Battery-free touch-aware user input using RFID tags
View Patent ↗Aspects of the present disclosure describe a battery-free touch sensing user interface (UI) for Internet of Things (IoT) and other smart spaces employing Radio Frequency Identification (RFID) readers and tags that we call RIO. With RIO, any surface may be a touch-aware surface by attaching RFID tag(s) thereto. RIO advantageously supports custom-designed RFID tags and therefore facilitates customized UIs to be easily deployed in a real-world environment. RIO employs impedance tracking that results from a human finger—or other appendage—touching a surface of an RFID tag, thereby changing a characteristic impedance of the RFID tag antenna. This change manifests as a change in the phase of the RFID backscattered signal and is advantageously used by RIO to track fine-grained touch movement over the RFID tag. Disclosed further are multi-tag environments in which RIO operates and demonstrations including continuous tracking of finger movement during a swipe to within 3 mm of its actual position.
1. A method comprising:
receiving radio frequency identification (RFID) backscatter signals output from an RFID tag;
determining a phase change of the backscattered signals;
querying the RFID tag continuously;
determining an average signal phase over a time interval;
determining one of the physical events occurring responsive to an object interacting with the RFID tag;
determining that one of the physical events occurred when a detected change in the signal phase change is larger than a threshold;
switching to a tracking mode upon determining that one of the events has occurred;
monitoring and determining, from the received backscatter signals, a change in an effective impedance of the RFID tag responsive to structural or physical events in objects that interact with the RFID tag; and
updating location of an object's interaction on a surface of the RFID during tracking mode responsive to a segmental dynamic time warping (SDTW) methodology.
2. The method of claim 1 further comprising: comparing two sequence segments by stretching and squeezing (warping) on of the sequences until a suitable match between them is determined.
3. The method of claim 1 applied simultaneously to more than one RFID tag.
4. The method of claim 1 further comprising determining a baseline impedance change in the RFID tag due to a desired event.