There is a fundamental difference between light bouncing around in an emdrive and the astronaut in the space station.
Light does not obey conservation of momentum under specific conditions.
This has been practically demonstrated:Optical diametric drive acceleration through action–reaction symmetry breakinghttp://www.nature.com/nphys/journal/v9/n12/full/nphys2777.html
Take a look at the equation for radiation pressure.F=hf/c...If that equation holds true, F=hf/c, then slowing light down INCREASES the force of radiation pressure. That is completely non-intuitive for me. It makes no sense whatsoever. Slower should be less force, right?
Key: Radiation pressure varies inversely with the speed of light.I'm still perplexed by this, and I wish to know more.
What's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.
This explains the tapered waveguide emdrive. At the big end the radiation pressure is close to hf/c0. At the little end, the light is much slower, approaching zero, so the radiation pressure is radically larger. The imbalance in forces makes the ship go.
Putting these together gives you the guts of Mr. Shawyer's emdrive theory, ignoring the bits around general relativity.
The net force is the large radiation pressure from the slow moving light in the near-cutoff or dielectric little end minus the small radiation pressure from the free space propagating big end
...What am I missing?
There is a fundamental difference between light bouncing around in an emdrive and the astronaut in the space station. It took me a while to grok this, but I think I can explain it now.
F=hf/cForce = Planck length times frequency divided by the speed of light.
It's a bad idea to write down physics equations in which the units do not match on either side. It's also a bad idea to misrepresent Planck's constant as "Planck length".
But the worst idea of all is to post such stuff on a public forum.It guarantees that people will not take seriously anything you say about physics ever again
FWIW, I admire the meepers doing what I cannot do, burn through iterations and generate 3D models. I vote for both us builders, meepers and theoretical types keep doing what we are doing...trying to help in our own way.p.s. NSF-1701 exoskeleton needed some strengthening today. Just got that completed. I'll post a pic in a minute.
Quote from: deltaMass on 07/22/2015 11:59 amIt's a bad idea to write down physics equations in which the units do not match on either side. It's also a bad idea to misrepresent Planck's constant as "Planck length".Fixed. Again. QuoteBut the worst idea of all is to post such stuff on a public forum.It guarantees that people will not take seriously anything you say about physics ever againI'll repeat it, in case I haven't been clear in disclaiming this already. I should not be taken seriously. I am seeking enlightenment, not providing it.
...Quote from: ElizabethGreene on 07/22/2015 04:53 amWhat's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.Something very interesting and important occurs as the cutoff is closely approached. The group velocity decrease exponentially....
Quote from: Ricvil on 07/21/2015 07:58 pmQuote from: X_RaY on 07/21/2015 07:26 pmupon reflection light undergoes a 180 degree phase change on metal surfacesYes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".This is a example of superposition principle to model boundary conditions.Know anything about increased skin depth and attenuation with evanescent modes? I read somewhere bends in the waveguide cause increased RF penetration and loss, and evanescent modes came to mind. Googled around for it briefly but didn't find anything. That would help explain selective sideband attenuation, but the big end, rather than the small end (with the low cutoff) is what's been observed to get hot.
Quote from: X_RaY on 07/21/2015 07:26 pmupon reflection light undergoes a 180 degree phase change on metal surfacesYes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".This is a example of superposition principle to model boundary conditions.
