Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1804171 times)

Offline meberbs

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@rfmwguy: If it's that esoteric, then perhaps a frustum is not an optimal shape. Perhaps the sidewalls need to follow some esoteric functional profile, as perhaps also do the end plates. But there's no way to get a handle on that sort of speculation without some hard mathematics behind your idea.

You are 100% correct. Trouble is, I cannot find sources that quantify entropy. Its certainly post-newtonian physics, which was solely focused on the 5% of "regular" matter and energy. I also agree that a Frustum may be happenstance, but an "opaque effect" may be focused there. The reason I say opaque is that if it was "solid" the Frustum would literally blow apart.  :o

Its similar to gravity. We have yet to determine how to make something "opaque" to it, something it affects less than normal matter.

I think you are very confused by what you are referring to. Entropy is not a weird, unknown or mysterious force (at least to scientists who regularly work with thermodynamics).

I'd like to clarify this a little since one of the biggest differences I've noticed between pseudo science and good science is precise definitions of terms.

You referred to entropy as a force a couple times. Entropy is not a force (It has units of energy per temperature.) This doesn't mean that it can't produce an effective force, but this would be the same way that a density gradient in a gas would cause an effective force (The higher density causes a higher pressure, which is force normalized by area)

Entropy per mass or entropy per mole can be considered comparable to the density in the example I just made (In fact, if someone wanted to go through the math, they could calculate the entropy changes for a density gradient situation and show how the resulting gas flow would be driven from an entropy perspective).

As I said before entropy is well understood. Boltzmann worked in the late 1800s and his gavestone has a version of the formula for absolute entropy of a system  The formula is here: http://en.wikipedia.org/wiki/Entropy#Statistical_mechanics This requires a complete description of the system to calculate, so it is not used much. Generally entropy deltas are easier to deal with, and are more relevant, but we do have a precise definition for absolute entropy and zero entropy (a perfect crystal at temperature absolute 0).

While entropy is post newtonian in the sense that it was developed after Newton died, it is definitely a part of classical physics, and I know of nothing in relativity or quantum that changes the concept of entropy. (although they provide interesting new systems to apply entropy calculations to and the divide-by-zero nature of black holes causes complications they haven't fully resolved)

I only have had time to read the conclusion section of the paper you referenced, but it appears they are not proposing a revolutionary way for entropy to result in a force. They seem to be using entropy as a tool to show how some of the acceleration attributed to dark energy may actually just be classical forces that weren't fully accounted for. It does not seem like they are claiming anything that would count as "new physics" or explain EM drive thrust.

I can't keep up with this thread all the time, but I try to stop by once in a while.

Offline WarpTech

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Hence, why I said the frustum needs to be longer, so we can have something "closer" to Zeng & Fan's waveguide for traveling waves. If we are confined to 0-length past the cut-off diameter, attenuation is minimized, reflection and Q are higher. If we extend it out a full wavelength, we may attenuate 66% of the energy. The other 33% will be reflected with a larger phase shift than what Shawyer's design allows.

Also, the standing waves in a damped cavity will also frequency shift due to the damping. That's what gives Shawyer's design "some" thrust, but as I said, it is the rate of attenuation that will exert a higher force. So a longer front end to give the waves some traveling room to be attenuated faster, is what I believe is needed.

In other words, "design" the thruster more like Zeng and Fan and less like Shawyer.
Todd

Prof. Yang's EM Drive is significantly longer than Shawyer's

Description Mode Shape  Length (m)   Db (m) Ds (m)   Frequency (GHz)  Q  Force / PowerInput (mN/kW)
Shawyer Demo  TE012    0.187           0.28    0.14921    2.45             45000   80-243
Yang                  TE012    0.24            0.201  0.1492       2.45               1531   1070

Both have the same frequency, same mode shape, same Small Diameter

Yang achieves 10 to 5 times greater force/input power by operating with 29 times lower Q with a 28% longer EM Drive and 39% smaller big diameter.  All the opposite of what Shawyer recommends.

The wavelength is 299700000 m/s /(2.45*10^9 1/s) = 0.122 m

So Yang's EM Drive (which has the same small diameter as Shawyer's Demo) has a length (0.24 - 0.187) = 0.053 m

Yang's EM Drive is therefore about 1/2 wavelength longer than Shawyer's EM Drive truncated cone length


The most important parameter to Zeng & Fan is the cone half-angle.  It is drastically different between them:

Shawyer   (180/Pi) ArcTan[(0.28 - 0.14921)/(2*0.187)] = 19.275 degrees

Yang        (180/Pi) ArcTan[(0.201 - 0.1492)/(2*0.24)] =    6.159 degrees

Shawyer's EM Drive has a cone half-angle more than 3 times greater.

