Wireless, Battery-Free, Multi-Modal Sensor System for Continuous Monitoring of Physiological Signals of Paraplegic Patients

Wireless, battery-free, skin-mountable pressure sensing systems that enable continuous and accurate measurement of pressure at skin interfaces hold immense potential in preventing the development of pressure injuries. However, there are still significant challenges in continuously tracking pressure with high sensitivity and stability over the required pressure range at critical sites for individuals sitting in wheelchairs. This research paper introduces a wireless, battery-free, multimodal sensor system designed for continuous measurement of pressure and temperature at specific locations of interest on human subjects, whether they are moving or stationary in a wheelchair. The pressure sensor incorporates a cracked metal film, which serves as the active layer, encapsulated with a passivation layer. Its design allows for membrane deflection, enabling excellent sensitivity, low hysteresis, and long-term stability over the pressure range necessary for this application. Moreover, the battery-free, wireless platform and movable sensing system provide stable and long-range communication capabilities at multiple mounting locations, accommodating both moving and stationary scenarios. Experimental evaluations of the pressure sensor and movable system include benchtop measurements, which are further validated through numerical simulations to showcase the functionality of the system. Finally, clinical trials involving patients with spinal cord injuries in wheelchairs demonstrate the feasibility and stability of the sensor and movable system in preventing pressure injuries acquired from sitting.