Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1803780 times)

Offline TheTraveller

...

My comments were in reference to copper mesh (very big holes with very small conductive surface area) and not to copper plate with holes in it, which according to the paper, shows a loss at the DSS 14 antenna of 43db transmission loss. That is a lot of loss for one bounce.
Of course, as I pointed out under cons: "perforation has to be significantly smaller than the microwave wavelength"

Maybe you didn't read my comments, which were about using copper mesh and not about using plate with holes punched in it. So now you go off on a tangent on holey plate which also shows massive reflection loss. What is your point?

As I originally said, there are no copper mesh waveguides.
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Offline TheTraveller


I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).
« Last Edit: 07/11/2015 04:02 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
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Offline aero

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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 experiment ever 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 prevents a non-sealed microwave cavity from experiencing buoyancy effects (important for EM Drive experiments)
* 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
* 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)

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).

And of course in a vacuum environment (space for example) all considerations of convection are void.

But for now, we are experimenting at a much more fundamental level than designing space drives.
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Offline SeeShells

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...

Build as you will, just understand there is NO data that I can find on how copper mesh works as a waveguide. That should maybe tell you something?

I'll build using solid and rigid copper than has a highly polished, scratch and ding free internal surface and is capable of being silver plated with a gold over flash.

Time will tell what results the copper mesh builders get.

Data here for example, in the Jet Propulsion Laboratory website:

http://ipnpr.jpl.nasa.gov/progress_report2/II/IIO.PDF

including waveguide and free space techniques. 

Mostly aerospace applications are interested in this.  You are not going to find people interested in making small-cross-section waveguides out of perforated plates, for commercial applications since durability much trumps any weight savings for commercial applications.

My comments were in reference to copper mesh (very big holes with very small conductive surface area) and not to copper plate with holes in it, which according to the paper, shows a loss at the DSS 14 antenna of 43db transmission loss. That is a lot of loss for one bounce.
I read this wrong?
It's only true where the E-field is normal to the plane of incidence..... at 2295 MHz AND 30 degree angle of incidence. We don't have that here.

Offline SeeShells

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I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).

And they reported the highest thrust with a calculated Q of just over 1500. Interesting.

Offline Rodal

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...
It's only true where the E-field is normal to the plane of incidence..... at 2295 MHz AND 30 degree angle of incidence. We don't have that here.

Excellent point, as in previous posts TT had posted that he was going to be resonating cavities with mode TE013.  Transverse electric modes have a magnetic field in the longitudinal direction, and only transverse electric fields (the electric fields in a TE mode are parallel to surfaces), therefore the emphasis on an E-field normal to the plane of incidence doesn't follow.  It is a non-sequitur to the mode shape that he said he was going to use, for any excitation using a transverse electric mode, at any microwave  frequency.
« Last Edit: 07/11/2015 04:39 PM by Rodal »

Offline SeeShells

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snip snip snip
----------------------
Are you putting your carousel on a anti-vibration stand?

Shell
----------------------
TheTraveler: My workshop has a leveled hand laid, not by me, firebrick floor on 200mm of leveled and hard packed sand, with 5m or so of carpeted work bench area. There will be plenty of vibration to trigger MOTOR mode.
----------------------

My recommendation would be to do a anti-vibration platform. I can show you how to make a variable mass platform with stuff you can get at your hardware store, very inexpensive to build but embodies the basics of a tunable media for vibration. (had a silly patent on it) It's a plastic tub with a sponge or large celled foam pad that can absorb water sitting on 4 foam pads.

Pop a laser in the middle of it on a 50-100mm long flexible spring so you'll catch short and long wave acoustic propagation that will be in your area. Shine it on a wall and watch the vibrations. You'll be surprised. Fill the tub slowly with water and watch the vibrations on the laser spot slowly fade. Go with too much water and the vibrations will increase, take water out.

Test with no vibration the EM drive carousel but keep your laser on to monitor vibrations. Take a wine glass fill it with water (or wine) tap it and touch it to your carousel and see if that starts movement, no? drink some (wine opps water) from the glass tap and do it again. Still nothing? Remove some water from the Anti-vibration table still monitoring the laser spot and when you get thrust record the laser spot vibrations with your video camera.

   

Offline rfmwguy

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I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).

And they reported the highest thrust with a calculated Q of just over 1500. Interesting.
Thus, Doc has maintained that Q is not necessarily a driving factor. Another reason I chose to mesh and not to polish...it ain't optical photons.

Offline TheTraveller


I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).

And they reported the highest thrust with a calculated Q of just over 1500. Interesting.

Actually that is not what Prof Yang claims in the 2013 paper you were quoting:

Quote
In Ref. [16], we applied the finite element method to numerically simulate the EM fields inside different cylindrical tapered resonant cavities resonating on the equivalent principal modes of TE011, TE012, TE111, and TM011, and calculated the relevant quality factors.

Then the EM thrusts produced by the microwave thrusters with these different tapered resonant cavities were theoretically predicted.

It was found that the thruster cavity made by copper and resonating on the equivalent TE011 mode has a quality factor 320,400 and generates total net EM thrust 411 mN for 1000 W 2.45 GHz incident microwave.

