Dielectric nano-fluid for electrostatic machines and actuators
An electrostatic machine employs a high dielectric fluid comprised of a dielectric liquid with suspended dielectric particles. Electrorheological effects are minimized through small particle sizes and steric coatings on those particles limiting the minimum particle-to-particle distance. Low particle volume densities provide greater torque density with managed reduced viscosity.
1. An electrostatic machine comprising:
a first and second electrode separated across a gap and supported to provide relative motion between the first and second electrode from electrostatic force between the first and second electrode from an applied voltage across the first and second electrode; and
a substantially nonconductive dielectric fluid positioned within the gap, the dielectric fluid comprising:
(a) a dielectric liquid; and
(b) a plurality of dielectric particles suspended in the dielectric liquid and having a core material with a permittivity greater than that of the dielectric fluid and an outer coating having a lower permittivity than the permittivity of the core material, operative to reduce the formation of viscosity enhancing structures of the dielectric particles.
2. The electrostatic machine of claim 1 wherein the dielectric particles have an average diameter less than 50 nm.
3. The electrostatic machine of claim 2 wherein the dielectric particles have an average diameter of less than 15 nm.
4. The electrostatic machine of claim 1 wherein coating further has a permittivity no greater than the dielectric fluid.
5. The electrostatic machine of claim 4 wherein the coating provides stable suspension of the dielectric particles within the dielectric liquid.
6. The electrostatic machine of claim 4 wherein the coating separates the core dielectric material of adjacent dielectric particles by at least 0.1 nm.
7. The electrostatic machine of claim 4 herein the coating is an organosilicon compound.
8. The electrostatic machine of claim 4 wherein the dielectric liquid is a nonpolar fluid and the coating provides a nonpolar outer surface to the dielectric particle.
9. The electrostatic machine of claim 1 wherein the dielectric particle provides a core material selected from the group consisting of barium titanate, titanium dioxide, strontium titanate, barium/strontium titanate, and calcium titanate.
10. The electrostatic machine of claim 1 wherein a particle volume fraction of the dielectric particles within the dielectric liquid is greater than 0.05 and less than 0.3.
11. The electrostatic machine of claim 10 wherein the particle volume fraction of the dielectric particles within the dielectric liquid is greater than 0.15 and less than 0.25.
12. The electrostatic machine of claim 1 permittivity of the dielectric liquid is greater than three and less than 15.
13. The electrostatic machine of claim 1 wherein the dielectric particles have a relative permittivity of greater than 10.
14. The electrostatic machine of claim 1 wherein the dielectric particles have a relative permittivity greater than 10 times the relative permittivity of the dielectric liquid.
15. The electrostatic machine of claim 1 wherein the first and second electrodes are on a stator and rotor of an electrostatic machine.
16. The electrostatic machine of claim 15 wherein the electrodes of the stator and rotor are opposed axially along an axis of a shaft about which the rotor rotates.
17. The electrostatic machine of claim 15 wherein the electrodes of the stator and rotor are opposed radially along the line of radius from an axis about which the rotor rotates.
18. The electrostatic machine of claim 1 wherein the first and second electrodes are on opposite walls of a flexible pouch or bellows holding the dielectric liquid.
19. The electrostatic machine of claim 1 wherein the outer coating reduces a propensity of the suspended dielectric particles to form into chains.
20. The electrostatic machine of claim 1 wherein the suspended dielectric particles include individual particles that are suspended independently of other particles.