Quote from: Rodal on 07/23/2015 05:29 pm Quote from: DrBagelBites on 07/06/2015 10:45 pmI thought I would chime in with questions for the AIAA conference. I am going to be attending the event, so I will be able to report back to you guys about what happens, other questions that were asked, etc. Let me know of a couple of definite questions that anyone would want me to ask during the Q and A, AIAA Propulsion and Energy Forum and ExpositionHilton Orlando, Orlando, Florida...TUESDAY, JULY 28, 2015 NFF-04. Future Flight Propulsion Systems ...5:00 PM - 5:30 PMDirect Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects Martin TajmarSuggested questions to Prof. Tajmar arranged in order of importance:Q1. What is the explanation for the very low Q (only 50) in your EM Drive experiments?. Shawyer has reported Q=45,000 for his Demonstrator at your same tested frequency of 2.45 GHz. Is it because you did not use the usual waveguide isolator and 3-stub tuner between the magnetron and test article?Has Prof. Tajmar's team grossly over-coupled the RF input to the EM Drive copper truncated cone? Over-coupling is a matter of putting a larger resistive load on the resonant cavity by shunting more of the source load onto the cavity. Over-coupling can give an "equivalent" bandwidth which includes more than one mode.Was Tajmar trying to match it w/ ~ 50 MHz ? How wide was the high filament current magnetron bandwidth?. _____________________________________________________Q2. why your experiments show approximately 60% different thrust force measurements when the EM Drive was physically rotated 180 degrees from the "forward" thrust tests to the "reverse" thrust tests? Shouldn't the thrust be the same regardless of space orientation? Is this orientation-dependence indicative of an experimental artifact or a dependence on an external field ?_____________________________________________________Q3. Does Prof. Tajmar think that the reason why Shawyer and Yang claimed much higher thrust (over 1,000 to 10,000 times greater force/InputPower than what Tajmar measured) is because Shawyer and Yang reported tests at ambient pressure (unlike Prof. Tajmar who has performed his tests in a vacuum), and Shawyer and Yang just reported thermal convection artifacts? If, not a nullification due to Shawyer and Yang not performing tests in vacuum, what does Prof. Tajmar think that the huge difference (1,000 to 10,000 times) is due to ?_____________________________________________________Q4: What does Prof. Tajmar think about the "motor", "generator" conjecture of Shawyer?: that the EM Drive will not register a significant acceleration unless motivated to do so by vibrations of unspecified magnitude and frequency to produce initial acceleration in the direction pointing from the big base to the small base. Does Prof. Tajmar think that the reason why he measured much lower thrust is because he didn't vibrate the EM Drive to provide such initial condition?Sorry for the major delay. Was out enjoying a nice weekend vacation with my family. I'll be sure to ask at least the first question. If I have the opportunity to ask more, that would be even better. I'll be covering the event and doing updates on /r/EmDrive just because it is easier to do on mobile. -I
Quote from: DrBagelBites on 07/06/2015 10:45 pmI thought I would chime in with questions for the AIAA conference. I am going to be attending the event, so I will be able to report back to you guys about what happens, other questions that were asked, etc. Let me know of a couple of definite questions that anyone would want me to ask during the Q and A, AIAA Propulsion and Energy Forum and ExpositionHilton Orlando, Orlando, Florida...TUESDAY, JULY 28, 2015 NFF-04. Future Flight Propulsion Systems ...5:00 PM - 5:30 PMDirect Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects Martin TajmarSuggested questions to Prof. Tajmar arranged in order of importance:Q1. What is the explanation for the very low Q (only 50) in your EM Drive experiments?. Shawyer has reported Q=45,000 for his Demonstrator at your same tested frequency of 2.45 GHz. Is it because you did not use the usual waveguide isolator and 3-stub tuner between the magnetron and test article?Has Prof. Tajmar's team grossly over-coupled the RF input to the EM Drive copper truncated cone? Over-coupling is a matter of putting a larger resistive load on the resonant cavity by shunting more of the source load onto the cavity. Over-coupling can give an "equivalent" bandwidth which includes more than one mode.Was Tajmar trying to match it w/ ~ 50 MHz ? How wide was the high filament current magnetron bandwidth?. _____________________________________________________Q2. why your experiments show approximately 60% different thrust force measurements when the EM Drive was physically rotated 180 degrees from the "forward" thrust tests to the "reverse" thrust tests? Shouldn't the thrust be the same regardless of space orientation? Is this orientation-dependence indicative of an experimental artifact or a dependence on an external field ?_____________________________________________________Q3. Does Prof. Tajmar think that the reason why Shawyer and Yang claimed much higher thrust (over 1,000 to 10,000 times greater force/InputPower than what Tajmar measured) is because Shawyer and Yang reported tests at ambient pressure (unlike Prof. Tajmar who has performed his tests in a vacuum), and Shawyer and Yang just reported thermal convection artifacts? If, not a nullification due to Shawyer and Yang not performing tests in vacuum, what does Prof. Tajmar think that the huge difference (1,000 to 10,000 times) is due to ?_____________________________________________________Q4: What does Prof. Tajmar think about the "motor", "generator" conjecture of Shawyer?: that the EM Drive will not register a significant acceleration unless motivated to do so by vibrations of unspecified magnitude and frequency to produce initial acceleration in the direction pointing from the big base to the small base. Does Prof. Tajmar think that the reason why he measured much lower thrust is because he didn't vibrate the EM Drive to provide such initial condition?
