Dielectric Ring Research Articles

Reply to Comments on “A Semi-Analytical Model of High-Permittivity Dielectric Ring Resonators for Magnetic Resonance Imaging”

Comments about the above article <xref ref-type="bibr" rid="ref1">[1]</xref> were proposed. We thank and reply to the authors of the comments about our model of high-permittivity dielectric ring resonators used as microscopy magnetic resonance probes. In this prospect, we reply part by part to the comments.

Comments on “A Semi-Analytical Model of High-Permittivity Dielectric Ring Resonators for Magnetic Resonance Imaging”

In the above article <xref ref-type="bibr" rid="ref1">[1]</xref>, the authors developed a novel magnetic resonance imaging mechanism based on a semi-analytical model containing a high-permittivity dielectric ring resonator and a low-permittivity dielectric core. We have several comments on this model and its solving process.

Resonant reflection of plane microwave electromagnetic waves by the linear dielectric-ring structures

Artificial materials with negative magnetic and dielectric permittivity have unique electrodynamic properties that are not present in natural materials. We present the results of studying of the main magnetic LC resonance induced by a plane electromagnetic wave of GHz range in the linear structures of subwavelength dielectric ring elements with a high relative permittivity. The dielectric constant of the ring material (capacitor ceramics) is 160. Resonant scattering on the main magnetic mode and wave properties of linear structures consisting of subwavelength dielectric elements in the form of flat thin rings were studied. A single ring or ring structures were arranged in such a way that the vectors of the electric and magnetic fields of a plane incident electromagnetic wave were parallel to the plane of the ring, whereas the wave vector was perpendicular to the plane of the ring. Linear structures consisting of two or three rings were oriented along the magnetic vector of the incident wave. The magnetic field probe was placed on the line of the axis of symmetry of the ring and structures relative to the wave vector at the side of the structures most distant from the antenna. The spectra of transmitted radiation were measured during resonant excitation of magnetic fields in a system of dielectric rings in the near (distance — 2 mm) and remote (distance — 30 mm) zones from the ring. It is shown that in the near wave zone, splitting of the resonant frequency occurs due to mutual inductance and interaction of the rings. As the number of rings increases, the number of additional peaks also increases. A bandwidth of ~200 MHz with an amplitude 25 dB greater than the amplitude of the incident electromagnetic wave in the specified spectrum appears between the split levels. In the far zone, the transmitted radiation at the resonance frequency for a single ring practically does not change due to the splitting of this resonance frequency due to the interaction of the rings in the structure. The results obtained can be used in the development of new materials.

Are there bound states in the continuum in a dielectric ring?

Trapping and confining electromagnetic waves is important in both basic research and a variety of applications. For these purposes, various physical mechanisms are exploited including bound states in the continuum, which have been actively investigated recently. Bound states in the continuum have been observed in various objects consisting of both one and a number of dielectric structures. In particular, these photonic states were observed in high-contrast dielectric cylinders in the regime of strong eigenmode coupling, which leads to destructive interference in the far-field zone. In this article, we present the results of a study of bound states in a continuum in a dielectric ring, i.e. cylinder with coaxial air hole. The dependence of the quality factor Q on the normalized diameter of the hole is discussed.

Scattering spectra of dielectric ring: microwave experiments

In recent years, dielectric ring resonators (RRs) have become an essential part of integrated optical circuits. This determines the growing interest in the study of the fundamental electromagnetic properties of these objects, which is far from complete. In particular, in the literature it is difficult to find information about light scattering spectrum, which should demonstrate a strong resonance character when the probe wavelength is comparable to the geometric dimensions of the RR, taking into account its dielectric constant. In this work, we present the results of an experimental study of the electromagnetic properties of a dielectric RR in the microwave range of the spectrum. The results of numerical calculations of the scattering spectrum are also presented, which demonstrate excellent agreement with the experimental data. In addition to the expected resonance character of the spectrum, we report the effects of strong light confinement, which are associated with Fano resonances between the eigenmodes and the component of the electromagnetic field scattered by the ring.

Resonant light scattering from dielectric ring of rectangular cross section

In this paper we present the results of numerical calculations of electromagnetic properties for cylindrical ring resonators (RRs) with rectangular cross-section and a dielectric permittivity corresponding to silicon ε = 12. The calculation of the scattering spectrum (Radar Cross Section) and the field distribution of the modes were performed at in-plane polarized light excitation. The presence of four side walls in the RRs determines a richer spectrum of eigenmodes in comparison with cylindrical whispering gallery modes of disk resonators and creates more possibilities and diversity for their practical applications.

