What I can't understand about Tajmar's build is he could have easily duplicated Shawyer's 1st Experimental EMDrive as it was driven by a non water cooled low cost 2.45GHz magnetron just as Tajmar used.His vacuum chamber is more than large enough to handle the 160mm diameter big end.At 16mN Force output, his measurement system could have easily measured the Force generated.This Tajmar mini EMDrive is really a very strange build.
So yes, a wide bandwidth RF source seems to be called for and one that can be both AM and FM modulated at the same time. From my readings to date, that appears to be a hard nut to crack for solid state RF amplifiers at the desired kW power levels due to their limited RF power bandwidth capabilities, so we may be forced into using magnetrons and just learn how best to feed their 4-to-20 kV high voltage anode requirements while working in a hard vacuum. However the more difficult problems are finding ways of reducing their mass and size so we can "fly" them on our torque pendulum. Cooling the magnetrons in a hard vacuum is also another problem we need to deal with since air cooling is out of the question and liquid cooling is a giant pain to deal with as well. About the only other way to cool these beasts in a hard vacuum is to use phase change material like paraffin wax that could give us several minutes of run times before we had to let the accumulated heat in the paraffin radiate to the vacuum chamber walls.
Got it figured.Tajmar's cavity has a measured 50MHz input bandwidth from 2.40GHz to 2.45GHz or the lower portion of the WiFi band.Most magnetrons output in the upper half of the WiFi band, 2.45GHz to 2.50GHz range as attached.If his magnetron output bandwidth was like that Paul March measured (as attached) then only about ~25% of the magnetron energy (2.40GHz - 2.45GHz) would be getting inside the cavity and the other ~75% (above 2.45GHz would be rejected.Which means the 663Ws forward power (at VSWR 1.622:1) drops to 167 real watts inside the frustum with 533W reflected back to heat the magnetron.With 167W in the cavity and a Q of 48.8 the predicted Force generation is 31uNs and at a Q of 20.2 is 13uNs. A SnowFlake is ~30uN, to give an idea of the magnitude of the Forces being generated here.This same effect of mismatched input and output bandwidths caused the serious dip in Prof Yang's Force versus power curve. The lower left rectangles, in the group of 6 charts, are the cavity input bandwidth and the other curve is the magnetron output bandwidth. Clear to see the massive mismatch that occurred and that totally messed up her data until they went back and found the reason for the massive dip.So history has maybe repeated itself and this cavity input / magnetron output bandwidth mismatch may have struck again.
Quote from: SeeShells on 07/27/2015 07:41 amQuote from: lmbfan on 07/27/2015 05:05 amA post over on reddit attributes the thrust to a phenomenon called sputtering. I was wondering how valid this interpretation is. It appears to depend on oxidation, which seems unlikely in a vacuum. Link:http://www.reddit.com/r/Futurology/comments/3emk49/direct_thrust_measured_from_propellantless_em/cthg9uoYou can answer that question by filling the enclosed Frustum with Sulfur hexafluoride,Sulfur hexafluoride is an inorganic, colorless, odorless, non-flammable, extremely potent greenhouse gas which is an excellent electrical insulator. SF 6 has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. But it is hard to keep in a perforated cavity. It is used in high power systems to prevent arcing.ShellAnother thing I like about SF6 is that is a dense gas so if the thrust is dependent on gas being present then there is a lot to work with. That said, I have no idea what frequency you would need to use it as a resonant gas.
