Touch sensor capacitance

QuickField simulation example

Touch sensor consists of two circular electrodes, transmitting Tx and receiving Rx rings, placed on the dielectric board. Presence of the conductive stylus in their vicinity affects the capacitance between electrodes.

Problem Type
Axisymmetric problem of electrostatics.

Geometry

Conducting rings thickness is 35 μm.

Given
Relative permittivity of dielectric is 4.7.

Task
Determine the capacitance of Tx and Rx electrodes as a function of a distance between the touch sensor and the stylus.

Solution
"Floating conductor" boundary condition is assigned to the stylus surface, there is no field inside the conductor.
Capacitance is a ratio of stored charge q to the potential difference ΔU between Rx and Tx electrodes.
Simulations are performed for different stylus positions. LabelMover tool is used to automate the series of calculations.

Results
Electric field distribution in and around the touch sensor:

• Video: Touch sensor capacitance. Watch on YouTube
  
• Download simulation files (files may be viewed using any QuickField Edition).