Interesting to see that unequal doppler shifts in the resonant cavity will de-tune it under the resultant acceleration (from the thrust), if the acceleration is too high (at this point above 0.5 m/s/s).
That's why it is proposed for use as a lifter instead of a thruster.
Since the group velocity is higher at the large end of the thruster, and lower at the small end, the doppler shifts are said to be unequal. This is my own misunderstanding of microwave resonant modes causing me difficulty. A true statement of the process might be far different. Assuming the doppler shifts are unequal:
The acceleration difficulty might be overcome by better modeling, which might allow the resonant frequencies in the 4 modes to be physically adjusted in real time based on the acceleration produced by the device (if any).
First we would need to find a way to mechanically adjust these resonant frequencies relatively independently of each other, by bowing out the surfaces non-symmetrically for example (maybe not a good example), using piezo elements on the outside of the resonator. Modeling could give guidance on just how much to morph the resonator, and piezo elements on the outside would do the work.
Basically the problem is that the doppler shifts become great enough to cause all the energy in the cavity to shift in frequency just enough so that it becomes out of the bandwidth of the resonator. In the paper (see emdrive for that) nothing is said about what will happen to the energy in this case, but it matters because the energy is no longer contained in the resonator. That is, you might not want to bump such a resonator while it is running or you will risk an explosion. If the Q of a superconducting resonator is going to be in the 10e9 range you might not have to bump it very hard. Would all the energy simply fill a cavity at a lower frequency if it could? If so, and the resonator will not accomodate that, the energy would have to be released.
I don't know if any work has been done in this area (managing resonances by mode) in microwave cavities.
Another interesting point missing from the literature on the website is that while an extensive discussion of the overall shape of the resonator is shown, there is no discussion of physical size requirements. Perhaps a very large (20 meters in the shortest dimension) resonator would be useless, even if lower excitation frequencies were used. Theoretically I guess there is no lower or upper frequency limit on the effect so long as the resonator can be built. A nanoresonator might be built that operates in the visible range for example, and millions of these could be placed on a small chip.
The microwave oven is a self-resonant power oscillator, so maybe a resonator could be built up to hold the gain element inside. The cavity would then self-resonate, powered by DC, instead of depending on an external input. The gain element might be tailored to prefer the two modes that do not support propulsion, and this would make it easier for this system to accumulate energy in the two modes that do support propulsion.
In this case if the cavity size changes under acceleration it might be enough to let the self-resonant system self-adjust (with the help of piezo shape shifting to maintain the relationship between the two modes that support propulsion).
Just a few speculations. Much theoretical and experimental work is waiting to be done here.
thomasjschum
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