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#2180 by Mulletron on 23 Jan, 2016 22:54
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I have to mention that one lesson I've learned while studying EmDrive is that, without fail, I can find a paper to support any cockamamie idea that I can possibly dream of; even if I stick to only citing information which is deemed reputable, and published in respected journals. I have yet to find any original idea. Confirmation bias is only one of many cognitive biases which one could fall prey to. Logical fallacies too. I constantly have to remind myself that my mind is hard wired to take shortcuts and to follow heuristics. My own mind is my worst enemy if I forget the above. I'm aware of the above pitfalls and it has helped me to filter out much of what I haven't posted.
I know that I have not lived up to this:
"Amateurs look for patterns, professionals look at error bars."
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
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#2181 by Tellmeagain on 23 Jan, 2016 23:00
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More information on EM Drive testing
It has has now been posted on Reddit that TT's initialQuoteresults are 10% of predicted
35 mN/kW (vs predicted 389 mN/kW)
Tested on scale, above results average of both directions
Loaded Q = 8700
"Short Pulse 1 sec"
The predicted value (389 mN/kW) is typical of the upper range of Shaywer's results.
The measured force/Power value 35 mN/kW (apparently using a digital scale), although being 10% of that, it is still
0.035 of the upper range of what Yang reported in air
8 times what NASA reported in air under mode shape TM212,
13 times what Iulian Berca reported (also using a scale)
178 times what Dave Distler reported using a teeter-totter balance
213 times what Tajmar (TU Dresden) reported in air
So, although it is a fraction of what Shawyer and Yang have reported, it is several times what other testers have reported
_____________________________________________________________
Due notice should be made in assessing these comparisons that:
* Tajmar's cavity is tiny (2.5 inches long) compared with the other ones, and it is known that is is expected that the smaller the EM Drive, the less efficient the anomalous force will be. Tajmar's cavity was also excited at an extremely low Q (Q=49) and it was overcoupled through a relatively huge waveguide.
* Distler's EM Drive was made with conical walls of perforated copper mesh, and reported as deviating from a conical shape
* Q's, mode shapes, and amount of coupled forward power differs between the different tests
* no photographs of the test setup have yet been reported
I want to have a look of his settings to evaluate Lorentz forces... But he left before I can do that. -
#2182 by SeeShells on 23 Jan, 2016 23:31
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I have to mention that one lesson I've learned while studying EmDrive is that, without fail, I can find a paper to support any cockamamie idea that I can possibly dream of; even if I stick to only citing information which is deemed reputable, and published in respected journals. I have yet to find any original idea. Confirmation bias is only one of many cognitive biases which one could fall prey to. Logical fallacies too. I constantly have to remind myself that my mind is hard wired to take shortcuts and to follow heuristics. My own mind is my worst enemy if I forget the above. I'm aware of the above pitfalls and it has helped me to filter out much of what I haven't posted.
I know that I have not lived up to this:
"Amateurs look for patterns, professionals look at error bars."
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
That's the truth.
I read hundreds of papers and it seemed each one had a special place related to the emdrive. Not anymore, although I have went back and read many of them again with a critical eye to detail and found out that while interesting they just didn't quite fit, some I still hold close because they still need data to fill in the blanks.
Don't get me wrong it wasn't a waste of time by any means, call it a higher education and the resolve to gain clean precise data from my tests. I said it before, data is king at this current juncture of the drive for without it all the papers in the world mean little.
Bear with me, I'm not as fast as I used to be but I am as nit picky as I ever was.
Shell -
#2183 by CuriousDreamer on 24 Jan, 2016 02:18
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I fall into the armature category that was mentioned earlier, looking for patterns rather than errors most of the time, but from what I have read I have come up with two thoughts about the source of thrust seen in the EMdrive. (Going under the assumption that thrust is produced when the correct conditions are met)
First, is it possible that the EM field inside the EMdrive is somehow interacting with the ambient electro-magnetic field of the room (or maybe planet?) causing the device to try to move along that field? I would assume that any magnetic interactions great enough to cause this would be detectable and easily ruled out, but as my user name suggests, I am curious.
