Tunable Radiation Pattern Research Articles

Adaptive museum lighting using CNN-based image segmentation

Modern smart lighting systems have the potential to improve lighting conditions by employing adaptive dimming. However, the light intensity pattern of the individual luminaires is often not optimally matching with the region(s) of interest. By using adaptive lighting fixtures with a tunable radiation pattern, much more targeted illumination can be enabled. The already demonstrated adaptive lighting fixtures are typically quite bulky, and require user input to optimize the emitted light. In this paper, a compact lighting fixture is proposed that consists of a high-power LED, a sequence of lenses, an adjustable mirror and tunable diffuser, to achieve an adaptive lighting functionality. This adaptive luminaire is integrated with an embedded system and camera, to realize autonomous beam adjustment based on computer vision in a museum setting. The embedded system performs semantic segmentation to detect painting masks, and adapts the light beam direction and spot size to the detected painting frame via a feedback loop. The system can be considered as a first demonstration of the integration between state-of-the-art computer vision and adaptive light fixtures for indoor lighting.

Magnetoplasmonic Nanoantennas for On-Chip Reconfigurable Optical Wireless Communications.

On-chip wireless communications require optical nanoantennas with dynamically tunable radiation patterns, which may allow for higher integration with multiple nanoantennas instead of two fixed nanoantennas in existing approaches. In this paper, we introduce a concept to enable active manipulation of radiated beam steering using applied magnetic fields. The proposed system consists of a highly directive Yagi-Uda-like arrangement of magnetoplasmonic nanoribs made of Co6Ag94 and immersed in SiO2. Numerical demonstration of the tilting of the radiated beam from the nanoantenna on its plane is provided with full-wave electromagnetic simulations using the finite element method. The tilt direction of the radiated beam can be changed by reversing the magnetization direction, while the conventional plasmonic nanoantenna pattern is recovered by demagnetizing the system. The geometry of the nanoantenna can be tailored to work at optical or infrared wavelengths, but a proof of concept for λ = 700 nm is conducted for taking advantage of the high magneto-optical activity of Co6Ag94. The design was based on experimental data for materials that can be fabricated via nanolithography, thus permitting magnetically on-chip reconfigurable optical wireless communications.

Smart lighting system with tunable radiation pattern

Smart lighting systems are capable of producing light when and where it is needed. Such functionality can be achieved with adaptive optical systems, which consist of one or multiple adjustable components, enabling illumination with a variable radiation pattern. This paper introduces the design of a compact, tunable optical system, allowing illumination with variable beam size and beam direction. We demonstrate how this system can be combined with computer vision and a feedback loop, to achieve a fully autonomous, smart illumination system.

A high efficiency fluidly reconfigurable antenna with detached feeding

AbstractIn this study, a pure water antenna with a tunable radiation pattern is proposed, which combines the idea of the Yagi antenna and the reflector antenna to realize a steerable directional beam. By sufficiently utilizing the excellent features of water: fluidity, transparency, and reconfigurability, this proposed design achieves a 360° beam coverage. In addition, a detached feeding structure is introduced to effectively avoid liquid leakage and corrosion. This type of antenna has 25 different working states covering the working frequency from 2.36 to 2.6 GHz (S11 < −10 dB), a high radiation efficiency (70%), and a maximum realized gain of 5.8 dB. This design is expected to be a promising candidate for the internet of things applications.

Radiation pattern direction control of THz antenna with applying planar graphene metasurface

In this paper an antenna with dynamically controllable radiation pattern direction, in the low THz frequency band, is designed and investigated. The radiating element is composed of a rectangular patch antenna on a grounded dielectric while, radiation pattern control is made possible through applying a superstrate, inspired by metasurface structures, with gap of 25μm from the antenna surface. The radiating patch as well as the ground plane are designed with gold while the metasurface consists of graphene loops and patches which are placed on the either sides of a dielectric with the same material of the antenna substrate. Tunable radiation pattern direction is provided through activating appropriate columns of the metasurface unit cells. With applying an electrostatic bias voltage the graphene surface conductivity increases and the corresponding unit cells resemble properties of metals and impose parasitic effects on the antenna radiation pattern, which through wise selection of the metasurface unit cells the antenna radiation pattern is tilted in the desired direction. It is shown that the antenna radiation pattern can be dynamically controlled in the wide range of ±35degrees, symmetrically, in the H-plane.

Nanoantenna with electrically tunable radiation pattern

In this article, an electrical approach is proposed for the purpose of tuning and beamforming of the radiation pattern of the nanoantenna. Interestingly, the main lobe direction of nanoantenna can be controlled and formed in a certain solid angle. The simulated results can be extremely useful in medical applications. In fact, we suggest a mechanism based on DC contacts as external sources, which are positioned around a nanostructure. On this basis, the main beam of the radiation pattern has the potential to turn with applying a DC voltage to each one of the contacts. In other words, the variation of DC voltage in contacts helps to rotate the radiation pattern of nanoantenna in a specific direction. The considered configuration as a nanoantenna is a core–shell spherical particle, which is composed of Silica and Gold. Moreover, the arrays of core–shell nanoantenna on the silver substrate and even without that are investigated. As a particular result, beamforming occurs by means of changing the DC voltage of contacts in the mentioned configuration of the core–shell nanoantenna. The operation frequency of all structures is equal to 550 THz (545 nm) as well.

