SAS contains two key mechanical com

SAS contains two key mechanical components called the Inverted Pendulum (IP) and the Geometric Anti-Spring (GAS) filter, which provide horizontal and vertical vibration isolation respectively. The resonant frequency of the IP can be lowered to ∼30 mHz and thus it can passively attenuate the ground motion at the microseismic peak (0.2-0.5 Hz), which contributes most of the RMS amplitude of the mirror displacement/velocity. The resonant frequency of the GAS filter can be lowered to ∼200 mHz and it enable us to achieve vertical attenuation performance comparable to that obtained by pendulums in the horizontal direction. Note that the lowest natural frequencies of the IP and GAS filters are limited by hysteretic behaviors of elastic components and thus can be potentially improved by investigating better elastic material in the future.