Mechanical filter | EPFL Graph Search

A mechanical filter is a signal processing filter usually used in place of an electronic filter at radio frequencies. Its purpose is the same as that of a normal electronic filter: to pass a range of signal frequencies, but to block others. The filter acts on mechanical vibrations which are the analogue of the electrical signal. At the input and output of the filter, transducers convert the electrical signal into, and then back from, these mechanical vibrations. The components of a mechanical filter are all directly analogous to the various elements found in electrical circuits. The mechanical elements obey mathematical functions which are identical to their corresponding electrical elements. This makes it possible to apply electrical network analysis and filter design methods to mechanical filters. Electrical theory has developed a large library of mathematical forms that produce useful filter frequency responses and the mechanical filter designer is able to make direct use o

Ultra low quantum decoherence nano-optomechanical systems

Mohammadjafar Bereyhi

Thermal motion of a room-temperature mechanical resonator typically dominates the quantum backaction of its position measurement. This is a longstanding barrier for exploring cavity optomechanics at room temperature. In order to enter the quantum regime of the optomechanical interaction, we need to be in the "backaction-dominated" regime, where we can study the limits of quantum measurement and how to circumvent them. To create a system which can enter the quantum regime, the optomechanical transducer has to satisfy certain criteria. A quantum-enabled optomechanical system consists of an optical cavity and a mechanical resonator with ultra low quantum decoherence, which are strongly coupled to each other via the optomechanical interaction.High stress silicon nitride has enabled nanomechanical resonators with exceptionally low dissipation at room temperature via several soft-clamping techniques. Achieving high optomechanical coupling to these coherent nanobeams results in high optomechanical cooperativities, thus alleviating the thermal motion barrier for room temperature quantum optomechanics. Monolithic integration of high-Q nanobeam resonators with optical cavities has been limited to doubly-clamped nanobeams due to the complexity of the device fabrication and long device sizes required for conventional soft-clamping using phononic crystals. In addition, the previous demonstrations of such systems showed limited optomechanical couplings thus a limited single photon cooperativity.I present the design, fabrication and characterization of three different classes of nanomechanical resonators clamp-tapered, fractal-like, and polygon resonators, which support perimeter modes, with Q factors exceeding 3 billion at room temperature and their optical readout using an integrated nearfield nano-optomechanical transducer using high stress silicon nitride. Our transducer features a one-dimensional Fabry-Perot optical cavity integrated with a high-Q nanomechanical resonator. The Fabry-Perot optical cavity is formed by patterning two photonic crystal reflectors on a silicon nitride waveguide designed for high-Q optical modes. Our approach allows individual optimization of optical and mechanical resonators, while maintaining a high optomechanical coupling rate due to large optomechanical mode overlap. Our best performing devices show on-chip optomechanical transducers with single photon cooperativities as high as 123 with mechanical quality factor of 120 million at room temperature. The developed system is of great interest to the optomechanics and sensing community. In quantum optomechanics, it will serve as a platform for quantum feedback control of the nanomechanical resonators to achieve motional ground state of a macroscopic resonator and generation of squeezed light at room temperature. Owing to their record value mechanical quality factors, the room temperature force sensitivity of our highest Q perimeter modes is on par with atomic force microscopy cantilevers at millikelvin temperature.Complete documentation of a nanofabrication process is the key to its reproducibility. Process-specific details of the fabrication techniques are usually missing in journal publications. To bridge this gap, I developed NanoFab-net.org. An online open-access tool that allows sharing process-specific fabrication reports, extracting the metadata and obtaining a unique digital object identifier (DOI) for each report.

EPFL2022

Interaction sol-structure dans le domaine des ponts intégraux

Damien Dreier

Over the past decades, an increasing number of integral bridges have been built. This type of bridge offers various advantages in comparison with standard bridges equipped with expansion joints and bearings. In particular, integral bridges require less maintenance since they have less mechanical elements. Therefore, cost of retrofitting and indirect costs such as time spent by users during the maintenance works is reduced. Moreover, the static efficiency is increased and the noise of circulation during its lifetime is reduced. However, for the design and analysis of this kind of structure, the soil-structure interaction needs to be investigated to take in account the monolithic behaviour of the bridge with the embankment near the abutment and the piers with the foundation. This interaction is complex and further research is needed. The report begins by a general introduction of the topic. Thereafter a brief description of the state-of-the-art on integral bridges is presented, as well as the main difficulties faced during design and the main actions that need to be considered. Limit states and numerical analysis on integral abutments and pier on shallow foundations are discussed towards a better understanding of the structural behaviour in order to improve current detailing and design practice. The study of integral abutments shows that soil-structure interaction should be considered at early stages of the design process. This allows introducing small geometric adaptations to improve detailing which in turn allows significantly increasing the long term performance of the integral abutment without a sensible increase of building costs. This set of new rules can further be applied to both new and existing bridges which require retrofitting of the expansion joints at the abutments. The study of the cracking limit state of piers shows the strong influence of the geometry of the shallow foundations on the soil-structure interaction. This two studies show that geometric adaptation in combination with accurate soil-structure modeling could lead to an increase of the current Swiss limit length for integral bridges which is now set at fixed to 60m.

EPFL2010