Respect for Tissue Representation Using Photoelastic Stress Analysis for Endovascular Surgery Simulation - Microsurgery: Advances, Simulations, and Applications - page 134

stress direction in the intensity measurements was observed
when retardation was 280 nm, where it contributed in 2.52%. The
contributions for 0 nm and 140 nm are 0% and 1.93%, respectively.
Considering the above error, equation (4.22) may be approximated
by [8]

¥
§ ¦

µ
· ¶

sin R 2 Q
M

–

z

I GN (4.24)

G

1

Studied Object
Orientation (deg)

0.9

1 30
4 60
7 90

105
120
135
150
165
180

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0 140 280 420 560

Retardation of the studied object [nm]

Figure 4.8 Variation of green light intensity with the direction of quarter-

wave plates.

4.5 Camera Calibration

A Toshiba IK-TF2 camera was used for capturing the photoelastic
images with ield of view of 48.4 mm × 36.3 mm. When calculating
the optical path length, blue light wavelength is not a parameter
of interest; however, to calculate Re, green light wavelength M G is
essential. A green ilter reduces the effect of red and blue light in
the green channel of the camera. M G is the principal wavelength
value captured by the camera's green channel, changing with the
environment illumination and lens coniguration.
By placing the variable retardation device with R = Q / 2, shown in
Fig. 4.7, normalized green light intensity can be deduced by reducing
equation (4.22) to