Yang's EM Drive is closer to a cylinder, which according to Zeng & Fan results in much greater attenuation.

Thank you for validating everything I just said!  8)

Offline Rodal

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Hence, why I said the frustum needs to be longer, so we can have something "closer" to Zeng & Fan's waveguide for traveling waves. If we are confined to 0-length past the cut-off diameter, attenuation is minimized, reflection and Q are higher. If we extend it out a full wavelength, we may attenuate 66% of the energy. The other 33% will be reflected with a larger phase shift than what Shawyer's design allows.

Also, the standing waves in a damped cavity will also frequency shift due to the damping. That's what gives Shawyer's design "some" thrust, but as I said, it is the rate of attenuation that will exert a higher force. So a longer front end to give the waves some traveling room to be attenuated faster, is what I believe is needed.

In other words, "design" the thruster more like Zeng and Fan and less like Shawyer.
Todd

Prof. Yang's EM Drive is significantly longer than Shawyer's

Description Mode Shape  Length (m)   Db (m) Ds (m)   Frequency (GHz)  Q  Force / PowerInput (mN/kW)
Shawyer Demo  TE012    0.187           0.28    0.14921    2.45             45000   80-243
Yang                  TE012    0.24            0.201  0.1492       2.45               1531   1070

Both have the same frequency, same mode shape, same Small Diameter

Yang achieves 10 to 5 times greater force/input power by operating with 29 times lower Q with a 28% longer EM Drive and 39% smaller big diameter.  All the opposite of what Shawyer recommends.

The wavelength is 299700000 m/s /(2.45*10^9 1/s) = 0.122 m

So Yang's EM Drive (which has the same small diameter as Shawyer's Demo) has a length (0.24 - 0.187) = 0.053 m

Yang's EM Drive is therefore about 1/2 wavelength longer than Shawyer's EM Drive truncated cone length


The most important parameter to Zeng & Fan is the cone half-angle.  It is drastically different between them:

Shawyer   (180/Pi) ArcTan[(0.28 - 0.14921)/(2*0.187)] = 19.275 degrees

Yang        (180/Pi) ArcTan[(0.201 - 0.1492)/(2*0.24)] =    6.159 degrees

Shawyer's EM Drive has a cone half-angle more than 3 times greater.

Yang's EM Drive is closer to a cylinder, which according to Zeng & Fan results in much greater attenuation.

Thank you for validating everything I just said!  8)
It is amazing that Yang achieves record thrust force and record thrust force/powerInput by doing the complete opposite of common wisdom:

* lowest Q of any recorded test   (common wisdom: highest Q the better)
* smallest cone angle, closest to cylinder  (common wisdom: highest cone angle the better)
* longer cavity than Shawyer's Demo at same small diameter
* smaller big diameter than Shawyer's Demo at same small diameter  (common wisdom: the larger the big diameter the better)

It is also noteworthy that both Shawyer and Yang (who achieve much larger forces):

* do not use dielectric inserts
* use TE012 mode with magnetic axial field

instead of NASA Eagleworks, who uses a dielectric insert and uses a higher transverse magnetic mode (TM212) with an electric axial field

Offline rfmwguy

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@rfmwguy: If it's that esoteric, then perhaps a frustum is not an optimal shape. Perhaps the sidewalls need to follow some esoteric functional profile, as perhaps also do the end plates. But there's no way to get a handle on that sort of speculation without some hard mathematics behind your idea.

You are 100% correct. Trouble is, I cannot find sources that quantify entropy. Its certainly post-newtonian physics, which was solely focused on the 5% of "regular" matter and energy. I also agree that a Frustum may be happenstance, but an "opaque effect" may be focused there. The reason I say opaque is that if it was "solid" the Frustum would literally blow apart.  :o

Its similar to gravity. We have yet to determine how to make something "opaque" to it, something it affects less than normal matter.

I think you are very confused by what you are referring to. Entropy is not a weird, unknown or mysterious force (at least to scientists who regularly work with thermodynamics).

