Two applications of the Fabry-Perot interferometric sensor

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Title: Two applications of the Fabry-Perot interferometric sensor
Author: Xie, Zhaoxia
Abstract: Two important applications of the fiber Fabry -Perot Interferometer (FFPI ) sensor are investigated : (1 ) an optical binary switch for aerospace application , and (2 ) an FFPI weigh -in -motion sensor for measuring the weight of trucks traveling down a highway . In the fiber optical switch , the FFPI sensor is bonded to a copper cantilever to sense the elongation of cavity length induced by force applied to the end of the cantilever via a pushed button . Light from a superluminescent diode light source passes through a scanned Michelson interferometer and is reflected from a sensing FFPI and a reference FFPI to produce a fringe pattern . A secondary interferometer uses a distributed feedback laser light source to compensate for irregularities in the mechanical scanning rate of the moving stage to achieve precision measurement of the optical path difference . The system is calibrated by applying known weights to the cantilever . The elongation measured by the FFPI sensor shows excellent linearity as a function of the force applied , and little hysteresis was observed . By comparing the measured force to a threshold , the system produces a binary signal that indicates the state of the pilotactuated system ; i . e . , whether or not the button has been pushed . In FFPI weigh -in -motion sensors system , the FFPI sensors are installed in metal bars so that they will experience the strain induced by applied loads and are connected to the Signal Conditioning Unit (SCU ) . The SCU determines the induced phase shift in the FFPI and produces voltage outputs proportional to the phase shifts . Laboratory Material Testing System tests show that the fiber optic sensor response is a fairly linear function of the axial displacement . In highway tests the FFPI sensors showed strong responses and consistently reproduced the expected characteristics of truck wheel crossings . A falling weight deflectometer was used to calibrate the sensor response and predict unknown loads . All sensors in steel bars and aluminum bars showed excellent repeatability and accurate predictions , with an average relative percentage error within 2 % . The study on sensor response variation with applied load positions shows a bell shaped distribution . Truck tests on the road sensors indicate that the repeatability of wheel crossings at similar position is good . The sensor can accurately measure axle spacing , speed , and truck class .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1019
Date: 2009-05-15

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Two applications of the Fabry-Perot interferometric sensor. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1019 .

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