Second, and this is me grasping at things I hardly even understand one quarter of, is it possible for the microwave resonance to be forming a quadrupole creating gravity waves that are pushing against the mass of whatever the EMdrive is pointing at propelling the smaller mass (the EMdrive) forward? If this were the case, could an EMdrive be locked in place and a scale set a short distance from the rear of the device to test for any force?
It may be that these ideas are dismissible out right, but I hope that they might spark an idea in someone more knowledgeable than my self.
~Dreamer
(edit- attached image of force test)
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#2184 by ThinkerX on 24 Jan, 2016 02:57
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Dang, but Traveler went from receiving his forming hoops to completed test in short order. He might have beat Iulian Berca's construction time.
I wonder - did he take shortcuts in the construction process that might have contributed to his less than expected results? Perhaps this ties in with his comment about 'needing to do more work with the local uni before publishing results.'
I am reminded here of Shell's test a couple months back that produced significant thrust but also melted her antenna. Something similar with Traveler, perhaps?
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#2185 by Rodal on 24 Jan, 2016 12:39
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More information on EM Drive testing
It has has now been posted on Reddit that TT's initialQuoteresults are 10% of predicted
35 mN/kW (vs predicted 389 mN/kW)
Tested on scale, above results average of both directions
Loaded Q = 8700
"Short Pulse 1 sec"
The predicted value (389 mN/kW) is typical of the upper range of Shaywer's results.
The measured force/Power value 35 mN/kW (apparently using a digital scale), although being 10% of that, it is still
0.035 of the upper range of what Yang reported in air
8 times what NASA reported in air under mode shape TM212,
13 times what Iulian Berca reported (also using a scale)
178 times what Dave Distler reported using a teeter-totter balance
213 times what Tajmar (TU Dresden) reported in air
So, although it is a fraction of what Shawyer and Yang have reported, it is several times what other testers have reported
_____________________________________________________________
Due notice should be made in assessing these comparisons that:
* Tajmar's cavity is tiny (2.5 inches long) compared with the other ones, and it is known that is is expected that the smaller the EM Drive, the less efficient the anomalous force will be. Tajmar's cavity was also excited at an extremely low Q (Q=49) and it was overcoupled through a relatively huge waveguide.
* Distler's EM Drive was made with conical walls of perforated copper mesh, and reported as deviating from a conical shape
* Q's, mode shapes, and amount of coupled forward power differs between the different tests
* no photographs of the test setup have yet been reported
New update on latest description of DoItYourself EM Drive experiment (I do my own editing: for example replacing the word "thrust" concerning force measurements as a completely closed cavity like the EM Drive should not be capable -unlike a rocket- of ejecting any mass and hence the word "thrust" may be considered inappropriate in this context (**)):
* No pictures provided. Answers: "Have a lot of stuff to clean up, as does Shell. When I have it all together, will post pics, video and data."(*) "Some good questions guys. Please understand I will answer them but not here as I don't want your questions and my answers spread all over the internet as then it becomes difficult for others to follow the Q&A process. That is why I set up my forum."
* no assessment of what mode shape was excited is provided, no discussion of thermal camera measurements are provided either.
* no measured natural frequency is provided
* force measurement: 2.2 mN (0.22g) @ Power= 63 W; Force/Power = 35 mN/kW, averaged from small end up & down test setups. Claims that there is "no evidence of significant thermal buoyancy", but simultaneously acknowledges having to average different readings for separate up and down measurements, and yet he does not disclose the different separate up and down measurements. Claims that the claimed lack of buoyancy maybe due to very short Rf on time. Says to wait 5 minutes between measurements and do low power tune just before every max power test run.
* Scale software is acknowledged as "not good. Can't do weight versus time curve on PC and save. Need better scale software to data log the weight changes versus time."
* VSWR ( (Voltage Standing Wave Ratio), a measure of how efficiently radio-frequency power is transmitted from a power source, through a transmission line, into a load (for example, from a power amplifier through a transmission line, to an antenna)) is acknowledged as "not good. Gets worse at max power". His assessment: "1/2 H field loop antenna/coupler diameter may not be ideal. May also be bad coaxial and/or SMA ("SubMiniature version A") connectors."