High-Quality Graphene-Based Tunable Absorber Based on Double-Side Coupled-Cavity Effect.

Graphene-based devices have important applications attributed to their superior performance and flexible tunability in practice. In this paper, a new kind of absorber with monolayer graphene sandwiched between two layers of dielectric rings is proposed. Two peaks with almost complete absorption are realized. The mechanism is that the double-layer dielectric rings added to both sides of the graphene layer are equivalent to resonators, whose double-side coupled-cavity effect can make the incident electromagnetic wave highly localized in the upper and lower surfaces of graphene layer simultaneously, leading to significant enhancement in the absorption of graphene. Furthermore, the influence of geometrical parameters on absorption performance is investigated in detail. Also, the device can be actively manipulated after fabrication through varying the chemical potential of graphene. As a result, the frequency shifts of the two absorption peaks can reach as large as 2.82 THz/eV and 3.83 THz/eV, respectively. Such a device could be used as tunable absorbers and other functional devices, such as multichannel filters, chemical/biochemical modulators and sensors.

Additively Manufactured Millimeter-Wave Dual-Band Single-Polarization Shared Aperture Fresnel Zone Plate Metalens Antenna

Fresnel zone plate (FZP) lens antenna, consisting of a set of alternative transparent and opaque concentric rings arranged on curvilinear or flat surfaces, have been widely used in various fields for sensing and communications. Nevertheless, the state-of-art FZP lens antennas are limited to a single band due to the frequency-dependent feature, which hinders their use in multi-band applications. In this work, a shared aperture dual-band FZP metalens antenna is proposed by merging two single-band FZP metalens antenna operating at distinct frequency bands seamlessly into one. Instead of using conventional metallic conductors, double-screen metagrids are devised in this work to form the concentric rings. Because the metagrids show distinct transmission/reflection properties at different frequencies, the performance of one set of concentric rings operating at the one band will not be affected by the other operating at the different band. In addition, to compensate for the phase shift introduced by the metagrids, an additional dielectric ring layer is added atop the FZP taking advantage of additive manufacturing. Thus, the radiation performance of the dual-band FZP lens antenna is comparable to that of each single FZP metalens antenna. For proof-of-concept, an antenna prototype operating at the dual band, 75 and 120 GHz with a frequency ratio of 1.6, is fabricated using an integrated additively manufactured electronics (AME) technique. The measured peak gains of 20.3 and 21.9 dBi are achieved at 75 and 120 GHz, respectively.

Super-collimation by axisymmetric diffractive metamirror.

We propose and demonstrate experimentally super-collimation of light beams by an axisymmetric diffractive metamirror-an axisymmetric concentric dielectric ring structure positioned in front of a mirror at a distance of several micrometers. By super-collimation, we mean the formation of a well-collimated beam characterized by a substantial enhancement of its axial component in the far-field domain. In the reported experiments, the axial intensity of the field was enhanced by around six times. Such axisymmetric super-collimators could be especially useful for improving the emission spatial quality of micro-lasers, when integrated as one (or both) resonator mirrors.

A Novel Ultrawideband Gear-Shaped Dielectric Ring Resonator Antenna

In this study, a novel ultrawideband (UWB) dielectric ring resonator (DRR) antenna has been proposed. DRR antennas include a single monopole antenna in the center of a ground plane and a dielectric with a symmetric structure around the monopole. This structure will lead to ultrawide band antenna. However, it is still possible to enhance the antenna bandwidth. In this study, we combine the DRR structure with an array antenna. The proposed antenna includes a circular array of four triangle resonators, which is rotated around the center of the triangle base to form a gear-shaped ring resonator antenna. In this design, characteristics of all these antennas are combined to enhance the antenna bandwidth including triangular dielectric resonator, circular array antenna, dielectric ring resonator structure, and a quarter-wave electric monopole. Triangular dielectric resonator antennas are wideband and in small size. Ring resonator antennas are inherently ultrawideband. Quarter-wave electric monopole and circular array structure can also enhance antenna bandwidth. This novel shape of the DRR antenna possesses the wider impedance bandwidth compared to similar works. Impedance bandwidth is 150% (5.2–36.1 GHz), and the bandwidth ratio is 1 : 6.9, which is much greater than earlier reports.

