Dielectric Permittivity Measurement Using Open-Ended Coaxial Probe—Modeling and Simulation Based on the Simple Capacitive-Load Model

Abstract

The study aim was to validate that dielectric permittivity measurement using the open-ended coaxial probe can be reliably modeled using electromagnetic modeling and simulations, followed by the postprocessing calculations based on the simple capacitive-load model. Saline solutions with various NaCl concentrations were used as materials under test (MUTs) to investigate how ionic conductivity affects the model validity. Two different solvers and simulation methods were used: FEKO for the frequency domain and CST for the time domain. Furthermore, we performed physical experiments with the same probe and MUTs, again implementing the capacitive-load model on the measurement data to observe the model validity. Relative error of the capacitive-load model with respect to the reference permittivity values, both in measurements and simulations, was within 10% for all cases except for the measured εr′ of 1M solution at the lowest frequencies. The model yielded average relative errors well below 1% for the physiological saline, which is relevant for biological materials. The error increased for higher concentrations and for the lowest simulated frequencies but was within the declared measurement accuracy of the probe itself. This makes the simple capacitive-load model valid for all analyzed concentrations in the microwave frequency range from 0.5 to 18 GHz.

Complex Permittivity of Ex-Vivo Human, Bovine and Porcine Brain Tissues in the Microwave Frequency Range

“…The measurements were performed using the open-ended coaxial probe method, described in detail in [ 23 ]. An open-ended coaxial probe is a precisely machined segment of a straight rigid coaxial transmission line.…”

“…We measured the permittivity using the slim form probe manufactured by Keysight Technologies (Santa Rosa, CA, USA) [ 23 , 24 ], having the outer diameter of 2.2 mm. Its operating frequency range is from 500 MHz to 50 GHz.…”

Design and characterisation of a broadband PCB coaxial sensor for non-invasive skin cancer analysis

“…These first obtained results make it possible to evaluate the capacity of the probe to analyze tissues over a wide frequency band, from 1 to 6 GHz, while maintaining small dimensions (current detection area of 2.8 mm diameter), with good capability to differentiate a normal skin from a tumor. Thanks to a calibration step, it is then possible to extract the dielectric properties of the synthesized phantom tissue with a good accuracy compared to the dielectric probes available in the industry [9] and seen in the litterature [10] [11] (Table 2). Our next goal will be to find a way to simplify the calibration process without reducing the probe performance and validate the measurement made with the phantom tissues with in vivo measurement.…”

Dielectric Spectroscopy Shows a Permittivity Contrast between Meningioma Tissue and Brain White and Gray Matter—A Potential Physical Biomarker for Meningioma Discrimination

“…The dielectric spectroscopy, i.e., the complex permittivity measurement, was performed using the standardized open-ended coaxial probe method, which is described in detail in our previous studies [ 44 , 46 , 47 ]. It is a non-invasive method (at the sample level), where an open-ended coaxial probe is put in contact with the sample acting as the material under test (MUT) ( Figure 1 ).…”

“…It is a non-invasive method (at the sample level), where an open-ended coaxial probe is put in contact with the sample acting as the material under test (MUT) ( Figure 1 ). A Slim Form Probe [ 46 , 48 ] was connected to N9927A FieldFox vector network analyzer (VNA) [ 49 ] and controlled by manufacturer-provided software Keysight Materials Measurement Suite; all equipment was manufactured by Keysight Technologies Inc., Santa Rosa, CA, USA. The name Slim Form Probe indicates that its diameter of only 2.2 mm is smaller than most other commercial probes.…”