Quote from: tchernik on 07/23/2015 07:51 pmRemarkable paper. Does this paper suggest a new kind of thruster we could build in practice? or is this un-physical due to it assuming things like Terawatts or input power or some such?Because it sounds mechanically simple. So, where's the catch?The catch is maybe in the following sentence in their paper:"hence for any momentum that is acquired by matter an opposite momentum is attributed to the electromagnetic field."Does that sentence preclude the device from being used as a thruster?
Remarkable paper. Does this paper suggest a new kind of thruster we could build in practice? or is this un-physical due to it assuming things like Terawatts or input power or some such?Because it sounds mechanically simple. So, where's the catch?
Quote from: aero on 07/23/2015 08:14 pmOf course they are. There are no losses, not because of the material model, but because of the sampling resolution, (node separation). They are a valid indication of whether or not the cavity model will resonate but more than that it is hard to say. I use them for that purpose, interpreting high Q's as strong resonance of the model and low or no Q's to indicate low or no resonance at that frequency/antenna configuration as modelled. We have known for a long time that Q's in the millions are not realistic for room temperature cavities.For interest, I've attached a movie of a mid-plane Y direction slice of the NSF frustum playing the Ez field. The movie covers about 400 cycles right before then after the Gaussian pulse ends - so shows the resonating cavity as the energy diminishes.I've also attached the ctl file I used to generate this case - note that I'm using quarter symmetry and a reduced resolution of 150 as I was centering in on the pulse behavior. In the movie, I've clamped the Ez values to +/- 0.028665 so that the effect of the source isn't overwhelming in the beginning when it's on.Note that in the ctl file, I've included an alternative Cu model that is taken from the reference: http://falsecolour.com/aw/meep_metals/investigation.html#SECTION00011600000000000000 where the author validated the Cu model inside meep.I'm running higher res (250) now and bracketing the interesting time period on output after the Gaussian pulse ends. I think we should probably naturally terminate the Gaussian source pulse instead of artificially terminating it to avoid the transients.WRT running a loop source, should be pretty easy, though the aliasing into the cartesian mesh is going to introduce some weird frequencies...
Of course they are. There are no losses, not because of the material model, but because of the sampling resolution, (node separation). They are a valid indication of whether or not the cavity model will resonate but more than that it is hard to say. I use them for that purpose, interpreting high Q's as strong resonance of the model and low or no Q's to indicate low or no resonance at that frequency/antenna configuration as modelled. We have known for a long time that Q's in the millions are not realistic for room temperature cavities.
It seems somewhere I read or heard Solidworks could output a C++ code to a output file for a object. It's been awhile so I might be wrong. If it can ,could that C++ code be used in MEEP for the loop antenna? Areo would be happy.
The stress at the small base is practically zero for all the previously shown time steps. In order to save bandwidth I only show the last step
Quote from: Rodal on 07/23/2015 06:13 pmThe stress at the small base is practically zero for all the previously shown time steps. In order to save bandwidth I only show the last stepTherefore (?), all of the energy is attenuated by the side walls before it reaches the small base?Todd
...I have a AC rheostat that I was thinking about putting on the current magnetron heater I'm using to drop the voltage lowering the output power and narrowing the bandwidth of the magnetron. I have about 3 volts to work with so it will be touchy. Thoughts here?
Quote from: dumbo on 07/23/2015 05:16 pmQuote from: frobnicat on 07/23/2015 04:40 pmThis was discussed in thread 2, thing is for a "propulsive effect" of constant thrust it relies on a non stationary ever increasing current :http://forum.nasaspaceflight.com/index.php?topic=36313.msg1350655#msg1350655They also have a more recent paper called "Relativistic Engine Based on a Permanent Magnet" (from July 13, 2015). The link is: http://lib-arxiv-008.serverfarm.cornell.edu/pdf/1507.02897v1.pdfRemarkable paper. Does this paper suggest a new kind of thruster we could build in practice? or is this un-physical due to it assuming things like Terawatts or input power or some such?Because it sounds mechanically simple. So, where's the catch?
