STEP project: Microwave Technology for Stone Eco-Efficient Production

Logo_Proyecto_STEP

The production chain in natural stone factories involves a drying stage in natural gas kilns, followed by the application of reinforcement resins to seal cracks or fractures, and finally a curing stage to harden the resins in natural gas furnaces.

These are the 2 eco-innovations achieved thanks to the STEP Project:

  • The industrial scale validation of a new microwave on-line processing system for rapid and continuous curing resin reinforcement of flat semi finished natural stone products, replacing conventional thermal systems based on natural gas and electric support elements.
  • Validation of water-based eco-resins based on nano-composites with zero emission of volatile organic compounds.

DIMAS participated in the project with the development of the new on-line open system for continuous marble drying and resin curing process with microwave energy.

STEP_furnace

Logo_EC_ECO_InnovationThe implementation of this development results in significant benefits for the natural stone sector in terms of efficiency, productivity and utilization of raw materials, as well as in health and safety aspects for employees of the production lines.

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

Dielectric Kit for Materials Characterization at Microwave Frequencies

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.

The Dielectric Kit for Vials is a new instrument developed by the Microwave Division of the institute ITACA to determine the complex permittivity (dielectric constant and loss factor) of a wide range of liquid, granular or powdered materials around the ISM frequency of 2.45 GHz. It is a complete solution which includes all necessary components to perform the generation, control and analysis of microwave signals, calculation of dielectric properties and display of results.

Two versions of the Dielectric Kit for Vials have been designed depending on the sample volume (with standard vials of 1mL or 8 mL). The measurement probe dimensions have been optimized in each case to provide repeatability and high accuracy in the determination of materials dielectric properties. Unlike other available equipment, calibration and adjustment with reference liquids is not necessary, and measurement of sample dielectric properties is fast and convenient.

OPERATION PRINCIPLE

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.

EXAMPLES OF MEASUREMENTS

This equipment is specially designed for liquid, granular or powdered materials. Solid materials might be measured if machined in rod shape with the inner vial dimensions. The following table shows some measurements of common materials. Comparisons with other measurement methods or published data are also included.

TECHNICAL SPECIFICATIONS

  • Frequency range: 1.5GHz to 2.6GHz (nominal, limited by MUT properties)
  • Dielectric constant: ε′<100
  • Loss factor: 0.001<ε′′<15
  • Accuracy: About 1% in dielectric constant and 2-5 % in the loss factor
  • Repeatability and Linearity 0.2%
  • Material under test assumptions:  (Minimum sample volume required :1mL (vial external diameter 4.1 mm) or 8 mL (vial external diameter 5.1mm), non-magnetic, isotropic, homogeneous (uniform composition). For granular materials (particle diameter < 2 mm) measurement repeatability is dependent on density variation.
  • Calibration: No calibration is needed
  • Microwave output: 0 dBm
  • Communication with PC: USB
  • Probe Materials: Aluminum
  • Dimensions: 190mm x 230mm x 85mm
  • Operating Temperature: 22-50 °C
  • Required OS: Windows XP/Vista/7

Microwave Technology for Sintering High-Quality Materials with Unique Properties

A recent study published in the International Journal of Applied Ceramic Technology has shown the benefits of using microwave technology as a sintering technique. In this work, lithium aluminosilicate was fabricated by three different methods: conventional, spark plasma and microwave sintering, from 1200 to 1300°C.

OLYMPUS DIGITAL CAMERAMicrowave technology developed by DIMAS made possible to obtain fully dense glass-free lithium aluminosilicate bulk material (>99%) with near-zero and controlled coefficient of thermal expansion and excellent mechanical properties (7.1 GPa of hardness and 110 GPa of Young’s modulus).

Microwave sintering, compared with the other techniques, demonstrated a number of benefits. The combination of rapid heating with low energy applied by the microwave technology (eco-friendly process) and the dramatic reduction in cycle time allowed densification without glass phase formation.

The microwave sintering technique developed in this work opens the opportunity to produce breakthrough materials with low or negative coefficient of thermal expansion and excellent mechanical properties, for example, in the design of new composite materials for space applications.

