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#2740
by
sghill
on 10 Feb, 2016 12:54
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Here is a really nice little article over at Space.com on the worst kept secret in physics at the moment (that happens to apply nicely to our discussions over here in the EMDrive thread).
http://www.space.com/31879-gravitational-waves-vs-gravity-waves.htmlIt's a lovely layman's primer on gravitational waves.
Evanescent modes are characterized by an exponential attenuation and lack of a phase shift and that lack of phase shift has made me go, now that's a interesting thing to be happening in the cavity.
Shell
That. Right there. Let's talk about that.
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#2741
by
rfmwguy
on 10 Feb, 2016 13:23
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Here is a really nice little article over at Space.com on the worst kept secret in physics at the moment (that happens to apply nicely to our discussions over here in the EMDrive thread).
http://www.space.com/31879-gravitational-waves-vs-gravity-waves.html
It's a lovely layman's primer on gravitational waves.
Evanescent modes are characterized by an exponential attenuation and lack of a phase shift and that lack of phase shift has made me go, now that's a interesting thing to be happening in the cavity.
Shell
That. Right there. Let's talk about that.
Lack of a phase shift in the time or frequency domain?
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#2742
by
Rodal
on 10 Feb, 2016 13:29
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If my memory is correct, there are only 2 self-consistent ways (that's it ! ) that have been discussed so far that the conservation of momentum and energy problem can be addressed from internal fields inside the EM Drive:
1) negative energy-mass
2) coupling to weakly interacting particles that make it through the cavity walls: Dark Matter axions, Quantum Vacuum virtual particle/antiparticle pairs, etc.
One may add 3) unified theories of General Relativity with electromagnetism to the above (but, I'm not sure of this, are there any that don't involve negative energy?)
Internal evanescent waves cannot, by themselves, result in a self-accelerating EM Drive, nor can they resolve the conservation of momentum-energy problem. (You cannot move the center of mass of a spacecraft by banging on the walls or moving the furniture inside the spacecraft).
Are evanescent waves being proposed to exist outside the EM Drive?
If so, it would best advance the discussion if DoItYourself experimenters would measure the near field of the EM Drive in their EM Drive experiments and provide measurements to verify whether evanescent waves do exist outside the EM Drive (and if so to show whether the evanescent waves are the result of very small holes and gaps in the imperfectly built EM Drive (*)).
Are DoItYourself experimenters planning to measure the (hypothetical) evanescent wave fields outside the EM Drive ? (*)
_____________-
(*) If they exist they must be the result of very small holes or gaps in the not-hermetically sealed EM Drive...
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#2743
by
rfmwguy
on 10 Feb, 2016 13:33
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Pick a piece of test equipment Doc.
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#2744
by
Rodal
on 10 Feb, 2016 13:34
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Pick a piece of test equipment Doc.
are you asking how to measure evanescent wave fields outside an EM Drive?
This can be done with a sub-wavelength antenna located at a sub-wavelength distance from the exterior surface, and scanning the surface of the EM Drive with it.
Due to the fact that microwave wavelengths at ~2.45 GHz are not tiny:
c=299792458 m/s
f = 2.45 *10^9 1/s
free space wavelength = 0.122 m = 4.82 inches
1/2 wavelength = 2.41 inches
1/4 wavelength = 1.20 inches
it should not be too difficult to make a near field microwave measurement.
Actually microwave Near Field Measurements are commonplace: microwave Near Field Measurements are used for non-destructive testing and in microwave microscopy, for example.
Please let me know whether I am missing some major roadblock that experimenters have in measuring the supposed external microwave near field that is being discussed(again: evanescent fields inside the EM Drive cannot by themselves explain the EM Drive self-acceleration, just like you cannot move a spacecraft by banging on the wall, moving the furniture inside it or with any electromagnetic field emitted inside it that does not make it to the outside of the EM Drive)
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#2745
by
rfmwguy
on 10 Feb, 2016 14:06
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Pick a piece of test equipment Doc.
are you asking how to measure evanescent wave fields outside an EM Drive?
This can be done with a sub-wavelength antenna located at a sub-wavelength distance from the exterior surface.
