1,257 research outputs found
Platonic crystal with low-frequency locally resonant snail structures. Wave trapping, transmission amplification and shielding
We propose a new type of platonic crystal. The proposed microstructured plate
includes snail resonators with low-frequency resonant vibrations. The
particular dynamic effect of the resonators are highlighted by a comparative
analysis of dispersion properties of homo- geneous and perforated plates.
Analytical and numerical estimates of classes of standing waves are given and
the analysis on a macrocell shows the possibility to obtain localization, wave
trapping and edge waves. Applications include transmission amplification within
two plates separated by a small ligament. Finally we proposed a design
procedure to suppress low frequency flexural vibration in an elongated plate
implementing a by-pass system re- routing waves within the mechanical system.Comment: 11 figures (20 files
Simultaneous cooling of coupled mechanical oscillators using whispering gallery mode resonances
We demonstrate simultaneous center-of-mass cooling of two coupled
oscillators, consisting of a microsphere-cantilever and a tapered optical
fiber. Excitation of a whispering gallery mode (WGM) of the microsphere, via
the evanescent field of the taper, provides a transduction signal that
continuously monitors the relative motion between these two microgram objects
with a sensitivity of 3 pm. The cavity enhanced optical dipole force is used to
provide feedback damping on the motion of the micron-diameter taper, whereas a
piezo stack is used to damp the motion of the much larger (up to m in
diameter), heavier (up to kg) and stiffer
microsphere-cantilever. In each feedback scheme multiple mechanical modes of
each oscillator can be cooled, and mode temperatures below 10 K are reached for
the dominant mode, consistent with limits determined by the measurement noise
of our system. This represents stabilization on the picometer level and is the
first demonstration of using WGM resonances to cool the mechanical modes of
both the WGM resonator and its coupling waveguide.Comment: 10 pages, 8 figure
Minimization of phonon-tunneling dissipation in mechanical resonators
Micro- and nanoscale mechanical resonators have recently emerged as
ubiquitous devices for use in advanced technological applications, for example
in mobile communications and inertial sensors, and as novel tools for
fundamental scientific endeavors. Their performance is in many cases limited by
the deleterious effects of mechanical damping. Here, we report a significant
advancement towards understanding and controlling support-induced losses in
generic mechanical resonators. We begin by introducing an efficient numerical
solver, based on the "phonon-tunneling" approach, capable of predicting the
design-limited damping of high-quality mechanical resonators. Further, through
careful device engineering, we isolate support-induced losses and perform the
first rigorous experimental test of the strong geometric dependence of this
loss mechanism. Our results are in excellent agreement with theory,
demonstrating the predictive power of our approach. In combination with recent
progress on complementary dissipation mechanisms, our phonon-tunneling solver
represents a major step towards accurate prediction of the mechanical quality
factor.Comment: 12 pages, 4 figure
Development of a 3-axis MEMS magnetometer based on Lorentz force
Dissertação de mestrado em Physics Engineering, (especialização em Devices, Microsystems and Nanotechnologies)Typical magnetometers found in the magnetic fields research are highly incompatible with the massive
MEMS technology industry that has been the object of study in the past years. This aspect leads to the
rapid increase in production costs and reliability reduction. Furthermore, most of the magnetometers that
are adapted to this technology are highly complex and with little to no adaptation to outer-space research.
In this work, a novel single-axis MEMS magnetometer based on the principle of the Lorentz force
capable of reading fields in the X or Y direction is designed and simulated with the description of a
fabrication method to be used. This magnetometer uses an innovative design for a current-carrying-bar
that’s highly adaptable to a variety of scenarios with a low 100Ω current resistance in each of its paths.
