FIGURE 8.32 Water leakage sensor. 8.18 Water leakage sensor. An evanescent loss sensor uses an optical fiber to sense wa

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Figure 8 32 Water Leakage Sensor 8 18 Water Leakage Sensor An Evanescent Loss Sensor Uses An Optical Fiber To Sense Wa 1 (85.24 KiB) Viewed 30 times

FIGURE 8.32 Water leakage sensor. 8.18 Water leakage sensor. An evanescent loss sensor uses an optical fiber to sense water leakage into the bottom of a boat. The fiber is strung close to the interior surface of the boat, but not touching it, so it does not detect condensation of water at the bottom. To ensure that the sensor will only detect water, the angle of incidence of the laser beam (see Figure 8.32) is adjusted so that the total reflection occurs at all permittivities lower than that of water. The relative per- mittivity of glass at optical frequencies is 1.65 and that of water is 1.34. Detec- tion occurs when the power transmitted along the optical fiber decreases because of transmission into the water through the interface. a. Calculate the angle of incidence, 0, of the light beam to ensure that water will be detected. Fiber Water Bottom of boat &=1.85 8.10 Problems b. If one wishes to detect any medium with relative permittivity , < 1.65 in contact with the fiber rather than limiting this to water, what is the incidence angle 0;? 451