Quote from: deltaMass on 05/08/2015 11:21 pmInteresting that breaking CofM means that translational invariance dies, and breaking Einstein's SR core principle means that inertial frame invariance dies. Interesting because you may notice that one is essentially the time derivative of the other. And further that breaking CofE means that time invariance dies.Perhaps that's a deep observation, but I'm not smart enough to know what it means. All I know is that, for a propellantless propulsor, we are forced to choose between killing off one or the other. If we got creative we could kill off both, maybe!I'm sure my physics friends down the pub here in Cupertino would simply shrug and say that, since momentum appears not be conserved in the first place, there's ample room for odd statements to be correspondingly made about energy conservation (and I have made them here on this forum).Perhaps there's an exit route out of this bind via playing off conservation of momentum against conservation of energy. Just a wild thought.The conundrum may be resolved in two words:Noether's theorem. In defining how symmetries are enforced, by extension it reveals where they are not.Specifically, time-dependent (ie. temporally variant) interactions are, by definition, non-conservative. Although we more commonly encounter such asymmetries in dissipative systems, there are, within electromagnetism at least, non-dissipative non-conservative systems.And before anyone protests, this isn't half as controversial as it may seem - any electrodynamics textbook will include a section on non-conservative, temporally variant EM interactions. By definition, CoE does not and cannot be applied to them. See Rutherford's first paper ca 1886 on magnetic entropy viscosity (Sv)... in such a delayed response, the time-dependent rise of B to a given H means input and output FxD integrals can be non-equitable, if their mechanical displacements are varied to sub- and super-Sv speeds respectively.Example: take two permanent magnets, at least one of which has appreciable Sv. Allow them to attract together before B can reach Bmax, obtaining our output FxD integral, then let B peak before separating them against this now-higher force, requiring an appropriately-greater input work integral due to the higher force over the same distance.... we've input more work than the interaction has output! Where'd the energy go? Not dissipated to heat (the magnetocaloric profiles are almost identical, and incidental since net change in B up vs down is equal for both integrals - ie. Sv isn't a direct heating mechanism). Rather, the answer's right there in the setup - the missing energy was spent entirely on displacement against a higher magnetic force. Or, looking at it from the alternative perspective, squandered away by not harvesting it in the first place during the initial delayed-response output displacement.We can repeat this interaction forever, dumping the same amount of mechanical energy into the vacuum (via the virtual photon exchanges mediating the force) each cycle. Calorimetry will show a continuing loss...
Interesting that breaking CofM means that translational invariance dies, and breaking Einstein's SR core principle means that inertial frame invariance dies. Interesting because you may notice that one is essentially the time derivative of the other. And further that breaking CofE means that time invariance dies.Perhaps that's a deep observation, but I'm not smart enough to know what it means. All I know is that, for a propellantless propulsor, we are forced to choose between killing off one or the other. If we got creative we could kill off both, maybe!I'm sure my physics friends down the pub here in Cupertino would simply shrug and say that, since momentum appears not be conserved in the first place, there's ample room for odd statements to be correspondingly made about energy conservation (and I have made them here on this forum).Perhaps there's an exit route out of this bind via playing off conservation of momentum against conservation of energy. Just a wild thought.
Quote from: maciejzi on 05/08/2015 11:45 pmQuote from: frobnicat on 05/08/2015 11:36 pmBecause Peltier effect can't quite reach cryogenic temperatures, for some thermodynamic reason I forgot. Maybe it changed with recent progress on the subject ? Please inquire : what are the limits of low temp. with Peltier effect, now and tomorrow ? Isn't the Peltier effect still quite low in efficiency ?The Peltier limits are below 100K, which is enough for high-temparature superconductors. The efficiency in such temperature is low, but probably that could be economically viable because of much smaller MW input power and smaller superconducting engine size. That said, I must sadly admit, that this engine won't probably move in free space. It may move on air cushion though, as in the experiments conducted so far on Earth.Anyway, if so, then it is at least good for new generation of rotorless helicopters, here on Earth.Stirling coolers are used where cryogenic temperatures are required. They are more efficient than Peltier devices. I have used very compact Stirling cooled IR detectors. Several companies make them, It takes about 1 Min. to reduce the temperature of the detector to 95 K, using 1 Watt. However the thermal mass is very tiny. NASA has been investigating Stirling coolers for liquifying rocket fuels (H2, O2) in space and for space telescope applications.
Quote from: frobnicat on 05/08/2015 11:36 pmBecause Peltier effect can't quite reach cryogenic temperatures, for some thermodynamic reason I forgot. Maybe it changed with recent progress on the subject ? Please inquire : what are the limits of low temp. with Peltier effect, now and tomorrow ? Isn't the Peltier effect still quite low in efficiency ?The Peltier limits are below 100K, which is enough for high-temparature superconductors. The efficiency in such temperature is low, but probably that could be economically viable because of much smaller MW input power and smaller superconducting engine size. That said, I must sadly admit, that this engine won't probably move in free space. It may move on air cushion though, as in the experiments conducted so far on Earth.Anyway, if so, then it is at least good for new generation of rotorless helicopters, here on Earth.