Highly directive switchable nanoantenna array based on dielectric omega particles at terahertz frequencies.

A high-refractive-index dielectric particle with the ability of supporting both electric and magnetic resonances, operating at 1-2 terahertz, is proposed. It is shown that the suggested omega-shaped nanoparticle is able to control the resonance frequencies independently by changing geometrical dimension. It is also demonstrated numerically that an asymmetric omega particle shows a tunable radiation pattern, depending on the incident frequency. The radiation beam can steer in the range of ±30°. The omega particle shows a directive radiation pattern with small back radiation, due to the constructive interference of the induced electric and magnetic moments. Therefore, the application of the proposed antenna in directivity enhancement is considered. Then, in order to achieve high directivity, omega particles are arranged in an array. Their employment for directivity enhancement has led to the maximum directivity of 11.8dB. Side-lobe level has the minimum amount of -18.3 dB, and total size of the structure is 400 μm×400 μm≅2.6λ×2.6λ in the x-y plane, while it does not exceed a quarter of a wavelength in height.

Phase-change material-based nanoantennas with tunable radiation patterns.

We suggest a novel switchable plasmonic dipole nanoantenna operating at mid-infrared frequencies that exploits phase-change materials. We show that the induced dipole moments of a nanoantenna, where a germanium antimony telluride (Ge3Sb2Te6 or GST for short) nanopatch acts as a spacer between two coupled metallic nanopatches, can be controlled in a disruptive sense. By switching GST between its crystalline and amorphous phases, the nanoantenna can exhibit either an electric or a balanced magneto-electric dipole-like radiation. While the former radiation pattern is omnidirectional, the latter is directive. Based on this property exciting switching devices can be perceived, such as a metasurface whose functionality can be switched between an absorber and a reflector. The switching between stable amorphous and crystalline phases occurs on timescales of nanoseconds and can be achieved by an electrical or optical pulse.

Amplified and directional spontaneous emission from arbitrary composite bodies: A self-consistent treatment of Purcell effect below threshold

We study amplified spontaneous emission (ASE) from wavelength-scale composite bodies--complicated arrangements of active and passive media--demonstrating highly directional and tunable radiation patterns, depending strongly on pump conditions, materials, and object shapes. For instance, we show that under large enough gain, $\mathcal{PT}$ symmetric dielectric spheres radiate mostly along either active or passive regions, depending on the gain distribution. Our predictions are based on a recently proposed fluctuating volume--current (FVC) formulation of electromagnetic radiation that can handle inhomogeneities in the dielectric and fluctuation statistics of active media, e.g. arising from the presence of non-uniform pump or material properties, which we exploit to demonstrate an approach to modelling ASE in regimes where Purcell effect (PE) has a significant impact on the gain, leading to spatial dispersion and/or changes in power requirements. The nonlinear feedback of PE on the active medium, captured by the Maxwell--Bloch equations but often ignored in linear formulations of ASE, is introduced into our linear framework by a self-consistent renormalization of the (dressed) gain parameters, requiring the solution of a large system of nonlinear equations involving many linear scattering calculations.

Single-molecule detection at high concentrations with optical aperture nanoantennas.

Single-molecule detection has become an indispensable technology in life science, and medical research. In order to get meaningful information on many biological processes, single-molecule analysis is required in micro-molar concentrations. At such high concentrations, it is very challenging to isolate a single molecule with conventional diffraction-limited optics. Recently, optical aperture nanoantennas (OANs) have emerged as a powerful tool to enhance the single-molecule detection under a physiological environment. The OANs, which consist of nano-scale apertures on a metallic film, have the following unique properties: (1) nanoscale light confinement; (2) enhanced fluorescence emission; (3) tunable radiation pattern; (4) reduced background noise; and (5) massive parallel detection. This review presents the fundamentals, recent developments and future perspectives in this emerging field.

Optical Nanoantennas with Tunable Radiation Patterns

We address new optical nanoantenna systems with tunable highly directional radiation patterns. The antenna comprises a regular linear array of metal nanoparticles in the proximity of an interface with high dielectric contrast. We show that the radiation pattern of the system can be controlled by changing parameters of the excitation, such as the polarization and/or incidence angles. In the case of excitation under the total reflection condition, the system operates as a nanoscopic source of radiation, converting the macroscopic incident plane wavefront into a narrow beam of light with adjustable characteristics. We derive also simple analytical formulas which give an excellent description of the radiation pattern and provide a useful tool for analysis and antenna design.

Tunable gradient refractive index optics using graded plasmonic crystals with semiconductor rods

Using numerical simulations, we demonstrate the feasibility of tunable gradient refractive index optics at terahertz frequencies based on two-dimensional graded plasmonic crystals (GPCs). They consist of semiconductor rods with spatially dependent radii. In the effective medium approximation, the GPCs can be considered as effective media with a graded effective dielectric permittivity. The semiconductor rods have the Drude-type dispersion. By varying free charge carrier concentration in the rods, it is possible to tune their permittivity. In accordance to effective medium theory, the effective permittivity of the whole GPC is changed at the same time. This property is used for the demonstration of a GPC-based lens with a tunable focus, beam deflector with tunable angle of the beam deflection, and the half Maxwell-fisheye and the Luneburg lens as antennas with tunable radiation patterns. In particular, these GPCs can be made invisible to the incoming radiation by equaling the real part of the rods permittivity to the permittivity of air background.