Quote from: lmbfan on 07/27/2015 05:05 amA post over on reddit attributes the thrust to a phenomenon called sputtering. I was wondering how valid this interpretation is. It appears to depend on oxidation, which seems unlikely in a vacuum. Link:http://www.reddit.com/r/Futurology/comments/3emk49/direct_thrust_measured_from_propellantless_em/cthg9uoYou can answer that question by filling the enclosed Frustum with Sulfur hexafluoride,Sulfur hexafluoride is an inorganic, colorless, odorless, non-flammable, extremely potent greenhouse gas which is an excellent electrical insulator. SF 6 has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. But it is hard to keep in a perforated cavity. It is used in high power systems to prevent arcing.Shell
A post over on reddit attributes the thrust to a phenomenon called sputtering. I was wondering how valid this interpretation is. It appears to depend on oxidation, which seems unlikely in a vacuum. Link:http://www.reddit.com/r/Futurology/comments/3emk49/direct_thrust_measured_from_propellantless_em/cthg9uo
Quote from: TheTraveller on 07/26/2015 06:54 pmWhat I can't understand about Tajmar's build is he could have easily duplicated Shawyer's 1st Experimental EMDrive as it was driven by a non water cooled low cost 2.45GHz magnetron just as Tajmar used.His vacuum chamber is more than large enough to handle the 160mm diameter big end.At 16mN Force output, his measurement system could have easily measured the Force generated.This Tajmar mini EMDrive is really a very strange build.I read a few pages ago that you guys speculated the dimensions of Tajmar EmDrive may actually be twice what we thought (because the dimensions in the paper may be radii instead of diameters). Whatever, the cavity is still very small, and the reason is quite obvious even if Tajmar didn't explain it in the paper.Tajmar had to build the cavity so small so the system "cavity + waveguide + magnetron" is light enough to hang on the torsion pendulum inside the vacuum chamber. The vacuum chamber is large, but the torsion pendulum, like Eagleworks', can sustain a limited weight.Paul March expressed the same doubts in Thread 2 when he thought about hanging a heavier magnetron on Eagleworks torsion pendulum instead of the lighter coax cable and RF amp:Quote from: Star-DriveSo yes, a wide bandwidth RF source seems to be called for and one that can be both AM and FM modulated at the same time. From my readings to date, that appears to be a hard nut to crack for solid state RF amplifiers at the desired kW power levels due to their limited RF power bandwidth capabilities, so we may be forced into using magnetrons and just learn how best to feed their 4-to-20 kV high voltage anode requirements while working in a hard vacuum. However the more difficult problems are finding ways of reducing their mass and size so we can "fly" them on our torque pendulum. Cooling the magnetrons in a hard vacuum is also another problem we need to deal with since air cooling is out of the question and liquid cooling is a giant pain to deal with as well. About the only other way to cool these beasts in a hard vacuum is to use phase change material like paraffin wax that could give us several minutes of run times before we had to let the accumulated heat in the paraffin radiate to the vacuum chamber walls. So It seems that for now we are stuck with high power magnetron = large thrust in ambient air with the risk of spurious effects; and low power solid state RF amp = precise but small thrust in a vacuum.The third way is to use 100W to 1kW solid state RM amps in ambient air, as @TheTraveller.
Quote from: TheTraveller on 07/26/2015 06:54 pmWhat I can't understand about Tajmar's build is he could have easily duplicated Shawyer's 1st Experimental EMDrive as it was driven by a non water cooled low cost 2.45GHz magnetron just as Tajmar used.His vacuum chamber is more than large enough to handle the 160mm diameter big end.At 16mN Force output, his measurement system could have easily measured the Force generated.This Tajmar mini EMDrive is really a very strange build.I read a few pages ago that you guys speculated the dimensions of Tajmar EmDrive may actually be twice what we thought (because the dimensions in the paper may be radii instead of diameters). Whatever, the cavity is still very small, and the reason is quite obvious even if Tajmar didn't explain it in the paper.Tajmar had to build the cavity so small so the system "cavity + waveguide + magnetron" is light enough to hang on the torsion pendulum inside the vacuum chamber. The vacuum chamber is large, but the torsion pendulum, like Eagleworks', can sustain a limited weight.Paul March expressed the same doubts in Thread 2 when he thought about hanging a heavier magnetron on Eagleworks torsion pendulum instead of the lighter coax cable and RF amp:Quote from: Star-DriveSo yes, a wide bandwidth RF source seems to be called for and one that can be both AM and FM modulated at the same time. From my readings to date, that appears to be a hard nut to crack for solid state RF amplifiers at the desired kW power levels due to their limited RF power bandwidth capabilities, so we may be forced into using magnetrons and just learn how best to feed their 4-to-20 kV high voltage anode requirements while working in a hard vacuum. However the more difficult problems are finding ways of reducing their mass and size so we can "fly" them on our torque pendulum. Cooling the magnetrons in a hard vacuum is also another problem we need to deal with since air cooling is out of the question and liquid cooling is a giant pain to deal with as well. About the only other way to cool these beasts in a hard vacuum is to use phase change material like paraffin wax that could give us several minutes of run times before we had to let the accumulated heat in the paraffin radiate to the vacuum chamber walls. So It seems that for now we are stuck with high power magnetron = large thrust in ambient air with the risk of spurious effects; and low power solid state RF amp = precise but small thrust in a vacuum.
