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A low-cost hybrid textile/PCB wearable rectenna is designed for smart on-body applications. It is an integration of a textile patch antenna and a highly efficient rectifier on a small PCB substrate, where the feeding aperture of the antenna is significantly miniaturized by exploiting an LC loading technique to have an effective integration with the rectifier. The feeding-rectifying circuitry is attached to the back of the antenna by normal sewing threads. The essential components are soldered on the small rigid PCB for a robust connection. The size of the rectenna is $0.817\times 0.817\,\,\lambda {0}^{2}$ while the rigid substrate area for the feeding-rectifying circuitry is only $0.278\times 0.147\,\,\lambda {0}^{2}$ ( $3.4\times1.8$ cm) at 2.45 GHz. The intrinsic dielectric/conduction loss of textile feedlines, the loss of antenna-to-rectifier interconnectors, the loss of soldering or gluing on textiles, and the loss due to body absorption from typical large feeding slots are constitutively reduced. The soldering points and the consequent hard-to-be-characterized parasitic effects on textiles are avoided. The proposed integration approach reduces the cost and eases the rectenna design, fabrication, and integration. As a result, the power conversion efficiency (PCE) of the rectifier reaches up to 39.5% at -20 dBm input power level whilst the experimental rectenna prototype achieves the state-of-the-art PCE of 41% at an extremely low incident power density of $0.4~\mu \text{W}$ /cm2. The maximum PCE is 56% at the -5 dBm input power. Finally, the possibility of harvesting datalink energy from PC/mobile phones as power source for wearable electronics is investigated.

Despite the elaborate varieties of iridescent colors in biological species, most of them are reflective. Here we show the rainbow-like structural colors found in the ghost catfish ( Kryptopterus vitreolus ), which exist only in transmission. The fish shows flickering iridescence throughout the transparent body. The iridescence originates from the collective diffraction of light after passing through the periodic band structures of the sarcomeres inside the tightly stacked myofibril sheets, and the muscle fibers thus work as transmission gratings. The length of the sarcomeres varies from ~1 μm from the body neutral plane near the skeleton to ~2 μm next to the skin, and the iridescence of a live fish mainly results from the longer sarcomeres. The length of the sarcomere changes by ~80 nm as it relaxes and contracts, and the fish shows a quickly blinking dynamic diffraction pattern as it swims. While similar diffraction colors are also observed in thin slices of muscles from non-transparent species such as the white crucian carps, a transparent skin is required indeed to have such iridescence in live species. The ghost catfish skin is of a plywood structure of collagen fibrils, which allows more than 90% of the incident light to pass directly into the muscles and the diffracted light to exit the body. Our findings could also potentially explain the iridescence in other transparent aquatic species, including the eel larvae ( Leptocephalus ) and the icefishes (Salangidae).

ispartof: ADVANCED THEORY AND SIMULATIONS vol:5 issue:12 status: published

In this communication, we propose a robust broadband anomalous refractor (BAR), which minimizes chromatic aberration. The design is based on engineering the dispersion curve of spoof surface plasmon polaritons (SSPPs) and manipulating the wavefront of the transmitted waves. We begin by deriving deflection conditions such that the discrete scatterers of the refractor need to have linear dispersion curves in the operating frequency band. The rich dispersion properties of the SSPP make it a good candidate for meeting the broadband deflection condition. Next, we design symmetric metallic blade structures (MBSs) to efficiently transform free-space waves into SSPPs and to realize the broadband linear dispersion relationship. The BAR is comprised of these MBSs with different strip heights. A prototype is designed, fabricated, and measured. Both the simulated and experimental results demonstrate excellent fixed-direction deflection in the 6.9–9.1 GHz band for the normal incidence case. Furthermore, the BAR still performs well when its outer profile is deformed to some extent, which is desirable in practical applications. This alternative approach to designing achromatic devices at microwave frequencies can be readily extended to higher frequencies.

