A fiber-optic pressure microsensor with a sensing element only 270 μm×270 μm×150 μm in size has been developed' and applied to actual balloon catheters. The sensing principle is based on the detection of optical reflection intensity changes from a diaphragm located in front of an optical fiber. The sensors have been fabricated using silicon micromachining, such as anisotropic etching and direct wafer bonding For the transmitting source and signal light, a multimode optical fiber 125 μm in diameter is used. This paper describes the miniaturization of the sensing element through an improved design and the use of thinner silicon wafers, and application of the pressure microsensor to actual balloon catheters 1.5 mm in outer diameter, We have found that there is a large pressure difference between the injector and the balloon which is due to the transmission loss that occurs in the tube from the injector to the balloon.# 1998 Elsevier Science S.A. All rights reserved
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