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#1580 by Rodal on 11 Jan, 2016 01:00
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We are in thread 6 now of the EM Drive. Has anybody derived what are the most efficient dimensions of the resonant cavity at radio frequencies ?
Yes, one can show this mathematically...
The bigger the better. Those pursuing small cavities are pursuing inefficient designs.
I'll be posting details and calculations on the days to come.
What got me thinking about this was re-reading MIT's Professor Arthur Von Hippel's book on his work during WWII at the Radiation Laboratory on dielectrics, waveguides and resonators and what he said about the quality factor of resonance Q.
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#1581 by meberbs on 11 Jan, 2016 01:06
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]So someone is using a cut-off formula which is known to apply only for an open waveguide, whereby the waveguide is completely filled with a dielectric medium with relative permittivity 2.2 (going from memory here) opening into what? What happens at the opening? How is this related to a closed resonant cavity, with copper walls, whereby there are two HDPE disks inserted at the small end, and there is no opening?
What happened to the difference we learnt at school between an open waveguide and a closed cavity?
Waiting for your cutoff & guide wavelength small end calcs for either the EW copper frustum or that of RfPlumber with and without a dielectric.
Serious, I'm interested to see your results and how you obtained them. You can do this?
Guide wavelength as normally defined is not a concept that even makes sense for a resonating cavity, unless I have missed something where you have given a definition that applies to a closed cavity.
Cutoff of the small end is also not clearly defined. You would have to define something such as lowest resonant frequency that near the small end looks similar to one of the mode types for a cylindrical cavity. (A good rigorous definition of this would be difficult)
For some geometry ratios, there could be resonant frequencies of the cavity that would have mode shapes that appear different from those of a cylindrical cavity. Without doing math, it is easy to show that resonances could exist below your calculation for a small end cutoff, by considering the limit where you take the small end diameter to 0, resulting in a cone. This would still be able to resonate without requiring x-ray frequencies. Whether these types of modes would be better or worse for thrust generation (assuming there is any to begin with) is completely unknown, since no experiments have claimed to excite that type of mode. Shawyer's advice is only worth taking for things he has done experiments on, due to the issues with his "theory". I have seen no reports of him actually experimenting with a "small end cut-off" mode shape. -
#1582 by oliverio on 11 Jan, 2016 01:09
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We are in thread 6 now of the EM Drive. Has anybody derived what are the most efficient dimensions of the resonant cavity ?
Yes, one can show this mathematically...
The bigger the better. Those pursuing small cavities are pursuing inefficient designs.
I'll be posting details and calculations on the days to come.
What got me thinking about this was re-reading MIT's Professor Arthur Von Hippel's book on his work during WWII at the Radiation Laboratory on dielectrics, waveguides and resonators and what he said about the quality factor of resonance Q.
I did see a paper mentioning using small optical cavities made from a specific material achieving Q factors over 10^7 if I recall correctly. Let me dig it up. (This is under laboratory conditions of course.)
If the emdrive effect is real, I see great potential in high-wavelength small cavities. A lot of investment is already moving towards this kind of tech for photonic computation and such, which helps lower the costs. -
#1583 by Rodal on 11 Jan, 2016 01:17
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We are in thread 6 now of the EM Drive. Has anybody derived what are the most efficient dimensions of the resonant cavity ?
Yes, one can show this mathematically...
The bigger the better. Those pursuing small cavities are pursuing inefficient designs.
I'll be posting details and calculations on the days to come.
What got me thinking about this was re-reading MIT's Professor Arthur Von Hippel's book on his work during WWII at the Radiation Laboratory on dielectrics, waveguides and resonators and what he said about the quality factor of resonance Q.
I did see a paper mentioning using small optical cavities made from a specific material achieving Q factors over 10^7 if I recall correctly. Let me dig it up. (This is under laboratory conditions of course.)
If the emdrive effect is real, I see great potential in high-wavelength small cavities. A lot of investment is already moving towards this kind of tech for photonic computation and such, which helps lower the costs.
OK you can have nano cavities like these:
http://www.nature.com/nature/journal/v425/n6961/full/nature02063.html
but these use light, instead of radio frequency. I was referring to using radio-frequency.
