Apple wants its touch screen devices and Mac touchpads to better withstand liquid spills without sustaining damage. The company has filed for a patent (number 20220011920) for “touch sensing with water rejection.”
About the patent filing
Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. However, as Apple notes, in reality, not all touches detected on a touch sensor panel are intended user input. For example, water droplets on the surface of the touch sensor panel can be detected as touches. Water droplets can result in unintended behavior by the device.
This can negatively affect user experience, particularly in wet environments. Apple wants it various devices to be able to tell when a liquid has been spilled on a touch screen or touchpad and not respond.
Summary of the patent filing
For the technically inclined, here’s Apple’s abstract of the patent filing: “Techniques for rejecting apparent (but false) touches caused by objects such as water droplets located in areas with parasitic capacitive paths to ground are disclosed. To minimize these false touches, one or more guard conductors can be located in proximity to the housing and driven with a stimulation signal to shield objects from being capacitively coupled to ground through the housing.
“In some examples images of touch can be obtained from a non-bootstrapped or bootstrapped scan and also an extended bootstrapped scan wherein the guard conductor is driven with a stimulation signal that has the same characteristics as the stimulation signal being applied to the sensed touch nodes. In some examples, the results of the extended bootstrapped scan can be subtracted from the non-bootstrapped or bootstrapped scan to identify and reject apparent touches resulting from capacitive coupling to ground.”