504 research outputs found
A Metastable Modular Structure Approach for Shape Morphing, Property Tuning and Wave Propagation Tailoring
The emerging concept of reconfigurable mechanical metamaterials has received increasing attention for realizing future advanced multifunctional adaptive structural systems partially due to their advantages over conventional bulk materials that are beneficial and desirable in many engineering applications. However, some of the critical challenges remain unaddressed before the concept can effectively and efficiently achieve real-world impacts. For instance, in the state-of-art, modules of mechanical metamaterials only reconfigure collectively to achieve global topology adaptation. As a result, the structure merely exhibits limited number of configurations that are discretely different from each other, which greatly undermines the benefits and impact of the reconfiguration effect. Additionally, most of the metamaterials investigations are focusing on the “materials” characteristics assuming infinite domain without considering the “structure” aspect of the systems. The effects of having finite domains and boundary conditions will generate new research issues and phenomena that are critical to real-world systems.
To address the challenges and fundamentally advance the state of the art of multifunctional adaptive structures, this dissertation seeks to create a paradigm shift by exploiting and harnessing metastable modular mechanics and dynamics. Through developing new analysis and synthesis methodologies and conducting rigorous analytical, numerical, and experimental investigations, this research creates a new class of reconfigurable metastructure that can achieve mechanical property and topology adaptation as well as adaptive non-reciprocal vibration/wave transmission.
The intellectual merit of this dissertation lies in introducing metastable modules that can be synergistically assembled and individually tuned to realize near continuous topology and mechanical property adaptation and elucidating the intricate nonlinear dynamics afforded by the metastructure. This research reveals different kinds of nonlinear instabilities that are able to facilitate the onset of supratransmission, a bandgap transmission phenomenon pertained to nonlinear periodic metastructure. In addition, utilizing this novel phenomenon, supratransmission, together with inherent spatial asymmetry of strategically configured constituents, the proposed metastructure is shown to be able to facilitate unprecedented broadband non-reciprocal vibration and wave transmission and on-demand adaptation.
Since the proposed approach depends primarily on scale-independent principles, the broader impact of this dissertation is that the proposed metastructure could foster a new generation of reconfigurable structural and material systems with unprecedented adaptation and unconventional vibration control and wave transmission characteristics that are applicable to vastly different length scales for a wide spectrum of applications.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147525/1/wuzhen_1.pd
Introduction: Localized Structures in Dissipative Media: From Optics to Plant Ecology
Localised structures in dissipative appears in various fields of natural
science such as biology, chemistry, plant ecology, optics and laser physics.
The proposed theme issue is to gather specialists from various fields of
non-linear science toward a cross-fertilisation among active areas of research.
This is a cross-disciplinary area of research dominated by the nonlinear optics
due to potential applications for all-optical control of light, optical
storage, and information processing. This theme issue contains contributions
from 18 active groups involved in localized structures field and have all made
significant contributions in recent years.Comment: 14 pages, 0 figure, submitted to Phi. Trasaction Royal Societ
Fano resonances in nanoscale structures
Nowadays nanotechnology allows to scale-down various important devices
(sensors, chips, fibres, etc), and, thus, opens up new horizon for their
applications. Nevertheless, the efficiency most of them is still based on the
fundamental physical phenomena, such as resonances. Thus, the understanding of
the resonance phenomena will be beneficial. One of the well-known examples is
the resonant enhancement of the transmission known as Breit-Wigner resonances,
which can be described by a Lorentzian function. But, in many physical systems
the scattering of waves involves propagation along different paths, and, as a
consequence, results in interference phenomena, where constructive interference
corresponds to resonant enhancement and destructive interference to resonant
suppression of the transmission. Recently, a variety of experimental and
theoretical work has revealed such patterns in different branches of physics.
