In-Situ Permittivity Measurements using Ring Resonators

Proper development of ground-penetrating radar (GPR) technology requires a unique understanding of the electromagnetic (EM) properties of targets and background media. Thus, electromagnetic characterization of targets and backgrounds is fundamental to the success or failure of UWB GPR as a threat detection technique. In many cases, threats are buried in soil. Soil properties directly affect the radar signature of targets and determine the depth at which they can be detected by radar. One such property is permittivity. A portable system recently developed at the U. S. Army Research Laboratory measures permittivity in-situ with minimal disturbance of the dielectric sample. The measurement technique uses ring resonators. Design equations and physical dimensions are presented for fabricating resonators at frequencies between 600 MHz and 2 GHz. Only a handheld vector network analyzer, coaxial cabling, and the ring resonators are necessary for each measurement. Lookup curves generated in simulation are referenced to calculate the complex permittivity of the sample. The permittivity measurement is explained step-by-step, and data is presented for samples of soils from Ft. Irwin, California and Yuma, Arizona.