【正文】 erature Sensors Bragg Grating Response to Focused Ultrasonic Fields 160 Temperature Sensors Feasibility of In Vivo… Bragg Grating… 161 Temperature Sensors 162 Temperature Sensors 163 Bragg Grating Response to Focused Ultrasonic Fields 164 Bragg Sensors Within the Nuclear Power Industry Nuclear Shield Monitoring Steam Pipe Monitoring Waste Conditioning and Disposal Monitoring 165 Applications to Power Transmission Lines Combined Bragg Grating/Current Transformer Current Metering Sensor Multiplexed Load Monitoring System for Power Transmission Lines Using Fiber Bragg Grating Magic Field Sensors 166 Other Applications 。(239。)39。as the tamp rises , strain on the grating is progressively released. 85 Extrinsic Temperature Compensation 2. Packaging the FBG in a liquid crystalline polymer has resulted in an improvement in temp stability by a factor of 10. 3. A cantilever is used with 2 FBG mounted on opposite surface, with one grating stretched while the other is pressed. Here ,the difference in the Bragg grating wavelengths is temp. independent because both Bragg gratings have the same temp sensitivity. 86 Intrinsic Temperature Compensation Reference Grating Tapered Grating DualWavelength Superimposed Gratings Multiple Bragg Grating Orders Simultaneous Measurement of Temperature and Strain Using PANDA Gratings in Dissimilar Diameter Fibers 87 Intrinsic Temperature Compensation Hybrid Bragg Grating/Long Period Grating Superimposed Gratings and PolarizationRocking Filters Bragg Gratings and Brillouin Scattering Combined Grating and InLine/Extrinsic Fiber Etalon Sensor Methods Bragg Grating Strain Rosettes DualCore Fiber Bragg Gratings 88 Intrinsic Temperature Compensation )()()( 1,gBGTgBTB VKKKKT?? ????? ?() 89 Polarization Stability of Interrogation Schemes ? Ecke et al. have found that laterally pressing or bending a fiber lead produces dynamical changes due to polarizationmode conversion, resulting in severe noise and systematic errors. ? shows that for a simple broadband source and spectrometerCCD arrangement, the passive Lyon depolarizer gives a dramatic improvement to the system stability, reducing wavelength errors to less then 1pm. 90 Polarization Stability of Interrogation Schemes 91 Multiplexing Techniques Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM) Spatial Division Multiplexing (SDM) Combined SDM/WDM/TDM 92 Multiplexing Techniques ? By sharing the source and processing electronics. the cost per sensor is reduced. reduces the overall system weight while enhancing durability. ? For FOS SDM (spatial Division Multiplexing ) TDM FDM WDM CDM (coherence domain multiplexing) 93 Multiplexing Techniques ? Limited to 10 FOS ,due to speed crosstalk S/N bandwidth 94 Wavelength Division Multiplexing (WDM) Parallel and Serial WDM Topologies WDM Schemes with Tunable Filters Combined WDM and Interferometric Detection 95 Parallel and Serial WDM Topologies WDM encodes each BGS with a unique slice of the available source spectrum , which defines the sensor’s operating rouge and is also associated with a specific spatial location along the optical fiber. Advantage The physical spacing between individual gratings may be as short as desired and the need for highspeed electrical signal processing, as is often required in TDM, is removed. 96 Parallel and Serial WDM Topologies 97 Parallel and Serial WDM Topologies 98 Time Division Multiplexing (TDM) Combined TDM and Interferometric Detection TDM and WDM 99 Time Division Multiplexing (TDM) 100 Spatial Division Multiplexing (SDM) SDM and WDM SDM and TDM 101 Combined SDM/WDM/TDM The serial multiplexing schemes of WDM amp。LLF S RF S RMl o n gs h o r t???? () Def An enhancement factor M Ref. Fig. 74 QuasiStrain Monitoring 75 Simultaneous Interrogation of Bragg Gratings and Interferometer Sensors 76 Simultaneous Measurement of Temperature and Strain Principle of Operation Extrinsic Temperature Compensation Intrinsic Temperature Compensation 77 Simultaneous Measurement of Temperature and Strain ? FBG can measure strain and temp simultaneously. for quasistatic signals any temp variation along the fiber will be indistinguishable from strain. for dynamic strain measure mentis, this is not true ,since the thermal fluctuation occur at low freq. That tend not to coincide with the resonance frequicies of intersts. 78 Table 79 Principle of Operation ))(00()(2121????TKK T?21,??() ?For an ideal sensor, with represent the phase intuited by for 2 system eigen mode (in this case the 2 FBG , ) ( , )T?12,??Here, assuming that the strainand tempinduced perturbation are linear. 80 Principle of Operation ? ? In practice, ))(()(1)())(()(2112121221221121????????????TTTTTTKKKKKKKKTTKKKK????? () () 81 Princ