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#640 by Bob Woods on 19 Jul, 2017 22:17
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This may have already been answered long ago, but; Has anyone considered that the EM drive is somehow tapping into the Earth's magnetic lines of force?
Yes and it is addressed in part by moving the test bed to different angles in respect to the magnetic field. Mono's test rig is on wheels or casters to make it easy and quick.
While the overall field seems quite low, the overall magnetic flow could be a factor.
Like I said, it likely was covered, but I'd like to put that out there in case it wasn't... -
#641 by JasonAW3 on 19 Jul, 2017 22:32
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This may have already been answered long ago, but; Has anyone considered that the EM drive is somehow tapping into the Earth's magnetic lines of force?
Yes and it is addressed in part by moving the test bed to different angles in respect to the magnetic field. Mono's test rig is on wheels or casters to make it easy and quick.
While the overall field seems quite low, the overall magnetic flow could be a factor.
Like I said, it likely was covered, but I'd like to put that out there in case it wasn't...
Ok, but what about magnetic isolation? Anybody test this rig in a Faraday cage? -
#642 by otlski on 19 Jul, 2017 23:20
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This may have already been answered long ago, but; Has anyone considered that the EM drive is somehow tapping into the Earth's magnetic lines of force?
Yes and it is addressed in part by moving the test bed to different angles in respect to the magnetic field. Mono's test rig is on wheels or casters to make it easy and quick.
While the overall field seems quite low, the overall magnetic flow could be a factor.
Like I said, it likely was covered, but I'd like to put that out there in case it wasn't...
Ok, but what about magnetic isolation? Anybody test this rig in a Faraday cage?
To be clear, it has been talked about and certain experimenters have capability to move the test bed; no one has done it with any rigor at say all four compass points, and no one appears to have the run-to-run repeatability or control over the other variables (level, CG). I don't know about testing in a Faraday cage. -
#643 by meberbs on 19 Jul, 2017 23:28
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Faraday cages don't provide magnetic isolation. Most metals just block electric fields or oscillating fields (because oscillating fields by definition are both electric and magnetic, and damping one damps both)This may have already been answered long ago, but; Has anyone considered that the EM drive is somehow tapping into the Earth's magnetic lines of force?
Yes and it is addressed in part by moving the test bed to different angles in respect to the magnetic field. Mono's test rig is on wheels or casters to make it easy and quick.
While the overall field seems quite low, the overall magnetic flow could be a factor.
Like I said, it likely was covered, but I'd like to put that out there in case it wasn't...
Ok, but what about magnetic isolation? Anybody test this rig in a Faraday cage?
Faraday cages have effectively been used by some (A vacuum chamber like used by NASA is a decent Faraday cage, depending on window size), but to block the Earth's magnetic field you would need mu-metal shielding. Pretty sure this has been discussed, but not implemented.
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#644 by Monomorphic on 20 Jul, 2017 02:14
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To be clear, it has been talked about and certain experimenters have capability to move the test bed; no one has done it with any rigor at say all four compass points, and no one appears to have the run-to-run repeatability or control over the other variables (level, CG). I don't know about testing in a Faraday cage.
Once I have the new high power amplifier working I will be testing at all four compass points. The torsional pendulum does have its own leveling system built into the legs of the stand.
The cavity is a faraday cage of sorts. I suppose people mean enclosing the electronics in a faraday cage. But it would be better to enclose everything in a mumetal box, if the geomagnetic field is suspected. That is prohibitively expensive for a cavity AND the battery, and electronics. Plus it introduces a large amount of ferromagnetic material to the test stand - which I've always been told should be avoided.
Included below are the plots from two tests done at different orientations to the geomagnetic field. In the first, the cavity is aligned east-west, in the second north-south. There was a large reduction in noise in the second plot because of mitigation efforts, so it is true that it is not a very rigorous comparison. Rerunning this experiment with proper controls is very high on my list.
