Case Studies Flashcards
(17 cards)
Give an overview of how a MEMS device is used in: Smartphones – MEMS Accelerometer
MEMS Device: Capacitive accelerometer
Function: Detects orientation, motion, and gestures (e.g., screen rotation, step counting). It uses a suspended mass and fixed electrodes to measure acceleration via changes in capacitance.
Give an overview of how a MEMS device is used in: Digital Microphones – MEMS Diaphragm
MEMS Device: MEMS diaphragm
Function: Converts sound waves into electrical signals. A thin diaphragm vibrates in response to sound pressure, changing capacitance between it and a fixed backplate.
Give an overview of how a MEMS device is used in: Inkjet Printers – MEMS Thermal Actuator
MEMS Device: Thermal bubble actuator (can include cantilevers)
Function:
A Microheater heats ink to form a bubble in a chamber inside a nozzel.
The exampsion of ink ejects a droplet through the nozzle.
The vacuum formed as ink cools draws more ink into the chamber from a resevoir.
Some designs use cantilever-like structures to control ink flow.
Give an overview of how a MEMS device is used in: Automotive Airbags – MEMS Accelerometer
MEMS Device: Capacitive accelerometer
Function: Detects rapid deceleration during a crash and triggers airbag deployment. The MEMS sensor measures sudden changes in velocity.
Also used in:
* Laptop Freefall Sensor
Parks the harddrive during freefall to prevent data loss.
* Pacemaker
Detects physical activity levels to adjust pacing rate accordingly.
Give an overview of how a MEMS device is used in: Hearing Aids – MEMS Microphone
MEMS Device: MEMS diaphragm
Function: Captures sound with high sensitivity and low power consumption. The diaphragm vibrates with sound pressure, modulating an electrical signal.
Give an overview of how a MEMS device is used in: Atomic Force Microscopes (AFM) – MEMS Cantilever
MEMS Device: Cantilever with a sharp tip
Function: Scans surfaces at the nanoscale. The cantilever deflects due to atomic forces, and this deflection is measured to create high-resolution images.
Give an overview of how a MEMS device is used in: Gyroscopes in Drones – MEMS Vibrating Structure Gyroscope
MEMS Device: Vibrating resonator
Function: Measures angular velocity. A vibrating mass experiences Coriolis forces when the device rotates, altering the vibration pattern.
Also used in:
* Fitness Tracker
Give an overview of how a MEMS device is used in: Projectors (DLP) – MEMS Micromirrors
MEMS Device: Micromirror array (uses torsional actuators)
Function: Each mirror tilts to reflect light toward or away from the screen, creating pixels. Actuation is often electrostatic, similar to parallel plate actuators.
Give an overview of how a MEMS device is used in: Optical Switches – MEMS Parallel Plate Actuator
MEMS Device: Electrostatic parallel plate actuator
Function: Moves mirrors or shutters to redirect light paths in fiber optic networks. Voltage applied between plates causes movement via electrostatic attraction.
Give an overview of how a MEMS device is used in: Pressure Sensors – MEMS Diaphragm
MEMS Device: Piezoresistive or capacitive diaphragm
Function: Measures pressure changes in automotive, medical, or industrial systems. Pressure deforms the diaphragm, altering resistance or capacitance.
Give an overview of how a MEMS device is used in: Smart Watches – MEMS Pressure Sensor
MEMS Device: Capacitive or piezoresistive diaphragm
Function: Measures barometric pressure to estimate altitude changes (e.g., stair climbing).
Also used in:
* Tyre Pressure Sensor
Give an overview of how a MEMS device is used in: Smart Inhalers – MEMS Air Flow Sensor
MEMS Device: MEMS cantilever air flow sensor
Function: Detects inhalation to trigger medication release and monitor usage.
A microscale cantilever is suspended in the airflow path.
When the user inhales, the airflow bends the cantilever.
The amount of deflection is measured (via piezoresistive or capacitive sensing) and used to calculate inhalation strength and duration.
Give an overview of how a MEMS device is used in: Insulin Pump – Thermal MEMS Flow Sensor
MEMS Device: Thermal flow sensor
Function: Precisely controls and monitors insulin delivery rates.
A tiny heater is placed between two temperature sensors on a microchannel.
When insulin flows through the channel, it carries heat downstream.
The temperature difference between the upstream and downstream sensors is proportional to the flow rate.
Give an overview of how a MEMS device is used in: Optical Image Stabilization in Cameras – MEMS Actuator
MEMS Device: Electrostatic or electromagnetic actuator
Function: Moves the lens or sensor to counteract hand shake and stabilize images.
What are some different MEMS accelerometer designs?
1) Capacitive (eg. cantilever structures or resonators)
2) Piezoelectric (low power!)
3) Piezoresistive
4) Thermal (heated gas bubble displacement)
How do resonance based accelerometers work?
- Resonating Element: A micro-scale beam or structure vibrates at a natural frequency.
- Acceleration Effect: When acceleration is applied, it causes a stress or strain on the resonator.
- Frequency Shift: This stress changes the tension in the resonator, altering its resonant frequency.
- Measurement: The shift in frequency is measured and correlated to the applied acceleration.
How do Thermal Acelerometers work?
based on convection.
- Heater Element: A tiny heater is placed at the center of a sealed cavity filled with gas (like air or argon).
- Temperature Sensors: Temperature sensors are symmetrically placed around the heater.
At Rest: When there’s no acceleration, the heat distribution is symmetrical.
Under Acceleration: Acceleration causes the heated gas bubble to shift due to inertia, changing the temperature distribution. - Measurement: The temperature difference between sensors is proportional to the applied acceleration.
Advantages:
* No moving mechanical parts → high shock resistance.
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Limitations:
* Lower sensitivity and slower response time compared to capacitive or piezoelectric types.
* Performance can be affected by ambient temperature.