Besides, to quote:
<< a high-Q cavity of optical wavelength size is difficult to fabricate, as radiation loss increases in inverse proportion to cavity size. With the exception of a few recent theoretical studie, definitive theories and experiments for creating high-Q nanocavities have not been extensively investigated. Here we use a silicon-based two-dimensional photonic-crystal slab to fabricate a nanocavity with Q = 45,000>>
and
http://www.nature.com/nmat/journal/v4/n3/full/nmat1320.html
<<which has resulted in the realization of nanocavities with extremely high-Q factors of 600,000, more than one order of magnitude higher than any previous reports. We have also shown theoretically that Q-factors greater than 20,000,000 may be obtained when optimizing the structure.>> -
#1584 by TheTraveller on 11 Jan, 2016 01:18
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Guide wavelength as normally defined is not a concept that even makes sense for a resonating cavity, unless I have missed something where you have given a definition that applies to a closed cavity.
Cutoff of the small end is also not clearly defined. You would have to define something such as lowest resonant frequency that near the small end looks similar to one of the mode types for a cylindrical cavity. (A good rigorous definition of this would be difficult)
For some geometry ratios, there could be resonant frequencies of the cavity that would have mode shapes that appear different from those of a cylindrical cavity. Without doing math, it is easy to show that resonances could exist below your calculation for a small end cutoff, by considering the limit where you take the small end diameter to 0, resulting in a cone. This would still be able to resonate without requiring x-ray frequencies. Whether these types of modes would be better or worse for thrust generation (assuming there is any to begin with) is completely unknown, since no experiments have claimed to excite that type of mode. Shawyer's advice is only worth taking for things he has done experiments on, due to the issues with his "theory". I have seen no reports of him actually experimenting with a "small end cut-off" mode shape.
Clearly Roger has experimentally discovered what works and what does not. His 0.82 cutoff rule is one example. -
#1585 by TheTraveller on 11 Jan, 2016 01:24
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Seems "emdrive" has been Trademarked under: "Vehicles and Products for locomotion by land, air or water"
http://www.scoop.it/t/emdrive/p/4057811868/2016/01/06/emdrive-trademark-registered-by-voith-patent-gmbh-dr-weitzel&ved=0ahUKEwiIof6Z2aDKAhUnMKYKHSoIDpoQFggiMAI&usg=AFQjCNEiZmljefL6tVHOJDQ4vr6dE7VjKg&sig2=CkJEuUJP8DSwBlzbZIy0kg -
#1586 by Rodal on 11 Jan, 2016 01:26
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Seems "emdrive" has been Trademarked under: "Vehicles and Products for locomotion by land, air or water"
Trademarked by Voith a number of years ago. Voith is a great company with great people, the best !. I used to be VP R&D for Voith at one of its divisions
https://www.google.com.au/url?sa=t&source=web&rct=j&url=http://www.scoop.it/t/emdrive/p/4057811868/2016/01/06/emdrive-trademark-registered-by-voith-patent-gmbh-dr-weitzel&ved=0ahUKEwiIof6Z2aDKAhUnMKYKHSoIDpoQFggiMAI&usg=AFQjCNEiZmljefL6tVHOJDQ4vr6dE7VjKg&sig2=CkJEuUJP8DSwBlzbZIy0kg
, and used to go to Heidenheim every few months. 
Great German Engineering !
_____________________________________________________________________________
EmDrive Motor-Gear-Unit
http://www.voith.com/en/products-services/power-transmission/motor-gear-unit-10190.html -
#1587 by A_M_Swallow on 11 Jan, 2016 01:33
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We are in thread 6 now of the EM Drive. Has anybody derived what are the most efficient dimensions of the resonant cavity ?
Yes, one can show this mathematically...
The bigger the better. Those pursuing small cavities are pursuing inefficient designs.
I'll be posting details and calculations on the days to come.
What got me thinking about this was re-reading MIT's Professor Arthur Von Hippel's book on his work during WWII at the Radiation Laboratory on dielectrics, waveguides and resonators and what he said about the quality factor of resonance Q.
To maximise efficiency the bigger the better is easy to believe. However in real life the cavity is restricted to the size of the satellite. Consequently most cavities will be sized to fit into a cubesat - 10 cm * 10 cm * 10 cm.
The other significant limitation is the size of launch vehicle fairings. The Falcon 9 fairing is 13.1 m height and 5.2 m in diameter, the maximum payload diameter is 4.6 m. This could be used for tugs to the Moon, Mars and beyond. -
#1588 by mwvp on 11 Jan, 2016 01:39
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(The following addresses cutoff and cascading frustrums, BTW)
I've begun the daunting task of writing up, analyzing, simulating and perhaps even building an EM Drive, as I understand it.
I call this the "NEPSOP (New Propulsion, Same Old Physics) conjecture". Or perhaps I'll call it the "Nibiruian Conjecture" (please don't ask why). Or perhaps you can suggest a better name. Anyways, for your bemusement, if not edification...
