Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1799676 times)

Offline mwvp

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Just for something to consider a bit later,

Notice that Yang's using a cavity-like "coupler" to the waveguide feed for her frustrum, with a network analyzer stuck in back. I'll repeat an earlier post - maybe, due to the small aperture, it constitutes a weakly-coupled, high-Q, double-tuned circuit with significant group delay that enhances the Sagnac-Ratchet effect responsible for the thrust. But maybe that enhancement results in a lowerering of the thrust vs. velocity curve also.

Just a SWAG.

Offline rfmwguy

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The pros and cons of a perforated mesh:

PROS:

* reduces weight (very important for aerospace applications and for EM Drive testing)
* reduces wind resistance effects (very important for large satellite dishes and for EM Drive testing to prevent gas effect that has plagued microwave pressure experiments since Maxwell's times, and as demonstrated on the first successful experiment to accurately measure microwave pressure, by Dr. Cullen in his Ph.D. thesis)
* visibility of what is happening inside the microwave cavity
*it prevents a microwave sealed cavity from becoming a pressure vessel as moist air inside it heats up and therefore pressure increases as PV=nRT (important for EM Drive experiments where an exhaust jet may be produced)
* it diminishes buoyancy effects (important for EM Drive experiments) See deltaMass's's post for more comprehensive discussion http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403300#msg1403300
* it prevents liquids like water (rain, snow, etc.) to collect inside (hat tip Shell)

CONS:

* perforation has to be significantly smaller than the microwave wavelength.  See X-Ray's post for more discussion: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403303#msg1403303
* perforation reduces stiffness, and therefore perforated mesh is more subject to distortion
* durability (the reduced stiffness of perforated plates means that eventually they will get distorted by handling stresses, this is the main reason why waveguides are not made of perforated meshes, as waveguides usually weigh little and durability concerns vastly exceed the benefits of weight saving for a waveguide)
* conductivity between wires and possibly anistropy of a wire mesh, impedance in perforated plates.  See zen-in's post:  http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403296#msg1403296
* spurious noise and other issues from some energy leakage.  See ElizabethGreene's post http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403288#msg1403288

the following COULD BE A CON OR A PRO depending on input power going into heat and time length of operation:

* CON: perforation means less thermally conductive metal to act as a heat sink, on the other hand the PRO: open perforation acts as a means to get convective heat transfer through the holes, so the con of reduced heat sink has to be compared with the benefits of convective heat transfer.  It basically depends on the thickness  (thermal diffusivity is most effective in the thickness direction than in lateral directions).  A thick non-perforated plate should be better than a thin perforated plate since thermal diffusivity through a metal is much, much faster than thermal convection, therefore the benefits of a thick plate will outweigh the benefits of a perforated thin sheet until enough heat is absorbed in the thick plate at which point thermal convection benefits of the perforated plate may outweigh the benefits of a thick non-perforated plate (depends on the speed of convection).

In outer space (vacuum) there is no thermal convection whatsoever, (hat-tip aero for reminding us of that) therefore the thermal sink advantage of a non-perforated plate are even more significant and have to be balanced against the weight savings for payload weight reduction from a perforated plate.
Another possible pro for mesh is lower power lost due to eddy currents:

https://en.m.wikipedia.org/wiki/Eddy_current

These are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.

Offline deltaMass

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.
You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/m

Since we're already far out, let's go even further. The highest known energy density due to an immaterial field is found near magnetars, and is about 1025 J/m3, and that's a pure B-field of gazillions of Tesla. That's 10,000 times the energy density of lead, btw.

There are quite a few active magnetars in this galaxy (and thousands of expired ones). Once we get this show on the road, we can go look  8)

https://en.wikipedia.org/wiki/Schwinger_limit
« Last Edit: 07/11/2015 10:30 PM by deltaMass »

Offline Blaine

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.