I'd like to clarify this a little since one of the biggest differences I've noticed between pseudo science and good science is precise definitions of terms.

You referred to entropy as a force a couple times. Entropy is not a force (It has units of energy per temperature.) This doesn't mean that it can't produce an effective force, but this would be the same way that a density gradient in a gas would cause an effective force (The higher density causes a higher pressure, which is force normalized by area)

(...)


its the nature of entropy that interests me and there are knowns due to classic thermodynamics. from a plain language standpoint, we measure and discuss 5% of the known universe, despite the majority of it being dark mass & energy. Some knowns could crossover, but odds are that cosmic expansion occurs because of a force/energy/mass we know little about. Therein lies a more than reasonable chance of significant discoveries, emdrive or otherwise. maybe we can agree that expansion due to dark energy is a natural force we do not fully comprehend yet.

Edit

Perhaps I should have said entropic force: https://en.m.wikipedia.org/wiki/Entropic_force

One final edit: Unification of Dark Matter and Dark Energy in a Modified Entropic Force Model - http://arxiv.org/pdf/1009.1506v3

Guess I am a couple of years behind ;)
« Last Edit: 06/12/2015 04:23 AM by rfmwguy »

Offline SeeShells

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@rfmwguy: If it's that esoteric, then perhaps a frustum is not an optimal shape. Perhaps the sidewalls need to follow some esoteric functional profile, as perhaps also do the end plates. But there's no way to get a handle on that sort of speculation without some hard mathematics behind your idea.

You are 100% correct. Trouble is, I cannot find sources that quantify entropy. Its certainly post-newtonian physics, which was solely focused on the 5% of "regular" matter and energy. I also agree that a Frustum may be happenstance, but an "opaque effect" may be focused there. The reason I say opaque is that if it was "solid" the Frustum would literally blow apart.  :o

Its similar to gravity. We have yet to determine how to make something "opaque" to it, something it affects less than normal matter.

I think you are very confused by what you are referring to. Entropy is not a weird, unknown or mysterious force (at least to scientists who regularly work with thermodynamics).

I'd like to clarify this a little since one of the biggest differences I've noticed between pseudo science and good science is precise definitions of terms.

You referred to entropy as a force a couple times. Entropy is not a force (It has units of energy per temperature.) This doesn't mean that it can't produce an effective force, but this would be the same way that a density gradient in a gas would cause an effective force (The higher density causes a higher pressure, which is force normalized by area)

(...)


its the nature of entropy that interests me and there are knowns due to classic thermodynamics. from a plain language standpoint, we measure and discuss 5% of the known universe, despite the majority of it being dark mass & energy. Some knowns could crossover, but odds are that cosmic expansion occurs because of a force/energy/mass we know little about. Therein lies a more than reasonable chance of significant discoveries, emdrive or otherwise. maybe we can agree that expansion due to dark energy is a natural force we do not fully comprehend yet.

Edit

Perhaps I should have said entropic force: https://en.m.wikipedia.org/wiki/Entropic_force

One final edit: Unification of Dark Matter and Dark Energy in a Modified Entropic Force Model - http://arxiv.org/pdf/1009.1506v3

Guess I am a couple of years behind ;)
And I keep on re-reading this.
http://www.sciencedaily.com/releases/2015/05/150527112953.htm

Offline SeeShells

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Intermission
For expanding your mind.
https://vimeo.com/66641648#

Offline zen-in

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There clearly isn't enough "thrust" (if there is thrust) to compensate friction, at least at those speeds. Actually there isn't even prograde thrust at all that would limit the decay, or if there is it appears very unconclusive to my eye, as the decay seems to continue at same rate, within margins of noise. Only in retrograde mounting there is maybe slightly more speed loss rate at activation (maybe adepts of Shawyer's theories will be delighted to see here an illustration of the distinction between motor mode and generator mode ?).

Which begs the question of what kind of friction there is ? Aerodynamic drag would tend to fall with speed, while the curves show a near linear decay in speed, constant deceleration, constant drag force... it looks more like a (very low) dry friction, until it falls below 150 and drag gets even higher. That looks contradictory to aerodynamic drag being the main contributor to the dissipative factor. This is to be characterised properly, especially if thrust effects are to be evaluated against this drag.

