Biomedical Engineering Reference
In-Depth Information
Fig. 8.30
(
a
) Measured reflection spectra of differently colored barbules of the male
P. muticus
under normal incidence.
Blue, green, yellow, and brown lines
represent the results for blue,
green, yellow, and brown barbules, respectively. (
b
) Schematic of a 2D photonic crystal used in
simulations.
Light gray area, dark gray dot, and white dot
indicate keratin matrix, melanin rod, and
air hole, respectively. The
red arrow
indicates the direction perpendicular to the cortex surface. (
c
)
Calculated photonic band structure for the electric vector parallel (
solid lines
) and perpendicular
(
dashed lines
) to the melanin rods. Frequency is in units of
c=a
,where
c
is the light speed in
vacuum and
a
is the lattice constant. The
inset
shows the irreducible Brillouin zone with
,
X
,
and
M
representing its center, edge center, and corner, respectively. Note that the
X
direction
is along the direction normal to the cortex surface. (
d
) Calculated reflection spectra under normal
incidence for generic 2D photonic crystals with a finite number of periods.
Blue, green, yellow, and
brown lines
represent the results for blue, green, yellow, and brown barbules, respectively, and the
corresponding number of periods is 10, 10, 6, and 4, respectively (Reproduced from [
124
])
Measured reflection spectra for differently colored barbules with a microspec-
trophotometer under normal incidence are shown in Fig.
8.30
. The blue and green
barbules display a single reflection peak, while the yellow and brown barbules show
two reflection peaks. For the blue and green barbules, their reflection peaks are
located into blue and green wavelengths, respectively. For the yellow barbule, the
main peak ranges from green to orange wavelengths, indicating that the yellow color
is a mixed color. The intensity of the secondary peak at blue wavelengths is too
small to contribute to coloration. For the brown barbule, however, the peak at blue
wavelengths has a intensity comparable to the broad reflection peak ranging from
green, yellow, orange to red wavelengths.
