From footsteps to wireless events: infrastructure-native battery-free interfaces for human-environment interactions

Future intelligent environments require infrastructure-native interfaces that can sense human activities and directly generate wireless communication events using standard protocols. Achieving this remains challenging because human footsteps are transient, irregular, and often low-force, whereas standard wireless protocols such as Bluetooth Low Energy (BLE) require substantial energy consumption. In this work, we present a self-powered floor interface that addresses this challenge through coordinated material, structural, and circuit design. The system integrates a high-performance PMN-PZT ceramic with a piezoelectric charge constant of d₃₃ = 962 pC/N for efficient energy transduction, a carefully engineered metallic substrate for enhanced stress transfer and recoverability, a threshold-regulated energy management circuit that regulates transient outputs into a usable burst-power window, and an ultra-low-power BLE interface for protocol-compatible transmission. With a 4.7 μF storage capacitor, the circuit provides 22.84 μJ of releasable energy, exceeding the approximately 17 μJ required for BLE cold start. Despite a footprint of only 30 mm, sub-millimeter thickness, and a prototype-level unit cost below $5, the system enables direct wireless triggering from a light actuation of approximately 12 N. Across 100 footstep trials involving 10 participants, the system achieved an average of 2.39 BLE packets per actuation, with up to 4 packets generated per event, and successfully delivered at least one wireless transmission in 97% of the trials. The proposed system directly translates irregular footsteps into reliable protocol-compatible wireless events and enables infrastructure-integrated human-environment interactions, including smart-home control, indoor localization, digital-twin interaction, and transportation-safety alerting. These results establish a practical route toward compact infrastructure-native battery-free interaction systems for future intelligent environments.