Optimizing Sensitivity of Capacitive Pressure Sensors for Improved Intraocular Pressure Monitoring

Abstract

This thesis analyzes and describes a wearable pressure sensor to detect intraocular pressure and guide clinician diagnosis of glaucoma. Although glaucoma has many
symptoms and risk factors, high intraocular pressure is the most predominant. A method to continuously and accurately record intraocular pressure measurements and fluctuations in a patient could lead to a more reliable glaucoma diagnosis and a better understanding of glaucoma progression. The proposed sensor consists of an ecoflex dielectric layer, between two graphene-silver nanowire spiral antenna electrodes which also act as the membrane structure. The sensor deflection depends on the intraocular pressure fluctuations; higher pressure leads to larger deflection values, therefore, larger capacitance change. The capacitance change leads to a shift of the resonant frequency, which is simulated in this thesis. The sensor must be smaller than 11 mm2
to fit on a commercial lens. Specifically, this thesis analyzes and simulates the effects
of electrode thickness and shape on the overall performance of the sensor. The optimum geometry of the capacitive sensor is analyzed to maximize sensor sensitivity and quality factor, with a correlated frequency appropriate for a wearable lens. Using Computer Simulation Technology, the optimized antenna dimensions are spiral-electrodes with a plate thickness of 350µm, and 3 spiral revolutions; leading to an increase in sensitivity of 1.4 MHz/mmHg.