Meander-Line Resonator Designs for 20- to 90-MHz Soil Permittivity Measurements
Abstract
We created new computer designs of meander-line resonators for soil permittivity measurement that are able to measure down to the 20-MHz decade and cover the 20- to 90-MHz range. The designs, subject to the condition of 50-omega line impedance, were derived by successive modifications of a 250-MHz line resonator model guided by computational electromagnetic modeling. Use of a higher dielectric substrate separating the resonator circuits from their grounding plane produced stronger and more-distinct resonances in addition to a far smaller and more practical footprint than with a lower dielectric substrate. In order to lower resonator operational frequency, it became necessary to increase substrate thickness because a lower bound on operational frequency was found that was an increasing linear function of the inverse of substrate thickness. Using measured permittivities of Yuma, Arizona, soils with several water contents from 2.5% to 15% for the modeling, designs performed best with our driest soil. Designs with fewer meander loops produced more-usable resonances for moister soils. Computed parameters for permittivity determination of homogeneous dielectric samples agreed with model-specified permittivity for sample depths of 25 mm or more but were unreliable for sample depths less than about 5 mm due to resonance nonlinearities.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2018
- Accession Number
- AD1056775
Entities
People
- Christopher S. Kenyon
Organizations
- United States Army Research Laboratory