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Optical Sensors Applications to Civil Engineering

Optical Sensors Applications to Civil Engineering. Ann Harrer Experimental Methods in Structures and Materials CEE 398 Spring 2004. Overview. Introduction All applications Theory Strain, Displacement, and Load sensors Civil engineering applications Advantages and Disadvantages

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Optical Sensors Applications to Civil Engineering

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  1. Optical SensorsApplications to Civil Engineering Ann Harrer Experimental Methods in Structures and Materials CEE 398 Spring 2004

  2. Overview • Introduction • All applications • Theory • Strain, Displacement, and Load sensors • Civil engineering applications • Advantages and Disadvantages • Further Information • Conclusions

  3. Introduction • Change in light beam(s) to determine different properties • Intensity, phase changes in wavelength • Types • Distributed – over wide area, distributed points • Point – single location • Use of fiber optics • Extrinsic – transducers external to fiber, fiber just transmit sensed quantity • Intrinsic – sensors embedded into the fiber

  4. Radiation Motion Sound Moisture Temperature Pressure Flow Radiation Liquid Level Displacement Vibration Rotation Acceleration Speed Position Moisture Chemical Species Force/Load pH Humidity Strain Velocity Electric Fields Acoustic Fields Magnetic Fields Applications

  5. Optical Sensor Measurements • Two technologies employed • Bragg Gratings • Fabry-Perot Cavity • Monitor changes in light and relate to strain • Typically employ use of fiber optics

  6. Bragg Gratings • Bragg-grating written into the fiber with a laser • Light hits the grating and wavelength is modified • Changes in the grating length, due to strains, will change the wavelength

  7. Fabry-Perot Cavity • Fiber optics with two mirrors on ends facing each other across a cavity • Light reflected in the mirror • Cavity length determined by light wavelength • Strain directly related to cavity length

  8. Strain: Bragg gratings • Attached to surface or embedded • Diameter max = 7mm • Gage length = 2.5 cm - 100 cm • Macroscopic strain of .02-25 mstrain

  9. Strain: Fabry-Perot Cavity • Attached to surface (welded) or embedded • Diameter = 0.5 mm • Length = 1-10 mm • 4000-10,000 mstrain

  10. Displacement • A fiber-optic LVDT • Based on same Fabry-Perot Cavity phenomenon • 25 mm range • Resolution of about 0.002 mm • Error of about 0.12%

  11. Force and Load • Incorporates use of a miniature fiber optic strain gage using Fabry-Perot cavity • Built into a stud or bolt and inserted into member • Capacity of 10,000 lb • Accuracy of within 10 lb • Resolution of 1 lb

  12. Civil Engineering Applications • Monitor dynamic loading on bridges • Monitor speed and location of train as well as any defects in rails (UIUC) • Intelligent structures highways, buildings, dams (UCLA) • Structural health, non-destructive evaluations

  13. Advantages For concrete and steel Cost effective (considering unit cost and labor) Not susceptible to corrosion Sensitive, comparable to typical strain gages Not susceptible to electric or magnetic fields interference Wide ranges Point and distributed sensitivity Small and light Disadvantages Expensive processing equipment Temperature can have effect on sensors Relatively new technology Have to be careful when handling and installing sensors Advantages/Disadvantages

  14. Further Information • Fiso Technologies, Inc. (www.fiso.com) • Pacific Northwest National Laboratory (www.pnl.gov) • University of California Los Angeles, Mechanical and Aerospace Engineering • University of Illinois Urbana-Champaign, Electrical and Computer Engineering

  15. Conclusions • Optical sensors can be used to measure a variety of different parameters • Two types of optical sensors, Fiber-optic Bragg Grating, and Fabry-Perot Cavity, can be used to measure strains in different civil engineering materials • Has advantages and disadvantages but comparable to typical gages used to measure the same parameters

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