Quote from: Mulletron on 03/31/2015 03:48 am....So my most likely candidate for unloaded testing is 2413.5mhz. I have no clue what mode is being excited here.....Yes you have been given a strong clue in this thread ( http://forum.nasaspaceflight.com/index.php?topic=36313.msg1352878#msg1352878 ) as to what mode is being excited here:Mode Frequency (GHz) [Exact sltn.] Frequency (GHz) [COMSOL FEA] Poynting Vector Cyl. TE012 2.20244 2.1794 0Cyl.TM311 2.45835 2.4068 Towards Small BaseCyl. TM212 2.49342 2.4575 ~ 0Clearly this frequency ( 2.4135 GHz) falls right in the range of the calculated frequency for mode Cyl. TM311, if the dimensions of your truncated cone are within 1% of the assumed dimensions (Big Diameter=11 inches, Small Diameter=6.25 inches and Axial Length=9 inches).It is the best mode to excite (in that frequency range) with a cavity lacking a polymer dielectric, because this mode shape (TM311) has a clear Poynting vector. The other modes have zero Poynting vectors in the longitudinal direction of the truncated cone.As to why the measured frequency (if correct) is closer to the Finite Element Analysis (FEA) solution, here are possible reasons:1) Internal dimensions of truncated cone may be 1% larger than the assumed internal dimensions in the exact solution analysis (Big Diameter=11 inches, Small Diameter=6.25 inches and Axial Length=9 inches).2) Flatness of the big base and the small base. The exact solution assumes spherical section surfaces for the bases while the Finite Element solution assumes them to be perfectly flat. This can be shown to make a small difference, and its sign (increasing or decreasing the frequency) depends on the electromagnetic mode shape.3) Internal Damping: damping decreases the frequency of the damped solution as compared to the undamped solution. The exact solution assumes infinite Q (undamped conditions). I attach again the predicted heating profile (at the big base) for this mode (TM311) from the exact solution
....So my most likely candidate for unloaded testing is 2413.5mhz. I have no clue what mode is being excited here.....
....For example, when messing around with the frustum hooked up to the SNA, it was refreshing to see how I could change the resonant frequencies at will just my applying pressure to the large end (raising the resonant freq) and then it would return to steady state when the large end rebounded. I knew I could do that, but it was neat to see it in action. The VSWR of TM212 was all around bad, around 5.3 or so. I think I can improve it by shortening the probe. It isn't on my list of things to do unless a reason comes up later for it.The VSWR of TM311 isn't great, but it'll do. I was able to get it down to 1.4 by really torquing down on the cable but it would go back to ~2. There's lots of quirks I've discovered, such as just the weight of the test cable applying pressure to the frustum walls slightly changes the measured results.....
Quote from: Mulletron on 04/01/2015 12:03 am....For example, when messing around with the frustum hooked up to the SNA, it was refreshing to see how I could change the resonant frequencies at will just my applying pressure to the large end (raising the resonant freq) and then it would return to steady state when the large end rebounded. I knew I could do that, but it was neat to see it in action. The VSWR of TM212 was all around bad, around 5.3 or so. I think I can improve it by shortening the probe. It isn't on my list of things to do unless a reason comes up later for it.The VSWR of TM311 isn't great, but it'll do. I was able to get it down to 1.4 by really torquing down on the cable but it would go back to ~2. There's lots of quirks I've discovered, such as just the weight of the test cable applying pressure to the frustum walls slightly changes the measured results.....@Mulletron, thanks for disclosing that information: as far as I know you are the first one reporting it, as I have not seen Shawer, Juan Yang or NASA Eagleworks disclose the above information.Could you please provide more information on the movement of the natural frequency: when applying pressure to the large end, roughly how much did the natural frequency change? roughly from what natural frequency (without outside pressure on the big end) to what natural frequency (by pushing the big end towards the inside)?Did you push the big end at its center? Roughly speaking how much was the displacement? would you say that it was very small, of the order of the thickness or less than the thickness of the big base plate?Thanks
If I'm understanding all of these efforts correctly (please correct me if I don't!), in layman's terms, an EM drive is a conductive cavity in which most radio frequencies (RF) can propagate freely, and come out of the other end with a minimal loss of energy. But, at certain frequencies, the cavity will resonate, containing and amplifying the energy of the RF signal. For certain cavity geometries at specific frequencies, the shape (or energy?) of the resonating photons will be pointed in one direction. This directionality seems to be important for making an EM drive work. Conventional wisdom says that the energy should dissipate as heat, but instead, the energy seems to be taking the form of net thrust.
