I now suspect there are two discrete phenomenon at work inside the emDrive.The first effect is very close to that described in Mr. Sawyer's theory paper. By ray tracing the paths of photons in a continuously tapered asymmetric waveguide you can see a small force is generated.The second effect is that discovered by the Nasa team, that a dielectric placed in an otherwise non-thrusting cavity will cause it to generate a force. I no longer believe this is due to the Sawyer effect. I believe this second effect is due to a very non-intuitive behavior of radiation pressure.My physics textbook (Serway) says that Radiation pressure P is equal to the Plank constant times the frequency of light divided by C. (1)The speed of light in a medium is equal to the speed of light in a vacuum divided by the index of refraction (n) (2)Substituting 2 into 1 yields:P= hf/(c/n)or, to make it more obvious...(3) P = hfn/c Radiation Pressure is increased by the index of refraction of the material surrounding the bounce.This effect has been confirmed experimentally (Jones, 1978) Radiation pressure is greater if the target mirror is immersed in a material with a higher index of refraction.(citation)The Measurement of Optical Radiation Pressure in Dispersive MediaR. V. Jones and B. LeslieProceedings of the Royal Society of London. Series A, Mathematical and Physical SciencesVol. 360, No. 1702 (Apr. 4, 1978) , pp. 347-363Published by: The Royal Societyhttp://www.jstor.org/stable/79586 (/citation)Serway also says that radiation pressure P is valid for emission or absorption, but is actually 2P for reflection. The cause for this is obvious. A reflection is actually an absorption followed by an emission. (4)The combined effect of (3) and (4) is, I suspect, the cause for the Nasa/dielectric effect.Consider a one-dimensional system where a photon is trapped in the vacuum space between two loss-less front-surface mirrors. it will bounce back and forth practically forever, generating no net thrust.At the left mirror impact the mirror receives a left push of -1 on absorption, and a left push of -1 on emission. The acceleration on the left mirror is -2. When the photons strike the right mirror, +1 for absorption, +1 for emission. The net thrust is zero.Now consider the case where the left mirror is immersed in another lossy material with the index of refraction of 1.5.ActionThrust from ActionNet thrust(start)0Transition v-dAbsorption at vacuum-fluid boundary.-1-1Transition v-dEmission at vac/fluid boundary.1.50.5Dielectric ReflectionAbsorption at left mirror-1.5-1Dielectric ReflectionEmission at left mirror.-1.5-2.5Transition d-vAbsorption at the fluid-vacuum boundary1.5-1Transition d-vEmission at the fluid-vacuum boundary-1-2Vacuum ReflectionAbsorption at the right Mirror1-1Vacuum ReflectionEmission at the right Mirror10(return to start condition)The radiation pressure is greater during the phase where the photons are in the lossy dielectric. Loss of one of these these photons during that phase results in a asymmetric force. This asymmetry is, I propose, the cause of the Nasa effect. The index of refraction of PTFE at microwave frequencies is complex, so this absorption and loss can occur.I propose to confirm the second effect experimentally by creating a traditional round symmetrical microwave resonator and operating it with and without a PTFE endplate inside the existing metal plate. If I am correct, this circular-non-tapered resonator will generate thrust when the PTFE endplate is in place.Do I fundamentally misunderstand any concepts here?Elizabeth Greene[email protected]Edited: copy and pasted the wrong theory, added table.
Quote from: deltaMass on 06/13/2015 08:25 amRe. the Baby EmDrive data: if friction be modelled going as w2, then in the absence of a driving forcew(t) -> e-tUnfortunately, the shape of that does not fit the shape of the undriven data, which is roughly a straight line of negative slope.Therefore the friction model isn't right.Neither does friction going as w fit: it yieldsw(t) -> 1/(1 + t)The friction model which fits the data is constant frictional force, independent of the rotational velocity.I've already analysed that and shown that the driving force cannot be determined without more data about the experiment. Specifically we need to know eithera) the frictional torque, orb) the moment of inertia of the cavity platform (I) AND the lever arm (R) of the cavityIn any case, I am abandoning the w2 friction model.Too bad it's a dead end, but I'm not surprised. Like I speculated on an earlier post, after the rig has been spinning for a time, the air in that bell jar is probably in some kind of "steady state" vortex losing energy through boundary layer interactions with the jar walls. Maybe an analogy is a ducted fan.
Re. the Baby EmDrive data: if friction be modelled going as w2, then in the absence of a driving forcew(t) -> e-tUnfortunately, the shape of that does not fit the shape of the undriven data, which is roughly a straight line of negative slope.Therefore the friction model isn't right.Neither does friction going as w fit: it yieldsw(t) -> 1/(1 + t)The friction model which fits the data is constant frictional force, independent of the rotational velocity.I've already analysed that and shown that the driving force cannot be determined without more data about the experiment. Specifically we need to know eithera) the frictional torque, orb) the moment of inertia of the cavity platform (I) AND the lever arm (R) of the cavityIn any case, I am abandoning the w2 friction model.