Thank you very very much.  Indeed that is sorta what I was trying to say when I posted about pilot waves earlier.  If these things were created the more exotic particles might be able to tunnel right on through.  And I know I said I was not going to be here for two more weeks, but here I am.
« Last Edit: 07/11/2015 10:21 PM by Blaine »
Weird Science!

Offline Blaine

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.
You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/m

That is because everyone blindly excepts the standard equations for quantum mechanics which is foolish IMHO.
Weird Science!

Offline deltaMass

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.
You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/m

That is because everyone blindly excepts the standard equations for quantum mechanics which is foolish IMHO.
Got something better?
("accepts" btw)
« Last Edit: 07/11/2015 10:27 PM by deltaMass »

Offline Blaine

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.
You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/m

That is because everyone blindly excepts the standard equations for quantum mechanics which is foolish IMHO.
Got something better?
("accepts" btw)

Well, no, I haven't anything better.  But that is because I never bothered to go back to college.   Yet, I can pick up on anything and would be willing to learn more.  So, I will sit back and listen for now.  Thank you.  Maybe I'll have something later when I study Louis de Broglie...
« Last Edit: 07/11/2015 10:34 PM by Blaine »
Weird Science!

Offline deltaMass

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I hope you see that we are all in the same boat. We simply go on with the best we have until some bright spark comes along with something better. That's the way it works and it's common sense.

And I suspect you just read that article about droplets and pilot wave theory and Bohm and de Broglie  ;)
« Last Edit: 07/11/2015 10:35 PM by deltaMass »

Offline rq3

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I have a question for the theorists.

Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?

So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.

A thought. Is this thing Q switching? As far as I can see, most of the devices demonstrating any thrust at all are energized with magnetrons on a 50 or 60 Hertz power supply. This means that the frustum is storing roughly 50 million microwave cycles before it it is abruptly switched off  for another 50 million microwave cycles. The cycle repeats.  Sounds an awful lot like a Q-switched laser to me.

I don't think I've seen any simulations, MEEP or otherwise, that account for this. None have run for simulated "on" periods of anything like 16-20 msecs (?), nor would I expect the simulations to be able to deal with the result.

Just a thought.

Rip

Offline X_RaY

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The pros and cons of a perforated mesh:

PROS:

* reduces weight (very important for aerospace applications and for EM Drive testing)
* reduces wind resistance effects (very important for large satellite dishes and for EM Drive testing to prevent gas effect that has plagued microwave pressure experiments since Maxwell's times, and as demonstrated on the first successful experiment to accurately measure microwave pressure, by Dr. Cullen in his Ph.D. thesis)
* visibility of what is happening inside the microwave cavity
*it prevents a microwave sealed cavity from becoming a pressure vessel as moist air inside it heats up and therefore pressure increases as PV=nRT (important for EM Drive experiments where an exhaust jet may be produced)
* it diminishes buoyancy effects (important for EM Drive experiments) See deltaMass's's post for more comprehensive discussion http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403300#msg1403300
* it prevents liquids like water (rain, snow, etc.) to collect inside (hat tip Shell)

CONS:

* perforation has to be significantly smaller than the microwave wavelength.  See X-Ray's post for more discussion: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403303#msg1403303
* perforation reduces stiffness, and therefore perforated mesh is more subject to distortion
* durability (the reduced stiffness of perforated plates means that eventually they will get distorted by handling stresses, this is the main reason why waveguides are not made of perforated meshes, as waveguides usually weigh little and durability concerns vastly exceed the benefits of weight saving for a waveguide)
* conductivity between wires and possibly anistropy of a wire mesh, impedance in perforated plates.  See zen-in's post:  http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403296#msg1403296
* spurious noise and other issues from some energy leakage.  See ElizabethGreene's post http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403288#msg1403288

the following COULD BE A CON OR A PRO depending on input power going into heat and time length of operation:

* CON: perforation means less thermally conductive metal to act as a heat sink, on the other hand the PRO: open perforation acts as a means to get convective heat transfer through the holes, so the con of reduced heat sink has to be compared with the benefits of convective heat transfer.  It basically depends on the thickness  (thermal diffusivity is most effective in the thickness direction than in lateral directions).  A thick non-perforated plate should be better than a thin perforated plate since thermal diffusivity through a metal is much, much faster than thermal convection, therefore the benefits of a thick plate will outweigh the benefits of a perforated thin sheet until enough heat is absorbed in the thick plate at which point thermal convection benefits of the perforated plate may outweigh the benefits of a thick non-perforated plate (depends on the speed of convection).

