Detection of Anti-Counterfeiting Markers through Permittivity Maps Using a Micrometer Scale near Field Scanning Microwave Microscope

[EN] This paper describes the use of microwave technology to identify anti-counterfeiting markers on banknotes. The proposed method is based on a robust near-field scanning microwave microscope specially developed to measure permittivity maps of heterogeneous paper specimens at the micrometer scale. The equipment has a built-in vector network analyzer to measure the reflection response of a near-field coaxial probe, which makes it a standalone and portable device. A new approach employing the information of a displacement laser and the cavity perturbation technique was used to determine the relationship between the dielectric properties of the specimens and the resonance response of the probe, avoiding the use of distance-following techniques. The accuracy of the dielectric measurements was evaluated through a comparative study with other well-established cavity methods, revealing uncertainties lower than 5%, very similar to the accuracy reported by other more sophisticated setups. The device was employed to determine the dielectric map of a watermark on a 20 EUR banknote. In addition, the penetration capabilities of microwave energy allowed for the detection of the watermark when concealed behind dielectric or metallic layers. This work demonstrates the benefits of this microwave technique as a novel method for identifying anti-counterfeiting features, which opens new perspectives with which to develop optically opaque markers only traceable through this microwave technique.This paper has been financially supported through the grant reference BES-2016-077296 of the call Convocatoria de las ayudas para contratos predoctorales para la formacion de doctores de 2016 by Ministerio de Economia y Competitividad (MINECO) and by European Social Funds (ESF) of European Union, and the project SEDMICRON-TEC2015-70272-R (MINECO/FEDER) supported by Ministerio de Economia y Competitividad (MINECO) and by European Regional Development Funds (ERDF) of European Union.Gutiérrez Cano, JD.; Catalá Civera, JM.; Plaza González, PJ.; Penaranda-Foix, FL. (2021). Detection of Anti-Counterfeiting Markers through Permittivity Maps Using a Micrometer Scale near Field Scanning Microwave Microscope. Sensors. 21(16):1-14. https://doi.org/10.3390/s21165463S114211

Dynamic measurement of dielectric properties of food snack pellets during microwave expansion

[EN] The in situ dielectric properties of a starch-based food pellet have been measured during microwave expansion. A dual-mode cylindrical cavity allowed simultaneous microwave heating and dielectric measurements of a single pellet inside a quartz tube, ensuring uniform heating during microwave processing. The cavity included additional measurement devices to correlate the dielectric properties with the main parameters of the expansion process, such as temperature, expansion time, pellet volume and absorbed power. A commercially available snack food pellet was Used as the test material for expansion experiments. Results indicated that dielectric constant (epsilon') and loss factor (epsilon") increased during heating, reaching a threshold value of epsilon' = 12.5 and epsilon" = 5.2, around a temperature of 115 degrees C when the material expanded and the dielectric properties dropped abruptly due to the loss of water content and the increase in size. This measurement procedure may provide useful material science information to improve the overall design of starch-based food pellets processed by microwaves. (C) 2017 Elsevier Ltd. All rights reserved.The work presented in this paper was funded by PepsiCo R&D.Gutiérrez Cano, JD.; Catalá Civera, JM.; Bows, J.; Penaranda-Foix, FL. (2017). Dynamic measurement of dielectric properties of food snack pellets during microwave expansion. Journal of Food Engineering. 202:1-8. https://doi.org/10.1016/j.jfoodeng.2017.01.021S1820

Sensor for Distance Measurement Using Pixel Grey-Level Information

An alternative method for distance measurement is presented, based on a radiometric approach to the image formation process. The proposed methodology uses images from an infrared emitting diode (IRED) to estimate the distance between the camera and the IRED. Camera output grey-level intensities are a function of the accumulated image irradiance, which is also related by inverse distance square law to the distance between the camera and the IRED. Analyzing camera-IRED distance, magnitudes that affected image grey-level intensities, and therefore accumulated image irradiance, were integrated into a differential model which was calibrated and used for distance estimation over a 200 to 600 cm range. In a preliminary model, the camera and the emitter were aligned

