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Main >> Applications >> Sample problems >> Touch sensor matrix

Touch sensor matrix

QuickField simulation example

Touch sensor matrix can detect the human finger position. It is an essential part of the capacitive touch screen. The matrix consists of two groups of electrodes: transmitters and receivers.

Problem Type
3D problem of electrostatics.

Geometry
Touch sensor matrix Touch sensor matrix can detect the human finger position. It is an essential part of the capacitive touch screen. The matrix consists of two groups of electrodes: transmitters and receivers. Rx Air Tx Board, 1 mm Dielectric film,   0.2 mm Glass,   0.5 mm Finger

Given
Relative permittivity of the materials: board 4.3, film 2, glass 5.

Task
Determine the mutual capacitances between Tx and Rx electrodes for an arbitrary finger position.

Solution
Finger is simulated as a floating conductor.
If we energize one pair of Tx and Rx electrodes with +1V and -1V electric potentials and leave other electrodes floating, then the mutual capacitance between these electrodes can be calclated as
C = 2 * Energy / ( Potential difference )²
Two problems are simulated: open air and with a finger. The variation of the capacitance is calculated then.

Results
Electric field distribution around the touch sensor. Capacitances open air is 1.5 pF, capacitance with finger is 1.63 pF.
Touch sensor matrix