I wonder, they do use one of those magnetic globe levitators system, don't they ? Those toys use an active electromagnet feedback system to stabilize altitude and vertical oscillations, on top of the stronger permanent magnet that does the heavy lifting. Couldn't the periods of this feedback enter in resonance or just happen to synchronise with the rotation period, leading to net torque being communicated from the electromagnet to the levitated rig (taking into account small deviations of magnetic materials wrt perfectly axisymmetric geometry) ?

One possible source of drag is eddy currents.   As the Aluminum cavity sweeps through the magnetic field created by the levitator any change in the field strength will induce currents in the Aluminum.   This can happen because of the wobbles seen in the rotation vs time curves.   The Aluminum block moves out of center slightly and the magnetic field strength around it is slightly weaker.   That will introduce Ohmic losses and the rotation rate will decrease faster than it would if there was no metal.

It's an interesting apparatus; very crafty construction.   I hope they collect lots of data from it and see what averages out.

Offline WarpTech

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Thank you for validating everything I just said! 

Do you think this model will still require a separate resonance chamber as per your original plan?

Yes, that's still a very valid design concept. I'm working on something else right now, the DC analysis of a coaxial cone. Why? Because, it's easier to model and understand what's what, with a pencil and paper. What I found is that the amount of energy stored inside, depends on the length. So a longer cone can store more energy as a magnetic field. It's a 1-turn inductor, with the B-field trapped inside. I just finished integrating the B-field pressure over the surface areas. Of course, Maxwell is always right and the SUM of the DC pressures balances, exactly as they should. No thrust. (With the bottom closed anyway.)

Later, I can see what happens when I integrate this with waves and a damping factor.

Todd





Offline WarpTech

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It is amazing that Yang achieves record thrust force and record thrust force/powerInput by doing the complete opposite of common wisdom:

* lowest Q of any recorded test   (common wisdom: highest Q the better)
* smallest cone angle, closest to cylinder  (common wisdom: highest cone angle the better)
* longer cavity than Shawyer's Demo at same small diameter
* smaller big diameter than Shawyer's Demo at same small diameter  (common wisdom: the larger the big diameter the better)
...

1. Q represents energy stored. If ALL the energy is stored, it doesn't do any "work". A lower Q does not imply more waste, it implies more work is being done. It can be due to thrust or heat.

2. Smaller cone angle has faster attenuation at higher energy modes = more thrust, lower Q.

3. Longer cavity means more stored energy, so she makes up for a lower Q by adding length. (conjecture)

4. Thought about this a little more today and the comment from @TheTraveler. (Get well soon!) The wavelength inside the cavity at the small end will be ~half what it is in free space, so the small end is actually probably the right size. It is still important to have a longer frustum to allow the stored energy to be attenuated faster, with fewer bounces.

I'm thinking the input port should be 1/4 wavelength from the large end. So resonance happens between the Feed and the large surface. The small end should be far away and designed to attenuate all the possible waves in the spectrum.

Todd

Offline Chrochne

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I am glad to see that this debate is now starting to explore the idea of increasing the thrust in this device. As a member of the general public, I see this as the only way now to really prove that this is something science community should look into.

Also thanks goes to Dr. Rodal that managed to return this debate into science again (and of course to editors as well).

And I am really looking forward to see some ideas on how to increase the thrust. Lets see what Eagleworks will come up with. I hope you are still follwing us Mr. Paul March! Its your turn now.

I am also glad to see, that another team managed to see the thrust. Congratulations to baby EmDrive team. I am looking forward for additional data they will send our way.


Offline dustinthewind

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There clearly isn't enough "thrust" (if there is thrust) to compensate friction, at least at those speeds. Actually there isn't even prograde thrust at all that would limit the decay, or if there is it appears very unconclusive to my eye, as the decay seems to continue at same rate, within margins of noise. Only in retrograde mounting there is maybe slightly more speed loss rate at activation (maybe adepts of Shawyer's theories will be delighted to see here an illustration of the distinction between motor mode and generator mode ?).

Which begs the question of what kind of friction there is ? Aerodynamic drag would tend to fall with speed, while the curves show a near linear decay in speed, constant deceleration, constant drag force... it looks more like a (very low) dry friction, until it falls below 150 and drag gets even higher. That looks contradictory to aerodynamic drag being the main contributor to the dissipative factor. This is to be characterised properly, especially if thrust effects are to be evaluated against this drag.

