New Test Mass (TM) Simulator - 2011

The TM simulator is developed during the GRS technology demonstrator project for ESA, in order to achieve a stable differential capacitance with the range from 6fF to 120fF. The differential capacitance in the simulator represents the displacement between the real TM and its enclosure with displacement sensing electrodes.

The main function and requirement of the TM simulator are as follows:
[1] Provide differential capacitance of 6 fF (10 µm), 24 fF (40 µm) and 120 fF (200 µm)
[2] The Q factor of the TM simulator shall be over 250
[3] The thermal sensitivity of the TM simulator shall be less than 20 ppm/K

The design concept of the TM simulator is as follows:
[1] Use ultra stable high Q ceramic material as the dielectric of the capacitors
[2] Use copper plates as the electrodes of the capacitors
[3] Use micrometer spindle to disturbe the electric field of the capacitors, in order to precisely adjust the capacitance