### Author Topic: EM Drive Developments Thread 1  (Read 1023210 times)

#### Rodal

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##### Re: EM Drive Developments
« Reply #2200 on: 10/17/2014 09:03 PM »
For the Shawyer Demonstrator Thruster, using the picture at the bottom of the page here: http://emdrive.com/

aero

Large Base Diameter =28 cm
Small Base Diameter =7.78 cm
Length = 38.1 cm (including both the truncated cone plus the straight cylinder)

NotSoSureOfIt Pot-Based

Large Base Diameter = 29.6 cm
Small Base Diameter = 18.8 cm

NotSoSureOfIt RFConnector-Based

Large Base Diameter =24.1 cm
Small Base Diameter =15.3 cm

Rodal

Large Base Diameter = 28 cm
Small Base Diameter = 15.9 cm
Length = 22.6 cm  (including only the truncated cone)

« Last Edit: 10/17/2014 09:09 PM by Rodal »

#### JohnFornaro

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##### Re: EM Drive Developments
« Reply #2201 on: 10/17/2014 09:45 PM »
If there is a moveable small end, then I can't guess what the interior of the cylinder looks like.

Compressed hummingbird wings, guys.

Y'all have no idea what's inside the device!

For the O.D. of the copper straight section I get 18.8 cm if that helps  (using the pot as ref)

15.3 cm using the RF connector, but not sure of the right connector and worse camera angle,  sooo ?

I offer to try my hand at dimensional analysis.  What is being used as the basis for the dimensional extrapolations you guys have come up with?

I would start with the nut diameter.  These are likely to be standard, and unlikely to be guessed at wrongly by a factor of two.
Sometimes I just flat out don't get it.

#### Rodal

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##### Re: EM Drive Developments
« Reply #2202 on: 10/17/2014 09:54 PM »
For the O.D. of the copper straight section I get 18.8 cm if that helps  (using the pot as ref)

15.3 cm using the RF connector, but not sure of the right connector and worse camera angle,  sooo ?

I offer to try my hand at dimensional analysis.  What is being used as the basis for the dimensional extrapolations you guys have come up with?

I would start with the nut diameter.  These are likely to be standard, and unlikely to be guessed at wrongly by a factor of two.
I calculated as follows:

Ratio = (SmallDiameterMeasuredwithCaliperOnScreen)/(LargeDiameterMeasuredwithCaliperOnScreen)

LargeDiameter = 28 cm [known data from Shawyer's report]

RodalEstimateOfSmallDiameter = Ratio * 28 cm

Hence no nuts were used, and no nuts were hurt for my analysis.

Now, is that nuts ?

For greater accuracy I can feed the image to Mathematica and perform a digital analysis, but at this stage is not required.

The two estimates from NotSoSureOfIt are close to mine.
« Last Edit: 10/17/2014 10:06 PM by Rodal »

#### IslandPlaya

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##### Re: EM Drive Developments
« Reply #2203 on: 10/17/2014 09:59 PM »
Can I congratulate all on the thread for make it one of the most posted and viewed on NSF.
Of course all this stuff is insanely interesting and if it can be developed then we are in sci-fi land
I had things to say early on in this thread but I have to stand back now and read the analysis...
Thank you guys. This is my fave thread on NSF!
Prof. McC. Please help us! I think your theory is true. Application to propulsion?
« Last Edit: 10/17/2014 10:02 PM by IslandPlaya »

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2204 on: 10/17/2014 10:12 PM »
...
Waiting for adjusted inputs...
We still would like to hear whether there is an argument that can be made, explaining the formulas that model the experimental results either as:

A) an experimental artifact
B) a photon rocket

You can use the whole data (including the outlier) if you like to make the argument.   For the photon rocket argument I don't understand how the photons get out of the EM Drive and how does it get to do better than a perfect photon rocket.

Can you make an experimental artifact argument?

Me ? Not really.

Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field and/or local field (damping system) and/or local ferromagnetic chamber walls. Those are words so this is not an argument yet. Please don't argue, yet.

