Biomedical Engineering Reference
In-Depth Information
slightly.different.in.each.case..In.
P. ulysses
,.the.concavities.are.broad.and.shallow.with.a.
multilayer.containing.10.layers.of.air.pockets,.similar.to.those.seen.in.the.feathers.of.birds..
They. generally. measure. in. the. range. of. 90-100. nm. deep. and. follow. the. contours. of. the.
concavity..Furthermore,.a.form.of.ridges.is.present.between.the.concavities.running.along.
the.length.of.the.scales,.and.the.concavities.undulate.along.the.length.of.the.scale.rather.
than.having.any.ribs..This.structure.has.a.primary.relection.peak.of.460.nm..Similarly.to.
Chrysiridia ripheus
,.the.concavities.in.the.scales.of.
P. palinurus
.contain.a.two-dimensional.
(2D).retro-relector.that.allows.for.limited.polarization.conversion.around.an.axis.parallel.
to.the.ridges.
In. contrast,. the. scales. on.
P. palinurus
,. while. very. similar,. have. concavities. that. are.
approximately.hemispherical..These.are.separated.along.the.length.of.the.scale.by.ribs.of.
construction.similar.to.that.of.the.ridges.running.down.the.scale,.although.these.ridges.
do.not.contain.lamella,.as.seen.in.scales.in.the.butterlies.of.the.
Morpho
.family..Unlike.the.
scales. of.
P. ulysses
,. it. is. possible. for. the. concavities. in. the. scales. of.
P. palinurus
. to. rotate.
polarized.light.of.any.initial.orientation.through.90°.due.to.multiple.relections.from.the.
high-angled.sides.of.the.concavities.that.have.an.almost.circular.symmetry.
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The.yellow.relection.from.the.base.of.the.concavity.has.a.spectrum.centered.around.540.
nm..The.blue.relection.from.the.sides.is.caused.by.the.opposing.sides.acting.as.retro-relect-
ing.surfaces,.with.both.relections.occurring.at.a.higher.angle.of.incidence,.around.45°,.such.
that.the.peak.is.signiicantly.blue.shifted..The.result.is.a.combination.of.yellow.spots.with.a.
blue.annulus.that.appears.macroscopically.green.due.to.a.pointillistic.mixing.effect.
16
25.1.3
Morpho Rhetnor
and
Morpho didius
Not.all.butterlies.have.color.producing.structures.within.the.bulk.of.their.scales..An.excel-
lent.example.of.scales.with.surface.structures.is.from.the.members.of.the.
Morpho
.family,.
which.are.found.in.South.and.Central.America..Due.to.their.distinctive.blue.color,.which.is.
so.bright.that.it.can.be.seen.a.quarter.mile.off,
17
.they.are.one.of.the.most.popular.butterlies.
to.be.used.in.fashion.jewellery.and.butterly.presentation.cases.
In.the.case.of.the.butterly.
Morpho rhetenor
,.the.scales.display.the.classic.Christmas.tree.
structure,.with.a.series.of.lamellae.that.project.perpendicularly.to.the.spine.and.approxi-
mately.parallel.to.the.base.of.the.ridge,.with.the.size.of.the.lamellae.decreasing.as.the.ridge.
tapers.toward.the.top..The.surface.of.the.scales.has.parallel.ridges.that.are.in.the.region.of.
500.nm.apart.and.1,500.nm.high..Each.ridge.is.about.70.nm.deep.and.has,.on.average,.10.
lamellae.on.each.side,.which.are.separated.by.a.similarly.sized.air.gap..While.this.system.
behaves.in.a.manner.similar.to.the.simple.multilayer.observed.in.
C. raja
,.the.discontinuity.
of.the.multilayers.limits.the.angles.over.which.the.brightest.relections.can.be.observed,.
and.thereby.limits.the.range.of.color.visible.in.the.iridescence..Furthermore,.the.lexibil-
ity. of. the. ridge. design. allows. the. peak. relectance. to. be. distributed. over. a. wider. angle..
Macroscopically,. the. scaled. nature. of. the. wing. results. in. the. relected. light. being. non-
specularly.relected,.with.the.peak.relection.distributed.over.a.range.of.angles..However,.
this.is.also.true.of.the.relection.from.a.single.scale.that.can.be.shown.to.be.relected.across.
a.broader.angle.than.would.be.expected.if.the.scales.were.not.curved.and.the.ridges.were.
not.subject.to.some.side-to-side.bending.or.tilting.
Another. example. of. a. butterly. with. a. similar. scale. is.
M. didius
.. This. butterly. differs.
from.
M. rhetenor
.in.that.it.has.two.sets.of.different.overlapping.scales.on.its.inner.wing.
surface,.the.upper.being.a.highly.transparent.scale.and.the.lower.being.an.iridescent.scale.
(Figure 25.4)..The.lower.of.the.two.is.structurally.and.dimensionally.very.similar.to.those.
of.
M. rhetenor
,. with. a. periodicity. of. approximately. 500.nm,. although. the. height. of. these.
