High frequency | EPFL Graph Search

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82&

Design of novel radiating elements for SATCOM phased arrays in Ku-Band

Baptiste Fernand Hornecker

The present thesis deals with the design of a planar antenna array for the communication between a civil aircraft (Dassault's Falcon) and an Inmarsat satellite. The final goal is to provide high speed Internet access in X/Ku-Band (8-12GHz / 12-18GHz), and possibly even in K/Ka- Band (18-27GHz / 17-40GHz). The study starts with the Ku-Band only, then evolves towards the transmission band and finishes with their Ka-Band counterparts. The main constraint of the thesis is that the final result should be a low profile antenna that will be easy to integrate below the fuselage of an aircraft. At the same time, the antenna has to provide a beam steering mechanism in order to track the position of the targetted satellite while the aircraft is moving. The usual way to achieve it is to implement some dedicated electronic chips below each radiating element of array. Dassault Aviation has its own alternate and more mechanical oriented solutions. Since the communication system is intended for top-notch business jets produced in small series, cost is not here a decisive criterion. This thesis assumes the existence of the beam-steering system and concentrates on a proof of concept and careful design of the antenna elements that will constitute the final array. They have to satisfy tight constraints in terms of size, return loss, mutual coupling with neighbors, efficiency, radiation pattern and dual circular polarization quality. Printed multilayer antennas have been retained as the best candidates, and themain parts of the thesis have been dedicated to their study. The thesis concludes with the presentation of an apparently completely unrelated and independant topic, namely the simulation of nanoscale 2D planar structures based on Graphene. The rationale for this last chapter is to provide a prospective study of the use of Graphene to create a variable capacitance. This component is always needed in the beamforming network of reconfigurable and scanning arrays. Our laboratory is developing a deep knowledge of the electromagnetic properties of Graphene-based devices and these varicaps could lead to very interesting applications in high frequencies, once the Graphene technology has definitely progressed. Thanks to electrostatics Green's functions, a variable capacitor based on Graphene has been simulated, and a Quantumeffect -the Quantum capacitance of Graphene- has been successfully tackled from a numerical point of view.

EPFL2016

High Frequency Effects of Impedances and Coatings in the CLIC Damping Rings

Eirini Koukovini Platia

The Compact Linear Collider (CLIC) is a 3 TeV e+e- machine, currently under design at CERN, that targets to explore the terascale particle physics regime. The experiment requires a high luminosity of 2x10^34 cm^2 s^-1, which can be achieved with ultra low emittances delivered from the Damping Rings (DRs) complex. The high bunch brightness of the DRs gives rise to several collective effects that can limit the machine performance. Impedance studies during the design stage of the DR are of great importance to ensure safe operation under nominal parameters. As a first step, the transverse impedance model of the DR is built, accounting for the whole machine. Beam dynamics simulations are performed with HEADTAIL to investigate the effect on beam dynamics. For the correct impedance modeling of the machine elements, knowledge of the material properties is essential up to hundreds of GHz, where the bunch spectrum extends. Specifically, Non Evaporable Getter (NEG) is a commonly used coating for good vacuum but its properties up to high frequencies were still widely unexplored. A new method using rectangular waveguides is proposed, benchmarked and applied for the first time to characterize NEG up to hundreds of GHz. The numerical tools used for the DR studies are applied and benchmarked with measurements in other light sources. In particular, single bunch measurements were performed in the ALBA light source and compared to the model prediction using HEADTAIL. The impedance budget of ALBA was estimated before and after the installation of a pinger magnet. Furthermore, studies were also carried out for the Swiss Light Source (SLS) upgrade to investigate the machine performance in terms of single bunch instabilities for lattices with negative momentum compaction factor.

EPFL2015

Accounting for inertia effects to access the high-frequency microrheology of viscoelastic fluids

Elena Bertseva, László Forró, Sylvia Jeney, Frank Scheffold

We study the Brownian motion of microbeads immersed in water and in a viscoelastic wormlike micelles solution by optical trapping interferometry and diffusing wave spectroscopy. Through the mean-square displacement obtained from both techniques, we deduce the mechanical properties of the fluids at high frequencies by explicitly accounting for inertia effects of the particle and the surrounding fluid at short time scales. For wormlike micelle solutions, we recover the 3/4 scaling exponent for the loss modulus over two decades in frequency as predicted by the theory for semiflexible polymers.

Amer Physical Soc2014

Design of novel radiating elements for SATCOM phased arrays in Ku-Band

Baptiste Fernand Hornecker

EPFL2016