Vibration energy harvesting technology for smart tire monitoring

A smart tire monitoring system uses tire information, such as temperature, pressure, acceleration, force, tire-road friction coefficient, in real time to monitor the driving safety of cars. A vibration energy harvester for a smart tire monitoring system converts the tire dynamic strain energy into electrical energy which is the power source of the wireless sensor module. The self-powered wireless sensor module consists of an electro-magnetic type energy harvester, a power conversion circuit, an acceleration sensor and a radio communication circuit. This research is focused on achieving high energy conversion efficiency, lightweight design, and long durability of the harvester because it is located at the inner surface of tire where extremely high pressure and acceleration exist. The energy harvester was made in a cylindrical shape with a length of 35 mm. The manufactured harvester was 9.4 g, the casing 10.8 g, the battery 2.6 g, the wireless acceleration sensor module 1.1 g, and the power conversion circuit module 1.2 g. So, the total weight of the wireless sensor module was less than 27 g. The monitoring system receives an acceleration signal from the wireless sensor module which is attached to the inner surface of a tire. An operating test of the monitoring system was carried out by using the tire driving test equipment. The average output power of the energy harvester was measured as about 5.7 mW at 60 km/h. The wireless sensor module was operated during about 11700 km (60 km / h * 6.5 h / day * 30 day). The test results showed that the energy harvester has sufficient power to maintain the operation of the wireless sensor module, and the sensor module has a sufficient durability.