The EM Drive is a dispersive, dissipative, high-Q conical resonator energized by microwaves at its resonant frequency. It exhibits either acceleration amplification and microwave damping, or acceleration damping and microwave amplification, depending on the direction of the acceleration applied to it. It is a thermodynamic, open, not closed system.
Cavity energy is dissipated due to waveguide skin losses, especially at the base. Dispersion is a key characteristic of the conical resonator. Acceleration causes Doppler spreading of the reverberating microwaves. Dispersion filters the lower sideband of the acceleration induced Doppler-spread energy for enhanced dissipation into heat at the base. A net unbalanced radiation pressure results, enhancing (or retarding according to orientation) the initiating acceleration. An extraordinary negative inertial resistance or inertial ratcheting will be a consequence, along with exhaust heat flux.
Since radiation pressure = 2 P / c , for a reflector, and P / c for an absorber, the ratio of base absorption and thermal dissipation to that of the apex, is that radiation pressure unbalance, that results in thrust. So oddly, thrust is the result of absorbed coherent microwave energy converted to heat in the base.
The efficiency can be improved by adding yet another stage - a second frustrum, tuned and excited by the first stages exhausted lower sideband. And a third stage again. The first stage contributes 50% to impulse, the second 25%, and the third, most likely final stage 12%. Such cascades are similarly exemplified in turbo-jet engines, and photosynthesis.
A waveguide can act as a high-pass filter. Waveguides are described using a propagation constant, gamma, composed off components alpha and beta. Near cutoff, the attenuation constant alpha and phase constant beta can display significant rate of change. In the context of the EM Drive, it is desirable to stay clear, stay on the high-side, of cutoff, due to the effects of alpha attenuating the energy; reducing the Q and energy intensity that gives us the radiation pressure and thrust. Yet, due to the large phase change of beta into the attenuating cutoff zone, greater Doppler red-shifting can be obtained from dispersion, therefore greater attenuation of the lower sideband, therefore greater acceleration amplification.
See https://en.wikipedia.org/wiki/Propagation_constant
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#1589 by TheTraveller on 11 Jan, 2016 01:40
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Consequently most cavities will be sized to fit into a cubesat - 10 cm * 10 cm * 10 cm.
The latest spreadsheet has a worked X band CubeSat thruster design that fits inside a 1U form factor. -
#1590 by TheTraveller on 11 Jan, 2016 01:49
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Seems "emdrive" has been Trademarked under: "Vehicles and Products for locomotion by land, air or water"
Trademarked by Voith a number of years ago. Voith is a great company with great people, the best !. I used to be VP R&D for Voith at one of its divisions
https://www.google.com.au/url?sa=t&source=web&rct=j&url=http://www.scoop.it/t/emdrive/p/4057811868/2016/01/06/emdrive-trademark-registered-by-voith-patent-gmbh-dr-weitzel&ved=0ahUKEwiIof6Z2aDKAhUnMKYKHSoIDpoQFggiMAI&usg=AFQjCNEiZmljefL6tVHOJDQ4vr6dE7VjKg&sig2=CkJEuUJP8DSwBlzbZIy0kg, and used to go to Heidenheim every few months. Great German Engineering !
_____________________________________________________________________________
EmDrive Motor-Gear-Unit
http://www.voith.com/en/products-services/power-transmission/motor-gear-unit-10190.html
Thanks for the link. Where it that unit referred to as an emdrive? Is just called a MGU (Motor Gear Unit) in the linked web page?? -
#1591 by RFPlumber on 11 Jan, 2016 01:51
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While my frustum as-built ended up below cut-off on the small end, I figured it may still be useful to test it as-is before modifying… And so I finally got to try out my test pendulum with a real frustum as opposite to a dummy load…
Can you guess the result?
Well, I am happy to confirm the same findings EW has already reported (at least for a cavity below cut-off).
There is no thrust.
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Thank you very much for carrying out your test and for reporting your Null results. As previously discussed there appear to be several Null, or "inconclusive", results by other people that have not been reported in the EM Drive wiki (*):
http://emdrive.wiki/Experimental_Results
It would be very much appreciated it if you could enter your experimental results in this EM Drive wiki.
_____________________________________________
(*) if Null and "inconclusive" reports are not reported in the same table where positive results are posted, then the table becomes biased towards claimed positive results. We should strive to have all results posted in the table, whether null, positive or "inconclusive"
My pleasure. EmDrive wiki updated (pointing to my NSF report above for now. Will do a summary write-up when I am done testing the remaining configurations). Would have been even better to actually observe some asymmetric force, but presumably it is all because of violated cut-off criteria. It's ok, I will fix it soon and give it another try.
