Apple's U.S. Patent No. 8,390,481 for "Sensing capacitance changes of a housing of an electronic device" describes a unique system in which a device's case, or housing, is used as a mode of input. The invention can be applied to any number of electronic portables, including smartphones like Apple's iPhone, laptops or other as-yet-unannounced products.
Originally imagined as a solution to make devices more aesthetically pleasing by removing buttons and keys, the patent goes on to cover a wide variety of use scenarios where input through a touchscreen may be difficult or inaccurate. For example, when a user has already registered a touch event on a common capacitive touchscreen, the device is incapable of recording additional input until the a finger is lifted from the screen. In another case, sweat or other contaminants can compromise the accuracy of a touch display by lowering the device's ability to detect a user's capacitance or inductance.
As noted by the patent language, a pressure-based form of input such as squeezing, pressing, or otherwise deforming a device's metal housing could prove useful in some situations.
By incorporating two separate pending patent applications, the system basically measures both the physical and electrical characteristics of the metal structure to determine how a user is interacting with a device.
Illustration of compatible devices with possible points of contact.
By measuring the electrical characteristics of the housing, such as the housing's capacitance, both before and during user interaction, the user's interaction can be sensed in a manner that is independent of the user's electrical characteristics and/or in a manner that may allow a pressure applied to the housing by the user to be quantified.
Sensors disposed within the housing, in some embodiments directly beneath the surface, can detect when deflection occurs, which in turn denotes stress or pressure. In some embodiments, the sensors are connected to a printed circuit board that can in turn illuminate a light or other indicator when a minimum amount of readable stress is applied.
To differentiate user directed input from unwanted signals that may come occur when the device is in a user's pocket, the capacitance across the surface of the housing is measured and applied to the time periods before and after a stress event takes place. In this way, the system can better determine if an input was intentional. Another embodiment shows that the system can be applied in a laptop, with a pressure sensitive keyboard being the main mode of input.
Illustration of illuminated indicators in a keyboard.
Describing the architecture of the device housing, the invention notes that small gaps disposed within the structure can be filled with dielectric material like foam to aid in capacitance measurements. As a working example, the largest change in capacitance across a specified area would indicate the largest area of deflection.
A processor can take the measurements with their corresponding deflection rates, and translate them into device actions. For example, a threshold stress level is reached when a user presses down on a certain area of a device's housing. The processor determines that the capacitance change is outside the bounds of normal readings and can trigger a UI event or other device feature in response. The system can be customized to detect patterns and varied sensitivities to support a broad range of tasks.
Whether Apple will implement the invention in an upcoming iPhone or other type of device is unclear, though the current iPhone 5's metal housing would be a prime candidate for such technology. The patent can also be deployed in other devices like the much-rumored iWatch which could boast a flexible structure.
Apple's patent was first filed for in 2009 and credits Aleksandar Pance, Nicholas Vincent King, Duncan Kerr and Brett Bilbrey as its inventors.