As fibre-optic type pressure measurement is versatile in many applications fields, it is gradually becoming popular. Its adaptability in bio-medical area has also been confirmed in which case, it can be used to monitor pressure in the human circulatory system. The basic diagram of the system is shown below.
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There are two optical fibre bundles called guides – input and output – arranged as shown in the end view, giving the proper perspective. Chopped light from source is focused on to input guide, which on emergence is reflected from a flexible membrane. The membrane may be made of aluminized plastic formed as a film. With pressures, P1 and P2 equal, the position of the membrane with respect to the input guide is so kept that 50% of the reflected light falls on the surrounding annular output guide. With P2 greater than P1, the membrane becomes convex towards the guides and more light falls on the output guide, while with P1 less than P2, the reverse occurs. A detector set at the other end of the output guide correspondingly receives varied amount of light with changing pressure. The detector can be calibrated for pressure.