But if anyone wants to help me putting up this argument (and then argue) :
for this argument I would need to know if there is a possibility of non linearities around 0 of conductivity in skin of cavity for strong RF fields. Even one part per thousand could be interesting. A small asymmetry in hysteresis for instance. Asking Mulletron and a few search of the available literature didn't float anything like that, at least for metal conductors (rather into semiconductors with more or less exotic composition, not plain copper). Or for dielectrics but I guess they don't have DC conduction to speak of. I don't know if it is because there is no such effect at all in conductors, or because this effect is generally ignored, or because it would be a complex special case of dielectric (non linear) very close conductor (eddy currents). How tight the dielectrics are encased in copper ? Also I would need to understand the geometry of eddy currents, and my EM course is long ago and wasn't specifically on microwave cavities or skin effects. So I'm a bit disarmed.

Can we do summary, for the seven data points, of qualitative boolean or discrete values like
1/ vacuum ?
2/ magnetic damping ?
3/ ferromagnetic walls nearby (vacuum chamber or else) ?
4/ offboard generator ?
5/ inverted pendulum or torsion balance ?
6/ thermal isolation casing ?
7/ ... ?

at least for all such boolean or discrete values for which we have values or likely guess for most of the data points ?

Could we also throw in the negative results while we are at it : Brady without dielectric, Brito/Marini/Galian without magnetic damping, what else ?

Maybe we could then see some patterns, some already discussed, maybe some others ...
« Last Edit: 10/17/2014 10:17 PM by frobnicat »

#### Rodal

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##### Re: EM Drive Developments
« Reply #2205 on: 10/17/2014 10:31 PM »
...
Waiting for adjusted inputs...
We still would like to hear whether there is an argument that can be made, explaining the formulas that model the experimental results either as:

A) an experimental artifact
B) a photon rocket

You can use the whole data (including the outlier) if you like to make the argument.   For the photon rocket argument I don't understand how the photons get out of the EM Drive and how does it get to do better than a perfect photon rocket.

Can you make an experimental artifact argument?

Me ? Not really.

Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field and/or local field (damping system) and/or local ferromagnetic chamber walls. Those are words so this is not an argument yet. Please don't argue, yet.

But if anyone wants to help me putting up this argument (and then argue) :
for this argument I would need to know if there is a possibility of non linearities around 0 of conductivity in skin of cavity for strong RF fields. Even one part per thousand could be interesting. A small asymmetry in hysteresis for instance. Asking Mulletron and a few search of the available literature didn't float anything like that, at least for metal conductors (rather into semiconductors with more or less exotic composition, not plain copper). Or for dielectrics but I guess they don't have DC conduction to speak of. I don't know if it is because there is no such effect at all in conductors, or because this effect is generally ignored, or because it would be a complex special case of dielectric (non linear) very close conductor (eddy currents). How tight the dielectrics are encased in copper ? Also I would need to understand the geometry of eddy currents, and my EM course is long ago and wasn't specifically on microwave cavities or skin effects. So I'm a bit disarmed.

Can we do summary, for the seven data points, of qualitative boolean or discrete values like
1/ vacuum ?
2/ magnetic damping ?
3/ ferromagnetic walls nearby (vacuum chamber or else) ?
4/ offboard generator ?
5/ inverted pendulum or torsion balance ?
6/ thermal isolation casing ?
7/ ... ?

at least for all such boolean or discrete values for which we have values or likely guess for most of the data points ?

Could we also throw in the negative results while we are at it : Brady without dielectric,
Brito/Marini/Galian without magnetic damping, what else ?

Maybe we could then see some patterns, some already discussed, maybe some others ...

Eliminate 5/ inverted pendulum or torsion balance ?
I did a fully coupled nonlinear analysis and the problem cannot be explained solely on that basis.
What it can do is to magnify another effect.

Concerning:  <<Could we also throw in the negative results while we are at it : Brady without dielectric>>

No, that is not a relevant result, did you have a chance to look at my posts regarding that? Conducted first in the their testing program, at a completely different frequency, way off the scale to the right on their S22 chart and their COMSOL Finite Element predictions.  I don't think it has anything to do with the dielectric.  At that frequency they didn't report any force measurements whatsoever (with or without).  Basically they were flying blind, they did that experiment at a different frequency, they did not report any Q at that frequency, and from the S22 plot it is likely there was no resonance at that frequency

Concerning <<Brito/Marini/Galian>>

Not relevant to microwave cavities.  Not relevant to Shawyer, China or NASA Eagleworks experiments. Only relevant to Woodward/March MET.