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#645 by otlski on 20 Jul, 2017 02:45
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To be clear, it has been talked about and certain experimenters have capability to move the test bed; no one has done it with any rigor at say all four compass points, and no one appears to have the run-to-run repeatability or control over the other variables (level, CG). I don't know about testing in a Faraday cage.
Once I have the new high power amplifier working I will be testing at all four compass points. The torsional pendulum does have its own leveling system built into the legs of the stand.
The cavity is a faraday cage of sorts. I suppose people mean enclosing the electronics in a faraday cage. But it would be better to enclose everything in a mumetal box, if the geomagnetic field is suspected. That is prohibitively expensive for a cavity AND the battery, and electronics. Plus it introduces a large amount of ferromagnetic material to the test stand - which I've always been told should be avoided.
Like with all aspects of this, the difficulty in successfully running the experiment should not be underestimated. In theory the amount of deflection in the torsion pendulum will be directly related to the thrust (assuming it is real) and the torsional spring rate. However, it does not end there. If the apparatus has a minor CG offset from the rotational axis, and an out of level condition exists, this will create a gravity pendulum which will either add or subtract from the stiffness thought to be established solely from the torsion wire. Whether it adds or subtracts from the stiffness depends on the vector of the CG offset relative to the tilt. The amount of stiffness change is related to that same vector and the magnitude of the CG offset. Since your thrust estimates will be driven by the amount of deflection and the supposed stiffness, the uncertainty due to level and CG are likely going to be a big wildcard. I say this with some experience where out of level conditions negatively impact our equipment (most of which have air bearings and torsion rods) with as little as 0.001" per foot out of level. This is not an easy level to achieve given casters etc. -
#646 by Monomorphic on 20 Jul, 2017 02:55
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The first 3D print failed 10 hours in because the plate separated from the support material. After a quick redesign, which made the flanges thicker, the print was successful after another 16 hours! Next step is to create a silicone mold and cast 4 duplicates out of epoxy resin. Then repeat the process for the small end. However, the small end is where the antennna is located, so some extra design work will need to go into how the coax attaches - with an eye to adding a linear actuator that controls the z position of the antenna.
Below is a progress shot of the second print, and the finished product.
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#647 by Monomorphic on 20 Jul, 2017 03:35
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If the apparatus has a minor CG offset from the rotational axis, and an out of level condition exists, this will create a gravity pendulum which will either add or subtract from the stiffness thought to be established solely from the torsion wire.
Great care is taken to make sure the torsional pendulum beam is level. Center of gravity is controlled via counterweights on both x and y axis. There are two bubble levels used to monitor CG as well as a high resolution 3-axis compass, 3-axis gyroscope, and 3-axis accelerometer: https://www.phidgets.com/?tier=3&catid=10&pcid=8&prodid=32
It is also important that the beam be as perfectly level as possible for the laser displacement sensors to function properly. -
#648 by mwvp on 20 Jul, 2017 04:50
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...
Reminds me of the Doppler shift for relativistic photon rockets. For beam powered photon rockets, the more relativistic the ship the higher percentage of beam energy gets converted to ship kinetic energy and it approaches 100% as v approaches c.
That is a very relevant observation that hasn't gotten its fair share of attention here; utilization aspect of propulsion efficiency. Usually efficiency is discussed as the fraction of input energy that ends up as exhaust kinetic energy, and not the fraction of input energy that ends up increasing the kinetic energy of the vehicle, the whole system.
As a didactic hypothetical, lets consider a battery-transmitter-antenna with mass approaching the limit of zero, and a very large transmitted power. It would accelerate at the limit approaching C. From a "rest" inertial-frame observer, the Doppler shift observed would make the transmitter power appear a near static electric charge, or magnetic dipole. All the transmitted power increases the kinetic energy of the ship, at efficiency/utilization approaches 100%. At 50%, you get an observed 1/2 frequency Doppler shift, and half efficiency.
