Novel Battery-Less Wireless Sensors for Traffic Flow Measurement


Krishna Vijayaraghavan, Rajesh Rajamani

November 2008

Report no. CTS 08-16

This project presents a novel battery-less wireless sensor that can be embedded in the road and used to measure traffic flow rate, speed and approximate 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 entirely from the short duration vibrations that results when an automobile passes over the sensor.

A significant portion of the project focuses 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 effect this 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 is shown 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 is evaluated using a number of experimental tests. Experimental results show that the sensor is able to harvest adequate energy for its operation from the passing of every axle over the sensor. The sensor can reliably and accurately measure traffic flow rate.

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