Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1797085 times)

Offline frobnicat

  • Full Member
  • ****
  • Posts: 518
  • Liked: 500
  • Likes Given: 151
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?

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/s, 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/cm would require a coil with an astonishing section of 5 trillion square meters, more than surface of India...

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2324
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2952
  • Likes Given: 2586
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.

Online aero

  • Senior Member
  • *****
  • Posts: 2736
  • 92129
  • Liked: 704
  • Likes Given: 236

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.
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...

I couldn't tell from the video at what point the source pulse cut off. Do you know?

As for the copper model used, it is the one developed by Aaron Webster here:
http://www.fzu.cz/~dominecf/meep/data/meep-metals.pdf

and using the pattern developed by Bala Krishna Juluri here:
http://juluribk.com/2011/04/27/plasmonic-materials-in-meep/

It is unfortunate that the data modelled was for wavelengths ranging from 2 x10-7 to 2 x 10-6 That is micro meter wavelength. Copper behaves quite differently in the millimeter  wavelength range.

Retired, working interesting problems

Online aero

  • Senior Member
  • *****
  • Posts: 2736
  • 92129
  • Liked: 704
  • Likes Given: 236
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.

I would be happy. I might even be able to get it compiled into meep and running. With help.
Retired, working interesting problems

Online WarpTech

  • Full Member
  • ****
  • Posts: 1223
  • Do it!
  • Vista, CA
  • Liked: 1290
  • Likes Given: 1739
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

Therefore (?), all of the energy is attenuated by the side walls before it reaches the small base?

Todd

Offline Rodal

  • Senior Member
  • *****
  • Posts: 5833
  • USA
  • Liked: 5901
  • Likes Given: 5248
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

Therefore (?), all of the energy is attenuated by the side walls before it reaches the small base?

Todd

This is a very unusual case.  The dipole antenna cannot excite a TE mode.  To best excite the TM mode it has to be oriented in the transverse direction.  In the previous run it was oriented in the transverse direction, it excited TM113 and the energy was felt at the small end.  See http://forum.nasaspaceflight.com/index.php?topic=37642.msg1406307#msg1406307 and the post below it.  Actually the highest stress was and highest force was at the small end.



In this case it is oriented in the longitudinal direction and the energy does not reach the small end.  There are no indications of having succeeded at exciting a mode.   The Meep output movies are very misleading because they do not give you the magnitude of the electromagnetic fields shown.  It is trying to excite TM113 again but the magnitude is extremely small.  In this case the electromagnetic field from the antenna has a huge a large magnitude spike and that's it.   Very little of anything else going on in the cavity besides the antenna.

« Last Edit: 07/24/2015 02:14 AM by Rodal »

Offline mwvp

  • Full Member
  • **
  • Posts: 254
  • Coincidence? I think Not!
  • Liked: 169
  • Likes Given: 30
...
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.
« Last Edit: 07/24/2015 03:56 AM by mwvp »

Online aero

  • Senior Member
  • *****
  • Posts: 2736
  • 92129
  • Liked: 704
  • Likes Given: 236
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

Therefore (?), all of the energy is attenuated by the side walls before it reaches the small base?

Todd

Dr. Rodal,
I suggest that I move the small base cuts one row toward the center to confirm that the cut I made was not actually inside the surface of the copper base. If you get markedly different results one row further inward, doesn't that mean that the current cut was most likely in the wrong place? And if you get very similar results, does that confirm the cut location? Or do I need to move the cut further inward to confirm? And even if the current cut is in the correct location, wouldn't a few cuts in toward the center tell us something? How many and how much?
Retired, working interesting problems

Online WarpTech

  • Full Member
  • ****
  • Posts: 1223
  • Do it!
  • Vista, CA
  • Liked: 1290
  • Likes Given: 1739
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

They 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

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?

Let's do the math:

N1 = 1000 turns
I1 = 100 A

Inductance ~ u0*10002 ~ millihenry to henry range

And they want to charge and discharge this inductor to 100A, in 0.3 nanoseconds each way... Hmmm

L*dI/dt ~ (1 Hy)*(100A)/(.3E-09) ~ 300,000,000,000 Volts!