I thought I would chime in with questions for the AIAA conference. I am going to be attending the event, so I will be able to report back to you guys about what happens, other questions that were asked, etc. Let me know of a couple of definite questions that anyone would want me to ask during the Q and A, AIAA Propulsion and Energy Forum and ExpositionHilton Orlando, Orlando, Florida...TUESDAY, JULY 28, 2015 NFF-04. Future Flight Propulsion Systems ...5:00 PM - 5:30 PMDirect Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects Martin Tajmar
And there's our answer! Look at TM01 mode graph. Since they normalized to Z0, (Eta), then c=1. This graph clearly shows that the group velocity for small kr is faster than light. Likewise, the TE11 mode gives the phase velocity as slower than light for small kr. Given the thrust to power ratio F/P = 1/v_phase. Then for small kr, there is an enormous thrust for very little power!
Quote from: WarpTech on 07/25/2015 10:40 pmAnd there's our answer! Look at TM01 mode graph. Since they normalized to Z0, (Eta), then c=1. This graph clearly shows that the group velocity for small kr is faster than light. Likewise, the TE11 mode gives the phase velocity as slower than light for small kr. Given the thrust to power ratio F/P = 1/v_phase. Then for small kr, there is an enormous thrust for very little power!This is over my head, please ELI5 what is the physical meaning of a "small kr"? Geometrically, does a "small kr" belongs to a particular region of a continuously- tapered waveguide? The apex maybe? We now understand that the group velocity exponentially decreases while approaching the small end (for a closed frustum, and if the cavity is properly designed as if it had a "cut-off diameter"). But you also says that group velocity becomes superluminal for small kr in TM01 mode, so what is the dependence between the two?
Quote from: flux_capacitor on 07/26/2015 12:09 pmQuote from: WarpTech on 07/25/2015 10:40 pmAnd there's our answer! Look at TM01 mode graph. Since they normalized to Z0, (Eta), then c=1. This graph clearly shows that the group velocity for small kr is faster than light. Likewise, the TE11 mode gives the phase velocity as slower than light for small kr. Given the thrust to power ratio F/P = 1/v_phase. Then for small kr, there is an enormous thrust for very little power!This is over my head, please ELI5 what is the physical meaning of a "small kr"? Geometrically, does a "small kr" belongs to a particular region of a continuously- tapered waveguide? The apex maybe? We now understand that the group velocity exponentially decreases while approaching the small end (for a closed frustum, and if the cavity is properly designed as if it had a "cut-off diameter"). But you also says that group velocity becomes superluminal for small kr in TM01 mode, so what is the dependence between the two?It is not kr but k times r: k * r , where:r is the spherical radius: the distance from the apex of the cone. k is the wavenumber (https://en.wikipedia.org/wiki/Wavenumber) k = 2 Pi/wavelength,k * r is the dimensionless distance from the apex of the cone, non-dimensionalized by kk * r = 0 is the apex of the cone, since r=0 is the apex of the cone
...BTW I'm surprised the Tajmar Q is a high as it is, considering the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. So maybe a Q of 48.8 is not that bad.
...EDIT: I didn't understand kr was actually k * rSo it depends on frequency besides distance from the apex.
Quote from: flux_capacitor on 07/26/2015 12:18 pm...EDIT: I didn't understand kr was actually k * rSo it depends on frequency besides distance from the apex.I agree, when I first saw the notation kr in Yang and Fan's paper I found that confusing too, as it could be interpreted as k sub r, a variable instead of two variables multiplied by each other. I don't like the notation kr. It would be better if the multiplication sign would be included or if big separation would be included to make it clear that it is the product of two variables, one of the variables (k) dependent on wavelength, and hence dependent on frequency.
