Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1803062 times)

Offline vulture4

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For the truncated spherical cone and indeed any closed surface Greg Egan demonstrates that there is no net force due to radiation pressure:
http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Cavity.html

Quote
maybe they just found a way to interact with neutrinos... instead of virtual particles...

Neutrinos do not have much mass. It would take a massive (sorry) flux of neutrinos to produce a detectable reaction force.
« Last Edit: 06/13/2015 08:58 PM by vulture4 »

Online WarpTech

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(*) Sorry, no, that's not what happens in the attenuation we are discussing.  The attenuation we are discussing is geometrical attenuation that does not result in heat losses, but rather change of phase.

Hmmm... isn't "attenuation" the opposite of "amplification" , consequently meaning a decrease in amplitude and the elongation of the frequency till in the end, it becomes zero?
A change of phase is just linear shift.

Although I understand that, when the wave hits the endplate, the effect of both situations means the wave no longer resonates between the plates , because frequency and distance have to match, I do not understand where the phase shift comes from....

I can understand that the waves change amplitude and frequency as they're dragged along the frustum side walls, because they loose some of their energy and consequently have to change in frequency/amplitude. At least that's how I understood (maybe wrongly?) Todd's idea.

I don't see why a wave would just shift it's phase, but keep amplitude and frequency the same?

I'm just trying to visualize what's happening and how a momentum transfer in a frustum could happen...

euh.. Do I have the wrong idea about this whole thing then...?

ah well, until we got some serious proof it actually works all theories mean nothing. Sad to see we got 2 DIY that have to postpone their builds, due to circumstances. All hopes are now on the EagleWorks setup.. that's, if they're ever allowed to report back to us in the future...  :-\

When the wave is reflected from the sidewall and not from the small end plate, the phase is advanced relative to waves reflected from the small end plate. That induces a relative phase shift, which causes interference.

What you said is perfectly true. The resonant wave loses energy on each bounce, and as it's amplitude "exponentially decays", the amount of momentum transferred on each bounce is less. This results in a NET thrust that is the difference between 2 exponentially decaying forces separated by a time delay or phase shift.

F1 ~ I2 * exp(-2t/T)
F2 ~ -I2 * exp(-2(t + dt)/T

The two are not equal, because the wave decays in the time longer time t + dt, before it can transfer its momentum to the other side.

Technically, microwaves are not even required to do this. It will work with any exponentially decaying pressures, that differ in rate (T1 =/= T2)or by a phase shift, t+dt.

I had worked out such a design many years ago. It can generate thrust, but not much. The trick is then to accelerate when charging and decelerate when discharging. Even Greg Egan's "proof" requires time-average of sin(wt) and cos(wt) result in 0-NET thrust. But if that time-average is NOT zero because the waves are decaying steadily throughout each cycle, then his equation will predict thrust, just as Yang's did.

Todd

Offline kml

For the truncated spherical cone and indeed any closed surface there is no net force due to radiation pressure:
http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Cavity.html

Quote
maybe they just found a way to interact with neutrinos... instead of virtual particles...

Neutrinos do not have much mass. It would take a massive (sorry) flux of neutrinos to produce a detectable reaction force.

The Solar neutrino flux seems pretty massive at 7E10/cm2 with 400keV typical energy.   That's almost an electorn's mass worth of energy each.  How much would it take to explain the forces observed?
« Last Edit: 06/13/2015 08:38 PM by kml »

Online WarpTech

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For the truncated spherical cone and indeed any closed surface there is no net force due to radiation pressure:
http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Cavity.html

Quote
maybe they just found a way to interact with neutrinos... instead of virtual particles...

Neutrinos do not have much mass. It would take a massive (sorry) flux of neutrinos to produce a detectable reaction force.

Greg Egan also said; "If the cavity contains a standing wave, then the fields will have a harmonic time dependence of the form sin(ωt) or cos(ωt), and over one complete cycle of the mode, a period of 2π/ω, all the fields will return to their origin values. So at each point in the interior of the cavity, we will have:

∫cycle (∂Si / ∂t) dt = Si(t0+2π/ω) – Si(t0) = 0
So, averaged over a complete cycle in the same way, each component of the net force on the wall will sum to zero."

When the sin(wt) or cos(wt) functions are multiplied by an exponential decay factor, their time average is not zero. So when Q is increasing or Q is decreasing, there should be thrust. If Q is steady, there will be no thrust.

Todd



Online Rodal

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For the truncated spherical cone and indeed any closed surface there is no net force due to radiation pressure:
http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Cavity.html

Quote
maybe they just found a way to interact with neutrinos... instead of virtual particles...

