Popular sensing patterns for capacitive touch screens are two layered matrix array on which diamond or rectangular electrodes are printed.
As expected, there another kind of sensing electrode pattern. Here, I try posting an exemplary patent on touch sensing patterns. Yes, reading this kind of patent is somewhat boring compared with reading cute UI patents from companies such as Apple. However, “sensing pattern” is also an important factor in designing a capacitive touch screen.
The patent US7202859 explains a sensor (or sensing pattern) as shown in the figure below. The X traces and Y traces are arranged in an intertwined pattern around each crossing.
The typical construction of the sensor matrix is shown below. In this case two X and Y traces are printed on separate layers. In other embodiments, two trace patterns are printed on opposite faces or the same face of the insulating layer.
In order to reduce capacitive coupling between X traces and Y traces, two methods are presented: 1) Traces become very thin around each crossing or 2) Either of X and Y traces is connected through via holes as shown in the Fig. 5 of the patent. This configuration is quite useful when two X and Y traces are disposed on the same face of the insulating layer.
Many variations of sensing patterns are also introduced (see Fig. 6 and Fig. 7 of the patent). Possible advantages of the Fig. 6 of the patent are:
Grouping traces in this manner can allow individual traces of the group to be arbitrarily narrow relative to the size of the spiral, which may be desirable for reasons including, and not limited to: cost, ease of manufacture, availability of fabrication expertise or equipment, availability of material and components, and specific sensor design. For example, one may want to design a touch-sensor which glows, or a touch screen through which a display can be viewed. One desirable property of a grouping of thin traces is to enable the overall trace matrix to pass light around individual traces, while still allowing the group as a whole to have sufficient surface area to achieve the desired sensitivity.
Source: Don A. Speck, et al. (Synaptics), Capacitive Sensing Pattern, US7202859, Apr. 10, 2007.
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