Microwave-triggered redox switching of materials enables hydrogen production and green chemistry

García-Baños, B.; Serra Alfaro, JM.; Catalá Civera, JM. (2020). Microwave-triggered redox switching of materials enables hydrogen production and green chemistry. AMPERE Newsletter. 105:1-5. http://hdl.handle.net/10251/165731S1510

Sample Movement Optimisation for Uniform Heating in Microwave Heating Ovens

A technique for improving the uniformity of heating patterns of dielectric samples in a multimode cavity is presented based on a strategic movement of the sample inside the microwave applicator. Different optimisation algorithms are compared to determine the best microwave irradiation period for each sample position. A new optimisation procedure that minimizes electric field variance is also presented and assessed

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

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

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

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

In-situ measurements of high-temperature dielectric properties of municipal solid waste incinerator bottom ash

[EN] Microwave heating is a potential green technology demonstrating many advantages over conventional heating methods. Prior to designing an industrial microwave process, however, a fundamental knowledge of the dielectric properties of the material to be thermally treated is imperative, as these properties determine the response of the material to an applied electromagnetic field. In this study, the fundamental interactions between microwave energy and municipal solid waste incinerator (MSWI) bottom ash (BA) are investigated through in situ complex permittivity measurements. Using an enhanced version of the cavity perturbation method, the dielectric properties were determined from room temperature up to 1100 degrees C at a frequency close to the industrial 2.45 GHz. The results demonstrated that BA is a low-loss microwave absorber up to 320 degrees C, above which microwave flash pyrolysis of the organic matter abruptly enhances the dielectric loss of BA, resulting in a thermal runaway. The addition of water and graphite to BA induces a higher dielectric constant and loss factor. The evolution of the dielectric properties as a function of temperature is correlated to changes in the material as determined by Simultaneous Differential Scanning Calorimetry, Thermogravimetric Analysis and High Temperature X-ray Diffraction. The reported results form a baseline for the assessment of the MSWI BA response under microwave irradiation.This work was supported by the European Community's Horizon 2020 Programme under Grant Agreement No. 721185 (MSCA-ETN NEW-MINE). This publication reflects only the authors' view, exempting the Community from any liability. Project website: http://new-mine.eu/.Flesoura, G.; García-Baños, B.; Catalá Civera, JM.; Vleugels, J.; Pontikes, Y. (2019). In-situ measurements of high-temperature dielectric properties of municipal solid waste incinerator bottom ash. Ceramics International. 45(15):18751-18759. https://doi.org/10.1016/j.ceramint.2019.06.101S1875118759451

New approach for the prediction of the electric field distribution in multimode microwave-heating applicators with mode stirrers

We present a new approach for inferring the electric field distribution inside materials in multimode cavities with mode stirrers.We calculate the electric field in the dielectric material by a two-dimensional modeling of a typical multimode microwave applicator with some mobile metallic sheets. We compare simulated results with classical approaches, such as Lambert’s law or a constant electric field distribution. The proposed method allows for a better understanding of how these structures can be applied for heating materials when computing the microwave energy absorption in the dielectric. Finally, we perform experimental tests in a microwave multimode oven for validating purposes.This work was supported in part by the Spanish Science and Technology Ministry under Project TIC2001-2778-CO2-02

An Accurate and Compact High Power Monocycle Pulse Transmitter for Microwave Ultra-Wideband Radar Sensors with an enhanced SRD model: Applications for Distance Measurement for lossy Materiel

[EN] In This paper, a high power sub-nanosecond pulse transmitter for Ultra-wideband radar sensor is presented. The backbone of the generator is considered as a step recovery diode and unique pulse injected into the circuit, which gives rise to an ultra-wide band Gaussian pulse. The transistor driver and transmission line pulse forming the whole network are investigated in detail. The main purpose of this work is to transform a square waveform signal to a driving pulse with the timing and the amplitude parameters required by the SRD to form an output Gaussian pulse, and then into high monocycle pulses. In simulation aspect, an improved output response is required, in this way a new model of step recovery diode has been proposed as a sharpener circuit. This proposition was applied to increase the rise-time of the pulses. For a good range radar, a high amplitude pulse is indispensable, especially when it comes to penetrate thick lossy materiel. In order to overcome this challenge, a simple technique and useful solution is introduced to increase the output amplitude of the transmitter. This technique consists to connect the outputs of two identical pulse generators in parallel respecting the restrictions required. The pulse transmitter circuit is completely fabricated using micro-strip structure technology characteristics. Waveforms of the generated monocycle pulses over 10V in amplitude with 3.5 % in overshoot have been obtained. Good agreement has been achieved between measurement and simulation results.The author gratefully acknowledges the financial support provided by Pierre and Marie Curie University under the EMMAG Scholarship. This study was supported by DIMAS group, ITACA institute at City Polytechnic of innovation from university Polytechnic of Valencia.Ahajjam, Y.; Aghzout, O.; Catalá Civera, JM.; Penaranda-Foix, FL.; Driouach, A. (2019). An Accurate and Compact High Power Monocycle Pulse Transmitter for Microwave Ultra-Wideband Radar Sensors with an enhanced SRD model: Applications for Distance Measurement for lossy Materiel. Advanced Electromagnetics. 8(3):76-82. https://doi.org/10.7716/aem.v8i3.676S76828

Effect of mode-stirrer configurations on dielectric heating performance in multimode microwave applicators

In this paper, several mode-stirrer configurations are compared in order to establish their influence on the electric-field uniformity within an irradiated dielectric sample inserted in a microwave- heating applicator. Two different scenarios are evaluated with metallic sheets moving inside the multimode applicator. The different stirrer configurations are tested and compared for low-, medium-, and high-loss dielectric sample materials. Additionally, a straightforward procedure based on a generalized plane-wave approach is proposed and evaluated as a computationally efficient alternative for calculating the electric-field distribution inside materials processed in these microwave applicators with mode stirrers. Although very different electric patterns are achieved depending on stirrer geometry and sample permittivity, the plane-wave approach has been shown to provide a very good approximation for medium and high lossy dielectric materials.This work was supported in part by the Spanish Science and Technology Ministry under Project TIC2001-2778-CO2-02