Full-wave analysis of dielectric-loaded cylindrical waveguides and cavities using a new four-port ring network

“© 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising 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.”In this paper, a full-wave method for the electromagnetic analysis of dielectric-loaded cylindrical and coaxial waveguides and cavities is developed. For this purpose, a new four-port ring network is proposed, and the mode-matching method is applied to calculate the generalized admittance matrix of this new structure. A number of analyses on dielectric-loaded waveguide structures and cavities have been conducted in order to validate and to assess the accuracy of the new approach. The results have been compared with theoretical values, numerical modeling from the literature, and data from commercial electromagnetic simulators. The method has been also applied to the accurate determination of dielectric properties, and we provide an example of these measurements as another way to validate this new method. © 1963-2012 IEEE.This work was supported by the Ministry of Science and Innovation of Spain under Project MONIDIEL (TEC2008-04109). The work of F. L. Penarada-Foix was supported by the Conselleria de Educacion of the Generalitat Valenciana for economic support (BEST/2010/210).Penaranda-Foix, FL.; Janezic, MD.; Catalá Civera, JM.; Canós Marín, AJ. (2012). Full-wave analysis of dielectric-loaded cylindrical waveguides and cavities using a new four-port ring network. IEEE Transactions on Microwave Theory and Techniques. 60(9):2730-2740. https://doi.org/10.1109/TMTT.2012.2206048S2730274060

Low temperature degradation behaviour of 10Ce-TZP/Al2O3 bioceramics obtained by microwave sintering technology

Zirconia is one of the most used ceramics, especially for biomedical applications, due to its exceptional mechanical properties. However, it is commonly known that its properties can be diminished owing to a low temperature degradation (LTD). This phenomenon consists on a spontaneous phase transformation, from tetragonal to monoclinic, under certain conditions, which is accelerated when the samples are exposed under high levels of humidity at a temperature range between 20-300 ºC. In addition to the fact that the monoclinic phase presents worse mechanical properties than the tetragonal one, there is a volume change of 4% between phases that gives rise to defects in the material as microcracks. Due to this reason, zirconia prostheses failed catastrophically inside the human body between 1999 and 2001 (1). Previous researches reveal that Al2O3 addition suppress the propagation of phase transformation (2). Thus, the aim of the present work is to study the hydrothermal ageing of zirconia doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) composite, which has been sintered by microwave employing two different frequencies: 2.45 and 5.8 GHz. Microwave heating technology is based on the absorption of electromagnetic radiation by the material, which allows the sample to be heated. So far, most microwave heating equipments use 2.45 GHz; accordingly, the novelty of this study is to employ a frequency of 5.8 GHz and to investigate its effect on LTD. LTD is carried out in an autoclaved in steam at 120 ºC and 1.2 bar, because these conditions accelerate the hydrothermal aging process (3). In order to characterize the degraded samples, micro-Raman spectroscopy, AFM, nanoindentation technique and electronic microscopy have been performed. References 1. Norton, M. R., Yarlagadda, R., Anderson, G. H. J. Bone Joint Surg. Br., 2002, 84–B, 631–635. 2. Fabbri, P., Piconi, C., Burresi, E., Magnani, G., Mazzanti, F., Mingazzini, C. Dent. Mater., 2014. 3. Presenda, Á., Salvador, M. D., Moreno, R., Borrell, A. J. Am. Ceram. Soc., 2015, 98, 3680–3689

Mechanical properties and coefficient of thermal expansion of β-eucryptite sintered by microwave technique

[ES]: La técnica de sinterización no convencional de microondas permite obtener materiales de ß-eucriptita en estado sólido cristalino con densidades cercanas a la teórica (~99 %). Se ha observado una diferencia considerable en estos materiales respecto a la técnica convencional en términos de densificación, microestructura, coeficiente de expansión térmica y propiedades mecánicas. Los valores de dureza y módulo de Young obtenidos mediante sinterización por microondas a 1200 ºC-5 min han sido relativamente altos, 6.8 GPa y 101 GPa, respectivamente, en comparación con el material obtenido mediante horno convencional (3.9 GPa y 58 GPa, respectivamente). Los datos dilatométricos obtenidos, incluyendo el intervalo de temperatura criogénica (-150 ºC a +150 ºC), muestran un coeficiente de expansión térmica controlado y negativo en todo el rango de temperaturas. La combinación de un calentamiento rápido junto con la reducción drástica en el tiempo de ciclo y el ahorro energético, hace que la técnica de microondas sean una clara alternativa a otro tipo de calentamientos.[EN]: Microwave non-conventional sintering technique allows obtaining fully dense glass-free β-eucryptite bulk material (∼99 %). A considerable difference in the densification, microstructure, coefficient of thermal expansion behaviour and mechanical properties, between conventional and non-conventional sintered specimens was observed. The hardness and Young’s modulus values obtained by microwaves at 1200 °C-5min have been relatively high, 6.8 GPa and 101 GPa, respectively, compared to conventional sintering (3.9 GPa and 58 GPa, respectively). Very low thermal expansion materials have been obtained in a wide temperature range including cryogenic temperatures (from -150 ºC to 150 ºC). The high heating rate along with the lower energy consumption makes microwave technique a clear alternative to other types of sintering methods.Los autores desean agradecer el apoyo financiero recibido de la UPV dentro de los proyectos SP20120621 y SP20120677 y, al gobierno español a través del proyecto (TEC2012-37532-C02-01). A. Borrell, agradece al Ministerio de Ciencia e Innovación su contrato de Juan la Cierva (JCI-2011-10498).Peer Reviewe