* Radio frequency is applied at minimum 80 mW "to manually tune freq for best VSWR" (Voltage Standing Wave Ratio),. Then maximum power is applied for a few seconds. Force change is claimed to be "immediate On and Off the Radio frequency. No delay can be determined." Precision of time measurement for this "immediate, no delay" assessment is not provided.
* Bench PSU (Power Supply Unit) is self-assessed as "too small. Hitting current limits that may be affecting the Rf amp. Need to replace with much bigger PSU or source the rechargeable Lithium Ions batteries I plan to use on the rotary table, use them to power the Rf amp & use bench PSU to trickle charge the batts."
* Concerning Lorentz forces, answers to user PotomacNeuron "Have answered your question on my forum. Frustum is fed via a single thin & flexible coax that can move. There are no ground loops. Alignment, spacing and cable droop between Rf amp output SMA (SMA="SubMiniature version A" connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw type coupling mechanism) and frustum input SMA are maintained in each test orientation by adjusting Rf amp SMA position relative to frustum SMA position."
* "Need to properly flange attach end plates & highly polish all interior surfaces. Need finger tips & palm working better to do that."
* No dimensions are provided, but the following data https://www.reddit.com/r/EmDrive/comments/40l1za/have_had_my_1st_build_design_data_confirmed/cz15iar may be appropriate (?) since it exactly matches the calculated Force/Power, and it features mode shape TE013 that user TheTraveller previously stated was recommended to him by Shawyer:Quote from: (edited and structured) from original posts by TheTravellerReturns, 7 days ago
Geometry of the frustum of a cone resonant cavity:
BigDiameter: 0.259 m = 10.20 in
SmallDiameter: 0.159 m = 6.26 in
Length : 0.288 m = 11.34 in
Shape of end plates = Flat
____________________________________________________________
Predicted Eigenvalues of Resonance:
Predicted mode shape = TE013
Predicted natural frequency = 2.4053 GHz
(Rodal: both the eigenfrequency and eigenmode probably predicted using TheTraveller's spreadsheet modeling the conical frustum as the summation of a large number of cylindrical cavities with different diameters)
____________________________________________________________
Predicted quality of resonance and predicted force/power
Predicted Q (unloaded)= 86,200 (Rodal: not clear as to how TheTraveller calculated a Q, what approximate formula he used, but this predicted Q is definitely in the theoretical range for TE013, and these dimensions for copper)
Predicted Force/Power=389 mN/kW (Rodal: probably predicted using Shawyer's formula, based on the above Q, the geometry, air as an internal medium and the predicted natural frequency and mode shape)
____________________________________________________________
Details of resonance excitation method, frequency tuning, and power amplifier
Coaxial-fed current loop antenna approximately located at the middle of the conical side wall of the frustum
No physical tuning by a screw-driven cylindrical section. Resonance tuning is electronic via adjustable frequency generator that can step Radio Frequency +-1kHz over what is described as a "wide range".
Radio frequency amplifier maximum power is 100 Watts, spanning frequencies between 0.5GHz to 2.5GHz. Power can be varied, under program control, from 80 mW to 100 W. Amplifier monitors & reports forward & reflected power.
Since the loaded Q was reported measured as Q = 8,700 instead of predicted Q=86,200, this would explain the factor of 10 discrepancy between the calculated force/power (389 mN/kW) and the measured force/power (35 mN/kW) as being (mostly) due to the fact that the measured Q was 1/10 of predicted. Showing a rather outstanding (from an Engineering accuracy viewpoint) precision of Shawyer's formula to predict the force/power as a function of Q, and geometry, for TheTraveller's experiment:
Shawyer prediction (for Q=8,700) = 39 mN/kW
TheTraveller's measurement = 35 mN/kW
Difference = 12%
https://www.reddit.com/r/EmDrive/comments/42eyum/we_have_thrust/
________________
(*) I have no idea as to why Shell is mentioned in this context, as my understanding is that Shell is not involved in his experiment, and therefore Shell cannot possibly be taking pictures of his experiment or cleaning it up.
