33
Appendix C
Technical Aspects
Th
e signal from the photodiode is converted to digital information and then
processed using a DSP (Digital Signal Processor). Th
is device performs the
spectral analysis and produces an LDF signal.
How it Works
Th
e Blood FlowMeter determines the blood fl ow perfusion by illuminating
the surface of the skin with laser light and measuring the backscattered light.
Various calculations are then performed on the returned signal which is then
turned into a continuous signal that represents the blood perfusion in the
illuminated area. Th
e block diagram below shows a very basic outline of the
fundamental components.
Th
e input channel is supplied with laser light at a wavelength of 830 nm
(visible red light) from an internal semiconductor laser diode which is
temperature controlled by means of a Peltier cell and fans.
Th
e laser light is transferred to the Probe connector by optic fi ber.
Figure C–1
Block diagram of the
Blood FlowMeter
Photodetector
DSP
Fiber Optic
Cables
Probe
Head
Signal
Converter
Signal
Outputs
BSC
LDF
Peltier Cell
Laser Diode
LCC
USB
