Biomedical Engineering Reference
In-Depth Information
actuation. in. both. directions,. the. stroke. of. the. mirror. can. be. increased. and. it. can. be. actuated. from.
its. neutral. position. (i.e.,. no. applied. voltage). rather. than. from. an. intermediate. position. as. is. typically.
obtained.by.the.application.of.an.ofset.bias.for.unidirectional.actuation.(Bonora.2006,.2010).
8.6.5 Magnetically Actuated Membrane Mirrors
he. membrane. mirrors. from. Imagine. Optics. and. ALPAO. use. electromagnetic. actuators. to. deform. a.
mirror.membrane.that.is.clamped.around.the.edge..he.membrane.has.small.magnets.bonded.to.it.that.
can.be.attracted.or.repelled.by.a.current.induced.in.opposing.induction.coils,.as.shown.in.Figure.8.29.
he.magnetically.actuated.DM52.(52.actuator).deformable.membrane.mirror.from.ALPAO.is.able.to.
generate.the.Zernike.polynomials.up.through.the.fourth.order.with.over.10.μm.of.surface.deformation,.
as. shown. in. Table. 8.2.. Higher-order. mirrors. with. additional. actuators. (88,. 97,. 241). are. able. to. make.
higher-accuracy.corrections.and/or.larger.amplitude.Zernike.corrections,.as.shown.in.
Figure.8.30
.
ALPAO.also.ofers.a.high-speed.version.of.their.DM..he.ALPAO.97.high-speed.DM.has.a.settling.
time.of.less.than.1.ms,.as.shown.in.
Figure.8.31
,
.ofering.high-bandwidth.(>900.Hz).correction.for.mak-
ing.fast.corrections.of.rapidly.changing.phenomenon.
8.6.6 electrostatically Actuated continuous Facesheet
Microelectromechanical System Mirrors
MEMS.DMs.are.so.named.by.the.MEMS.fabrication.processes.that.are.used.to.fabricate.them..Rather.
than.the.bulk.micromachining.and.bonding.process.that.is.used.for.membrane.mirrors,.MEMS.mirrors.
typically. use. the. surface. micromachining. process.. his. allows. for. fabrication. of. complex. structures,.
enabling.more.localized.actuation.for.high-order.correction.
FIGuRE 8.29
Magnetically.actuated.deformable.membrane.mirror..An.array.of.magnetic.“voice”.coils.each.cre-
ates.a.localized.magnetic.ield.when.a.current.is.passed.through.them..he.direction.of.the.ield.can.be.controlled.
by.the.direction.of.the.current..An.array.of.permanent.magnets.is.bonded.to.a.lexible.membrane..When.the.elec-
tromagnets. are. powered,. they. induce. a. force,. either. attractive. or. repulsive,. between. the. coil. and. the. permanent.
magnet,.pushing.or.pulling.on.the.membrane.
TABlE 8.2
ALPAO.Hi-Speed.Deformable.Mirror.Characteristics
Array.Size.(Order)
37
52
69
97
88
241
Stroke.(μm).Tip-Tilt
±60
±20
Stroke.(μm).3.×.3.Array
>30
>14
Stroke.(μm).Inter-Actuator
>3
>3
Aperture.Diameter.(mm)
7.5
9.0
10.5
13.5
15
20
Pitch.(mm)
1.5
2.5
Bandwidth.(Hz)
>750
>750