(Folks, I am not sarcastic or otherwise negative to this whole EmDrive thing. In fact, quite the opposite. It is just that I am finding so much smoke and mirrors around what should have been a very simple experiment, that it is starting to look really strange and suspicious...)
I am truly surprised by the magnitude of presumably thermal effects which accompany these tests at ambient pressure. To the point that I think I can describe a sure way of constructing a working "EmDrive" which will successfully pass most of the tests... All it takes is a reasonably hermetical frustum with a pin sized hole at one side. Tell me it isn't so. It is almost like any EmDrive test at ambient pressure needs to first show that the effect (if any) is not because of air flow. IMHO, one of the ways is to demonstrate that the observed directional force actually changes with the Q factor of the cavity while dissipated power stays constant.
For these runs, can you define what each channel is measuring in the run .csv file?
Results for all 8 runs have been post-processed in Excel.
All data files are available at https://drive.google.com/open?id=0B3jbXEyEMvU8R3d3SEp3cmN4dnc. Pendulum platform weight was ~4 kg. Given the 3m suspension from the ceiling, the scale factor is ~13 uN / 1 um of mid-point displacement.
And
Can you clarify your file naming convention so we have a better idea which file means what?
Yes, sure. Ch1 is pendulum position (the value is in Volts, scale is 1V = 1000 um, conversion to force for this run is 1 um ~ 13 uN). Ch2 is High-Voltage on command (0 to 5 V change), Ch3 is RF on command (0 to 5 V change). Each run also includes 3 CSV files for Ch1 min, max and mid-point as-detected.
Test run files are like "BigE-East-2A-Battery-Run1", where BigE - is Big end of the frustum, East/West is direction for the big end, 1A/2A battery is the battery capacity used (the 2A*h battery is approx 100g heavier than the 1A*h, this changes the conversion factor for the platform a little bit, but given it ended up weighting ~ 4kg, the difference is very minor).
Regardless of whether the frustum is oriented East or West the mid-points of pendulum oscillation appear to follow the same pattern during the run (attached).
Those oscillations are pretty nasty and swamping all but the strongest signals.
...
With the oscillation in there swamping everything, I frankly couldn't confirm or deny that you have anything or nothing other than a noisy oscillator that responds well when you apply the high-voltage.
For the reddit trolls, this is neither a positive nor a null result. It's a characterization of a test environment showing measurement concerns prior to a test.
One is welcome to infer one's own conclusions from this data. I, for one, definitely do not see any directional force, let along one being reasonably coincidental with applied RF power. Yet, despite all noise and oscillations I can easily see the electrostatic force, which, btw, in this setup is only around 300-400 uN.
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#1592 by Rodal on 11 Jan, 2016 01:57
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The picture that I showed is the picture of what Voith trademarked as their "EMDrive" Motor Gear Unit
Thanks for the link. Where it that unit referred to as an emdrive? Is just called a MGU (Motor Gear Unit) in the linked web page??
For applications see:
http://resource.voith.com/vt/publications/downloads/1970_e_g_1480_en_atm_broschuere_gear_units_2014-08.pdf
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#1593 by TheTraveller on 11 Jan, 2016 01:59
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I am truly surprised by the magnitude of presumably thermal effects which accompany these tests at ambient pressure. To the point that I think I can describe a sure way of constructing a working "EmDrive" which will successfully pass most of the tests... All it takes is a reasonably hermetical frustum with a pin sized hole at one side.
I plan to address the pin hole hot air jet concern in 2 ways:
1) real time monitoring of internal frustum pressure.
2) acceleration times of 10 to 30 minutes continually operating / accelerating. -
#1594 by TheTraveller on 11 Jan, 2016 02:15
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The picture that I showed is the picture of what Voith trademarked as their "EMDrive" Motor Gear Unit
Thanks for the link. Where it that unit referred to as an emdrive? Is just called a MGU (Motor Gear Unit) in the linked web page??
For applications see:
http://resource.voith.com/vt/publications/downloads/1970_e_g_1480_en_atm_broschuere_gear_units_2014-08.pdf
The image you posted is shown in the PDF, as attached, but not labelled as an emdrive as you did. In fact in the PDF emdrive is never mentioned.
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#1595 by Rodal on 11 Jan, 2016 02:17
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So, count yourself lucky that you have me here to identify it for ya, even when the report never identifies it as such...
