Non-contact hand interaction with smart phones using the wireless power transfer features

The interaction between human and smart phones is mainly based on press buttons and touch screens. As wireless charging based on wireless power transfer (WPT) coils is standardized and becoming a competitive feature for smart phones in recent years, it is also possible to control smart phones without contact by interacting with their wireless charging coils. In this paper, a non-contact method to interact with smart phones based on their wireless charging coils is proposed and investigated. A Colpitts oscillator is built and tested using a standard WPT coil as part of the resonant tank elements. Experiment results show that the resonant frequency of the coil is heavily influenced by hand movement, which could be further interpreted as the interaction between human and smart phones. By analyzing the resonant frequency changes of multiple coils embedded into a phone, it is possible to determine which hand movement is performed by a user.