And the EM drive, unlike BAE, is dissipating half the power (optimally) to create an unbalanced radiation pressure. So make that 25% for a compact EM drive that radiates heat rather than radiation.
Optimally, to create an efficient Doppler-shift approaching 0 Hz, the cavity Q must be high enough to match the Doppler shift from cavity acceleration. If it were 0.1 M/S^2, f=3 GHz, Doppler shift would be around 1 Hz, and the cavity Q needs to be 10^9, a billion. Five orders of magnitude more than our non-superconducting cavities can muster. And what precision will be needed, and control system bandwidth and design, to keep that cavity in tune?
So its no wonder measured thrust is five orders of magnitude down. Not to mention the torsion scales used just measure static, not dynamic thrust. I would expect some static thrust to be present from the resistance of the waveguide phase-shifting reflected power.
And I'm not surprised to see Shawyer mounting his frustrum on springs, as if he were going to shake it to increase acceleration and improve efficiency; as if it were a Woodward device, exploiting increased inertia not moment to moment in mass, but according to which direction the frustrum was accelerating and which direction energy was exchanged between the field and the frustrum motion....
I wondered if one could fool Mother Nature by coupling EM radiation in one direction to relativistic electrons in or on the cavity preferentially over the reverse direction and thus convert more energy into kinetic energy going one way. I though this might break the conversion limit. Probably not but it's fun to think about.
Yep, I think electron beams could have very desirable properties, including dispersion from relativistic effects.
How a magnetron tube is coupled to the frustum should be taken into account. What inertial back-action effects between sloshing fields in the cavity, and the mass of the affected electrons in the tube would occur? Could a beam-tube be designed as a kinetic transducer?
In your last post, you mentioned laser gain-media. Electrons moving in cavities/waveguides can function as gain-media and transducers. They even call them "free-electron lasers" Of course, so can semiconductors. Particle accelerator, especially relativistic, is a non-trivial exercise above my pay-grade. But you could think of a magnetron tube, or a semiconductor negative-resistance oscillator configuration as a sort of "laser" gain medium.
Another useful characteristic of magnetrons and other beam tubs is they can be tuned with electric and magnetic fields, and can thus be used as parametric and non-reciprocal components. Might as well make friends with non-linearity because you've got to deal with it. -
#649 by Notsosureofit on 20 Jul, 2017 16:22
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Optimally, to create an efficient Doppler-shift approaching 0 Hz, the cavity Q must be high enough to match the Doppler shift from cavity acceleration. If it were 0.1 M/S^2, f=3 GHz, Doppler shift would be around 1 Hz, and the cavity Q needs to be 10^9, a billion. Five orders of magnitude more than our non-superconducting cavities can muster. And what precision will be needed, and control system bandwidth and design, to keep that cavity in tune?
Interesting point, but what formula are you using to calculate the Doppler shift vs acceleration ? -
#650 by SeeShells on 20 Jul, 2017 18:43
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The first 3D print failed 10 hours in because the plate separated from the support material. After a quick redesign, which made the flanges thicker, the print was successful after another 16 hours! Next step is to create a silicone mold and cast 4 duplicates out of epoxy resin. Then repeat the process for the small end. However, the small end is where the antennna is located, so some extra design work will need to go into how the coax attaches - with an eye to adding a linear actuator that controls the z position of the antenna.
Monomorphic,
Below is a progress shot of the second print, and the finished product.
How long before you think your "pie" will be done?
And how are you securing your "EM-Pie-Plate" together?
My Very Best,
Shell
PS: It looks much better than I though it could. -
#651 by Monomorphic on 20 Jul, 2017 19:26
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How long before you think your "pie" will be done?
And how are you securing your "EM-Pie-Plate" together?
I will probably have the big end-plate finished over the weekend, or by next week. I'm working out what kind of filler I should mix in with the epoxy resin. I'm leaning towards foam beads to save weight, but I have to use the right foam or it will dissolve in the epoxy and leave a big mess.
