Passive isolation systems rely on n

Passive isolation systems rely on natural characteristics of mechanical oscillators for vibration reduction of suspended objects. Since a mechanical oscillator can filter out vibration components only above its natural resonant frequency, reduction of low frequency vibration such as motion induced by microseismism (between 0.2-0.5 Hz) is not easily achieved by passive systems. Active isolation systems, which implement vibration sensors, actuators and controllers (servos), isolate the target objects from seismic vibration actively with feedback and feedforward controls. Active systems in principle can reduce the targets’ vibration in any frequency band, if vibration sensors with sufficient sensitivities and low noise levels are used.