Nonradiating Photonics with Resonant Dielectric Nanostructures

Nonradiating sources of energy have traditionally been studied in quantum mechanics and astrophysics, while receiving a very little attention in the photonics community. This situation has changed recently due to a number of pioneering theoretical studies and remarkable experimental demonstrations of the exotic states of light in dielectric resonant photonic structures and metasurfaces, with the possibility to localize efficiently the electromagnetic fields of high intensities within small volumes of matter. These recent advances underpin novel concepts in nanophotonics, and provide a promising pathway to overcome the problem of losses usually associated with metals and plasmonic materials for the efficient control of the light-matter interaction at the nanoscale. This review paper provides the general background and several snapshots of the recent results in this young yet prominent research field, focusing on two types of nonradiating states of light that both have been recently at the center of many studies in all-dielectric resonant meta-optics and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the continuum}. We discuss a brief history of these states in optics, their underlying physics and manifestations, and also emphasize their differences and similarities. We also review some applications of such novel photonic states in both linear and nonlinear optics for the nanoscale field enhancement, a design of novel dielectric structures with high-$Q$ resonances, nonlinear wave mixing and enhanced harmonic generation, as well as advanced concepts for lasing and optical neural networks.Comment: 22 pages, 9 figures, review articl

A high-resolution and low-cost mesoscale tactile force sensor based on mode-localization effect and fabricated using rapid prototyping

This paper presents a novel design of a high resolution and low-cost tactile force sensor, based on the concept of mode-localization in two weakly coupled resonators (WCRs). The sensor is fabricated at mesoscale by utilizing rapid prototyping techniques. The two WCRs in the sensor are operated at resonance by using an electrostatic ac-tuation. Change in the oscillation amplitude ratios and resonant frequency shift, corresponding to an input force is utilized as an output metric for the measurement of force. The application of an applied force on the WCRs in-duced electrostatic strain, which acted as a negative stiffness perturbation. The outer body of sensor is manufac-tured using a soft silicone elastomer and shaped using molds based on laser cutting technique. The proposed tac-tile force sensor is analyzed numerically through finite-element-method (FEM) based simulations. For the testing of tactile force sensor, an actuation and sensing electronics scheme is developed. The experimental results re-vealed that the sensor is capable of measuring input force up to 20 mN with a relative amplitude ratio (AR) and resonant frequency shift based sensitivity of 27040 ppm/mN and 3553 ppm/mN respectively. The experimen-tally evaluated resolution for the sensor is 7.3 µN. The sensor shows the stability in response to the thermal varia-tions and low-frequency vibrational environments

Collective dynamics of strain-coupled nanomechanical pillar resonators

Semiconductur nano- and micropillars represent a promising platform for hybrid nanodevices. Their ability to couple to a broad variety of nanomechanical, acoustic, charge, spin, excitonic, polaritonic, or electromagnetic excitations is utilized in fields as diverse as force sensing or optoelectronics. In order to fully exploit the potential of these versatile systems e.g. for metamaterials, synchronization or topologically protected devices an intrinsic coupling mechanism between individual pillars needs to be established. This can be accomplished by taking advantage of the strain field induced by the flexural modes of the pillars. Here, we demonstrate strain-induced, strong coupling between two adjacent nanomechanical pillar resonators. Both mode hybridization and the formation of an avoided level crossing in the response of the nanopillar pair are experimentally observed. The described coupling mechanism is readily scalable, enabling hybrid nanomechanical resonator networks for the investigation of a broad range of collective dynamical phenomena

Análise dinâmica de cristais fonônicos e metamateriais elásticos utilizando abordagens semi-analíticas e numéricas