The 'pie' will be secured together with epoxy and possibly other means like pegs between the pieces. I may also use the current flat copper end-plate as a backing since it is the same diameter. -
#652 by Bob012345 on 20 Jul, 2017 19:55
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Optimally, to create an efficient Doppler-shift approaching 0 Hz, the cavity Q must be high enough to match the Doppler shift from cavity acceleration. If it were 0.1 M/S^2, f=3 GHz, Doppler shift would be around 1 Hz, and the cavity Q needs to be 10^9, a billion. Five orders of magnitude more than our non-superconducting cavities can muster. And what precision will be needed, and control system bandwidth and design, to keep that cavity in tune?
So its no wonder measured thrust is five orders of magnitude down. Not to mention the torsion scales used just measure static, not dynamic thrust. I would expect some static thrust to be present from the resistance of the waveguide phase-shifting reflected power.
Thanks for the response. If this idea worked, one might try incorporating Prof. Woodward's neat trick of vibrating the parts of the cavity, the end plates, that would need to fool the waves into seeing a few orders of magnitude higher acceleration. Semiconductor based MHz range mechanical resonators might be useful.How a magnetron tube is coupled to the frustum should be taken into account. What inertial back-action effects between sloshing fields in the cavity, and the mass of the affected electrons in the tube would occur? Could a beam-tube be designed as a kinetic transducer?
In your last post, you mentioned laser gain-media. Electrons moving in cavities/waveguides can function as gain-media and transducers. They even call them "free-electron lasers" Of course, so can semiconductors. Particle accelerator, especially relativistic, is a non-trivial exercise above my pay-grade. But you could think of a magnetron tube, or a semiconductor negative-resistance oscillator configuration as a sort of "laser" gain medium.
Thanks. It would be interesting to see if these kinds of devices experienced high internal stresses or even as yet unexplained forces....
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#653 by LowerAtmosphere on 20 Jul, 2017 20:47
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How long before you think your "pie" will be done?
And how are you securing your "EM-Pie-Plate" together?
I will probably have the big end-plate finished over the weekend, or by next week. I'm working out what kind of filler I should mix in with the epoxy resin. I'm leaning towards foam beads to save weight, but I have to use the right foam or it will dissolve in the epoxy and leave a big mess.
The 'pie' will be secured together with epoxy and possibly other means like pegs between the pieces. I may also use the current flat copper end-plate as a backing since it is the same diameter.
Looks beautiful so far. Please also consider using one or more of the following options to compress the plates together and prevent the pieces from being lossy along the seams:
1. A ring strap/clamp and/or plastic vacuum wrap,
2. Using rivets and screws through the edges in a symmetric pattern,
3. Cutting a groove and adding a protrusion along one of the inner sides to slot the pieces together,
4. A press to push the pieces together and maybe even spot weld them together (unrealistic but still the best known method for fusing components seamlessly),
5. Heat treatment/light welding/soldering and polish.
Thank you for your hard work and dedication, we all eagerly await your latest test campaign. -
#654 by knowles2 on 20 Jul, 2017 23:06
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Just thought I pop in an tell you guys and girls that EM Drive made an experience on CBS Salvation. First time I seen EM Drive show up in a science fiction show.
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#655 by Req on 21 Jul, 2017 00:12
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Just thought I pop in an tell you guys and girls that EM Drive made an experience on CBS Salvation. First time I seen EM Drive show up in a science fiction show.
https://forum.nasaspaceflight.com/index.php?topic=42978.msg1701347#msg1701347 -
#656 by mwvp on 21 Jul, 2017 01:16
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Optimally, to create an efficient Doppler-shift approaching 0 Hz, the cavity Q must be high enough to match the Doppler shift from cavity acceleration. If it were 0.1 M/S^2, f=3 GHz, Doppler shift would be around 1 Hz, and the cavity Q needs to be 10^9, a billion. Five orders of magnitude more than our non-superconducting cavities can muster. And what precision will be needed, and control system bandwidth and design, to keep that cavity in tune?
