A Fiber Optic RF Resonant Cavity Sensor for Strain Sensing-Forrcs

  • Jeffrey S. Schoenwald
  • Ross H. Messinger


A fiber optic vibration and strain sensor described by Rogowski et al [1] implemented a radio frequency (rf) phase locked loop in an optical strain gauge bonded to or embedded in a composite structure. A laser is modulated at radio frequency by a voltage controlled oscillator. The phase delay through the optical fiber transmission line is compared to the source oscillator, and the resulting error signal shifts the oscillator, locking the phase. Strain in the specimen (a composite panel) produces a change in optical phase length in the fiber. Tracking the frequency change gives a measure of the integrated strain transduced into the fiber from the strained panel. Strain level sensitivity on the order of 0.1 microstrains has been reported [1]. However, considerable confusion surrounds the performance of the reported sensor, since noise presumed to arise from cladding/core mode interference and splice reflections makes significant filtering necessary, reducing the bandwidth of the sensor, e.g., increasing the response time to detect strains [2]. This limits vibration control applications.


Voltage Control Oscillator Syntactic Foam Gauge Factor Foam Core Fiber Loop 
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  1. 1.
    R. Rogowski, M. Holben, Jr., and I Heyman, “A Method for Monitoring Strain in Large Structures: Optical and Radio Frequency Devices,” in Rev. Prog. Nondestructive Evaluation, 7A, D. O. Thompson and D. E. Chimenti, Eds., (Plenum Press, NY, 1988), pp. 559–563.Google Scholar
  2. 2.
    R. Rogowski, Personal Communication.Google Scholar
  3. 3.
    M. Born, and E. Wolf, Principles of Optics, Oxford, Pergamon Press, 1965 (5th Ed.), pp. 323–329.Google Scholar

Copyright information

© Plenum Press, New York 1991

Authors and Affiliations

  • Jeffrey S. Schoenwald
    • 1
  • Ross H. Messinger
    • 2
  1. 1.Rockwell International Science CenterThousand OaksUSA
  2. 2.Space Systems DivisionDowneyUSA

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