Effects of humidity on the interaction between a fused silica test mass and an electrostatic drive

• Interaction between a fused silica plate and an electrostatic drive was investigated.
• The interaction force is time and relative humidity dependent.
• Numerical model of the interaction was developed.
• Charge redistribution is shown to be the cause of the interaction force evolution.

Interaction of a fused silica test mass with electric field of an electrostatic drive with interdigitated electrodes and influence of ambient air humidity on this interaction are investigated. The key element of the experimental setup is the fused silica torsional oscillator. Time dependent increase of the torque acting on the oscillator's plate after application of DC voltage to the drive is demonstrated. The torque relaxation is presumably caused by the redistribution of electric charges on the fused silica plate. The numerical model has been developed to compute the time evolution of the plate's surface charge distribution and the corresponding torque.