EM Drive Developments - related to space flight applications - Thread 2

[TheTraveller]

Do we have the Flight Thruster Dimensions?

I have found

bD: .265m
height: .164m

freq: 3.85GHz

DF: ?
sD: ?

Those are EXTERNAL dimensions. As far as I can find Shawyer has never given the Df for the Flight Thruster. He has stated the Q as 60,000, then later 50,000.

[TheTraveller]

IULIAN:

Hi,
.......snip
Iulian

Another thing to consider; From your video you have the unit on the end of a looped spring hanging from a shelf....  For the Downwards test you are trying to force the unit downwards AGAINST the natural TENSION of the spring...  you need to measure just how much energy it takes to pull the spring down as much as the unit did when you powered it up.!

The original "thrust was with the aid of the spring pulling the unit upwards. 

Placing the complete unit onto a balance board "like a child's see-saw,  American teeter-totter"  with an equal weight on the other end will enable you to perform these types of measurements

Shawyer likes his Teeter Totters.

Paul March said EW is building a version of the Shawyer Teeter Totter balance beam.

May be the way to measure the forces generated.

[Rodal]

This is also interesting for TM010 mode. Note where the H (magnetic) field is located. At the big end, right where Shawyer feeds in the Rf in the Demonstrator & Flight Thruster EM Drives.

Backs up the Patent mention of TM01 mode.

Fairly clear to me, TM010 is probably Shawyers EM Drive mode.

What is clear is that TM010 is definitely not the mode shape at the reported frequency and dimensions of Shawyer's Flight Thruster

Even at the lower frequency (almost 1/2 of the Flight Thruster) used by NASA Eagleworks (below 2 GHz with a dielectric) they are into a much higher mode shape: TM212

and look at the natural frequency shown on the image you posted above for NASA Eagleworks: TM010 is below 1 GHz without a dielectric

The TM01 mode is the mode shown to have the highest reflection, per Zeng and Fan's paper.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-17-1-34&id=175583

It also has fairly high attenuation. To raise Q, Shawyer needed more reflection, so he made the cone angle greater, which may or may not be counter productive at the lower attenuation value depending on how high a Q he can get. You can see why in the attachments.

You are correct.  The lowest modes have the highest amplitudes.  This is a basic fact in everything that has to do with resonance, from vibration of structures to electromagnetic resonance.

Here are two more facts:

1) Although the highest thrust is achieved with the highest Design Factor, approaching the value of 1, Shawyer's actual experiments were conducted with geometries having a Design Factor significantly lower than 1.

2) Although the lowest modes are known to have the highest amplitudes and Shawyer has written about mode TM010 the fact is that Shawyer's actual experiments were conducted with geometries and frequencies that excited modes much higher than TM010. 

Fact #1 is not being argued against because everybody can calculate the Design Factor with a simple Excel spreadsheet or a calculator.

Fact #2 is presently argued here by those that presently do not have the capability to calculate the actual mode shapes of a truncated cone.  But this is not a discussion about politics or economics, where people with completely different views can argue indefinitely without ever arriving at a conclusion.  Mother Nature has physical laws that govern the electromagnetic resonance of these cavities based on their geometry. 

There is no TM010 for a truncated cone.  A truncated cone has to have a variation of the electromagnetic field in the longitudinal direction.  What is being labeled as TM010 is a degenerate mode that has a variation in the longitudinal direction and is closest to the cylindrical TM010.

The fact is that to excite cylTM010 (the degenerate mode close to TM010) at 2.45 GHz or higher frequencies will take different geometrical dimensions than Shawyer used in his experiments or that are being discussed in this thread.  This is self-evident to anyone that has the capability to calculate the mode shapes of truncated cones and/or has had experience with analysis of resonance and vibration problems. 

All I have to do is to plug the dimensions of the small and big diameter and the height of the frustum in Mathematica and in a few seconds I get the mode shapes.  Those that do not have the capability to calculate the mode shapes are advised to click at the picture below, identify mode shape cylTM010 (the lowest line at the bottom of the picture) and read the vertical axis to ascertain the frequency associated with this mode shape (here shown for a huge variation in small diameter, going from almost a pointy cone at the left to a perfect cylinder at the right).

[Fugudaddy]

When i saw the people start thinking i died i was concerned. I wanted to post when i have some results but now i`m forced me to post some unfinished work

Something to remember in regards to the latest results Iulian posted; the request from the people here was to first flip the thing over and see if there was still thrust, to counter the effects of buoyancy.

It seemed that his latest tests showed that there was, indeed, some actual thrust effect that can't be attributed to hot air.