In light of the emergence of nonclassical effects, a paradigm shift in the conventional macroscopic treatment is required to accurately describe the interaction between light and plasmonic structures with deep-nanometer features. Towards this end, several nonlocal response models, supplemented by additional boundary conditions, have been introduced, investigating the collective motion of the free electron gas in metals. The study of the dipole-excited core-shell nanoparticle has been performed, by employing the following models: the hard-wall hydrodynamic model; the quantum hydrodynamic model; and the generalized nonlocal optical response. The analysis is conducted by investigating the near and far field characteristics of the emitter-nanoparticle system, while considering the emitter outside and inside the studied topology. It is shown that the above models predict striking spectral features, strongly deviating from the results obtained via the classical approach, for both simple and noble constitutive metals. ispartof: Nanoscale Advances vol:4 issue:10 ispartof: location:England status: Published online

Determining the chirality of molecules and nanoparticles often relies on circular dichroism and optical rotation: two chiral optical (chiroptical) effects in the linear optical regime. Although these linear effects are weak compared to nonlinear chiroptical effects, they have the advantage of being measured in isotropic liquids - free from the complications of anisotropy. Recently, a nonlinear effect: hyper-Rayleigh scattering optical activity (HRS OA) has been shown to reliably distinguish between the two chiral forms of Ag nanohelices, suspended in isotropic liquids. However, this first demonstration of HRS OA also opened new questions. For instance, at a fundamental level, it is not clear what the role of interactions between nanoparticles is. Moreover, the influence of the ultrafast pulse chirp is unknown. Here, we demonstrate HRS OA from well below two Ag nanohelices in the illumination volume, precluding any interactions. Additionally, we performed the first measurements of HRS depolarization ratios in this system and find a value of ≈1. We also show that HRS is highly robust against the chirp of the ultrafast pulses. An important reason for the strong (down to single nanohelix) sensitivity of our experiments is the large chiroptical interaction at the fundamental frequency; this point is illustrated with two sets of numerical simulations of the electromagnetic near-fields. Our results highlight HRS OA as a highly sensitive experimental method for characterization of chiral solutions/suspensions, in tiny illumination volumes. ispartof: NANOSCALE vol:14 issue:10 pages:3888-3898 ispartof: location:England status: published

In this work, we apply the group representation theory to systematically study polarization singularities in the in-plane components of the electric fields supported by a planar electromagnetic (EM) resonator with generic rotation and reflection symmetries. We reveal the intrinsic connections between the symmetries and the topological features, i.e., the spatial configuration of the in-plane fields and the associated polarization singularities. The connections are substantiated by a simple relation that links the topological charges of the singularities and the symmetries of the resonator. To verify, a microwave planar resonator with the D8 group symmetries is designed and numerically simulated, which demonstrates the theoretical findings well. Our discussions can be applied to generic EM resonators working in a wide EM spectrum, such as circular antenna arrays, microring resonators, and photonic quasi-crystals, and provide a unique symmetry perspective on many effects in singular optics and topological photonics.

Molecular fluorescence may strongly be affected by plasmonic environments, especially the ones with deep-nanometer features, associated with the emergence of nonclassical effects. Such effects are largely investigated by a nonlocal hydrodynamic model with additional boundary conditions, describing the collective motion of the free electron gas in metals. The study of a fluorophore in the presence of the nano core–shell topology is performed, by employing the following models: the hard-wall hydrodynamic model and the generalized nonlocal optical response. The analysis is conducted by investigating the fluorescence rates of the system, while considering the fluorophore located inside and outside the nanoparticle. It is demonstrated that the rates generated by the above models may considerably differ from the ones obtained via the classical approach. The optimal fluorescence enhancements for different size and material parameters are found both inside and outside the studied topology.

The nanoscale systems are of great importance in modern science and technology, offering a wide range of possible daily life applications. In order to characterize the electromagnetic (EM) properties of metallic nanotopologies, the commercialized computational tools COMSOL, CST, and Lumerical have been widely used. In this work, the performance of the above tools is compared, through the investigation of the plane wave response of canonical spherical and cubical nanoparticles. It is demonstrated that not all EM field solvers provide an accurate description of the nanoparticle's behavior.

