Quote from: Mulletron on 01/27/2015 06:14 pm....Found some time to read over this patent. It is a gold mine of good info. Great find. A couple takeaways I found is that it confirms that TE modes are highly desirable compared to TM. Also this caught my eye:QuoteIt has been found possible to predict the resonances approximately by defining a phase shift per unit length as 21r/ \g, where Ag is given by the usual formula for circular wave-guides of diameter D, but where D and hence Ag vary along the cone. If this phase shift is integrated from the location of the cut-off diameter to the position of the plunger or movable end wall, resonances will be found when the integral has values of 11 pi." Looks like math for predicting resonant modes for cones. It looks like some of the text got messed up in the character translation over to Google patents, see the bold part.Glad you agree that this 1969 patent is a gold mine for people interested in EM Drives.Please see the attached Adobe Acrobat .pdf file of page 3 of the original patent, top of column 4, for the actual formulas and symbolsThe patent states "n * Pi" instead of "11 * Pi""2 * Pi / Lambda_{g} " instead of b]21r/ \g[/b] "Lambda_{g}" instead of "Ag " where Lambda_{g} must mean the waveguide's wavelength

....Found some time to read over this patent. It is a gold mine of good info. Great find. A couple takeaways I found is that it confirms that TE modes are highly desirable compared to TM. Also this caught my eye:QuoteIt has been found possible to predict the resonances approximately by defining a phase shift per unit length as 21r/ \g, where Ag is given by the usual formula for circular wave-guides of diameter D, but where D and hence Ag vary along the cone. If this phase shift is integrated from the location of the cut-off diameter to the position of the plunger or movable end wall, resonances will be found when the integral has values of 11 pi." Looks like math for predicting resonant modes for cones. It looks like some of the text got messed up in the character translation over to Google patents, see the bold part.

It has been found possible to predict the resonances approximately by defining a phase shift per unit length as 21r/ \g, where Ag is given by the usual formula for circular wave-guides of diameter D, but where D and hence Ag vary along the cone. If this phase shift is integrated from the location of the cut-off diameter to the position of the plunger or movable end wall, resonances will be found when the integral has values of 11 pi."

I'm puzzled as to why you are using an excitation frequency of 2.45 GHz which does not correspond to any natural frequency of the cavity. If you want to excite TE110 you should use an excitation frequency of 2.32677 GHz (using the speed of light in air, while if you use the speed of light in vacuum it would be 2.32745 GHz). The natural frequency of mode shape TE110, 2.33 GHz, is independent of the length of the cavity.

QuoteI'm puzzled as to why you are using an excitation frequency of 2.45 GHz which does not correspond to any natural frequency of the cavity. If you want to excite TE110 you should use an excitation frequency of 2.32677 GHz (using the speed of light in air, while if you use the speed of light in vacuum it would be 2.32745 GHz). The natural frequency of mode shape TE110, 2.33 GHz, is independent of the length of the cavity.It's very simple. 2.45 GHz is a given.Cavity length and radius are the independent variables to be adjusted to establish resonance at 2.45 GHz.And yes, I'm quite sure I want TE 1,1,1 mode.

Isn't it possible to increase radius while leaving length at or around 12 cm? I would prefer that but can't find a radius that works with 2.45 GHz.

Well according the above posts and others, http://forum.nasaspaceflight.com/index.php?topic=36313.msg1320981#msg1320981 we're all getting pretty adept at using our skills/resources for calculating resonant modes of cylinders, which is a good first step. Well I'm learning new skills as I go along. So I can do cylinders all day, cones...not so much..yet. I certainly didn't come to the table knowing how to calculate resonant modes of anything 5-6 months ago.I'm trying to figure out how to use the (2 * Pi ) / (Lambda_{g} ) expression from the patent or the Volumetric Mean approach (which is better?) toward calculating resonant modes of conical frustums. I think the holy grail would be a quick and easy correction to convert from cylinder solutions to conical frustums. So the (2 * Pi ) / (Lambda_{g} ) above, does that mean what when I take 6.28 and divide that by x wavelength, and get a multiple of pi, that diameter or can support a resonant mode?Trying to figure out how to convert this cylinder to a cone, by keeping the diameter as the small diameter, adjusting the length to arrive at the new large diameter along a 45 or 90 degree cone, and still maintain resonance @ 2.45ghz TE111:2.45ghz, TE111L=0.1224489mD=0.08278945m

..So the (2 * Pi ) / (Lambda_{g}) above, does that mean what when I take 6.28 and divide that by x wavelength, and get a multiple of pi, that diameter or can support a resonant mode?...

