Development of a multi-temperature calibration method for measuring dielectric properties of food

Abstract

In the most commonly used, open-ended coaxial probe method, dielectric properties of food products are measured after calibrating the instrument at 25 °C using air (open circuit), short (short circuit) and deionized water. Measurement accuracy may be compromised when dielectric properties are measured at temperatures other than 25 °C. The main objective of this study was to systematically perform calibration at multiple temperatures, quantify measurement errors and develop a method for multitemperature calibration to measure dielectric properties of materials over a wide temperature range. The dielectric properties of deionized water were measured from 1 to 90 °C after calibrating the dielectric measurement system using air, short and deionized water at six different temperatures (1, 25, 40, 55, 70, and 85 °C). The temperature-dependent dielectric properties of water calibrated at six temperatures were then compared with the reported values at two typical microwave frequencies of 915 and 2450 MHz. The results showed that the 25 °C calibration is valid for dielectric constant measurement, but not valid for dielectric loss factor measurement at temperatures far from the calibration temperature. Multitemperature calibration is helpful for reducing errors and improving the accuracy of the temperature-dependent dielectric properties measurement, especially for low-loss materials. Calibrations at two temperatures (25 and 85 °C) within the range studied were found to be suitable for the temperature-dependent dielectric properties measurement. The dielectric properties of lasagna components (ricotta cheese, pasta, and meat sauce) were measured using this multitemperature calibration method.

Challenges in Radiofrequency Pasteurization of Shell Eggs: Coagulation Rings

“…Dielectric properties were measured using the open‐ended coaxial probe method (E4991A, Agilent Technologies, Inc., Santa Clara, Calif., U.S.A.) coupled with a temperature controlled chamber (MCBH‐1.2‐.33‐.33‐H/AC, Cincinnati Sub‐Zero Products, Inc., Cincinnati, Ohio, U.S.A.). The instrument setup and calibration procedure was performed at 20 °C and is described in detail by Chen and others (). While the liquid yolk and white can be measured using the same test cell used by the aforementioned authors, the eggshells required a different test cell because it has been shown that the dielectric properties of powders are affected by density (Nelson ).…”

Multiphysics Modeling of Microwave Heating of a Frozen Heterogeneous Meal Rotating on a Turntable

“…The dielectric properties of lasagna components were measured using a multipoint temperature calibration method (Chen and others ). The temperature‐dependent dielectric properties of lasagna components were shown in Figure .…”

Investigation of Thermal Effects in Coaxial Probe Method and Dielectric Characterization of Glycerol up to 140°C

“…Thus, variants that may be equivalent to the isothermal condition are desirable from a practical point of view. In this work, heterothermal variant 1, 2 and 3 calibrations are investigated and compared with the isothermal case, since they are faster and require less complex apparatus or equipment, such as temperature controllers, samplers and microclimatic chambers [15]. The remaining heterothermal variants are not suitable from this point of view.…”

“…Concerning the temperature of each standard, [9] reports that you can leave only the reference liquid at the temperature of measurement, with no evidence that it is effective. An assessment carried out by [15] demonstrates that the relative error of measurement increases with the thermal difference between the calibration temperature (T ) and the measurement temperature (T ), and that it is more significant for ′′ than for ′ . Obviously, the closer Tcal is to T , the less the error will be.…”

“…Obviously, the closer Tcal is to T , the less the error will be. Furthermore, [15] also states that a detailed description of this method has not yet been reported in the literature. Reference [16] makes an assessment to the accuracy of the method…”