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Pressure and temperature sensor designs are based on the Fabry-Perot interferometer, in which two parallel, minimally separated, partially reflecting surfaces form an optical reflecting cavity. If one of these parallel surfaces is a pressure sensitive diaphragm, changes in external pressure cause a change in depth of the optical reflecting cavity, which in turn alters optical cavity reflectance spectra. For temperature, the outer surfaces of a thin silicon layer define the optical reflecting cavity; as temperature changes, the refractive index of silicon changes and this in turn alters optical cavity reflectance spectra.
The instrument contains an 850 nm LED whose emissions reach the sensor via an optical fiber. In the sensor's optical reflecting cavity, the spectral distribution of LED light is modified as a function of cavity depth, and this spectrally altered light is reflected back down the fiber to the instrument. Light returning to the instrument is optically split into two spectral components; the photocurrents from these two components form a ratiometric signal which in turn correlate with changes in the measured parameter.
The pressure sensor has been manufactured and sold for industrial applications since 1988, and for selected medical applications (by Integra NeuroCare) since 1993. The combination of small size, high performance, and immunity to electromagnetic noise make this pressure sensor an obvious choice for modern cardiovascular product applications.
The temperature sensor is new to the medical market. It's operating range, response time, and measurement resolution make it ideal for medical applications where electromagnetic interference is present.
- Wolthuis et. al. "Development of Medical
Pressure and Temperature Sensors Employing Optical Spectrum Modulation"
in IEEE Transactions on Biomedical Engineering, vol. 38, no. 10, pp 974-981,
1991
- Reesink et. al. "Feasibility Study of a Fiber Optic System for Invasive
Blood Pressure Measurements" in Catheterization and Cardiovascular Interventions,
vol. 57, pp 272-276, 2002.