The core idea is rooted in mechanical resonance. Every object has a natural frequency at which it vibrates. By carefully designing the shape and geometry of these small metal tags, each one produces a distinct ultrasonic signature when it is disturbed, tapped, or moved. These signatures act like fingerprints. When a tag vibrates, it emits sound waves in the ultrasonic range, frequencies too high for humans to hear but detectable by standard microphones. Because the signal is tied to physical structure rather than software, it is inherently stable and difficult to spoof. This enables a new class of sensing systems: • Touch detection without capacitive sensors • Object tracking without cameras • Interaction logging without wearables • Environmental awareness without power consumption One of the most interesting properties is robustness. Unlike many sensing systems that degrade in noisy environments, these ultrasonic signatures remain distinguishable even when surrounded by other ...