I wonder, they do use one of those magnetic globe levitators system, don't they ? Those toys use an active electromagnet feedback system to stabilize altitude and vertical oscillations, on top of the stronger permanent magnet that does the heavy lifting. Couldn't the periods of this feedback enter in resonance or just happen to synchronise with the rotation period, leading to net torque being communicated from the electromagnet to the levitated rig (taking into account small deviations of magnetic materials wrt perfectly axisymmetric geometry) ?

One possible source of drag is eddy currents.   As the Aluminum cavity sweeps through the magnetic field created by the levitator any change in the field strength will induce currents in the Aluminum.   This can happen because of the wobbles seen in the rotation vs time curves.   The Aluminum block moves out of center slightly and the magnetic field strength around it is slightly weaker.   That will introduce Ohmic losses and the rotation rate will decrease faster than it would if there was no metal.

It's an interesting apparatus; very crafty construction.   I hope they collect lots of data from it and see what averages out.

Hmm this gets me thinking about the standing or non-standing waves in the cavity.  Let us say, that for some reason attenuation of light is happening at the top end so reflected light is weaker than light from the bottom.  As a result the wave is no longer a standing wave and is instead a traveling wave or semi (standing-traveling wave).  We all know if you hold a magnet near an aluminum plate and move it it will drag the plate because of the resistance to change in magnetic field.  So maybe the semi-traveling waves could do the same to the cavity and drag it along?  Does that sound like a possibility? 

Offline Rodal

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...Hmm this gets me thinking about the standing or non-standing waves in the cavity.  Let us say, that for some reason attenuation of light is happening at the top end so reflected light is weaker than light from the bottom.  As a result the wave is no longer a standing wave and is instead a traveling wave or semi (standing-traveling wave).  We all know if you hold a magnet near an aluminum plate and move it it will drag the plate because of the resistance to change in magnetic field.  So maybe the semi-traveling waves could do the same to the cavity and drag it along?  Does that sound like a possibility?
You can move an object by using a magnet from the outside.

However you cannot accelerate the center of mass of an object by moving a magnet  inside it.

An Astronaut with a powerful magnet inside the ISS can move the magnet all she/he wants,  and still will not be able to accelerate the center of mass of the ISS. 
« Last Edit: 06/12/2015 11:31 AM by Rodal »

Offline Rodal

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1. Q represents energy stored. If ALL the energy is stored, it doesn't do any "work". A lower Q does not imply more waste, it implies more work is being done. It can be due to thrust or heat.

2. Smaller cone angle has faster attenuation at higher energy modes = more thrust, lower Q.

3. Longer cavity means more stored energy, so she makes up for a lower Q by adding length. (conjecture)

4. Thought about this a little more today and the comment from @TheTraveler. (Get well soon!) The wavelength inside the cavity at the small end will be ~half what it is in free space, so the small end is actually probably the right size. It is still important to have a longer frustum to allow the stored energy to be attenuated faster, with fewer bounces.

I'm thinking the input port should be 1/4 wavelength from the large end. So resonance happens between the Feed and the large surface. The small end should be far away and designed to attenuate all the possible waves in the spectrum.

Todd

Shawyer criticizes the use of dielectric inserts inside the EM Drive because they lower the Q (because they have a tan delta > 0 and hence they introduce further losses).  However, notice that the use of a dielectric insert can also be criticized from the point of view of lowering the amount of geometrical attenuation.
Keeping the geometry of the truncated cone constant, inserting a dielectric has the effect of significantly lowering the natural frequency of the truncated cone.  Lowering the natural frequency has the effect of allowing mode shapes to occur that otherwise would have been cut-off without the dielectric.  The common practice of inserting the dielectric at the small end, next to the small end base (as done by NASA Eagleworks) has the effect of preventing the cut-off of mode shapes that would have been otherwise cut-off at the small end.

Notice that NASA Eagleworks reported thrust force is orders of magnitude smaller than the reported thrust force by the UK and Chinese researchers who don't use dielectric inserts.  The effect of the dielectric in lowering the natural frequency and preventing cut-off of modes can be more important than the effect of lowering the Q because the tan delta of these dielectric inserts is very small (for example, for the dielectric used by NASA Eagleworks, HDPE), the tan delta (responsible for lowering Q) is small: only 0.00031 @ 3 GHz  while  the relative permittivity (responsible for lowering the natural frequency) is not small: 2.26 @ 3 GHz .(http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm)

So, the geometrical attenuation theory of thrust also says that it is a bad idea to use dielectric inserts, because they prevent cut-off, they prevent evanescent waves that would otherwise occur.  Thus, the geometrical attenuation theory is in accord with experiments also in this respect, as the experiments show that the highest thrust forces have been produced without dielectric inserts.
« Last Edit: 06/12/2015 01:39 PM by Rodal »

Offline rfmwguy

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1. Q represents energy stored. If ALL the energy is stored, it doesn't do any "work". A lower Q does not imply more waste, it implies more work is being done. It can be due to thrust or heat.