That seems like a big enough deal to me, even if, at this time, the actual exact numbers are still being determined. The more results that are out there is the more data that can be analyzed.

I don't want to speak for Iulian, but it seems his goal is similar to TheTraveller's; make a practical model and tweak from there.

As an aside- science teachers should show this thread to students. This is science in all it's hands on, get dirty, push ideas back and forth and come up with answers to things that don't seem to have answers glory.

[kdhilliard]

We also really need FAQ a lot :-P. Too much folks are asking about the questions that were already answered and properly tested before.

Chrochne, a few brave NSF soles are working on that over at http://emdrive.echothis.com/ and they could use some assistance if you can spare some time.

As I'll never have time to read through the previous 200+ pages ...

Lobo, you may be interested in scanning Paul March's posts (March, a.k.a. Star-Drive, is an engineer at Eaglewoks), perhaps starting with his 2015-02-06 report on their recent vacuum results, and the follow-ups discussing the magnitude of the expected thermal effects on their thrust stand in comparison to their thrust measurements.  Unfortunately, if you view them from his profile's posts list, there is no way to tell if there are any attached images short of clicking on the post and viewing it in the appropriate forum, which is important for posts such as with this 2015-02-07 response to Rodal.  You can, of course, view a list of his attachments separately, but it would be useful if it were possible to pull up a list of one user's posts with attachments displayed, all in one place.

In any case, if you or anyone else wishes to step through this history, please take notes and contribute to the wiki.

~Kirk

[Rodal]

This is also interesting for TM010 mode. Note where the H (magnetic) field is located. At the big end, right where Shawyer feeds in the Rf in the Demonstrator & Flight Thruster EM Drives.

Backs up the Patent mention of TM01 mode.

Fairly clear to me, TM010 is probably Shawyers EM Drive mode.

There is no TM010 for a truncated cone. TM010 means m=0;n=1;p=0. 

p=0 means constant electromagnetic field in the longitudinal direction. That is a basic fact.

If the mode would be constant in the longitudinal direction, it would make absolutely no difference where to plug the RF connection. 

The picture you posted shows a variation of the electromagnetic field in the longitudinal direction, therefore it is obvious that this cannot be TM010.

Truncated cones do not have the mode shape TM010.

A truncated cone has to have a variation of the electromagnetic field in the longitudinal direction. 

What is being labeled as TM010 is a "degenerate" mode that has a variation in the longitudinal direction and is closest to the cylindrical TM010.

COMSOL's Finite Element Analysis does not give the values of m,n,p, it only gives the natural frequencies and the mode shape images.  NASA's FEA analyst had to come up with a designation for the mode (there is no standard notation for truncated cone mode shapes).  He chose this designation because this degenerate mode had a frequency below that of the other mode that "looks" like TM011.

This degenerate mode has no analogous mode in a cylindrical cavity.

In a truncated cone, TM010 gets cut-off and mode TM011 gets bifurcated into two degenerate modes: one with a lower frequency and another one with a higher frequency.

This mode can only take place in a truncated cone.


Another "bread crumb": concerning "Patent mention of TM01 mode", there are an infinite number of TM modes having m=0, n=1, and p=1,2,3...Infinity.  None of them (for a truncated cone) have p = 0

[deltaMass]

Do you have a way to estimate feed impedance from feed position, for a given mode?
Or, put another way - given the mode, what is the locus of (50 + j0) ohm feed points?

[rfmwguy]

...HDPE has an unusual Dielectric Constant (K or E) variance of 1 to 5 while PTFE has confined K of 2-2.1. This is probably why HDPE is not normally used in MW circuits...unpredictability or randomness, if you will. In essence, a puck/layer of HDPE would present a wide K variance across its surface to EM, unlike PTFE. Few materials have this: http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm
...

HDPE is not random.  It is fairly straightforward to characterize as having well determined properties, based on its molecular weight for example, and method of manufacture.  If the properties of HDPE would be random or difficult to characterize, believe me that HDPE would not be used for biomedical applications, which have higher standards for material properties than many commercial applications do.

What happened here is that you are looking at this row:

High Density Polyethylene (HDPE), Molded   1.0 - 5.0

instead of looking at this one, which is the appropriate row to look at:

Polyethylene LDPE/HDPE     2.26 @ 1 MHz
                                                2.26 @ 3 GHz

Those are the appropriate properties for the NASA Eagleworks dielectric.
Now: that's a narrow range, and it even gives you data at the GHz range for direct application to microwaves.