Due to the fact that microwave wavelengths at ~2.45 GHz are by no means small
c=299792458 m/s
f = 2.45 *10^9 1/s
free space wavelength = 0.122 m = 4.82 inches
1/2 wavelength = 2.41 inches
1/4 wavelength = 1.20 inches
it is not difficult to make a near field microwave measurement.
Microwave Near Field Measurements are commonplace.
My question relates to the measurement value you would like to see. IOW, most are wideband and and not single frequency devices. A common dipole will not be very frequency selective.
So, are you looking for a microvolt per millimeter value only at source frequency? What orientation axis and how many depth of field points would you like to see?
Reason I ask is the kickstarter budget allows me to purchase test gear but the sensitivity and measurement methods need to be defined. You can help with this. Suggestions?
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#2746
by
Rodal
on 10 Feb, 2016 14:27
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Pick a piece of test equipment Doc.
are you asking how to measure evanescent wave fields outside an EM Drive?
This can be done with a sub-wavelength antenna located at a sub-wavelength distance from the exterior surface.
Due to the fact that microwave wavelengths at ~2.45 GHz are by no means small
c=299792458 m/s
f = 2.45 *10^9 1/s
free space wavelength = 0.122 m = 4.82 inches
1/2 wavelength = 2.41 inches
1/4 wavelength = 1.20 inches
it is not difficult to make a near field microwave measurement.
Microwave Near Field Measurements are commonplace.
My question relates to the measurement value you would like to see. IOW, most are wideband and and not single frequency devices. A common dipole will not be very frequency selective.
So, are you looking for a microvolt per millimeter value only at source frequency? What orientation axis and how many depth of field points would you like to see?
Reason I ask is the kickstarter budget allows me to purchase test gear but the sensitivity and measurement methods need to be defined. You can help with this. Suggestions?
If the EM Drive is made of metal walls much thicker than the skin depth, as it is supposed to be made of, and there are no holes or gaps due to imperfect construction (or from using walls made of a copper mesh for example), and if the wall thickness is millimeters thick copper, there should not be any evanescent fields outside the EM Drive at ~2.45GHz, since the skin depth is micrometers.
If there are external evanescent wave fields (
is that why evanescent wave field are being discussed 
), they should be the result of very small holes and gaps due to imperfect construction, or in your case, rfmwguy because you used a copper mesh full of holes.
So your question cannot be answered without knowing whether you are making the EM Drive walls with holes and gaps, and if so where are those holes and gaps located, and what is their size. If there are no holes and gaps, and the wall are mm thick, there should not be any exterior evanescent wave fields.
So this is a question to be answered by those making the EM Drive (hole and gaps? size? location?) and those proposing the existence of evanescent wave fields outside the EM Drive.
aero has conducted numerical studies with Meep purposely including small gaps, that can answer your question as to what is the field strength expected from a near field due to a given size gap, hole location and size.
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#2747
by
rfmwguy
on 10 Feb, 2016 14:42
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Got it. I don't have an working theory on evanescent wave propogation outside of solid metal walls. I'm trying to learn more about this proposal.
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#2748
by
rfmwguy
on 10 Feb, 2016 14:56
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Keep forgetting to remind everyone who might be having storage issues on computers or virtual drives that there is a no-charge, secure location for emdrive related files of any type. They will be safely stored and accessable by you only if you so choose. Myself and another nsf member have set this up. Total space is in the terabyte region. PM me for details. Only stip is it must be emdrive related and you be a member in good standing with nsf. It is independent of nsf, however.
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#2749
by
mwvp
on 10 Feb, 2016 15:44
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Got it. I don't have an working theory on evanescent wave propogation outside of solid metal walls. I'm trying to learn more about this proposal.
There effectively is none beyond a few skin-depths. There is in/beyond dielectrics, but not conductors.
Good illustration at the 25 minute point.
If folks here watched a few of these lectures, such matters wouldn't be discussed. Really is sad to spend time ignorantly chattering when you could be learning and understanding. Just sayin. Sorry.