Permittivity Spectrum of Low-Loss Liquid and Powder Geomaterials Using Multipoint Reentrant Cavities

[EN] Permittivity is a useful tool to characterize the composition and quality of many geomaterials. In general, the non-resonant permittivity measurement methods exhibit a higher degree of uncertainty than their resonant counterparts. In resonant measurements, the reduction in uncertainty comes typically with a loss in broadband. This article describes the theory, design, and application of multipoint coaxial reentrant resonant cavities applied to low-loss geomaterials at different temperatures. Specifically, a full-wave method based on circuit analysis is developed and applied for a circular corrugated waveguide. Moreover, the mode-matching method is applied to calculate the generalized admittance matrix (GAM). Two multipoint cavities and software were built and validated. The first cavity has five resonant frequencies, between 170 MHz and 2.3 GHz, and the second has four resonant frequencies, between 1.3 and 8.6 GHz. Thus, this method allows for ¿broadband-resonant¿ measurements. The permittivity values of liquid hydrocarbons, powdered kerogen, and pyrite are shown.Alvarez, JO.; Penaranda-Foix, FL.; Catalá Civera, JM.; Gutiérrez Cano, JD. (2020). Permittivity Spectrum of Low-Loss Liquid and Powder Geomaterials Using Multipoint Reentrant Cavities. IEEE Transactions on Geoscience and Remote Sensing. 58(5):3097-3112. https://doi.org/10.1109/TGRS.2019.2948052S3097311258

Directional Coupler Calibration for Accurate Online Incident Power Measurements

© 2021 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] This letter proposes a calibration method to properly measure the incident power in a directional coupler (DC) when the measurement configuration has low directivity. The proposed method is based on measurements of short-circuits placed at different distances to calibrate the DC response. Results show that the method is clearly robust and provides accurate measurements even for directivities as low as 10 dB.This work was supported by the European Regional Development Fund (ERDF) through the Valencia Region 2014-2020 Operational Program under Project IDIFEDER/2018/027.Penaranda-Foix, FL.; Catalá Civera, JM.; Gutiérrez Cano, JD.; García-Baños, B. (2021). Directional Coupler Calibration for Accurate Online Incident Power Measurements. IEEE Microwave and Wireless Components Letters. 31(6):624-627. https://doi.org/10.1109/LMWC.2021.3070788S62462731

Resonance energy transfer and superradiance mediated by plasmonic nanowaveguides

We show how both the subwavelength confinement associated with surface plasmons and the one-dimensional character of plasmonic waveguides can be exploited to enhance the coupling between quantum emitters. Resonance energy transfer and the phenomenon of superradiance are investigated in three different waveguiding schemes (wires, wedges, and channels) by means of the Finite Element Method. We also develop a simplified model that is able to capture the main features of the numerical results. © 2010 American Chemical Societ

Microwave calorimeter for dielectric and thermal analysis of materials

[EN] A fast method for microwave processing and measurement of dielectric and thermal properties of materials as a function of temperature has been developed (MW-DETA). Unlike previous approaches, the method provides totally new quantitative measurements of the thermal parameters, which are fundamental for calculating the specific heat and in particular, the energy requirements of electrification of materials processing via microwave heating.The in-situ measurement of dielectric properties of the sample with temperature, together with the precise numerical modelling of the thermal process, provided the necessary information to quantify the thermal and microwave losses and, therefore, the precise amount of power delivered to the sample that is converted into heat.Compared to conventional calorimeters, microwave heating reduces the experimental time and improves the uniformity of heating, which leads to a fast and reliable method to determine the thermal properties of the material under test with different operation modes, either constant or variable heating rates.The functionality of the thermal parameters measurement system has been demonstrated by heating and measuring a ceramic sample of Macor up to 400 degrees C. Accuracy reached in the thermal process has been validated by comparison with a conventional DSC analysis.This research project has received funding from the Ministerio de Universidades by the European Union- NextGenerationEU programme under the grant Margarita Salas (MS/2) . Funding for open access charge: CRUE-Universitat Politecnica de Valencia.Sánchez-Marín, JR.; Gutiérrez Cano, JD.; Plaza González, PJ.; Penaranda-Foix, FL.; Catalá Civera, JM. (2022). Microwave calorimeter for dielectric and thermal analysis of materials. Energy. 263. https://doi.org/10.1016/j.energy.2022.12590926

