Optimizing Capacitive Pressure Sensor Geometry: A Design of Experiments Approach with a Computer-Generated Model

Abstract

This study presents a comprehensive investigation into the design and optimization of capacitive pressure sensors (CPSs) for their integration into capacitive touch buttons in electronic applications. Using the Finite Element Method (FEM), various geometries of dielectric layers were meticulously modeled and analyzed for their capacitive and sensitivity parameters. The flexible elastomer polydimethylsiloxane (PDMS) is used as a diaphragm, and polyvinylidene fluoride (PVDF) is a flexible material that acts as a dielectric medium. The Design of Experiment (DoE) techniques, aided by statistical analysis, were employed to identify the optimal geometric shapes of the CPS model. From the prediction using the DoE approach, it is observed that the cylindrical-shaped dielectric medium has better sensitivity. Using this optimal configuration, the CPS was further examined across a range of dielectric layer thicknesses to determine the capacitance, stored electrical energy, displacement, and stress levels at uniform pressures ranging from 0 to 200 kPa. Employing a 0.1 mm dielectric layer thickness yields heightened sensitivity and capacitance values, which is consistent with theoretical efforts. At a pressure of 200 kPa, the sensor achieves a maximum capacitance of 33.3 pF, with a total stored electric energy of 15.9 × 10^-12 J and 0.468 pF/Pa of sensitivity for 0.1 dielectric thickness. These findings underscore the efficacy of the proposed CPS model for integration into capacitive touch buttons in electronic devices and e-skin applications, thereby offering promising advancements in sensor technology.

Keywords: PDMS; PVDF; capacitive pressure sensor; design of experiment; dielectrics; optimization; sensitivity.

Figure 1

Schematic diagram of the capacitive pressure sensor.

Figure 2

(a) 2D stress components, (b) The electric field in the dielectric layer.

Figure 3

Proposed sensor geometry, (a) Geometry of the circular shape CPS. Geometries of the dielectric layer are arranged in a circular shape, (b) Conical shape, (c) Cut spherical shape, (d) Cubical shape, and (e) cylindrical shape. (f) Geometry of the cubical shape CPS. Geometries of the dielectric layer are arranged in a square shape (g) Conical, (h) cut spherical, (i) cubical, and (j) Cylindrical shape.

Figure 4

Meshing to the circular CPS consisting of cylindrical dielectric, (a) Normal mesh, (b) Fine mesh, and (c) Finer mesh.

Figure 5

RSM optimization plot for the maximum sensitivity of CPS.

Figure 6

Contour plots to show the displacement of diaphragm and dielectric material and the electric potential in CPS. (a–c) displacement at 0, 100, and 200 kPa. (d–f) Electric potential distribution at 0, 100, and 200 kPa.

Figure 7

(a) Effect of pressure on the capacitance and total electrical energy stored for 0.1 mm dielectric thickness, (b) capacitive sensitivity characteristics, (c) Effect of pressure on the diaphragm displacement, and (d) von Mises stress analysis.

Figure 8

Sliced contour plot of the vertically half cross-section of the CPS to show the temperature effect. (a–c) displacement due to 20 °C at 20, 100, and 200 kPa. (d–f) displacement due to 30 °C at 20, 100, and 200 kPa.

Figure 9

Variation in the capacitance due to the change in the operating temperature of the CPS.

Figure 10

Mesh optimization for the electrical and mechanical parameters. (a) Capacitance against pressure, (b) Total electrical energy against pressure, (c) Displacement magnitude against pressure, and (d) von Mises stress against pressure.