James Woodward in the US has been boldly experimenting with capacitors which appear to show thrust since the 1990s. I was recently reading about one of them, and to me it looks very much like the emdrive. Also, as I will show tentatively below, the thrust from it can be predicted quite well by quantised inertia, in a far simpler way to Woodward's own explanation which mis-predicts the thrust by several orders of magnitude (ie: I admire his experiments, but I do not accept his theory).
Woodward's thrusters or Mach Effect Thrusters (see Mahood, 1999, Tajmar, 2017) typically look like the image below. An AC current is input into a capacitor (the vertical black lines) making an EM field. There is a dielectric in between (yellow) or sometimes to the side, which is a piezo-electric material (PZT) that vibrates when the EM field is applied. The setup is asymmetric because there is a heavy reaction mass (plate), here shown on the left.
Quantised inertia predicts that this contraption should move towards the end with the large brass plate (just as it is observed to do) just as the emdrive moves towards its narrow end, because in both cases Unruh waves are more damped at the end with the massive plate, so photons of the em field will always gain mass on going towards the wide end or the end with less metal, and so, to conserve momentum, the thruster itself must thrust left. The above also looks similar to the horizon drive.
So, let's get a bit more quantitative. A simplified version of the QI thrust formula is
F=(PQL/c) x ((1/w1)-(1/w2))
where F is the thrust towards the end with the massive plate, P is the power input, Q is the quality factor, L is the length and w1 and w2 are the 'widths' of the cavity at the two ends (which affects the amount of Unruh-damping). Now, how can we model exactly the damping of the Unruh waves by the two end caps' thickness? I cannot yet do it in detail, but one way to do it, to predict the maximum thrust obtainable would be to assume that the thin brass cap on the right does not damp the Unruh waves, so the photon can see the cosmos and w2 = the Hubble scale. The other end, being thicker, does damp the Unruh waves so the width (w1) there is roughly the distance between the centre of the dielectric and the middle of the brass end plate. The particular experiment I will look at is Mahood (1999) for which L=0.025m and P=145 W. To estimate Q, I have had to use the dissipation constant of 2% given for another thruster in a report by March and Palfreyman (2006). So Q=2pi x 100%/2% = 314. The thrust toward the large plate end is then predicted (in a very crude way) by QI to be
F = (145 x 314 x 0.025 / 3x10^8) x (1/0.025 - 1/huge)
F = 15x10^-5 N
The observed thrust was 5x10^-5 N (Mahood, 1999) so the prediction by QI is not bad, and far better than Woodward's model which was several orders of magnitude out (according to Mahood, 1999). As expected from the assumptions, the QI prediction overestimates the thrust. This is obviously a very crude calculation, which is why I'm spouting it here, and not in a journal yet, but it is interesting that QI predicts this Mach Effect Thruster, and also of course the emdrive, galaxy rotation, cosmic acceleration...etc. The thruster may allow a new way to test QI, and could be an example of the horizon drive. I do need to look at the other thrusters because I believe some of them were not asymmetric, and build up a more statistically-significant results list for comparison with the predictions of QI.
Mahood, Thomas L. (February 1999). "Propellantless propulsion: Recent experimental results exploiting transient mass modification". AIP Conference Proceedings. Space Technology and Applications International Forum-STAIF 2000, Albuquerque, New Mexico. 458. American Institute of Physics. pp. 1014–1020. Link
Tajmar,M., 2017. Mach-effect thruster model. Acta Astronautica, 141, 8-16.
March, P. and A. Palfreyman, 2006. The Woodward effect: math modelling & continued experimental verifications at 2 to 4 MHz. CP813, STAIF-2006.