Dielectric Hemisphere Research Articles

Si3N4 Dielectric Hemi-sphere Arrayed Plasmonic Metasurface With Top Metal Coating for Multiresonant Absorption in NIR Regime

Si3N4 Dielectric Hemi-sphere Arrayed Plasmonic Metasurface With Top Metal Coating for Multiresonant Absorption in NIR Regime

Microwave demonstration of Purcell effect enhanced radiation efficiency

We experimentally demonstrate a Purcell effect-based design technique for improved impedance matching, and thus enhanced the reflection coefficient from a small microwave emitter. Using an iterative process centred on comparing the phase of the radiated field of the emitter in air with that of the emitter in a dielectric environment, we optimise the structure of a dielectric hemisphere above a ground plane surrounding a small monopolar microwave emitter in order to maximise its radiation efficiency. The optimised system shows very strong coupling between the emitter and two omnidirectional radiation modes at 1.99 GHz and 2.84 GHz, yielding Purcell enhancement factors of 1762 and 411 times increase respectively, and near perfect radiation efficiency.

Electro-Orientation and Electro-Rotation of Metallodielectric Janus Particles.

The electro-rotation (EROT) and electro-orientation (EOR) behavior of metallodielectric spherical Janus particles (JP) are studied analytically and verified experimentally. This stands in contrast to previous either heuristic or numerically computed models of JP dipoles. First, we obtain frequency-dependent analytic expressions for the corresponding dipole terms for a JP composed of dielectric and metallic hemispheres by applying the "standard" (weak-field) electrokinetic model and using a Fourier-Legendre collocation method for solving two sets of linear equations. EROT and EOR spectra, describing the variation of the JP's angular velocity on the forcing frequency of a rotating and nonrotating spatially uniform electric field, respectively, are explicitly determined and compared against experiments (different JP sizes and solution conductivities). While a favorably good agreement between theory and experimental measurements was found for the frequency response (∼8% difference), there is still a factor of ∼2 difference in the amplitude of the angular velocity, which necessitates further future improvements to the model.

Electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in nematic liquid crystals.

We study the electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in two nematic liquid crystals (LCs) having the same sign of conductivity anisotropy (Δσ) but opposite signs of dielectric anisotropy (Δε). The applied ac electric field is parallel and perpendicular to the director for positive and negative dielectric anisotropy LCs, respectively. We show that the Janus dipolar particles propel faster than the non-Janus dipolar particles in both LCs. The propelling speed of the Janus dipolar particles is also significantly higher compared to the quadrupolar Janus particles studied previously. We map the electroosmotic flow fields surrounding a Janus dipolar particle using microparticle image velocimetry (μ-PIV) and show that the flow on a metal hemisphere is stronger than that on a dielectric hemisphere. Altogether, Janus dipolar particles demonstrate efficient electrophoresis compared to both Janus and non-Janus quadrupolar particles. These findings may be useful for applications in active matter, microrobotic and microfluidic devices.

DEVELOPMENT OF A SYSTEM OF ELECTRODES FOR A BIOIMPEDANCE SPECTROMETRY DEVICE

A system of electrodes for a bioimpedance spectrometry device has been developed. This device measures the resistance of biological tissues for given frequencies of electric current. The device is able to assess the state of organs and tissues of biological structures in case of breast cancer, as well as under various external influences. It differs from all existing bioimpedance spectrometry devices in that it has small dimensions, is capable of changing the frequencies of the probing current and at the same time immediately fixing the impedance values, and the system of electrodes has a hemispherical shape, and to obtain more accurate impedance data, each electrode is equipped with a spring that is attached to a dielectric hemisphere. The aim of the study is to study breast cancer using the developed system of electrodes for a bioimpedance spectrometry device. Patients with breast cancers were studied using a bioimpedance spectrometry device. The study of the impedance data obtained from the subjects with the presence of cancer in the breast and breast without deviations showed that the impedance of the breast affected by cancer lies in the range of 13...20 Ohm, depending on the frequency of the current. That is, the electrical resistance of the patient's affected chest is reduced to 13.6 %. The analysis showed that the diagnostics of cancer diseases can be carried out by the developed device for bioimpedance spectrometry.