Orientador: José Maria Campos dos SantosTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Nesta tese, os métodos de expansão em ondas planas (PWE), expansão em ondas planas melhorado (IPWE) e expansão em ondas planas estendido (EPWE) são utilizados para obter a estrutura de banda de cristais fonônicos (PnCs) e de metamateriais elásticos (EMs) uni- (1D) e bi-dimensionais (2D), isto é, estruturas arti?ciais projetadas para criarem bandas proibidas de Bragg e/ou localmente ressonantes. Estas estruturas periódicas estão sendo aplicadas em vários ramos da ciência e possuem diversas aplicações ¿ controle passivo/ativo de vibração, ?ltros/barreiras acústicas, metamateriais para captação de energia, guias de onda, dentre outras. A principal aplicação considerada nesta tese é o controle passivo de vibração. Primeiro, as formulações do PWE, IPWE e EPWE são apresentadas para alguns casos e vantagens e limitações são discutidas. Os casos considerados são PnCs 1D de barra, cristais sônicos 2D e EMs 1D de viga de Euler-Bernoulli. Posteriormente, alguns exemplos de propagação de ondas mecânicas nestas estruturas periódicas são abordados através da análise da estrutura de banda. Em seguida, algumas aplicações dos PnCs e EMs para controle passivo de vibração são discutidas em artigos anexados. Inicialmente, a estrutura de banda e a resposta forçada harmônica de um PnC simples de viga de Euler-Bernoulli são calculadas. Vários métodos são aplicados e os resultados simulados podem localizar a posição e a largura das bandas proibidas de Bragg próximas dos resultados experimentais. Posteriormente, é considerada a formação de bandas proibidas de ondas de ?exão em um PnC de placa com diferentes inclusões em redes quadrada e triangular, considerando-se a teoria de Mindlin-Reissner. O melhor desempenho é encontrado para a inclusão com seção transversal circular em uma rede triangular. Em seguida, a estrutura de banda de ondas elásticas se propagando em PnCs com nanoestruturas de carbono e em nanocristais fonônicos piezoelétricos com diferentes tipos de rede e inclusão são calculadas. Bandas proibidas totais entre os modos XY e Z são observadas para todos os tipos de inclusão. A piezoeletricidade in?uencia signi?cativamente as bandas proibidas para inclusão circular vazada em frequências mais baixas. Posteriormente, um PnC magnético-elétrico-elástico 2D é considerado. Diferentes tipos de rede e de inclusão também são considerados. A piezoeletricidade e o piezomagnetismo in?uenciam signi?cativamente as bandas proibidas. Finalmente, são considerados EMs 1D de viga de Euler-Bernoulli e 2D de placa ?na. A in?uência de ressonadores de um grau de liberdade e de múltiplos graus de liberdade periodicamente conectados nas células unitárias do EM de viga de Euler-Bernoulli e EM 2D de placa ?na são investigadas. Diferentes con?gurações da distribuição dos ressonadores são consideradas para investigar os mecanismos de formação das bandas proibidas, isto é, ressonância local e espalhamento de BraggAbstract: In this thesis, plane wave expansion (PWE), improved plane wave expansion (IPWE) and extended plane wave expansion (EPWE) methods are used in order to obtain the band structure of one- (1D) and two-dimensional (2D) phononic crystals (PnCs) and elastic metamaterials (EMs), i.e., arti?cial structures designed to open up Bragg-type and/or locally resonant band gaps. Such periodic structures are being applied in many branches of science, and have many applications ¿ passive/active vibration control, acoustic barriers/?lters, metamaterials-based enhanced energy harvesting, waveguides, among others. The main application considered in this thesis is passive vibration control. First, PWE, IPWE and EPWE formulations are presented for some cases and advantages and drawbacks are discussed. The cases regarded are 1D PnC rods, 2D sonic crystals and 1D EM Euler-Bernoulli beams. Afterwards, some examples of mechanical wave propagation in these periodic structures are addressed by means of band structure analysis. Next, some applications of PnCs and EMs for passive vibration control are discussed in attached papers. Initially, the band structure and harmonic forced response of a simple 1D PnC Euler-Bernoulli beam are carried out. Several approaches are applied and the simulated results can localize the Bragg-type band gap position and width close to the experimental results. Next, it is considered the formation of ?exural wave band gaps in a PnC plate with different inclusions in square and triangular lattices, considering Mindlin-Reissner theory. The best performance is found for circular cross section inclusion in a triangular lattice. Afterwards, the band structure of elastic waves propagating in carbon nanostructure PnCs and nano-piezoelectric PnCs with different types of lattice and inclusion are calculated. Full band gaps between XY and Z modes are observed for all types of inclusions. Piezoelectricity in?uences signi?cantly the band gaps for hollow circular inclusion in lower frequencies. After that, a magnetoelectroelastic 2D PnC is considered. Different types of lattice and inclusion are also addressed. Piezoelectricity and piezomagnetism in?uence signi?cantly the band gaps. Finally, elastic wave propagating in 1D EM Euler-Bernoulli beams and in 2D EM thin plates is regarded. The in?uence of single degree of freedom and multiple degrees of freedom resonators periodically attached in unit cells of the EM Euler-Bernoulli beam and 2D EM thin plate are investigated. Different con?gurations of resonator distribution are carried out in order to investigate the band gap formation mechanisms, i.e., local resonance and Bragg scatteringDoutoradoMecanica dos Sólidos e Projeto MecanicoDoutor em Engenharia Mecânic