2. Smaller cone angle has faster attenuation at higher energy modes = more thrust, lower Q.

3. Longer cavity means more stored energy, so she makes up for a lower Q by adding length. (conjecture)

4. Thought about this a little more today and the comment from @TheTraveler. (Get well soon!) The wavelength inside the cavity at the small end will be ~half what it is in free space, so the small end is actually probably the right size. It is still important to have a longer frustum to allow the stored energy to be attenuated faster, with fewer bounces.

I'm thinking the input port should be 1/4 wavelength from the large end. So resonance happens between the Feed and the large surface. The small end should be far away and designed to attenuate all the possible waves in the spectrum.

Todd

Shawyer criticizes the use of dielectric inserts inside the EM Drive because they lower the Q (because they have a tan delta > 0 and hence they introduce further losses).  However, notice that the use of a dielectric insert can also be criticized from the point of view of lowering the amount of geometrical attenuation.
Keeping the geometry of the truncated cone constant, inserting a dielectric has the effect of significantly lowering the natural frequency of the truncated cone.  Lowering the natural frequency has the effect of allowing mode shapes to occur that otherwise would have been cut-off without the dielectric.  The common practice of inserting the dielectric at the small end, next to the small end base (as done by NASA Eagleworks) has the effect of preventing the cut-off of mode shapes that would have been otherwise cut-off at the small end.

Notice that NASA Eagleworks reported thrust force is orders of magnitude smaller than the reported thrust force by the UK and Chinese researchers who don't use dielectric inserts.  The effect of the dielectric in lowering the natural frequency and preventing cut-off of modes can be more important than the effect of lowering the Q because the tan delta of these dielectric inserts is very small (for example, for the dielectric used by NASA Eagleworks, HDPE), the tan delta (responsible for lowering Q) is small: only 0.00031 @ 3 GHz  while  the relative permittivity (responsible for lowering the natural frequency) is not small: 2.26 @ 3 GHz .(http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm)

So, the geometrical attenuation theory theory of thrust also says that it is a bad idea to use dielectric inserts, because they prevent cut-off, they prevent evanescent waves that would otherwise occur.  Thus, the geometrical attenuation theory is in accord with experiments also in this respect, as the experiments show that the highest thrust forces have been produced without dielectric inserts.

I agree, dielectrics add a needless loss variable if you are not concerned with overall size. They "warp" space for em in a way. We only used them for cavity designs where miniaturization was required. They had higher losses and added mass (no free lunch). Always a balance for flight hardware...performance vs size, doc.

Offline Notsosureofit

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FYI

Thanks to @rfmwguy for the term "Entropic Force".  Much more descriptive than "false force" I've been using.

Still post-it-noting away on the entropy solution to see if it agrees.

The reasoning here is that if it can be explicitly shown to be the same "Entropic" force, then there is no problem with CoM.

« Last Edit: 06/12/2015 02:00 PM by Notsosureofit »

Offline Rodal

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FYI

Thanks to @rfmwguy for the term "Entropic Force".  Much more descriptive than "false force" I've been using.

Still post-it-noting away on the entropy solution to see if it agrees.

The reason here is that if it can be explicitly shown to be the same "Entropic" force, then there is no problem with CoM.
There is some possible confusion (as per a prior post discussing the concept of Entropy in Chemistry and Thermodynamics) with the concept of Entropy that I would like to clarify here.

The paper (Entropic Accelerating Universe: http://arxiv.org/pdf/1002.4278v3) discusses the concept of Entropy as information content, as defined by Shannon at MIT after WWII, that has had a huge impact in Science. 

Shannon defined the entropy Η of a discrete random variable X and probability mass function P(X) as the Expectation of the negative of the natural log of the probability mass function P:

H = E[- ln[P(X)]]

This definition uses Information Theory.  It can be extended to the continuous case by integration of a random variable with probability density function f(x).