The interaction between light and plasmonic structures at the deep-nanometer scale, which is essentially governed by nonclassical effects, has been increasingly investigated by the hydrodynamic model. Several hydrodynamic models have been introduced, in order to describe the motion of the free electron gas in metals. In this work, by employing the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM), the nonlocal response of an isolated metallic nanoparticle, excited by a dipole emitter, is investigated. The analysis is performed for the local density of states of an emitter coupled with a spherical nanoparticle, which may be treated analytically. Both radial and tangential emitters are studied, while varying the emitter–nanoparticle separation, and the nanoparticle’s size and material. It is shown that HW-HDM and Q-HDM may generate striking spectral features, which do not arise within the classical approach.

© 1963-2012 IEEE. In this paper, we propose a general boundary integral equation (BIE) approach for solving both exterior (e.g., scattering) and interior (e.g., guided wave propagation) problems involving general plasmonic waveguiding structures with arbitrary cross-sectional geometries and with a continuous translational symmetry in the direction of wave propagation. Contrary to the field-based approach which deals with the electric and magnetic fields, we employ a potential-based formalism instead, involving vector and scalar potentials, and match them at the media interfaces. The proposed approach can handle not only conventional plasmonic waveguides on the order of a few hundred nanometers but also those whose critical sizes are a few nanometers and in which the nonlocal hydrodynamic effects need to be accounted for. The BIEs describing the interaction of light with the plasmonic waveguide are solved by the method of moments (MoM) algorithm. Two illustrative examples, the first one of which deals with the scattering problem, while the second computes the dispersion diagram of a plasmonic cylinder, are considered for both local and nonlocal cases. An excellent agreement is observed between the numerical and theoretical results, with the latter being derived from the generalized Mie theory. ispartof: IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION vol:67 issue:6 pages:3948-3960 status: published

Background Diabetes has severe impacts on the health of patients. The differentiation of mesenchymal stem cells (MSCs) into islet-like cell clusters (ICCs) is an effective protocol for the treatment of diabetes. microRNAs (miRs) regulate multiple cellular processes including cell differentiation. This study sought to identify the mechanism of miR-365-3p in the differentiation of bone marrow MSCs (bMSCs) into ICCs. Methods Initially, the differentiation of bMSCs into ICCs was induced. Then, the miR-365-3p expression pattern in the bMSCs and ICCs was detected. Next, the miR-365-3p expression pattern was silenced in bMSCs to assess the effect on differentiation efficiency and measure the expressions of ICC marker genes during the differentiation of bMSCs into ICCs. The miR-365-3p downstream target genes were predicted and verified. Paired box protein 6 (Pax6) was downregulated in bMSCs with silenced miR-365-3p to evaluate the differentiation of bMSCs into ICCs. Furthermore, the Pax6 downstream pathway was evaluated. Results The differentiation of bMSCs into ICCs was successfully induced. The miR-365-3p expression in bMSCs was higher than that in ICCs. miR-365-3p downregulation in bMSCs facilitated the differentiation of bMSCs into ICCs, as evidenced by elevated releases of insulin and C-peptide in ICCs and elevated expressions of ICC marker genes. Our findings denoted that miR-365-3p targeted Pax6. Inhibition of Pax6 expression annulled the promotion of miR-365-3p downregulation on the differentiation of bMSCs into ICCs. Increased phosphorylation levels of MEK and ERK were identified in ICCs after downregulation of miR-365-3p however they were decreased after downregulation of Pax6. Conclusions This study supported that miR-365-3p inhibited the differentiation of bMSCs into ICCs via targeting Pax6 and inhibiting the MEK/ERK pathway.

