Ultra-Low-Noise Seismic Piezoelectric Accelerometer With Integral FET Amplifier

The design of a seismic piezoelectric (PE) accelerometer with integral electronics (IEPE) having probably the lowest noise floor (for its size and weight) and lowest (near-dc) operating frequencies ever reported to date among this type of sensors is presented. The accelerometer frequency range is from 0.003 to 200 Hz at the ±3 dB level. The noise floor (equivalent input noise acceleration) is about 600, 55, 37, 7 and 3 nG/√(Hz) at frequencies 0.1, 0.5, 1, 10 and 100 Hz, respectively. The sensor incorporates the ultra-low-noise FET-input charge amplifier and the PE transducer operated in the flexural, circular bender bimorph mode. Key factors for low-noise operation are discussed. The contribution of the PE transducer noise and charge amplifier noise is shown at a frequency range from 0.1 to 200 Hz. In addition to ultra-low-noise and near-dc frequency response, the designed accelerometer has other parameters impressive for the seismic IEPE sensors: output impedance ≤ 10 Ω, 100°C maximum operating temperature and 250 G pk shock limit. The sensor´s noise floor was measured directly at the National Institute of Standards and Technology (NIST). The experimental results have good correlation with the noise values evaluated based on the measured charge amplifier noise and the theoretical PE transducer thermal noise. The ultra-low-noise floor of the designed sensor allowed using it in the stabilization platform, which carries the world´s most frequency stable laser system used for the atomic clock research conducted by NIST.