Rodal, thank you for the kind reply. I am giddy to see the Aquino paper. It means I'm on the right path. That the paper is only 8 months old is even more encouraging. I simply need to run faster and catch up.
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.
...But what happens if that ball suddenly changes from an elastic object into a non elastic object, like clay?when all the kinetic energy is absorbed and all of its momentum is transferred to one side?Isn't that what happens when an electromagnetic wave is attenuated?...
Do not forget that the tennis ball is actually coming from outside the space station, just as the electromagnetic waves are pumped from the outside into the frustum. (as Todd previously said).Do not be fooled by the illusion that it ricochets inside the space station.The starting energy of the ball has not been created inside the space station, hence seen from within the space station, there was no action(ball throwing) prior to the reaction (ball moving). The ball entered the space station at full kinetic energy level through a small portal, never to get out again.It also means, as has been identified (probably correctly) that the lower your Q and the faster you can convert you tennis ball into a clay ball, the bigger the remaining momentum will be...The error in the analogy is that you describe the tennis ball to have started its action within the space station, were in reality, it didn't.
(*) 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.
Quote from: aero on 06/13/2015 02:30 amAnd if you have problems operating meep, ask and I'll try to answer .Thanks. I ran a couple examples & looked up your Bradycone.txt file from your recent 5/31 post. Any reason you're using the Harminv rather than the frequency domain solver? It would seem to be a better choice for speed, if all that's desired is the steady-state mode pattern.
And if you have problems operating meep, ask and I'll try to answer .
Quote from: WarpTech on 06/13/2015 01:50 amMy interpretation of kr on these diagrams is, 2pi x number of wavelengths. So these diagrams show 5, 10, 15 wavelengths. You can understand that a frustum that is 1/2 wavelength long, does not have enough length to absorb much energy, and it should be several wavelengths long I think. It makes a good resonator, but a very poor thruster.Toddr is the spherical radial distance from the apex of the cone as defined here:Don't forget the factor of 2 Pi in the definition of k k r = 2 Pi r /wavelengthin the horizontal axis is a dimensionless expression of spherical radial distance, so that it can be applied for any size fustrum.For example, k r = 5 means 2 Pi r /wavelength = 5so that it means a spherical radial distance of r = 5 wavelength / ( 2 Pi ) = 0.80 wavelength so:kr 5 10 15r (wavelengths) 0.80 1.59 2.39 You have to get very close to the apex of the cone to get geometrical attenuation (unless θ is small)
My interpretation of kr on these diagrams is, 2pi x number of wavelengths. So these diagrams show 5, 10, 15 wavelengths. You can understand that a frustum that is 1/2 wavelength long, does not have enough length to absorb much energy, and it should be several wavelengths long I think. It makes a good resonator, but a very poor thruster.Todd
Quote from: Rodal on 06/13/2015 12:52 pmI 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.A risky step I'm taking here, but I do not agree with the magnet or tennis ball analogy...I know moment is depending on mass and velocity. When masses are not equal, velocity has to be proportional at the inverse ratio of the mass.When the ball hits the interior wall, it looses a part of its momentum due to speed (energy) loss. Energy loss comes from the elastic deformation of both wall (very little) and the tennis ball. Some energy will also be lost due to air resistance when traveling back to the other side, where another impact will generate a slightly smaller , but opposite momentum, after which the ball travels back, etc...The amount of times it bounces back and forth, is basically an indirect representation our Q value. Normally, as we all learned, it should equalize out in the end, giving a nul result...But what happens if that ball suddenly changes from an elastic object into a non elastic object, like clay?when all the kinetic energy is absorbed and all of its momentum is transferred to one side?Isn't that what happens when an electromagnetic wave is attenuated?Do not forget that the tennis ball is actually coming from outside the space station, just as the electromagnetic waves are pumped from the outside into the frustum. (as Todd previously said).Do not be fooled by the illusion that it ricochets inside the space station.The starting energy of the ball has not been created inside the space station, hence seen from within the space station, there was no action(ball throwing) prior to the reaction (ball moving). The ball entered the space station at full kinetic energy level through a small portal, never to get out again.It also means, as has been identified (probably correctly) that the lower your Q and the faster you can convert you tennis ball into a clay ball, the bigger the remaining momentum will be...The error in the analogy is that you describe the tennis ball to have started its action within the space station, were in reality, it didn't.now.. i'll throw myself for the lions...
Second test of the baby EM drive and problems with oscillation. I think they are looking for suggestions to resolve this?https://www.youtube.com/watch?v=Y8uyIgzdzS4&feature=youtu.beMore info.https://hackaday.io/project/5596-em-drive/log/19417-torsion-test-no-data-due-to-oscillations
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.