In order to describe light-matter interaction at deep-nanometer scale, which is governed by nonclassical phenomena, a semiclassical hydrodynamic model with additional boundary conditions has been introduced. This model investigates the motion of the charged gas in metals, characterized by nonlocal material parameters. Based on different treatments of the nonlocality, several hydrodynamic models have been proposed. This work employs the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM). The study is performed for the mode structure (natural modes) of a spherical metallic nanoshell, supplemented by the plane wave response of the system. It is shown that the main transverse resonances of HW-HDM and Q-HDM experience nearly identical blueshifts in comparison to the classical resonances. The corresponding longitudinal resonances show noticeable spectrum shifts.

The electromagnetic properties of plasmonic nano-antennas and scatterers with the characteristic dimensions at deep-nanometer scale, governed by quantum mechanical effects, have been extensively studied by a hydrodynamic approach. Several hydrodynamic models, together with additional boundary conditions, have been proposed to deal with the collective motion of the free electron gas in metals. In this work, four hydrodynamic models, namely the hard-wall hydrodynamic model, the curl-free hydrodynamic model, the shear forces hydrodynamic model, and the quantum hydrodynamic model are employed. The study is performed for a deep-nanometer metal core–dielectric shell sphere, excited by a plane wave. It is demonstrated that the far field characteristics of the core–shell nanosphere are largely affected by the choice of a specific hydrodynamic model.

We show strong coupling of a mid-infrared microscale resonator with ultra-localised plasmonic nanocavity modes. This enables new types of mixing between IR absorption and surface-enhanced Raman scattering (SERS), opening up new types of ultrasensitive molecular detection. Nanoscale localized optical cavities are self-assembled by depositing Au nanoparticles onto few μm metal discs with molecular spacers. Coupling between the microscale resonator and nanocavity in this nanoparticle-on-resonator (NPoR) scheme, reveals extreme near-field enhancements resulting in boosted SERS intensities. We anticipate that such near-field enhancements open new horizons in single-molecule photonic circuits and molecular optomechanics.

Much attention has been attracted by the nonlocal hydrodynamic model, which provides the first-order approximation of non-classical effects, essentially governing the light-matter interaction at deep-nanometer scale. Several hydrodynamic models, together with additional boundary conditions, have been introduced to describe the behavior of the free electron gas in metals. This work investigates the performance of the following models: the hard wall hydrodynamic model (HW-HDM), the quantum hydrodynamic model (Q-HDM), the curl-free hydrodynamic model, and the shear forces hydrodynamic model. The analysis is conducted for the mode structure (natural or quasi-normal modes) of a canonical spherical nanoparticle. In contrast to HW-HDM and Q-HDM, the other two models break down, due to artifactual mode interference.

In order to model the interaction between light and plasmonic structures at deep-nanometer scale, which is governed by non-classical effects, a nonlocal hydrodynamic approach has been extensively studied. Several hydrodynamic models have been proposed, solving the coupled equations: the linearized hydrodynamic equation of motion and the electrodynamic Maxwell’s equations, by employing additional boundary conditions. This work compares four hydrodynamic models: the hard wall hydrodynamic model (HW-HDM), the curl-free hydrodynamic model (CF-HDM), the shear forces hydrodynamic model (SF-HDM), and the quantum hydrodynamic model (Q-HDM). The analysis is conducted for a metallic spherical nanoparticle, as an example. The above hydrodynamic models are also compared with experiments available in literature. It is demonstrated that HW-HDM and QHDM outperform the other two hydrodynamic models.

This work illustrates the effect of nano-antenna shape on the efficiency of a complete nano-rectenna system for one specific geometry: the bowtie. The bowtie geometry is very well known for its wider band characteristics compared to the straight dipole. Based on full wave electromagnetic field solvers, the radiation efficiency and maximum matching efficiency for nano-bowties with different lengths and base angles are calculated. The results demonstrate that by adopting the bowtie topology, the radiation efficiency for an aluminum dipole can be improved from 51% to 61%, while the relative total efficiency can be improved from 46% to 57%, compared to the common straight nano-dipole mainly used in literature.