Quote from: Rodal on 07/26/2015 12:33 pmQuote from: flux_capacitor on 07/26/2015 12:18 pm...EDIT: I didn't understand kr was actually k * rSo it depends on frequency besides distance from the apex.I agree, when I first saw the notation kr in Yang and Fan's paper I found that confusing too, as it could be interpreted as k sub r, a variable instead of two variables multiplied by each other. I don't like the notation kr. It would be better if the multiplication sign would be included or if big separation would be included to make it clear that it is the product of two variables, one of the variables (k) dependent on wavelength, and hence dependent on frequency.I concur. Following this idea: since k = 2 Pi/wavelengthA small k implies a longer wavelength so a lower frequency.A small k*r is dimensionless but implies both a low operating frequency and a short distance from the apexIn a closed cavity there are two ways of getting closer to the apex:1- Increase the cone angle so the apex is closer to the small end plateor2- Make the end plate as smaller as possibleSince we saw Yang's design with a low cone angle is more efficient, we should not try (1) but (2). Which is difficult since the lower the frequency, the bigger the frustum.Am I right on this?But how the group velocity can become superluminal while it decreases is still beyond me.
Quote from: TheTraveller on 07/26/2015 12:20 pm...BTW I'm surprised the Tajmar Q is a high as it is, considering the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. So maybe a Q of 48.8 is not that bad.Now put those thoughts together concerning the natural frequency: 2.45 GHz is NOT a subharmonic response it is the natural frequency of this device, as calculated by COMSOL Finite Element analysis.For the same reason you are discussing above: <<the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. >>you canNOT use a formula for a close, perfect truncated cone to calculate the natural frequency of this device. The huge hole lowers the natural frequency of TE111 from over 4 GHz to 2.45 GHz.Do a back of the envelope analysis and you will see.This is why CERN and other particle accelerators use FEA to calculate natural frequencies for open cavities. Once you have a hole in the cavity that represents 37% of the total surface of the cavity, of course the natural frequency is going to be much lower than calculated ignoring the hole.Not a subharmonic response, it is the natural frequency of the cavity taking into account the huge hole from the side waveguide.If you don't believe it, please consult particle accelerator literature, where cavities with huge holes are common.
Quote from: TheTraveller on 07/26/2015 12:54 pmQuote from: Rodal on 07/26/2015 12:26 pmQuote from: TheTraveller on 07/26/2015 12:20 pm...BTW I'm surprised the Tajmar Q is a high as it is, considering the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. So maybe a Q of 48.8 is not that bad.Now put those thoughts together concerning the natural frequency: 2.45 GHz is NOT a subharmonic response it is the natural frequency of this device, as calculated by COMSOL Finite Element analysis.For the same reason you are discussing above: <<the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. >>you canNOT use a formula for a close, perfect truncated cone to calculate the natural frequency of this device. The huge hole lowers the natural frequency of TE111 from over 4 GHz to 2.45 GHz.Do a back of the envelope analysis and you will see.This is why CERN and other particle accelerators use FEA to calculate natural frequencies for open cavities. Once you have a hole in the cavity that represents 37% of the total surface of the cavity, of course the natural frequency is going to be much lower than calculated ignoring the hole.Not a subharmonic response, it is the natural frequency of the cavity taking into account the huge hole from the side waveguide.If you don't believe it, please consult particle accelerator literature, where cavities with huge holes are common.Looking at the side image, it appears the WR40 waveguide is attached to the magnetron but then drops down in size through 2 other smaller then smaller waveguide sections as the cavity side wall is not 86mm long.Suspect there may be an iris between one of the waveguide to waveguide couplings. Probably at the coupling nearest to the cavity side entrance. Also expect to see some impedance tuning screws as Shawyer told me he has never heard of a successful EMDrive build without having the ability to tune for impedance matching.Both the CAD image and the COMSOL image (most important, as this was used for analyis of natural frequency purposes) show a big opening instead of an Iris. The COMSOL FEA analysis was modeled as if there is a huge opening, not an Iris. They would not have gone through the time and expense of doing the COMSOL analysis based on a wrong model of the opening.Also, and most important, the COMSOL FEA analysis shows the distortion of the electromagnetic field due to the huge opening for the waveguide at the right
Quote from: Rodal on 07/26/2015 12:26 pmQuote from: TheTraveller on 07/26/2015 12:20 pm...BTW I'm surprised the Tajmar Q is a high as it is, considering the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. So maybe a Q of 48.8 is not that bad.Now put those thoughts together concerning the natural frequency: 2.45 GHz is NOT a subharmonic response it is the natural frequency of this device, as calculated by COMSOL Finite Element analysis.For the same reason you are discussing above: <<the opening size of the WR340 waveguide is 86 x 43mm, 3,698mm area. Frustum side wall area 10,064.2 mm and the hole in the side wall for the waveguide is ~37% of the total. >>you canNOT use a formula for a close, perfect truncated cone to calculate the natural frequency of this device. The huge hole lowers the natural frequency of TE111 from over 4 GHz to 2.45 GHz.Do a back of the envelope analysis and you will see.This is why CERN and other particle accelerators use FEA to calculate natural frequencies for open cavities. Once you have a hole in the cavity that represents 37% of the total surface of the cavity, of course the natural frequency is going to be much lower than calculated ignoring the hole.Not a subharmonic response, it is the natural frequency of the cavity taking into account the huge hole from the side waveguide.If you don't believe it, please consult particle accelerator literature, where cavities with huge holes are common.Looking at the side image, it appears the WR40 waveguide is attached to the magnetron but then drops down in size through 2 other smaller then smaller waveguide sections as the cavity side wall is not 86mm long.Suspect there may be an iris between one of the waveguide to waveguide couplings. Probably at the coupling nearest to the cavity side entrance. Also expect to see some impedance tuning screws as Shawyer told me he has never heard of a successful EMDrive build without having the ability to tune for impedance matching.