Concerning <<6/ thermal isolation casing ?>>

What is that? Please elaborate

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2206 on: 10/17/2014 10:33 PM »
The upper gizmo is the motor and at the bottom it's driving a variable resistor as position feedback.  It probably was fed w/ a fixed frequency generator.
Hanging out the back is prob a limit switch.

Shawyer's demonstrator : isn't it possible that it's a thread driving a plate in longitudinal position inside the cylinder, that is an adjustable length cavity ? Is that what you mean by "fed with a fixed frequency" : the cavity is adjusted to fit the frequency and not the inverse ? Isn't all that documented by Shawyer ? Or is it in NDA ?

#### Rodal

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##### Re: EM Drive Developments
« Reply #2207 on: 10/17/2014 10:39 PM »
....
Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field ...

Interaction with the Earth's magnetic field is also first in my list of experimental artifacts.

Why would an interaction with the Earths' magnetic field be oriented along the cone axis and would favor a larger difference between the diameters of the bases of the truncated cone?
« Last Edit: 10/17/2014 10:49 PM by Rodal »

#### IslandPlaya

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##### Re: EM Drive Developments
« Reply #2208 on: 10/17/2014 10:40 PM »
The upper gizmo is the motor and at the bottom it's driving a variable resistor as position feedback.  It probably was fed w/ a fixed frequency generator.
Hanging out the back is prob a limit switch.

Shawyer's demonstrator : isn't it possible that it's a thread driving a plate in longitudinal position inside the cylinder, that is an adjustable length cavity ? Is that what you mean by "fed with a fixed frequency" : the cavity is adjusted to fit the frequency and not the inverse ? Isn't all that documented by Shawyer ? Or is it in NDA ?
If you have an adjustable cavity that allows you to tune it. However if your microwave source is not stable then you are are screwed. cf Rodal and his mate saying that RF emitters with a variance of < 1Hz are available but not used in the current experiments.

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2209 on: 10/17/2014 10:56 PM »
Eliminate 5/ inverted pendulum or torsion balance ?
I did a fully coupled nonlinear analysis and the problem cannot be explained solely on that basis.
What it can do is to magnify another effect.
ok

Quote
Concerning:  <<Could we also throw in the negative results while we are at it : Brady without dielectric>>

No, that is not a relevant result, did you have a chance to look at my posts regarding that? Conducted first in the their testing program, at a completely different frequency, way off the scale to the right on their S22 chart and their COMSOL Finite Element predictions.  I don't think it has anything to do with the dielectric.  At that frequency they didn't report any force measurements whatsoever (with or without).  Basically they were flying blind, they did that experiment at a different frequency, they did not report any Q at that frequency, and from the S22 plot it is likely there was no resonance at that frequency
I concede I might not have the chance to look more than briefly at your posts concerning that. Are we to think that "dielectric vs no_dielectric" is to be considered irrelevant, or that "all relevant results used dielectric" ? Then we have a boolean column full of yes. That is an information by itself.

Quote
Concerning <<Brito/Marini/Galian>>

Not relevant to microwave cavities.  Not relevant to Shawyer, China or NASA Eagleworks experiments. Only relevant to Woodward/March MET.
Yeah alright, I forgot we had two different approaches to deal with.

Quote
Concerning <<6/ thermal isolation casing ?>>

What is that? Please elaborate
Well as I understood Brito et all negative results, they used a phase changing thing around their system to have thermal isolation during the runs. Was that it, should I read again? But since this experiment is not relevant, discard this criteria (I guess nobody else doing microwave cavities have been through that trouble, so this is a boolean column full of no).

What I'm most interested in, at the moment for making an argument, is if the boolean column (2/ permanent local magnetic field OR 3/ nearby ferromagnetic mass) is full of yes.

