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QuietSeisTM
An Ultra-low noise MEMS accelerometer for Seismology
[email protected]@sercel.com
April 10th, 2018
Introduction
SERCEL• 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
Introduction
Context• 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
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-180
-150
-120
-90
-60
-30
0
0,01 0,1 1 10 100
Ph
ase
(deg
rees
)
Frequency (Hz)
Phase response2Hz seismometer (damping 0,7)
Introduction
Context
• MEMS accelerometers often perceived as too noisy at low frequencybecause of 1/f noise
- True for most of the seismic MEMS on the market
• Latest generation of digital closed-loop MEMS accelerometer, initiallydesigned for seismic imaging, exhibits very good noise performances at low frequency.
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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
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MEMS Noise measurements
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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
MEMS Noise measurements
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Low frequency noise measurement
• Basement of office building in peri-urban area
• Vibration isolation platform (f0~2,7Hz) • 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
MEMS Noise measurements
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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
MEMS Noise measurements
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Low frequency noise measurement
Noise limited by
ambient vibrations
above ~2Hz
5Hz 10Hz
MEMS 1/f noise lower than :
• 10Hz-geophone noise below ~2Hz
• 5Hz-geophone noise below ~0,1Hz
• NHNM down to ~0,1Hz
MEMS Noise measurements
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Low frequency Dynamic Range
Full scale @ +/-13m/s² pk :• Vertical MEMS Dyn. Range ~131dB
0,02-2Hz
Dyn. Range
133dB
Dyn. Range
126dB
Full scale
+/- 5 m/s² pk
(3,5m/s² rms)
MEMS Noise measurements
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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
Earthquake detection
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IRAN-IRAK border M7.4 earthquake
• Nov 12th,2017• 18:18:19 (UTC)
Earthquake detection
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MEMS Noise
floor (typ.)
Earthquake ground acceleration
(Clinton, 2002)
MEMS Full scale
5m/s² pk
Vertical axis MEMS Vertical axis MEMS Vertical axis MEMS Vertical axis MEMS accelerometeraccelerometeraccelerometeraccelerometer
(Power (Power (Power (Power spectrumspectrumspectrumspectrum))))
Natural frequency
of isolation platform
Earthquake detection
t=180s � 18:25:09 in NANTES
P-wave @ 18:25:06 in CLF
t=515s � 18:30:24 in NANTES
S-wave @ 18:30:35 in CLF
Good correlation with
CLF seismic station!
Conclusion
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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
Bibliography
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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, 332-342.
• Lainé J., 2014, A high-sensitivity MEMS-based accelerometer: The Leading Edge 33/11, 1234-1242
• Observatoire GEOSCOPE (doi: 10.18715/GEOSCOPE.G), Centre de Données de l'Institut de Physique du Globe de Paris.
http://geoscope.ipgp.fr/index.php/fr/catalogue/description-d-un-seisme?seis=us2000bmcg
