Proceedings 17th International Conference on Microwave and High Frequency Heating最新文献

{"title":"DIELECTRIC MONITORING OF THE PAN FIBER STABILIZATION PROCESS","authors":"J. Hofele, G. Link, J. Jelonnek","doi":"10.4995/ampere2019.2019.9788","DOIUrl":"https://doi.org/10.4995/ampere2019.2019.9788","url":null,"abstract":"Carbon fiber composites are key components of future lightweight applications. But, due to the energy intensive production of carbon fibers, the final material costs are not competitive if compared to steel or aluminum even though the mechanical properties are superior [1]. Hence, a new approach is necessary. Microwave heating might be the solution [2]. For the successful design of an appropriate system, the knowledge of the temperature-dependent dielectric properties of the raw material together with the chemical process during the production is mandatory. The production process starts from the Polyacrylonitrile fiber (PAN fiber) and consists of two major stages: the initial stabilization and the final carbonization. The most significant energy saving is expected at the stabilization stage [3]. The dielectric properties of conventionally stabilized PAN fibers and virgin PAN fibers were measured at room temperature in a TM010-mode cylindrical cavity using the cavity perturbation method. The measured differences in the dielectric constants and the material densities of both fibers (see Table 1) leads to the assumption that the change in the dielectric properties can be followed during the stabilization process and allows controlling the chemical reaction. Currently a system is set up that enables the in-situ recording of the chemical reaction during the stabilization process by using conventional heating. Figure 1 shows the schematic of the setup. The PAN fibers are located in a quartz tube. The conventional heating bases on the controlled flow of hot air. Thermocouples measure the temperatures at the entry and the exit points of the hot air. It is expected that the data acquired from the measurements will provide useful information about the reaction kinetics, which is important for the design of a microwave assisted stabilization process.","PeriodicalId":277158,"journal":{"name":"Proceedings 17th International Conference on Microwave and High Frequency Heating","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130705559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MILLIMETER WAVE ABSORPTION IN HYDROXYAPATITE AND 3YSZ CERAMICS IN WIDE TEMPERATURE RANGE","authors":"A. Eremeev, S. V. Egorov, V. V. Kholoptsev","doi":"10.4995/ampere2019.2019.9754","DOIUrl":"https://doi.org/10.4995/ampere2019.2019.9754","url":null,"abstract":"In the field of ceramic-based materials processing the last three decades has been marked by significant academic and industry interest in Additive Manufacturing (AM) technology due to its capability to produce ceramic parts with complex geometry and customizable materials properties. Conceptually, AM technology is a layer-by-layer fabrication of three dimensional physical parts directly from computer-aided design [1]. Solidification of the parts prepared from substances containing ceramic powder may be performed either by conventional heat treatment of a part as whole or by directed energy deposition. Both these strategies can be implemented using gyrotron-based millimeter-wave facilities allowing alternatively both the uniform heating of large-size parts in multi-mode cavities and local heating by focused wave-beams [2]. Hydroxyapatite- and yttria-stabilized zirconia-based ceramics are widely used in biomedical applications due to their high biocompatibility. The knowledge of their microwave absorption variation with temperature and porosity as the materials are densified, is necessary to optimize the scheme of microwave heating. 8 mm diameter disks for the measurements were prepared by uniaxial compacting from commercially available hydroxyapatite (HA) powder and yttria-stabilized zirconia (3YSZ) powder (Tosoh corp.). The measurements were performed at 24 GHz 3 kW gyrotron system. Samples for measurements were placed into the gyrotron system applicator and surrounded with porous alumina based thermal insulation. The design of the applicator and insulation allowed performing optical measurements of both the sample size and temperature distribution over the surface of the sample using a digital monochrome CCD camera. Measurements were made by the calorimetric method, when the microwave power absorbed in the sample is determined basing on the difference of the heating/cooling rates at the moments of intentional abrupt change of the microwave power at different sample temperatures. Absorption coefficient was determined as a division of the absorbed power to the incident microwave power. Special calibration experiments were made for determining microwave power density in the applicator and inside the thermal insulation. The method allows to measure absorption coefficients in situ during the sintering process. Absorption coefficients of HA were obtained in the range of 200 C - 1200 C, and for 3YSZ - in the range of 400 C - 1400 C both in situ during sintering and for as sintered samples. Dependencies of the absorption coefficients on the temperature and porosity are discussed.     References Vaezi, M., et al., Int. J. Adv. Manuf. Technol., 2013, 67, 1721–1759. Bykov, Yu., Eremeev, A., et al., IEEE Trans. Plasma Science, 2004, 32, 67–72.","PeriodicalId":277158,"journal":{"name":"Proceedings 17th International Conference on Microwave and High Frequency Heating","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116599716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MEASUREMENT OF THE DIELECTRIC PROPERTIES OF LIQUID CRYSTAL MATERIAL FOR MICROWAVE APPLICATIONS","authors":"Juan R. Sánchez, V. Nova, C. Bachiller, B. Villacampa, Alberto de la Rua, R. Kronberger, Felipe L. Peñaranda, V. Boria","doi":"10.4995/ampere2019.2019.9983","DOIUrl":"https://doi.org/10.4995/ampere2019.2019.9983","url":null,"abstract":"Liquid Crystal (LC) is an anisotropic liquid material which flows like a liquid, but at the same time its molecules have an orientational order like in the solid state [1]. Thus, LC is a promising dielectric material for designing reconfigurable devices at microwave frequencies. In order to optimize the design of reconfigurable microwave devices, accurate values of the dielectric permittivity and the loss tangent of LCs are needed. However, new LCs are not well characterized at these frequencies because of its recent use for microwave applications. Therefore, the characterization in this frequency range is required for its practical use within microwave components and devices [2].   In this work, the split-cylinder resonator method has been used for the characterization of LCs at two frequency points, i.e. 5 and 11 GHz. The method is based on the measurement of the resonance frequency and quality factor of the two states of the LC molecules for extracting the complex dielectric permittivity [3].   For achieving these two states, no electric or magnetic fields are needed, just the cell must be turned 90º inside the cavity. The dielectric properties (permittivity and loss tangent) of four different LC samples, GT3-23002 from Merck and QYPD193, QYPD142, and QYPD036 from Qingdao QY Liquid Crystal Co, have been obtained. The highest values of the dielectric anisotropy are presented for the samples QYPD036 and QYPD193, together with the highest values of the corresponding loss tangent parameters. Furthermore, it is observed for all the LCs that the loss tangent decreases and the dielectric anisotropy increases at higher frequencies, which must be taken into account in the development of reconfigurable microwave devices.","PeriodicalId":277158,"journal":{"name":"Proceedings 17th International Conference on Microwave and High Frequency Heating","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129241689","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}