Transfer function of an ultralow frequency vibration isolation system

We have measured the transfer function of the recently proposed folded pendulum which has a resonant period up to 66 s. Results confirm that the dynamic behavior of the folded pendulum closely approximates that of a simple pendulum of the same period. The system can provide a simple one‐dimensional seismic isolation stage for laser interferometer gravitational wave antennas, as well as having application to very low frequency seismometers.