EE 4900: Fundamentals of Sensor Design
1
Lecture 7
Inertial Sensing with
Accelerometers and Gyroscopes
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Inertial Sensing
2
Q: What are we measuring?
A: Acceleration (accelerometers) and
Rate of Rotation or Angular Velocity (gyroscopes)
SI units: m/s2 (acceleration), rad/s (gyro)
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Inertial Sensing
3
Accelerometers
Analog Devices ADXL337
Texas Instruments TLV2772
STMicrelectronics LIS3DH
Gyroscopes
Analog Devices ADXRS646
Bosch BMG160
MEMSIC VG800CA-200
Ref: http://www.analog.com/media/en/news-marketing-collateral/product-selection-guide/MEMS_Inertial_Sensors_Selection_Tables.pdf
EE 4900 Fundamentals of Sensor Design
Suketu Naik
4
Applications of Accelerometer
Accelerometer can detect acceleration, displacement, tilt (angle of
orientation)
Smartphone: Up/Down, Sideways
Orientation
Medical CPR Device:
measure the rate and depth
of chest compressions
Machine Vibration Measurement
for Condition Based Monitoring
Ref: http://www.engadget.com/2012/05/22/the-engineer-guy-shows-how-a-smartphone-accelerometer-works/
EE 4900 Fundamentals of Sensor Design
Suketu Naik
5
Applications of Gyroscope
Gyroscope can detect angular rate (angular velocity) or rate of
Unmanned Aircraft System
rotation
Helicopter Inertial Measurement Unit (IMU)
Automotive Safety and
control
Mouse
EE 4900 Fundamentals of Sensor Design
(UAS)IMU
Ships Inertial Navigation
System (INS)
Suketu Naik
Types of Magnetic Sensors
6
 Accelerometers

 Gyroscopes
 Inertial Measurement Unit (IMU)
EE 4900 Fundamentals of Sensor Design
Suketu Naik
7
Basics of Accelerometer

Types of accelerations include linear acceleration (deceleration),
vibration (periodic acceleration and deceleration), shock (instantaneous
acceleration), tilt (a slow change in position with respect to gravity)

Measured by g-force: low-g sensing (< 20g, human motion), high-g
sensing (motion in machines, vehicles, airplanes, ships)

Force -> Change in capacitance -> Converted to voltage -> digitize ->
microprocessor to correct/perform an action

Measurements performed by Accelerometer
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Accelerometer: Performance Parameters




8
Measurement Range: +/- g (linear output range)
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
Ref: Analog Devices Datasheet
Zero-g bias level: output level with no
acceleration
Noise density: µg/ √(Hz)
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,
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Evolution of Accelerometer
9
Analog Devices ADXL Series
ASIC
Bosch Sensortec Series
MEMS
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Example of an Accelerometer System
10
Analog Devices IMU ADIS 16334
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Examples of MEMS Accelerometers
11
Operational Principle
Ref:
http://www.princeton.edu/mae/people/faculty/soboyejo/re
search_group/research/mems/
Ref: K. Sharma, et. al., “Design Optimization of
MEMS Comb Accelerometer”, ASEE Zone 1
Conference, Mar, 2009, West Point, NY
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”,
M.S. Thesis, Carnegie Mellon University, May 2008
Example of Triaxial MEMS Accelerometer [1/2]
12
Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Example of Triaxial MEMS Accelerometer [2/2]
Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013
EE 4900 Fundamentals of Sensor Design
13
Suketu Naik
Accelerometer Model




14
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 fullbridge configuration
Higher sensitivity with lower
resonant frequency
Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”, M.S. Thesis, Carnegie Mellon University, May 2008
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Types of Magnetic Sensors
15
 Accelerometers
 Gyroscopes

 Inertial Measurement Unit (IMU)
EE 4900 Fundamentals of Sensor Design
Suketu Naik
16
Coriolis Effect
Coriolis effect in action on the atmosphere
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Coriolis Force
EE 4900 Fundamentals of Sensor Design
17
Suketu Naik
18
Gyroscope
MEMS Gyroscope principles
Gyro on rotating platform
y
Ωz (constant)‫‏‬
z
Drive mode
Proof mass and operational principle
x
ar
Fc
Fc
at
Coriolis Force
= 2mΩz dr/dt
Sense
mode
moving outward
=-2mΩz dr/dt
moving inward
Gyroscopes measure angular velocity or the rate of rotation
EE 4900 Fundamentals of Sensor Design
Suketu Naik
19
Gyroscope: Functional Operation
Capacitive sensing
Comb Capacitor
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
Gyroscope Transfer
Function

Output
Voltage
(mV)
Analog
Output: Sense Electronics generate a
voltage output proportional to the
acceleration
EE 4900 Fundamentals of Sensor Design
Scale Factor
[mV/deg/s]
Input
Angular
Rate
[deg/s]
Suketu Naik
Gyroscope: Performance Parameters
Feb 22, 2011
20
Noise floor
in the output of
gyroscope
Zero-rate-output
(ZRO)
of gyroscope
Angular rate input range
Bandwidth (drive-mode)
in which the gyroscope
can produce a
meaningful output
(sense-mode)
Drive and sense electronics have an impact on the performance
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Gyroscope Model
EE 4900 Fundamentals of Sensor Design
21
Suketu Naik
Examples of MEMS Gyroscope
22
Ref: C. Acar, et. al., “An Approach for Increasing Drive-Mode Bandwidth of MEMS Vibratory Gyroscopes”, Journal of MEMS, vol .14, no. 3, 2005
EE 4900 Fundamentals of Sensor Design
Suketu Naik
23
Examples of MEMS Gyroscope
Ref: S. Bhave, et. al., “An Integrated, Vertical-drive, In-plane-sense Microgyroscope”, 12th International Conference in Solid State
Sensors, Boston, June, 2003
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Examples of MEMS Gyroscope
24
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
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Types of Magnetic Sensors
25
 Accelerometers
 Gyroscopes
 Inertial Measurement Unit (IMU)

EE 4900 Fundamentals of Sensor Design
Suketu Naik
Inertial Measurement Unit (IMU)
26
 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/
EE 4900 Fundamentals of Sensor Design
Suketu Naik
Inertial Measurement Unit (IMU)
IMU on PCB
27
Silicon MEMS IMU by Silicon Sensing
Ref: ETH Zurich
GPS aided- altitude heading reference
system Ref: Moog
9 Degrees of Freedom (DOF) IMU by
Sparkfun*
IMU: Gyroscopes are integrated with accelerometers,
magnetometers and GPS receivers
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
EE 4900 Fundamentals of Sensor Design
Suketu Naik
IMU in UAV/UAS
EE 4900 Fundamentals of Sensor Design
28
Suketu Naik