hp mems seismic sensor - iris.edu · 2 introduction hp mems inertial sensing technology has been...
TRANSCRIPT
2
Introduction
HP MEMS Inertial Sensing Technology has been optimized to produce a
breakthrough performance needed for Seismic Imaging requirements.
Outline:
• Sensor Design
• Specifications
• Noise Optimization
• Test Results
• QC Self Tests
• Conclusions
– Three single crystal silicon wafers hermetically bonded under vacuum • Pressure controlled for low thermal mechanical noise
• CTE match of substrates results in temperature stability
– Surface Electrodes • Constant gap allows large proofmass travel in open loop
• Three phase electrode configuration allows full sensitivity and range at any orientation or wafer alignment
– Custom ASIC • Low noise demodulation of capacitive sensor
• Low power
• 24 bit digital output
Stator wafer
suspension bondelectrodes
MEMS wafer
Cap wafer
HP MEMS Seismic Sensor Key Features
4
Sensor Node and Tether Head Assembly
5
Voyager Seismic Sensor Specifications
Max acceleration amplitude Peak (Highest Gain Mode) +/- 80 mG
Peak (Lowest Gain Mode) +/- 320 mG
Noise spectral density Noise density < 13 nG/rt Hz
Dynamic range 120 dB
Harmonic distortion THD @ 12Hz, 68.4 mg pk acceleration (0.7 in/s pk velocity)
< -80 dB
Analog to digital conversion
Depth 24 bit (20 ENOB)
Sample Rate 2ms or 4ms
Passband 1-200Hz (2ms)
Cross axis sensitivity All axes <-40 dB
Tilt Detection Resolution of vertical component of sense axis due to sensor tilt
+/- 2%
Sensor Recovery Time High Gain Mode - 300mg acceleration <1.6 seconds
Auxiliary Channel External Input into ASIC ADC 2V Fully Differential Input
Sensor power < 56mW
Operating temperature Minimum -40C
Maximum +70C
6
Noise Testing Results at USGS Vault
10-3
10-2
10-1
100
101
102
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
Frequency [Hz]
Unf
ilter
ed P
ower
Spe
ctra
l Den
sity
[G/r
tHz]
HP MEMS
Reference Seismometer
USGS Low NoiseModel of the Earth
USGS High NoiseModel of the Earth
HP MEMS Accelerometer with discreet electronics and USGS Reference Sensor
• GS-13 short period seismometer
– 10ng/rthz base band noise floor demonstrated (matching model prediction)
7
Sensor Noise Optimization
m
TbkN B
tm
4
dxdC
NN e
p
2
0222
JptmT NNNNoise
Lower
Noise
Larger Mass
Larger Electrode Area
Reduced Damping
Lower Parasitic Capacitance
Where
dxdC
NN e
p
2
0
m
TbkN B
tm
4
Thermal Mechanical Noise Position Noise
Low ASIC Noise
Johnson Noise
TRkN bJ 4
TRkN bJ 4
Lower Resistance
8
USGS Sensor Testing Results
Magnitude 6.7 earthquake recorded
•Epicenter – Gulf of California
•>1250 km away from test facility (ABQ)
HP MEMS sensor matched reference sensor
down to 25 mHz
0 200 400 600 800 1000 1200 1400 1600 1800-2
-1
0
1
2x 10
5
Time [s]
AD
C C
ount
s H
P M
EM
S
0 200 400 600 800 1000 1200 1400 1600 1800-2
-1
0
1
2
3x 10
5
Time [s]
AD
C C
ount
s G
S-1
3
10-2
10-1
100
101
102
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
Frequency [Hz]U
nfilt
ered
Pow
er S
pect
ral D
ensi
ty [G
/rtH
z]
HP MEMS
Reference Seismometer
USGS High NoiseModel of the Earth
USGS Low NoiseModel of the Earth
9
Maximum Acceleration ranges from 80mg to 320mg Sensor Gain Modes
Lower gain results in higher accelerations
detected with lower power consumption
• (56mW @ 80mg Gain Mode)
• (43mW @ 320mg Gain Mode)
Lower gain trade-offs:
• Increased Noise Floor
• Higher THD @ full range
Gain mode is user selectable at any value
between max detectable accelerations of
80-320mg.
10
-0.15 -0.1 -0.05 0 0.05 0.1 0.15-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Displacement [m]
Out
put [
V]
Linear Response
Nonlinear Response
-3 -2 -1 0 1 2 3
-10
-8
-6
-4
-2
0
2
4
6
8
10
Displacement [m]
Out
put [
V]
Linear Response
Nonlinear Response
VOYAGER SENSOR nonlinearity Two main sources of nonlinearity
• Sinusoidal output due to design of electrode configuration • Non-linear forces from electrode voltages.
Both non-linearities are known functions of displacement and can be compensated for in the sensor processor before final data output
• Digital compensation to account for the known non-linear output of the sensor will be
implemented to achieve distortion requirement of < -80 db
11
Compensation Results Applied correction algorithm drastically reduces the error in the output
Simulation shows 30 dB reduction in THD
• THD at 68.4mG = <-90dB
0 5 10 15 20
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Time [ms]
Acc
eler
atio
n [G
]
Input
Uncorrected Output
Corrected Output
0 5 10 15 20
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Time [ms]
Acc
eler
atio
n [G
]
Input
Uncorrected Output
Corrected Output
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
Max Amplitude [G]
THD
[dB
]
Uncompensated
Compensated
12
Sensor Saturation Recovery Time
0 1 2 3 4 5 6 7 8 9-1
-0.5
0
0.5
1O
utp
ut
[V]
0 1 2 3 4 5 6 7 8 9-2
-1
0
1
2
Time [s]
Ou
tpu
t [V
]
16 bit
24 bit
0.0
0.5
1.0
1.5
2.0
2.5
0 0.1 0.2 0.3 0.4 0.5
Re
cov
ery
Tim
e (
Se
con
ds)
Acceleration (g)
Sensor Recovery Time vs Acceleration
320mg GainMode
80mg Gain Mode
Sensor ring-down after large acceleration input
13
Micro Controller on Sensor Board used for sensor self test processing
Sensor QC Self Tests
• Sensor On-Line Calibration Sensor can calibrate scale factor during data acquisition
• Ring-down Test Frequency, Time Constant determined
• High Frequency Noise Test Noise floor of sensor measured above resonance (Ambient Noise attenuated)
• ASIC Self Test Filter response
Amplifier High Freq Noise Test
• Tilt Detection
• Temperature
• RMS Noise
14
Conclusions The HP MEMS accelerometer has been optimized to meet the performance requirements for Seismic Imaging.
−Open-loop operation results in low power consumption (<56mW)
−MEMS mechanical frequency response flat to DC
−Cross Axis sensitivity demonstrated to be < -50db
• Noise floor < 13ng/rtHz
−On-Board Microcontroller enables on-line THD compensation, self tests and
calibration
Sensor not commercially available. HP and Shell are exploring options to bring sensor technology to market
15
Acknowledgements
HP Corvallis:
Rod Alley, Jenny Wu, ZZ Zhang, Bob Bicknell, Dennis Lazaroff, Dave Cook,
George Corrigan, Jeremy Sells, Mike Delos-Rey, Brian Homeijer (currently
with Sandia National Labs), Chris Davis
HP Labs Palo Alto:
Bob Walmsley, Pete Hartwell (Currently with Apple), Lenny Kiyama
Bob Hutt at the USGS ASL
HP Confidential Shell Confidential
Thank You