New paper about Dielectric Kit for Vials (DKV)

IEEE_Trans_On_Instrum_and_MeasA recent work about the Dielectric Kit for Vials (DKV) developed by Microwave Division has been published in the IEEE Transactions on Instrumentation and Measurement Journal.

Dielectric materials have many applications ranging from microwave components and subsystems to industrial and manufacturing processes. Often in these applications, a successful design greatly depends on an accurate knowledge of the complex permittivity of the materials at these frequencies.

DKV is a simple, portable, affordable, and robust device intended to help both specialized metrologists and nonspecialized personnel to accurately measure the dielectric properties of materials used in a wide range of microwave applications around the 2.45GHz ISM frequency. The device is specifically appropriate for measuring liquids, semisolids, powders, and granular materials, but it can also be used for solids, if properly machined to fit into the container.

DKV

Dielectric Kit for Vials

The measurement process consists of placing a 1 mL Pyrex vial containing the sample inside a microwave cavity and measuring the resonant parameters of the cavity without the need of additional calibration measurements of reference materials, simplifying the measurement procedure and minimizing the measurement uncertainty.

The paper describes the DKV design and electromagnetic modelling, and provides dielectric properties of several materials in a wide range of dielectric constant and loss factor values, including uncertainty and a comparative study with other well-established instruments and methods. It provides an accuracy of 1.5% in the dielectric constant and 5% in the loss factor, which is particularly relevant since the losses of materials considered in the paper spread throughout four orders of magnitude (from 10−3 to 10).

You will find additional information about the technical specifications of DKV here, and several practical examples:

DIMAS at IGARSS2018

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The Microwave Division of ITACA has participated in the 38th annual symposium of the IEEE Geoscience and Remote Sensing Society (GRSS) [IGARSSS 2018] held in Valencia from July 22nd to 27th, 2018.

Dimas has published a paper in collaboration with ARAMCO SERVICES COMPANY in Houston (Texas-USA) that shows the permittivity of Shale at different frequencies from 1 GHz to 3.5 GHz with a Dimas equipement based on a resonant TM0np cavity and measurements performed at different harmonics.

The method has been validated with Rexolite values with an excellent match.

Paper at the European Microwave Week

Dimas group participated in the European Microwave Week that was held in Nuremberg in October 2017, with the paper entitled “Analysis of an Overmoded Re-Entrant Cavity“. It was authored by David Marques-Villarroya, Felipe Penaranda-Foix, Beatriz Garcia-Banos, Jose Manuel Catala-Civera, Jose Daniel Gutierrez-Cano.

The paper deals with the well knows reentrant cavity, but taking into account the complete set of modes and presenting a chart to fully charaterize the cavity. It is based on the Circuit Analisys Method, being developed in the Microwave Division of ITACA Research Institute since some years ago.

The paper was selected for a short video presentation that can be found here and also in this YouTube link:

New paper published at IEEE MTT

DIMAS has published in April 2017 a new research paper at IEEE Transactions on Microwave Theory and Techniques. It is entitled “Enhanced Full-Wave Circuit Analysis for Modeling of a Split Cylinder Resonator” and presents another way of analysing the split resonator by circuit analysis. Circuit analysis applied to electromagnetic strutures is a technique that DIMAS has been developing last years, with several publications and applications specially in the field of dielectric characterization of material (dielectrometry).

 

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Split cavity and circuit analysis

In this case the improvement consists of using higher modes in the circuit characterization of all the simple networks that appear when the original structure is segmented into smallest and simplest ones. Then, not only the TM0np modes can be analysed but also all the set of TE and TM resonant modes that appear in the split cavity resonator.
The main application will be the possibility of using more resonant modes to characterize planar materials and to increase the frequency band where the permittivuity is calculated.
This paper is a part of the research work performed by David Marqués-Villarroya in his way to get the PhD in Electrical Engineering, and is the result of an extension of the original paper published in the International Microwave Symposium (IMS) held in San Francisco (USA) in May 2016.

New research paper in the “Journal of Food Engineering”

DIMAS has published a new research paper in early 2017 in the Journal of Food Engineering. The paper is entitled: “Dynamic measurement of dielectric properties of food snack pellets during microwave expansion“.

This is the result of a collaboration between PepsiCo R&D and DIMAS.

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Calorimeter facility at DIMAS laboratory

The papers presents in situ dielectric properties measurements of a starch-based foodfood pellet during microwave expansion. To do this, a dual-mode cylindrical cavity that allowed simultaneous microwave heating and dielectric measurements of a single pellet inside a quartz tube was used, ensuring uniform heating during microwave processing.
This systemm in shown in the figure. It is a DIMAS facility that 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.

DIMAS participates in COSMIC european project

DIMAS is participating in the COSMIC (European Training Network for Continuous Sonication and Microwave Reactors) european project.
The kick-off of the project was held in Leuven (Belgium) in March 2017, where all the 12 partners (beneficiaries and partner organizations) participated and exchanged discussions about the future of the project.
All the 15 students that will be devolping their PhD in the frame of this project also participated in the kick-off meeting and also discussed with the host partners the activity to be done during their visits along the duration of the project.
DIMAS will host four of these students: two of them will arrive from KU Leuven (Belgium), one from UCL (UK) and the last one from Universidad de Zaragoza (Spain).
The student hosted by DIMAS will perform experiments with the microwave facilities available at DIMAS laboratory.

