Geometric anti-spring vertical accelerometers for seismic monitoring

A new low-frequency, very-low noise, vertical accelerometer is presented. The sensor has been designed to be part of an array of few hundred such devices to be used to predict local gravity fluctuations. These fluctuations, acting on the mirrors of gravitational wave interferometers, are a fundamental source of noise that can only be subtracted from the recorded signal. The motion of a 36 g mass supported by loaded springs is monitored by a high-resolution capacitance sensor; a feedback force actuator keeps the mass in the equilibrium position. The feedback signal is proportional to the acceleration in the frequency range 0–150 Hz. The accelerometer spectral sensitivity is better than 10−9 m/Hz in the same band, with a dynamic range exceeding 150 dB.