Conjugated topological interface-states in coupled ring resonators

The optical properties of topological photonics have attracted much interest recently because its potential applications for robust unidirectional transmission that are immune to scattering at disorder. However, researches on topological series coupled ring resonators (T-SCRR) have been much less discussed. The existence of topological interface-states (TIS) in the T-SCRR is described for the first time in this article. An approach has been developed to achieve this goal via the band structure of dielectric binary ring resonators and the Zak phase of each bandgap. It is found that an ultra-high-Q with complete transmission is obtained by the conjugated topological series coupled ring resonators due to the excitation of conjugated topological interface-states, which is different from those in conventional TIS. Furthermore, the problem of transmission decreases resulting from high-Q increases in the traditional photonic system is significantly improved by this approach. These findings could pave a novel path for developing advanced high-Q filters, optical sensors, switches, resonators, communications and quantum information processors.

Intensification of the wastewater treatment process with electrolytic gases

High regulatory requirements for the quality of treated water discharged into watercourses and wear and tear of local treatment facilities dictate the need to develop new technological solutions in the field of water treatment systems. In this regard, technologies that implement methods of electrophysical or electrochemical impact on polluting components in the processed liquid have found wide application in the treatment of waste and substandard waters. In this case, on the one hand, in order to increase the efficiency of collecting pollutants, it is necessary to strive to increase the number and decrease the size of electrolytic gas bubbles providing this collection, and on the other hand, it is necessary to optimize the operating modes of the electrode system and the material execution of the electrodes themselves, since the time of their operation depends on this. To solve this compromise problem, the design of an electroflotator has been developed, in which an electrode system is installed in the lower part of the tank, consisting of vertical anodes and cathodes. Each pair of them has the shape of cylinders and is fixed on the side surfaces of the dielectric ring separating them. The height of the ring from above and from below is made greater than the height of the anode and cathode by an amount equal to the annular gap between the adjacent anode and cathode. This design of the spacer ring prevents current leakage from the cathode to the anode and, accordingly, the dissolution of the anode ends. If the height of the ring above and below is executed by an amount less than the annular gap, there is a twofold increase in the density of the anode current at the ends of the anode and cathode, intensifying the dissolution of the anodes and the ingress of dissolution products into the solution and onto the walls of the electrodes, increasing their electrical resistance and reducing the performance of treatment facilities by liquid to be cleaned.

Efficient particle collection using concentric optical ring array

Trapping is the first as well as the most important step in various optical manipulations. However, when the concentration of sample is extremely low, optical trapping cannot be performed efficiently because the samples are usually out of the action radius of the trapping well. In this paper, numerical simulation results are presented to illustrate an active and efficient optical collection mechanism. We propose the optical collection mechanism by using an array of concentric dielectric rings, in which a series of nanoholes are introduced with optimized separations and radius to form trapping centers. When the incident wavelength is tuned in order, the trapped particles will be transferred from an outer ring to its inner neighboring ring, and finally be collected to the center of the rings. The mechanism reported here paves the way for efficient particle collection, and may find potential applications in various optical manipulations.

Broadband frequency control of light using synthetic frequency lattices formed by four-wave-mixing Bragg scatterings

Recent exploration in synthetic frequency lattices has re-formed the methods of manipulating the light spectrum by analogizing the diffraction management in real space, which can be created by employing electro-optic modulation (EOM) in dielectric waveguides or ring resonators. In the presence of effective gauge potential, that is, the accumulated phase of mode transfer between adjacent lattice sites, the frequency spectrum of incident light can be flexibly tailored. However, the finite bandwidth and modulation depth of EOM vastly restrain the frequency shift and efficiency of mode transfer. Here we experimentally demonstrate that the synthetic frequency lattice can be created with the nonlinear process of four-wave-mixing Bragg scattering. The bandwidth of frequency manipulation is expanded up to terahertz and the frequency shift can be larger than 200 GHz. Furthermore, we can realize effects such as negative refraction and perfect imaging in frequency dimension by changing the effective gauge potentials. The study provides a powerful and promising approach to precisely control light frequency in broadband and may benefit all-optical modulation in optical telecommunication systems.