NASA Eagleworks did not use a molded product (see my previous posts, given the identity of the product used by NASA). 

Having said that, the fact that this website gives properties for HDPE in two completely different rows, with different ranges, and does not explain the differences does not give me a good impression about the quality of the data in this website (which is also the same website I initially found when I was quickly looking for the HDPE properties)

Authoritative handbooks like this one give much more reliable data than these websites: http://bit.ly/1Lr0pSt

Of course, the best thing is to have analytical instruments to properly characterize the material properties of a polymer, which is what we did.


Note that in this same website they also have this funny note, acknowledging that they had the tan delta for PTFE off by a factor of 10 until Craig  found the error !!!!!

Thanks to Craig B. for correcting the loss tangent for Teflon (0.00028 rather than 0.0028).

Well dang, here I thought we had nailed down the mystery acceleration. Alas, we still have this systemic anomaly ( I love that phrase). All along I thought we could point our fingers at the chirality of twisted polymer crystals.  http://www.esrf.eu/UsersAndScience/Publications/Highlights/2011/scm/scm4

Agree See, not sure we should give up on the thrust differences between HDPE and PTFE. All else being the same, why the difference? You or Doc might have some insight into the chemistry, but EM properties are what we're interested in.

Base question is: Why does HDPE preform better than PTFE in high EM field experiments? (HDPE does have roughly half the thermal resistance of PTFE).

Here's an old Bulgarian Science Foundation paper where an HDPE was studied using MW (2-10 GHz) : ftp://213.176.96.142/sciencedirect48477b28-4072-20141124031119.pdf

Seems they are quite interested in absorption and reflection performance with the introduction of acetylene carbon black (CB) into HDPE. Doncha love mixing  chemistry and electronics? 

"It is obvious that the CB concentration influence on the microwave properties is the strongest in the frequency range 2–3 GHz. At optimum CB concentration (17.5 mass%), the coefficient of attenuation reaches 5 dB/mm,
while the coefficient of reflection is close to the starting HDPE coefficient, i.e., the absorption
activity is more than 10 times greater than the reflection activity."

[deltaMass]

...Base question is: Why does HDPE preform better than PTFE in high EM field experiments? (HDPE does have roughly half the thermal resistance of PTFE)....

Paul March's answer is that it has to do with the imaginary components of the electric permittivity and magnetic permeability, and the choice was based on his experience working with Prof. Woodward.

I haven't found values for the imaginary components of the electric permittivity and magnetic permeability of HDPE in the literature.

To assess this issue we need actual experimental values of the imaginary components of the electric permittivity and magnetic permeability of HDPE.

Perhaps counterintuitively, these imaginary components are dissipative. Which is A Bad Thing. Probably

[Rodal]

...perhaps counterintuitively, these imaginary components are dissipative. Which is A Bad Thing. Probably

Of course they are dissipative, but it is straightforward to show that the time-average value of the Poynting vector, which is zero for a non-dissipative homogeneous cavity becomes non-zero for an asymmetric cavity with a dielectric with dissipative properties (one can show this even just based on the electric Tan Delta, as I did in the thread many pages ago).

Even a cavity just having one end hotter than the other will result in propulsion (due to thermal radiation as in the Pioneer anomaly), albeit very small to justify the researchers claims (solely based on thermal radiation).

[phaseshift]

I also think the cavity length needs to be adjusted on the Demonstrator Thruster to .187m....

0.187 m is the minimum axial length.  The Demonstrator has a gear-driven mechanism at the small end in order to change the internal length to tune the cavity.

Could you please figure out -from the picture- the maximum length for the Demonstrator so that we can put both these values (minimum length and maximum length) in the wiki (http://emdrive.echothis.com/Experimental_Results) for EM Drive ?

How can the maximum be determined? We have no idea what is inside the cylinder. It could be almost empty except for the plate or chock full of more gears.  .187 is the end of the cone, any additional possible length is up to what's inside.ideas?

[Star One]

Haven't seen anyone post this to the thread so far.

https://hackaday.io/project/5596-em-drive

Plus interview with the team leader.

http://n-o-d-e.net/post/119343131451/building-a-diy-emdrive

[phaseshift]

Either use the thickness of the interior plate and gears equal to zero, or use your best guesstimate.

Which is pretty much the length of the cylinder - why don't we put that in the wiki.   It's up to anyone's interpretation of the thickness of the plate and dimensions of internal mechanisms that determine what the maximum is - setting that to zero is the cylinder length. Publishing what we think the cylinder length is allows additional estimates to be worked out by others.