Quote from: frobnicat on 07/23/2015 04:40 pmThis was discussed in thread 2, thing is for a "propulsive effect" of constant thrust it relies on a non stationary ever increasing current :http://forum.nasaspaceflight.com/index.php?topic=36313.msg1350655#msg1350655They also have a more recent paper called "Relativistic Engine Based on a Permanent Magnet" (from July 13, 2015). The link is: http://lib-arxiv-008.serverfarm.cornell.edu/pdf/1507.02897v1.pdf
This was discussed in thread 2, thing is for a "propulsive effect" of constant thrust it relies on a non stationary ever increasing current :http://forum.nasaspaceflight.com/index.php?topic=36313.msg1350655#msg1350655
Quote from: Rodal on 07/23/2015 07:27 pmI just calculated Yang/Shell TM113 with my program:Q =45,039 Yang/Shell (copper) natural frequency for TM113 = 2.4941 GHzQ =50,175 rfmwguy/NSF-1701(copper) Used the following material properties:epsilon0 = 8.854187817*10^-12); mu0 = 0.999991(*copper*)*4*Pi*10^(-7);resistivity = 1.678*10^(-8)(*copper*);For using same material constants, I get If I use brass or bronze I will get a lower Q. For example, for:resistivity = 1.437*10^(-7) high strength brassgiving:Q= 15,391 (Yang/Shell) high strength brassQ= 17,146 (rfmwguy/NSF1701) high strength brass what material model are you using to get Q's in the millions? are you using the Drude model ?The Drude model.Quote____________PS: I edited my prior message, eliminating reference to the 60 million Q, as it appears that all the Q's from Meep runs are suspect.Of course they are. There are no losses, not because of the material model, but because of the sampling resolution, (node separation). They are a valid indication of whether or not the cavity model will resonate but more than that it is hard to say. I use them for that purpose, interpreting high Q's as strong resonance of the model and low or no Q's to indicate low or no resonance at that frequency/antenna configuration as modelled. We have known for a long time that Q's in the millions are not realistic for room temperature cavities.
I just calculated Yang/Shell TM113 with my program:Q =45,039 Yang/Shell (copper) natural frequency for TM113 = 2.4941 GHzQ =50,175 rfmwguy/NSF-1701(copper) Used the following material properties:epsilon0 = 8.854187817*10^-12); mu0 = 0.999991(*copper*)*4*Pi*10^(-7);resistivity = 1.678*10^(-8)(*copper*);For using same material constants, I get If I use brass or bronze I will get a lower Q. For example, for:resistivity = 1.437*10^(-7) high strength brassgiving:Q= 15,391 (Yang/Shell) high strength brassQ= 17,146 (rfmwguy/NSF1701) high strength brass what material model are you using to get Q's in the millions? are you using the Drude model ?
____________PS: I edited my prior message, eliminating reference to the 60 million Q, as it appears that all the Q's from Meep runs are suspect.
Quote from: flux_capacitor on 07/23/2015 08:10 pmQuote from: tchernik on 07/23/2015 07:51 pmRemarkable paper. Does this paper suggest a new kind of thruster we could build in practice? or is this un-physical due to it assuming things like Terawatts or input power or some such?Because it sounds mechanically simple. So, where's the catch?The catch is maybe in the following sentence in their paper:"hence for any momentum that is acquired by matter an opposite momentum is attributed to the electromagnetic field."Does that sentence preclude the device from being used as a thruster?The catch appears to be the same as the previous paper, starting from the same idea (eq. 21 in new paper) and arriving at similar conclusion (eq. 48) that a force is proportional to the second derivative of current driven in a loop. While nothing factually wrong is written, nothing hints at a "rectification" (no square term for instance) and nothing justify the deceptive mention of microwave currents as an implied mean to reach a steady state net force (just before conclusion). By eq. 48, For a steady state net force the second derivative of current must be constant, that makes a current not only increasing constantly but also accelerating in rate of increase. A stationary current (AC, DC, AC+DC, random of constant magnitude envelope...) would amount to 0 net thrust averaged.Taking the numbers for making this flying saucer to fly (last part before conclusion) 1.9*10^22 A/s², so first second of hovering needs about 10^22 A, and only increasing quadratically. Any copper coil would sublimate instantly, going superconducting niobium-tin @ 200000 A/cm² would require a coil with an astonishing section of 5 trillion square meters, more than surface of India...
Quote from: frobnicat on 07/23/2015 11:28 pmQuote from: flux_capacitor on 07/23/2015 08:10 pmQuote from: tchernik on 07/23/2015 07:51 pmRemarkable paper. Does this paper suggest a new kind of thruster we could build in practice? or is this un-physical due to it assuming things like Terawatts or input power or some such?Because it sounds mechanically simple. So, where's the catch?The catch is maybe in the following sentence in their paper:"hence for any momentum that is acquired by matter an opposite momentum is attributed to the electromagnetic field."Does that sentence preclude the device from being used as a thruster?The catch appears to be the same as the previous paper, starting from the same idea (eq. 21 in new paper) and arriving at similar conclusion (eq. 48) that a force is proportional to the second derivative of current driven in a loop. While nothing factually wrong is written, nothing hints at a "rectification" (no square term for instance) and nothing justify the deceptive mention of microwave currents as an implied mean to reach a steady state net force (just before conclusion). By eq. 48, For a steady state net force the second derivative of current must be constant, that makes a current not only increasing constantly but also accelerating in rate of increase. A stationary current (AC, DC, AC+DC, random of constant magnitude envelope...) would amount to 0 net thrust averaged.Taking the numbers for making this flying saucer to fly (last part before conclusion) 1.9*10^22 A/s², so first second of hovering needs about 10^22 A, and only increasing quadratically. Any copper coil would sublimate instantly, going superconducting niobium-tin @ 200000 A/cm² would require a coil with an astonishing section of 5 trillion square meters, more than surface of India...Typically for these sorts of propellantless ideas, the theoretical ease of achievement of goals is, from easiest to hardest:1. Producing a unidirectional force of small magnitude2. Demonstrating (at least local, apparent) overunity3. Lifting off Earth's surface.So I'd suggest looking at forces in the microNewton range and seeing if anything realistic can be constructed. I'll probably have a play around with it. What's intriguing is that to which @frobnicat alludes; namely, that the square law for current does not appear symmetrical, and so the reset phase of the cycle back down to zero current again might be imagined to be accomplished with less total work done than was done by the force in the quadratic current phase of the cycle. This is tantamount to a force rectification, but one would need to do some gnarly integrals (I think) in order to prove that Integral[F0.ds] differs from Integral[F1.ds]. If you see what I mean (I'm not expressing this very well, sorry).
