Electromagnetically controlled segmented mirror, electromagnetic actuator for use therein and method for manufacturing the same

A mirror comprising:

• an actuator array with a plurality of spatially distributed electromagnetic actuators,
• a plurality of mirror segments which are movable relative to each other, respective mirror segments being mechanically coupled to an actuation rod of a respective electromagnetic actuator of the actuator array,
• wherein the electromagnetic actuators each comprise a soft-ferromagnetic yoke, with an at least substantially cylindrical circumferential wall covered at a first end with a base and at a second end with a top,
• wherein the circumferential wall defines an axis in an axial direction from the base end to the top,
• wherein the soft-ferromagnetic yoke comprises, in the axial direction, a base yoke section, an intermediate yoke section and a top yoke section,
• wherein the base yoke section forms the base and a first axial section of the circumferential wall, as well as a base protrusion surrounded with space by the first axial section of the circumferential wall,
• wherein the intermediate yoke section forms a second axial section of the circumferential wall, and
• wherein the top yoke section forms the top and a third axial section of the circumferential wall, as well as a top protrusion surrounded with space by the third axial section of the circumferential wall,
• wherein the base yoke section and/or the top yoke section house an electromagnetic coil in the space between their protrusion and their axial section of the circumferential wall,
• wherein the intermediate yoke section holds at least one permanent magnet fixed with a first magnetic pole facing an inner surface of the cylindrical wall, and with a second magnetic pole facing an inner space in the intermediate yoke section,
• wherein the permanent magnet exerts an attractive force having negative stiffness on an axially movable core element housed in the inner space,
• wherein at least one of the base and the top define an axially extending opening through which protrudes an actuation rod fixed to the axially movable core element,
• wherein the actuator further comprises:
• a first membrane and a second membrane of an at least substantially non-magnetic material,
• wherein the first membrane is arranged between the base yoke section and the intermediate yoke section and
• wherein the second membrane is arranged between the intermediate yoke section and the top yoke section,
• wherein the axially movable core element is flexibly restrained between the first and the second membrane, and
• wherein the first membrane and the second membrane, together, form a resilient element having a stiffness with a value that is equal to or greater than a magnitude of the negative stiffness.