Isn't it possible to increase radius while leaving length at or around 12 cm? I would prefer that but can't find a radius that works...

Quote from: Rodal on 01/24/2015 11:39 pm...What did you use for the bandwidth source around the frequency of interest (Drive frequency 2.45 E+9 Hz)? Could you try running all these cases again, everything the same as before except with a significantly narrower bandwidth source around the frequency of interest ? . Reportedly harminv does a better job the narrower the source is around the frequency of interest .Ok, I did run it again with bandwidth = 0.2 * Drive frequency, for cases up to resolution of 80, but I didn't get anything. Once I narrow the bandwidth to exclude the resonant frequency at 1.87 GHz, there are no resonances within the bandwidth. Harminv does work better at identifying the resonant frequency with narrower bandwidth, when the frequency is within the bandwidth. I set the drive frequency to 1.873 GHz, narrowed the bandwidth to 0.07 * frequency and got this:frequency Quality factor error1,873,339,229.3075 Hz 18,325,307.0778158 1.673972608680621e-7+0.0i....

...What did you use for the bandwidth source around the frequency of interest (Drive frequency 2.45 E+9 Hz)? Could you try running all these cases again, everything the same as before except with a significantly narrower bandwidth source around the frequency of interest ? . Reportedly harminv does a better job the narrower the source is around the frequency of interest .

Meanwhile, I would particularly appreciate @NotSoSureOfIt 's comments regarding Wolf's suggestion on how to calculate the resonances of a truncated cone cavity (lines 60 to 75 of column 3 and lines 1 to 11 of column 4) of the US patent #3,425,006 (which I attach below as an Adobe Acrobat .pdf document).Publication number US3425006 APublication date Jan 28, 1969Filing date Feb 1, 1967Priority date Feb 1, 1967Inventors Wolf James MOriginal Assignee Johnson Service Co

Quote from: Rodal on 01/28/2015 12:06 pmMeanwhile, I would particularly appreciate @NotSoSureOfIt 's comments regarding Wolf's suggestion on how to calculate the resonances of a truncated cone cavity (lines 60 to 75 of column 3 and lines 1 to 11 of column 4) of the US patent #3,425,006 (which I attach below as an Adobe Acrobat .pdf document).Publication number US3425006 APublication date Jan 28, 1969Filing date Feb 1, 1967Priority date Feb 1, 1967Inventors Wolf James MOriginal Assignee Johnson Service CoMmmm.. That's the argument that I used to come up w/ "volumetric". Been otherwise occupied, but I'll take a look at it as time permits.Edit: Lessee, that's the "guide" wavelength, for equal phase planes.Basically, you want to solve for the k[sub z] w/ R as a function of z.like k[sub z]^2 = (omega/c)^2- (X[sub m,n]/R[fn z])^2 or X'

We performed some very early evaluations without the dielectric resonator (TE012 mode at 2168 MHz, with power levels up to ~30 watts) and measured no significant net thrust.

Quote from: aero on 01/27/2015 11:17 pmIsn't it possible to increase radius while leaving length at or around 12 cm? I would prefer that but can't find a radius that works with 2.45 GHz.Yes, it's possible. If you insist in specifying the exciting frequency as 2.45GHz and the length (12 cm) of the cylindrical cavity, and having the diameter as the variable to be adjusted, then.... = 8.332965999678832` centimetersinstead of the diameter=7.54898 centimeter you used.

@Aero, is the reason why you insist in keeping a frequency of 2.45GHz in your modeling because you are looking at making a small EM Drive using a kitchen's microwave's magnetron as the source (which are nominally ~ 2.45 GHz) ?