Development of an electrode unit for a bioimpedance spectrometry device

An electrode unit of a bioimpedance spectrometry device has been developed. This device measures the resistance of biological tissues for specified frequencies of electric current. The device is capable of evaluating the condition of organs and tissues of biological structures in case of breast cancer, as well as in case of various external influences. It differs from all existing devices of bioimpedance spectrometry by the fact that it has small dimensions, is able to change the frequencies of probing current and at the same time to fix impedance values. The electrode unit has a hemispherical shape and to obtain more accurate impedance data each electrode is equipped with a spring which is fixed on a dielectric hemisphere. The purpose of the research is to study breast cancer using the developed electrode unit of the bioimpedance spectrometry device. Patients with malignant neoplasms of the breast were examined with the use of the bioimpedance spectrometry device. The study of impedance data obtained from the patients with and without breast cancer showed that the impedance of the breast affected by cancer lies within 13...20 ohms, depending on the current frequency. That is, the electrical impedance of the affected patient’s breast decreases by up to 13.6 percent. The analysis showed that the developed bioimpedance spectrometry device allows to diagnose cancerous diseases.

Photonic nanojets with ultralong working distance and narrowed beam waist by immersed engineered dielectric hemisphere.

Engineered spherical micro-lens can manipulate light at sub-wavelength scale and emerges as a promising candidate to extend the focal length and narrow the focal spot size. Here, we report the generation of photonic nanojets (PNJs) with an ultralong working distance and narrowed beam waist by an immersed engineered hemisphere. Simulations show that a two-layer hemisphere of 4.5 µm radius exhibits a PNJ with the working distance of 9.6 µm, full width at half maximum of 287 nm, and length of 23.37 λ, under illumination of a plane wave with a 365 nm wavelength. A geometrical optics analysis indicated that the formed PNJ behind the immersed two-layer hemisphere results from the convergence of light of the outer-hemisphere fringe area, which refracts into and passes through the outer hemisphere and then directly leaves the outer-hemisphere flat surface. Thus the embedded hemisphere is comparable to an immersed focusing lens with high numerical aperture, which can promise both long working distance and narrowed beam waist. This is further demonstrated with the corresponding embedded-engineered single-layer hemisphere, whose spherical face is partly cut parallel to the hemispherical flat surface. In addition, the hemisphere is compatible with adjacent laser wavelengths. Finally, a spot size smaller than 0.5 λ is demonstrated in the lithography simulation. Due to these hemispheres low cost, they have potential in far-field lithography for pattern arrays with line width less than 0.5 λ.

Terahertz Metamaterial with Multiple Resonances for Biosensing Application.

A sickle-shaped metamaterial (SSM) based biochemical sensor with multiple resonances was investigated in the terahertz frequency range. The electromagnetic responses of SSM were found to be four resonances, namely dipolar, quadrupolar, octupolar and hexadecapolar plasmon resonances. They were generated from the interactions between SSM and perpendicularly incident terahertz waves. The sensing performances of SSM-based biochemical sensors were evaluated by changing ambient environments and analyte varieties. The highest values of sensitivity and figure of merit (FOM) for SSM covered with analyte thin-films were 471 GHz/RIU (refraction index unit) and 94 RIU−1, respectively. In order to further investigate the biosensing ability of the proposed SSM device, dielectric hemispheres and microfluidic chips were adopted to imitate dry and hydrous biological specimens, respectively. The results show that the sensing abilities of SSM-based biochemical sensors could be enhanced by increasing either the number of hemispheres or the channel width of the microfluidic chip. The highest sensitivity was 405 GHz/RIU for SSM integrated with microfluidic chips. Finally, three more realistic models were simulated to imitate real sensing situations, and the corresponding highest sensitivity was 502 GHz/RIU. The proposed SSM device paves the way to possible uses in biochemical sensing applications.

Design and Simulation of Slot Dimensions in Aperture Coupled Hemispherical Dielectric Resonator Antenna

Aperture coupled novel shaped Hemispherical Dielectric Resonator Antenna (HDRA ) and the various dimensions of slots are designed and analyzed by hfss software. The dielectric constant of dielectric hemisphere is € =9.8 and the substrate of dielectric constant is 2.96. aperture coupled novel shaped Hemispherical Dielectric Resonator Antenna (HDRA ) parameters are presented in this paper.. The effects of changing the slot length , slot width and position of slot on the antenna parameters and are presented in this paper, which are used for directive gain applications. As the change of slot dimension , it is observed that at the resonant frequency, it gives high gain and high negative return loss

