Combining thermal insulation and mobile communication in buildings: influence of laser-treated glazing on microwave propagation

With the purpose of reducing the heating energy in buildings, it is common practice to install energy-efficient windows to increase the thermal insulation of a façade. These insulating glass units (IGIJ) include a thin silver coating acting as an infrared mirror which reduces the thermal losses that occur through radiation, but at the same time reflects the microwaves for mobile communication. To address this drawback, a specific laser treatment is performed on the silver coating which strongly improves the transmission of microwaves through the window. In this study, the attenuation of microwaves signal was analyzed inside the SolAce unit in the "NEST" research building at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) in Dübendorf. Two configurations (with and without laser-treated glazing) were carried out by interchanging two hinged windows. The results showed a significant improvement in signal strength in the configuration with laser-treated IGUs. A transmission loss contour plot of the SolAce unit showed a highly directional propagation of the wave which suggests that more than two windows should be treated to achieve better mobile communication in the entire unit. The novel patterned coating is thus especially valuable in the building sector to increase the microwave signal for mobile communication. To the best of our knowledge, this is the first implementation and testing of laser-treated coating for energy-efficient glazing in the building sector.

Le mur à haute performance thermique

Thierry Voellinger

The scope of this research includes the development of composite concrete façade elements that are thin, loadbearing and of high thermal performance. The research applies to manufactured precast concrete elements and focuses on improving their structure in terms of their construction but also their cost and environmental impact. During the last four decades, society’s energy efficiency awareness has been steadily growing in everyday life and in scientific circles. The Swiss Federal Institutes of Technology are promoting a plan known as the 2000 Watt Society (Société à 2000 Watts) which would reduce the energy consumption of the country’s inhabitants. In the context of Swiss construction, Minergie type labels are a requirement ensuring improved living conditions at lower energy consumption levels. These new ambitions increase the thermal requirements which in turn lead to the inevitable thickening of the building envelope. In a Swiss urban context, such as the Geneva region in particular, land is increasingly rare and the price of leasable surface continues to rise. As a result, the materials commonly used for insulation are economical but bulky ; they increase the thickness of the façades and significantly reduce the usable surface available for buildings. In an urban context such as this, what is the suitable dimension and fair price of a wall ? The method used was to analyze the strategies that would result in the correct dimensions of high thermal performance walls. Diminishing their width increases the area of livable surface while maintaining the wall’s thermal, static and sustainable standards. The objective was to establish a process for determining the composition of products that carry the Minergie-P and Minergie-Eco label. To this end, several tests and a pilot project for an individual house were carried out using optimum high thermal performance precast concrete walls as a model. The test demonstrated the feasibility of this type of wall. The innovation was to place between the two layers of concrete, a high thermal performance Vacuum Insulated Panel (VIP) type material and a traditional one. This combination allowed optimizing the thickness of the wall while responding to construction constraints. The proportion of the combination of insulation materials was selected according to their thermal performance, environmental impact and price. The goal was to maintain a constant thickness from the stages of project design to its completion. The argument of this dissertation is based on the conviction and the importance to commit to the use of high thermal performance construction materials overall in the future. At present, in the midst of a fossil fuel crisis, this is no longer just an individual concern. Indeed, the scarcity of fossil fuels and global warming are vital and critical problems that can be solved by using appropriate architecture solutions such as heat traps.

EPFL2012

Atomic layer deposition of Ni and Ni80Fe20 for tubular spin-wave nanocavities

Maria Carmen Giordano

Magnetic thin films and magnetic nanostructures have become essential components of modern technological applications. Modern branches of magnetisms focus on spin-charge coupling (spintronics) and the collective excitation of spin waves in magnetically ordered materials (magnonics). In particular, spin waves represent a promising charge-free medium to encode and transmit information in the GHz frequency regime, relevant for microwaves technologies. The ever-increasing demand for compact and portable electronic and telecommunication devices leads to the need for further miniaturization and high integration density of their functional components. These aspects have prompted nanomagnetism to venture the third dimension. This development is also motivated by novel physical phenomena and functionalities predicted to arise from three-dimensional (3D) complex magnetic configurations. In order to advance the research in 3D spintronics and 3D magnonics, it will be essential to have control over the fabrication of 3D nanoarchitectures and to access the new properties of individual nanostructures emerging from new complex 3D spin-textures. These two challenges are addressed in this thesis. Ferromagnetic nanotubes (NTs) represent the ideal 3D system for the study of shape dependent static and dynamic magnetic properties. Their magnetic configurations, as well as the spin wave confinement and propagation inside them, can be engineered by changing their geometrical parameters. First, in order to fabricate 3D magnetic device architectures, we explored atomic layer deposition (ALD). The thickness and quality of the thin films deposited with ALD are irrespective of the geometry of the surface on which they are deposited. This characteristic makes it ideal to fabricate 3D nanomagnets by magnetically coating 3D nanotemplates, e.g. nanowires (NWs) in the case of NTs. In this thesis we propose ALD processes for the conformal coating by means of two ferromagnetic materials conventionally used in planar spintronics and magnonics systems: Ni and permalloy (Py, Ni80Fe20), the second material expected to have a lower spin wave damping. By identifying correlations between ALD process parameters and thin film properties we optimized the materials in terms of conformality, electrical resistivity, anisotropic magnetoresistance (AMR) effect, spin wave damping and, in the case of permalloy, also stoichiometry. The optimized materials were then transferred onto GaAs nanowires templates, obtaining ferromagnetic NTs with hexagonal cross sections. We achieved Ni NTs with the lowest resistivity ever reported in similar ALD-grown Ni systems and a large AMR effect. We observed the lowest spin waves damping for permalloy NTs, exhibithing a value comparable with permalloy thin films achieved with conventional planar deposition techniques. Second, we investigated magnetic states and spin waves confinement in nanotubes experimentally and via micromagnetic simulations. We combined magnetoresistance measurements with Brillouin light scattering spectroscopy (BLS) and micromagnetic simulations to study Ni and Py NTs. BLS measurements, performed while irradiating NTs with microwaves, show that these nanotubes form spin-wave nanocavities which impose discrete wave vectors and confine GHz microwave signals on the nanoscale. Our experimental results show that the confinement can be engineered by changing the NT's geometrical parameters and magnetic states.

EPFL2021

Le mur à haute performance thermique

Thierry Voellinger

EPFL2012

Atomic layer deposition of Ni and Ni80Fe20 for tubular spin-wave nanocavities

Maria Carmen Giordano

EPFL2021