MEMS sensors are microelectromechanical systems that use mechanical and electrical components to detect and measure physical quantities. There are several types of MEMS sensors including inertial, optical, pressure, and chemical sensors. Common MEMS sensors are used in smartphones for functions like orientation detection, motion sensing, proximity detection, ambient light sensing, and fingerprint scanning. Other applications of MEMS sensors include robot vacuums that use infrared, cliff, and object sensors to navigate, and smartwatches that measure heart rate using green LEDs, infrared light, or a combination. Emerging applications of MEMS sensors include molecular identification sensors and 3D scanners.

1. MEMS Sensors
An introduction to MEMS sensors, current applications, and their future
Presented by Jennifer Chin
September 2nd, 2016
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2. Preface
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3. MEMS Sensors
A system that uses mechanical devices and electrical signals
Micro
Electrical Sensing
Mechanical
Systems
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4. How they Sense
Capacitive Sensing
Measures properties of conductive material
Piezoelectric Sensing
Measures properties by converting mechanical force into electrical charge
Piezoresistive Sensing
Measures properties by converting mechanical force into electrical resistance 4

5. Active Sensors
Actively scans surroundings and compiles data to compare and measure
changes
Relies on transmissions and feedback to detect changes in the area of coverage
Sends out a signal (i.e. microwave pulses, ultrasonic frequencies, or radio waves)
that bounces off a target, and gathers data from the sensor upon reflection
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6. Passive Sensors
Detects and responds to inputs from the physical environment without producing
any transmissions
Passive sensors activate after detecting environmental inputs such as vibrations,
light, radiation, heat, or other physical signals occurring in the sensor’s
environment
Ex. Mechanical Sensors
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7. Types of MEMS Sensors
1. Inertial
2. Optical
3. Pressure
4. Chemical
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8. Sensors in Use Today
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9. iPhone 5s and Up
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Main Sensors
1. Three-Axis Gyroscope
2. Accelerometer
3. Proximity Sensor
4. Ambient Light Sensor
5. Touch ID Fingerprint Sensor
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10. 3-Axis Gyroscope and Accelerometer
- Gyroscope: Sensor that assumes orientation
through spinning wheel with free axis rotation
- Uses: Autofocus on camera and landscape viewing of
photos and keyboard
- Accelerometer: Sensor that measures
acceleration of a moving or vibrating object
- Uses vary from Maps application to pedometers to app
store games
Passive/Inertial
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11. Proximity Sensor
- Shuts off illumination and touch sensitivity when
sensor is activated
- How it Works: Emits an electromagnetic beam and
looks for changes in the return signal
Active/Optical
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12. Ambient Light Sensor
- Senses lighting and adjusts screen brightness
accordingly
- How it Works: Uses a photodiode that converts
light into current and voltage
- Can perceive brightness just as our eyes can
Passive/Optical
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13. Touch ID Fingerprint Sensor
- Scans finger to unlock iPhone
- How it Works: Uses capacitive sensing to
scan and read fingerprint
- Capacitive Sensing: When a finger hits the
screen, an electrical charge is transferred to the
finger. This completes the circuit, creating a
voltage drop at a specific point on the screen.
Passive/Capacitive
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14. iRobot: Roomba
Uses sensors to navigate itself throughout
room and vacuum
Main Sensors:
1. Infrared Transmitter/Receiver
2. Object Sensor
3. Cliff Sensors
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15. Infrared Transmitter/Receiver
- Roomba uses infrared transmitter and receiver to
roughly map out and measure the room
- How it Works: The sensor sends out an infrared
signal through the transmitter and analyzes the return
time to the receiver
Active/Optical
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16. Object Sensor
- When Roomba bumps into a wall or an
object, it backs up and changes direction
- How it Works: Behind the bumper is the
object sensor. When the bumper retracts the
object sensor is activated
Passive/Inertial
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17. Cliff Sensor
- Roomba uses cliff sensors to avoid going
down stairs
- How it Works: The cliff sensors send out
infrared signals. If they do not return
immediately, Roomba changes direction.
Active/Optical
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18. Collaboration of Sensors
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19. Apple Watch: Heart Rate Sensor
Measures heart rate throughout the day so
users can check it at a glance
Main Sensors:
1. Green LEDs
2. Infrared Light Blasters
3. Photodiode Sensors
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20. Method 1: Green LEDs*
1. Green LEDs flash hundreds of times per second
1. Photodiode Sensor measures the absorption of the LEDs
a. Red blood absorbs green light and reflects red light
b. When blood is flowing, the absorption is higher than in between heart beats
* High power consumption
Active/Optical 20

21. Method 2: Infrared Light Blasters*
1. Infrared Light
a. Shoots out to measure heart rate about every 10 minutes
1. Photodiode Sensor measures the absorption of infrared light
a. Non-visible light can also be absorbed
b. Same concept as Method 1
* Not as reliable as Green LEDs 21

22. Sensors in the Future
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23. SCiO: Molecular Sensor
Reads the chemical make up of materials using
Near-Infrared sensors
Main Sensor:
1. Near-Infrared Sensor (NIR)
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24. Near-Infrared (NIR) Sensor
SCiO uses the NIR optical sensor to read and analyze
the chemical make up of organic materials
How it Works: The NIR sensor emits a near-infrared
light that is then reflected back from the object. The
NIR light is broken down into a spectrum and read by
the transmitter
Optical/Active
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25. Structure Sensor (3D Scanner)
Portable device that takes a rapid 3D scan of
objects and people
Main Sensor:
1. Infrared Sensor
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26. Infrared (IR) Sensor
Structure Sensor uses two infrared sensors to
measure the depth and distance of objects in
order to create a 3D scan.
How it Works: The IR sensor uses a specific
receiver selected to read the IR signal. The
receiver measures the intensity of the return signal
and determines the distance of the object
Active/Optical
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27. 謝謝你的照顧和教導
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