Fundamentos de ingeniería de mecanismos compuestos por imanes y superconductores en estado Meissner

A partir del desarrollo analítico para el cálculo de fuerzas entre superconductores e imanes basado en el modelo Pérez-Díaz/García-Prada (PDGP) hemos extendido su definición al cálculo de pares entre superconductores e imanes en estado Meissner completo. De las expresiones resultantes se han derivado varias pautas para la optimización y diseño de mecanismos levitantes. Hemos desarrollado un algoritmo para poder utilizar el modelo PDGP en programas de elementos finitos. Hemos estudiado además la sensibilidad a la caracterización del mallado. Hemos verificado experimentalmente la validez de estos algoritmos basados en el modelo PDGP mediante dos procedimientos. El primero basado en medidas de fuerza entre imán y superconductor y el segundo midiendo el ángulo de alineamiento entre imán y superconductor. En ambos casos obtenemos un buen acuerdo entre experimento y predicción teórica. Además, se ha demostrado que existe un fenómeno de alineamiento mecánico entre imanes y superficies superconductoras. Se ha estudiado este efecto analizando parámetros como el tamaño del imán y la altura sobre el superconductor. El acuerdo entre las medidas de fuerza y los valores calculados ha sido lo suficientemente bueno que nos ha permitido desarrollar un método mecánico para la determinación del campo de penetración inicial para superconductores de tipo II. Este método ha resultado ser más simple que los habituales hasta la fecha, además de proporcionar información adicional como la localización de la penetración inicial que otros métodos no pueden. Hemos utilizado las herramientas desarrolladas y verificadas para su cálculo en aplicaciones mecánicas concretas. Hemos calculado el comportamiento de un imán sobre una esfera superconductora comparando nuestros resultados con los obtenidos mediante otras expresiones para el cálculo de fuerzas basadas en el método de las imágenes. En una segunda aplicación, hemos aplicado el modelo para el cálculo de la interacción entre imán y superconductor toroidal demostrando que existe un efecto de volteo (o flip effect) entre un imán y un superconductor toroidal que puede ser utilizado en mecanismos levitantes. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Pérez-Díaz/García-Prada have proposed a model for the calculation of forces between magnets and superconductors in the Meissner state (PDGP model). This model has been extended to include a calculation of torque. From this extended model we have derived some guidelines for the design and optimization of levitating mechanisms. A FEM algorithm was programmed in order to use the PDGP model in a practical and universal way. We also studied the model’s sensitivity to the refinement of the mesh. This algorithm, based on the PDGP model, has been experimentally verified by the following two procedures. The first was based on the force measured between a magnet and a superconductor. The second measured the alignment angle between a magnet and a superconductor. Both procedures supported the experimental and theoretical predictions. Furthermore, a mechanical alignment effect between magnet and superconductor surfaces has been shown. This agreement is strong enough that we can develop a mechanical method for determining the first penetration field for type II superconductors. This method turns out to be simpler and intrinsically more precise than other methods and additionally, it can provide not only the value of the first penetration, but also the point where that first penetration of the field takes place. Finally, we have used the tools that have been developed and verified to calculate some specific mechanical applications. We have calculated the mechanical behavior of a magnet over a superconducting sphere, comparing our results to those obtained by other expressions based on the method of the images. In a second application, we have used the tools based on the PDGP model in order to calculate the mechanical interaction of a magnet and a superconducting torus; a flip effect on the stable orientation between a magnet and a superconducting torus was demonstrated. This effect could be used to design different levitating mechanisms

Modelling and Test of an Integrated Magnetic Spring-Eddy Current Damper for Space Applications

This article belongs to the Special Issue Actuators and Dampers for Vibration Control: Damping and Isolation Applications.We present the design, manufacturing, and dynamical characterization of a mechanical suspension made by a passive magnetic spring and an eddy current damper integrated into a single device. Three configurations with 2, 3, and 4 permanent magnets axially distributed with opposite polarizations are designed, simulated, manufactured, and tested. Stiffness of 2410, 2050, 2090 N/m and damping coefficient of 5.45, 10.52 and 17.25 Ns/m are measured for the 2-, 3-, and 4-magnets configurations, respectively. The magnetic suspension provides good mechanical properties combined with excellent cleanness and high reliability, which is very desirable in mechanical systems for space applications.The research leading to these results has received funding from the Spanish Ministerio de Economía y Competitividad under the Plan Estatal de I+D+I 2013-2016, grant agreement no ESP2015-72458-EXP

