SI-MT/SI-MKB/SI-HTB
WORLD PRECISION IN STRU MENTS
11
the pattern is symmetrical with respect to the center beam. When the scan arrives at the
part of the CCD chip which is hit by the fi rst order diffraction of the pattern, the output
voltage increases to a peak level, and the fi rst order of diffraction is captured (Fig. 11).
Then, the intensity signal decreases again. The sarcomere length is calculated from the
fi rst order diffraction distance.
Muscle Tissue
Laser
CCD Camera
Center Laser Beam
First Order of Diffraciton
D
Fig. 11 (Left)The distance between the center laser beam and the fi rst order diffraction is
captured with a one-dimensional CCD camera. Then, the sarcomere spacing is calculated.
Fig. 12 (Right) The output voltage of the camera peaks as it scans over the spot where the fi rst
order diffraction hits the CCD screen.
The sarcomere spacing can be specifi cally calculated using geometry:
s =
x
D
2
/L
2
+1
= wavelength of the laser (650nm)
s= grating constant (The grating constant is the sarcomere length.)
D=distance from the muscle to the camera
L=measured distance from the center beam of the laser to the fi rst order of diffraction
The results of this calculation are shown on the LCD display of the
SI-SARCAM
module.
For a quick approximation, the sarcomere length can be calculated using the formula:
s =
x (D/L). The sarcomere lengths reported by the analog outputs are approximations
using this formula.
Fig. 13 The geometry of the system is shown above
NOTE
: If the sarcomeres all have the same length, the laser diffraction line is very narrow.
When the sarcomere order is more random, wider diffraction lines result from the lines of
the shorter sarcomeres superimposed on the lines of the longer sarcomeres. This provides
a qualitative method for judging how much the sarcomeres get disordered during a