Complex (imaginary) fields in a waveguide would be understood as superpositions of real/propagating, sidewall reflected fields, and superluminal phase velocity would also be understood as a superposition/interference effect, likewise group velocity.
Or perhaps I just think I know and am mistaken.
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#2750
by
rfmwguy
on 10 Feb, 2016 16:05
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Got it. I don't have an working theory on evanescent wave propogation outside of solid metal walls. I'm trying to learn more about this proposal.
There effectively is none beyond a few skin-depths. There is in/beyond dielectrics, but not conductors.
Good illustration at the 25 minute point.
If folks here watched a few of these lectures, such matters wouldn't be discussed. Really is sad to spend time ignorantly chattering when you could be learning and understanding. Just sayin. Sorry.
Complex (imaginary) fields in a waveguide would be understood as superpositions of real/propagating, sidewall reflected fields, and superluminal phase velocity would also be understood as a superposition/interference effect, likewise group velocity.
Or perhaps I just think I know and am mistaken.
Thanks, I will watch the link. I've not heard of evanescent wave propagation thru metal either. Seams, holes, cracks? Yes.
Haven't followed this topic on nsf as I'm focusing more on particle theories...another rabbit hole for sure...
Edit...good video, reminds me a bit about panel antennas I studied in another lifetime...incident waves and vectoring. That was about the time I got out of cellular and into 100 kW stuff.
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#2751
by
1
on 10 Feb, 2016 19:54
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To explain something in a clear simple way (unless we going into quantum physics then all bets are off) shows a good understanding of the subject and you did a very nice job of it.
I don't know about anyone else, but I've just read one of the best posts I can recall for a while. @1, don't stray too far. It is clear you have a personal understanding of physics and have the skill to communicate effectively. That is severely lacking in most online venues. Well done. We have no gold stars, but I've invented a virtual one for you. 
My thanks to you both. I've been lurking here for quite some time, but rarely post because I'm usually pretty outclassed knowledge-wise by many of the other members here; especially in the main forums. And as a guy who's closer to 'average joe' than 'industry expert' in aero/astronautics, I have a great appreciation for posters who take the time to organize their thoughts in a clear fashion and post with a supportive tone. Even in the areas that I do specialize I'm often quite content to take a backseat to those with greater real-world experience such as you two, Rodal, and some others. I've learned a lot here over the years; and if I'm going let the internet erode my work productivity (hint: I am) better here than anywhere else. Thanks again for the kind words, and good luck with your builds!
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#2752
by
rfmwguy
on 10 Feb, 2016 20:09
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To explain something in a clear simple way (unless we going into quantum physics then all bets are off) shows a good understanding of the subject and you did a very nice job of it.
I don't know about anyone else, but I've just read one of the best posts I can recall for a while. @1, don't stray too far. It is clear you have a personal understanding of physics and have the skill to communicate effectively. That is severely lacking in most online venues. Well done. We have no gold stars, but I've invented a virtual one for you.
My thanks to you both. I've been lurking here for quite some time, but rarely post because I'm usually pretty outclassed knowledge-wise by many of the other members here; especially in the main forums. And as a guy who's closer to 'average joe' than 'industry expert' in aero/astronautics, I have a great appreciation for posters who take the time to organize their thoughts in a clear fashion and post with a supportive tone. Even in the areas that I do specialize I'm often quite content to take a backseat to those with greater real-world experience such as you two, Rodal, and some others. I've learned a lot here over the years; and if I'm going let the internet erode my work productivity (hint: I am) better here than anywhere else. Thanks again for the kind words, and good luck with your builds!
Shell and I are going into areas without a roadmap or blueprint. Its frustrating but fun at times. Encouragement from anyone, even non-believers makes the hours worthwhile. Thanks for hanging with us and remember, we have no correct theory or absolute belief system. All inputs are welcomed and our esteemed members like Doc, frobnicat, Zen-in and several others will politely correct us when we stray too far...not that I've ever done that
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#2753
by
rfmwguy
on 10 Feb, 2016 20:46
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Housekeeping note -
I caught one of my posts with a very long url that messes up page widths on many devices.
