Modeling and experiment of the suspended seismometer concept for attenuating the contribution of tilt motion in horizontal measurements

Abstract

Tilt-horizontal coupling in inertial sensors limits the performance of active isolation systems such as those used in gravitational wave detectors. Inertial rotation sensors can be used to subtract the tilt component from the signal produced by horizontal inertial sensors, but such techniques are often limited by the sensor noise of the tilt measurement. A different approach is to mechanically filter the tilt transmitted to the horizontal inertial sensor, as discussed in this article. This technique does not require an auxiliary rotation sensor and can produce a lower noise measurement. The concept investigated uses a mechanical suspension to isolate the inertial sensor from input tilt. Modeling and simulations show that such a configuration can be used to adequately attenuate the tilt transmitted to the instrument, while maintaining translation sensitivity in the frequency band of interest. The analysis is supported by experimental results showing that this approach is a viable solution to overcome the tilt problem in the field of active inertial isolation.

A six degree-of-freedom fused silica seismometer: design and tests of a metal prototype

“…In the case where we infer the X motion of the platform by looking only at the horizontal readout, we will get the typical tilt-to-horizontal coupling [25][26][27][28]. This coupling is present in all 1D seismometers and is given by the equation…”

“…The total noise of the seismometers, shown in figure 7, becomes larger than the ground motion below ≈30 mHz. In order to avoid large motions of the aLIGO platforms below 10 mHz, aLIGO utilises a blended control scheme [8,28]. The aLIGO platforms follow the signals from the inertial sensors only above the blending frequency.…”

“…The key problem comes from the coupling of the aLIGO platform tilt to its horizontal motion. This coupling scales very unfavourably as g/ω 2 , where g is the local gravitational acceleration, and ω is the angular frequency of the platform motion [25][26][27][28]. The aLIGO detectors already utilise custom beam rotation sensors [18] developed by the University of Washington to measure the tilt motion of the ground.…”

A 6D interferometric inertial isolation system

“…Two approaches are currently being explored in the LIGO-Virgo collaboration to reduce low-frequency tilt-coupling. The first aims to develop a seismometer that is insensitive to tilt in a particular frequency band [22,23]. The second aims to actively stabilize the tilt-motion of the isolated platforms using 1D rotation sensors.…”

Location effect and adjustment scheme of the translation-tilt compensation bench for accelerometer performance investigation

“…Inertial sensors such as accelerometers and seismometers are sensitive to both the horizontal acceleration and the tilt of ground due to the gravity. The separation of tilt and horizontal motion, the reduce of tilt-horizontal coupling are very important in seismometry [18,19]. Different from the separation and removing of horizontal-tilt effect, we considered the utilizing of horizontal-tilt effect.…”