Touchscreen Capacitance Computation

Capacitive sensors measure changes in capacitance to detect differences in their environment. They
are commonly used as touchscreens to detect the location of fingers or a stylus on the screens ofsmart phones, tablets, computer screens, music players, and computer touch pads, though many other®
uses exist in scientific research and industry. XFdtd can compute the capacitance of complex sensor
designs, allowing the designer to choose the best geometry for their needs without prototyping.

Design Requirements
Touchscreen assemblies typically consistof a durable surface, such as glass, on
top of one or more layers of transparent
conductors, adhesive, and dielectrics.
The self- and mutual-capacitance ofeach conductor is measured by sensing
electronics attached to the conductor
assemblies.
Changes in this matrix of capacitances
represent the location of objects(s) near thescreen. It is useful for designers to be able
to predict this capacitance matrix for touchscreen designs, including the “rest” value of the matrix
when there are no objects to be sensed, and in proximity to fingers, styli, etc.

XFdtd Capabilities for Touchscreen Capacitance Simulations
The electrostatic solver in XFdtd can compute the matrix of self- and mutual-capacitance between
any number of conductors in the geometry. The geometry can be created within XF or imported
from any supported CAD file formats and may
be of almost any arbitrary shape and complexity.
Simulations can consist of the touchscreen assembly
only or may be as complex as the complete
device (mobile phone, tablet, etc.) and/or fingers
or a stylus, in order to evaluate the installed
performance of the sensors. If desired, the transient
solver in XF can compute charge and discharge
cycles by adding the appropriate components andswitching to the touchscreen assembly.

Analysis of Specific Use Cases
Using XF’s Poseable Hands, many configurations of typical touchscreen usage can be evaluated.

Single Touch

Pinch and Zoom

TypingSimilarly, a stylus can be analyzed.
Using a parameter sweep in XF, thelocation of the tip can be moved along
the displacement line without needing
to recreate the stylus for each location.

Starting point
Displacement line
Ending point

XFdtd Electrostatic
Solver Benefits
XF provides the following benefits
to designers and manufacturers oftouchscreen assemblies and devices:

Stylus with 1 mm tip

Parameterize tip location

䡲 Characterize self- and mutual-capacitancematrix for arbitrary, complex sensor designs:• Touchscreen in isolation• With one or more objects in proximity (single and multi-touch situations)䡲 Designs may be imported from CAD in any of XF’s supported formats or created from the XF
solids modeler䡲 Extensive support for complex geometries allows for analysis within fully populated devices
䡲 Compatible with XF’s Poseable Hands and third-party biological files

Remcom, Inc.
315 S. Allen St., Suite 416
State College, PA 16801 USA+1.888.7. REMCOM (US/CAN)+1. 814 . 861.1299 phone+1. 814 . 861.1308 fax

sales@remcom.com

www.facebook.com/remcomsoftware©2015 Remcom Inc. All rights reserved.
TCHSCRN-0415

Visit www.remcom.com for more information