The project science and technology objectives are to develop:

1.-Resource-efficient multiphase reactions in the fields of organic synthesis (C–H, C=C and C=C bond activation) and nanoparticle synthesis (for use in catalysis and health applications);
2.-Intensified reactors that efficiently integrate milliflow technology with ultrasound and/or microwave actuation;
3.-Knowledge-based assessment and decision methodologies to evaluate and select process-intensification technologies.

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Group photo during the kick-off meeting in Leuven

New paper published in Journal Materials

logo_journal_materialsA recent work developed by Microwave Division has been published in the Journal Materials, as a part of the Special Issue “Microwave Materials Processing”.

Microwave-assisted processes have recognized advantages over more conventional heating techniques. However, the effects on the materials microstructure are still a matter of study, due to the complexity of the microwaves-matter interaction, especially at high temperatures. Recently developed advanced microwave instrumentation allows the study of high temperature microwave heating processes in a way that was not possible before.

In this paper, different materials and thermal processes induced by microwaves have been studied through the in situ characterization of their dielectric properties with temperature.

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The figure shows an example of the dielectric properties of a ceramic frit sample together with the sample height up to 1200ºC. Important variations in the sample height are also observed during the process, due to different reactions and transformations. At temperatures above 450ºC the water inside the sample passes to a gas state. The gas tries to exit leading to the expansion of the sample. On the contrary, a contraction takes place above 900ºC, due to the melting of the sample.

The dielectric properties of the sample slightly increase with increasing temperature up to 700ºC. At this temperature, the dolomite decomposition starts, and a sharp change is observed in dielectric constant and loss factor.  A second increase starts about 900-1000ºC, due to the melting of the sample. The effect of the melting is more pronounced in the sample loss factor, reaching from very low values at room temperature to high values at the end of the process.

This and other examples presented in the paper illustrate how the dielectric properties correlate very well to the material transformations at increasing temperatures. This knowledge is crucial in several aspects:

  • to analyze the effects of the microwave field on the reaction pathways
  • to design and optimize microwave-assisted processes
  • to predict the behavior of materials leading to repeatable and reliable heating processes

 

Best Poster Award in GCMEA Conference

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DiMaS group has participated in the Third Global Congress on Microwave Energy Applications -GCMEA-. Our contribution entitled “Study of microwave thermal processes through in situ Raman and dielectric spectroscopy” was awarded with the Best Poster Award of the conference. We congratulate our researcher J.D. Gutiérrez for the quality of his work.

In the poster, it was explained that the use of microwave energy for materials processing is well known, however, the heating mechanisms and the particular thermal behavior of materials under high frequency electromagnetic fields is still a matter of research.  Recent works highlight the need of further investigations to understand the microwave-matter interactions behind the materials thermal processes.

The strategy presented in the poster consists of linking the information given by dielectric properties to the thermal processes that occur in the material. To this end, Raman spectroscopy is applied to obtain information about the microstructure and the chemo-physical changes in the materials. The in situ combination of both techniques (dielectric and Raman) in real time during microwave processing gives useful and innovative information about the heating mechanisms of different materials.

Best Poster Award

DiMaS group in collaboration with CSIC Institute of Ceramic and Glass, has participated in the 15th International Conference on Microwave and High Frequency Heating held in Cracow (Poland) in September, 2015.

Our joint contribution entitled “DIELECTRIC PROPERTIES OF CERAMIC FRIT UP TO 1200ºC AND CORRELATION WITH THERMAL ANALYSIS”, developed in theAward_01 frame of the european DAPhNE project (DAPHNE- Development of adaptive ProductioN systems for Eco-efficient firing processes), has been awarded with the Best Poster Award of the conference.

This award confirms the increasing interest on the in situ dielectric characterization of materials under microwave processing at high temperatures (>1000ºC), and its use for the identification of thermal processes induced by the high-frequency electromagnetic fields.

This work, as other similar shown in publications tab, is the result of years of collaboration between both research groups in the field of microwave-sintering of materials with microwave power with in-situ dielectric characterization.

New paper at IEEE Trans. on MTT

DIMAS Group published a new paper at the IEEE Tras. on Microwave Theory and Techniques [1]

This paper presents a new system developed at DIMAS laboratory and consists of a new microwave cavity and heating system for microwave processing and in situ dynamic measurements of the complex permittivity of dielectric materials at high temperatures (around 1000 ºC).The method is based on a dual-mode cylindrical cavity where heating and testing are performed by two different swept frequency microwave sources and a cross-coupling filter that isolates the signals coming from both sources.

This system provides the dielectric propertieOLYMPUS DIGITAL CAMERAs 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.

The functionality of the microwave dielectric measurement system has been demonstrated by heating and measuring glass and ceramic samples up to 1000 ºC.

Additionally, the correlation of the complex permittivity with the heating rate, temperature, absorbed power, and other processing parameters can help to better understand the interactions that take place during microwave heating of materials at high temperatures compared to conventional heating.

 

[1] José M. Catalá-Civera, Antoni J. Canós, Pedro Plaza-González, José D. Gutiérrez, Beatriz García-Baños, and Felipe L. Peñaranda-Foix, “Dynamic Measurement of Dielectric Properties of Materials at High Temperature During Microwave Heating in a Dual Mode Cylindrical Cavity”. IEEE Trans. on MTT, Vol. 63, No. 9, Sep. 2015, pp. 2905-2914. DOI: 10.1109/TMTT.2015.2453263