Flexible Battery‐Free Wireless Sensor Array Based on Functional Gradient‐Structured Wood for Pressure and Temperature Monitoring

Abstract Approximately 4.5% to 7.0% of hospitalized patients suffer from pressure ulcers. Mitigating risks for pressure ulcers through sensors remains a challenge and a high requirement. A simple, low‐cost, battery‐free, multi‐parameter passive wireless flexible sensor (MPWFS) for all‐around pressure and temperature monitoring to prevent pressure ulcers is developed. The pressure sensing unit is fabricated with functional gradient‐structured balsa wood and has high sensitivity of 0.34 kPa −1 with a wide detection range of 0–20 kPa. The temperature sensing unit, which is 0.4 mm × 0.2 mm, is embedded in the surface of the pressure sensing unit, enabling temperature monitoring with a resolution of 0.1 °C. The flexible Radio Frequency energy‐harvesting unit, data acquisition, and processing, as well as Bluetooth‐Low‐Energy wireless transmission, are integrated within a 20 mm × 20 mm unit. It acquires continuous temperature and pressure data without a battery at any position more than 1 m away from the power transmitter. Moreover, the combination of the sensor array design with a mobile terminal provides the MPWFS's various benefits, including tracking changes in the supine posture, warning about pressure ulcers, and monitoring falls out of bed. This study presents a new method for long‐term bedridden patient care.