Active control based energy harvesting for battery-lesswireless traffic sensors: Theory and experiments

This paper presents a novel battery-less wireless sensor that can be embedded in the road and used to measure traffic flow rate, speed and vehicle weight. Compared to existing inductive loop based traffic sensors, the new sensor is expected to provide increased reliability, easy installation and low maintenance costs. The sensor uses power only for wireless transmission and has zero idle power loss. Hence the sensor is expected to be extremely energy efficient. Energy to power this sensor is harvested from the short duration vibrations that results when an automobile passes over the sensor. Since all of the earlier work in literature on vibration energy harvesting has focused on continuous sources of vibration, this paper focuses on short duration vibrations and on developing low power control algorithms that can be implemented on the sensor using an analog circuit. To this effect this paper develops and compares three control algorithms "fixed threshold switching", "maximum voltage switching" and "switched inductor" for maximizing this harvested energy. The "switched inductor" algorithm is shown to be the most effective at maximizing harvested energy. Experimental results are presented in the final section of the paper and show that adequate energy can be harvested from the passing of each axle of a vehicle to enable successful wireless transmission of data.