We present RFIBricks, an interactive building block system based on ultrahigh frequency radio-frequency identification (RFID) sensing. The system enables geometry resolution based on a simple yet highly generalizable mechanism: an RFID contact switch, which is made by cutting each RFID tag into two parts, namely antenna and chip. A magnetic connector is then coupled with each part. When the antenna and chip connect, an interaction event with an ID is transmitted to the reader. On the basis of our design of RFID contact switch patterns, we present a system of interactive physical building blocks that resolves the stacking order and orientation when one block is stacked upon another, determines a three-dimensional (3D) geometry built on a two-dimensional base plate, and detects user inputs by incorporating electromechanical sensors. Because it is calibration-free and does not require batteries in each block, it facilitates straightforward maintenance when deployed at scale. Compared with other approaches, this RFID-based system resolves several critical challenges in human-computer interaction, such as 1) determining the identity and the built 3D geometry of passive building blocks, 2) enabling stackable token+constraint interaction on a tabletop, and 3) tracking in-hand assembly.

This paper presents a technique enabling distributed batteryless near-field identification (ID) between two passive radio frequency ID (RFID) tags. Each conventional ultra-high-frequency (UHF) RFID tag is modified by connecting its antenna and chip to a reed switch and then attaching a magnet to one of the reed switch's terminals, thus transforming it into an always-on switch. When the two modules approach each other, the magnets counteract each other and turn off both switches at the same time. The coabsence of IDs thus indicates a unique interaction event. In addition to sensing, the module also provides native haptic feedback through magnetic repulsion force, enabling users to perceive the system's state eyes-free, without physical constraints. Additional visual feedback can be provided through an energy-harvesting module and a light emitting diode. This specific hardware design supports contactless, orientation-invariant sensing, with a form factor compact enough for embedded and wearable use in ubiquitous computing applications.