#### aero

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##### Re: EM Drive Developments
« Reply #2210 on: 10/17/2014 10:59 PM »

Another way to get at the length of the cavity is to look at the half wavelength multiples for resonance. But the wavelength is so short that it is not very helpful. Knowing the length and the wall taper (=.53) will give the small end diameter. I assume that the cone extends inside the cylinder some unknown distance.

lamda   n   2d=n*Lamda    d, m
0.12236   1   0.122364269    0.0612
0.12236   2   0.244728537    0.1224
0.12236   3   0.367092806    0.1835
0.12236   4   0.489457074    0.2447
0.12236   5   0.611821343    0.3059
0.12236   6   0.734185611    0.3671
0.12236   7   0.85654988    0.4283

I think we've had guesses for all of those values of n, except perhaps n=4. But maybe n = 3, as it does for Brady's device.
Retired, working interesting problems

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2211 on: 10/17/2014 11:22 PM »
....
Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field ...

Interaction with the Earth's magnetic field is also first in my list of experimental artifacts.

Why would an interaction with the Earths' magnetic field be oriented along the cone axis and would favor a larger difference between the diameters of the bases of the truncated cone?

Good questions.
Can earth magnetic field account for the order of magnitude of results ? This I could help to address with rough estimates. The direction, axis and magnitude dependence on geometry, I have no precise idea right now and am unsure I could contribute. Thinking about it (part time).

#### Rodal

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##### Re: EM Drive Developments
« Reply #2212 on: 10/17/2014 11:29 PM »
For the Shawyer Demonstrator Thruster, using the picture at the bottom of the page here: http://emdrive.com/

aero (updated based on pixels)

Large Base Diameter =28 cm
Small Base Diameter =16.7 cm
Length = 21.0 cm  (including only the truncated cone)
Slope of Cone = ((28 - 16.7)/2)/21.0 = 0.2690

NotSoSureOfIt Pot-Based

Large Base Diameter =  28 cm
Small Base Diameter = (18.8 cm/29.6 cm)*28 cm = 17.78 cm

NotSoSureOfIt RFConnector-Based

Large Base Diameter = 28 cm
Small Base Diameter =(15.3 cm / 24.1 cm) * 28 cm =  17.78 cm

Rodal

Large Base Diameter = 28 cm
Small Base Diameter = 15.9 cm
Length = 22.6 cm  (including only the truncated cone)
Slope of Cone = ((28 - 15.9)/2)/22.6 = 0.2677

Average

Large Base Diameter = 28 cm
Small Base Diameter = 16.79 cm
Length = 20.89 cm

Median = @aero

Large Base Diameter = 28 cm
Small Base Diameter =16.7 cm
Length = 21.05 cm

Notes:

Average and median lengths calculated based on average of cone slopes (0.2683) calculated by aero and Rodal, and the average and median diameters respectively. For example (28.00-16.79)/(2* 0.2683) = 20.89

I adjusted notsosureofit's estimates for the large diameter to be Shawyer's published value (28 cm) and the small diameter accordingly as shown.

Range = 17.78 cm -  15.9 cm  = 1.88 cm
HalfRange/Average = 5.60%  (not bad     )
(Average-Median)/Average: 0.5% (pretty symmetric     )
(ratio of slopes calculated by aero & Rodal) - 1 = 0.2690/ 0.2677 - 1= 0.49% (very close    )
Also, three different independent measurements:
aero: pixels
notsosureofit: pot and RFconnector
rodal: caliper
« Last Edit: 10/18/2014 12:38 AM by Rodal »

#### Rodal

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##### Re: EM Drive Developments
« Reply #2213 on: 10/17/2014 11:37 PM »
....
Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field ...

Interaction with the Earth's magnetic field is also first in my list of experimental artifacts.

Why would an interaction with the Earths' magnetic field be oriented along the cone axis and would favor a larger difference between the diameters of the bases of the truncated cone?

Good questions.
Can earth magnetic field account for the order of magnitude of results ? This I could help to address with rough estimates. The direction, axis and magnitude dependence on geometry, I have no precise idea right now and am unsure I could contribute. Thinking about it (part time).
I'm not too concerned with the order of magnitude at this point in time because the inverted torsional pendulum can amplify whatever effect is thrusting the device  (maybe even dark matter  ).  I would think that the main thing to do is to find a classical experimental artifact that also acts along the axis of the cone, that depends on orientation of the big base and that it is larger with increasing difference between the base diameters.

