Historical research guide · 0561 · 2021
High-accuracy thrust measurements of the EMDrive and elimination of false-positive effects
M. Tajmar · O. Neunzig · M. Weikert
In one minute
Martin Tajmar’s SpaceDrive group at TU Dresden built the instrument the EMDrive question needed. Earlier campaigns had reported about one millinewton per kilowatt from microwaves bouncing inside a tapered copper cone — a force some five hundred times what the same power would give as pure light. Tajmar, Neunzig and Weikert rebuilt their balance until every artefact they could find was gone: an inverted counterbalanced double pendulum instead of a torsion arm, the 9 kg thruster hung from a bearing below its suspension point, the amplifier run off an on-board battery so no cable or liquid-metal contact could push on it. That instrument resolves forces below a nanonewton. Sweeping 1850 to 2000 MHz through four resonances, they find every reading inside the noise, and their sensitivity floor sits at the light-pressure limit itself. The paper’s real gift is the artefact catalogue: it shows exactly how a heating cavity fakes a thrust that even reverses sign when you turn the thruster around.
Connection
This is chapter 1’s evidence ladder built as hardware: a measurement floor set at the photon-thrust limit, so that any future propellantless claim has a published bar to clear. It also hands chapters 3, 8 and 11 something more useful than a number — the mechanism by which thermal expansion, magnetic cables and liquid-metal feedthroughs manufacture convincing thrust signatures, and the mounting geometry that removes them. The open ground the authors name themselves is the superconducting cavity, where the quality factor rises by orders of magnitude and nobody has yet looked.
From the source
Thermal expansion of a powered cavity, acting through the way it is mounted, produces a force plateau with the correct on-off timing and the correct sign change when the thruster is turned around: a cage mount gave 1.5 µN for 10 W of input, and bolting the cavity to the cage raised that to 20 µN — the same one micronewton per watt reported in earlier campaigns.Section 4.1 and Section 3 item 4; Fig. 6A and Fig. 6B
An inverted counterbalanced double pendulum, with the thruster package hung from a bolt bearing beneath the upper platform and damped in software through the calibration voice coil, carries a 9 kg payload at sub-nanonewton noise — the lowest reported for a balance of that capacity.Section 4.1; Fig. 1, Fig. 3 and Fig. 4
Powering the EMDrive from an on-board battery pack removes the whole class of feedthrough artefacts, including the current-dependent surface-tension force of several micronewtons that the authors found in liquid-metal pin contacts — the technique many earlier setups had adopted precisely to avoid cable stiffness.Section 3 item 3; Section 4 item 4
Sweeping 1850 to 2000 MHz in 5 MHz steps, through four identified resonances covering hybrid, TE312 and TM212 modes, every thrust reading stayed inside a noise level of 10 to 30 nN, against a photon-thrust benchmark of 36 nN for the 11 W reaching the cavity.Section 5; Fig. 11 and Fig. 13; Table 1
The resulting bound places any anomalous EMDrive force at or below the classical radiation-pressure value of 3.3 nN per watt, which is two orders of magnitude below the earlier reported results even allowing for the lower quality factor of this cavity — a quantitative limit every proposed mechanism now has to work inside.Section 6, Conclusion and outlook; Table 1
The regime the authors leave open is the superconducting cavity, which Shawyer had suggested and which would raise the quality factor by many orders of magnitude; that is the next measurement this group names for itself.Section 6, final paragraph
The way in
https://doi.org/10.1007/s12567-021-00385-1How to cite it
M. Tajmar, O. Neunzig, M. Weikert (2021) High-accuracy thrust measurements of the EMDrive and elimination of false-positive effects doi:10.1007/s12567-021-00385-1