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Electromagnetic actuators capable of generating a symmetrical bidirectional force are disclosed. The electromagnetic actuators include a housing made of a ferromagnetic material and a shaft made of a magnetically inert material movable along an axis within the housing. In one type of actuator, capti

Electromagnetic actuators capable of generating a symmetrical bidirectional force are disclosed. The electromagnetic actuators include a housing made of a ferromagnetic material and a shaft made of a magnetically inert material movable along an axis within the housing. In one type of actuator, captive permanent magnets are arranged on opposite interior end walls of the housing and an electromagnetic coil is mounted on a central portion of the shaft. The electromagnetic coil is capable of generating a force when energized that causes linear displacement of the shaft in either direction along its axis depending on the direction of current through the electromagnetic coil. In another type of actuator, captive electromagnetic coils are arranged on opposing inner end walls of the housing, and a permanent magnet is mounted on a central portion of the shaft. The electromagnetic coils are capable of generating a force when energized that causes linear displacement of the shaft in either direction along its axis depending on a direction of current through the electromagnetic coils.

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1. An electromagnetic actuator capable of generating a symmetrical bidirectional force comprising: a housing comprising a ferromagnetic material, wherein the housing has a first end wall, a second end wall opposite the first end wall, and a side wall interconnecting the first and second end walls;a

1. An electromagnetic actuator capable of generating a symmetrical bidirectional force comprising: a housing comprising a ferromagnetic material, wherein the housing has a first end wall, a second end wall opposite the first end wall, and a side wall interconnecting the first and second end walls;a first captive permanent magnet arranged on the first end wall and having an inward facing pole;a second captive permanent magnet arranged on the second end wall and having an inward facing pole arranged to repel the inward facing pole of the first permanent magnet causing the first and second permanent magnets to have opposing magnetic fields;a shaft comprising a magnetically inert material, wherein the shaft is movable along a longitudinal axis extending between the first and second end walls, and comprises a central portion interposed between the first and second permanent magnets; andan electromagnetic coil arranged on the central portion of the shaft, wherein the electromagnetic coil is capable of generating a force when energized that causes linear displacement of the shaft in either direction along the longitudinal axis depending on a direction of current through the electromagnetic coil. 2. The electromagnetic actuator according to claim 1, wherein the housing defines a central cavity;the first permanent magnet is arranged on an inner surface of the first end wall, and wherein a first zone comprising a non-ferromagnetic material is interposed between an outer side surface of the first permanent magnet and an inner surface of the side wall;the second permanent magnet is arranged on an inner surface of the second end wall, and wherein a second zone comprising a non-ferromagnetic material is interposed between an outer side surface of the second permanent magnet and the inner surface of the side wall;the central portion of the shaft is arranged in the central cavity of the housing; andan air gap is interposed between an outer surface of the electromagnetic coil and the inner surface of the side wall. 3. The electromagnetic actuator according to claim 2, wherein the first zone comprises a first air gap, and the second zone comprises a second air gap. 4. The electromagnetic actuator according to claim 2, wherein the shaft is central to and parallel with the side wall, and perpendicular to the first and second end walls. 5. The electromagnetic actuator according to claim 1, wherein the first end wall has a first central opening, and the second end wall has a second central opening;the first permanent magnet has a first central hole;the second permanent magnet has a second central hole; andthe shaft has a first end portion extending through the first central hole and the first central opening, and a second end portion extending through the second central hole and the second central opening. 6. The electromagnetic actuator according to claim 1, wherein the ferromagnetic material comprises a soft ferromagnetic material having a relative permeability of at least 750μr. 7. The electromagnetic actuator according to claim 1, wherein the ferromagnetic material comprises 400 series stainless steel, 416 stainless steel, mild steel, soft iron, an iron-silicon alloy, an iron-cobalt-vanadium alloy, or a combination thereof. 8. The electromagnetic actuator according to claim 1, wherein the first permanent magnet and/or the second permanent magnet comprise an assembly of permanent magnets. 9. The electromagnetic actuator according to claim 1, wherein the first permanent magnet and the second permanent magnet comprise a permanent magnet or an assembly of permanent magnets having a maximum energy product (BHmax) of greater than 16 megaGauss-Oersteds. 10. The electromagnetic actuator according to claim 1, wherein the first permanent magnet and the second permanent magnet comprise a neodymium-iron-boron magnet, an assembly of neodymium-iron-boron magnets, a samarium-cobalt alloy magnet, an assembly of samarium-cobalt alloy magnets, or a combination thereof. 11. The electromagnetic actuator according to claim 1, wherein the magnetically inert material comprises fiber reinforced resin, fiber reinforced epoxy resin, fiberglass reinforced resin, fiberglass reinforced epoxy resin, carbon fiber reinforced resin, carbon fiber reinforced epoxy resin, aramid fiber reinforced resin, aramid fiber reinforced epoxy resin, or a combination thereof. 12. The electromagnetic actuator according to claim 1, wherein the electromagnetic coil comprises a multi-coil assembly of electromagnetic coils. 13. The electromagnetic actuator according to claim 1, wherein the electromagnetic coil has increasing numbers of wire turns with increasing distance from the longitudinal axis. 14. The electromagnetic actuator according to claim 1, wherein the electromagnetic coil comprises an insulated conductive wire, an insulated copper magnet wire, an insulated aluminum wire, an insulated copper-coated aluminum wire, or a combination thereof. 15. The electromagnetic actuator according to claim 1, further comprising a magnetic field tuning element comprising a permanent magnet or an assembly of permanent magnets located on or in the side wall. 16. The electromagnetic actuator according to claim 15, wherein the permanent magnet and/or or the assembly of permanent magnets of the magnetic field focusing element comprises a neodymium-iron-boron magnet, an assembly of neodymium-iron-boron magnets, a samarium-cobalt alloy magnet, an assembly of samarium-cobalt alloy magnets, or a combination thereof. 17. The electromagnetic actuator according to claim 1, further comprising a magnetic field focusing element comprising an assembly of permanent magnets circumferentially positioned on or in the side wall to form a ring magnet that is polarized in a radial direction perpendicular to the longitudinal axis. 18. The electromagnetic actuator according to claim 1, wherein a core of an axial cancellation field comprising a substantially reduced magnetic field and a substantially reduced flux density extends along the longitudinal axis between the first and second permanent magnets having opposing magnetic fields. 19. The electromagnetic actuator according to claim 1, wherein a core of a radial cancellation field comprising a substantially reduced magnetic field and a substantially reduced flux density extends from the central portion of the shaft in a plane perpendicular to the longitudinal axis. 20. The electromagnetic actuator according to claim 1, wherein a substantially constant force that is linearly proportional to a drive current is generated over at least 90 percent of an actuation distance of the bidirectional linear displacement of the shaft along the longitudinal axis. 21. The electromagnetic actuator according to claim 20, wherein the substantially constant force is generated at opposite ends of travel of the electromagnetic coil. 22. The electromagnetic actuator according to claim 1, which exhibits a substantially uniform force at all displacement distances within an actuation range between the first and second permanent magnets in the absence of latching forces. 23. The electromagnetic actuator according to claim 1, wherein the actuator generates linear and bidirectional movement or force in the absence of an elastic element, a mechanical return element, or a spring.