The purpose of this Review is to demonstrate that this kind of resonant
scattering is related to the Fano resonances, known from atomic physics. One of
the main features of the Fano resonances is the asymmetric profile. The
asymmetry comes from the close coexistence of resonant transmission and
resonant reflection. Fano successfully explained such a phenomenon in his
seminal paper in 1961 in terms of interaction of a discrete (localized) state
with a continuum of propagation modes. It allows to describe both resonant
enhancement and resonant suppression in a unified manner. All of these
properties can be demonstrated in the frame of a very simple model, which will
be used throughout the Review to show that resonant reflections observed in
different complex systems are indeed closely related to the Fano resonances.Comment: This review paper was submitted to Review of Modern Physics. But all
comments are still welcome
Dissipative solitons in pattern-forming nonlinear optical systems : cavity solitons and feedback solitons
Many dissipative optical systems support patterns. Dissipative solitons are generally found where a pattern coexists with a stable unpatterned state. We consider such phenomena in driven optical cavities containing a nonlinear medium (cavity solitons) and rather similar phenomena (feedback solitons) where a driven nonlinear optical medium is in front of a single feedback mirror. The history, theory, experimental status, and potential application of such solitons is reviewed
Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]
We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines
Spatial Resonator Solitons
Spatial solitons can exist in various kinds of nonlinear optical resonators
with and without amplification. In the past years different types of these
localized structures such as vortices, bright, dark solitons and phase solitons
have been experimentally shown to exist. Many links appear to exist to fields
different from optics, such as fluids, phase transitions or particle physics.
These spatial resonator solitons are bistable and due to their mobility suggest
schemes of information processing not possible with the fixed bistable elements
forming the basic ingredient of traditional electronic processing. The recent
demonstration of existence and manipulation of spatial solitons in emiconductor
microresonators represents a step in the direction of such optical parallel
processing applications. We review pattern formation and solitons in a general
context, show some proof of principle soliton experiments on slow systems, and
describe in more detail the experiments on semiconductor resonator solitons
which are aimed at applications.Comment: 15 pages, 32 figure
Semiconductor Nanowires: Optical Properties and All-Optical Switching
The optical properties of semiconductor nanowires are both important from a fundamental materials physics standpoint and necessary to understand in engineering applications: nanowire photovoltaic devices, sensors, and lasers, among others, could all benefit. Unfortunately, these optical properties are not easy to ascertain. Transmission times are short, in-coupling of white probe light is difficult, and the angle-resolved measurements typically used to determine material dispersion relations in bulk materials are hindered by diffraction effects at subwavelength nanowire end facets.
Here, we present a series of experimental techniques and theoretical models developed to study of the optical properties of active nanowire waveguides. Beginning with a technique for determining the waveguide dispersion of individual ZnSe nanowires, we demonstrate enhanced properties with respect to bulk material. After investigating propagation loss in individual CdS nanowires, the theoretical model was then refined to quantify the strength of light-matter coupling, where size-dependence was observed. The knowledge gained from these studies was put to use in the first demonstration of all-optical switching in individual semiconductor nanowires. The switch concept was then extended into an all-optical nanowire NAND gate. These developments highlight the importance of semiconductor nanowires as both model materials systems and novel devices
Classical and fluctuation-induced electromagnetic interactions in micronscale systems: designer bonding, antibonding, and Casimir forces
Whether intentionally introduced to exert control over particles and
macroscopic objects, such as for trapping or cooling, or whether arising from
the quantum and thermal fluctuations of charges in otherwise neutral bodies,
leading to unwanted stiction between nearby mechanical parts, electromagnetic
interactions play a fundamental role in many naturally occurring processes and
technologies. In this review, we survey recent progress in the understanding
and experimental observation of optomechanical and quantum-fluctuation forces.
Although both of these effects arise from exchange of electromagnetic momentum,
their dramatically different origins, involving either real or virtual photons,
lead to different physical manifestations and design principles. Specifically,
we describe recent predictions and measurements of attractive and repulsive
optomechanical forces, based on the bonding and antibonding interactions of
evanescent waves, as well as predictions of modified and even repulsive Casimir
forces between nanostructured bodies. Finally, we discuss the potential impact
and interplay of these forces in emerging experimental regimes of
micromechanical devices.Comment: Review to appear on the topical issue "Quantum and Hybrid Mechanical
Systems" in Annalen der Physi
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