Design and Performance of a Radio Frequency Identification Scanning System for Sediment Tracking in a Purpose-Built Experimental Channel

Abstract

Sediment transport studies that use radio frequency identification (RFID) tracers are now common in hydraulic studies because of the information the technique provides on the spatial and temporal variability of sediment movement. The technique has been underused relatively in laboratory studies, however, because of issues related to tag orientation and spatial resolution. The objectives of the current study were to (1) describe the design and construction of a flume and a RFID tracking system with the ability to locate tracer stones during experiments; and (2) present the results from preliminary performance tests. The design and tests were completed for vertically oriented RFID transponders, which was realistic for tracers in transport on the basis of a parallel effort to develop gyroscopic tracer stones. The constructed flume was unique because it was designed with a space under the floor of the channel that accommodated an RFID detection carriage. The carriage used three multiplexers and 12 antennae in combination with a laser rangefinder to detect and estimate the position of tracer stones. Wireless communication with a desktop computer was used. A programmable logic control system controlled the movement of the carriage. Preliminary tests conducted with vertically oriented RFID tags showed that a 23-mm RFID tag could be detected up to 21 cm above the flume floor with a streamwise position accuracy of ±1 cm. Steel cross members and multiple RFID tags locally decreased the detection range and precision of the position estimate. Zones of nondetection became larger as tags were closer together, and antennae only reliably detected the closest tag. When the antenna spacing was ∼20 cm, the system was capable of operating in a maximum tracer density of 25 particles/m2. Spatially, nonuniform distributions of tracers required lower densities for reliable detection and positioning. Continued development using different antenna array designs and anticollision RFID tracers should increase the resolution and allow higher tracer densities.