04 / FRINGING-FIELD TACTILE SENSING

Palm Tactile Sensor Design
Using Fringing Fields

Research on a three-axis palm tactile sensor design using fringing fields.

Electrostatic Simulation4-Channel DesignPalm Sensing

CAD design of the palm sensor with electrode PCB, dielectric, conductive contact layer and support.

Capacitance simulation · Electrode and hardware designRESEARCH PROJECT / 04

Electrode configuration

4 channels

Differences of opposing channels and their mean

Lateral displacement range

±0.50 mm

Simulations along the x and y axes

Compression displacement range

0–0.25 mm

Comparison of capacitance responses

01 / RESEARCH NOTES

Fringing fields and electrode arrangement

At the edges of finite electrodes, the electric field extends beyond the overlap region. This is the fringing effect. Lateral motion changes both the overlap area and the edge field, whereas compression changes the electrode gap.

An initial lateral offset between the upper and lower electrodes was introduced to compare capacitance changes under lateral motion and compression. The calculated response includes both overlap-area and fringing-field effects.

Definitions of electrode length, width, initial offset and dielectric gap. Schematic, not to scale.

02 / RESEARCH NOTES

Comparison of electrode geometries

Electrode geometries were compared at a relative permittivity of 2.75 and an applied voltage of 1 V. Length and offset were varied first, followed by comparisons of how width and gap affect lateral and compression responses.

Within the investigated range, increasing width changed the compression response more than the absolute shear response. A length of 5 mm and widths of 2–3 mm were considered as candidates based on geometry and available area. The relationship between offset and width remains a design assumption requiring further comparison.

Electrode lengths compared: 1–5 mm
Electrode widths compared: 1–5 mm
Relative permittivity / applied voltage: 2.75 / 1 V
Single-electrode shear comparison: 0.50 mm total travel

Capacitance changes with electrode length, offset and width: electrostatic simulation results for prescribed displacements.

03 / RESEARCH NOTES

Four-channel displacement response

Differences between opposing electrode channels form the x/y signals, while the channel mean forms the compression signal. In pure-axis displacement simulations, lateral capacitance spans were 385.78 fF and 385.79 fF, and the mean increase under compression was 80.58 fF.

Simulated responses to pure-axis displacement
Response	Applied displacement	Capacitance change
x differential	−0.50 to +0.50 mm	385.78 fF span
y differential	−0.50 to +0.50 mm	385.79 fF span
Compression mean	0 to 0.25 mm	80.58 fF increase

Pure-axis capacitance responses of the four-channel structure. The plotted outputs are capacitance, not force.

Research scope
These simulations prescribe electrode displacement. Converting the response to contact force requires mechanical evaluation and force calibration that account for dielectric deformation and assembly conditions.

04 / RESEARCH NOTES

Palm sensor hardware design

The electrode PCB, dielectric, conductive silicone serving as the common moving electrode, and metal support were designed. The next steps are to fabricate the module, check the channel layout and initial capacitance, and compare controlled-displacement tests against reference force measurements.

Assembly CAD of the palm sensor. The work presented covers simulation and hardware design.

Sources and interpretationThis research is at the electrostatic simulation and hardware CAD design stage. Capacitance values are calculated responses to prescribed electrode displacements.