110 research outputs found
Frequency modulated self-oscillation and phase inertia in a synchronized nanowire mechanical resonator
Synchronization has been reported for a wide range of self-oscillating
systems. However, even though it has been predicted theoretically for several
decades, the experimental realization of phase self-oscillation, sometimes
called phase trapping, in the high driving regime has been studied only
recently. We explored in detail the phase dynamics in a synchronized field
emission SiC nanoelectromechanical system with intrinsic feedback. A richer
variety of phase behavior has been unambiguously identified, implying phase
modulation and inertia. This synchronization regime is expected to have
implications for the comprehension of the dynamics of interacting
self-oscillating networks and for the generation of frequency modulated signals
at the nanoscal
Role of fluctuations and nonlinearities on field emission nanomechanical self-oscillators
A theoretical and experimental description of the threshold, amplitude, and
stability of a self-oscillating nanowire in a field emission configuration is
presented. Two thresholds for the onset of self-oscillation are identified, one
induced by fluctuations of the electromagnetic environment and a second
revealed by these fluctuations by measuring the probability density function of
the current. The ac and dc components of the current and the phase stability
are quantified. An ac to dc ratio above 100% and an Allan deviation of 1.3x10-5
at room temperature can be attained. Finally, it is shown that a simple
nonlinear model cannot describe the equilibrium effective potential in the
self-oscillating regime due to the high amplitude of oscillations
Simple modeling of self-oscillation in Nano-electro-mechanical systems
We present here a simple analytical model for self-oscillations in
nano-electro-mechanical systems. We show that a field emission self-oscillator
can be described by a lumped electrical circuit and that this approach is
generalizable to other electromechanical oscillator devices. The analytical
model is supported by dynamical simulations where the electrostatic parameters
are obtained by finite element computations.Comment: accepted in AP
Universal Vectorial and Ultrasensitive Nanomechanical Force Field Sensor
Miniaturization of force probes into nanomechanical oscillators enables
ultrasensitive investigations of forces on dimensions smaller than their
characteristic length scale. Meanwhile it also unravels the force field
vectorial character and how its topology impacts the measurement. Here we
expose an ultrasensitive method to image 2D vectorial force fields by
optomechanically following the bidimensional Brownian motion of a singly
clamped nanowire. This novel approach relies on angular and spectral tomography
of its quasi frequency-degenerated transverse mechanical polarizations:
immersing the nanoresonator in a vectorial force field does not only shift its
eigenfrequencies but also rotate eigenmodes orientation as a nano-compass. This
universal method is employed to map a tunable electrostatic force field whose
spatial gradients can even take precedence over the intrinsic nanowire
properties. Enabling vectorial force fields imaging with demonstrated
sensitivities of attonewton variations over the nanoprobe Brownian trajectory
will have strong impact on scientific exploration at the nanoscale
Performance of field-emitting resonating carbon nanotubes as radio-frequency demodulators
International audienceWe report on a systematic study of the use of resonating nanotubes in a field emission (FE) configuration to demodulate radio frequency signals. We particularly concentrate on how the demodulation depends on the variation of the field amplification factor during resonance. Analytical formulas describing the demodulation are derived as functions of the system parameters. Experiments using AM and FM demodulations in a transmission electron microscope are also presented with a determination of all the pertinent experimental parameters. Finally we discuss the use of CNTs undergoing FE as nanoantennae and the different geometries that could be used for optimization and implementation. © 2011 American Physical Society
Steering self-organisation through confinement
Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter
Structural study of the smectic-C twist grain boundary phase (TGBC) under external electric field
We report structural X-ray studies on well-aligned TGBC samples
under an external DC electric field applied perpendicular to the pitch
direction. On increasing the field, the helical structure is
progressively distorted and finally unwound in a way which confirms
the previously assumed picture of local spontaneous polarizations
perpendicular to the helical axis (helielectric model). In terms of
de Gennes' analogy with type-II superconductors, the behaviour is
analogous to a static distorsion of the Abrikosov flux lattice by a
spatially modulated Laplace force
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