I very specifically remember being spanned on the spec anny from 700 to 2700, and when the sweeper would start over, at around 800mhz sweeper frequency, I'd see harmonics at the other end of the sweep being chased.During this, you can even see a spike at the end:https://drive.google.com/folderview?id=0B4PCfHCM1KYoZWphS29nSDZkZVE&usp=sharing&tid=0B4PCfHCM1KYoTXhSUTd5ZDN2WnMI was sweeping from 800-2600, and spanned from 700-2700, and there are spikes outside my sweep that max hold picked up.So I guess that means that there are n higher order modes inside these cavities happening too.
Quote from: RotoSequence on 04/01/2015 05:07 amIf I'm understanding all of these efforts correctly (please correct me if I don't!), in layman's terms, an EM drive is a conductive cavity in which most radio frequencies (RF) can propagate freely, and come out of the other end with a minimal loss of energy. But, at certain frequencies, the cavity will resonate, containing and amplifying the energy of the RF signal. For certain cavity geometries at specific frequencies, the shape (or energy?) of the resonating photons will be pointed in one direction. This directionality seems to be important for making an EM drive work. Conventional wisdom says that the energy should dissipate as heat, but instead, the energy seems to be taking the form of net thrust.If that is an accurate summary of the graphs, simulations and related discussion then I will have to disagree. A long time ago an RF engineer friend explained to me that cavities, filters and LC circuits are never dissipative. The power either goes through them or is reflected. If an RF signal with 20 MHz of bandwidth at 2085 MHz is sent through a 5 pole cavity filter with 5 MHz passband a large fraction of the RF power is simply reflected back to the amplifier. It is for this reason that isolators (circulators with a 50 Ohm load on one port) are used between the amplifier and a filter. The green on black graphs shown above, unless I am mistaken are S12 plots. Most of the power is transmitted through the cavity. More power is reflected at frequencies where there are dips in the S12 plot. This is where the reflection coefficient (SWR) is higher. Inside the cavity the Poynting vector is directed from the input port to the output port. Outside the cavity the Poynting vector is inside the dielectric of the coax; pointing away from the PA. An interesting experiment would be to decrease the length of the coax from the PA to the cavity by 2-3 cm. This will change the position of the dips in the S12 plot. Any reflected power, or return wave as it's sometimes called, will be dissipated as heat inside the amplifier.
Quote from: RotoSequence on 04/01/2015 05:07 amIf I'm understanding all of these efforts correctly (please correct me if I don't!), in layman's terms, an EM drive is a conductive cavity in which most radio frequencies (RF) can propagate freely, and come out of the other end with a minimal loss of energy. But, at certain frequencies, the cavity will resonate, containing and amplifying the energy of the RF signal. For certain cavity geometries at specific frequencies, the shape (or energy?) of the resonating photons will be pointed in one direction. This directionality seems to be important for making an EM drive work. Conventional wisdom says that the energy should dissipate as heat, but instead, the energy seems to be taking the form of net thrust.If that is an accurate summary of the graphs, simulations and related discussion then I will have to disagree. A long time ago an RF engineer friend explained to me that cavities, filters and LC circuits are never dissipative. The power either goes through them or is reflected. ....
Real (as opposed to theoretical) tuned circuits always have resistive losses and some times nonlinear effects.
know this one has a big giggle factor but Dave Pares has updated his website again with more experimental results. It is a species of EM drive if real.http://www.paresspacewarpresearch.org/Projet_Space_Warp/Experiment_5.htm
i know this one has a big giggle factor but Dave Pares has updated his website again with more experimental results. It is a species of EM drive if real.http://www.paresspacewarpresearch.org/Projet_Space_Warp/Experiment_5.htm
That's all good, (I think) but how does the big end vs. small end affect the strength of the Poynting vector and hence magnitude of the force? Likely not at all on average? But the strength varies continuously so for small dx in positive direction it increases in strength but for same small dx in negative direction it decreases in strength. (Not sure I have the signs right.) But momentum is not the same even for the same electron/positron pair.I am postulating that the strength of the fields in the axial direction is related to the geometry of the cavity in the axial direction. Or perhaps even the mode of the resonance. It seems unlikely that the strength is constant from one end to the other.
First, we may obtain some information from the simultaneous Poynting vectors as shown in Figures 5 and 6. If we consider a transverse wave causing field line oscillations, the Poynting vectors behave very differently depending on whether the wave is traveling or standing. Figure 9 is a diagram of the Poynting vectors for the two different schemes. Even though the wave amplitudes for both conditions are set to be the same and the magnitude of Poynting vector oscillations is consequently the same, the traveling wave propagates energy, while the standing wave produces no net energy flux. The Poynting vectors in Figures 5 and 6 more resemble the traveling wave pattern. Thus for the Pc3-4 wave activities in our observations the traveling wave component is stronger. We may also estimate the resonant condition by examining the phase difference between dE and dB [e.g., Singer et al., 1982]. If the phase difference is 90, the wave is standing and a resonant condition is reached.