Projected Capacitive
Structure
Used on smartphones, projected capacitive is the most widespread touch screen, isn't it? How is the structure like?
There are various structures in projected capacitive technology. "One sheet piled-up structure" has X and Y electrodes piled on one sheet. "One sheet two-sided structure" has X and Y electrodes on its surface and backside of one sheet respectively. "Two-sheets-laminated structure" consists of two sheets facing each other with electrodes in between.
So, a projected capacitive sensor has X and Y electrodes, and there are several ways to put them together.
Right, the two-sheets-laminated structure is introduced in this museum.
In the two-sheets-laminated structure of projected capacitive, X electrodes are forming on one glass, and Y electrodes are forming on another glass. The two glass sheets are laminated in the way that two electrode sides are facing. The X and Y electrodes are intersecting in matrix.
This looks similar to digital matrix resistive. Two conductive layers are facing with matrix of electrodes in between.
Yes, but unlike digital matrix resistive, touched points will not be conducted in projected capacitive. I will explain more details in the sensing method section.
Sensing Method
There are two types of sensing methods in projected capacitive technology. They are GRID type and wire sensing type. GRID type will be introduced here.
Human body is conductive since it contains a lot of water. When a finger comes close to the patterning of X and Y electrodes, a capacitance coupling will occur between the finger and the electrodes. The capacitance coupling makes the electrostatic capacitance between the X and Y electrodes change. The touch sensor detects touched points as it checks where on the electrode lines the electrostatic capacitance changed.
OK, projected capacitive technology make use of conductivity of human body. Then, I imagine that projected capacitive can detect only fingers just like surface capacitive. Am I right?
Yes, but projected capacitive can detect gloved finger as well. Let me introduce features of projected capacitive technology here.
Features
- Projected capacitive supports multiple touches, thus supports various elaborate inputs.
- Projected capacitive has relatively long life because it has no moving parts in operation.
- Projected capacitive has high durability.
- Sensitivity of the sensor can be adjusted. If sensitivity is adjusted to high level, the touch screen can be operated over a cover glass or cover plastic sheet. These cover sheets provide additional durability, environmental resistance, and a lot of flexibility in design.
- If sensitivity is increased, projected capacitive can be operated with gloved fingers.
- Projected capacitive touch screen is excellent at optical property.
- Projected capacitive responds to light touch. No pressure force is needed for detection.
- Projected capacitive requires an advanced technology to measure electrostatic capacitance and achieve precise locational information from it. Unlike resistive technology, it does not work simply by connecting a touch screen with a controller sourced from somewhere. A projected capacitive touch screen and controller need to be designed together.
- Projected capacitive is susceptible to electrical noise due to its detection mechanism. Noise from LCD is especially influential to the sensor. Recently, various methods are developed to improve tolerance for noise.
- Projected capacitive requires fine pattering, thus takes high processing cost.
- The notable application of projected capacitive is smartphone. Projected capacitive has also been dominant in personal devices such as portable PC, mobile game, and portable audio player.
- Although it is not introduced here, wire sensing method is superior in environment resistance, thus strong at raining, wind, and temperature change. It can be operated either by bare hand or gloved hand. From these strong points, wire sensing technology is used for digital signage, and other outdoor terminals.