Theory and Experiment of UWB Archimedean Conformal Spiral Antennas

A conformal UWB Archimedean spiral antenna on a dielectric hemisphere is theoretically and experimentally investigated. The analysis method, design, and optimization of this type of spherical antennas is performed using an efficient spatial domain method of moments in conjunction with triangular basis functions and asymptotic Green’s functions. A special conformal mapping is used to enhance the impedance bandwidth and axial ratio (AR) bandwidth for a circularly polarized spherical spiral antenna. Emphasis is given to the efficient asymptotic approach in spherical multilayered media. To validate the theory, a UWB leaky-wave conformal spiral antenna was designed, manufactured, and tested. The measured results indicate a pretty wideband behavior for this antenna starting from 1.7 to 6 GHz (1.8 octaves) in its input impedance responses. The circular polarization is maintained over 1.26 octave with less than 3 dB AR.

Characteristics of photonic nanojets from two-layer dielectric hemisphere**Project supported by State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences; Sichuan Provincial Department of Education, China (Grant No. 16ZA0047); the State Key Laboratory of Metastable Materials Science and Technology, Yansan University, China (Grant No. 201509); and the Large Precision Instruments Open

The properties of the photonic nanojet generated by a two-layer dielectric microsphere are studied. Simulation results indicate that this novel structure can generate a photonic nanojet outside its volume when the refractive index contrast relative to the background medium is higher than 2:1 in the condition of plane wave incidence. When the refractive index is smaller than 2, we show that an ultralong nanojet generated by the two-layer hemisphere has an extension of 28.2 wavelengths, and compared with the homogeneous dielectric hemisphere, it has superior performance in jet length and focal distance. Its dependence on the configuration and refractive index is investigated numerically. According to the simulation of the two-layer dielectric microsphere, a photonic nanojet with a full width at half maximum (FWHM) less than 1/2 wavelength is obtained and the tunable behaviors of the photonic nanojet are demonstrated by changing the reflective indices of the material or radius contrast ratio.

Propulsion of Active Colloids by Self-Induced Field Gradients.

Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

Spinning Janus doublets driven in uniform ac electric fields

We provide an experimental proof of concept for a robust, continuously rotating microstructure-consisting of two metallodielectric (gold-polystyrene) Janus particles rigidly attached to each other-which is driven in uniform ac fields by asymmetric induced-charge electro-osmosis. The pairs (doublets) are stabilized on the substrate surface which is parallel to the plane of view and normal to the direction of the applied electric field. We find that the radius of orbit and angular velocity of the pair are predominantly dependent on the relative orientations of the interfaces between the metallic and dielectric hemispheres and that the electrohydrodynamic particle-particle interactions are small. Additionally, we verify that both the angular and linear velocities of the pair are proportional to the square of the applied field which is consistent with the theory for nonlinear electrokinetics. A simple kinematic rigid body model is used to predict the paths and doublet velocities (angular and linear) based on their relative orientations with good agreement.

Alternating current induced-charge electrophoresis of leaky dielectric Janus particles

We hereby provide a semi-analytic and numerical solution for the nonlinear, induced-charge electrophoretic motion of an electrically inhomogeneous Janus sphere—comprising two hemispheres with differing dielectric permittivities—under the application of a uniform, time-dependent (ac) electric field. No assumptions are made regarding the size of the electric double layer (EDL) and thus the analysis remains valid even in the case of nanoparticles where the particle radius can be of the same order as the EDL thickness. We consider a number of practical and realistic configurations of metallic and dielectric hemispheres and predict the variations in particle mobility as a function of the conductivity of the two hemispheres and the electrolyte, the frequency of the applied electric field and the EDL length. It is determined that there exist critical values for the conductivity of each hemisphere and the frequency of the applied field, which when exceeded, can cause the mobility to decay rapidly to zero.

Plasmon nanofocusing in a dielectric hemisphere covered in tapered metal film

We propose and analyze a new type of mechanically robust optical nanofocusing probe with minimized external environmental interference. The probe consists of a dielectric optical fiber terminated by a dielectric hemisphere - both covered in thin gold film whose thickness is reduced (tapered) along the surface of the hemisphere toward its tip. Thus the proposed probe combines the advantages of the diffraction-limited focusing due to annular propagation of the plasmon with its nanofocusing by a tapered metal wedge (i.e. a metal film with reducing local thickness). The numerical finite-element analysis demonstrates strongly subwavelength resolution of the described structure with the achievable size of the focal spot of ~20 nm with up to ~150 times enhancement of the local electric field intensity. Detailed physical interpretations of the obtained results are presented and possible application as a new type of SNOM probe for subwavelength imaging, spectroscopy and sensing are also discussed.