In outer space (vacuum) there is no thermal convection whatsoever, (hat-tip aero for reminding us of that) therefore the thermal sink advantage of a non-perforated plate are even more significant and have to be balanced against the weight savings for payload weight reduction from a perforated plate.
Another possible pro for mesh is lower power lost due to eddy currents:

https://en.m.wikipedia.org/wiki/Eddy_current

These are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.

The penetration depth is only a few Ám. You don't want to build a cavity with such thin material.May be you can build got a ceramic with thin Cu- inlay, but the weight would be almost as high as in the metal case. Like rodal said the stiffness is a important factor.
If the metal is thinner than the penetration depth thermal heat will be higher and the field leaks out, standard penetration depth as per definition 1/e ~37% of the field strength.
Did you ever seen a very thin metal film on a ceramic in a cooking microwave oven? I am sure you did ;)
But yes there is potential to reduce the mass. :)
« Last Edit: 07/11/2015 11:26 PM by X_RaY »

Offline SeeShells

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Just a very quick note as it's a crazy day here for a Sat.

Perforated on .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html 
Which will be a Oxygen Free High Conductivity Copper and it's the same stuff used in waveguides. But I'm putting holes in it!!!

Have a great Saturday. I'll be back on later.

Shell


Offline Rodal

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...
Another possible pro for mesh is lower power lost due to eddy currents:

https://en.m.wikipedia.org/wiki/Eddy_current

These are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.
Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches.  Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68  th of that thickness (1.47 %) .

EDIT: If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html  instead, the skin thickness is 1/769 th of that thickness (0.13 %)
« Last Edit: 07/12/2015 12:06 AM by Rodal »

Offline deltaMass

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Just a very quick note as it's a crazy day here for a Sat.

Perforated on .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html 
Which will be a Oxygen Free High Conductivity Copper and it's the same stuff used in waveguides. But I'm putting holes in it!!!

Have a great Saturday. I'll be back on later.

Shell
Pounds and inches and a local Silicon Valley company to boot - disgraceful! :(

Offline rfmwguy

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Another possible pro for mesh is lower power lost due to eddy currents:

https://en.m.wikipedia.org/wiki/Eddy_current

These are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.
Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches.  Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68  th of that thickness (1.47 %) .

If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html  instead, the skin thickness is 1/769 th of that thickness (0.13 %)
Would less surface area in mesh translate into less overall loss?

Offline rfmwguy

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Another possible pro for mesh is lower power lost due to eddy currents:

https://en.m.wikipedia.org/wiki/Eddy_current

These are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.
Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches.  Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68  th of that thickness (1.47 %) .

If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html  instead, the skin thickness is 1/769 th of that thickness (0.13 %)
Would less surface area in mesh translate into less overall loss?
Great point, yes roughly proportional to the area.
Whew...this was one of the reasons I chose to go this route, doc.

Offline Rodal

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Whew...this was one of the reasons I chose to go this route, doc.
I added it to the pro's with a link to your message

Offline pierre

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FYI if anyone needs to do long runs of MEEP simulations with a fine grid that requires lots of memory, you may want to take a look at https://cloud.google.com/compute/

Google offers computation time on Linux computers with up to 32 CPU cores and 208 GB (!) of RAM. I would suggest the batch/preemtible mode, since it's cheaper.

Offline frobnicat

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On sealed and closed cavities vs. open cavities, both in air and containing air.