Neutrinos do not have much mass. It would take a massive (sorry) flux of neutrinos to produce a detectable reaction force.

Greg Egan also said; "If the cavity contains a standing wave, then the fields will have a harmonic time dependence of the form sin(ωt) or cos(ωt), and over one complete cycle of the mode, a period of 2π/ω, all the fields will return to their origin values. So at each point in the interior of the cavity, we will have:

∫cycle (∂Si / ∂t) dt = Si(t0+2π/ω) – Si(t0) = 0
So, averaged over a complete cycle in the same way, each component of the net force on the wall will sum to zero."

When the sin(wt) or cos(wt) functions are multiplied by an exponential decay factor, their time average is not zero. So when Q is increasing or Q is decreasing, there should be thrust. If Q is steady, there will be no thrust.

Todd

I agree that there will be a non-zero Poynting vector in the gedankenmodell you propose above.  I don't follow that a non-zero Poynting vector must mean acceleration of the center of mass of the whole drive system, which is what is at stake.
Even when the Poynting vector average is zero, it fluctuates harmonically, yet that harmonic fluctuation around zero does not translate into a harmonic variation of position of the center of mass.  Moreover, for a cavity with gradient losses, the time-average of the Poynting vector will be non-zero, yet the center of mass will not accelerate as the flux of the Poynting vector in that case is related to the gradient energy losses.

The problem here is that the Poynting vector is internal to the cavity and even if there is a non-zero time-averaged Poynting vector that does not necessarily mean that the center of mass will accelerate.  That remains to be proven, as in all the cases we know of in Nature nothing accelerates the center of mass if the forces or energy are applied internally.  All the cases we know of in propulsion (including a photon rocket) involve either a loss of mass or energy to the exterior or the action of external fields on the object whose center of mass accelerates.

If the evanescent waves leak to the outside, that may produce acceleration of the center of mass.
« Last Edit: 06/13/2015 09:05 PM by Rodal »

Online Rodal

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I found this keyboard for Math Symbols:

http://math.typeit.org/

It also has Greek letters, everything  ;)


I'm putting this link in the first page of this thread, for easy reference.
« Last Edit: 06/13/2015 10:20 PM by Rodal »

Offline jmossman

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Second test of the baby EM drive and problems with oscillation. I think they are looking for suggestions to resolve this?

...

More info.

https://hackaday.io/project/5596-em-drive/log/19417-torsion-test-no-data-due-to-oscillations
I find this quite bizarre. The motion seems to have little to do with the natural frequency or its friction, and little to do with whether the drive is on or off. It seems instead to be showing a chaotic time series of air circulation flows local to the apparatus.

A vacuum chamber is called for!
Probably due to the heat from the light fixture creating  natural thermal convection currents.  The power from this Baby EM Drive is so small that its effect on the environment is overwhelmed by the light fixture.  It is common in Germany to use this kind of light (particularly annoying in hotel rooms ). 

Short of using a vacuum chamber they should explore lighting that produces a minimum of  heat.

Here are a couple of other suggestions that come to mind:

1) move the light source (and any other potential heat sources) above apparatus;  hot air rises, so placing light nearer to the ceiling will help with any thermal currents from the lighting.  Shadows in the video suggest the lighting source was below the apparatus (which would likely maximum thermal currents from lighting)
2) to further reduce thermal effects from lighting, I'd recommend turning the light on once per second to enable the time lapse video  (that should reduce heating by a factor of ~60)
3) using a couple of crude LED's for lighting that provide just enough lighting to determine if oscillations are reduced
4) measuring temperature of different areas of the room might help identify other possible sources of thermal effects;  (i.e. what type of floor is in the room?, etc);  hanging blankets/sheets on the walls and the door might help, as might placing a blanket on the floor
5) enclosing the lower portion of the pendulum in a "jar" or box;  maybe use a large cardboard box with the top open?
6) vibrations might be contributing to the oscillations;  choosing a different linkage between string and ceiling might help.  A true "spring" might not help;  perhaps a large block of rubber would be better to provide some isolation?  choice of string material might also unintentional amplify the oscillations/vibrations

Offline SeeShells

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If the evanescent waves leak to the outside, that may produce acceleration of the center of mass.

This is why I'm somewhat quiet. It seems that evanescent waves might be the key to this thing and I'm digging.

 It's interesting a evanescent wave is a standing wave, and could be considered a static stress-energy pressure gradient, only if static and not acting like the off tuned harmonics of a frustum. Evanescent waves are found in near-field regions out to 1/3 wavelength of any RF antenna.