Lower the power of the magnetron and stabilize the output so less is lost in spurious non-Q effects and one last thought I've had is modifying a fanless CPU cooler to keep the magnetron cooler.http://www.acousticpc.com/images/a_nofan_cr-95c_copper_fanless_cpu_cooler.jpgI'm still thinking about this one.Shell
My design predicts around 100mN from 100W narrow band Rf. Maybe 50% more if the Prof Yang short cylinders at each end trick works and eliminates the need for highly accurate and highly polished end plates.BTW that is 1N/kW. As Prof Yang's team has already achieved that back in 2010 and without the 2013 short cylindrical flat end plates, 2N/kW should be doable and maybe bettered. Prof Yang has also shown 4N/kW but only over a small power span.Above 4N/kW, further gains may be hard won without going superconducting but can't see that tech getting the reliability needed for deep space human rated applications. Probably better to then turn to scale up a 400N/100kW EMDrive and start doing human exploration and colonisation of the solar system.Might even help Paul March fund & build his WarpStar1. Hey not so crazy a private EMDrive powered space ship. Only need 126,000Ns. Yeah just dreaming. Maybe.........
Quote from: TheTraveller on 07/27/2015 09:16 amMy design predicts around 100mN from 100W narrow band Rf. Maybe 50% more if the Prof Yang short cylinders at each end trick works and eliminates the need for highly accurate and highly polished end plates..Might even help Paul March fund & build his WarpStar1. Hey not so crazy a private EMDrive powered space ship. Only need 126,000Ns. Yeah just dreaming. Maybe.........the WarpStar1 however was ME (Mach Effect) right?Speaking of which, Tajmar and Heidi Fern will tomorrow be speaking about both EM and ME drives at AIAA. here, LiveFeed for tomorrowedit: found the right one!http://livestream.com/AIAAvideo/events/4212872?origin=event_published&mixpanel_id=136b121d63432e-06c456027-316f6852-13c680-136b121d635aad&acc_id=10115456&medium=emailAIAA Propulsion & Energy 2015
My design predicts around 100mN from 100W narrow band Rf. Maybe 50% more if the Prof Yang short cylinders at each end trick works and eliminates the need for highly accurate and highly polished end plates..Might even help Paul March fund & build his WarpStar1. Hey not so crazy a private EMDrive powered space ship. Only need 126,000Ns. Yeah just dreaming. Maybe.........
Speaking of which, Tajmar and Heidi Fern will tomorrow be speaking about both EM and ME drives at AIAA. http://livestream.com/AIAAvideo/events/4212872?origin=event_published&mixpanel_id=136b121d63432e-06c456027-316f6852-13c680-136b121d635aad&acc_id=10115456&medium=emailAIAA Propulsion & Energy 2015
Quote from: aceshigh on 07/27/2015 12:06 pmSpeaking of which, Tajmar and Heidi Fern will tomorrow be speaking about both EM and ME drives at AIAA. http://livestream.com/AIAAvideo/events/4212872?origin=event_published&mixpanel_id=136b121d63432e-06c456027-316f6852-13c680-136b121d635aad&acc_id=10115456&medium=emailAIAA Propulsion & Energy 2015Excuse me, but i don't see any of those 2 listed on the schedule. Any info on what time they are supposed to talk ?Thanks
Quote from: WarpTech on 07/25/2015 09:26 pmQuote from: Rodal on 07/25/2015 08:11 pmQuote from: WarpTech on 07/25/2015 08:03 pm...I haven't used perturbation theory since circa 1992. That would take a great deal of effort for something I find to be trivially obvious. Look at the attached equation for the wave vector in a circular waveguide. If w0 = wmn, there is no propagation. There can be however, periodic boundary conditions and localized standing waves. On the other hand, even if w0 > wmn such that it is a traveling wave. There is an inertial frame where the group velocity is zero, and the same situation applies, periodic in z, with a stationary resonant standing wave.Now, what is the difference if I slowly increase w0, or slowly decrease wmn by introducing a taper? Nothing, as far as I can see. The end result is the same, a traveling wave that is accelerating. Why does this need to be proven? it's obvious. If not, why isn't it? I am not considering a closed ended frustum here. Only the tapered waveguide vs a straight waveguide. It is only a resonant cavity in 2D, the circular cross section, not the length. Bessel function is the solution for a circle. It shifts frequency for the same reason "time dilation" occurs in a gravitational field. It is in a potential energy gradient.ToddIt is the difference between a spherical wave and a flat wave. The flat wave solution with the cylindrical Bessel function in the cross section applies to a perfect cylinder. The tapered, conical waveguide does not have the flat wave solution in general, only as an approximation. The flat wave solution does not respect the boundary conditions of the lateral surface of the cone. See the paper of Yang and Fan: they consider an open waveguide and they had to use the spherical wave solution. You asked for comments. Your solution is an approximation to the spherical wave solution. The objection can be raised that the accuracy of the amplification factor is unknown, as the solution is predicated on a flat wave that does not exactly respect the boundary conditions for an open conical waveguide (or section of a cone). The cylindrical Bessel function is assumed ab initio. Satisfaction of boundary conditions is not discussed in your paper.I appreciate the help. Now i understand the issue. However, wouldn't a ray-vector approach show the same behavior without the need for spherical harmonics?Below is what Zeng & Fan wrote for impedances. Impedance is basically u0*velocity. The TE mode is the phase velocity, the TM mode is the group velocity. How do we plot this as a function of kr? I can't interpret something I don't understand and this just looks like gibberish to me, without some way to plot it out and visualize it. Sorry, I'm an engineer not a mathematician. ToddI think they are Henkel spherical functions. I could plot it with Mathematica but I have some $$$ work to do. Didn't Zeng and Fan have some plots of impedance in their paper?
