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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
ECE 5900/6900: Fundamentals of Sensor Design
Lecture 7Inertial Sensing with
Accelerometers and Gyroscopes
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Inertial Sensing
Q: What are we measuring?
A: Acceleration (accelerometers) and
Rate of Rotation or Angular Velocity (gyroscopes)
SI units: m/s2 (acceleration), rad/s (gyro)
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Inertial Sensing
Accelerometers
Analog Devices ADXL337
Gyroscopes
Texas Instruments TLV2772 STMicrelectronics LIS3DH
Ref: http://www.analog.com/media/en/news-marketing-collateral/product-selection-guide/MEMS_Inertial_Sensors_Selection_Tables.pdf
Analog Devices ADXRS646 MEMSIC VG800CA-200Bosch BMG160
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Applications of Accelerometer
Accelerometer can detect acceleration, displacement, tilt (angle of
orientation)
Smartphone: Up/Down, Sideways
Orientation
Ref: http://www.engadget.com/2012/05/22/the-engineer-guy-shows-how-a-smartphone-accelerometer-works/
Machine Vibration Measurement
for Condition Based Monitoring
Medical CPR Device:
measure the rate and depth
of chest compressions
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Applications of Gyroscope
Gyroscope can detect angular rate (angular velocity) or rate of
rotation
Automotive Safety and
controlMouse
Helicopter Inertial Measurement Unit (IMU)
Unmanned Aircraft System
(UAS)IMU
Ships Inertial Navigation
System (INS)
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Accelerometers
Gyroscopes
Inertial Measurement Unit (IMU)
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Basics of Accelerometer
Measurements performed by Accelerometer
Types of accelerations: Linear acceleration (deceleration),
Vibration (periodic acceleration and deceleration), Shock
(instantaneous acceleration), Tilt (a slow change in position with
respect to gravity)
Measured in g-force: low-g sensing (< 20g, human motion), high-g
sensing (motion in machines, vehicles, airplanes, ships)
Force Change in capacitance Converted to voltage A/D
Microprocessor to correct/perform an action
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Accelerometer: Performance Parameters
Measurement/Linear Range: +/- g
Sensitivity:
Ratio of change in acceleration as input to the output signal
Measured as mV/g for analog output, and LSB/g for digital
output
Zero-g bias level: output level without any acceleration
Noise density: µg/ √(Hz)
Frequency Response or
Bandwidth
Ref: J. Wu, et. al., "A low-noise low-offset capacitive sensing amplifier for a 50-μg/√Hz monolithic CMOS MEMS accelerometer,"
IEEE Solid-State Circuits, vol.39, no.5, pp. 722- 730, May 2004,
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Accelerometer: Performance Parameters
Analog Devices ADXL337 Datasheet
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
ADXL337 Schematic
Analog Devices ADXL337 Datasheet
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Evolution of Accelerometer
Analog Devices ADXL Series
Bosch Sensortec Series ASIC
MEMS
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Example of an Accelerometer System
Analog Devices IMU ADIS 16334
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Examples of MEMS Accelerometers
Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”,
M.S. Thesis, Carnegie Mellon University, May 2008
Ref: K. Sharma, et. al., “Design Optimization of
MEMS Comb Accelerometer”, ASEE Zone 1
Conference, Mar, 2009, West Point, NY
Ref:
http://www.princeton.edu/mae/people/faculty/soboyejo/re
search_group/research/mems/
Operational Principle
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Example of Triaxial MEMS Accelerometer [1/2]
Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Example of Triaxial MEMS Accelerometer [2/2]
Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Accelerometer Model
Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”, M.S. Thesis, Carnegie Mellon University, May 2008
Proof mass movement
changes due to the external
force
Movement is measured by
change in capacitance
between proof mass and
fixed electrodes
Common-mode output
signal for half-bridge or full-
bridge configuration
Higher sensitivity with lower
resonant frequency
Change in Voltage given
an acceleration
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Accelerometers
Gyroscopes
Inertial Measurement Unit (IMU)
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Coriolis Effect
Coriolis effect in action on the atmosphere
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Coriolis Force
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
GyroscopeMEMS Gyroscope principles
Proof mass and operational principle
Gyroscopes measure angular velocity or the rate of rotation
x
y
z
Coriolis Force
Gyro on rotating platform
= 2mΩz dr/dtmoving outward
=-2mΩz dr/dt moving inward
at
ar
Fc Fc
Ωz (constant)
Sense mode
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Gyroscope: Functional Operation
Capacitive sensing
Proof mass is driven by a periodic sinusoidal drive signal
On a rotating platform, Coriolis effect causes motion in the sense axis
Capacitance between the proof mass and sense plate(s) changes Sense electronics detect the Coriolis acceleration from the change in capacitance between the proof mass and the sense plate
The rate of rotation is derived from the Coriolis acceleration and the drive velocity
Digital output: Sense Electronics generate a pulse stream with frequency proportional to the acceleration Analog Output: Sense Electronics generate a voltage output proportional to the acceleration
Input AngularRate [deg/s]
Output Voltage(mV) Scale Factor
[mV/deg/s]
Comb Capacitor
Gyroscope TransferFunction
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Feb 22, 2011
Gyroscope: Performance Parameters
Zero-rate-output (ZRO)of gyroscope
Angular rate input range
Bandwidth (drive-mode) in which the gyroscope can produce a meaningful output (sense-mode)
Noise floorin the output ofgyroscope
Drive and sense electronics have an impact on the performance
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Gyroscope Model
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Examples of MEMS Gyroscope
Ref: C. Acar, et. al., “An Approach for Increasing Drive-Mode Bandwidth of MEMS Vibratory Gyroscopes”, Journal of MEMS, vol .14, no. 3, 2005
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Ref: S. Bhave, et. al., “An Integrated, Vertical-drive, In-plane-sense Microgyroscope”, 12th International Conference in Solid State
Sensors, Boston, June, 2003
Examples of MEMS Gyroscope
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Ref: S. Alper, et. al., “A high-performance silicon-on-insulator MEMS gyroscope operating at atmospheric pressure”, Sensors and Actuators A, vol.
135, pp. 34-42, 2007
Examples of MEMS Gyroscope
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Accelerometers
Gyroscopes
Inertial Measurement Unit (IMU)
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Inertial Measurement Unit (IMU)
IMUs provide motion, position, and navigational
sensing from a single device over more than 6 DOF
IMUs sense translational movement in three perpendicular axes
(surge, heave, sway) and rotational movement about three
perpendicular axes (roll, pitch, yaw)
Ref: http://www.instructables.com/id/9-Degrees-of-Freedom-IMU/
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Inertial Measurement Unit (IMU)IMU on PCBRef: ETH Zurich
GPS aided- altitude heading reference
system Ref: Moog
IMU: Gyroscopes are integrated with accelerometers,
magnetometers and GPS receivers
Silicon MEMS IMU by Silicon Sensing
9 Degrees of Freedom (DOF) IMU by
Sparkfun*
Ref: Magnetometers provide additional 3 DOF by compensating for change in magnetic field in Yaw (heading) measurement
https://sites.google.com/site/myimuestimationexperience/sensors/magnetometer
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
IMU in UAV/UAS
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