Thermal Energy can cause physical changes to materials such as
- Thermal expansion . contraction
- Electrical resistance
- Optical Radiation emission
- Phase changes
MEMs devices can transduce thermal energy to create
Microactuators and microsensors
Two types of microactuators
Thermal bimorph
Fluid dispensers
Three types of micro sensors are
- Thermal bimorph
- micro thermocouples
- Thermo resistive sensors
What do inkjet printers use?
The phase change aspect of microthermal actuation
What principle for bimorph actuators operate on?
Differential thermal expansion produces motion
> Width differential in two different arms creates one arm with a large heat sink and a temp differential. This causes one side to heat up and expand. Bending at the thin flexure
Four modes of heat transfer
- conduction (through solid matter)
- natural thermal convection (from surface into stationary fluid)
- Forced convection ( from surface into a moving fluid)
- Radiation ( electromagnetic radiation through air or vacuum from a surface)
Thermal heat capacity is analogous to
electrical capacitance
Thermocouples work by ___
- two wires of dissimilar materials joined at one point
- transduces, and coverts thermal energy into electrical energy
The seebeck coefficient describes__
The voltage difference developed for a given temperature difference
What is a thermister?
A thermal resistor with significant temp sensitivity
4 point probe measurement
- Uses voltmeter and ammeter.
- No v drops across the probes
- ## The current through the ammeter is the current under test
How does a pirani gauge work?
- thermal conduction across a gap is related to the mean free path of the gas in the gap
- thermal conduction can then be related to gas pressure
How does a MEMs thermal accelerometer work?
A bubble of hot air is created between two temp sensors.
- under acceleration, the bubble will move in the opposite direction of acceleration (buoyancy), setting off one of the temp sensors
Hot wire anemometry is used for
Measuring fluid velocity
Thermal bubble anemometer
Uses the same structure as a thermal accelerometer, using forced convection rather than acceleration to move thermal bubble
