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This method relies on the
phenomenon of “microbending.” Light is routed through the fiber more
efficiently when the fiber is perfectly straight. When it is forced
to move through small angles, a bit of the light is lost through the
sides. When the fiber cable is moved or when pressure is applied,
small changes in the intensity of the light detected can be observed.
This technique has been used to monitor ground motion caused by humans and
vehicles. The circuit is powered by
a +5v source. A single resistor, R1, controls the LED current. The
Amplifier circuit has a low DC gain but a high X100 gain to AC signals. |
