Characteristic impedance | EPFL Graph Search

The characteristic impedance or surge impedance (usually written Z0) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. Alternatively, and equivalently, it can be defined as the input impedance of a transmission line when its length is infinite. Characteristic impedance is determined by the geometry and materials of the transmission line and, for a uniform line, is not dependent on its length. The SI unit of characteristic impedance is the ohm. The characteristic impedance of a lossless transmission line is purely real, with no reactive component. Energy supplied by a source at one end of such a line is transmitted through the line without being dissipated in the line itself. A transmission line of finite length (lossless or lossy) that is terminated at one end with an impedance equal to the characteristic i

Analytical Methods for the Study and Design of Integrated Switched Oscillators and Antennas for Mesoband Radiation

Jose Felix Vega Stavro

This thesis was carried out within the framework of a scientific cooperation project entitled “Application of High Power Electromagnetics to Human Safety” developed by the EPFL, the National University of Colombia and Los Andes University, Colombia. The project was funded by the Swiss Agency for Development and Cooperation (SDC) through the EPFL Centre Coopéation & Développement (CODEV). The Scientific Cooperation aimed at the study and development of techniques for the generation of high power electromagnetic signals for the disruption or preemptive activation of Improvised Explosive Devices (IEDs) during humanitarian clearance activities. The results and conclusions of the thesis will be applied to the construction of a resonant radiator, which can be used for securing humanitarian demining operations in Colombia. The thesis is devoted to the analysis of a specific type of resonant radiators known as Switched Oscillators (SWO). An SWO is a radiator constituted by a high voltage charging circuit that drives a quarter-wave transmission line resonator connected to an antenna. An SWO can produce high-amplitude, short duration, electromagnetic fields, with a moderate bandwidth, when compared to the main resonance frequency. The outcome of the thesis can be also be used in electromagnetic compatibility applications, for the production of resonant, high power electromagnetic fields, with the aim of testing the immunity of electronic systems against Intentional Electromagnetic Interference (IEMI) attacks. The thesis is divided in three parts. The first part deals with the electrostatic design of an SWO. A method for producing an optimized design of the electrodes forming the spark gap of the SWO is presented. The method is based on the generation of a curvilinear coordinate space on which the electrodes are conformal to one of the coordinate axis of the space. Laplace equation is solved in the interelectrodic space, obtaining an analytical solution for the electrostatic distribution. Furthermore, using appropriate mathematical manipulations, we derive an analytical expression for the impedance of the transmission line formed by the proposed electrodes. The second part of the thesis is devoted to the analysis of SWOs in the frequency domain. An original analysis approach, based on the chain-parameter technique, is proposed in which the SWO and the connected antenna are described using a two-port network using which a transfer function between the input voltage and the radiated field is established. A closed form expression of the resonance frequency of the SWO is also obtained. The developed technique makes it possible to study the response of an SWO when connected to an arbitrary antenna with a frequency-dependent input impedance. The final part of the thesis presents the construction and test of an SWO prototype. The prototype design is based on the theoretical developments presented in the first two parts of the thesis. The realized SWO is experimentally characterized using different antennas. It is characterized by an input voltage of 30 kV and a resonance frequency of 433 MHz. Radiated electric fields using monopole antennas were in the order of 10 kV/m at a distance of 1.5 m. The prototype is used for testing the validity of the electrodynamic model for the analysis of SWOs connected to frequency dependent antennas. Different monopole antennas connected to the SWO are considered and the radiated fields are measured and compared with theoretical calculations. It is shown that the developed theoretical model is able to reproduce with a good accuracy the behavior of the SWO connected to a frequency dependent antenna.

EPFL2013

Compact Microstrip Feedings with an Elevated Ground Plane for Thick Folded SIW

Juan Ramon Mosig, Lei Wang, Qi Wu

Folded substrate integrated waveguide (FSIW) has been proposed for further size reduction, while keeping the advantages of traditional SIW. FSIW-based horn antennas are very promising in millimeter wave applications. To improve the bandwidth and efficiency of such antennas, a thick substrate is preferred but the microstrip feeding line becomes unacceptly wide to obtain a reasonable impedance. This paper introduces compact microstrip feeding lines with elevated ground plane for thick FSIW. Arbitrary characteristic impedance can be achieved without increasing the width of the feeding line, which will be very useful for the integration with other millimeter circuit components.

Ieee2016

Electroacoustic absorbers for the low-frequency modal equalization of a room: what is the optimal target impedance for maximum modal damping, depending on the total area of absorbers?

Véronique Adam, Sami Driss Karkar, Hervé Lissek, Etienne Thierry Jean-Luc Rivet

Electroacoustic absorbers consist of loudspeakers, shunted with an electrical circuit designed to obtain a given acoustic impedance. Their design and principles are now well understood. Unidimensional experiments, using plane waves under normal incidence in ducts, agree perfectly with simulations and confirm the validity of the model: the low-frequency absorption is maximal (and total) when the acoustic impedance at the diaphragm of the loudspeaker is purely resistive and equals the characteristic impedance of the medium. However, the working principle of an absorber in a 3D acoustic domain is somehow dierent: the absorber should bring a maximum of additional damping to each eigenmode, in order to realize a modal equalization of the domain. The target acoustic impedance value of the absorber can therefore dier from the characteristic impedance of the medium. Thus, extension of 1D results to the tridimensional case brings up several challenges, such as dealing with non trivial geometry, the finite size of the absorber, as well as the absence of simple formula to determine eigenmodes and their damping in a relatively general framework. In order to define the optimal target value for the acoustical impedance of an absorber in a realistic case, and to sense how this optimal value depends on some parameters, this paper proposes to address the following cases: a 1D case, under normal incidence, where the absorber has a sensibly smaller area than the cross-section of the duct, another 1D case, where the absorber is parietal, that is to say, under grazing incidence, and a 3D case, where absorbers have a given orientation and position, but a varying area.

2014

Analytical Methods for the Study and Design of Integrated Switched Oscillators and Antennas for Mesoband Radiation

Jose Felix Vega Stavro

EPFL2013