Transmission head/probe

Figure 5. Single-point IR sensor head layouts a transmission probe with fibre coupling b transflectance probe with variable pathlength and single fibre coupling c (diffuse) reflection probe with single illumination fibre and collection fibre bundle d two-reflection ATR probe with fibre-optic coupling e multi-reflection ATR probe (DiComp -type) f ATR fibre...

Hence, in contrast to transmission spectroscopy, where the sample intercepts the path of the IR beam, in ATR the sample is placed on an IR-transparent crystal (IRE, internal reflection element), permitting total internal reflection. In vivo (or in situ) experimentation is permitted by virtue of one of several design arrangements (a) the region of skin under study may be placed directly in contact with the crystal (b) a remote fiber-optic probe (with IRE head) may be used to transfer the IR beam from the source to the sample and ultimately to the detector and (c) samples removed from the subject may be placed directly onto the crystal. 

The fuel cell seal samples were tested using the Microtech Model 44 Probe Station. A block diagram of the TDR measurement system is shown in Figure 4-5. The sample is mounted on the wafer chuck, and both ends of the transmission line embedded in the sample are connected to the TDR sampling head. 

The Pundit Plus for use in transmission mode is shown in Figure 4.24. The A1220 Ultrasonic Flaw Tester is an example of a multi-headed ultrasonic probe for use in reflection mode is shown in Figure 4.25. 

Alternatively, it is possible to install fibre optic probes directly in the main stream in-line while the IR spectrophotometer remains remotely in a low vibration laboratory environment. In-line analysers, which do not remove any sample from the line, have the minimum possible lag time and do not change the sample physically or chemically from its nature in the process. Recently, bundles of 500 /xm optic fibres have been developed for the 5000-900 cm (2000-11,000 nm region), which permit transmission of IR energy over distances of several metres. Lowry et al. [76] have evaluated fibre-optic cables that might prove useful in FTIR remote sampling applications. The various optical fibres (chalcogenide, silver halide, heavy metal fluoride or sapphire) differ in their spectral window [77]. Due to the thermal stability and the spectral window, sapphire fibres are considered suitable for in-line characterisation of polymer melts in a production line (e.g. in an extruder head) as an alternative to discontinu-ously operating conventional off-line transmission IR spectroscopy of polymer films [78]. 

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