(**) No reaction has yet been proven, but even if a reaction were to be shown, a better word than "thrust" should be chosen, hence the word chosen by NASA "anomalous force" is more appropriate for the time beingQuote from: Wikipedia article on ThrustThrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction on that system.
(Bold added for emphasis)
https://en.wikipedia.org/wiki/Thrust
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#2186 by rfmwguy on 24 Jan, 2016 14:03
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I was hoping my videos and pics of nsf-1701 would be sort of a model for experimenters to slowly release data. I think what has deterred tt and shell currently is the negative commentary those generated on agenda-driven forums away from here. I can't say as I blame them for being more guarded with sharing images as they occur. Sad to say that juvenile posting behavior sort of spoiled the way info is release imo.
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#2187 by Rodal on 24 Jan, 2016 14:12
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I was hoping my videos and pics of nsf-1701 would be sort of a model for experimenters to slowly release data. I think what has deterred tt and shell currently is the negative commentary those generated on agenda-driven forums away from here. I can't say as I blame them for being more guarded with sharing images as they occur. Sad to say that juvenile posting behavior sort of spoiled the way info is release imo.
While I understand the human emotion of loudly screaming "Eureka, I discovered something" as soon as that feeling is felt, on the other hand, thinking with a cool head we must agree that if an experimenter does not feel confident about releasing pictures, why should the experimenter be confident about releasing claimed measurements?
It gives the feeling that the data is very preliminary and that the experimenter does not feel confident enough that everything has been checked by the experimenter, and is concerned with others finding faults in the experiment if pictures are released revealing the experimental setup, as a "picture is worth a thousand words".
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#2188 by TheUberOverLord on 24 Jan, 2016 14:30
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I was hoping my videos and pics of nsf-1701 would be sort of a model for experimenters to slowly release data. I think what has deterred tt and shell currently is the negative commentary those generated on agenda-driven forums away from here. I can't say as I blame them for being more guarded with sharing images as they occur. Sad to say that juvenile posting behavior sort of spoiled the way info is release imo.
While I understand the human emotion of loudly screaming "Eureka, I discovered something" as soon as that feeling is felt, on the other hand, thinking with a cool head we must agree that if an experimenter does not feel confident about releasing pictures, why should the experimenter be confident about releasing claimed measurements?
It gives the feeling that the data is very preliminary and that the experimenter does not feel confident enough that everything has been checked by the experimenter, and is concerned with others finding faults in the experiment if pictures are released revealing the experimental setup, as "picture is worth a thousand words".
Can you also see how negative it can and does come across when some post responses to any potential positive news with responses like and/or similar to?
If this is true then why did you not......
If this really happened then why have you failed to also provide........
I agree with rmfwguy, that there are better ways to go about making requests for additional information and data like:
When you get time, could you please post.....
Is it possible to also provide .... about your test results.
Why some can't respectfully make requests for additional information and data without being condescending while doing so. Amazes me. I'm not saying you do that. But some do.
Don -
#2189 by Rodal on 24 Jan, 2016 14:37
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...
Yes, I agree , and I can also see that one cannot possibly disclose all data and all pictures, immediately, at the same time that a measurement is sensed, and one feels like loudly screaming "Eureka".
Can you also see how negative it can and does come across when some post responses to any potential positive news with responses like and/or similar to?
If this is true then why did you not......
If this really happened then why have you failed to also provide........
I agree with rmfwguy, that there are better ways to go about making requests for additional information and data like:
When you get time, could you please post.....
Is it possible to also provide .... about your test results.
Why some can't respectfully make requests for additional information and data without being condescending amazes me. I'm not saying you do that. But some do.
Don
But stillQuoteIt gives the feeling that the data is very preliminary and that the experimenter does not feel confident enough that everything has been checked by the experimenter, and is concerned with others finding faults in the experiment if pictures are released revealing the experimental setup, as a "picture is worth a thousand words".
Usually, researchers wait to disclose measurements, because they have the experience that as humans, we all make mistakes over and over again, and everything needs to be double-checked.
