Soil dielectric characterization during freeze–thaw transitions using L-band coaxial and soil moisture probes

Soil microwave permittivity is a crucial parameter in passive microwave retrieval algorithms but remains a challenging variable to measure. To validate and improve satellite microwave data products, precise and reliable estimations of the relative permittivity (εr=ε/ε0=ε′-jε′′; unitless) of soils are required, particularly for frozen soils. In this study, permittivity measurements were acquired using two different instruments: the newly designed open-ended coaxial probe (OECP) and the conventional Stevens HydraProbe. Both instruments were used to characterize the permittivity of soil samples undergoing several freeze–thaw cycles in a laboratory environment. The measurements were compared to soil permittivity models. The OECP measured frozen (εfrozen′=[3.5; 6.0], εfrozen′′=[0.46; 1.2]) and thawed (εthawed′=[6.5; 22.8], εthawed′′=[1.43; 5.7]) soil microwave permittivity. We also demonstrate that cheaper and widespread soil permittivity probes operating at lower frequencies (i.e., Stevens HydraProbe) can be used to estimate microwave permittivity given proper calibration relative to an L-band (1–2 GHz) probe. This study also highlighted the need to improve dielectric soil models, particularly during freeze–thaw transitions. There are still important discrepancies between in situ and modeled estimates and no current model accounts for the hysteresis effect shown between freezing and thawing processes, which could have a significant impact on freeze–thaw detection from satellites.

Resonant coaxial SMA microwave permittivity sensor

Resonant coaxial SMA microwave permittivity sensor is introduced. It is constructed using only commercially available SMA connectors. The sensor is tested in two different frequency ranges for two different dielectric constant ranges, from 1 to 10 and from 10 to 80. Presented sensor is designed, fabricated, simulated, and tested. Good agreement between simulations and measurements is shown. The sensor is also applicable for differential permittivity measurements.

Soil dielectric characterization at L-band microwave frequencies during freeze-thaw transitions

Soil microwave permittivity is a crucial parameter in passive microwave retrieval algorithms but remains a challenging variable to measure. To validate and improve satellite microwave data products, precise and reliable estimations of the relative permittivity (ɛr = ɛ / ɛ0 = ɛ’ - jɛ’’; unitless) of soils are required, particularly for frozen soils. In this study, permittivity measurements were acquired using two different instruments: the newly designed open-ended coaxial probe (OECP) and the conventional Stevens HydraProbe. Both instruments were used to characterize the permittivity of soil samples undergoing several freeze/thaw cycles in a laboratory environment. The measurements were compared to soil permittivity models. We show that the OECP is a suitable device for measuring frozen (ɛ’frozen = [3.5;6.0], ɛ’’frozen = [0.4;1.2]) and thawed (ɛ’thawed = [6.5;22.8], ɛ’’thawed = [1.4;5.7]) soil microwave permittivity. We also demonstrate that cheaper and widespread soil permittivity probes operating at lower frequencies (i.e. Stevens HydraProbe) can be used to estimate microwave permittivity given proper calibration relative to an L-band (1–2 GHz) probe. This study also highlighted the need to improve dielectric soil models, particularly during freeze/thaw transitions. There are still important discrepancies between in situ and modelled estimates and no current model accounts for the hysteresis effect shown between freezing and thawing processes which could have a significant impact on freeze/thaw detection from satellites.

Parallel-strip line stub resonator for permittivity characterization

A new type of a microwave permittivity sensor with a short open stub as a resonator is introduced. The open stub is realized as a double-sided parallel-strip line without a substrate and can be totally immersed into the measured material. It provides high sensitivity of the resonant frequency nearly proportional to the ratio of square roots of dielectric constants of the measured materials. The sensor is tested in two different frequency ranges and for two different dielectric constant ranges (oils and ethanol-water mixture). Its technology is without any additional technological processes such as vias, air-bridges or defected ground structures. Presented sensor is designed, fabricated and tested showing good agreement between simulations and measurements.

Microwave Materials Permittivity and Permeability Measurement Methods

Methods for measuring the microwave permittivity and permeability of materials are considered. The specific features and applicability conditions of measurement methods in transmission lines and in free space are shown, and the measurement errors are analyzed along with the calibration procedures applied for reducing the errors. Individual sections of the articles contain descriptions of scalar, resonance, quasistatic, and quasioptic methods. It has been determined that out of many existing techniques, the NicolsonRossWeir measurement method in a coaxial line and also the method for measuring the permeability of thin ferromagnetic films with the use of a shortcircuited strip cell are most widely applied. By using these methods, the majority of matters concerned with studying the microwave properties of materials can be solved.