PhD about materials sintering with microwaves

On Friday April 10th, 2015, a PhD using Microwave power to sinter materials was presented at UPV by Dr. Rut Benavente. The PhD is entitled: “DESARROLLO DE MATERIALES CERÁMICOS AVANZADOS CON ALTAS PRESTACIONES MEDIANTE TÉCNICAS NO CONVENCIONALES DE SINTERIZACIÓN: MICROONDAS” (“Development of Advanced Ceramic Materials with High Performances by Non-Conventional Techniques: Microwaves“)

Calorimeter for materials sintering

Calorimeter for materials sintering

The PhD is using a microwave applicator (shown in the figure) designed by DIMAS group. This applicator is optimized for sintering materials and is based on a tunable cylindrical cavity that allows to control the microwave power applied to the sample. This allows the engineers to control the heating speed of the sample to achieve the appropriate temperature at the correct time.

Additionally this applicator can be used for vacuum experiments or differente atmosphere inside the reaction tube, and even a Raman Spectroscopy or video recording can be included in the system to improve the performance.

The PhD shows the results for litium aluminosilicates (called LAS) and LAS composites, like LAS/Al2O3 or LAS/Graphene.

A list of publications related with this PhD is available in this site in the publications section (press here)

Portable Impedance Measurement System

The Microwave Division (DIMAS) of the ITACA Research Institute develops specific equipment for microwave processes to be used according to industrial conditions: simple, affordable and robustness, while retaining a useful subset of their current functionality. Aside from these applications, portable, accurate and low cost network analyzer provide an accessible platform for new and interesting applications of network analysis at industrial level to be developed.

Figure 1 shows the block diagram of a low power network analyzer developed for off-line impedance measurements in industrial environments.

Fig. 1. Schematic diagram of the reflectometer system based on two AD-8302 radio receiver

 Microwave source is implemented as a close- loop PLL microwave synthesizer. Receiver is composed by two AD8302 integrated RF detectors shifted 90º, to avoid phase ambiguity. Due to the dual Matched Logarithmic Amplifiers with Phase Detector of the IC, the receiver presents a dynamic range of 45 dB and a high stability with the temperature (-25ºC to 50ºC) from low frequencies up to 2.7GHz.

The separation of forward and reverse waves is carried out by two directional couplers to increase directivity. Output voltage signals from the detectors are digitalized in a multichannel analog to digital converter and processed in a microprocessor connected with a serial link to a personal computer or PLC controller. Digital lines for the control of the synthesizer are also driven by the microprocessor to synchronize the whole measurement procedure.

Fig. 2 shows a picture of a low power network analyzer developed for off-line measurements in magnitude and phase of impedance (reflection) at 2.45 GHz in a standard WR340 waveguide. The equipment is a complete solution for network analysis which includes all necessary components to perform the generation, separation, control and analysis of microwave signals and display of results.

Fig. 2. Picture of low power Vector Reflectometer around 2.45 GHz manufactured from the schematic of Fig.1

Calibration or adjustments with reference loads is not necessary and measurements are simple and fast. The waveguide reflectometer allows a non-experienced user in high frequency measurements a fast tuning or adjusting of a microwave applicator.

CONTROL SOFTWARE

The Vector reflectometer is driven from a PC or PLC controller, connected through a USB, RS-232 or CAN serial link. For PC interface, a Labview-based software has been developed to perform all the necessary functions with a user-friendly interface (Windows XP/Vista/7).

The control software permits the automatic measurement of module and phase of the reflection coefficient and impedance. Representation modes include: logarithmic magnitude, phase and Smith Chart.

TECHNICAL SPECIFICATIONS:

  • Frequency range: 2.2 to 2.6 GHz (extended to other ranges)
  • Waveguide: WR340
  • Microwave power level: 0 dBm
  • Dynamic Range: 40/45 dB
  • Uncertainty: +-0.1dB / +- 1º
  • Measurement rate: up to 4 sweeps per second
  • Operating Temperature: 10-50 °C