Numerical Study of Extremely Wideband-Modified Biconical Radiation Structures for Electronic Support Measures Application

Using the finite difference time domain (FD-TD) method, this paper studies radiation structures that can have multiple tunable frequency bands between 0.4 GHz and 4 GHz, a fixed band in [3.97, 5.36] GHz and an extremely wideband from 6.14 GHz to 68.27 GHz, where a frequency band is defined by the voltage standing wave ratio (VSWR) less than or equal to two. The base radiation structure has a modified-biconical antenna configuration, called base MBA, and is fed by a square-coaxial line with characteristic impedance close to 50 ohms. A dielectric ring and an outer dielectric cover are used between the two modified cones to enlarge the frequency band and strengthen the structure. An equal number of metallic-rings can be stacked at both circular-ends of cones in the base MBA to tune the positions of the frequency bands that are lower than 4 GHz and to alter their vertical polarization (V-pol) patterns. However, compared with those of the base MBA, these stacked metallic rings do not make significant changes to the VSWR in the [3.97, 5.36] GHz and [6.14, 28.27] GHz bands and the radiation patterns in the [6.14, 28.27] GHz band. The simulation results show that the base MBA and its metallic-ring-loaded versions all have V-pol radiation characteristics at all frequency bands and have donut-shaped omnidirectional patterns only when the wavelength is bigger than the length of the structure. When the wavelength is less than the size of the radiation structure, the donut shape is modified with ripples on the V-pol radiation pattern. Sometimes deep notches could be observed when MBAs operated at the higher end of the extremely wideband. A 0.2 mm cube was used to construct the antenna structures with the consideration of using the 3D metal/dielectric printer technology to build the antennas in the future.

A Novel Multipactor Suppression Circulator Using Transformation Dielectrics

Due to the multipactor discharge breakdown, ferrite circulators have become the most susceptible component losing efficacy in high-power applications such as satellite payload systems. To date, effective suppression method of multipactor without affecting the electrical performance while keeping a high level of stability during in-orbit operation is still a technological challenge. In this article, a novel method based on the composite dielectric transformation is proposed for the considerable improvement of the multipactor breakdown threshold. The transformation medium is composed of dielectric rings of different permittivity, which could realize the uniform field transformation from the susceptibility region of multipactor to the dielectric/vacuum interface without acute change and discontinuity. In addition, the transformation medium is designed to guarantee little perturbance of the electrical performance and great convenience of fabrication and assembly. The experimental results of the S-band circulator using this method demonstrated that while keeping very low insertion loss and isolation level, this method has improved more than 9 dB (≥850%) of multipactor threshold, showing very promising application potentials in antimultipactor designs for the spacecraft payload system.

Filtering Quasi-Yagi Strip-Loaded DRR Antenna With Enhanced Gain and Selectivity by Metamaterial

This paper presents a design approach of broadband filtering quasi-Yagi DRR Antenna using a strip-loaded dielectric ring resonator (DRR) and near-zero-index (NZI) metamaterial (NZIM). The ring strip is loaded to the inside wall of the DRR so that the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01δ</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21δ</sub> modes of the DRR can be close. Meanwhile, they function as a dual-mode magnetic dipole (M-dipole) driver and can be differentially excited at the same time for designing a wideband quasi-Yagi antenna. Benefiting from the dual-mode operation of the strip-loaded DRR, the end-fire gain across the operating band of the antenna is stable with preliminary bandpass filtering characteristics. To improve the in-band gain and enhance the filtering capability, a new coplanar NZIM with wideband NZI characteristic and dual transmission notches in the lower and upper stopbands of the preliminary gain passband, is introduced and put in the front of the DRR driver. To verify the proposed design concept, an X-band filtering quasi-Yagi antenna with the NZIM is fabricated and measured. Good agreement between the simulated and measured results can be observed. The wideband antenna has a measured -10 dB impedance bandwidth of about 16% (8.5 - 10 GHz). Within it, the peak gain of antenna reaches 8.3 dBi and 1-dB gain fractional bandwidth is about 10.8%. Meanwhile, it exhibits good gain bandpass response due to the transmission notches of the NZIM.