The picture that I showed is the picture of what Voith trademarked as their "EMDrive" Motor Gear Unit
Thanks for the link. Where it that unit referred to as an emdrive? Is just called a MGU (Motor Gear Unit) in the linked web page??
For applications see:
http://resource.voith.com/vt/publications/downloads/1970_e_g_1480_en_atm_broschuere_gear_units_2014-08.pdf
The image you posted is shown in the PDF, as attached, but not labelled as an emdrive as you did. In fact in the PDF emdrive is never mentioned.
________
Anyway, the following publication (2015) identifies the same unit with the tradename EMDrive, on page 33:
http://resource.voith.com/vt/publications/downloads/1981_e_g_1570_en.pdf
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#1596 by RFPlumber on 11 Jan, 2016 02:37
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I am truly surprised by the magnitude of presumably thermal effects which accompany these tests at ambient pressure. To the point that I think I can describe a sure way of constructing a working "EmDrive" which will successfully pass most of the tests... All it takes is a reasonably hermetical frustum with a pin sized hole at one side.
I plan to address the pin hole hot air jet concern in 2 ways:
1) real time monitoring of internal frustum pressure.
2) acceleration times of 10 to 30 minutes continually operating / accelerating.
And then some other air-related effect will bite you. Like the attached "chimney" one for my setup, which I am starting to suspect is very real (and is amplified by the large asymmetrical cavity on the platform).
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#1597 by Rodal on 11 Jan, 2016 02:54
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Seems "emdrive" has been Trademarked under: "Vehicles and Products for locomotion by land, air or water"
http://www.scoop.it/t/emdrive/p/4057811868/2016/01/06/emdrive-trademark-registered-by-voith-patent-gmbh-dr-weitzel&ved=0ahUKEwiIof6Z2aDKAhUnMKYKHSoIDpoQFggiMAI&usg=AFQjCNEiZmljefL6tVHOJDQ4vr6dE7VjKg&sig2=CkJEuUJP8DSwBlzbZIy0kg
By the way TT, "Alain" in that link you quote asks who is Dr. WeitzelQuoteAlain ....'s insight: Now is who is Dr Weitzel and who work for Voith having relation with EmDrive...
I have to check but there may be ironic surprises.
ANSWER: Dr. Weitzel, who is a very nice gentleman (an Attorney with a Ph.D. in Mechanical Engineering), was the Director of the patent and license department of Voith, and that's why he is listed as the correspondent for Voith's trademark EmDrive, his firm DR. WEITZEL & PARTNER
http://weitzel-patente.de/ecom/index.php?article_id=12&clang=1
There are no "ironic surprises" about this...
EMDrive is a European trademark that belongs to Voith (see; https://tmdb.eu/trademark_registration/trademark_007201189_ohim_emdrive ) with registration date 13.8.2009 , for this product: (*)
____
(*) In the USA the trademark EMDrive belongs to ElectroMotive Designs LLC (registration date 2012-12-11): https://trademarks.justia.com/778/89/emdrive-77889765.html
http://busride.com/2012/09/full-tilt-power-kicks-in-as-needed/ -
#1598 by TheTraveller on 11 Jan, 2016 02:59
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I am truly surprised by the magnitude of presumably thermal effects which accompany these tests at ambient pressure. To the point that I think I can describe a sure way of constructing a working "EmDrive" which will successfully pass most of the tests... All it takes is a reasonably hermetical frustum with a pin sized hole at one side.
I plan to address the pin hole hot air jet concern in 2 ways:
1) real time monitoring of internal frustum pressure.
2) acceleration times of 10 to 30 minutes continually operating / accelerating.
And then some other air-related effect will bite you. Like the attached "chimney" one for my setup, which I am starting to suspect is very real (and is amplified by the large asymmetrical cavity on the platform).
You need to show the upward heat rising from the frustum, that is assuming it was taking the Rf power. What you are showing is the case if the frustum had a VERY bad VSWR and all the Rf power was reflected back to the amp and thermalised there. -
#1599 by TheTraveller on 11 Jan, 2016 03:08
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EMDrive is a trademark that belongs to Voith, for this product:
I have done a few Trademarks and as I remember the rules, you need to continually display the Tm next to the Trademarked words and note the Trademark ownership somewhere in the document or lose it. But that is Australia and the EU may be different.
Yet in your linked PDF, there is not a Tm next to the words EmDrive nor is the Trademark acknowledged anywhere in the document. EmDrive is only used once.
, and used to go to Heidenheim every few months. 
