Browsing by Author "Vijayaraghavan, Krishna"

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    Enhancement and Field Test Evaluation of New Battery-Less Wireless Traffic Sensors
    (Center for Transportation Studies, 2011-10) Pruden, Sean; Vijayaraghavan, Krishna; Rajamani, Rajesh
    This project focused on the enhancement of a previous battery-less wireless traffic flow sensor so as to enable it to provide weigh-in-motion (WIM) measurements and provide enhanced telemetry distance. The sensor consists of a 6-feet-long device which is embedded in a slot in the road flush with the pavement. As a vehicle travels over the sensor, vibrations are induced in the sensor. Using piezoelectric elements, energy is harvested from the vibrations and used to power the electronics in the sensor for signal measurements and wireless transmission. The sensor’s performance was evaluated by embedding it in a slot in concrete pavement and driving various vehicles of known weight over it at a number of different speeds on different days. The sensor was found to meet the specification of 500 feet telemetry distance. It was able to provide WIM measurements with an accuracy of better than ±15% in the absence of vehicle suspension vibrations. However, much of the WIM data during the latter period of sensor testing was obtained in the presence of significant suspension vibrations. The project also evaluated the use of 4 consecutive WIM sensors in the road to remove the influence of suspension vibrations.
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    Novel Battery-Less Wireless Sensors for Traffic Flow Measurement
    (Center for Transportation Studies, University of Minnesota, 2008-11) Vijayaraghavan, Krishna; Rajamani, Rajesh
    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.