upon reflection light undergoes a 180 degree phase change on metal surfaces
Quote from: mwvp on 07/21/2015 10:12 pmQuote from: Ricvil on 07/21/2015 07:58 pmQuote from: X_RaY on 07/21/2015 07:26 pmupon reflection light undergoes a 180 degree phase change on metal surfacesYes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".This is a example of superposition principle to model boundary conditions.Know anything about increased skin depth and attenuation with evanescent modes? I read somewhere bends in the waveguide cause increased RF penetration and loss, and evanescent modes came to mind. Googled around for it briefly but didn't find anything. That would help explain selective sideband attenuation, but the big end, rather than the small end (with the low cutoff) is what's been observed to get hot.If the antenna is close of big base then I have a possible explanation.The antenna is a pertubation on the shape of the cavity, and the tappered conical cavity has many modes very close each other at some frequencys. This is a scenario of a "ghost mode" rising.In waveguides, a ghost mode is a localized resonance of very high Q which concentrates very high EM fields in a region of few lambdas. If the length of the cavity is greater than the extension of the ghost mode region ( in the case near the big base), then the small base will not feel the strong field of the ghost mode.The magnetron can amplify the strenght of ghost mode too.Then the big base is hot because the proximity of the ghost mode, and the small base not.
@SeeShell - Your .png and .csv files data is/are up have been uploaded here:https://drive.google.com/folderview?id=0B1XizxEfB23tfm04QWNVVVVvT3gtcVAzRUp6T1BCLVpoV0EyeVVKR2ZxQkp2a3NKcUNPMU0&usp=sharingI uploaded my meep data request file/form to hopefully explain what the data is, although it needs more English and fewer Scheme statements. The inside big end is at row 15 and small end at row 216 of the csv files, and the total run meep time t = 13.054 (6527 timesteps).
Quote from: mwvp on 07/22/2015 10:08 am...Quote from: ElizabethGreene on 07/22/2015 04:53 amWhat's interesting for our purposes is not what happens at the cutoff frequency f=c/2a, but what happens between cutoff f=c/2a and where an entire wavelength will fit in the waveguide f=c/a.Something very interesting and important occurs as the cutoff is closely approached. The group velocity decrease exponentially....Cut-off is a concept that applies to constant section waveguides. It does not apply to tapered waveguides, as it has been remarked and shown in several peer-reviewed papers I have pointed out in the paper I wrote about cut-off frequencies of the truncated cone used for the EM Drive (which I attach below).As shown by several authors, and latest by Zeng and Fan (often quoted by Todd "WarpTech") in a tapered waveguide all modes run continuously from a travelling wave region through a transition to an evanescent wave region and the value of the attenuation increases as the cone vertex is approached.I have also shown this in detail for the EM Drive for several geometries: there is no such thing as cut-off unless you approach a small end of zero dimensions (which is impractical). One can safely reduce the small diameters of the EM Drives used by Shawyer, NASA and Yang to only 20% of its tested value without reaching cut-off per se. Now, whether it is better or worse to have such a longer cone remains to be explored (as the whole issue of whether the EM Drive force is real or an experimental artifact also remains to be proven). But that the cut-off concept does not apply is well confirmed by now. In a tapered waveguide modes do not get cut-off, instead the modes persist, with a larger diameter region where the wave is a travelling wave to a transition region to a region near the apex where the wave becomes evanescent.
...Dr. Rodal, To make this work with the 1/2 centerline 6.1 degree angle of my cavity I need to rerun your numbers and spreadsheet it. Can you help here?Shell
Quote from: SeeShells on 07/22/2015 03:20 pm...Dr. Rodal, To make this work with the 1/2 centerline 6.1 degree angle of my cavity I need to rerun your numbers and spreadsheet it. Can you help here?ShellWhat are the parameters of what you would like to have calculated:Big Diameter = metersSmallDiameter = metersAxial Length measured perpendicular to ends = metersEnds= Flat or Spherical Excitation Frequency = GHz
Wikipedia has changed the title of the article from EM Drive to https://en.wikipedia.org/wiki/RF_resonant_cavity_thrusterPerhaps we should change the title of this thread as well, in the upcoming thread 4 to RF resonant cavity thruster - related to space flight applications ?or Microwave cavity thruster - related to space flight applications ?keeping up with Wikipedia, in a more descriptive name that is not tied (as the name "EM Drive" is) to the commercial enterprise of Roger Shawyer?Feedback?PS: I don't like the use of acronyms like "RF" or "EM"