Piezoelectric Actuator Characterizations for Isolation Testing of Suspension Systems

Seismic noise is the major source of noise at frequencies below 100 Hz in current LIGO detectors. Thus, the suspension systems of future detectors must isolate this noise in order to increase their sensitivity; the design for the final stage suspension systems that actively damp and isolate seismic noise is the focus of this research. The design of our suspension system is composed of a double-double pendulum suspended from cantilever springs supported by a flexure stage. This stage contains piezoelectric actuators arranged so that the stage can be shaken in all three dimensions independently which simulates seismic noise with a controlled, large amplitude suitable of testing the isolation abilities of our suspension system. Early tests have uncovered some anomalies in the response of the flexure stage to the one-dimensional driving of the actuators. Some of these have been resolved by making mechanical adjustments to the stage. The rest are possibly due to the mechanical properties of the actuators, which is currently being investigated. Early results of this investigation show that although similar, each actuator vibrates with a slightly different amplitude when driven with the same voltage. This can be corrected by “tuning ” each actuator with the appropriate change in voltage. The new tuning protocol is developed and expounded on in this paper