Scan velocity, Fourier transform

Instruments IR-85 Fourier Transform infrared spectrometer, through an IBM GC-IR interface. The interface consisted of a gold-coated Pyrex light-pipe with potassium bromide windows. A scan rate of 6 scans/sec and a spectral resolution of 8 cm- - were used for data acquisition. Samples were introduced into the system via splitless injections. A fused silica capillary column, 30 m x 0.32 mm i d DB-WAX (dj 1.0 pm), was employed with the outlet end connected directly to the GC-IR light-pipe entrance. Helium was used as the carrier gas at an average linear velocity of 41.4 cm/sec (35°C). No make-up gas was employed in the system. The column temperature was programmed from 35°C to 180°C at 2°C/min. The GC-IR light-pipe assembly was maintained at 170°C. 

Because A(f) P/ X(f) has the term cos2nft, Fourier transformation of A(f) / X(f)p (in the frequency domain) has a peak at t. Therefore, if the sound velocity is known, we can calculate the location (depth) or the thickness of the layer from the values r. Furthermore, a two-dimensional scanning technique is successfully utilized to image the distribution of the layer in the medium as described in Sect. 4. 

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