It appears there are two rods entering the cavity, probably for stability.  How they attach to the plate is going to take up a few millimeters and could add a handful of millimeters to the thickness of the plate. 

I'll jump on this in a bit - certainly after, and not before, morning coffee.

[phaseshift]

Haven't seen anyone post this to the thread so far.

https://hackaday.io/project/5596-em-drive

Plus interview with the team leader.

http://n-o-d-e.net/post/119343131451/building-a-diy-emdrive

I like they went to 25GHz.    Also interesting they are 3D printing plastic parts and then coating with metal. 

[deltaMass]

Haven't seen anyone post this to the thread so far.

https://hackaday.io/project/5596-em-drive

Plus interview with the team leader.

http://n-o-d-e.net/post/119343131451/building-a-diy-emdrive

Excellent set of strategies these guys are using. In parallel they're doing a Shawyer/Chinese replication attempt @2.4 GHz, and also building a 25 GHz beast with the aim of popping it into a PocketQub and sending it into space (which one of them has already done with a different project).

[kdhilliard]

Regarding Shawyer's prediction for the direction of thrust vs. acceleration (big-endian vs. little-endian):

Traveller, can you recommend another of Shawyer's papers to read where I can find this argument?

Page 4 [of the Toulouse 2010 paper] explains it.

Thanks Traveller.  I just finished reading it.  The theory portion contains a bit more exposition but gives the same equations as in the V 9.4 Theory Paper, with the exception that V 9.4 also analyzes a cavity with a dielectric-filled end section (so equation (9) from the 2010 paper corresponds with the slightly different equation (11) of V 9.4 since he doesn't introduce the thrust multiplier effect of Q in V 9.4 until the dielectric-filled end section analysis).

As an aside, I found interesting:

The resulting design must also ensure a low taper slope, to minimise the axial component of side wall forces.

It is clear that if the minimum dimension was the cut off diameter, force F_g2 would be zero. However because there would still be a significant small end plate area, the projected area of the side wall would not equal the area of the large end plate. Thus any attempt to show a resultant zero net force due to equalisation of areas is incorrect.

He seems to be saying that the axial component of the sidewall forces could be an issue, possibly counterbalancing much of the difference of forces between the end plates (all but that proportional to the area of the small end when reduced to the cut off diameter), but I can't find anywhere else in the paper where he accounts for these forces.


Anyhow, back to direction of thrust vs. acceleration:

Note that to maintain the principle of the conservation of momentum, the acceleration of the waveguide due to thrust, is opposite to the actual thrust direction. Thus, in Fig 3, the sign convention for the waveguide velocity axis is:
                      <-----        ----->
Acceleration Vector  Thrust Vector

When the waveguide is accelerated along the acceleration vector, the thrust approaches a maximum of 1. However, as the velocity of the waveguide increases in the direction of thrust, the thrust will decrease to zero.

That's it.

He gives no explanation as to how a device which is expelling no reaction mass is in violation of conservation of momentum when it accelerates in one direction but not when accelerating in the opposite direction.

I'd have understood had he written, "To maintain the principle of conservation of momentum, forces on the sidewalls must counteract the difference of end plate forces, resulting in no net force and no acceleration."  But then there wouldn't be much to discuss.  (I'd also understand him were he to say that his device was constructed from exotic matter, had negative inertial mass, and thus accelerated in the opposite direction of the net force applied to it, but he makes no such claims.)

~Kirk, who is reminded of a "backwards rotating" Crookes radiometer.

Edit: Grammar

[Rodal]

...Base question is: Why does HDPE preform better than PTFE in high EM field experiments? (HDPE does have roughly half the thermal resistance of PTFE)....

Paul March's answer is that it has to do with the imaginary components of the electric permittivity and magnetic permeability, and the choice was based on his experience working with Prof. Woodward.

I haven't found values for the imaginary components of the magnetic permeability of HDPE or PTFE in the literature.

We can ascertain the (non-dimensionalized) imaginary values of the electric permittivity from the electric Tan Delta from here: http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm


HDPE             0.00031 @ 3 GHz  (from the later row, not from the molded product row)
PTFE              0.00028 @ 3 GHz
Nitrile Rubber 0.034 @ 3 GHz

It shows HDPE having 11% higher electric Tan Delta than PTFE, which is not much of a difference, but at least in the right direction to produce more thrust.

