Electrostatically actuated device
View Patent ↗A device including a bottom electrode on a substrate and a top electrode on a substrate separated by a fixed distance from each other. Semi-insulator layers with proper electrical conductivity are attached to the bottom and top electrodes. Disposed between the substrates is a flexible S-shaped polymer stack having electrode layers with one end of the stack attached to the top substrate and the other end in contact with the bottom substrate. When a voltage is applied between the stack and the electrode layer on the bottom substrate, the stack is induced by electrostatic force to deflect in a rolling wave-like motion. While the voltage applied between the stack and bottom electrode is turned off, the static charges on the semi-insulator layer can move away quickly due to the proper electrical conductivity of the semi-insulator layer.
1. An actuator device driven by electrostatic forces, comprising:
a substrate having a smooth surface;
a substrate electrode forming a layer on the smooth surface;
a flexible membrane overlaying the substrate electrode, the flexible membrane including:
a flexible electrode layer,
a fixed portion attached to an underlying surface of the substrate, and
a movable portion that is movable with respect to the substrate electrode; and
a semi-insulator separating the substrate electrode from the flexible electrode layer and having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm.
2. The actuator device according to claim 1 , further comprising:
a second substrate having a second smooth surface;
a second substrate electrode forming a second layer on the second smooth surface;
the flexible membrane overlaying the substrate electrode or the second substrate electrode depending on a voltage differential applied between the second substrate electrode, the substrate electrode, and the flexible electrode layer, the flexible membrane further comprising:
a second fixed portion attached to a second underlying surface of the second substrate, and
the movable portion that is movable with respect to the substrate electrode and the second substrate electrode; and
a second semi-insulator separating the second substrate electrode from the flexible electrode layer, the second semi-insulator having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm; and
wherein the smooth surfaces are sufficiently smooth to allow adhesion between the smooth surfaces that are in contact.
3. The actuator device according to claim 1 , wherein the movable portion defines a generally constant air gap between the substrate electrode and the flexible membrane.
4. The actuator device according to claim 2 , wherein the movable portion defines a generally constant air gap between the second substrate electrode and the flexible electrode layer.
5. The actuator device according to claim 2 , wherein the movable portion defines a generally decreasing air gap between the second substrate electrode and the flexible electrode layer.
6. The actuator device according to claim 2 , wherein the flexible membrane defines a contact zone where an air gap decreases to zero at a location between the second substrate and the flexible membrane.
7. The actuator device according to claim 2 , wherein an air gap between the flexible membrane and the substrate or the second substrate generally maintains shape with or without a generation of an electrostatic force between the flexible electrode layer and the substrate electrode or the second substrate electrode.
8. The actuator device according to claim 2 , wherein the substrate electrode and the second substrate electrode underlie or overlie substantially an entire area of the movable portion of the flexible membrane.
9. The actuator device according to claim 2 , wherein the semi-insulator and the second semi-insulator are attached to, and overlie, the substrate electrode and the second substrate electrode, respectively.
10. The actuator device according to claim 2 , wherein surface areas of the substrate electrode and the second substrate electrode each comprise generally a same surface area as the flexible electrode layer.
11. The actuator device according to claim 2 , wherein a first shape of the substrate electrode and a second shape of the second substrate electrode are generally the same as a shape of the flexible electrode layer.
12. The actuator device according to claim 2 , wherein the flexible membrane has a generally rectangular shape.
13. The actuator device according to claim 2 , wherein the flexible membrane is generally curled away from the underlying substrate or the underlying second substrate when application of the voltage differential generates an electric field deflecting the flexible membrane in a rolling wave-like motion moving from the fixed portion to the second fixed portion or from the second fixed portion to the fixed portion.
14. The actuator device according to claim 2 , comprising an electro-thermally responsive device, wherein the flexible membrane transduces between electrical energy and heat energy.
15. The actuator device according to claim 14 , wherein the flexible membrane is an electromechanically responsive membrane comprising an even number of stacked electromechanically responsive layers and the flexible electrode layer between adjacent electromechanically responsive layers.
16. The actuator device according to claim 1 , wherein the movable portion defines a generally decreasing air gap between the substrate electrode and the flexible electrode layer.
17. The actuator device according to claim 1 , wherein the flexible membrane defines a contact zone where an air gap decreases to zero at a location between the substrate and the flexible membrane.
18. An electrostatically actuated electrocaloric cooling device, comprising:
a first substrate defining a smooth surface;
a first substrate electrode forming a layer on the smooth surface of the first substrate;
a second substrate defining a smooth surface;
a second substrate electrode forming a layer on the smooth surface of the second substrate;
a flexible electrocaloric stack including two layers comprising polymers and three flexible electrode layers, the flexible electrocaloric stack overlaying the first substrate electrode or the second substrate electrode depending on a voltage differential applied between the first substrate electrode, the second substrate electrode, and the flexible electrode layer, the flexible electrocaloric stack further including:
a first fixed portion attached to an underlying surface of the first substrate,
a second fixed portion attached to an underlying surface of the second substrate, and
a movable portion that is movable with respect to the first substrate electrode and the second substrate electrode,
a first semi-insulator separating the first substrate electrode from the flexible electrocaloric stack and having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm; and
a second semi-insulator separating the second substrate electrode from the flexible electrocaloric stack and having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm; and
a voltage source, wherein an application of a voltage differential between the flexible electrode layer and the first substrate electrode or the second substrate electrode creates an electrostatic force moving the movable portion to attach the movable portion to the first substrate or the second substrate; and
wherein:
an application of a voltage differential on said flexible electrocaloric stack creates a temperature difference absorbing heat from said first substrate and transferring the heat to said second substrate, and
a major portion of the first semi-insulator and the second semi-insulator comprises a polymer.
19. The device of claim 18 , wherein:
the polymer comprises polyimide, polyurethane, polyacrylate, polyvinylidene fluoride or polydimethylsiloxane and a conductive component comprising graphite powder, one or more carbon nanotubes, graphene, one or more metal nanowires, one or more metal nanoparticles, or a conductive polymer,
the electrodes of the flexible electrocaloric stack comprise one or more carbon nanotubes, one or more silver nanowires, one or more copper nanowires, one or more conducting polymers, or a layer of metal,
the first semi-insulator and the second semi-insulator each independently comprise a layer having a thickness of 0.2-100 μm,
the flexible electrocaloric stack has a thickness of 1-50 μm, and
the smooth surfaces are sufficiently smooth to allow adhesion between the smooth surfaces that are in contact.
20. An electrocaloric cooling device, comprising:
a first substrate electrode;
a first semi-insulator layer on the first substrate electrode and having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm;
a second substrate electrode;
a second semi-insulator layer having a bulk electrical resistivity greater than 10 7 Ωcm but less than 10 13 Ωcm but less than 10 13 Ωcm; and
a flexible membrane comprising a flexible electrode moving between a first physical contact with the first semi-insulator layer and a second physical contact with the second semi-insulator layer in response to a voltage differential applied between the flexible electrode, the second substrate electrode, and the first substrate electrode.