In the end I have no problem with immediately releasing partial data, (I would still prefer a picture and researchers being strong enough to take criticism emanating from pictures of their messy preliminary testing) but we must all understand that it is preliminary data, and it doesn't matter whether the data comes from a DoItYourself experiment, or a large Institution R&D like CERN, all preliminary data is subject to revision, double-checking etc.
When OPERA experimental results were announced early, the researchers announced the results of the experiment with the stated intent of promoting further inquiry and debate.
That's a researcher's spirit: promoting skeptical inquiry and debate.Quote from: WikipediaIn 2011, the OPERA experiment mistakenly observed neutrinos appearing to travel faster than light. Even before the mistake was discovered, the result was considered anomalous because speeds higher than that of light in a vacuum are generally thought to violate special relativity, a cornerstone of the modern understanding of physics for over a century.[1][2]
OPERA scientists announced the results of the experiment in September 2011 with the stated intent of promoting further inquiry and debate. Later the team reported two flaws in their equipment set-up that had caused errors far outside their original confidence interval: a fiber optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast.[3] The errors were first confirmed by OPERA after a ScienceInsider report;[4] accounting for these two sources of error eliminated the faster-than-light results.[5]
In March 2012, the collocated ICARUS experiment reported neutrino velocities consistent with the speed of light in the same short-pulse beam OPERA had measured in November 2011. ICARUS used a partly different timing system from OPERA and measured seven different neutrinos.[6] In addition, the Gran Sasso experiments BOREXINO, ICARUS, LVD and OPERA all measured neutrino velocity with a short-pulsed beam in May, and obtained agreement with the speed of light.[7] -
#2190 by TheUberOverLord on 24 Jan, 2016 14:46
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...
Yes, I agree , and I can also see that one cannot disclose all data and all pictures at the same time that a measurement is made.
Can you also see how negative it can and does come across when some post responses to any potential positive news with responses like and/or similar to?
If this is true then why did you not......
If this really happened then why have you failed to also provide........
I agree with rmfwguy, that there are better ways to go about making requests for additional information and data like:
When you get time, could you please post.....
Is it possible to also provide .... about your test results.
Why some can't respectfully make requests for additional information and data without being condescending amazes me. I'm not saying you do that. But some do.
Don
But stillQuoteIt gives the feeling that the data is very preliminary and that the experimenter does not feel confident enough that everything has been checked by the experimenter, and is concerned with others finding faults in the experiment if pictures are released revealing the experimental setup, as "picture is worth a thousand words".
Usually, researchers wait to disclose measurements, because they have the experience that as humans, we all make mistakes over and over again, and everything needs to be double-checked.
In the end I have no problem with releasing partial data, (I would still prefer a picture and researchers being strong enough to take criticism emanating from pictures of their preliminary testing) but we must all understand that it is preliminary data, and it doesn't matter whether the data comes from a DoItYourself experiment, or a large Institution R&D like CERN, all preliminary data is subject to revision, double-checking etc.
Well, personally I think there is no "Golden Standard" of how preliminary data is released nor should there be in a forum like this by tests being done by DIY's. Nor should there be any attempt to implement one in a forum like this. Because there could never be a consensus of what is acceptable as any "Golden Standard" of how preliminary data is released. In forums like this by DIY's.
That all said. It's not asking much for everyone to realize that preliminary data will be released as the DIY decides and when making requests for more information and data relating to any preliminary data that one should be respectful vs. condescending while doing so. That alone might help the process along while also limiting negative and condescending rants about any specific DIY test results.
After all. If the goals are getting more factual data. Publicly verbally "Waterboarding" ("Joke") a DIY who posted preliminary data. Most likely won't speed that process up, any faster.
Don -
#2191 by Eer on 24 Jan, 2016 15:00
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I was hoping my videos and pics of nsf-1701 would be sort of a model for experimenters to slowly release data. I think what has deterred tt and shell currently is the negative commentary those generated on agenda-driven forums away from here. I can't say as I blame them for being more guarded with sharing images as they occur. Sad to say that juvenile posting behavior sort of spoiled the way info is release imo.
While I understand the human emotion of loudly screaming "Eureka, I discovered something" as soon as that feeling is felt, on the other hand, thinking with a cool head we must agree that if an experimenter does not feel confident about releasing pictures, why should the experimenter be confident about releasing claimed measurements?