Zones optimized multilevel diffractive lens for polarization-insensitive light focusing

In this study, we present the numerical design and experimental demonstration of an all-dielectric low refractive index polarization-insensitive multilevel diffractive lens (MDL) at microwave frequencies. The proposed MDL structure is composed of concentric rings (zones) having different widths and heights. Here, the heights and widths of each dielectric concentric rings of lens structure are optimized by using the differential evolution (DE) algorithm to obtain the desired polarization-insensitive focusing performance. The DE method is incorporated with the three-dimensional finite-difference time-domain method to design an MDL structure and evaluate its wave focusing ability. The design frequency is fixed to 10 GHz and, at the design frequency, the DE method is applied to achieve light focusing with the full-width at half-maximum (FWHM) values of 0.654λ and 0.731λ for transverse-magnetic (TM) and transverse-electric (TE) polarizations, respectively, where λ is the wavelength of incident light in free space. Moreover, focusing efficiencies and numerical apertures are calculated as 60.3% and 0.853 at the design frequency, respectively, for both polarizations. Besides, experimental verifications of the numerical results are carried out in microwave regime where the MDL design is fabricated by 3D printing technology by using a polylactic acid material. In the microwave experiments, MDL focuses the TM and TE polarized waves at the focal distances of 71.82 mm and 69.3 mm with the FWHM values of 0.701λ and 0.887λ, respectively. We believe that the proposed design approach can be further expanded to design low refractive index lenses for visible and near-infrared wavelengths.

Primary measuring transducer of moisture content for grain quality control

The main task of the research is the development of the primary capacitive measuring transducer that can perform testing influences on the material under research, applied for automatic “type uncertainty” method error compensation, that takes place because of the method of measurement imperfection. To estimate the relevant level of testing influences a group of different materials with 2, 2.5, 3 and 3.5 dielectric permittivity values was taken for 0, 10, 20, 30 and 40% of moisture content control points. The primary measuring transducer of moisture content is organized with an electrode system in a form of V-type plates, which is fixed on the internal surface of two dielectric rings. Testing influences on the substance are reproduced directly in the capacitive primary transducer by simple metallic plates with fixed thickness introduction into the space between separate electrodes of an electrode system. A prototype product of the primary measuring transducer had been experimentally tested together with the new method of moisture measurement, which includes two additive, two multiplicative and two complementary testing influences on the material under research. Moisture content with nominal values 0, 10, 20 and 30% was reproduced by certain group of grains with different dielectric permittivity values. Experimental setup of an adaptive moisture meter was assembled using the substitution method of measurement to provide good accuracy for the conditions of capacitance measurement in substances with significant dielectric losses. The accuracy of moisture measurement was defined as discrepancy between average measured and nominal moisture content and as an uncertainty of this discrepancy in a form of type A uncertainty.

A Novel Hybrid Plasmonic Resonator With High Quality Factor and Large Free Spectral Range

Whispering gallery (WG) mode resonators are experiencing a surge in the application of biosensing, attributing to high speed, flexibility, low cost, multi-analyte detection and compatibility with extra optical elements. The decoration of localized surface plasmon nanostructures to a dielectric WG mode resonator offers unprecedented sensitivity compared with a pure dielectric resonator. However, at the moment, the experimental quality (Q) factors of dielectric micro rings always achieve the value of 104 to 106, whereas the only reported hybrid counterpart possesses the Q factor of 300 and most studies are focused on the theoretical design. The resulting experimental detection limits (DLs) are in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU, which is one order of magnitude lower than the best value of hybrid resonators. The hybrid resonator should possess the experimental Q factor of 5000 to 10000 so as to match their purely dielectric rivals. We demonstrated a novel hybrid plasmonic WG mode resonator working on the multimode resonance mechanism. Under the condition of the multimode resonance, predominant field was distributed on the waveguide surface resulting in an improved bulk sensitivity. The multimode resonance promoted satisfied resonance frequency reduced and thus a high Q factor and a low value of DL could be achieved in the experiment. Afterwards, the resonator was made via micro-and nanofabrication. It was shown that the experimental Q factor of 5685 and the free spectral range larger than 35 nm, which were superior to the previously reported value to our best knowledge. Hypoglycemia and Hyperglycemia will produce noticeable organ damage over time. Early detection of glucose concentration is crucial for clinical diagnosis. The proposed resonator was used for the detection of glucose solution. The experimental sensitivity was 428 nm/RIU and the DL was 1.31 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU. The device with a footprint of 1500 μm × 12.7 μm, is able to integrate with other optical elements and developed as a commodity in the future.