An Ultra-low noise MEMS accelerometer for Seismology

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Mervin Stewart Nash
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1 QuietSeis TM An Ultra-low noise MEMS accelerometer for Seismology April 10 th, 2018

2 SERCEL Introduction French company founded in 1956, subsidiary of CGG More than 1500 employees in 8 countries and 14 sites Market leader in seismic instrumentation for O&G exploration in marine, land and transition zones Longstanding culture of technological innovation 2

Context Introduction Sensors for low frequency seismic applications (<2Hz): -

bulky, costly, power consuming, not deemed industrial.

conditions: amplitude & phase distortions detrimental to the fidelity of the signal

3 Context Introduction Sensors for low frequency seismic applications (<2Hz): - Geophones (10Hz, ~5Hz) - Seismometers (1-2Hz) - Force Balance Accelerometers (FBA) bulky, costly, power consuming, not deemed industrial.. phase rotation at low frequency, manufacturing tolerances, aging, environmental conditions: amplitude & phase distortions detrimental to the fidelity of the signal Phase (degrees) Phase response 2Hz seismometer (damping 0,7) ,01 0,1 1 Frequency (Hz)

market Latest generation of digital closed-loop MEMS accelerometer, initially

4 Introduction Context MEMS accelerometers often perceived as too noisy at low frequency because of 1/f noise - True for most of the seismic MEMS on the market Latest generation of digital closed-loop MEMS accelerometer, initially designed for seismic imaging, exhibits very good noise performances at low frequency. 4

5 MEMS accelerometer Some benefits of MEMS accelerometer No sensor leveling required, can be used in any orientation Measures its own tilt (DC response) Compact and very low power Digital closed-loop architecture: - Frequency response flat and highly stable in amplitude and phase (down to DC): Perfect time synchronization of events between sensors - Very low distortion - Very fast clip recovery time 5

6 MEMS Noise measurements Noise floor for seismic imaging (Lainé, 2014) Noise measured above 1Hz in LSBB (France) <15ng/sqrt(Hz) above 10Hz 1/f noise at low frequency not characterized 6

MEMS Noise measurements Low frequency noise measurement Basement of office building in periurban area Vibration isolation platform (f 0 ~2,7Hz)

7 MEMS Noise measurements Low frequency noise measurement Basement of office building in periurban area Vibration isolation platform (f 0 ~2,7Hz) Soundproof acoustic chamber Data acquired at night over the course of several months Raw data processed using ANSS/USGS Matlab script: ANSS_noise_rms_rev4.m 7

Hz and 5Hz geophone channels low noise 24 bits

8 MEMS Noise measurements Low frequency noise measurement 2 QS-DB boards: Vertical and horizontal QuietSeis MEMS accelerometer UART serial data transmission to external device 10 Hz and 5Hz geophone channels low noise 24 bits / ADC Velocity data converted in acceleration QS-DB 8

9 MEMS Noise measurements Low frequency noise measurement 5Hz 10Hz Noise limited by ambient vibrations above ~2Hz MEMS 1/f noise lower than : 10Hz-geophone noise below ~2Hz 5Hz-geophone noise below ~0,1Hz NHNM down to ~0,1Hz 9

10 MEMS Noise measurements Low frequency Dynamic Range Dyn. Range 133dB Full scale +/- 5 m/s² pk (3,5m/s² rms) Dyn. Range 126dB 0,02-2Hz Full +/-13m/s² pk : Vertical MEMS Dyn. Range ~131dB 10

test site is being scheduled with a French seismology

11 MEMS Noise measurements Comparative testing vs. Trillium Compact broadband seismometer in a low noise test site is being scheduled with a French seismology institution. Test site Noise PPSD (vertical) Trillium Compact QS-DB 11

12 Earthquake detection IRAN-IRAK border M7.4 earthquake Nov 12th, :18:19 (UTC) 12

13 Earthquake detection Earthquake ground acceleration (Clinton, 2002) MEMS Full scale 5m/s² pk MEMS Noise floor (typ.) Vertical axis MEMS accelerometer (Power spectrum) Natural frequency of isolation platform 13

14 Earthquake detection t=180s 18:25:09 in NANTES 18:25:06 in CLF t=515s 18:30:24 in NANTES 18:30:35 in CLF Good correlation with CLF seismic station!

Conclusion A new MEMS accelerometer with improved noise floor and reduced 1/f noise contribution has been evaluated for very weak signals and very

New possibilities for low frequency, weak signal applications: Ambient seismic noise imaging and monitoring Seismology - Replacement of Force

15 Conclusion A new MEMS accelerometer with improved noise floor and reduced 1/f noise contribution has been evaluated for very weak signals and very low frequency measurements. A noise floor below NHNM down to 0.1 Hz has been demonstrated. New possibilities for low frequency, weak signal applications: Ambient seismic noise imaging and monitoring Seismology - Replacement of Force Balance Accelerometers, seismometers, Structural Health Monitoring of large structures - Operational Modal Analysis using ambient vibrations Active stabilization platforms in low noise or low-g environments 15

16 Bibliography References Clinton J.F., Heaton T.H., 2002, Potential Advantages of a Strong-motion Velocity Meter over a Strong-motion Accelerometer: Seismological Research Letters Volume 73, Number 3, Lainé J., 2014, A high-sensitivity MEMS-based accelerometer: The Leading Edge 33/11, Observatoire GEOSCOPE (doi: /GEOSCOPE.G), Centre de Données de l'institut de Physique du Globe de Paris. 16

Using Micro-ElectroMechanical Systems (MEMS) accelerometers for earthquake monitoring

Environmental Systems & Services Pty Ltd PO Box 939 Hawthorn VIC 3122 Australia www.esands.com esands@esands.com Using Micro-ElectroMechanical Systems (MEMS) accelerometers for earthquake monitoring Adam