The impact of chorionicity on pregnancy outcome and neurodevelopment at 2 years old among twins born preterm: the EPIPAGE-2 cohort study

OBJECTIVE To compare the short‐ and mid‐term outcomes of preterm twins by chorionicity of pregnancy. DESIGN Prospective nationwide population‐based EPIPAGE‐2 cohort study. SETTING 546 maternity units in France, between March and December 2011. POPULATION A total of 1700 twin neonates born between 24 and 34 weeks of gestation. METHODS The association of chorionicity with outcomes was analysed using multivariate regression models. MAIN OUTCOME MEASURES First, survival at 2‐year corrected age with or without neurosensory impairment, and second, perinatal, short‐, and mid‐term outcomes (survival at discharge, survival at discharge without severe morbidity) were described and compared by chorionicity. RESULTS In the EPIPAGE 2 cohort, 1700 preterm births were included (850 twin pregnancies). In all, 1220 (71.8%) were from dichorionic (DC) pregnancies and 480 from monochorionic (MC) pregnancies. MC pregnancies had three times more medical terminations than DC pregnancies (1.67 versus 0.51%, P < 0.001), whereas there were three times more stillbirths in MC than in DC pregnancies (10.09 versus 3.78%, P < 0.001). Both twins were alive at birth in 86.6% of DC pregnancies compared with 80.0% among MC pregnancies (P = 0.008). No significant difference according to chorionicity was found regarding neonatal deaths and morbidities. Likewise, for children born earlier than 32 weeks, the 2‐year follow‐up neurodevelopmental results were not significantly different between DC and MC twins. CONCLUSIONS This study confirms that MC pregnancies have a higher risk of adverse outcomes. However, the outcomes among preterm twins admitted to neonatal intensive care units are similar irrespective of chorionicity

