On the Use of Mechanical Filters to Attenuate the Transmission of Tilt Motion to Inertial Sensors
Inertial sensors such as seismometers, geophones, and accelerometers cannot distinguish horizontal motion from tilt motion. Rotation measurements can be used to subtract the tilt component from horizontal measurements, but the noise in the tilt sensor is often a limiting factor. No mechanism can change the dual sensitivity of inertial sensors to tilt and translation, but the transmission of ground motion can be mechanically filtered in a frequency-dependent way. This article discusses the use of mechanical filters to reduce the transmission of tilt motion from the ground to inertial instruments, which can be applied to existing sensors, or considered for integration in the design of new horizontal sensors. The limitations of this approach are related to (1) geometrical couplings due to the separation between the reference point and the input point of the mechanical filter, (2) residual tilt transmission through the joints stiffness, (3) effects of the mechanical filtering on the signal-to-noise ratio of the horizontal motion measurement, and (4) practical difficulties with the implementation of such concepts, including thermal noise in the flexures. This study analyzes and quantifies the benefits and limitations of the mechanical filtering approach for seismic studies and for seismic isolation applications.
© 2016 Seismological Society of America. Manuscript received 16 February 2016; Published Online 12 April 2016. This work was carried out within the LIGO laboratory. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation, and operates under Cooperative Agreement PHY-0757058. Advanced LIGO was built under Award PHY-0823459. This document has been assigned LIGO Laboratory Document Number LIGO-P1400060. The authors are very grateful to Kate Dooley, Krishna Venkateswara, the reviewers, and editors for their comments and suggestions which were very valuable in improving this article.
Published - BSSA987-1001.pdf