So what happens when the Frustum T-mode harmonics collapse creating in the small end decaying evanescent waves?

 http://en.wikipedia.org/wiki/Evanescent_wave

Then this crops up
http://iopscience.iop.org/0295-5075/76/2/189;jsessionid=B5C4696705DCDDFC9F814A979EDDF64E.c3
EPL (Europhysics Letters) Volume 76 Number 2
A. A. Stahlhofen and G. Nimtz 2006 Europhys. Lett. 76 189 doi:10.1209/epl/i2006-10271-9
Former QED-based studies of evanescent modes identified these with virtual photons. Recent experimental studies confirmed the resulting predictions about non-locality, non-observability, violation of the Einstein relation and the existence of a commutator of field operators between two space-like separated points. Relativistic causality thus is violated by the near-field phenomenon evanescent modes while primitive causality is untouched.

Back to digging...

Shell

Offline vulture4

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The two are not equal, because the wave decays in the time longer time t + dt, before it can transfer its momentum to the other side.
In the most extreme case, where the photon is completely absorbed, all its momentum is transferred to the endplate on the first contact. But even in this case, the momentum applied to the endplate will be equal and opposite to the momentum applied to the power source when the photon was generated, so there would be no net thrust.

The most efficient way to achieve thrust from photon momentum is to remove the resonator entirely and simply emit the photons away from the spacecraft in a coherent beam.
« Last Edit: 06/13/2015 09:54 PM by vulture4 »

Offline deltaMass

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That's all well and good, except that thrusts are being recorded by different teams at a level 100x - 1000x bigger than a photon rocket could provide using the same power. I think that's what keeps us here:
a) there should be no thrust, but apparently there is
b) it's much bigger than a photon rocket's, apparently

Offline rfmwguy

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Humble suggestion to Aachen team. Focus first on vertical displacement. Simple 4:1 moment arm fulcrum (teeter totter). Longer moment arms the better. Small frustum plate end facing down. Look for movement against gravity and thermal ballooning (lift). Large open room. All air and lights off, better yet, no electricity. Activate outside of room. Shoot a video  :)

Offline snoozdoc

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Quote from: Rodal

... No virtual particles.  No 5 D Branes.  No Woodward instant-action from afar hypothesis.  No neutrinos.  No breaking of CoM. No dark energy. No dark mass.  No fifth force.

What?  You mean I have been sweating over Maxwell's Equations, General Relativity, and all my tensor calculus books for nothing?  You really mean I won't be able to discover new physics with my $300 of parts that I have strewn (to my wife's disgust) across the kitchen table?  I had really hoped I wouldn't need a $20 billion Large (or preferably smaller) Hadron Collider (the one in Geneva won't fit in my back yard  :( )and that my hack of a kitchen appliance would net me the next Nobel prize!

Oh well ... maybe I can get a job at the local community college teaching all the math I have so recently learned.   ;)
« Last Edit: 06/13/2015 10:16 PM by snoozdoc »

Offline aero

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But the issue we are struggling with is that if there is no mass or no energy being emitted outside the device, how can anything done inside it accelerate its center of mass?  Doing so would run counter to the law of conservation of momentum, one of our most cherished laws in Physics.

I can move a spacecraft by hitting it with tennis balls from the outside.  Or by using a magnet on it from the outside.   I cannot move the center of mass of a spacecraft by asymmetrically using a magnet on the inside or asymmetrically hitting its internal walls with tennis balls.  One needs to either emit mass or energy to the outside to have propulsion.

this is where you need Dr White's explanation right? In that case, the virtual particles are everywhere and I guess they move through the device too. Like if it was water and the device a propeller. Somehow it would be interacting with particles that go through the matter of the device?

maybe they just found a way to interact with neutrinos... instead of virtual particles...


depending of the case, IF the measurements are real, EVEN if this can never be used for a space drive, it would still be very interesting from a pure scientific standpoint depending on what is causing the effect.

@aero in his MEEP FDTD computations gets the evanescent waves to emanate to the outside and outperform a photon rocket.  No virtual particles.  No 5 D Branes.  No Woodward instant-action from afar hypothesis.  No neutrinos.  No breaking of CoM. No dark energy. No dark mass.  No fifth force.

Just not nearly enough force. Better than a Photon rocket though, that's true.
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Offline deltaMass

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...