Interesting point, but what formula are you using to calculate the Doppler shift vs acceleration ?
I'm not using a formula, just reason. I refer to (field) energy "sloshing" around (at the group velocity). What determines group velocity, guide wavelength and dispersion? In a frustrum, coupling between the mode-sections is maximum. So its pretty much the size and Q of the cavity. Slow amplitude variations caused by small Doppler spreads will be filtered. And in our accelerating context, its the stale, old energy built up in the cavity that experiences the largest phase-shifts for a small acceleration. But that stale, old energy will decay in a lower Q cavity, leaving only newer, fresher energy to produce a smaller amplitude variation for a smaller phase shift.
For equations, I just posted the link to Macken's book, Appendix ch. 1. Bradshaw (at Arxiv) on Dispersion has good material on Doppler shifts, Snell's law/scattering on moving media and dispersive meda. And Rumpf has Maxwell's equ. for moving media, but doesn't elaborate. I can cite, if your specific about what you're after.
I can't give you an analytical solution, but I know how to go about solving a simplified approximation. A rigorous 3D simulation could be done by modifying Meep a bit, and running it a fast, very fast machine. I would give it a shot for money, but not for fun. -
#657 by spupeng7 on 21 Jul, 2017 07:57
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New breakthrough discovery-every quantum particle travels backwards. physics.org, 7-18
John,
What is this about?
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this is the product of desperation. the quantum is never going to make sense in linear time alone. Attempts will be made to trick the math into agreement with experiment until a better understanding of time itself is achieved. My bet is that a complex conjugate of the real time measurement is required. This would relieve the problem of direction at least, maybe much more.
To a John from a John..
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#658 by Bob Woods on 21 Jul, 2017 16:25
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#659 by Rodal on 21 Jul, 2017 17:01
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FYI: Pions & Gravitons?
https://goo.gl/m7RhtP
free pdf of the article (the article is behind a paywall in the Nature link): https://arxiv.org/ftp/arxiv/papers/1703/1703.10682.pdf
This experiment concerns a solid-state flat-spacetime (no gravitons) analogue to a curved spacetime gravitational anomaly (the axial anomaly, responsible for the decay of a neutral pion into two photons. Similarly in a curved spacetime the axial-gravitational anomaly can give rise to the decay of the pion into two gravitons.). This experiment does not involve gravitons or actual detection of any gravitational anomaly in real spacetime.
https://www.ibm.com/blogs/research/2017/07/scientists-observe-gravitational-anomaly-on-earth/Quote from: www.ibm.com/blogs/research/2017/07/scientists-observe-gravitational-anomaly-on-earth/Appearing in a paper published today in Nature, an international team of physicists, material scientists and string theoreticians, have observed such a material, an effect of a most exotic quantum anomaly that hitherto was thought to be triggered only by the curvature of space-time as described by Einstein’s theory of relativity. But to the surprise of the team, they discovered it also exists on Earth in the properties of solid state physics, which much of the computing industry is based on, spanning from tiny transistors to cloud data centers.
The experiment uses the mathematical techniques from string theory - but it doesn't prove anything concerning string theory as a quantum gravity theory of our universe. But it does validate some of the analytical methods used in string theory (string theory derived holography), which worked great for this particular physical material experiment in flat spacetime
https://arxiv.org/pdf/1610.04413.pdf
The authors of
https://arxiv.org/pdf/1311.0878.pdf
proposed this experiment precisely because the gravitational anomaly is considered to be impossible to probe in high energy contexts. It is really not possible (now or in the foreseeable future to our greatgrandchildren) to prove or disprove string theory (or its competitor theories of quantum gravity like quantum loop gravity) in a high energy context or to detect gravitons.
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