Readout instrumentation for Fabry-Perot sensors
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Continuous monitoring of blood glucose levels (BGL) on intensive care unit (ICU)patients opens up for the possibility of keeping insulin at normal levels. Thismethod is called intensive insulin therapy (IIT) and reduces both recovery time,chances for complications and death, thus saves the hospital resources. BeforeIIT can be employed as the standard treatment, better products are needed forcontinuous glucose monitoring (CGM).GlucoSet A/S is currently developing a CGM system based on a Fabry-Pérot(FP) hydrogel sensor that responds to BGL by changing length. By sending alight spectrum to the sensor and measuring the interference pattern returned,information about the length of the sensor cavity is achieved; the frequency ofthe interference pattern directly depends on the length of the cavity.In this thesis an accurate quadrature demodulation technique (QDT) used by GlucoSettoday in a scientific setup, it transfered over to a 32-bit microcontrollerunit (MCU) based platform. Simulation of critical parameters such as superluminescentlight emitting diode (SLED) light source bandwidth is conducted andperformance improving alterations are made on the algorithm to make it performfaster calculations. The results showed that the QDT can be implemented on a32-bit MCU; when the SLED bandwidth is 80nm the phase estimate calculatescavity length with a <0.21% error(~±50 nm), while the QDT phase estimatetracks changes in cavity length with a <0.013% error(~±3 nm). If real sensormeasurements yields the same accuracy as simulated in this thesis, less accuratecomponents are suggested tested to benefit from an accuracy/price trade-off asfurther work.