Time-frequency analysis of enhanced GPR detection of RF tagged buried plastic pipes

Ground Penetrating Radar (GPR) is a well-received non-destructive technique for the detection of underground utilities, such as water/gas pipes, sewers, power cables, and telecommunication ducts. However, radar signatures of plastic pipes are generally weak when the surrounding soils are attenuative and/or the pipe and soils have similar electromagnetic characteristics. In order to increase the radar visibility of these pipes, attaching Radio Frequency (RF) tags to them is a useful method. In this paper we designed two types of Bowtie-Omega shaped RF tags. The finite element method (FEM) simulation and measurement of the designed tags show strong resonances in the GPR spectrum, and by conducting GPR B-scans stronger radar signatures are observed when the RF tags are buried in our 2.0x1.5x0.75 m tank filled with dry sand. Furthermore, we implement a simple processing procedure based on Short-time Fourier Transform (STFT), by which strong time-frequency domain response of the tags is clearly seen at those designed resonant frequencies, and disappear when tags are not inserted. The resulting detection of the hollow plastic pipe in both time and frequency domains due to the co-located tag is evidently enhanced.