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Piezo Touch Panels

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Capacitance Switches
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Capacitance Touch Switches

The Basics

Capacitance Switches take advantage of the body’s natural of electrostatic field. When the user’s finger touches the screen, the conductive element of the screen interacts with the electrostatic properties of the user’s body to dynamically form a capacitor. The location of the touch can be determined by one of several technologies. The touch location is then transferred to a computer either connected to, or built into the device which interprets the contact.


Sensing the Touch

The capacitive touchscreen panel uses an insulator such as glass coated with a transparent conductive material like indium tin oxide. This technology has it’s limitations but works quite well in applications like industrial controls and kiosks.


Projected Capacitive Touch

PCT is a more sophisticated technology implemented to allow the interpretation of multiple touch points and more accurate location recognition. In Projected Capacitive Touch an XY array is created by etching a layer to form a grid pattern or by etching 2 discrete perpendicular layers of conductive material.
Applying a small voltage to the grid creates a grid of capacitors. When a person’s finger comes close to this grid the capacitance changes at that precise point on the grid.
This type of technology also permits multi-touch sensing.


Other Systems

Other technologies such as Mutual Capacitance Screen and Self Capacitance Screen have been implemented in Apple’s iPhone.
Mutual Capacitance uses two discrete layers; one layer is the driving layer with lines that carry current and the second layer is perpendicular sensing lines which sense the changes in current at nodes created by the grid.
Self Capacitance works with a single layer consisting of a grid of discrete electrodes connected to capacitance sensing circuitry.


The Future

For a truly amazing demonstration of the future possibilities of Multi-Touch systems click to see a video of Jeff Han’s presentation at the TED conference


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