It shows Nitrile Rubber as having much higher electric Tan Delta that either HDPE or PTFE, which does not agree with Paul March's experiments, as his experiments showed Nitrile Rubber used as a dielectric produced less thrust.  However Nitrile Rubber usually has mineral fillers that strongly affect its properties.  Without knowing exactly the type of Nitrile Rubber compound (including its filler content) used by Paul March it is impossible to extract conclusions.
Also, as dissipation takes place, the temperature of the polymer rises. Materials with higher Tan Delta will get hotter.  As they get hotter, the Tan Delta value changes, (just based on the WLF equation for example). So the effect of Tan Delta is very nonlinear.

Ideally, one would want to have temperature sensors inside the cavity, particularly looking at the dielectric or near it, to understand what is going on.


That reference ( http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm ) is not very high quality, as previously discussed, but it is the first one that showed up in a Google search.

Anybody care to look for more references for Tan Delta (electric and magnetic) for HDPE and PTFE and Nitrile Rubber compounds?


Relative electric permittivity

HDPE         2.26 @ 3 GHz
PTFE          2.0 - 2.1
Neoprene   4 @ 3 GHz


Glass Transition Temperature

HDPE    - 110 C  (difficult to determine, dependent on crystallinity)
PTFE     - 115 C  (difficult to determine, dependent on crystallinity)
Neoprene -50 C


Upper Temperature

HDPE        135 C (Melting point)
PTFE         327 C (Melting point)
Neoprene  121 C (Max service temperature)


From the above properties, one concludes:

1) HDPE and PTFE are both semi-crystalline while Neoprene rubber is not.  Perhaps the superior thrust performance of HDPE and PTFE is due to their semi-crystallinity (van Tiggelen effect)

2) HDPE has slightly (~10%) higher real and imaginary components of the electric permittivity than PTFE

3) HDPE and PTFE have similar glass transition temperatures (both difficult to determine due to their crystallinity)

4) PTFE has a much higher melting temperature than HDPE. 

So HDPE may have outperformed due to any of these possibilities:

a) by chance, the extruded HDPE obtained from McMaster Carr by NASA had higher crystallinity than the PTFE (van Tiggelen effect)

b) HDPE gets hot and softens during operation of the EM Drive introducing nonlinearity of its electric permittivity which maybe benefitial to an asymmetric thrust effect. (Neoprene has a huge Tan Delta, therefore it gets much hotter than HDPE, perhaps too hot to operate effectively.)

c) HDPE may have higher imaginary component of its magnetic permeability than PTFE.  (This is completely unknown as to magnitude and relevance).

[RonM]

Looking at the difference in melting points between HDPE and PTFE, the "improved" performance might be due to out gassing from HDPE as it is over heated.

What is the temperature inside the device during a test run?

[TheTraveller]

Another "bread crumb": concerning "Patent mention of TM01 mode", there are an infinite number of TM modes having m=0, n=1, and p=1,2,3...Infinity.  None of them (for a truncated cone) have p = 0

After doing some more reading, it seems clear that Shawyer is only interested in resonance between the end plates at the frustum's effective electrical length, which depends on the integral of the constantly changing guide wavelength from one end plate to the other. Operational Rf wavelength is then some multiple of that effective wavelength. For non adjustable Rf generators, having the ability to vary the frustum length will allow operation at resonance. Here we need to fully understand, the physical end plate separation will not have a subharmonic relationship with the Rf generators wavelength.

Shawyers method to calc the frustum's effective electrical length:

You need to develop a numerical model that calculates the guide wavelength, for the chosen mode, at discrete small increments along the cavity length and then integrate them into an effective wavelength for the whole cavity.

As I want to operate in TM01 mode, as stated in Shawyer's patent and several of his publications, the big and small end cutoff wavelengths and the associated guide wavelengths (as in the quote) are different to TE mode. This  recommended method which only focuses on length resonance, as mentioned in many of the Shawyer publications, seems to be different to what NASA and other have done, are doing.

What this means is Shawyer is treating his frustum as a resonate cylinder that has variable guide wavelengths from one end to the other. His only interest in the radius or diameter is how it effects the guide wavelength and what the integral of all the constantly changing guide wavelength over the length of the cylinder is.

[Rodal]

Looking at the difference in melting points between HDPE and PTFE, the "improved" performance might be due to out gassing from HDPE as it is over heated.

What is the temperature inside the device during a test run?

No reported internal temperatures for NASA Eagleworks.

Externally, the hottest face was the big diameter covered with fiber-reinforced epoxy facing the outside, hence external outgassing of the epoxy is probably just as or more likely to produce thrust than internal outgassing of HDPE (more free volume in fiber-reinforced epoxy than in HDPE and the epoxy is on the outside)