Design and analysis of a non-hysteretic passive magnetic linear bearing for cryogenic environments

In this study, the mechanical design and analysis of a magnetic levitating linear bearing suitable for working in the nonhysteretic range of forces is presented. The semi-cylindrical design of the superconductor provides stable equilibrium positioning and restoring forces in all degrees of freedom except for two with a cylindrical magnet floating along the axis of revolution/displacement. Using finite element analysis, it has been proven that the magnet can float stably and passively in a complete non-hysteretic Meissner state. This non-hysteretic passive linear bearing could be suitable for long-stroke precision positioning. The high translational symmetry of the magnetic field seen by the superconductor assures a usable long stroke of around 90mm with full performance and 150mm with reduced performance. This linear bearing in combination with an actuating system for only one degree of freedom could be used for accurate precision positioning systems for cryogenic environments with zero hysteresis in the movement.European Community's Seventh Framework Progra

Design and test of cryogenic cold plate for thermal-vacuum testing of space components

This paper proposes a novel cryogenic fluid cold plate designed for the testing of cryogenic space components. The cold plate is able to achieve cryogenic temperature operation down to -196 °C with a low liquid nitrogen (LN2) consumption. A good tradeoff between high rigidity and low thermal conduction is achieved thanks to a hexapod configuration, which is formed by six hinge-axle-hole articulations in which each linking rod bears only axial loads. Thus, there is not any stress concentration, which reduces the diameter of rod sections and reduces the rods' thermal conduction. This novel design has a unique set of the following properties: Simple construction, low thermal conduction, high thermal inertia, lack of vibrational noise when cooling, isostatic structural behavior, high natural frequency response, adjustable position, vacuum-suitability, reliability, and non-magnetic. Additionally, the presented cold plate design is low-cost and can be easily replicated. Experimental tests showed that a temperature of at least -190 °C can be reached on the top surface of the cold plate with an LN2 consumption of 10 liters and a minimum vibration frequency of 115 Hz, which is high enough for most vibration tests of space components.The research leading to these results received funding from the Spanish Ministerio de Economía y Competitividad inside the Plan Estatal de I+D+I 2013-2016 under grant agreement n° ESP2015-72458-EXP. The authors wish to recognize the work of Alba Martínez Pérez in the preparation of figures, the work of Miguel Fernández Muñoz in 3D model preparation, and the assistance of Hector Cruz Rosco during thermal and dynamic tests. The authors especially wish to recognize the work of Jorge Serena de Olano in CNC manufacturing

Design and experimental characterization of a novel passive magnetic levitating platform

This work proposes a novel contactless vibration damping and thermal isolation tripod platform based on Superconducting Magnetic Levitation (SML). This prototype is suitable for cryogenic environments, where classical passive, semi active and active vibration isolation techniques may present tribological problems due to the low temperatures and/or cannot guarantee an enough thermal isolation. The levitating platform consists of a Superconducting Magnetic Levitation (SML) with inherent passive static stabilization. In addition, the use of Operational Modal Analysis (OMA) technique is proposed to characterize the transmissibility function from the baseplate to the platform. The OMA is based on the Stochastic Subspace Identification (SSI) by using the Expectation Maximization (EM) algorithm. This paper contributes to the use of SSI-EM for SML applications by proposing a step-by-step experimental methodology to process the measured data, which are obtained with different unknown excitations: ambient excitation and impulse excitation. Thus, the performance of SSI-EM for SML applications can be improved, providing a good estimation of the natural frequency and damping ratio without any controlled excitation, which is the main obstacle to use an experimental modal analysis in cryogenic environments. The dynamic response of the 510 g levitating platform has been characterized by means of OMA in a cryogenic, 77 K, and high vacuum, 1E-5 mbar, environment. The measured vertical and radial stiffness are 9872.4 N/m and 21329 N/m, respectively, whilst the measured vertical and radial damping values are 0.5278 Nm/s and 0.8938 Nm/s. The first natural frequency in vertical direction has been identified to be 27.39 Hz, whilst a value of 40.26 Hz was identified for the radial direction. The determined damping values for both modes are 0.46% and 0.53%, respectively.Ministerio de Economía y Competitivida

