Energy harvesting and speed sensing with a hybrid rotary generator for self-powered wireless monitoring

Real-time onboard health monitoring systems are critical for the railway industry to maintain high service quality and operational safety. However, the issue with power supplies for monitoring sensors persists, especially for freight trains that lack onboard power. Here, we propose a hybrid piezoelectric-triboelectric rotary generator (HPT-RG) for energy harvesting and vehicle speed sensing. The HPT-RG incorporates a rotational self-adaptive technique that softens the equivalent stiffness, enabling the piezoelectric non-resonant beam to surpass resonance limitations in a low-frequency region. The experiments demonstrate the feasibility of using the HPT-RG as an energy harvesting module to collect the rotational energy of the freight rail transport and power the wireless temperature sensors. To allow multiple monitoring in confined spaces on trains, a triboelectric sensing module is added to the HPT-RG to sense the operation speed and mileage of vehicles. Furthermore, the generator exhibits favorable mechanical durability under more than 600 h of official testing on the train bogie axle. The proposed HPT-RG is essential for creating a truly self-powered, maintenance-free, and zero-carbon onboard wireless monitoring system on freight railways.