Microwave sensor system for continuous monitoring of adhesive curing processes

A microwave sensor system has been developed for monitoring adhesive curing processes. The system provides continuous, real-time information about the curing progress without interfering with the reaction. An open-coaxial resonator is used as the sensor head, and measurements of its resonance frequency and quality factor are performed during cure to follow the reaction progress. Additionally, the system provides other interesting parameters such as reaction rate or cure time. The adhesive dielectric properties can also be computed off-line, which gives additional information about the process. The results given by the system correlate very well with conventional measurement techniques such as differential scanning calorimetry, combining accuracy and rate with simplicity and an affordable cost. © 2012 IOP Publishing Ltd.The authors thank Rut Benavente Martinez for her assistance in the DSC experiments. The contract of BG-B is financed by the Ministry of Science and Innovation of Spain, through the 'Torres Quevedo' Sub-programme, which is also co-financed by the European Social Fund (ESF). This work has been financed by the Ministry of Science and Innovation of Spain through the project MONIDIEL (TEC2008-04109).García Baños, B.; Catalá Civera, JM.; Penaranda-Foix, FL.; Canós Marín, AJ.; Sahuquillo Navarro, O. (2012). Microwave sensor system for continuous monitoring of adhesive curing processes. Measurement Science and Technology. 23(3). https://doi.org/10.1088/0957-0233/23/3/035101S233Jost, M., & Sernek, M. (2008). Shear strength development of the phenol–formaldehyde adhesive bond during cure. Wood Science and Technology, 43(1-2), 153-166. doi:10.1007/s00226-008-0217-2Costa, M. L., Botelho, E. C., Paiva, J. M. F. de, & Rezende, M. C. (2005). Characterization of cure of carbon/epoxy prepreg used in aerospace field. Materials Research, 8(3), 317-322. doi:10.1590/s1516-14392005000300016Chen, J., & Hojjati, M. (2007). Microdielectric analysis and curing kinetics of an epoxy resin system. Polymer Engineering & Science, 47(2), 150-158. doi:10.1002/pen.20687Sernek, M., & Kamke, F. A. (2007). Application of dielectric analysis for monitoring the cure process of phenol formaldehyde adhesive. International Journal of Adhesion and Adhesives, 27(7), 562-567. doi:10.1016/j.ijadhadh.2006.10.004Núñez, L., Gómez-Barreiro, S., Gracia-Fernández, C. A., & Núñez, M. R. (2004). Use of the dielectric analysis to complement previous thermoanalytical studies on the system diglycidyl ether of bisphenol A/1,2 diamine cyclohexane. Polymer, 45(4), 1167-1175. doi:10.1016/j.polymer.2003.12.024Lefebvre, D. R., Han, J., Lipari, J. M., Long, M. A., McSwain, R. L., & Wells, H. C. (2006). Dielectric analysis for in-situ monitoring of gelatin renaturation and crosslinking. Journal of Applied Polymer Science, 101(5), 2765-2775. doi:10.1002/app.21631Cordovez, M., Li, Y., & Karbhari, V. M. (2004). Assessment of Dielectrometry for Characterization of Processing and Moisture Absorption in FRP Composites. Journal of Reinforced Plastics and Composites, 23(4), 445-456. doi:10.1177/0731684404031980Das, N. K., Voda, S. M., & Pozar, D. M. (1987). Two Methods for the Measurement of Substrate Dielectric Constant. IEEE Transactions on Microwave Theory and Techniques, 35(7), 636-642. doi:10.1109/tmtt.1987.1133722Fioretto, D., Livi, A., Rolla, P. A., Socino, G., & Verdini, L. (1994). The dynamics of poly(n-butyl acrylate) above the glass transition. Journal of Physics: Condensed Matter, 6(28), 5295-5302. doi:10.1088/0953-8984/6/28/007Givot, B. L., Krupka, J., & Belete, D. Y. (s. f.). Split post dielectric resonator technique for dielectric cure monitoring of structural adhesives. 13th International Conference on Microwaves, Radar and Wireless Communications. MIKON - 2000. Conference Proceedings (IEEE Cat. No.00EX428). doi:10.1109/mikon.2000.913931Canos, A. J., Catala-Civera, J. M., Penaranda-Foix, F. L., & Reyes-Davo, E. (2006). A novel technique for deembedding the unloaded resonance frequency from measurements of microwave cavities. IEEE Transactions on Microwave Theory and Techniques, 54(8), 3407-3416. doi:10.1109/tmtt.2006.877833Marks, R. B., & Williams, D. F. (1992). A general waveguide circuit theory. Journal of Research of the National Institute of Standards and Technology, 97(5), 533. doi:10.6028/jres.097.024Harrington, R. F. (1967). Matrix methods for field problems. Proceedings of the IEEE, 55(2), 136-149. doi:10.1109/proc.1967.5433Baker-Jarvis, J., Janezic, M. D., Domich, P. D., & Geyer, R. G. (1994). Analysis of an open-ended coaxial probe with lift-off for nondestructive testing. IEEE Transactions on Instrumentation and Measurement, 43(5), 711-718. doi:10.1109/19.328897Taylor, B. N. (1994). Guidelines for evaluating and expressing the uncertainty of NIST measurement results. doi:10.6028/nist.tn.1297Casalini, R., Corezzi, S., Livi, A., Levita, G., & Rolla, P. A. (1997). Dielectric parameters to monitor the crosslink of epoxy resins. Journal of Applied Polymer Science, 65(1), 17-25. doi:10.1002/(sici)1097-4628(19970705)65:13.0.co;2-tPreu, H., & Mengel, M. (2007). Experimental and theoretical study of a fast curing adhesive. International Journal of Adhesion and Adhesives, 27(4), 330-337. doi:10.1016/j.ijadhadh.2006.06.004Harper, D. P., Wolcott, M. P., & Rials, T. G. (2001). Evaluation of the cure kinetics of the wood/pMDI bondline. International Journal of Adhesion and Adhesives, 21(2), 137-144. doi:10.1016/s0143-7496(00)00045-2Garcia-Banos, B., Canos, A. J., Penaranda-Foix, F. L., & Catala-Civera, J. M. (2011). Noninvasive Monitoring of Polymer Curing Reactions by Dielectrometry. IEEE Sensors Journal, 11(1), 62-70. doi:10.1109/jsen.2010.2050475He, Y. (2001). DSC and DEA studies of underfill curing kinetics. Thermochimica Acta, 367-368, 101-106. doi:10.1016/s0040-6031(00)00654-7Núñez-Regueira, L., Gracia-Fernández, C. A., & Gómez-Barreiro, S. (2005). Use of rheology, dielectric analysis and differential scanning calorimetry for gel time determination of a thermoset. Polymer, 46(16), 5979-5985. doi:10.1016/j.polymer.2005.05.06

Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery

One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeon’s navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions

Effect of microwave sintering on microstructure and mechanical properties in Y-TZP materials used for dental applications

The aim of this work is to study the application of microwave sintering to consolidate yttria-stabilized zirconia polycrystalline (Y-TZP) ceramics commonly applied in dentistry, so as to obtain highly dense materials and fine microstructure with shorter sintering cycles. Three Y-TZP materials are considered: two commercially available for dental applications and one laboratory studied powder. Microwave sintering was carried out at 1200 and 1300 degrees C for 10 min and conventional sintering at 1300 and 1400 degrees C for 2 h. Relative density, Vickers hardness and fracture toughness values for sintered samples were determined. Microwave sintering results, generally, in improved mechanical properties of the materials in terms of hardness and fracture toughness compared to conventional sintering and, in some cases, at lower sintering temperatures. A finer grain microstructure (final grain size < 250 min) was obtained with microwave sintering for both commercial materials. Fracture toughness values differ significantly between sintering techniques and chosen parameters. These results suggest that microwave heating can be employed to sinter Y-TZP commercial ceramics for dental applications obtaining improving the mechanical properties of the materials with a very important time and energy consumption reduction. Crown Copyright (C) 2015 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.The authors would like to thank the financial support received from Universidad Politecnica de Valencia under Project 5P20120677 and Ministerio de Economia y Competitividad (MINECO) and co-funded by ERDF (European Regional Development Funds) through the Project (IEC2012-37532-C02-01). A. Borrell acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva Contract (JCI-2011-10498) and the Generalitat Valenciana for the financial support under Project GV/2014/009. A. Presenda acknowledges the Generalitat Valenciana for his Santiago Grisolia program scholarship (GRISOLLV2013/035). The authors would also like to acknowledge Prof. Dr. M. F. Sold from the Faculty of Medicine and Odontology at the Universidad de Valencia for supplying the commercial materials.Presenda, Á.; Salvador Moya, MD.; Penaranda-Foix, FL.; Moreno, R.; Borrell Tomás, MA. (2015). Effect of microwave sintering on microstructure and mechanical properties in Y-TZP materials used for dental applications. Ceramics International. 41(5, Part B):7125-7132. https://doi.org/10.1016/j.ceramint.2015.02.025S71257132415, Part

Fabrication of near-zero thermal expansion of fully dense beta-eucryptite ceramics by microwave sintering

Microwave heating is proposed as non-conventional technique for the sintering of optimal lithium aluminosilicate compositions of &#946;-eucryptite system. The coefficient of thermal expansion and mechanical properties of the sintered samples has been studied under the influence of microwave heating. The ad hoc synthesized &#946;-eucryptite together with the microwave sintering technique developed in this work open the opportunity to produce breakthrough materials with low or negative coefficient of thermal expansion and excellent mechanical properties, as a Young s modulus of 110 GPa. The combination of rapid heating with low energy applied by the microwave technology (eco-friendly process) and the dramatic reduction in cycle time allows densification without glass phase formation. Results of the coefficient of thermal expansion of the &#946;-eucryptite ceramics presented here under cryogenic conditions will be of value, for example, in the future design of new composite materials for space applicationsThe authors would like to thank Dr. Emilio Rayon for performing the nanoindentation analysis in the Materials Technology institute (ITM) of the Polytechnic University of Valencia (UPV) and your financial support received of UPV under Projects SP20120621 and SP20120677 and Spanish Government through the Project MONIDIEL (TEC2008-04109). A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for a Juan de la Cierva contract (JCI-2011-10498) and SCSIE of the University of Valencia.Benavente Martínez, R.; Borrell Tomás, MA.; Salvador Moya, MD.; Garcia-Moreno, O.; Penaranda-Foix, FL.; Catalá Civera, JM. (2014). Fabrication of near-zero thermal expansion of fully dense beta-eucryptite ceramics by microwave sintering. Ceramics International. 40(1):935-941. https://doi.org/10.1016/j.ceramint.2013.06.089S93594140