Subwavelength optical resonators and scatterers are dramatically expanding the toolset of the optical sciences and photonics engineering. By offering the opportunity to control and shape light waves in nanoscale volumes, recent developments using high-refractive-index dielectric scatterers gave rise to efficient flat-optical components such as lenses, polarizers, phase plates, color routers, and nonlinear elements with a subwavelength thickness. In this work, we take a deeper look into the unique interaction of light with rod-shaped amorphous silicon scatterers by tapping into their resonant modes with a localized subwavelength light source-an aperture scanning near-field probe. Our experimental configuration essentially constitutes a dielectric antenna that is locally driven by the aperture probe. We show how leaky transverse electric and magnetic modes can selectively be excited and form specific near-field distribution depending on wavelength and antenna dimensions. The probe's transmittance is furthermore enhanced upon coupling to the Fabry-Perot cavity modes, revealing all-dielectric nanorods as efficient transmitter antennas for the radiation of subwavelength emitters, in addition to constituting an elementary building block for all-dielectric metasurfaces and flat optics.

Recent progress in nanofabrication has redrawn the boundaries of the applicability of chiroptical (chiral optical) effects. Chirality, often expressed as a twist in biomolecules, is crucial for pharmaceuticals, where it can result in extremely different chemical properties. Because chiroptical effects are typically very weak in molecules, plasmonic nanomaterials are often proposed as a promising platform to significantly enhance these effects. Unfortunately, the ideal plasmonic nanomaterial has conflicting requirements: its chirality should enhance that of the chiral molecules and yet it should have no chiroptical response on its own. Here, we propose a unique reconciliation to satisfy the requirements: a racemic plasmonic nanomaterial, consisting of equal amounts of opposite chiral unit cells. We show how diffraction spectroscopy can be used to unveil the presence of chirality in such racemic nanogratings in the far-field. Our experiments are supported by numerical simulations and yield a circular intensity difference of up to 15%. The physical origin is demonstrated by full wave simulations in combination with a Green's function – group-theory-based analysis. Contributions from Circular Dichroism in the Angular Distribution of Photoelectrons (CDAD) and pseudo/extrinsic chirality are ruled out. Our findings enable the far-field measurement and tuning of racemic nanomaterials, which is crucial for hyper-sensitive chiral molecular characterization.

ispartof: ADVANCED THEORY AND SIMULATIONS vol:2 issue:9 status: published

In this work, we present a unified approach to model the optical response from a classical local and a nonclassical nonlocal hydrodynamic interface. The modeling is based on a boundary integral equation (BIE) representation. This representation is general for both 2D and 3D problems and can be numerically solved by the Method of Moments (MoM) algorithm. An example is then demonstrated for the 2D and 3D case. A very good agreement with the generalized Mie theory has been demonstrated.

Polarized optical dark-field spectroscopy is shown to be a versatile noninvasive probe of plasmonic structures that trap light to the nanoscale. Clear spectral polarization splittings are found to be directly related to the asymmetric morphology of nanocavities formed between faceted gold nanoparticles and an underlying gold substrate. Both experiment and simulation show the influence of geometry on the coupled system, with spectral shifts Δλ = 3 nm from single atoms. Analytical models allow us to identify the split resonances as transverse cavity modes, tightly confined to the nanogap. The direct correlation of resonance splitting with atomistic morphology allows mapping of subnanometre structures, which is crucial for progress in extreme nano-optics involving chemistry, nanophotonics, and quantum devices.

This research was supported by UK Engineering and Physical Sciences Research Council grants EP/G060649/1 and EP/L027151/1 , and ERC grant LINASS 320503 . F.B. thanks the supports from the Winton Programme for the Physics of Sustainability. Publisher PDF

Since deep nanoscale systems are increasingly studied, accurate macroscopic theories dealing with quantum mechanical effects are in high demand. Concerning the electromagnetic response of nanoplasmonic systems, several hydrodynamic models have been proposed, each introducing an additional boundary condition (ABC) to describe the behavior of the plasmonic electron cloud. Four hydrodynamic approaches with four different boundary conditions are compared: the hard wall hydrodynamic model with the Sauter ABC, the curl-free hydrodynamic model with the Pekar ABC, the shear forces hydrodynamic model with the specular reflection ABC, and the quantum hydrodynamic model with the corresponding ABC. This is done by investigating near- and far-field features of a metallic nanosphere. It is shown that different hydrodynamic models may result in an entirely different prediction of the nanoparticle’s response. These models are validated by using other local and nonlocal response models and experimental results. ispartof: Advanced Theory and Simulations vol:1 issue:12 status: published