Quote from: Rodal on 07/25/2015 08:11 pmQuote from: WarpTech on 07/25/2015 08:03 pm...I haven't used perturbation theory since circa 1992. That would take a great deal of effort for something I find to be trivially obvious. Look at the attached equation for the wave vector in a circular waveguide. If w0 = wmn, there is no propagation. There can be however, periodic boundary conditions and localized standing waves. On the other hand, even if w0 > wmn such that it is a traveling wave. There is an inertial frame where the group velocity is zero, and the same situation applies, periodic in z, with a stationary resonant standing wave.Now, what is the difference if I slowly increase w0, or slowly decrease wmn by introducing a taper? Nothing, as far as I can see. The end result is the same, a traveling wave that is accelerating. Why does this need to be proven? it's obvious. If not, why isn't it? I am not considering a closed ended frustum here. Only the tapered waveguide vs a straight waveguide. It is only a resonant cavity in 2D, the circular cross section, not the length. Bessel function is the solution for a circle. It shifts frequency for the same reason "time dilation" occurs in a gravitational field. It is in a potential energy gradient.ToddIt is the difference between a spherical wave and a flat wave. The flat wave solution with the cylindrical Bessel function in the cross section applies to a perfect cylinder. The tapered, conical waveguide does not have the flat wave solution in general, only as an approximation. The flat wave solution does not respect the boundary conditions of the lateral surface of the cone. See the paper of Yang and Fan: they consider an open waveguide and they had to use the spherical wave solution. You asked for comments. Your solution is an approximation to the spherical wave solution. The objection can be raised that the accuracy of the amplification factor is unknown, as the solution is predicated on a flat wave that does not exactly respect the boundary conditions for an open conical waveguide (or section of a cone). The cylindrical Bessel function is assumed ab initio. Satisfaction of boundary conditions is not discussed in your paper.I appreciate the help. Now i understand the issue. However, wouldn't a ray-vector approach show the same behavior without the need for spherical harmonics?Below is what Zeng & Fan wrote for impedances. Impedance is basically u0*velocity. The TE mode is the phase velocity, the TM mode is the group velocity. How do we plot this as a function of kr? I can't interpret something I don't understand and this just looks like gibberish to me, without some way to plot it out and visualize it. Sorry, I'm an engineer not a mathematician. Todd
Quote from: WarpTech on 07/25/2015 08:03 pm...I haven't used perturbation theory since circa 1992. That would take a great deal of effort for something I find to be trivially obvious. Look at the attached equation for the wave vector in a circular waveguide. If w0 = wmn, there is no propagation. There can be however, periodic boundary conditions and localized standing waves. On the other hand, even if w0 > wmn such that it is a traveling wave. There is an inertial frame where the group velocity is zero, and the same situation applies, periodic in z, with a stationary resonant standing wave.Now, what is the difference if I slowly increase w0, or slowly decrease wmn by introducing a taper? Nothing, as far as I can see. The end result is the same, a traveling wave that is accelerating. Why does this need to be proven? it's obvious. If not, why isn't it? I am not considering a closed ended frustum here. Only the tapered waveguide vs a straight waveguide. It is only a resonant cavity in 2D, the circular cross section, not the length. Bessel function is the solution for a circle. It shifts frequency for the same reason "time dilation" occurs in a gravitational field. It is in a potential energy gradient.ToddIt is the difference between a spherical wave and a flat wave. The flat wave solution with the cylindrical Bessel function in the cross section applies to a perfect cylinder. The tapered, conical waveguide does not have the flat wave solution in general, only as an approximation. The flat wave solution does not respect the boundary conditions of the lateral surface of the cone. See the paper of Yang and Fan: they consider an open waveguide and they had to use the spherical wave solution. You asked for comments. Your solution is an approximation to the spherical wave solution. The objection can be raised that the accuracy of the amplification factor is unknown, as the solution is predicated on a flat wave that does not exactly respect the boundary conditions for an open conical waveguide (or section of a cone). The cylindrical Bessel function is assumed ab initio. Satisfaction of boundary conditions is not discussed in your paper.
