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26 April 2007 Mechanical monolithic sensor for low-frequency seismic noise measurement
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This paper describes a new low-frequency seismic sensor for geophysical applications. The instrument is basically a monolithic tunable folded pendulum with an interferometric readout system, that can be configured as seismometer or as accelerometer. The monolithic mechanical design and the introduction of a laser interferometric technique for the readout implementation make it a very sensitive and compact instrument with a very good immunity to environmental noises. The theoretical sensitivity curve is calculated considering the brownian noise, the readout noise and the data acquisition noise. Preliminary tests on the mechanical performances of the monolithic structure and on the optical readout have been performed. Interesting result is the measured resonant frequency of the instrument of ≈ 150mHz obtained with a rough tuning, demonstrating the feasibility of a resonant frequency of the order of 5mHz with a more refined tuning. The transfer function of the folded pendulum in open loop configuration is calculated measuring the resonant frequency and the quality factor for several step responses. Then a PID controller is added to implement the closed loop configuration. The mechanics of the seismic sensor, the optical scheme of the readout system, the theoretical predictions and the preliminary experimental performances as accelerometer are discussed in detail, together with the foreseen further improvements.
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Fausto Acernese, Rosario De Rosa, Gerardo Giordano, Rocco Romano, and Fabrizio Barone "Mechanical monolithic sensor for low-frequency seismic noise measurement", Proc. SPIE 6529, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2007, 65292B (26 April 2007);

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