Quote from: aero on 03/10/2015 10:26 pm....QuoteI did calculate the Eagleworks cavity without the HD-PE dielectric section.And what number did you get?See http://forum.nasaspaceflight.com/index.php?topic=36313.msg1339803#msg1339803The frequency for the TM221 mode shape (without the dielectric) is 2.00709 GHz.Is there another particular mode you are interested to know the frequency for?
....QuoteI did calculate the Eagleworks cavity without the HD-PE dielectric section.And what number did you get?
I did calculate the Eagleworks cavity without the HD-PE dielectric section.
Quote from: Rodal on 03/10/2015 10:39 pmQuote from: aero on 03/10/2015 10:26 pm....QuoteI did calculate the Eagleworks cavity without the HD-PE dielectric section.And what number did you get?See http://forum.nasaspaceflight.com/index.php?topic=36313.msg1339803#msg1339803The frequency for the TM221 mode shape (without the dielectric) is 2.00709 GHz.Is there another particular mode you are interested to know the frequency for?I'll need to think on that. It seems, from the images you posted, that the mode is the same for you and Eagleworks. So what (if anything) is close to freq = 1.937115E+009 Hz? And was the Eagleworks photos taken with that drive frequency?
Quote from: Rodal on 03/10/2015 01:42 amQuote from: Notsosureofit on 03/10/2015 01:29 am@ RODALJust got a minute but from your p expression;If L1/c1 = L2/c2del f = (1/2*f)*((c1*c2)/(L1*L2))*b^2*((1/dD1^2)-(1/dD2^2))might be a solution ??Got to check the thinking later.Night !I find your previous expressiondel f = ( f/(2*c^2)) * (c1^2-c2^2)more physically appealing, since it goes to zero for equal dielectric constants, regardless or their dielectric length, while on the other hand del f = (1/2*f)*((c1*c2)/(L1*L2))*b^2*((1/dD1^2)-(1/dD2^2))goes to zero for equal dielectric lengths, regardless of their dielectric constants.The previous expression is only valid approximation for a "uniformly varying dielectric". There is no L1 and L2 in that case.What do you think might maximize the second expression ? (valid only for L1/c1 = L2/c2 )
Quote from: Notsosureofit on 03/10/2015 01:29 am@ RODALJust got a minute but from your p expression;If L1/c1 = L2/c2del f = (1/2*f)*((c1*c2)/(L1*L2))*b^2*((1/dD1^2)-(1/dD2^2))might be a solution ??Got to check the thinking later.Night !I find your previous expressiondel f = ( f/(2*c^2)) * (c1^2-c2^2)more physically appealing, since it goes to zero for equal dielectric constants, regardless or their dielectric length, while on the other hand del f = (1/2*f)*((c1*c2)/(L1*L2))*b^2*((1/dD1^2)-(1/dD2^2))goes to zero for equal dielectric lengths, regardless of their dielectric constants.
@ RODALJust got a minute but from your p expression;If L1/c1 = L2/c2del f = (1/2*f)*((c1*c2)/(L1*L2))*b^2*((1/dD1^2)-(1/dD2^2))might be a solution ??Got to check the thinking later.Night !
Quote from: aero on 03/10/2015 11:17 pmQuote from: Rodal on 03/10/2015 10:39 pmQuote from: aero on 03/10/2015 10:26 pm....QuoteI did calculate the Eagleworks cavity without the HD-PE dielectric section.And what number did you get?See http://forum.nasaspaceflight.com/index.php?topic=36313.msg1339803#msg1339803The frequency for the TM221 mode shape (without the dielectric) is 2.00709 GHz.Is there another particular mode you are interested to know the frequency for?I'll need to think on that. It seems, from the images you posted, that the mode is the same for you and Eagleworks. So what (if anything) is close to freq = 1.937115E+009 Hz? And was the Eagleworks photos taken with that drive frequency?Take a look at the enclosed report from Paul March for a mode which NASA's COMSOL analyst identified as TM112 "like TM110 at top, and TM111 at bottom" with a frequency of 1.9355 GHz.I only calculated a few modes.Regarding your question "And was the Eagleworks photos taken with that drive frequency?" I presume that the photo was taken for the EM Drive with a dielectric (which would give a slightly lower frequency) while my computation was without the dielectric.
@RodalCan there be a resonance in the empty cavity at the low frequency of 1.6859 GHz?
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Dr. Rodal:....Acknowledge that "neoprene" rubber covers a multitude of formulations, but it turns out that most if not all of them have low Q-factors at microwave frequencies that disqualify them from this application even if they have a large electrostrictive coefficient. What counts in this low power EM-drive dielectric "amplifier" appears to be a dielectric with the largest electrostrictive/piezoelectric coefficient combined with a high Q-factor at microwave frequencies.Best, Paul M.