It gives the feeling that the data is very preliminary and that the experimenter does not feel confident enough that everything has been checked by the experimenter, and is concerned with others finding faults in the experiment if pictures are released revealing the experimental setup, as "picture is worth a thousand words".
Can you also see how negative it can and does come across when some post responses to any potential positive news with responses like and/or similar to?
If this is true then why did you not......
If this really happened then why have you failed to also provide........
I agree with rmfwguy, that there are better ways to go about making requests for additional information and data like:
When you get time, could you please post.....
Is it possible to also provide .... about your test results.
Why some can't respectfully make requests for additional information and data without being condescending while doing so. Amazes me. I'm not saying you do that. But some do.
Don
"The tragedy of the commons" is that information shared with enthusiasm, while shared by many, also generates criticism that can be withering and dispiriting, whether that was the intention, or not.
I grew up with someone loving, but who also could always, always find some way to improve, something that could have been done better, something that needed undoing and redone. It had a chilling effect.
I've spent the past two decades learning my craft from a master, someone who established the gold standard for what could be accomplished in his field. It has been both exhilarating and crushing.
I see echos of that here, and I've carefully taken stock of what I can contribute and what I cannot.
For some, criticism is best received when it is constructive and encouraging, and not dismissive or demanding. For those, like me, the commons is not always a friendly place to work, unless you first polish and scrub and prepare for the cut-throat process of unrestrained peer- (and pseudo-peer-) review. Public forums make it all the more important.
Signed,
Someone who is glad he pulled out of the Meeper crowd when it became evident he lacked the physics background to debug what he was doing ... -
#2192 by SeeShells on 24 Jan, 2016 16:18
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He is correct but forgot the other half of the equation. One picture will generate a thousand questions.
When I've posted pictures I've been pelted with a thousand questions and I feel obliged in answering them all. I don't mind sharing and showing because we all want to know but the bigger question isn't being taken care of. You all will notice my posts have slowed down as well as pictures, because I simply need to focus on my build. I saw something on my last power up and I'll be danged I do so want to share that with you all this next go around.
Please bear with me as I focus on my build and have some patience and some faith.
My Best,
Shell
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#2193 by aero on 24 Jan, 2016 17:28
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@Dr. Rodal and meepers - I finally discovered how to determine the turn-off time of the meep Gaussian pulse. Meepers can use that turn-off time to collect data before, during and after Gaussian run turn-off if any of our resident physicists are still interested in seeing such data.
The run time is simply this, in cycles of the drive frequency. Drive cut-off cycle = 10 * drive frequency /bandwidth multiplier. Since bandwidth = Bandwidth multiplier * drive frequency, cut-off cycle can be calculated using any bandwidth the meeper wishes to code. Here are some calculated and confirmed values.; BWmultiplier run time
; 0.2 56.00000028 cycles
; 0.1 106.0000005599 cycles
; 0.05 206.0000011199 cycles
; 0.025 406.0000022398 cycles
; 0.015 672.6666666667 cycles
This data results when using drive frequency = 2.45 GHz, and cg = 6. (cg is the idle time between cut-off and Harminv start, and is intended to allow time for cut-off induced transients to disapate.) I was surprised to discover that the cut-off cycle is independent of resolution though of course run time still increases with increasing resolution.
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#2194 by Rodal on 24 Jan, 2016 18:25
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It has already been predicted and explained (by distinguished ex NSF user DeltaMass
, honours degree in Physics , Oxford University ) and experimentally verified by other DoItYourself experimenters in previous EM Drive threads that digital scales will show anomalous spurious forces from EM Drive tests if not effectively shielded.
The drawing of TheTraveller's testing set-up (unfortunately we have to rely on a schematic drawing because no pictures have been provided for the claimed test set-up up to now) shows what appears to be (from the hand-drawn sketch) a flat plate "double-side PCB shield" located between the EM Drive and the digital scale. No dimensions or specification for this PCB shield appear to have been provided but it is noteworthy that to have complete shielding one should preferably have a complete enclosure rather than just a double-side PCB shield flat plate between the EM Drive and the digital scale.