Could not find anywhere else in the paper she mentions Q.

Fig 13 in the paper that you refer to is not the cavity Q but as they say in the paper is
Quote
According to the return loss testing method of the passive parts of microwave apparatus,[17] the resonating property of the thruster cavity can be tested with a microwave network analyzer.

Figure 13 shows the measured relation between the frequency and the return loss of the thruster cavity.

The return loss is defined as Lr = 10lg (Pr/Pi) (dB), where Pr and Pi are respectively the reflected and the incident microwave power.

When Lr=0, the power is completely reflected from the cavity.

At the point Lr = Lrmin, the power is reflected on a minimum level, which denotes that the cavity is in resonant
state and the frequency is defined as resonant frequency f0.

We define the resonant frequency band as Df = f2 􀀀 f1 at Lr = 0.707Lrmin.

Figure 13 shows that the resonant frequency and band are f0 = 2.450 GHz and Df = 0.0016 GHz, respectively.

The circumstance shows that when the microwave output frequency ranges from 2.4492 GHz to 2.4508 GHz, more than 50% of microwave power can be absorbed by the resonant cavity to generate the EM thrust.
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
Herman Melville, Moby Dick

Offline TheTraveller


I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).

And they reported the highest thrust with a calculated Q of just over 1500. Interesting.
Thus, Doc has maintained that Q is not necessarily a driving factor. Another reason I chose to mesh and not to polish...it ain't optical photons.

Doc is incorrect.
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
Herman Melville, Moby Dick

Offline SeeShells

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I suggest you might be lucky to get 100W inside the cavity as the magnetron output is all over the board.

...

Could you please elaborate?

Do you mean 100 W at the resonant frequency?

Microwave magnetrons can have a +-30MHz bandwidth. If you designed a cavity bandwidth wide enough to suck all that up, the Q would be around 41.

So you design for a Q as high as possible and hope one of the narrow band variable frequency bursts (see the attachment) will occur at the right frequency and get inside, which means a lot of the magnetron energy will be reflected back to the magnetron and the Rf system better have a way to deal with the reflected microwave energy.

In the attached Chinese image you can see the method they developed to deal with using high Q cavities, fed with wide band magnetron energy with a lot of reflected energy coming back from the cavity. (upper right)

Variable freq narrow band Rf gens with 100W Rf amp coax connection eliminates so many issues and boils the Rf feed system down to KISS (Keep It Simple Stupid).

And they reported the highest thrust with a calculated Q of just over 1500. Interesting.
Thus, Doc has maintained that Q is not necessarily a driving factor. Another reason I chose to mesh and not to polish...it ain't optical photons.

Doc is incorrect.
I'm with rfmwguy (and doc) in saying that the figures are totally out of reality of a Q of hundreds of thousands!

Offline TheTraveller

snip snip snip
----------------------
Are you putting your carousel on a anti-vibration stand?

Shell
----------------------
TheTraveler: My workshop has a leveled hand laid, not by me, firebrick floor on 200mm of leveled and hard packed sand, with 5m or so of carpeted work bench area. There will be plenty of vibration to trigger MOTOR mode.
----------------------

My recommendation would be to do a anti-vibration platform. I can show you how to make a variable mass platform with stuff you can get at your hardware store, very inexpensive to build but embodies the basics of a tunable media for vibration. (had a silly patent on it) It's a plastic tub with a sponge or large celled foam pad that can absorb water sitting on 4 foam pads.

Pop a laser in the middle of it on a 50-100mm long flexible spring so you'll catch short and long wave acoustic propagation that will be in your area. Shine it on a wall and watch the vibrations. You'll be surprised. Fill the tub slowly with water and watch the vibrations on the laser spot slowly fade. Go with too much water and the vibrations will increase, take water out.

Test with no vibration the EM drive carousel but keep your laser on to monitor vibrations. Take a wine glass fill it with water (or wine) tap it and touch it to your carousel and see if that starts movement, no? drink some (wine opps water) from the glass tap and do it again. Still nothing? Remove some water from the Anti-vibration table still monitoring the laser spot and when you get thrust record the laser spot vibrations with your video camera.

 

I believe differential air vibrations on the bigger end area compared to the smaller end area will cause natural air borne vibrations to generate small acceleration Forces toward the small end. Eliminating air borne vibration will need a vacuum chamber much bigger than the 150mm dia bell jar I have.

My big end internal diameter is 400mm and the small end internal is 148.7mm with internal length between the spherical end plates of 267.5mm. Df is 0.925 with resonance at TE013 of 2.45GHz.

Have saved your post and image for possible future use.
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
Herman Melville, Moby Dick

Offline phaseshift

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Howdy all,

been lurking for a while as I have just too much on my plate to participate as fully as I would like - but today's read through made me think of something.

As TheTraveller has mentioned he is going to be silvering and gold plating the inside of his frustum.  What if the frustum were built first with only solid copper then run all the tests and collect data.  Then silver the insides (remove some copper from the outside of the frustum to compensate for the mass change) and rerun the tests. Do the same with gold.  If there is a change in measured 'thrust' what would be the explanation if nothing else about the test system or the frustum changed? Would this not bolster the idea that there is actual thrust.  Maybe trying to prove a delta in thrust would be easier.