Quote from: frobnicat on 03/10/2015 05:03 pm....Quote from: Star-Drive on 03/11/2015 02:46 amDr. Rodal:....Acknowledge that "neoprene" rubber covers a multitude of formulations, but it turns out that most if not all of them have low Q-factors at microwave frequencies that disqualify them from this application even if they have a large electrostrictive coefficient. What counts in this low power EM-drive dielectric "amplifier" appears to be a dielectric with the largest electrostrictive/piezoelectric coefficient combined with a high Q-factor at microwave frequencies.Best, Paul M.Paul,(*) Neoprene® is Dupont's trade name for Chloroprene rubber (CR), so in the rest of this post I will refer to it by its technical name Chloroprene rubber (CR). The fact that NASA Eagleworks tested a dielectric made of Chloroprene rubber (CR) and found out that this rubber material is "disqualified for this (EM Drive) application" because the measured thrust using this rubber material as a dielectric is insignificant compared to using PTFE or HD-PE has important consequences that should be pointed out.Since Chloroprene rubber (CR) has a coefficient of thermal expansion up to 158% greater than the coefficient of thermal expansion of HD PE:THERMAL EXPANSIONChloroprene rubber (CR) 125*10^(-6) to 190*10^(-6) 1/(deg K) http://techcenter.lanxess.com/docs/pdft/e5-14.pdfHigh Density Polyethylene (HD PE) 120*10^(-6) 1/(deg K) http://www.engineeringtoolbox.com/pipes-temperature-expansion-coefficients-d_48.htmlThis experimental finding further nullifies @frobnicat's conjecture that the experimental measurements are an artifact due to thermal expansion of the dielectric.(According to @frobnicat's conjecture, based on thermal expansion, under no condition should the thrust force measurement have been smaller for Chloroprene rubber (CR) than for HD PE)(*)LIST of MANUFACTURER TRADENAMES for Chloroprene rubber (CR)Lanxess (Bayer AG) BAYPRENEDenka Kagaku Kogyo CHLOROPRENEShowa Denko SHOPRENETOSOH Corporation SKYPRENEDuPont NEOPRENEhttp://en.wikipedia.org/wiki/Chloroprene
Hey fellas, long time lurker, first time poster here.I'm not even going to pretend to understand half the maths that have been tossed around in this thread. I'm in complete awe of the work you guys have been doing to solve this mystery. I do have a question though, and forgive me for my ignorance.Does anyone know if this effect scales with the size of the frustum? Could the frequency of the microwaves be adjusted to allow the same level of force in a microscopic frustum that is shown Nasa's macroscopic frustum? If this is the case, would a sequence of many millions of tiny frustums not provide a great deal more force than one large frustum?
Quote from: Rodal on 03/12/2015 01:30 pmQuote from: frobnicat on 03/10/2015 05:03 pm....Quote from: Star-Drive on 03/11/2015 02:46 am.......@Frobnicat's conjecture is based on the shifting of the center of mass due to thermal expansion.
Quote from: frobnicat on 03/10/2015 05:03 pm....Quote from: Star-Drive on 03/11/2015 02:46 am.......
Not only Chloroprene-Rubber (CR) has a higher coefficient of thermal expansion than High-Density-Polyethylene-HDPE, but Chloroprene-Rubber (CR) also has a higher density than High-Density-Polyethylene-HDPE.So this further nullifies @Frobnicat's conjecture.According to @frobnicat's conjecture, the denser, higher-thermal-expansion material ("Neoprene®") should have produced a higher measured "thrust", but NASA Eagleworks results show the opposite: the denser, higher-thermal expansion material ("Neoprene®") resulted in insignificant thrust....
Quote from: Polonius on 03/12/2015 06:38 pmHey fellas, long time lurker, first time poster here.I'm not even going to pretend to understand half the maths that have been tossed around in this thread. I'm in complete awe of the work you guys have been doing to solve this mystery. I do have a question though, and forgive me for my ignorance.Does anyone know if this effect scales with the size of the frustum? Could the frequency of the microwaves be adjusted to allow the same level of force in a microscopic frustum that is shown Nasa's macroscopic frustum? If this is the case, would a sequence of many millions of tiny frustums not provide a great deal more force than one large frustum?One thing one knows for sure is that the smaller the frustum, the higher the natural frequency, so in order to excite a given mode shape, one would have to use higher excitation frequencies for smaller frustrums.@Notsosureofit has disclosed in this forum's thread his plans to test a smaller cavity with a higher excitation frequency, and his plan to use a Gunn diode (http://en.wikipedia.org/wiki/Gunn_diode) to generate the microwaves inside the cavity.Concerning the use of literally "millions" of these devices (as in an Integrated Circuit), this could no longer involve microwaves (if possible at all) but it would mean much higher frequencies, because the wavelengths get cut-off due to the size of the cavity hence a much smaller cavity implies that the lowest natural frequency must be much higher.
....My conjecture is not about dielectric disc's CoM shift playing an important role in the thrust (did I say that ? Where ?) ...
http://web.ornl.gov/~webworks/cppr/y2001/pres/111404.pdf)).
Quote from: Rodal on 03/12/2015 09:16 pmhttp://web.ornl.gov/~webworks/cppr/y2001/pres/111404.pdf)).The subject of thermal "pumping" is one that will have to be carefully considered in any Cavandish experiment. What procedures are best for it's elimination ? Making sure the CG of the heated object doesn't move ?
@Rodal,Yes, that was about recoil forces, my arguments are still valid, a block of material starting to expand thermally will push a wall against which it is resting, whether the expanding material is the hot gas of an explosion or a block of PTFE heating from the left against copper at 0.1°C/s, it's only a (huge) difference of magnitude, not of nature (as far as recoil is concerned). Done some number, such recoil is not significant given inertia of pendulum. Like 0.1µN on the 1st second of heating. Kind of, order of magnitude. Please call it 0 if you feel so inclined. But I will continue to stand on my position on italic statement (separate post later to avoid mixing).....