Because Peltier effect can't quite reach cryogenic temperatures, for some thermodynamic reason I forgot. Maybe it changed with recent progress on the subject ? Please inquire : what are the limits of low temp. with Peltier effect, now and tomorrow ? Isn't the Peltier effect still quite low in efficiency ?
Quote from: SeeShells on 05/09/2015 12:00 amI was wondering in your testing did you use a smoke stick also called a smoke pencil to check for air flows around the EM Drive in ambient air conditions?That is a very good idea. I don't think it has been suggested before. There was some discussion on convective air flow and the possiblity it may explain the anomalous force measured by EW early in thread 1. However interest in that explanation has dissipated and Dr. Rodal's analysis of thermal-mechanical effects as a conventional explanation has replaced it.
I was wondering in your testing did you use a smoke stick also called a smoke pencil to check for air flows around the EM Drive in ambient air conditions?
Quote from: zen-in on 05/09/2015 05:40 amQuote from: SeeShells on 05/09/2015 12:00 amI was wondering in your testing did you use a smoke stick also called a smoke pencil to check for air flows around the EM Drive in ambient air conditions?That is a very good idea. I don't think it has been suggested before. There was some discussion on convective air flow and the possiblity it may explain the anomalous force measured by EW early in thread 1. However interest in that explanation has dissipated and Dr. Rodal's analysis of thermal-mechanical effects as a conventional explanation has replaced it.Thank you and I did review of the very nice workup by Dr. Rodal after he pointed it out. It's not only heat convection I was thinking of, but any aberrations in air movement other than the expected thermal currents from the EM device.
Those who cannot remember the past are condemned to repeat it.
In the first step, we will replicate the original EM-Drive thruster. It will be driven by a high power RF source (magnetron) which is easily available. The second step will be a miniaturization by using higher frequencies. To achieve this, a numerical simulation of the waves inside the cone frustum must be made to obtain the optimal geometry for the cone. A high frequency generator in the 20-30 GHz range has to be built with the power of a few watts
Quote from: SeeShells on 05/09/2015 11:40 amQuote from: zen-in on 05/09/2015 05:40 amQuote from: SeeShells on 05/09/2015 12:00 amI was wondering in your testing did you use a smoke stick also called a smoke pencil to check for air flows around the EM Drive in ambient air conditions?That is a very good idea. I don't think it has been suggested before. There was some discussion on convective air flow and the possiblity it may explain the anomalous force measured by EW early in thread 1. However interest in that explanation has dissipated and Dr. Rodal's analysis of thermal-mechanical effects as a conventional explanation has replaced it.Thank you and I did review of the very nice workup by Dr. Rodal after he pointed it out. It's not only heat convection I was thinking of, but any aberrations in air movement other than the expected thermal currents from the EM device.Quote from: Jorge Ruiz de Santayana "George Santayana"Those who cannot remember the past are condemned to repeat it.1873 Maxwell derives equations showing that radiation will give rise to stresses on a surface due to the electromagnetic energy density (Maxwells' stress tensor). 1876 Bartoli attempts to measure the radiation pressure on a reflecting surface experimentally but he is unable to overcome disturbing effects due to the heating of the reflecting surface which gives rise to convection currents of air and to the radiometer effect ( https://en.wikipedia.org/wiki/Crookes_radiometer#Explanations_for_the_force_on_the_vanes ), which are collectively described by Bartoli and other scientists of the period, as "gas action." 1900 Lebedew, using light waves is the first person in history to succeed in eliminating these unwanted artifact effects by performing the experiments in a partial vacuum. He used a torsion balance and a highly reflecting mirror in his measurements.1902 Nichols and Hull made a thorough investigation of the unwanted artifact effects collectively called "gas action" and accurately establish the accuracy of Maxwell's predicted stress tensor. Nichols and Hull also performed experiments in a partial vacuum using a torsion balance and a highly reflecting mirror in their measurements.1949 Carrara and Lombardini qualitatively demonstrate the existence of radiation pressure at microwave frequencies to the correct order of magnitude, but no quantitative results are obtained. They employ a free wave method, which involves a very difficult refraction problem due to air, which precludes a quantitative assessment.1950 Cullen is the first person to accurately measure radiation pressure at microwave frequencies. Cullen uses power ranging from 10 to 50 watts in his microwave pressure measurements, at a wavelength of 10 cm, measuring 6.77 microNewtons/kW. Cullen used a torsion balance and a highly reflecting mirror in his measurements. Cullen performed his experiments in ambient air conditions. It was impossible to obtain a stable baseline, even on a relatively short-term basis of a minute's duration. This continual drifting of the baseline was found to be due to air convection currents set up by small and changing temperature gradients within the microwave waveguides. The remedy was to reduce the air resistance of the reflecting end plate so that the convection currents would have no appreciable effect. The reflecting end plate was replaced by a system of concentric wire rings (shown on Fig. 12 of Cullen's paper). The rings acted as an almost perfect reflector of the electromagnetic waves but at the same time had a small effective cross-section to air currents. NASA, Shawyer, Yang, and other EM Drive researchers would be well advised to experiment with replacing the end plates of the EM Drive with this system of concentric rings, in order to address the problem of air convection currents that has plagued radiation pressure experiments in ambient conditions ever since Maxwell 140 years ago. Even in a partial vacuum, if one uses for example bilayer plates of copper/glass-fiber-reinforced epoxy with the reinforced polymer on the external surface, there is the possibility of outgassing in a vacuum producing a false positive. The use of a mesh precludes this problem both in ambient air conditions and in a vacuum.Attachment: ABSOLUTE POWER MEASUREMENT AT MICROWAVE FREQUENCIESBy A. L. CULLEN, Ph.D., B.Sc.