Tham khảo tài liệu 'encyclopedia of smart materials (vols 1 and 2) - m. schwartz (2002) episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | a Transmission type NIRS-based High inc b Evanescent type NIRS-based Fluorimetry-base Transmission-type for Index-base c Distal end type Fluorimetry-based Reflection type for Index-based Figure 6. Constructions of sensing parts of NIRS-based fluorimetry-based and index-based fiberoptic sensors a transmission type b evanescent type c distal end type. to determine the properties of the polymer s optical absorption to select a proper measuring instrument. For instance monitoring the cure of the epoxy-amine resin system requires the 1500 to 1700-nm range which includes the absorption bands of epoxy amine C-H and O-H groups 4 5 . The sensing part of the optical fiber is fabricated so that the light propagates through the polymer. Two configurations of fiber-optic sensors are suggested 4-8 . One is a transmission-type sensor and the other is an evanescenttype sensor. The transmission-type sensor has a simple structure in which the sensor has a gap as shown in Fig. 6a. A configuration that uses a bore metal capillary is proposed to fix the input and output fibers 6 . When the sensor placed in liquid polymer the gap is filled by it. Then light propagates through the polymer in the gap. The evanescent-type sensor consists of a fiber which has a stripped cladding region as shown in Fig. 6b. An evanescent wave is light transmitted in the cladding of the fiber. In the stripped region of the evanescent-type sensor the evanescent wave transmits in the polymer instead of in the silica cladding of the fiber. The refractive index of the fiber core must be larger than that of the resin to propagate light in the stripped region 4 . An example of the application of an NIRS-based sensor is shown in Fig. 7. The figure shows that the absorption peak of epoxy decreases due to a decrease in epoxy molecules from cross-linking in the epoxy-amine resin system in the curing process. Note that the behavior of absorption peaks is sometimes complex due to the overlaps of peaks related to .