Quote from: SeeShells on 07/23/2015 11:28 pmIt seems somewhere I read or heard Solidworks could output a C++ code to a output file for a object. It's been awhile so I might be wrong. If it can ,could that C++ code be used in MEEP for the loop antenna? Areo would be happy.I would be happy. I might even be able to get it compiled into meep and running. With help.
Been there, done that years ago. The integral around the current loop is easy. Optimization leads to making the loop smaller so that a higher current can be achieved. Eventually, you end up with a dipole antenna. Until that point, I found the integral of the E field to be practically impossible to do by hand. For the dipole antenna, I was able to use a near field approximation. Then, I found the charge density on the antenna moves to exert forces that oppose the change in magnetic flux. This results in simply a unidirectional, 1/4-wave dipole antenna array, whose thrust is proportional to the output power by 1/c. Have fun!Todd
Quote from: WarpTech on 07/24/2015 03:22 amBeen there, done that years ago. The integral around the current loop is easy. Optimization leads to making the loop smaller so that a higher current can be achieved. Eventually, you end up with a dipole antenna. Until that point, I found the integral of the E field to be practically impossible to do by hand. For the dipole antenna, I was able to use a near field approximation. Then, I found the charge density on the antenna moves to exert forces that oppose the change in magnetic flux. This results in simply a unidirectional, 1/4-wave dipole antenna array, whose thrust is proportional to the output power by 1/c. Have fun!ToddExcellent! I have only one caveat, and it's this odd square-law dependence for the current and its possible resultant force rectification over a cycle. Did you look at this specifically?
Quote from: SeeShells on 07/23/2015 02:29 pm...I have a AC rheostat that I was thinking about putting on the current magnetron heater I'm using to drop the voltage lowering the output power and narrowing the bandwidth of the magnetron. I have about 3 volts to work with so it will be touchy. Thoughts here?You do know the heater is at a deadly 4kV potential, the rheostat must handle perhaps 10A for a 30W filament? Could always use a plastic tube to tune it. I was thinking either lithium batteries, or probably an opto-isolated mosfet PWM by a controller. The opto-isolator is all that protects the fragile electronics and perhaps myself from a Very Bad (last) Day.
Quote from: aero on 07/24/2015 12:31 amQuote from: SeeShells on 07/23/2015 11:28 pmIt seems somewhere I read or heard Solidworks could output a C++ code to a output file for a object. It's been awhile so I might be wrong. If it can ,could that C++ code be used in MEEP for the loop antenna? Areo would be happy.I would be happy. I might even be able to get it compiled into meep and running. With help.That may not be necessary or cycle-consuming overkill, as I think I read that Meep has a magnetic-current source, and can employ point or patch sources. So although a discrete stitched-together loop might be more true to life, a square 1/2" patch normal to the sidewall might be faster, simpler & expedient.
Quote from: deltaMass on 07/24/2015 04:37 amQuote from: WarpTech on 07/24/2015 03:22 amBeen there, done that years ago. The integral around the current loop is easy. Optimization leads to making the loop smaller so that a higher current can be achieved. Eventually, you end up with a dipole antenna. Until that point, I found the integral of the E field to be practically impossible to do by hand. For the dipole antenna, I was able to use a near field approximation. Then, I found the charge density on the antenna moves to exert forces that oppose the change in magnetic flux. This results in simply a unidirectional, 1/4-wave dipole antenna array, whose thrust is proportional to the output power by 1/c. Have fun!ToddExcellent! I have only one caveat, and it's this odd square-law dependence for the current and its possible resultant force rectification over a cycle. Did you look at this specifically?Yes, it's not odd. EM waves are 2nd order derivatives of the potential. In the paper he is integrating to get the potential, so the emitted radiation is 2nd order effect. 1st order EM waves don't propagate. The effect is maximized at 1/4 wavelength separation, but it's there at other separations at reduced thrust. I've heard from lots of people who had the same idea over the years.So... getting back to thrust-to-power ratios. What do you think of this result (attached) for an open-ended, tapered waveguide? Given my parameterization in the first equation is correct for small angles that is...Todd