emdrive research!
There are other ways to isolate a resonator. The latest Yang design used a ferrite Iris and tuning screws to minimize reflected energy back to the magnetron. His prior design used a Microwave Circulator, like a one-way traffic roundabout, to isolate the resonator. Any energy that reflected out of the resonator was passed into a microwave absorber and the energy radiated as heat.
On a related note, BN.com has a couple of <$15 copies of Guru's Electromagnetic Field Theory Fundamentals. I'm working through it now, and am making progress with (despite?) self-taught calculus.
One more plug: Walter Lewin, formerly of MIT, has posted his Physics courses and coursework on youtube. His channel is here:
https://www.youtube.com/channel/UCiEHVhv0SBMpP75JbzJShqwDoes that help?
Apologises for the blackout.
Seems I picked up a super bug during my 2 stays in hospital. So back again where I got the infection. NOT happy about that! Was told it is a low level infection and is curable. I getting a bit concerned that this whole prostate cancer exercise is going from one op and you are done to not looking good. Until my op, last time I was in a hospital was when I was 14 and broke my elbow joint. I'm late 60's, use no meds, pressure, heart rate, cholesterol, etc in middle to low side range for a 40 year old. Don't eat junk food. All fresh and naturally grown fruit and veggies. Lots of Salmon. Do enjoy a glass or 2 of a nice Aussie Shiraz. So this whole hospital experience has really opened up my eyes. These guys just guess at what to do next........................
Had a bad reaction to the 1st round of anti superbug drugs. Had me tripping out. Not good to have a mobile phone when tripping out. Have restored my Google Drive public access. Did delete a few posts here and on Reddit until the nurse took my phone away for a few days.
Have no idea when I will get back home.
Well, the good news is you're back. The bad news is that all those conspiracy theories we hatched up are bunkum
Could not locate docs on performance related to this specific version. It just seemed it was later than shawyers loop design and only one I could confirm had a dielectric.
(Edit) also note the correct way to measure Q ...2 port.
This seems like a good place for Paul March's full post where the referenced image was attached.
I probably speak for many silent readers when I say: This has been the best ongoing discussion I have ever followed on the internet. I am incredibly excited for rfmwguy's upcoming experiments and seeing pictures of Sea Shells' setup and future tests. Thank you everyone for trying to figure this thing out.
http://forum.nasaspaceflight.com/index.php?topic=36313.1100Dr. Rodal & Crew:
The Eagleworks team has already build a 6061 aluminum frustum cavity with 1/4" thick walls and O-ring end caps meant to hold a 1 Bar pressure differential with internal nickel/copper/silver/gold plating system on all interior surfaces with plating thickness of 10-to-15 microns for the first three layers and 0.5 microns for exposed to the RF gold layer. Sadly the gold layer was just as thick as the rest of the plated layers and textured as well, so as far as the applied ~2.0 GHz RF was concerned it was only interacting with the rough gold layer. This had the effect of cutting the resonant Q-factor for this aluminum frustum by almost a factor of three over our copper frustum for the resonances of interest.
At the same time we also tried using a smaller volume, higher-K (e-r=~40) ceramic dielectric resonator discs in the Al cavity mounted at its small OD end, while driving it at its TE011 mode if memory serves. Bottom line was that this configuration was a total bust in regards to thrust production in our torque pendulum system running at this resonant mode. This aluminum frustum design also turned out to be ~4X times the mass of the thin walled copper cavity even while using lower density aluminum for its construction. This exercise was a tribute to the fact that one should never ASSUME that you know what you are doing until proven otherwise! And oh yes, and only try one variation in the design at a time or one will get lost, fast!
Best, Paul M.