If there are things that could be pointed to as a possible cause of change in thrust wouldn't they be easier to compensate for then the complex systems and measurement devices being proposed.  Measuring absolute thrust seems really hard.
« Last Edit: 07/11/2015 05:40 PM by phaseshift »
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Offline aero

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All this talk of Q is interesting, and it does concern me in the sense that we need to see long runs from meep but the question to me becomes, "How long should the run be?" And there, the definition of Q becomes a problem. I have attached an image of what Wikipedia says about it. Which one are we using?

The problem, as it looks to me is that it will take several thousand cycles for the energy stored to reach steady state, everything before that is transient. So again, "How long should the run be?"
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Offline TheTraveller

As first discussed by Paul March of NASA (hat tip) before TT joined this Forum thread, Prof. Yang actually details her very unorthodox calculation method which she uses to arrive at the strambotic supercalifragilisticexpialidociously high qualitiy factor of <<It was found that the thruster cavity made by copper and resonating on the equivalent TE011 mode has a quality factor 320,400 >>

As others said, if somebody can get a Q=320,400 (calculated with conventional methods) there is an excellent commercial business unrelated to thrust that can use such ultra high Q's at ambient temperature.

My point was fig 13 is not a Q graphic, It is a return loss bandwidth graphic, so people should stop saying she got the highest Force at a Q of 1,500 because that is totally incorrect and not a proper understanding of fig 13.

Plus Prog Yang never said it.
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Herman Melville, Moby Dick

Offline aero

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Howdy all,

been lurking for a while as I have just too much on my plate to participate as fully as I would like - but today's read through made me think of something.

As TheTraveller has mentioned he is going to be silvering and gold plating the inside of his frustum.  What if the frustum were built first with only solid copper then run all the tests and collect data.  Then silver the insides (remove some copper from the outside of the frustum to compensate for the mass change) and rerun the tests. Do the same with gold.  If there is a change in measured 'thrust' what would be the explanation if nothing else about the test system or the frustum changed? Would this not bolster the idea that there is actual thrust.  Maybe trying to prove a delta in thrust would be easier.

If there are things that could be pointed to as a possible cause of change in thrust wouldn't they be easier to compensate for then the complex systems and measurement devices being proposed.  Measuring absolute thrust seems really hard.

Welcome.
I think a big problem is trying to get two runs in a row that give the same results. Until that is accomplished, measuring deltas is not really feasable.
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Offline phaseshift

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Welcome.
I think a big problem is trying to get two runs in a row that give the same results. Until that is accomplished, measuring deltas is not really feasable.

It would seem that a large enough number of runs would produce something of statistical value that could be compared between setups.
"It doesn't have to be a brain storm, a drizzle will often do" - phaseshift

Offline TheTraveller

Howdy all,

been lurking for a while as I have just too much on my plate to participate as fully as I would like - but today's read through made me think of something.

As TheTraveller has mentioned he is going to be silvering and gold plating the inside of his frustum.  What if the frustum were built first with only solid copper then run all the tests and collect data.  Then silver the insides (remove some copper from the outside of the frustum to compensate for the mass change) and rerun the tests. Do the same with gold.  If there is a change in measured 'thrust' what would be the explanation if nothing else about the test system or the frustum changed? Would this not bolster the idea that there is actual thrust.  Maybe trying to prove a delta in thrust would be easier.

If there are things that could be pointed to as a possible cause of change in thrust wouldn't they be easier to compensate for then the complex systems and measurement devices being proposed.  Measuring absolute thrust seems really hard.

I intend to start with a highly polished, scratch and ding free copper interior surface as Roger Shawyer recommended to me. I do intend to make at least 3 experimental cavities and one of them will be, after testing, silver electropolished electroplated with a very thin gold over flash, just enough to stop the silver oxidizing.
« Last Edit: 07/11/2015 05:46 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
Herman Melville, Moby Dick

Offline TheTraveller

As first discussed by Paul March of NASA (hat tip) before TT joined this Forum thread, Prof. Yang actually details her very unorthodox calculation method...

Care to share her method so I can study it?
« Last Edit: 07/11/2015 05:50 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
Herman Melville, Moby Dick

Offline Rodal

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This was discussed back in May:


http://forum.nasaspaceflight.com/index.php?topic=36313.msg1369553#msg1369553

Quote from: Rodal
Paul March has addressed  and explained this as follows: Chinese (Prof. Yang) calculated loaded Q factors are much higher than the Q's reported by Shawyer and by NASA' Eagleworks because of the unorthodox way that the Chinese calculate their loaded Q factors.  Instead of using the S11 zero dB reference plane to measure their -3dB down bandwidths from, as is done elsewhere, the Chinese use the most negative dB S11 value located at the resonance frequency and measure up 3dB toward the S11 zero  dB plane.  Therefore, of course, the bandwidth figures used by the Chinese in this unorthodox calculation are going to be ridiculously small which yields correspondingly artificially large values of the calculated Q-factor. .
« Last Edit: 07/11/2015 06:03 PM by Rodal »

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