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2214 on: 10/18/2014 12:50 AM »
....
Right now my bet would be something in the line of induced DC component interacting magnetically with either earth magnetic field ...

Interaction with the Earth's magnetic field is also first in my list of experimental artifacts.

Why would an interaction with the Earths' magnetic field be oriented along the cone axis and would favor a larger difference between the diameters of the bases of the truncated cone?

Good questions.
Can earth magnetic field account for the order of magnitude of results ? This I could help to address with rough estimates. The direction, axis and magnitude dependence on geometry, I have no precise idea right now and am unsure I could contribute. Thinking about it (part time).
I'm not too concerned with the order of magnitude at this point in time because the inverted torsional pendulum can amplify whatever effect is thrusting the device  (maybe even dark matter  ).  I would think that the main thing to do is to find a classical experimental artifact that also acts along the axis of the cone, that depends on orientation of the big base and that it is larger with increasing difference between the base diameters.

So, this makes the "inverted torsional pendulum" criteria relevant somehow, sorry to ask because of poor memory and shallow reading : do all the relevant experiments done with this apparatus ?

If I'm going through this very cavalier and maybe senseless calculation from Brady a :
around 20W power, around 0.2m linear sizes, around 2µm skin depth for most eddy currents
earth magnetic field, say B=50µT
copper resistivity rho is approx. 1.7e-8 Ohm m
lets say a conductive strip of copper around .8m length .2m large 2µm thick.
has a resistance of R = rho length / (large thick) = 0.034 Ohm
that's a good conductor
To get a dissipation of 20W the current (RMS) would be (from P=RI²)  I=sqrt(P/R)=24A
This is not a DC current, but if it were, a DC current like that on l=.2m forward part .2m backward part (normal to B field), rad=.1m around a centre of rotation, would amount to a force of B l I on each branch, and that is a torque of 2 B l I rad =  5e-5 Nm  (give or take).
I think (but I'll think again) that a current loop in a locally homogeneous B field can't generate thrust, only torque. But when mounted on an arm at distance d around a pivot, something that undergo an imposed torque will transmit the torque that could appear as a tangential thrust of torque/d (please comment on that one, correct ?). I don't know if we could understand "inverted torsional pendulum" as equivalent to "arm on pivot", guess not, but if we could, with d=0.5m, that would look like a thrust of torque/d = 100µN
Brady a reports 90µN

Note the (most) silly hypothesis in bold.

Now, basically, if we have a local B field 1000 times that of earth because of strong permanent magnet in the vicinity (around 50mT), and there is an acdc_ratio of 1 part per 1000 AC -> DC asymmetry in conduction (welcome back to the weak rectifier hypothesis) then magnitude could be up to the job. Also a ferromagnetic wall nearby could serve to couple with 20mA DC but don't know how to estimate that.

If the instabilities of inverted torsional pendulum make it so that  a torque of (acdc_ratio times 50µNm) can explain things, so well, but the problem is that acdc_ratio is probably very small, or 0.

Must sleep now. Evening at the cinema to see Jean-Luc Godard's latest movie in 3D, Adieu au langage, exhausting.

#### Rodal

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##### Re: EM Drive Developments
« Reply #2215 on: 10/18/2014 12:54 AM »
OK, we reached agreement on Shawyer's big rig.

Now we (aero and hopefully notsosureofit and hopefully JohnFornaro) can work on the small drive.

aero ==> take a look at the PM I sent you the slope

I'll continue tomorrow, but this is the last I had on that:

For the Experimental Thruster, using Fig. 6 of Shawyer's report (http://www.emdrive.com/IAC-08-C4-4-7.pdf) I get:

Large Base Diameter = 16 cm = 0.16 m
Small Base Diameter = 11 cm = 0.11 m  (+41% greater than @aero's estimate)
Length = 15.8 cm = 0.158 m (-11% less than @aero's estimate)
« Last Edit: 10/18/2014 12:56 AM by Rodal »

#### ThinkerX

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##### Re: EM Drive Developments
« Reply #2216 on: 10/18/2014 01:26 AM »
From the 1st of the two papers linked to earlier (electromagnetic fields modifying special relativity) -

Quote
There are no details in the literature as to the precise dimensions of the cavities used in the experiments, so that an example roughly similar to the overall dimension reported and with the proportions observed in the published photographs will be used. Assuming a wall of thickness 1 mm, and a copper mass density of 8.9×103 kg/m3, we have σ = 8.9kg/m2.