Design and Modeling a Tunable Non-Hermitian Acoustic Filter

In this thesis, we explore an application of a non-Hermitian acoustic system with tunable loss in filtering specific frequencies from an upcoming signal at will. Using the commercial computational software, we design our proposed tunable filter made of a phononic super-lattice. The super-lattice consists of two sublattices connected in series. The first sublattice is Hermitian, whereas the other can be Hermitian or Non-Hermitian depending on the amount of loss induced in it. By introducing the loss in the system, we observe the generation of absorbed resonances that can be seen in the reflection spectrum. The range of the filtered frequencies can be controlled by adjusting the degree of non-Hermiticity and designing the first sublattice\u27s resonances. The resonances in the first sub-lattice can be adjusted by increasing or decreasing the number of unit cells in the sub-lattice. Our tunable acoustic filter can be extended to higher frequency ranges, such as ultrasound and other areas, such as photonics. In addition, we explore the geometry-induced non-Hermitian mode couplings and study the different modes in a system of acoustic ring resonators with induced loss and study the field localization within the system

Master of Science

thesisThe design, working principle, fabrication, and characterization of ultrasensitive ferromagnetic and magnetoelectric magnetometer are discussed in this thesis. Different manufacturing techniques and materials were used for the fabrication of the two versions of the magnetometer. The ferromagnetic microelectromechanical systems (MEMS) magnetometer was fabricated using low-pressure chemical vapor deposition (LPCVD) of silicon nitride, yielding low compressive stress, followed by patterning. The built-in stress was found to be -14 Mpa using Tencor P-10 profilometer. A neodymium magnet (NdFeB) was used as a foot-mass to increase the sensitivity of the device. A coil (Ø=3 cm), placed at a distance from the sensor (2.5-15 cm), was used to produce the magnetic field. The response of the ferromagnetic MEMS magnetometer to the AC magnetic field was measured using Laser-Doppler vibrometer. The ferromagnetic sensor's average temperature sensitivity around room temperature was 11.9 pV/pT/-C, which was negligible. The resolution of the ferromagnetic sensor was found to be 27 pT (1 pT = 10-12 T). To further improve the sensitivity and eliminate the use of the optical detection method, we fabricated a Lead Zirconate titanate (PZT) based magnetoelectric sensor. The sensor structure consisted of a 9 mm long, and 0.17 mm thick PZT beam of varying widths. A neodymium permanent magnet was used as a foot-mass in this case as well. The magnetic field from the coil generated a driving force on the permanent magnet. The driving force displaced the free end of the PZT beam and generated a proportional voltage in the PZT layer. The magnetoelectric coupling, i.e., the coupling between mechanical and magnetic field, yielded a sensor resolution of ~40 fT (1 fT = 10-15 T); an improvement by three orders of magnitude. We used high permeability Mu sheets (0.003"") attached to copper plates (0.125"") to shield stray magnetic fields around the sensor. For both the ferromagnetic MEMS and the magnetoelectric magnetometer, the initial output was improved by using external bias and parametric amplification. By applying an external DC magnetic field bias to the sensor, the effective spring compliance of the sensor was modified. Electronic feedback reduced the active noise limiting the sensor's sensitivity. We used magnetic coupling to enhance the sensors' sensitivity and to reduce the electronic noise. Two identical sensors, with identical foot-mass (permanent magnet), was used to show coupling. The magnet on one of the sensors was mounted in NS polarity, whereas, on the other it was in SN polarity. When excited by the same external AC magnetic field (using coil), one of the sensors was pulled towards the coil and the other was pushed away from it. Adding the individual sensor output, using a preamplifier, an overall increase in sensors' output was observed. The techniques mentioned above helped to improve the output from the sensor. The sensitivity of the sensor can be improved further by using a 3-axis magnetic field cancellation system, by eliminating the AC and DC stray magnetic field, by using coupled-mode resonators and by increasing the surface field intensity of the foot-mass. The magnetometers, thus, developed can be used for mapping the magnetic print of the brain

A robust optimised multi-material 3D inkjet printed elastic metamaterial

This paper presents and validates a novel elastic metamaterial design, that is optimised for broadband robust vibration control of a structure in the presence of uncertainties, and realised using multi-material additive manufacturing. A novel concept resonator design that allows the resonance frequency to be flexibly tuned via both geometrical and material property modifications is presented and characterised. A unit cell consisting of 12 of these resonators is then proposed. The resonance frequencies and damping ratios of this elastic metamaterial unit cell when attached to a parametrically uncertain example structure are then optimised using a Particle Swarm Optimisation to maximise the mean attenuation in kinetic energy of a structure with parametric uncertainties, based on an analytical model of the system. The performance of the optimised metamaterial is then validated experimentally, and it is shown that the realised metamaterial design is able to achieve a mean of 3.5 dB of broadband attenuation in the presence of uncertainties in the structure. In addition, in the presence of structural uncertainties the robustly optimised design achieves 0.5 dB greater mean attenuation than a design optimised on the nominal structural response alone, and reduced variation in attenuation for different levels of uncertainty