Modeling and Relative Permittivity Modulation of Cu/PDMS Capacitive Flexible Sensor for Pressure Sensing

Abstract

This study aims to establish an equivalent parallel capacitance model for a copper/polydimethylsiloxane (Cu/PDMS) capacitive flexible pressure sensor and modulate its relative permittivity to optimize pressure sensing performance. The Cu/PDMS composite material is an ideal dielectric layer for sensors due to its high dielectric constant and tunable elasticity. By adjusting the different mixing ratios of PDMS and copper particles in micro size, the components and structure properties of the composite material can be modified, thereby affecting the electrical and mechanical performance of the sensor. We used finite element analysis (FEA) to model the sensor structure and studied the capacitance changes under various normal loading conditions to assess its sensitivity and distribution characteristics. Experimental results show that the sensor has good sensitivity and repeatability in the pressure range of 0 to 50 kPa. Additionally, we explored the effect of the addition of carbon black particles. It could be inferred that the added carbon black can enhance electrical properties due to its conductivity, which would be consequenced by the distribution optimization of Cu particles for carbon black's low density, and it can mechanically restore some flexibility up to nearly 20%. Through these studies, our work can provide theoretical support for the design and application of flexible pressure sensors.

Keywords: capacitive; flexible sensor; relative permittivity modulation; tactile sensor.

Figure 1

Capacitive sensor structure diagram.

Figure 2

Diagram of normal force.

Figure 3

Schematic distribution of conductive particles in the dielectric layer.

Figure 4

Diagram of the formation process of the composite dielectric layer. (a) Local schematic diagram of dielectric layer. (b) Dielectric layer of multilayer structure. (c) Composite dielectric layer structure.

Figure 5

Schematic modeling of a composite dielectric layer.

Figure 6

Schematic diagram of Cu/PDMS composite dielectric layer preparation.

Figure 7

Dielectric constant of carbon black/PDMS composites with different mass fractions.

Figure 8

Characterization of 40 wt% Cu/PDMS composite dielectric layer.

Figure 9

Cu/PDMS cross-sectional view and equivalent model.

Figure 10

Cross-sectional view of double-layer Cu/PDMS dielectric layer bonding.

Figure 11

Relative permittivity of different deposition layer locations.

Figure 12

Relative permittivity of different CB doped with 40% Cu.

Figure 13

The curve of relative dielectric constant versus temperature.

Figure 14

Equivalent models of Cu/CB/PDMS composite.

Figure 15

Sensor assembly process of Cu/PDMS composite sensors.

Figure 16

Physical diagram of the array sensor.

Figure 17

Three test samples. (a) PDMS materials; (b) Cu/PDMS composites; (c) CB/Cu/PDMS composite materials.

Figure 18

Schematic diagram of the experimental platform.

Figure 19

Stress–strain curves for PDMS, Cu/PDMS, and Cu/CB/PDMS composite material.

Figure 20

Sensor compression simulation model. (a) Schematic diagram of dielectric layer simulation mode; (b) schematic diagram of grid division.

Figure 21

Simulation results under central area loading. (a) Stress distribution results; (b) strain distribution results.

Figure 22

Simulation results under local area loading. (a) Stress distribution results; (b) strain distribution results.

Figure 23

Sensor capacitance simulation model.

Figure 24

Sensor potential distribution.

Figure 25

Sensor capacitance simulation model and potential distribution.

Figure 26

Composite dielectric layer simulation model.

Figure 27

Theoretical versus simulated values for composite dielectric layer models.

Figure 28

Distributed normal force output characteristic curve.

Figure 29

Standard deviation of the amount of change in capacitance.

Figure 30

The principle of concentrated force test.

Figure 31

Repeatability test curve.