An amplitude-modulated method is approached through the use of a capacitive-readout system and
an off-resonance frequency of operation to achieve the detection baseline of a 1aF capacitive variation
at a 20nT magnetic field. This involves the use of various mechanisms to increase the quality factor and
reduce the overall stiffness of the device to increase its displacement caused by the Lorentz force. The
device is also to be operated at a 500Pa atmosphere to reduce the damping and, at the same time,
increase the quality factor. A thermomechanical noise below 3 /√ with a frequency of operation
at around 4977 Hz was deemed necessary to adapt the design to another previously designed single-axis
MEMS magnetometer capable of reading fields in the Z direction.
Various simulation and design tools are used to predetermine the best properties at which the
magnetometer will be operated to its highest capabilities. Through these simulations, a 50Hz bandwidth
magnetometer, required for spatial research, is achieved with a capacitance variation of 1.37aF at 20nT
surpassing the initial requirements. A 1.77 /√ thermomechanical noise is obtained, well below
the baseline that was defined for this work.
A fabrication layout was developed with all lithography masks designed, and a microfabrication process
flow was devised. The microfabrication process run was partially completed and it’s still ongoing.Os magnetómetros tÃpicos encontrados na investigação de campos magnéticos são altamente
incompatÃveis com a enorme indústria da tecnologia MEMS que tem sido objeto de estudo nos últimos
anos. Este aspeto leva ao rápido aumento dos custos de produção e à redução da fiabilidade. Para além
disso a maioria dos magnetómetros adaptados a esta tecnologia são altamente complexos e com pouca
ou nenhuma adaptação à investigação espacial.
Neste trabalho, um novo magnetómetro MEMS de um único eixo baseado no princÃpio da força de
Lorentz capaz de ler campos na direção X ou Y é concebido e simulado com a descrição de um método
de fabrico a ser utilizado. Este magnetómetro utiliza um desenho inovador para uma barra condutora
que é altamente adaptável a uma variedade de cenários com uma baixa resistência de 100Ω em cada
um dos seus caminhos. Um método de modulação em amplitude é abordado através da utilização de
um sistema de leitura capacitiva e uma frequência de operação com um desvio da ressonância
para alcançar a linha de base de deteção de uma variação capacitiva de 1aF para um campo magnético
de 20nT. Isto envolve a utilização de vários mecanismos para aumentar o fator de qualidade e reduzir a
rigidez geral do dispositivo para aumentar o deslocamento causado pela força de Lorentz. O dispositivo
deve também ser operado a uma atmosfera de 500Pa para reduzir o amortecimento e, ao mesmo tempo,
aumentar o factor de qualidade. Um ruÃdo termomecânico inferior a 3 /√ com uma frequência de
operação de cerca de 4977 Hz foram consideradas necessárias para adaptar o desenho a outro
magnetómetro MEMS de um eixo, previamente concebido, capaz de ler campos na direção Z.
Várias ferramentas de simulação e desenho são utilizadas para pré-determinar as melhores propriedades
em que o magnetómetro será operado até às suas capacidades mais elevadas. Através destas
simulações, um magnetómetro de 50Hz de largura de banda, necessário para a investigação espacial,
é alcançado com uma variação de capacidade de 1.37aF a 20nT, ultrapassando os requisitos iniciais. É
obtido um ruÃdo termomecânico de 1.77 /√, bem abaixo da linha de base que foi definida para
este trabalho.
Foi desenvolvido um esquema de fabricação com todas as máscaras litográficas concebidas, e foi
concebido um fluxo de processo de microfabricação. A execução do processo de microfabricação foi
parcialmente concluÃda e ainda está em curso.This work was framed in the scope of the Project (Link4S)ustainability - A new generation connectivity
system for creation and integration of networks of objects for new sustainability paradigms [POCI-01-
0247-FEDER-046122 | LISBOA-01-0247-FEDER-046122], financed by the Operational Competitiveness
and Internationalization Programmes COMPETE 2020 and LISBOA 2020, under the PORTUGAL 2020
Partnership Agreement, and through the European Structural and Investment Funds in the FEDER
component
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