Institute of Information and Communication Technologies (ITACA)

In situ dynamic measurements of the complex permittivity of dielectric materials at high temperatures

For quality control

A system that provides the dielectric properties of materials as a function of temperature by an improved cavity perturbation method during heating, with an accuracy of the complex permittivity better than 5% with respect to a rigorous analysis (full wave method) of the cavity.

Applications

Quality control of food sauces.

Technology Overview

The equipment comprises a source (PLL Microwave Synthesizer), which generates the microwave stimulus, a set of directional couplers to separate reflected and transmitted signals, a microwave receiver based on the AD-8302 integrated circuit for magnitude and phase detection and a measurement probe, where the material to be measured is placed. A control unit (Microprocessor System) is connected through a USB link to a personal computer which includes all the required processing to determine dielectric properties from the measurements and to transform the outputs into the desired representation.

The dielectric probe is designed as a microwave resonator where the interaction of the signals with the material takes place. Vials containing the material under test are introduced in the microwave resonator though a hole at the top of the probe. After sample insertion, the probe response (resonant frequency and quality factor) is shifted depending on the sample dielectric properties. From the measurement of the new response, the complex permittivity of the sample is calculated by using the electromagnetic model of the structure by a numerical procedure.

The Vials Dielectric Kit is fully controlled by a Labview-based software, which has been developed to perform all the necessary functions with a user-friendly interface.

References

[1] Felipe L. Penaranda-Foix, Jose M. Catala-Civera, Jose D. Gutierrez-Cano and Beatriz Garcia-Banos, “Directional Coupler Calibration for Accurate Online Incident Power Measurements”. IEEE Microwave and Wireless Components Letters, Vol. 31, No. 6, June 2021, pp. 624-627. https://doi.org/10.1109/LMWC.2021.3070788

[2] J. D. Gutiérrez-Cano, J. M. Catalá-Civera, F. L. Penaranda-Foix and P. J. Plaza-González, “Improved open-ended coaxial probe for temperature-dependent permittivity measurements of foodstuff at radio frequencies”. Journal of Food Engineering, Vol. 316, March 2022, on-line September 22nd, 2021. https://doi.org/10.1016/j.jfoodeng.2021.110823

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