Evaluation of Apple Maturity with Two Types of Dielectric Probes

Dielectric Properties of Glass Beads with Talc as a Reference Material for Calibration and Verification of Dielectric Methods and Devices for Measuring Soil Moisture

This paper presents dielectric measurements of talc, glass beads, and their mixtures under different moisture and salinity levels. The measurements were conducted using a prototype seven-rod probe (15 mm long central rod) connected to a single port of vector network analyzer. The samples were moistened with distilled water and KCl solutions in order to obtain six different moisture content levels. The complex dielectric permittivity was determined from vector network analyzer reflection-coefficient measurements based on the open-water-liquid calibration procedure. Next, the fitting of volumetric water content-real part of dielectric permittivity calibration curves was performed for each material at selected frequencies, and the obtained relations were compared with well-known calibration equations. Additionally, a salinity index for the tested materials was calculated. It was concluded that pure talc is not an optimal material for the calibration and verification of dielectric methods. The calibration curves obtained for glass beads and the mixtures of glass beads with talc gave results close to well-known reference calibration functions. Additionally, the addition of talc caused the data points to be less scattered. Moreover, the values of the salinity index for the tested materials were in a good agreement with literature data for sand. The obtained results indicated that glass beads with the addition of talc can be used as a reference material for the calibration and verification of dielectric methods and devices for soil moisture measurement.

Dielectric properties of muscle and adipose tissue-mimicking solutions for microwave medical imaging applications

The aim of the present study was to synthesize mixture solutions which can accurately mimic the dielectric properties of biological tissues, specifically muscle and adipose tissues between 500 MHz and 50 GHz. Mixtures utilizing concentrations of bovine serum albumin (BSA) dissolved in phosphate buffered saline (PBS) and Ringer's solutions were synthesized to mimic in vivo and ex vivo muscle tissues. Solutions consisting of concentrations of peanut oil and Triton X-100 (TX) in PBS and Ringer's solutions were also synthesized to mimic in vivo and ex vivo adipose tissue. Results were then analysed and compared to measured dielectric properties of in vivo and ex vivo biological tissues from another previous study. Good agreement with said dielectric property measurements were obtained since the solutions from this study yielded low RMSE and RMSRE values. This implied that such solutions can be utilized in the construction of human body phantoms for narrowband and ultra-wideband microwave devices for near field breast cancer imaging.

A Seven-Rod Dielectric Sensor for Determination of Soil Moisture in Well-Defined Sample Volumes

This paper presents a novel seven-rod sensor used for time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR) measurements of soil water content in a well-defined sample volume. The probe directly measures the complex dielectric permittivity spectrum and for this purpose requires three calibration media: air, water, and ethanol. Firstly, electromagnetic simulations were used to study the influence of the diameter of a container on the sensitivity zone of the probe with respect to the measured calibration media and isopropanol as a verification liquid. Next, the probe was tested in three soils-sandy loam and two silt loams-with six water contents from air-dry to saturation. The conversion from S 11 parameters to complex dielectric permittivity from vector network analyzer (VNA) measurements was obtained using an open-ended liquid procedure. The simulation and measurement results for the real part of the isopropanol dielectric permittivity obtained from four containers with different diameters were in good agreement with literature data up to 200 MHz. The real part of the dielectric permittivity was extracted and related to the moisture of the tested soil samples. Relations between the volumetric water content and the real part of the dielectric permittivity (by FDR) and apparent dielectric permittivity (by TDR) were compared with Topp's equation. It was concluded that the best fit to Topp's equation was observed in the case of a sandy loam. Data calculated according to the equation proposed by Malicki, Plagge, and Roth gave results closer to Topp's calibration. The obtained results indicated that the seven-rod probe can be used to accurately measure of the dielectric permittivity spectrum in a well-defined sample volume of about 8 cm³ in the frequency range from 20 MHz to 200 MHz.