An easy workaround when you notice this in your own posts is to use a free url converter. Copy and paste the long url and get a tiny url:
http://tinyurl.com
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#2754
by
aero
on 10 Feb, 2016 21:15
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I'm in the process of refining rfmwguy's NSF-1701A meep model hoping for some useful data. I don't know how useful it is but I thought the attached two gif were interesting enough to share. As the names indicate, they are exactly the same component and view. The difference is that the second .gif is more nearly converged.
The gifs contain 9 cycles of drive frequency, starting one cycle before power cut-off and continuing 8 cycles beyond power cut-off. All at 0.1 cycle slices. I found it interesting that the un-converged gif holds at the drive frequency for a little time then starts to walk away, presumably to the cavity natural resonant frequency. That same thing could happen in the real world when the cavity geometry shifts, from heating perhaps.
I recall that with a magnetron source, power cut-off happens 60 times per second. And note that the other 23 sets of gifs mostly behave like these two, these two are representative even if more dramatic.
I'm sorry, but I can't get the first one to run on the forum. Anyone?
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#2755
by
rfmwguy
on 10 Feb, 2016 21:25
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Thanks Aero. Don't think I've seen anything quite like this. No motion in first pic. Steady-state in second. I might add that the new dimentions I came up with are based solely on vna scans of a prototype.
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#2756
by
wallofwolfstreet
on 10 Feb, 2016 21:50
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I hate to rain on your parade, but I definitely agree with the assessment that the emdrive is not at TRL 1. Exact definitions vary, but it is generally accepted that TRL 1 is where a defined scientific phenomena has reached a point of understanding where people can begin to propose technology concepts (i.e. real world applications that make use of the phenomenon as the operating principle). TRL 1 requires therefore that the underlying phenomenon is well documented, it's basic characteristics understood and the variables that impact the phenomenon are known. This is clearly not the case for the emdrive, as we still don't know IF it works, much less HOW.
Here is the DOD's take on TRL 1 from the
wiki page:
TRL 1: Basic principles observed and reported
Description:
Lowest level of technology readiness. Scientific research begins to be translated into applied research and development (R&D). Examples might include paper studies of a technology’s basic properties.
Supporting Information:
Published research that identifies the principles that underlie this technology. References to who, where, when.
Is there any published information that identifies the principles underlying the emdrive? (And of course Shawyer's publications are a non-starter since they aren't even internally consistent, much less consistent with known physics)
If we want to stick with NASA, seeing as this is NSF:
TRL 1: Basic principles observed and reported
Description:
This is the lowest "level" of technology maturation. At this level, scientific research begins to be translated into applied research and development
So the emdrive still doesn't fit the bill, in my opinion. Without any knowledge of the emdrives operating principle, all research on it is as basic and blue sky as can be.
As someone who works with TRLs (although not the exact definitions given above), I would call the emdrive a pre TRL technology concept. It is too speculative in performance, and unjustified theoretically, to warrant a TRL. No one has proposed and proven, via experimentation, what the supposed operating principle of the emdrive is. No operating principle, no TRL 1 (in my opinion at least).
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#2757
by
aero
on 10 Feb, 2016 22:12
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Thanks Aero. Don't think I've seen anything quite like this. No motion in first pic. Steady-state in second. I might add that the new dimentions I came up with are based solely on vna scans of a prototype.
But that's not how it works on my machine. Can you download the first one and see if it is a gif, or just a png with a gif extension. On my machine it walks all over.
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#2758
by
zen-in
on 10 Feb, 2016 23:05
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I stated the same conclusion several months ago but it is easy to see that someone could assign anything from TRL1 - TRL3 to the em-drive if physics is overlooked. I don't see anything in the TRL descriptions that rules out new physics. The descriptions for each TRL are somewhat vague and ambiguous. For example TRL4 is achieved if the experiment has been done in a lab environment. No mention is made about independent replication of the experiment or about the rigor of the protocol.
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#2759
by
aero
on 10 Feb, 2016 23:21
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), they should be the result of very small holes and gaps due to imperfect construction, or in your case, rfmwguy because you used a copper mesh full of holes.