The scale relies on a moving vertical platform which makes completely enclosing the scale problematic.
Shawyer attempted to shield the EM Drive in one of his experiments:
Tajmar in his experiment at TU Dresden also attempted to shield the EM Drive itself (see picture below).
As pointed out by Dr. Radu, for example,
● The noise source, the coupling path and the antennas are all frequency and mode shape dependent, and this increases very much the complexity of the problem.
● All the EMI problems deal with parasitics. The characterization of all the EMI aspects is never part of the data sheet, making all modeling attempts very difficult.
● Double shield from materials with the same magnetic behavior (Cu + Al) is worse than a single shield with equivalent thickness. Radu writes that in general, equal thickness is best. There is a difference between laminated shields and double shields (air separation). From TT's description it looks like he is using a laminated shield ("double sided PCB" a copper double-sided printed circuit board). FR-4 glass-fiber-reinforced-epoxy is the primary insulating polymer substrate upon which the vast majority of rigid PCBs are produced. So I imagine that he is using 2 thin layers of copper foil laminated to both sides of an FR-4 panel. The thickness of the metal shield needs to be larger than the skin depth for the radiating frequency, and proper attention has to be paid to joints.
Source parameters that influence the effectiveness of shielding are:
● Source polarization
● Source - aperture distance
● Beam-pattern vs receive antenna position
● Antenna - enclosure coupling strength
● Dr. Radu's opinion is that numerical simulation of shielding (FDTD as in Meep, FEM as in COMSOL, MoM as in FEKO, etc.) - <<can’t be used for real life situations, no physical insight, difficult to characterize the noise source, internal reflections, large size of the file, etc.>> hence he/she states that experimental methods are the only real validation of shielding, and that, in the end, all these are about material and thickness of the shield, and to a little extent about the geometry of the complete enclosure and distance, positioning of the radiating source(s).
attachment: slide from Dr. Radu, Principal Engineer, EMC design Sun Microsystems
www.dphu.org/uploads/attachements/books/books_542_0.pdf
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#2195 by RFPlumber on 24 Jan, 2016 22:03
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...
Since the loaded Q was reported measured as Q = 8,700 instead of predicted Q=86,200, this would explain the factor of 10 discrepancy between the calculated force/power (389 mN/kW) and the measured force/power (35 mN/kW) as being (mostly) due to the fact that the measured Q was 1/10 of predicted. Showing a rather outstanding (from an Engineering accuracy viewpoint) precision of Shawyer's formula to predict the force/power as a function of Q, and geometry, for TheTraveller's experiment:
Shawyer prediction (for Q=8,700) = 39 mN/kW
TheTraveller's measurement = 35 mN/kW
Difference = 12%
...
Just pointing to possible issues around Q values involved.
- It is my understanding that Shawyer's formula requires the unloaded Q.
- Predicted Q=86,200 is the unloaded Q value.
- Reported Q=8,700 is a loaded Q value. Assuming critical coupling, the unloaded Q is then 2x that.
- How was this last value of 8,700 measured? TT has previously referred to Roger using the "-3 dB from the _minimum_ of S11" method which has no sense for Q value, but which, again, according to TT quoting Shawyer, "was better matching the observed results".
This last point makes me think that with enough creativity one can always measure the "Q" value in such a way as to explain any observed force.
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#2196 by rq3 on 24 Jan, 2016 22:47
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As is my wont, I follow lots of "weird science", and found the paper regarding Woodward's latest attempts with the Mach Effect interesting. Apparently they pull 3 micronewton measurements out of the noise with some confidence.
https://www.researchgate.net/publication/283007333_Theory_of_a_Mach_Effect_Thruster_II
Just food for thought, especially the treatment of thermal effects, which seems to be a bugbear here.
Edit: changed archaic "bug-a-bear" to "bugbear" -
#2197 by Rodal on 24 Jan, 2016 22:56
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As is my wont, I follow lots of "weird science", and found the paper regarding Woodward's latest attempts with the Mach Effect interesting. Apparently they pull 3 micronewton measurements out of the noise with some confidence.
https://www.researchgate.net/publication/283007333_Theory_of_a_Mach_Effect_Thruster_II
Just food for thought, especially the treatment of thermal effects, which seems to be a bug-a-bear here.