We further consider the copper cavity to have r1 = 18 cm, r2 = 36 cm, and θ0 = 22◦. For this cavity, the lowest TM mode corresponds to the order n = 5.75632 of the Legendre polynomial, with a resonant frequency ν = 1.05GHz. For a resistivity η = 1.72×10−8 Ωm the quality factor for this mode is Qcav = 3.13×104. The next two TM modes have the same order n = 5.75632, and resonant frequencies ν = 2.05GHz
11 and ν = 2.76GHz, with quality factors Qcav = 3.11 × 104 and Qcav = 5.24 × 104, respectively.

What Minotti used for his calculations.

#### Rodal

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##### Re: EM Drive Developments
« Reply #2217 on: 10/18/2014 01:28 AM »
My estimate is that applying these geometric corrections
( http://forum.nasaspaceflight.com/index.php?topic=29276.msg1272692#msg1272692   )
to Shawyer's and China's experiments, and using McCulloch's formula now leads to appreciable underprediction of their experimental forces.

I very much congratulate aero for finding this signiificant error:  the small diameter of the Shawyer EM Drive was actually 4 times larger (16 cm instead of 4 cm).

We are going to need to explore the other formulas as well as aero's proposal for using the Unruh wavelength in McCulloch's formula, but first we have to come to an agreement on what is the slope of  a cone. (aero uses the word taper instead, and to communicate well we need to understand each other's definitions).

The slope of a truncated cone is

slope= (BigRadius - SmallRadius)/Length = (BigDiameter - SmallDiameter)/(2*Length)

and therefore it is 1/2 of what aero calls taper. Where the slope = Tangent[angle], therefore the angle (in radians) is ArcTan[slope]

For Shawyer's Demo Drive, the slope is 0.268 (instead of 0.53).

The cone angle for Shawyer's Demo Drive is ArcTan[0.268] = 15 degrees = 0.262 radians
« Last Edit: 10/18/2014 02:18 AM by Rodal »

#### Notsosureofit

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##### Re: EM Drive Developments
« Reply #2218 on: 10/18/2014 01:49 AM »
Couple things:
Won't get back to the lab til monday for measurements from picture
Both end plates have something else going on.  Looks likr the top one has a tuning plate(?) of some kind, not motorized
Why the extra plate below the bottom, can't see in pic

Found another paper that was bothering me in the piles behind the desk
"Ionization instabilities and resonant acoustic modes", Physics of Plasmas, V8, N0.11, p.5018

It was concerned w/ the coupling of ions w/ dust particles.  Reminds me of RF w/ axions  (Ya, I'm still chasing the axion connection) no cavities involved, but "It is found that an unstable dust-acoustic mode of nonzero real frequency can be generated via a resonance phenomenon."  ... "As the charge on dust particles exceeds a threshold, multiple low-frequency modes with large growth rates are excited suddenly."

I just had to throw that in cuz I finally found the d**m thing !  (You youngsters can play w/ it for now)

Ok, so in practical terms it means you can (theoretically)induce feedback into the coupling constant if you can set up the dispersion relations properly.

« Last Edit: 10/18/2014 02:08 AM by Notsosureofit »

#### JohnFornaro

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##### Re: EM Drive Developments
« Reply #2219 on: 10/18/2014 02:26 AM »
FWIW:

I converted the JPEG to a 8 bit gray TIF; imported into AutoCAD R14; scaled it so the big end was 28 cm.  To an arbitrary level of accuracy, since these are old eyeballs.:

1st Flange to 2nd flange:  3.0214284 cm
2nd flange to Cylinder 16.59242861 cm
Cylinder: 13.5771431 cm

Diameter of big end: 28 cm
Diameter of cylinder: 17.2052288 cm

Nuts to you all.
Sometimes I just flat out don't get it.

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