Effect of water content on the dynamic measurement of dielectric properties of food snack pellets during microwave

[EN] The evolution of dielectric properties of starch-based food pellets with different moisture contents was measured during microwave expansion to determine the effect of water content on the expansion dynamics. Dynamic dielectric measurements were found to be an excellent procedure to in situ monitor and characterize the different stages in the material transformation of food pellets during microwave expansion. Although the maximum bulk expansion of pellets was achieved at a moisture content of approximately 8% (wet basis), comparative analysis showed that a moisture content 10-11% produced the best results considering the tradeoff between the foaming and expansion temperature. This was due to the high expansion index and an expansion temperature that was sufficiently lower than the onset temperature for pellet scorching, which provides an operating window to maximize expansion and minimize the likelihood of burning. Dielectric measurements during microwave heating in short on/off cycles prior to pellet expansion suggested that the water was not as dielectrically bound for high moisture content pellets. (C) 2018 Elsevier Ltd. All rights reserved.The work presented in this paper was funded by PepsiCo R&D. The views expressed in this manuscript are those of the authors and do not necessarily reflect the position or policy of PepsiCo Inc.Gutiérrez Cano, JD.; Hamilton, IE.; Catalá Civera, JM.; Bows, J.; Penaranda-Foix, FL. (2018). Effect of water content on the dynamic measurement of dielectric properties of food snack pellets during microwave. Journal of Food Engineering. 232:21-28. https://doi.org/10.1016/j.jfoodeng.2018.03.018S212823

High-Resolution Detection of Rock-Forming Minerals by Permittivity Measurements with a Near-Field Scanning Microwave Microscope

[EN] The identification of the minerals composing rocks and their dielectric characterization is essential for the utilization of microwave energy in the rock industry. This paper describes the use of a near-field scanning microwave microscope with enhanced sensitivity for non-invasive measurements of permittivity maps of rock specimens at the micrometer scale in non-contact mode. The microwave system comprises a near-field probe, an in-house single-port vectorial reflectometer, and all circuitry and software needed to make a stand-alone, portable instrument. The relationship between the resonance parameters of the near-field probe and the dielectric properties of materials was determined by a combination of classical cavity perturbation theory and an image charge model. The accuracy of this approach was validated by a comparison study with reference materials. The device was employed to determine the permittivity maps of a couple of igneous rock specimens with low-loss and high-loss minerals. The dielectric results were correlated with the minerals comprising the samples and compared with the dielectric results reported in the literature, with excellent agreements.This paper has been financially supported through the grant reference BES-2016-077296 of the call Convocatoria de las ayudas para contratos predoctorales para la formacion de doctores de 2016 by Ministerio de Economia y Competitividad (MINECO) and by European Social Funds (ESF) of European Union, and the project SEDMICRON-TEC2015-70272-R (MINECO/FEDER) supported by Ministerio de Economia y Competitividad (MINECO) and by European Regional Development Funds (ERDF) of European Union.Gutiérrez Cano, JD.; Catalá Civera, JM.; López Buendía, ÁM.; Plaza González, PJ.; Penaranda-Foix, FL. (2022). High-Resolution Detection of Rock-Forming Minerals by Permittivity Measurements with a Near-Field Scanning Microwave Microscope. Sensors. 22(3):1-17. https://doi.org/10.3390/s2203113811722