Analysis and design of heating systems for advanced automotive Radomes

Abstract

The main purpose of this thesis is to study how we could obtain a transparent heating system for a Radome. In the context of this thesis, transparent have two different meanings that are tied due to the objective of our research. First, transparent means that the heating system have not to disturb the electromagnetic radiation from the radar. And, secondly, and because of the industrial nature of this thesis, the heating system have not to be seen by an external observer, or, we can also say that it has not to disturb the aspect of the exterior decoration of the Radome. After previous studies of different possible options, we get focus on Transparent Conductive Oxides (TCO) applications to get a heating system different from these that already exist to warm, defrost, and avoid ice on the surface of Radomes used on some vehicles [1], [2], [3]. Different elements and concepts needed to be considered for the developing of the TCO: - How to deposit TCO - Optimal sheet resistance - Optimal circuit designs - Effect of radar polarization - Attenuation of radar electromagnetic waves - Adhesion of the TCO on the substrate - Heating and attenuation requirements from vehicle’s companies - Electrical connection and Power supply

Considering all the points mentioned we will be able to design two different heating systems based on TCO’s that are transparent to the human eye and minimize the attenuation of electromagnetic radiation of the radar. The TCO depositions are used in two different ways depending on how important the polarization of the radar radiation is for the heating system, this way we can differentiate two heating systems: First, we see from previous studies made at the company, that a very thin film with a high resistance, more than 3500 Ohms/square, is almost transparent to the radar and it does not require any more process than the deposition. In this case the most important point is that no definite orientation of the film is needed since the film is homogeneous. So, it is not conditioned by the polarization of the radar radiation. In this part of the thesis, we develop thin film coatings of Indium Tin Oxide (ITO) and Al doped ZnO (AZO) at the Univeristy of Barcelona and at the University of Zaragoza. The development of this system is explained in chapter 3.

Secondly, we developed a system similar to those we have today commercially that uses copper heating wires, but in our approach, we do it with TCO wires that are not visible for human eye and that are placed on the surface of the Radome. In this way we improve the thermal efficiency of the heating system with respect to copper wires systems since our heating system is almost in direct contact to ice and water, solely a film of few microns of varnish would protect the system from the outside in a real case. In this case the attenuation of radar radiation caused by the heating system is between -0.1 dB and -0.2 dB. when the heating wires are correctly oriented with the radar polarization. In this part of the Thesis, we just use ITO as the TCO material for the wires. The development of this system is explained in chapter 5.

El principal propòsit d’aquesta tesis és estudiar com podem aconseguir un sistema d’escalfament transparent per a un Radome. En el context de la tesis, transparent té dos significats diferents però lligats degut als objectius de la recerca. Primer, transparent es refereix a que el sistema d’escalfament no ha de destorbar la radiació electromagnètica del radar. I, segon, i degut a la naturalesa industrial de la tesis, el sistema d’escalfament no ha de se visible per un observador exterior, o, dit d’una altre manera no pot destorbar l’aspecte de la decoració exterior del Radome. Després d’un estudi previ de diferents possible opcions, ens hem centrat en l’ús de Òxids Conductors Transparents (o TCO per les sigles en anglès) per tal d’aconseguir un sistema d’escalfament diferent als que existeixen per escalfar, descongelar i evitar el gel a la superfície dels Radomes utilitzats en alguns vehicles [1],[2],[3]. La manera com hem utilitzat els dipòsits de TCO es poden diferenciar a partir de com d’important és la polarització de la radiació del radar pel sistema d’escalfament, d’aquesta manera podem diferencia dos sistemes d’escalfament: Primer, a partir d’ una capa molt prima amb una resistència per sobre dels 3500 Ohms/quadrat , que és pràcticament invisible pel radar i no requereix cap més procés de dipòsit. En aquest cas el punt més important és que no hi ha cap orientació preferida del sistema ja que la capa és homogènia en tota la superfície. Segon, desenvolupem un sistema amb fils de ITO que no son visibles per l’ull humà col·locats a la superfície del Radome. En aquest cas l’atenuació produïda a la radiació del radar pel sistema d’escalfament estaria entre els -0.1 dB i els -0.2 dB.