....I would be curious to know if anyone can explain why the difference between the Wikipedia formula calculation of resonant frequency and the resonant frequency obtained by integrating Maxwell's equations in the time domain then doing Fourier analysis to calculate the resonant frequencies. In a nutshell, meep ...
Lightly following this thread but you folks are veering into territory I DO actually understand and I felt the need to correct some misconceptions.Why is there the "assumption" that no matter how much (or little) an operational EM-Drive would generate it would be of military/geo-political value beyond, say, extending the service life of spy, communications, etc satellites? That it provides for greatly enhanced (or even practical) kinetic bombardment weapons? That it has some sort of huge military purpose that will ignite an arms race?Really? No. Only if it has enough thrust to power an aircraft with a reasonable (turbine-generator) amount of power and is more efficent AND more powerful than current jet or rocket engines. Otherwise its simply a low-thrust station keeping and manuever system with a long service life A thrust of 0.09lb to 0.9lb per KW as noted in the cited paper isn't that great really. Again the main advantge is you don't have to carry propellant/reaction mass. The main "geopolitical" ramification of the EM-Drive would be that satellite servicing is going to look a lot LESS attractive since with it you'd (supposedly) never have to fill up maneuvering system every again which was the major driver for that concept. Hidden "Rods-From-Gods" in deep space ready to rain down on anyone, anywhere and "undetectable" due to the EM-Drive? Uh, NO just no.First of all: There is no "stealth" in space. Period. http://www.projectrho.com/public_html/rocket/spacewardetect.phpYour rod carrier is going to be spotted and tracked. The EM-Drive requires power, which is going to have heat that is going to have to be rejected, which is going to be "visible" to anyone looking in the right direction. The EM-Drive itself (according to one post above) "emits" radiation which can be detected with the right sensor set up. And lastly you CAN see objects in space if you look carefully enough. Even if you used solar panels to provide the power for the EM-Drive they are going to "reflect" some of the energy they recieve AND they are going to be sources of waste heat for the energy they absorb but do not use.I wonder if anyone has pointed out that IF this "works" the way it would seem to what they've invented is basically the "Space:1889" Ether Propeller Randy
http://en.wikipedia.org/wiki/Space:_1889
I don't know Randy. All the talk about Dark Energy, Dark Matter and Quantum Vacume are starting to sound a lot like the Aether concept!I guess everything old is new again.
But is it the Edison, Zepplin, or Armstrong type?
The first subscript (m) is the azimuthal mode number: it indicates the number of full-wave patterns around the circumference of the waveguide. It is zero for modes in which there is no variation in the circumferential direction.The second subscript (n) is the radial mode number: it indicates the number of half-wave patterns across the diameter. The radial mode number (n) plus one indicates the number of nodes across the diameter (counting as nodes the end nodes).The third subscript (p) is the longitudinal mode number. It indicates the number of full-wave patterns along the longitudinal length of the waveguide. It is zero for modes in which there is no variation in the longitudinal direction.
....I did double check everything as you advised and there does not seem to be anything wrong with my meep simulation.....
....So the cavity does not resonate at 2.45 GHz and therefore my dimensions must be wrong.
....Here are my results.Resolution number of time steps resonant frequency Q error 1 2 none detected 2 4 none detected 3 6 none detected 4 8 none detected 5 10 1.84921E+009 negative 2 e-4 10 20 1.85128E+009 negative 2 e-4 20 40 1.86441E+009 ~ 500 6 e-4 40 80 1.87262E+009 ~ 1200 3 e-4 80 160 1.86992E+009 ~ 300 13 e-4 160 320 1.87042E+009 ~ 80 47 e-4 The detected frequency bounces around consistently with the error which can be taken as estimating the number of significant digits of the frequency detected. The quality is very low. I take that to be a result of the cavity dimensions being incorrect for the resonant frequency detected as they are also incorrect for the drive frequency.....
.. I am setting my simulation in 2-D, running in 64-bit single precision....
.....The quality is very low. I take that to be a result of the cavity dimensions being incorrect for the resonant frequency detected as they are also incorrect for the drive frequency.I would seriously like to know how to properly design a resonant cavity for a selected resonant mode. I can tinker with the dimensions in meep and get higher quality factors, but that is not very efficient and forces me to guess the mode by looking at images of the wave pattern.
Quote from: aero on 01/24/2015 09:03 pm.....The quality is very low. I take that to be a result of the cavity dimensions being incorrect for the resonant frequency detected as they are also incorrect for the drive frequency.I would seriously like to know how to properly design a resonant cavity for a selected resonant mode. I can tinker with the dimensions in meep and get higher quality factors, but that is not very efficient and forces me to guess the mode by looking at images of the wave pattern.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 .
Quote from: Rodal on 01/24/2015 11:39 pmQuote from: aero on 01/24/2015 09:03 pm.....The quality is very low. I take that to be a result of the cavity dimensions being incorrect for the resonant frequency detected as they are also incorrect for the drive frequency.I would seriously like to know how to properly design a resonant cavity for a selected resonant mode. I can tinker with the dimensions in meep and get higher quality factors, but that is not very efficient and forces me to guess the mode by looking at images of the wave pattern.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+0.0iAs you can see the quality factor is much higher and the processing error is much lower. The only problem is that it is not the frequency I had hoped for. I did some further searching and found two things. 1 - The value of the J'0(1) Bessel function = 1.8411837813 which agrees with the number we have.2 - Meep doesn't actually excite the cavity with Gaussian noise, rather it uses the derivative of a Gaussian signal, whatever that means.I really don't think this particular problem is in the meep software. As I wrote before, I searched the discussion list, which goes back at least 8 years, and there is no mention of this particular problem. If it were in meep, some user would have encountered it long ago. A 25% discrepancy is hard to overlook. There is a chance that it is in my general understanding of how to model using meep, but my knowledge of meep is far superior to my knowledge of resonant cavity design so using Occam's razor, it is most likely that my cavity design is the problem.Dr. Rodal, I really appreciate your efforts on my behalf. I will continue to look into the details of resonant cavity design. Maybe it has something to do with the cavity length. But actually, that doesn't seem very likely at all. What do you know about Gaussian noise derivatives and could that be a simple frequency correction? But, when generated with a continuous wave at 2.45 GHz, the field images don't show any resonance.
@RodelQuoteThe first subscript (m) is the azimuthal mode number: it indicates the number of full-wave patterns around the circumference of the waveguide. It is zero for modes in which there is no variation in the circumferential direction.The second subscript (n) is the radial mode number: it indicates the number of half-wave patterns across the diameter. The radial mode number (n) plus one indicates the number of nodes across the diameter (counting as nodes the end nodes).The third subscript (p) is the longitudinal mode number. It indicates the number of full-wave patterns along the longitudinal length of the waveguide. It is zero for modes in which there is no variation in the longitudinal direction.I did double check everything as you advised and there does not seem to be anything wrong with my meep simulation. Neither could I find any questions related to my problem on the Internet. That leads me to think that my problem is still my understanding of mode shapes and cavity dimensions. I thought I had TE1,1, but from the above, for the mode to be TE 1,1, the cavity radius needs to be 1/4 wavelength and the circumference should support 1 full wave pattern. The wavelength for 2.45 GHz is 0.1223642686 in vacuum. So, for the vacuum filled cavity to resonate at 2.45 GHz in the TE 1,1 mode the radius needs to be 0.0305910671 meters. But simply plugging that radius into the formula calculates a resonance frequency of ~2.92GHz in air. So it seems evident that I am still confused about modes and use of the formula to calculate resonance frequencies. Would you lead me through the example of a resonant cavity dimensions for 2.45 GHz resonance? I also note that driving the cavity from my previous post at 2.45 GHz, R = 0.0377449, there is no sign of resonance in the field images. So the cavity does not resonate at 2.45 GHz and therefore my dimensions must be wrong.
NASA plans to upgrade their equipment to higher power levels, use vacuum-capable RF amplifiers with power ranges of up to 125 W, and design a new tapered cavity analytically expected to produce thrust in the 0.1 N/kW range. Then, the test article will be shipped to other laboratories for independent verification and continued evaluations of the technology, at Glenn Research Center, the Jet Propulsion Laboratory and the Johns Hopkins University Applied Physics Laboratory.
....First here's what I have about mode numbering from various sources:ME from thread 1: T(MorE)mnp. m is the # of 1/2 wavelengths around a half circumference...Navy Neets mod 11 (screenshot below): The first subscript indicates the number of full-wave patterns around the circumference of the waveguide....Oracle: http://en.wikipedia.org/wiki/Transverse_mode In circular waveguides, circular modes exist and here m is the number of half-wavelengths along a half-circumference....Rodal: The first subscript (m) is the azimuthal mode number: it indicates the number of full-wave patterns around the circumference of the waveguide. ....So there is conflicting information. Rodal and the Navy agree, the oracle and me are different....As far as n or p go, I'm not even going to look at them until I get some feedback about the m discrepancies....