The sealed cavity will exhibit a buoyancy effect because increased temperature will cause the enclosed air to exert wall pressure and cause slight ballooning of the cavity walls. For example, a sealed thin aluminium soft drink can when heated a few tens of degrees will exhibit on order 50 ug-w of buoyancy.

The open cavity will lose heated air in order to maintain constant pressure with the outside. Thus its weight will decrease because a volume of heated air weighs less than that same volume of colder air.

Both effects cause an apparent loss in weight. It's to be expected that an open cavity will produce a bigger weight loss than a sealed cavity, because of the high stiffness of the sealed cavity.

This weight loss can readily be factored out by either
a) measuring thrust in the horizontal direction, or
b) differencing the measured weights with thrust-downward resp. thrust-upward

For b) we would still have asymmetric convection flows if the frustum is "naked", i.e. with direct convective cooling on the outside, making for a non null difference even in the absence of real thrust. Perforated walls are not a guarantee against that as the aerodynamic drag is only slightly lower (I guess we are not speaking of a light mesh with high hole/wire diameter ratio). For a) also there can be asymmetric convective aerodynamic effects... In both cases a signal must be interpreted within the hard to predict envelopes of such effects.

Short of running the experiment in vacuum, maybe accessible to DIYers to rule out those problems with some level of confidence is to dress the frustum with some thermal blanket. This has the unfortunate consequence of forbidding long steady state mode of operation, and requiring long pauses between runs to evacuate heat. But at this stage sceptics wait for optimisation of scientific control of the existence of thrust at all, not yet of its harnessing.

One of the very few experimental nullification (down to some sensitivity) in the domain of "exhaustless" propulsion, was mentioned earlier in thread 1, by Brito, Marini, Galian. They use phase change material around the active elements of the system (Mach effect : capacitor+coil) to swallow the heat (up to some limited amount) without much movements of mass nor much temperature changes, which would be a plus for the case of the resonant cavity of EM thruster, limiting thermal drift of geometry. At equal thermal capacity, thin copper+phase change material could experience much lower temperature rise (->expansion) than thick copper alone.

Null Findings on Electromagnetic Inertia Thruster Experiments using a Torsion Pendulum

Quote
The  capacitor-coil assembly is  wired as a tank circuit and  mounted in a common acrylic  housing  filled  with a Phase Change Material (PCM), for limited thermal control of the assembly.

For the casual reader (clearly not you deltaMass !), this is about a test of Mach effect device, which is not the same kind of system as discussed here (EM drive). I'm citing this because it is nevertheless a test of an "exhaustless propulsion" claim, and a successful nullification (i.e. good experimental procedures to meditate).

I don't see in the paper how the rising volume or pressure of enclosed air is handled, is it vented or not ? But since it is an horizontal set up there is no direct effect of buoyancy, and with the active elements thermally isolated there is no risk of asymmetric "thrusting" aerodynamic convection on the outside. If it is vented it can be vented radially or axially to avoid some recoil (jet effect) imparted on the measured torque.

Offline deltaMass

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Just to note that there have been dozens of experiments on The Woodward Effect which have returned a result compatible with the null hypothesis. This is not something that one normally hears about, though.

Many nails in that coffin, sad to say.

Offline dumbo

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For the current case of long runs with a small lattice and modest resolution, memory should not be an issue. And run time might not be an issue for some. It is for me because I am required (by the wife) to turn my computer off at night. With 32 complete cycles requiring just less than 1 hour run time, 100 cycles should complete in less that 3 hours but 1000 cycles would exceed my allotted run window of about 14 hours maximum. A 30 hour computer run is not that bad in a laboratory environment. It's just to much for me to do at home. If I can learn how to start meep from saved data, that may be an easy solution. But if it is decided that 10,000 cycles are needed, well, that's not so easy.

10,000 cycles the rate of 32 cycles per hour is just some 300 hours of computing time. At the current Amazon EC2 price of $0.11/hour (c4.large instance type), we are talking like $35 in total, to get some numerical data for the theorists to demolish. :P

Is there any chance you could share the input files used for the last run?


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