Just not nearly enough force. Better than a Photon rocket though, that's true.
Well, it is only 2-D at the moment, and we don't fully understand why the force is greater than a photon rocket, so perhaps if we understand it better, we could construct a better model (3-D ?), perhaps with better constitutive properties (imaginary susceptibility? coupling coefficients? nonlinear coefficients?) that would show even greater response.
This is known as "The Edison Phase"

Offline flux_capacitor

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It is frustrating that they have not yet disclosed the internal dimensions of the Baby EM Drive, (last time I checked), although people have asked them in their blog.  NASA (Paul March) and Iulian Berca promptly disclosed their geometry, etc.  Need the internal dimensions to find out what are the nearby natural frequencies and mode shapes, to know what mode shapes are being excited, and their participation.

I asked them again today in the comments on their web site, and they finally revealed the cavity parameters:

Height 24.37mm

Diameter 1: 29.64mm

Diameter 2: 16.12mm


+ Small dameter top edge to centre of injector: 5.60mm

Offline aero

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...

Just not nearly enough force. Better than a Photon rocket though, that's true.
Well, it is only 2-D at the moment, and we don't fully understand why the force is greater than a photon rocket, so perhaps if we understand it better, we could construct a better model (3-D ?), perhaps with better constitutive properties (imaginary susceptibility? coupling coefficients? nonlinear coefficients?) that would show even greater response.  Then, again, the force may really be less than a photon rocket in the final analysis.

No, the last image I posted was from a 3-D run and for that 3-D Brady cavity run, Meep did calculate Force/Power about 5/c, or 5 times greater than a Photon rocket. (that was the image with the dielectric through the sides.) Of course the image is in 2-D but it was of an axiel slice through the center of the 3D cavity.

And here are some more cavities. All modeled in 3D, with the image showing the central slice of the cavities. I used Dr. Rodal's posted dimensions and the cavities are Brady, Shawyer Demo and Yang. They do certainly look different.
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Offline TheTraveller

Baby EmDrive dimensions now released.

Height         24.37mm
diameter1   29.64mm
diameter2   16.12mm
small dameter top edge to centre of injector   5.60mm.

To confirm what is the excitation frequency and input power? Can then work out the excitation mode and expected thrust.

The attached suggests ,that at 24GHz, it is not excited in TE01x as none of the possible end plate spacing match the actual
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Offline ThinkerX

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So...at this point, we have both MEEP modeling AND a number of shaky (sometimes literally) experiments indicating these devices somehow violate CoE and CoM.  Or at least appear to do so.  To radically different extents.  I can't help but wonder if we aren't somehow missing something very basic that would permit this results.

Offline flux_capacitor

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Wait a minute, I missed something… and I can't find it searching the thread. Where did we obtain Yang's frustum dimensions from? A few pages ago we complained she didn't published them.
« Last Edit: 06/13/2015 11:00 PM by flux_capacitor »

Offline ElizabethGreene

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... you seem to violate CoM but don't let that be a brick wall just because someone tells you it does ...

As it relates to the EmDrive I've put Conservation of momentum on a shelf for later examination. Candidly, I have quietly wondered if it might have a loophole or two for someone who was clever enough to find them. I seriously doubt I'm that clever.

Playing in that vein, I have a related thought experiment.

Imagine the space shuttle in orbit. The cargo bay doors are open. An astronaut equipped with an MMU fires his gas jets, accelerates from space outside the shuttle, and smacks into the back wall of the cargo bay. The astronaut transfers his momentum to the shuttle, and recieves a concussion for his trouble.

The momentum flow is Gas from the Jets go left, shuttle goes right. CoM is satisfied.

Two asprin later the astronaut+mmu is in the cargo bay with the bay doors closed and sealed. The bay is a hard vacuum. The astronaut reluctantly fires the MMU jets and smacks into the back wall again. A small amount of momentum is transferred to the shuttle, and the astronaut rethinks his "glamorous" career with Nasa.

For conservation of momentum to be satisfied the force of the gas striking the inside of the cargo bay must exactly balance the force of the shuttle to the right for there to be no net momentum change. This exact balance of gas pressure does not match my understanding of gas behavior at all. I expect instead to see the all kinds of non-Newtonian action in the gas as it expands randomly into the bay in all directions. Turbulence and brownian motion will rob energy out of the gas literally left and right.

I also don't see what would prevent the astronaut from pulling out a vacuum pump and compressing it back into the MMU's cylinders for another shot.

I have an idea about how to test this here on earth, but the EmDrive work seems much more urgent and promising.

Could someone point out the obvious flaw in my thought experiment?  Despite having it drawn on my bathroom mirror since October, I've still not managed to see it.

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