...I haven't used perturbation theory since circa 1992. That would take a great deal of effort for something I find to be trivially obvious. Look at the attached equation for the wave vector in a circular waveguide. If w0 = wmn, there is no propagation. There can be however, periodic boundary conditions and localized standing waves. On the other hand, even if w0 > wmn such that it is a traveling wave. There is an inertial frame where the group velocity is zero, and the same situation applies, periodic in z, with a stationary resonant standing wave.Now, what is the difference if I slowly increase w0, or slowly decrease wmn by introducing a taper? Nothing, as far as I can see. The end result is the same, a traveling wave that is accelerating. Why does this need to be proven? it's obvious. If not, why isn't it? I am not considering a closed ended frustum here. Only the tapered waveguide vs a straight waveguide. It is only a resonant cavity in 2D, the circular cross section, not the length. Bessel function is the solution for a circle. It shifts frequency for the same reason "time dilation" occurs in a gravitational field. It is in a potential energy gradient.Todd
[Huge URL needs to be shortened with URL shortener]..Zeng not solve the boudary condition for the conical problem. He uses the standard solutions for free space....
Quote from: Ricvil on 07/27/2015 02:32 pm[Huge URL needs to be shortened with URL shortener]..Zeng not solve the boudary condition for the conical problem. He uses the standard solutions for free space....Zeng and Fan (https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-17-1-34&id=175583 ) express the boundary conditions for the conical problem in Equations 4 (for TE modes) and 7 (for TM modes) of their paper.The solution is an eigenvalue problem.In Table 1 of their paper they give eigenvalues for TE11,TM01,TM11 and TE01 modes as a function of the cone half angle from Pi/24 to Pi/2.
...which will launch a TE mode that is coupled to the resonant iris which then reflected a matched source to the frustum sidewall which should then excite a TM mode in the frustum transverse axis which is at approx a right angle to rectangular waveguide. The diagram which shows a similar setup with the E-probe in the rectangular wave guide end wall will launch a TM mode which will be matched by the iris and reflect a matched source to the frustum wall but should excite a TE mode in the frustum. It will interesting to see his mode data.
...If his magnetron output bandwidth was like that Paul March measured (as attached) then only about ~25% of the magnetron energy (2.40GHz - 2.45GHz) would be getting inside the cavity and the other ~75% (above 2.45GHz would be rejected....
Quote from: Rodal on 07/27/2015 02:58 pmQuote from: Ricvil on 07/27/2015 02:32 pm[Huge URL needs to be shortened with URL shortener]..Zeng not solve the boudary condition for the conical problem. He uses the standard solutions for free space....Zeng and Fan (https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-17-1-34&id=175583 ) express the boundary conditions for the conical problem in Equations 4 (for TE modes) and 7 (for TM modes) of their paper.The solution is an eigenvalue problem.In Table 1 of their paper they give eigenvalues for TE11,TM01,TM11 and TE01 modes as a function of the cone half angle from Pi/24 to Pi/2.The Zeng expressions do not solve equation (1) . You may use the the "eingen values" expressions into (2) ,(3), (5) ,(6) and no one of that solves (1).
@rfmwguyChatted up some of the companies at the conference, asked the ones in R&D about any sort of electromagnetic engines/propulsions they may be working on. No dice. Most or all are researching hall thrusters/ion propulsion/etc. ...