Publications de Niklaus Johner

Optimal percolation of disordered segregated composites

Thomas Maeder, Peter Ryser, Claudio Grimaldi, Niklaus Johner

We evaluate the percolation threshold values for a realistic model of continuum segregated systems, where random spherical inclusions forbid the percolating objects, modellized by hard-core spherical particles surrounded by penetrable shells, to occupy lar ...

2009

On the origin of transport non-universality and piezoresistivity in segregated conductor-insulator composites and application to thick-film resistors

Niklaus Johner

In this thesis we address the description of electrical transport properties of disordered conductor-insulator composites, mostly by numerical Monte Carlo simulations and analytical study of realistic tunnelling-percolation models. Such composites are basi ...

EPFL2009

Electron tunneling in conductor-insulator composites with spherical fillers

Gianluca Ambrosetti, Thomas Maeder, Peter Ryser, Claudio Grimaldi, Niklaus Johner

We report on our Monte Carlo calculations of the conductivity of monosized and conducting spherical particles dispersed in a homogeneous matrix, with interparticle transport mechanism given by electron tunneling. We show that our numerical results can be r ...

2009

Optimisation of a Thick-Film 10...400 N Force Sensor

Thomas Maeder, Peter Ryser, Giancarlo Corradini, Niklaus Johner, Gregory Affolter

The ring-on-ring bending principle allows the fabrication of simple, low-cost thick-film piezoresistive sensors for compressive forces in the 10 to 400 N range. However some imperfections are encountered in its basic embodiment, such as relatively high for ...

Elsevier2008

Percolative properties of hard oblate ellipsoids of revolution with a soft shell

Gianluca Ambrosetti, Peter Ryser, Claudio Grimaldi, Niklaus Johner

We present an in-depth analysis of the geometrical percolation behavior in the continuum of random assemblies of hard oblate ellipsoids of revolution. Simulations were carried out by considering a broad range of aspect-ratios, from spheres up to aspect-rat ...

2008

Transport exponent in a three-dimensional continuum tunneling-percolation model

Peter Ryser, Claudio Grimaldi, Niklaus Johner

The tunneling-percolation mechanism of conduction in disordered conductor-insulator composites is studied for a realistic continuum model where conducting and impenetrable spherical particles are dispersed in a three-dimensional continuum insulating materi ...

2008

Apparent nonuniversality in finite segregated tunneling-percolaiton models

Peter Ryser, Claudio Grimaldi, Niklaus Johner

We investigate the tunneling-percolation mechanism of DC transport nonuniversality for conducting particles of diameter Φ placed in series within the bonds of length Lof a regular lattice model. When L/Φ→∞ the resulting bond conductance distribution functi ...

2007

Piezoresistivity and tunneling-percolation transport in apparently nonuniversal systems

Peter Ryser, Claudio Grimaldi, Niklaus Johner

We formulate a generalized tunneling-percolation model that describes the electrical properties of conductor-insulator cellular disordered systems. This model predicts and explains the experimentally observed universal and nonuniversal behaviors of such pr ...

2007

Study of the impact of high-voltage trimming on several characteristics of model TFRs and their stability

Thomas Maeder, Peter Ryser, Niklaus Johner, Caroline Jacq

In this work we study in more details the impact of voltage trimming on different characteristics of model thick-film resistors (TFRs). Two series of RuO2-based TFRs with different conducting grain sizes are studied. As the composition of model pastes is c ...

2007

Perceived health and comfort in relation to energy use and building characteristics

Claude-Alain Roulet, Niklaus Johner

Within the European research project Health Optimisation Protocol for Energy-efficient Building (HOPE), 96 apartment buildings and 64 office buildings (of which approximately 75% have been designed to be energy-efficient) were investigated. The building ch ...

2006

High-Voltage Sensitivity Studies of Model Thick-Film Resistors

Thomas Maeder, Peter Ryser, Claudio Grimaldi, Niklaus Johner, Adrian Kambli, Caroline Jacq

In this work we seek to better understand the mechanisms governing pulse voltage trimming in disordered conductor-insulator composites. Therefore, we investigate the effect of the composition of thick-film resistors (TFRs) on sensitivity to high voltage pu ...

2006

Multicriteria analysis of health, comfort and energy-efficiency of buildings

Claude-Alain Roulet, Niklaus Johner

In order to cope with sustainable development policy, buildings should be at least healthy, comfortable and energy efficient. Criteria for assessing individually the occupant's perceived health, the provided thermal, visual, acoustical comfort, the indoor ...

2005

Correlations between SBS, perceived comfort, energy use and other building characteristics in european office and residential buildings

Claude-Alain Roulet, Niklaus Johner

Within the European research project HOPE, 67 office buildings and 97 residential ones were investigated using checklists addressing the building characteristics and questionnaires to the occupants asking their perceived comfort (thermal visual, acoustical ...

2005

Sick Building Syndrome and Building Characteristics

Claude-Alain Roulet, Niklaus Johner

Within the European research project HOPE, 64 office buildings were audited regarding in-door environment quality and building characteristics. Of those buildings, two groups are se-lected: 21 buildings with low prevalence of the sick building syndrome, an ...

2005