© 1963-2012 IEEE. Modeling the interaction between light and a plasmonic nanoantenna, whose critical dimension is of a few nanometers, is complex owing to the 'hydrodynamic' motion of free electrons in a metal. Such a hydrodynamic effect inevitably leads to a nonlocal material response, which enables the propagation of longitudinal electromagnetic waves in the material. In this paper, within the framework of a boundary integral equation and a method of moments algorithm, a computational scheme is developed for predicting the interaction of light with 3-D nonlocal hydrodynamic metallic nanoparticles of arbitrary shape. The numerical implementation is first demonstrated for the test example of a canonical spherical structure. The calculated results are shown to be in the excellent agreement with the theoretical results obtained with the generalized Mie theory. In addition, the capability of treating 3-D structures of general shapes is demonstrated by ellipsoids and dimers. ispartof: IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION vol:66 issue:9 pages:4759-4771 status: published

Plasmonic nanostructures have demonstrated a remarkable ability to control light in ways never observed in nature, as the optical response is closely linked to their flexible geometric design. Due to lack of mirror symmetry, chiral nanostructures allow twisted electric field hotspots to form at the material surface. These hotspots depend strongly on the optical wavelength and nanostructure geometry. Understanding the properties of these chiral hotspots is crucial for their applications; for instance, in enhancing the optical interactions with chiral molecules. Here, the results of an elegant experiment are presented: by designing 35 intermediate geometries, the structure is enantiomorphed from one handedness to the other, passing through an achiral geometry. Nonlinear multiphoton microscopy is used to demonstrate a new kind of double-bisignate circular dichroism due to enantiomorphing, rather than wavelength change. From group theory, a fundamental origin of this plasmonic chiroptical response is proposed. The analysis allows the optimization of plasmonic chiroptical materials. V.K.V. acknowledges support from the Royal Society through the University Research Fellowships. Nuno Braz acknowledges support from the EPSRC grant reference EP/G037256/1. The authors would like to acknowledge the C2 project (C24/15/015) and the PDMK/14/126 project of KU Leuven, the FWO long term stay abroad project grant V405115N, and the Methusalem project funded by the Flemish government. The authors are grateful to Hongjian Tao, Deputy Director of Department of International Cooperation and Exchanges in the Ministry of Education of the People's Republic of China, for facilitating the collaboration between the UK, Chinese, and Belgian teams. All data supporting this study are openly available from the University of Bath data archive at https://doi.org/10.15125/BATH-00483.

Within the framework of the Boundary Element Method (BEM), we develop a computational scheme to account for nonlocal hydrodynamic effects in three -dimensional metallic nanoparticles of arbitrary shape. In contrast to conventional field-based methods, the reported scheme is formulated based on vector and scalar potentials. Especially, an extra scalar potential is introduced to describe longitudinal fields due to the hydrodynamic motion of electrons. The computational scheme is demonstrated for a canonical structure, i.e. sphere, for far field properties, e.g. scattering cross sections, and an excellent agreement is found with generalized Mie theory.

Symmetry holds a prominent position in defining the optical response of a nanoantenna. In this work, we harness a mathematical tool, group representation theory, combine it with the eigenmode analysis for a nanoantenna, and illustrate how the symmetry allows or forbids the energetic coupling (i.e., interference) between a nanoantenna’s eigenmodes. We do this especially using a nanobar structure and a symmetric cross structure. Further, the consequence of symmetry-breaking is illustrated by an asymmetric cross-shaped nanostructure, i.e., a strong asymmetric Fano-type resonance line shape due to mode interference is observed with the physics behind elaborated. Both numerical and experimental evidences are provided.