So 100A x 3E11V = 30 Terawatts of peak power!  (Give or take a couple of orders of magnitude, eh? )

Between equations 15 and 16, the author seems to hand-wave the canceling of the E field, and continues with only the B field that does not cancel. Unfortunately, such a large E field will cause material to polarize, across the magnetic moment and it cannot be neglected. It will (practically) nullify the force, except for leakage, which makes it a simple photon rocket as @deltaMass surmised. I know this because I've beat this idea to death over the past 20 years. My first paper on warp drive used precisely this idea of phased antenna arrays because the magnetic field does exactly what they're saying. It was wrong when the E field is considered too. I think it's a photon rocket, nothing more.
Todd

 

Online WarpTech

  • Full Member
  • ****
  • Posts: 1223
  • Do it!
  • Vista, CA
  • Liked: 1290
  • Likes Given: 1739
I just calculated Yang/Shell TM113 with my program:

Q =45,039 Yang/Shell (copper)  natural frequency for TM113 = 2.4941 GHz
Q =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 brass

giving:

Q=  15,391  (Yang/Shell)  high strength brass
Q=  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.

The only reason this would even matter is to determine the steady state stored energy. As long as we don't do that, and don't allow it to run so long that the stored energy becomes unrealistic, this is not an issue at all. What is important is the relative value of stored energy remains realistic, not the Q. IMO.
Todd


Offline deltaMass

  • Full Member
  • ****
  • Posts: 955
  • A Brit in California
  • Liked: 671
  • Likes Given: 275
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?

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/s, 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/cm 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 magnitude
2. Demonstrating (at least local, apparent) overunity
3. 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).

Online WarpTech

  • Full Member
  • ****
  • Posts: 1223
  • Do it!
  • Vista, CA
  • Liked: 1290
  • Likes Given: 1739
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?

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/s, 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/cm 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 magnitude
2. Demonstrating (at least local, apparent) overunity
3. 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).

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

Offline mwvp

  • Full Member
  • **
  • Posts: 254
  • Coincidence? I think Not!
  • Liked: 169
  • Likes Given: 30
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.

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.

Offline deltaMass

  • Full Member
  • ****
  • Posts: 955
  • A Brit in California
  • Liked: 671
  • Likes Given: 275
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
Excellent! 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?

Online WarpTech

  • Full Member
  • ****
  • Posts: 1223
  • Do it!
  • Vista, CA
  • Liked: 1290
  • Likes Given: 1739
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
Excellent! 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


Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2324
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2952
  • Likes Given: 2586
...
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.

I have a large 1000W rheostat that we used in the prototype lab, this will be used on the input AC voltage 110VAC to drop the input and the heater current (sorry to confuse you). It will vary the out power as well. No, I don't want to have a bad day either.

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2324
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2952
  • Likes Given: 2586
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.

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.
Good idea on the pad. The Solidworks output file was mentioned to me about 12-14 years ago by my programmer who also worked with Cad. I don't remember if he wrote a program or not to do it.  It was just knocking on a door I remembered hoping to help aero.

Offline deltaMass

  • Full Member
  • ****
  • Posts: 955
  • A Brit in California
  • Liked: 671
  • Likes Given: 275
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
Excellent! 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
At first look I can't find the obvious error, but F/P has to equal 1/c, so it cannot be right.

Offline RERT

Dr. Rodal -

When I mentioned that the effect might be an academic curiosity, I was referring to the fact that the conducting walls are infinitely thin. The induced surface current radiates on both sides, both into and out of the 'cavity'.

R.

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2324
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2952
  • Likes Given: 2586
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
Dr. Rodal,
Are you planning to do a slice through the center?
------
We continue by showing the stress tensor component sigma xx at the circular cross-sectional yz plane at  x=97, located on the interior, between the big end and the middle of the frustum.
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403635#msg1403635
------

Tags: