Thermoelastic device comprising an expansive element formed from a preselected material
View Patent ↗A thermoelastic device comprising an expansive element is disclosed. The expansive element is formed from a material, which is preselected by calculating a dimensionless constant for the material. The dimensionless constant is indicative of the potential effectiveness of the material in a particular application, such as a micro-electromechanical system.
1. A thermoelastic device comprising an expansive element formed from a preselected material, said material being selected on the basis of ε, wherein εγ is a dimensionless constant for that material in accordance with the formula:
ɛ
γ
=
E
γ
2
T
ρ
C
wherein E is the Young's modulus of the material; γ is the coefficient of thermal expansion; T is the maximum operating temperature, ρ is the density and C is the specific heat capacity, and
the preselected material is selected from the group including silicides and carbides of titanium; borides, silicides, carbides and nitrides of tantalum, molybdenum, niobium, chromium, tungsten, vanadium, and zirconium.
2. The thermoelastic device of claim 1 , wherein the dimensionless constant is normalized relative to that of silicon to a value ε, said normalized value being calculated by deriving the value εγ for the preselected material at the relevant temperature value and dividing this by the value of ε obtained for silicon at that same temperature.
3. The thermoelastic device of claim 1 , wherein the preselected material is selected on the basis of both mε and ε, where
m
ɛ
=
ⅆ
ɛ
ⅆ
T
=
E
γ
2
ρ
C
[
N
/
m
2
1
/
°
C
.
2
kg
/
m
3
Nm
/
kg°
C
.
]
[
(
EQ6
)
]
4. The thermoelastic device of claim 1 , wherein the preselected material is further selected on the basis that it has a pre-determined resistivity range.
5. The thermoelastic device of claim 4 , wherein the resistivity range is between 0.1 μΩm and 10.0 μΩm.
6. The thermoelastic material of claim 1 , wherein the preselected material is further selected on the basis that it has at least one of the following properties:
a resistivity between 0.1 μΩm and 10.0 μΩm;
chemically inert in air;
chemically inert in the chosen ink; or
depositable by CVD, sputtering or other thin film deposition technique.
7. The thermoelastic device of claim 1 , which is a thermal bend actuator.
8. A micro-electromechanical system comprising one or more thermoelastic devices according to claim 7 .