Making a link between information entropy and thermodynamic entropy is not self evident, and has been the cause of arguments in the Physics and in the Information Theory community.

For example, Chemists are more interested in changes in entropy as a system spontaneously evolves away from its initial conditions, in accordance with the second law of thermodynamics, rather than an unchanging probability distribution. In classical thermodynamics the entropy is defined in terms of macroscopic measurements and makes no reference to any probability distribution, which is central to the definition of information entropy used in this paper.
« Last Edit: 06/12/2015 03:22 PM by Rodal »

Offline Notsosureofit

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Yes, there is considerable confusion centered about the inclusion of temperature vs information.

None the less, unlike the cylindrical cavity where the absolute entropy is maximized in an inertial frame, the tapered cavity distribution is maximized in an accelerated frame of reference.

Working from there.  Kantor not a big help.

Offline Rodal

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Yes, there is considerable confusion centered about the inclusion of temperature vs information.

None the less, unlike the cylindrical cavity where the absolute entropy is maximized in an inertial frame, the tapered cavity distribution is maximized in an accelerated frame of reference.

Working from there.  Kantor not a big help.

How do we know that the truncated cone entropy distribution is maximized in an accelerated frame or reference?

This has been the cause of much discussions in these threads, for example @frobnicat, @deltaMass and @wallofwolfstreet insisting that there is no preferred frame of reference, that the photons don't accelerate, and that everything should be based on frame-indifference.  They insist on applying frame-indifference to the cavity.

Furthermore, @deltaMass insists on using just simple Galilean frame-indifference as he maintains the velocity, and change of velocity of the cavity is much below the speed of light.  Given Shawyer's experiment on an air bearing showing a delta V of only 2 cm/s it is difficult to argue against the fact that the metal cavity itself should be governed by Newtonian mechanics.  So the issue is the photons and how to describe their momentum, and the gradient imposed by the geometrical gradient in the cavity.
« Last Edit: 06/12/2015 02:30 PM by Rodal »

Offline RotoSequence

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How do we know that the truncated cone entropy distribution is maximized in an accelerated frame or reference?

This has been the cause of much discussions in these threads, for example @frobnicat, @deltaMass and @wallofwolfstreet insisting that there is no preferred frame of reference, that the photons don't accelerate, and that everything should be based on frame-indifference.  They insist on applying frame-indifference to the cavity.

To be fair, doesn't the bulk of experimental evidence outside the realm of EM Drives support frame indifference?
« Last Edit: 06/12/2015 02:27 PM by RotoSequence »

Offline Rodal

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How do we know that the truncated cone entropy distribution is maximized in an accelerated frame or reference?

This has been the cause of much discussions in these threads, for example @frobnicat, @deltaMass and @wallofwolfstreet insisting that there is no preferred frame of reference, that the photons don't accelerate, and that everything should be based on frame-indifference.  They insist on applying frame-indifference to the cavity.

To be fair, doesn't the bulk of experimental evidence outside the realm of EM Drives support frame indifference?

No, you cannot apply frame-indifference to anisotropic materials, for example.  They have preferential embedded material coordinates.   One cannot apply frame-indifference to large strain deformations of anisotropic metals for example, or to anisotropic fluids.

Frame indifference in general only applies to a conceptual, idealized isotropic world.

A lot of the discussion in this thread treats materials very simplistically as if one could just use rigid body dynamics.  That may also be fine for the EM Drive.  I certainly support using rigid body dynamics and isotropy until it can be shown otherwise.  (*)

The only anisotropic theory I have seen so far is van Tiggelen's extraction of momentum from the QV through chiral anisotropy.

I am just pointing out that one cannot be a frame-indifferent absolutist in general as it prevents characterization and analysis of anisotropic fluids for example.

There is no absolutist frame-indifference principle in Nature.  However, applying Occam's razor, astronomical observations show an isotropic universe at large scales and we might as well use the simplest models unless required otherwise.

The experimental observation that rotating NASA's EM Drive by 180 degrees significantly changes the reported forces sounds more like an experimental artifact, so also the differences between prograde and retrograde in the the Baby EM Drive experiments, need to be assumed as artifacts until proven otherwise.

_________
(*) In the discussion with notsosureofit we are discussing, something else: the need for an accelerated frame of reference.
« Last Edit: 06/12/2015 02:48 PM by Rodal »

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