I wrote those questions before the paper was released, based on information from knowledgeable sources (apparently the information I got was good). Upon reading the final paper, I would move this question up, as questions 2 and 3 are pretty much answered in the paper:Q4Q1: What does Prof. Tajmar think about the "motor", "generator" conjecture of Shawyer?: that the EM Drive will not register a significant acceleration unless motivated to do so by vibrations of unspecified magnitude and frequency to produce initial acceleration in the direction pointing from the big base to the small base. Does Prof. Tajmar think that the reason why he measured much lower thrust in vacuum is because he didn't vibrate the EM Drive to provide such initial condition? Could this also be a reason as to the variability in experimental results ?
Quote from: Rodal on 07/26/2015 01:33 pmAs in copyright law:Quote from: Copyright Fair UseWhy are you using the image? If it is “…for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research…” you’re on the right track..Amazing that the same person that posted a link to a copyright infringement place is now pontificating on the use of an image to discuss an aerospace research issue, which is a well-known accepted and valid practice.The liability isn't on your part, it's on Chris Bergin's and NSF's; since the site receives ad revenues, there's a degree of profit that comes from hosting the material on his part, and I'm not sure the thread's intentions of teaching individuals and performing academic study is sufficient to warrant the placement of significant excerpts without NSF inheriting some legal liabilities. Of course, I could be wrong; copyright law and controlling the distribution of information for money is a huge pain in the butt.
As in copyright law:Quote from: Copyright Fair UseWhy are you using the image? If it is “…for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research…” you’re on the right track..Amazing that the same person that posted a link to a copyright infringement place is now pontificating on the use of an image to discuss an aerospace research issue, which is a well-known accepted and valid practice.
Why are you using the image? If it is “…for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research…” you’re on the right track..
Quote from: RotoSequence on 07/26/2015 01:41 pmQuote from: Rodal on 07/26/2015 01:33 pmAs in copyright law:Quote from: Copyright Fair UseWhy are you using the image? If it is “…for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research…” you’re on the right track..Amazing that the same person that posted a link to a copyright infringement place is now pontificating on the use of an image to discuss an aerospace research issue, which is a well-known accepted and valid practice.The liability isn't on your part, it's on Chris Bergin's and NSF's; since the site receives ad revenues, there's a degree of profit that comes from hosting the material on his part, and I'm not sure the thread's intentions of teaching individuals and performing academic study is sufficient to warrant the placement of significant excerpts without NSF inheriting some legal liabilities. Of course, I could be wrong; copyright law and controlling the distribution of information for money is a huge pain in the butt.Fine, I removed the single image that was used for research purposes to answer a technical question.Do you see the flagrant difference between that and this poster that is now pontificating after he posted a link to a copyright infringement place?
Gentlemen, you have a considerable audience here, more interested in EmDrive developments related to space flight applications. Please settle this issue via PM. You are both two very valuable persons, and I enjoy reading your thoughts most of the time when they are not against one's behavior. Science needs you two. Another matter. Today I wrote a clarification on Physics Stack Exchange about group velocity in a waveguide and momentum transmission, which is different than electromagnetic waves propagating in free space. If you think the content there has worth, please go to the post, read it and upvote If you think it is incomplete or false, comments are of course welcome:http://physics.stackexchange.com/questions/190018/does-radiation-force-depend-on-group-velocity-or-on-phase-velocity/196014#196014I've commented on this mainly because what was stated previously on Wikipedia about phase velocity in a waveguide (which is superluminal) was IMO false.