Xie, Zhaoxia (2006-08). Two applications of the Fabry-Perot interferometric sensor. Doctoral Dissertation. Thesis uri icon

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.
  • 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.

publication date

  • August 2006