Improving the learning of engineering students with interactive teaching applications

Over decades, Mechanical Engineering students often find some difficulties to grasp some contents and/or struggle with some parts of the course. With the increasing development of new technologies, promising innovations can be implemented enhancing learning and improving success rates. In this study, a new learning interactive method is proposed and evaluated using the experience of over 600 students of Mechanical Engineering. This study describes a 4-year experiment based on new interactive applications for education. The experiment has been implemented using E-learning techniques and new technologies (a combination of remote and virtual examples, videos, quizzes, and theory). Specifically, several applications have been programmed to be executed on different devices, such as mobile phones and PC/laptops (Android and Windows). The experiment is applied using small applications that help the students identify the most challenging contents and guide them throughout step-by-step. The main objective of this interactive method is to help students find their lack of knowledge and offer them contents to cover it. These didactic applications are portable and intuitive. Thanks to these interactive applications, it is possible to accomplish better practices of “E-learning” and “Computer Simulation and Animation” together. Since they are portable applications, they allow the student to interact and check conceptual understandings at any place. Students really appreciate this aspect. The results of the course titled Mechanism and Machine Theory have been analyzed during these four last years in which these interactive applications have been offered to the students.The authors wish to thank the "Convocatoria De Innovación Docente 2017-2018" of the UC3M

Analysis of the geometric parameters influence in PCB fixtures for 2D multipole magnetization patterning of thin layer micro-magnets

Magnetic actuators, magnetic gears, vibrational energy harvesters and other micro-electromagnetic devices requires micro-magnetic rotors with alternant magnetizations to optimize their performance. Different approaches have been used for multipole magnetization of micro-magnets like fixed micro-fixtures, thermomagnetic patterning or laser machining. The main limitation of the previous techniques is that the inversion of the magnetic polarizations is only partially done. In this work, a concept based on 2D multipole magnetization printing of micro-magnets is proposed and analyzed to overcome current limitations. The fixtures are designed to be printed on a standard 35 μm PCB. The dependence of the magnetizing field with respect to the geometrical parameter of the fixture is analyzed. Maps of the required current for the magnetizing fields are also given. Some design recommendations to optimize the magnetizing field and to minimize current, thus the heat, are given.Universidad de Alcal

Miniaturized high gain flexible spiral antenna tested in human-like tissue

A miniaturized helical antenna is presented in this work. The antenna is flexible, it is 6100 μm long and it has a diameter of 352 μm. This antenna has such a small cross-section, that permits to be implanted in the human body with fine syringes and minimally invasive surgeries. The antenna can be used to receive power and/or send information in medical devices. The antenna is made of biocompatible materials: polytetrafluoroethylene (PFTE) and copper. The fundamental parameters of the antenna have been simulated and experimentally measured in animal human-like tissues, showing good agreement. The resonant frequency of the antenna is 4.7 GHz, with a reflection coefficient of −25.1 dB, and a gain of −4.7 dBi. As expected, the resonant frequency decreases inside biological tissues comparing to the free-space open-air measurement. Reducing the resonant frequency is an advantage because power signals can penetrate deeper into body tissues

Model-based systems engineering applied to trade-off analysis of wireless power transfer technologies for implanted biomedical microdevices

Decision-making is an important part of human life and particularly in any engineering process related to a complex product. New sensors and actuators based on MEMS technologies are increasingly complex and quickly evolving into products. New biomedical implanted devices may benefit from system engineering approaches, previously reserved to very large projects, and it is expected that this need will increase in the future. Here, we propose the application of Model Based Systems Engineering (MBSE) to systematize and optimize the trade-off analysis process. The criteria, their utility functions and the weighting factors are applied in a systematic way for the selection of the best alternative. Combining trade-off with MBSE allow us to identify the more suitable technology to be implemented to transfer energy to an implanted biomedical micro device.European Commissio

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio