24 research outputs found
Thermoelastic Damping in MEMS Gyroscopes at High Frequencies
Microelectromechanical systems (MEMS) gyroscopes are widely used, e.g. in
modern automotive and consumer applications, and require signal stability and
accuracy in rather harsh environmental conditions. In many use cases, device
reliability must be guaranteed under large external loads at high frequencies.
The sensitivity of the sensor to such external loads depends strongly on the
damping, or rather quality factor, of the high frequency mechanical modes of
the structure. In this paper, we investigate the influence of thermoelastic
damping on several high frequency modes by comparing finite element simulations
with measurements of the quality factor in an application-relevant temperature
range. We measure the quality factors over different temperatures in vacuum, to
extract the relevant thermoelastic material parameters of the polycrystalline
MEMS device. Our simulation results show a good agreement with the measured
quantities, therefore proving the applicability of our method for predictive
purposes in the MEMS design process. Overall, we are able to uniquely identify
the thermoelastic effects and show their significance for the damping of the
high frequency modes of an industrial MEMS gyroscope. Our approach is generic
and therefore easily applicable to any mechanical structure with many possible
applications in nano- and micromechanical systems
Signatures of single site addressability in resonance fluorescence spectra
Pioneering methods in recent optical lattice experiments allow to focus laser
beams down to a spot size that is comparable to the lattice constant. Inspired
by this achievement, we examine the resonance fluorescence spectra of two-level
atoms positioned in adjacent lattice sites and compare the case where the laser
hits only one atom (single site addressing) with cases where several atoms are
illuminated. In contrast to the case where the laser hits several atoms, the
spectrum for single site addressing is no longer symmetric around the laser
frequency. The shape of the spectrum of fluorescent light can therefore serve
as a test for single site addressing. The effects we find can be attributed to
a dipole-dipole interaction between the atoms due to mutual exchange of
photons.Comment: 9 Pages, 4 figure
Use of a porous membrane for gas bubble removal in microfluidic channels: physical mechanisms and design criteria
We demonstrate and explain a simple and efficient way to remove gas bubbles
from liquid-filled microchannels, by integrating a hydrophobic porous membrane
on top of the microchannel. A prototype chip is manufactured in hard,
transparent polymer with the ability to completely filter gas plugs out of a
segmented flow at rates up to 7.4 microliter/s per mm2 of membrane area. The
device involves a bubble generation section and a gas removal section. In the
bubble generation section, a T-junction is used to generate a train of gas
plugs into a water stream. These gas plugs are then transported towards the gas
removal section, where they slide along a hydrophobic membrane until complete
removal. The system has been successfully modeled and four necessary operating
criteria have been determined to achieve a complete separation of the gas from
the liquid. The first criterion is that the bubble length needs to be larger
than the channel diameter. The second criterion is that the gas plug should
stay on the membrane for a time sufficient to transport all the gas through the
membrane. The third criterion is that the gas plug travel speed should be lower
than a critical value: otherwise a stable liquid film between the bubble and
the membrane prevents mass transfer. The fourth criterion is that the pressure
difference across the membrane should not be larger than the Laplace pressure
to prevent water from leaking through the membrane
Out-of-equilibrium physics in driven dissipative coupled resonator arrays
Coupled resonator arrays have been shown to exhibit interesting many- body
physics including Mott and Fractional Hall states of photons. One of the main
differences between these photonic quantum simulators and their cold atoms
coun- terparts is in the dissipative nature of their photonic excitations. The
natural equi- librium state is where there are no photons left in the cavity.
Pumping the system with external drives is therefore necessary to compensate
for the losses and realise non-trivial states. The external driving here can
easily be tuned to be incoherent, coherent or fully quantum, opening the road
for exploration of many body regimes beyond the reach of other approaches. In
this chapter, we review some of the physics arising in driven dissipative
coupled resonator arrays including photon fermionisa- tion, crystallisation, as
well as photonic quantum Hall physics out of equilibrium. We start by briefly
describing possible experimental candidates to realise coupled resonator arrays
along with the two theoretical models that capture their physics, the
Jaynes-Cummings-Hubbard and Bose-Hubbard Hamiltonians. A brief review of the
analytical and sophisticated numerical methods required to tackle these systems
is included.Comment: Chapter that appeared in "Quantum Simulations with Photons and
Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by
D.G.Angelakis, Quantum Science and Technology Series, Springer 201
Thermoelastic damping in MEMS gyroscopes at high frequencies
Abstract Microelectromechanical systems (MEMS) gyroscopes are widely used, e.g., in modern automotive and consumer applications, and require signal stability and accuracy in rather harsh environmental conditions. In many use cases, device reliability must be guaranteed under large external loads at high frequencies. The sensitivity of the sensor to such external loads depends strongly on the damping, or rather quality factor, of the high-frequency mechanical modes of the structure. In this paper, we investigate the influence of thermoelastic damping on several high-frequency modes by comparing finite element simulations with measurements of the quality factor in an application-relevant temperature range. We measure the quality factors over different temperatures in vacuum, to extract the relevant thermoelastic material parameters of the polycrystalline MEMS device. Our simulation results show a good agreement with the measured quantities, therefore proving the applicability of our method for predictive purposes in the MEMS design process. Overall, we are able to uniquely identify the thermoelastic effects and show their significance for the damping of the high-frequency modes of an industrial MEMS gyroscope. Our approach is generic and therefore easily applicable to any mechanical structure with many possible applications in nano- and micromechanical systems
Degenerate optomechanical parametric oscillators: Cooling in the vicinity of a critical point
Degenerate optomechanical parametric oscillators are optical resonators in
which a mechanical degree of freedom is coupled to a cavity mode that is
nonlinearly amplified via parametric down-conversion of an external pumping
laser. Below a critical pumping power the down-converted field is purely
quantum-mechanical, making the theoretical description of such systems very
challenging. Here we introduce a theoretical approach that is capable of
describing this regime, even at the critical point itself. We find that the
down-converted field can induce significant mechanical cooling and identify the
process responsible of this as a cooling-by-heating mechanism. Moreover, we
show that, contrary to naive expectations and semi-classical predictions,
cooling is not optimal at the critical point, where the photon number is
largest. Our approach opens the possibility for analyzing further hybrid
dissipative quantum systems in the vicinity of critical points.Comment: We will appreciate comments and (constructive) criticis
Accord cadre INRA-AFME. Convention 1985: 4. Groupement VEREDIA (Valorisation energetique des residus et economie d'energie dans les industries agroalimentaires)
CNRS RP 400 (405) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc
Eosinophils and eosinophil-associated disorders: immunological, clinical, and molecular complexity
Eosinophils and their mediators play a crucial role in various reactive states such as bacterial and viral infections, chronic inflammatory disorders, and certain hematologic malignancies. Depending on the underlying pathology, molecular defect(s), and the cytokine- and mediator-cascades involved, peripheral blood and tissue hypereosinophilia (HE) may develop and may lead to organ dysfunction or even organ damage which usually leads to the diagnosis of a HE syndrome (HES). In some of these patients, the etiology and impact of HE remain unclear. These patients are diagnosed with idiopathic HE. In other patients, HES is diagnosed but the etiology remains unknown — these patients are classified as idiopathic HES. For patients with HES, early therapeutic application of agents reducing eosinophil counts is usually effective in avoiding irreversible organ damage. Therefore, it is important to systematically explore various diagnostic markers and to correctly identify the disease elicitors and etiology. Depending on the presence and type of underlying disease, HES are classified into primary (clonal) HES, reactive HES, and idiopathic HES. In most of these patients, effective therapies can be administered. The current article provides an overview of the pathogenesis of eosinophil-associated disorders, with special emphasis on the molecular, immunological, and clinical complexity of HE and HES. In addition, diagnostic criteria and the classification of eosinophil disorders are reviewed in light of new developments in the field