Novel batteryless wireless sensor for traffic-flow measurement

This paper presents a novel batteryless wireless sensor that can be embedded in the road and used for the measurement of traffic-flow rate. Compared with existing inductive loop-based traffic sensors, the new sensor is expected to provide increased reliability, easy installation, and low cost. The sensor requires no external power source and has zero idle power loss. Energy to power this sensor is harvested from the short-duration vibrations that result when an automobile passes over the sensor. Since much 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: 1) fixed threshold switching, 2) maximum voltage switching, and 3) switched inductor. The switched inductor algorithm is shown to be the most effective at maximizing harvested energy. Experimental results are presented and validate the fact that adequate energy can be harvested from each passing vehicle to enable successful wireless transmission of traffic data.