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U of MNUniversity of Minnesota
Center for Transportation Studies

New Battery-less Wireless Traffic Sensors as a Replacement for Loop Detectors

Principal Investigator:

Rajesh Rajamani, Professor, Mechanical Engineering

Project Summary:

This project focused on the development of new battery-less wireless sensors that can be embedded in the road and used to measure traffic volume, vehicle speed, vehicle length, and number of axles per vehicle. Each proposed sensor consists of two components: a piezoelectric element embedded in the road and a data processing unit located on the road shoulder. Compared to existing loop detectors, the proposed sensors have significant advantages in cost and installation, and will consume zero energy during operation. A significant portion of the project focused on developing low power control algorithms that can harvest energy efficiently from the short duration vibrations that result when a vehicle passes over the sensor. To this end, the report develops and compares three control algorithms "fixed threshold switching," "maximum voltage switching," and "switched inductor" for maximizing this harvested energy. The novel "switched inductor" algorithm with a dual switch control configuration was found to be the most effective at maximizing harvested energy. All three of the developed control algorithms can be implemented using simple low power analog circuit components. The developed sensor was evaluated using a number of experimental tests. Experimental results found that the sensor was able to harvest adequate energy for its operation from the passing of every axle over the sensor, and the sensor was shown to be capable of accurately measuring traffic flow rates.

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