Patterning: Direct Transfer Patterning of Electrically Small Antennas onto Three‐Dimensionally Contoured Substrates (Adv. Mater. 9/2012)

A process to stamp conductors onto contoured surfaces is reported by S. R. Forrest, A. Grbic, and co-workers on page 1166. This process has the potential to provide an inexpensive and rapid method to print metallic patterns onto arbitrarily contoured substrates, which has extensive applications. Here, electrically small antennae are printed onto dielectric hemispheres. These antennae offer bandwidths approaching the fundamental limit, while maintaining some of the highest reported efficiencies to date. Cover design by C. Pfeiffer and P. Haley.

Measurements and Analysis of a Helical Antenna Printed on a Layered Dielectric Hemisphere

Radiation characteristics of a helical wire that is printed on the surface of a dielectric hemisphere have been studied theoretically and experimentally. Rigorous analyses have been performed using the method of moments (MoM). As expected, the dielectric hemisphere reduces the antenna's operating frequency and bandwidth. Furthermore, it has improved the 3 dB circular polarization beamwidth considerably. Hemispherical structures that consist of one, or two, dielectric layers have been considered. The experimental and computed results are in close agreement with each other.

Superconducting Test Cavity With Dielectric Concentrator for High Q, High Surface Field

A superconducting test cavity and cryostat are being developed to support the testing of round wafer samples of new superconducting materials. The cavity is designed to test these samples in surface fields up to and beyond the BCS limit of Nb. The design is optimized to produce maximum surface field on the sample compared with that elsewhere in the cavity. It operates in the TE011 mode. A dielectric hemisphere of low-loss sapphire is located just above the wafer surface and serves to concentrate the surface field. The sapphire is cooled by a column of superfluid He, with sufficient heat transport to maintain high Q throughout the rf pulse. It should be possible to test a sample to twice the BCS limit of Nb while measuring the rf surface resistance of the sample.

Dielectrophoretic Assembly of Metallodielectric Janus Particles in AC Electric Fields

"Janus" particles with two hemispheres of different polarizability or charge demonstrate a multitude of interesting effects in external electric fields. We reported earlier how particles with one metallic hemisphere and one dielectric hemisphere self-propel in low-frequency alternating current (AC) electric fields. Here, we demonstrate the assembly of such Janus particles driven by AC electric fields at frequencies above 10 kHz. We investigated the relation between field-induced dielectrophoretic force, field distribution, and structure of the assemblies. The phase space for electric field intensity and frequency was explored for particle concentrations large enough to form a monolayer on a glass surface between two gold electrodes. A rich variety of metallodielectric particle structures and dynamics were uncovered, which are very different from those obtained from directed assembly of plain dielectric or plain conductive particles under the action of fields of similar frequency and intensity. The metallodielectric particles assemble into new types of chain structures, where the metallized halves of neighboring particles align into lanes along the direction of the electric field, while the dielectric halves face in alternating direction. The staggered chains may assemble in various orientations to form different types of two-dimensional metallodielectric crystals. The experimental results on the formation of staggered chains are interpreted by means of numerical simulations of the electric energy of the system. The assembly of Janus metallodielectric particles may find applications in liquid-borne microcircuits and materials with directional electric and heat transfer.

Analysis of a Dielectric Resonator Antenna by Applying a Combined Semi-Analytical Method and Simulation

The radiation properties of a hemispherical dielectric resonator, consisting of a monopole antenna placed in a dielectric hemisphere is theoretically examined. A method based on the combination of Green's function theory, in conjunction with the Method of Auxiliary Sources (MAS), is used to solve analytically and calculate the electromagnetic field at any arbitrary point of the structure. The Green's function theory is used to calculate the response of the hemisphere to an excitation consisting of an elementary dipole placed inside its volume. The Method of Auxiliary Sources (MAS) is applied by distributing a set of elementary dipoles along the axis of the antenna probe. A number of matching points, lying on the surface of the cylindrical antenna, are used to calculate the dipole moments of the auxiliary sources, by imposing appropriate boundary conditions. Additionally, the input impedance and the current distribution on the antenna are also derived through application of the above-mentioned methodology. The numerical results are finally validated by comparing them with the simulation results of the relevant configuration elicited using a commercial simulation FEM tool.