[Nakano, Fujii, T Yamamoto, Enomoto]

When we tried to decouple the actuator of MN L of EMTY, we observed nonlinear behaviors in the actuation of MN.
We excited MN L at 0.2 Hz and then so many harmonics of 0.2 Hz were seen in the TM Y sensor.
We measured the spectra of TM Y with the bias current in MN Y. See the following spectra.

Since we first suspected that there might be some saturation in electronics such as the coil driver, we measured the spectra with the bias current decreased. This indeed changed the behavior, but not significantly.
Then we measured the spectra with the bias currrent increased, then the nonlinearity DID decrease.
See the follwoing time series. Nonlinear oscillaiton seen in TMY significantly changed depending on MN Y bias.
This indicates that the nonlinear issue is not in electronics but in actuators themselves or in mechanics. By the way, the first thing I came up with from the word of nonlinear behavior in mechanics was that some parts are touching.

Note:
- We did the measurement in ALIGNED state.
- TM alignment was kept at a certain point. DC alignment change due to the MN bias was compensated by BF Y

Who ordered such a fancy thing?