(Eng.), Associate Member.(published February, 1952.)http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=828862
....Dr. Rodal,How much of effect would the use of a ring (or mesh) have on ohmic losses in the endplate for some of the excited modes tested at EW? Any hunches for the effect on the cavity Q? (i.e. aren't the losses going to be larger for the ring/mesh versus a solid sheet of copper?)For in-air testing, the use of a ring/mesh makes perfect sense. I'm just curious as to the predicted effect on Q (perhaps neglible?). Engineering is almost always a series of tradeoffs; minimizing a known noise source during delicate force measurements would seem like a much more important design parameter than maximizing Q at this stage.Thanks,James
Quote from: jmossman on 05/09/2015 05:33 pm....Dr. Rodal,How much of effect would the use of a ring (or mesh) have on ohmic losses in the endplate for some of the excited modes tested at EW? Any hunches for the effect on the cavity Q? (i.e. aren't the losses going to be larger for the ring/mesh versus a solid sheet of copper?)For in-air testing, the use of a ring/mesh makes perfect sense. I'm just curious as to the predicted effect on Q (perhaps neglible?). Engineering is almost always a series of tradeoffs; minimizing a known noise source during delicate force measurements would seem like a much more important design parameter than maximizing Q at this stage.Thanks,JamesFair point. A detailed discussion of the effect of the ring mesh is not trivial. I refer you to Cullen's discussion of the effect on the pressure measurement (not taking into account Q, because Cullen tested an open waveguide) in Cullen's paper attached in my post above. The effect of a ring mesh has been further understood during the past 65 years, thanks to great advances on numerical calculations. Given the fact that the highest measured thrust forces, and the highest measured thrust force/InputPower were obtained with the lowest Q reported (Q~1500 see my notes concerning this) by Prof. Yang in China, while high Q force measurements at NASA Eagleworks have resulted in much lower forces and force/InputPower, a proportional relationship between force and Q remains to be experimentally corroborated (it is actually negated by the Chinese experiments). Furthermore, the theoretical considerations advanced by Todd in these pages put more emphasis on the attenuation (which may be supported by NASA Eagleworks findings that they only measured thrust forces with an insert polymer dielectric and no forces without it). Finally, it is not clear that the portion of the Q due to reflection of the low frequencies (larger wavelength) of the resonant microwave spectrum would be impaired by the mesh. My microwave oven has a conductive metal mesh on the inside of the transparent glass, so that the microwaves are reflected, to prevent microwaves from escaping the microwave.BOTTOM LINE: I would suggest for experimenters to try 4 different kinds of ends:1) A solid reflecting end (copper or aluminum)2) A ring-wired mesh as used by Cullen3) A transparent glass (transparent to microwaves)4) An open end And compare the results. Such tests would be very valuable both for scientific and engineering purposes to understand what is being measured.
...1) A solid reflecting end (copper or aluminum)2) A conductive wire mesh3) A transparent glass (transparent to microwaves)4) An open end And compare the results. Such tests would be very valuable both for scientific and engineering purposes to understand what is being measured.
Quote...1) A solid reflecting end (copper or aluminum)2) A conductive wire mesh3) A transparent glass (transparent to microwaves)4) An open end And compare the results. Such tests would be very valuable both for scientific and engineering purposes to understand what is being measured.Apart for the conductive wire mesh it would seem to me that Shawyer likely tested the other ways (why would you use something when you can use nothing? etc.) and found out that the best results were with a solid reflecting end.
I keep looking at this and thinking it's not right.It looks to symmetrical.COMSOL's website says the RF module can do far field calculations, and the antenna placement would appear to put at least part of the frustum in the near field. It looks by eyeball that the software is only looking at the far field being reflecting off the small end of the frustum.Or am I missing something?
@RodalHave you posted your exact solution code here?I have my Mathematica fired up and ready to go!
Quote from: deltaMass on 05/09/2015 09:54 pm@RodalHave you posted your exact solution code here?I have my Mathematica fired up and ready to go!No I only posted the graphic results. Greg Egan posted a solution for constant in the transverse (aximuthal) direction modes, but arbitrary variation in the other directions . Greg Egan's solution will not address the Cyl TM212 being shown above, but it does address other modes like TE012 that have been discussed, see: http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Cavity.html