Thank you so much for pointing towards this paper, which I had not previously seen.
I am impressed that Fearn is using Wolfram Mathematica (
) and that she writes about QuoteWe are currently modeling the device with COMSOL and ANSYS software
ANSYS is among the best Finite Element Analysis multiphysics programs.
Fearn/Woodward have a much more sophisticated theory than Shawyer's and they are using more sophisticated analysis tools. Fearn has had a very invigorating effect on Woodward's theory, not just continuing it but in further developing its foundations and in using analysis tools (previous experimental results by Woodward were lacking in numerical analysis with COMSOL and ANSYS to understand thermal and other effects).
I had previously placed for comparison with the EM Drive experimental data http://emdrive.wiki/Experimental_Results the previous experimental results by Fearn/Woodward, of only 2 microNewtons, with force/power barely 3.5 times of a photon rocket
Any reactionless propellant-less scheme is interesting, particularly if it beats a perfectly collimated photon rocket
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#2198 by spupeng7 on 25 Jan, 2016 00:32
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Q: Is it possible to do an RF version of this nice resonance chart?
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#2199 by Rodal on 25 Jan, 2016 00:39
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Q: Is it possible to do an RF version of this nice resonance chart?
Many people talk about Q in these threads as if it would be some special electromagnetic concept, which is not. Q is just the inverse of damping, that's all it means physically speaking.
Don't let the RF people jargon distract you from the physical meaning of Q.
The electromagnetic RF resonance is analogous to the mechanical resonance in a spring/mass/dashpot dynamic system. That's the beauty of math: similar equations, with different parameters, you have resonance on both.
Microwave resonant cavities can be represented and thought of as simple LC circuits. For a microwave cavity, the stored electric energy is equal to the stored magnetic energy at resonance as is the case for a resonant LC circuit.
(Neglecting damping for simplicity purposes)
This is the same equation as the equation of mechanical resonance as for a harmonic oscillator spring mass system:
The quality factor of resonance Q and the damping ratio ζ are related to each other as follows:
and Q and tan delta are related as follows:
the main noteworthy difference (besides the huge difference in frequency) is the much higher values of Q achieved in an electromagnetic cavity, one can readily see this for example because the dynamic mechanical tan delta:
For mechanical resonance:
tan delta = E"/E' is about 0.05 (or higher) @ 30 Hz for polymers so that Q ~20
For electromagnetic resonance:
for a dielectric like HDPE one can have
electromagnetic tan delta = 0.00031 @ 3 GHz so that Q ~ 3,225
and for a copper cavity the size of the EM Drive with just air inside it, you can have Q ~85,000 for mode TE012 because the only damping comes from the resistivity of the metal to a current going through it
So that much higher Q (much lower damping) can be achieved in an electromagnetic cavity than in a mechanical resonator
While for many mechanical applications one may consider high resonance to be "disastrous" as written in the chart that you attached to your post (for example in earthquakes, or in vehicles) and one may want to have high damping and avoid resonance, for electromagnetic cavity resonance purposes as in particle accelerators (and according to Shawyer for the EM Drive) one wants a high Q and to be in high resonance
Actually, some people are dreaming about using superconductivity for EM Drives, which could drive the Q to several million.
So when people talk about the EM Drive truncated cone having a high Q, think of a spring/mass/dashpot system at high resonance with low damping. Then you will see why momentum is conserved, and a spring/mass/dashpot system is going to give you no propulsion by itself in space, even if has the shape of a truncated cone and is vibrating at 2.45 GHz
If there is an anomalous force, one has to go into weird stuff like Woodward's Mach effect hypothesis or some "new physics", that's why Dr. White at NASA has proposed his Quantum Vacuum hypothesis and he immediately rejected Shawyer's "explanation"
, honours degree in Physics , Oxford University ) and experimentally verified by other DoItYourself experimenters in previous EM Drive threads that digital scales will show anomalous spurious forces from EM Drive tests if not effectively shielded.
) and that she writes about