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This paper presents the mathematical modeling based design and simulation of normal mode MEMS capacitive pressure sensor for blood pressure sensing application. The typical range of blood pressure is 80 -120 mm Hg. But this range varies in case of any stress, hypertension and some other health issues. Analytical simulation is implemented using MATLAB ® . Basically, normal mode capacitive pressure sensors have a fixed backplate and a moveable diaphragm which deflects on application of pressure with the condition that it must not touch the backplate. Deflection depends on material as well as thickness, shape and size of diaphragm which can be of circular, elliptical, square or rectangular shape. In this paper, circular shape is chosen due to higher sensitivity compared to other diaphragm shapes. Deflection, base capacitance, change in capacitance after applying pressure and sensitivity is reported for systolic and diastolic blood pressure monitoring application and study involves determining the optimized design for the sensor. Diaphragm deflection shows linear variation with applied pressure, which follows Hook's Law. The variation in capacitance is logarithmic function of applied pressure, which is utilized for analytical simulation.

A complete analysis of the translational and rotational modes of a model lateral suspension is presented. The derived formulae quantify spurious-mode resonant frequencies for cross-axis translation and rotation, and on-axis translation, and can provide very simple expressions for the rejection ratios in terms of the geometry of the suspensions. It is shown that the introduction of intermediate frames, coupling equivalent points of the lateral suspension either side of the suspended mass, can provide much improved dynamics. To investigate the derived relationships, suspensions have been fabricated using through-wafer deep reactive-ion etching (DRIE). Using analysis of the suspension dynamics under the rastered beam of a scanning electron microscope, the various modes of the suspension have been visualized and quantified. These observations are in good agreement with the derived formulae, taking into account the actual profile of the beams fabricated in DRIE. Further finite element analysis across a broad range of suspensions is consistent with the derived formulae. A design heuristic is provided for rapidly optimizing micromachined lateral suspensions by incorporating intermediate frames.

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In Micro-electro-mechanical Systems (MEMS) based pressure sensors and acoustic devices, deflection of a membrane is utilized for pressure or sound measurements. Due to advantages of capacitive pressure sensor over piezoresistive pressure sensors (low power consumption, less sensitive to temperature drift, higher dynamic range, high sensitivity), capacitive pressure sensors are the 2nd largest useable MEMS-based sensor after piezoresistive pressure sensors. We present a normal capacitive pressure sensor, for continuous sensing of normal and abnormal Intraocular Pressure (IOP). The composite membrane of the sensor is made of three materials, i.e., Si, SiO 2 and Si 3 N 4 . The membrane deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity and non-linearity are discussed in this work. Mathematical modeling is performed for analytical simulation, which is also compared with Finite Element Method (FEM) simulations. MATLAB ® is used for analytical simulations and CoventorWare ® is used for FEM simulations. The variation in analytical result of deflection in membrane w.r.t. FEM result is about 7.19%, and for capacitance, the variation is about 2.7% at maximum pressure of 8 kPa. The nonlinearity is about 4.2492% for the proposed sensor for fabrication using surface micro-machining process.

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