Spherical Dielectric Resonator Research Articles

Transition from Phononic to Geometrical Mie Modes Measured in Single Subwavelength Polar Dielectric Spheres

Spherical dielectric resonators are highly attractive for light manipulation, thanks to their intrinsic electric and magnetic resonances. Here, we present measurements of the mid-infrared far-field thermal radiation of single subwavelength dielectric spheres deposited on a gold substrate, of radii ranging from 1 to 2.5 μm, which agree quantitatively with simulated absorption cross sections. For SiO2 microspheres, we evidence the excitation of both surface phonon-polariton (SPhP) modes and geometrical electric and magnetic Mie modes. The transition from a phonon-mode-dominated to a Mie-mode-dominated emission spectrum is observed, with a threshold radius of ∼1.5 μm. We also show that the presence of the metallic substrate augments the computed spheres absorption cross-section due to increased local field enhancement, arising from the near-field interaction of the spheres oscillating charges with their image in the metallic mirror. In contrast, measurements of single subwavelength SPhP-inactive PTFE spheres reveal that the mid-infrared response of such lossy spheres is dominated by their bulk absorption. Our results demonstrate how engineering the geometrical and dielectric properties of subwavelength scatterers can enable the control of thermal emission near room temperature, with exciting perspectives for applications such as radiative cooling.

Perturbation theory of nearly spherical dielectric optical resonators

Dielectric spheres of various sizes may sustain electromagnetic whispering-gallery modes resonating at optical frequencies with very narrow linewidths. Arbitrary small deviations from the spherical shape typically shift and broaden such resonances. Our goal is to determine these shifted and broadened resonances. A boundary-condition perturbation theory for the acoustic vibrations of nearly circular membranes was developed by Rayleigh more than a century ago. We extend this theory to describe the electromagnetic excitations of nearly spherical dielectric cavities. This approach permits us to avoid dealing with decaying quasinormal modes. We explicitly find the frequencies and the linewidths of the optical resonances for arbitrarily deformed nearly spherical dielectric cavities, as power series expansions by a small parameter, up to and including second-order terms. We thoroughly discuss the physical conditions for the applicability of perturbation theory.

Subnanoliter Sensing of Dielectric Properties of Liquid-in-Flow at 190 GHz

Dielectric properties (permittivity and loss tangent) of various liquids (water, methanol, propanol, acetone, and isopropanol) are determined by analyzing the frequency detuning effects of different millimeter-wave resonators exposed by the liquid-under-test. Alumina ceramic spherical dielectric resonators, fed from a thin-film circuit, form a resonator fixture operating at 190 GHz. Subnanoliter amount of liquid, carried in a glass tube, is exposed to the resonator. Analysis of the setup by means of electromagnetic field simulations reveals the liquid’s dielectric properties. Extracted data match well with properties obtained from Debye models. Measurement sensitivity is discussed with respect to frequency shift, sensed volume, and dielectric contrast. Obtained sensitivity figure-of-merit outperforms alternative techniques at such high frequency.

High-Gain Dielectric Endfire Antenna by Forward Scattering of Dielectric Spheres

Forward scattering of an electromagnetic wave on a spherical dielectric resonator is applied to enhance endfire directivity of tapered dielectric rod radiators. An analysis of electromagnetic wave scattering using Mie theory shows that the superposition of fundamental transverse electric and magnetic dipole modes of dielectric spheres increases directivity in forward direction. A compact arrangement with four dielectric spheres is shown to increase the directivity of a dielectric slab radiator by more than 6 dB for a prototype antenna operating around 90 GHz, and by almost 4 dB for another antenna operating at 200 GHz.

Low-loss and tunable millimeter-wave filters using spherical dielectric resonators

AbstractMillimeter-wave band-pass filters using spherical dielectric resonators are presented. The dielectric spheres are sandwiched between metal plates and are excited by a simple microstrip line structure on a thin-film circuit board. As such, these filters could also be implemented in the back-end-of-line layers of an integrated circuit. A single resonator, based on a diameter 0.6 mm alumina ceramic sphere, is shown to resonate with high unloaded Q-factor of 750 at 170 GHz. A three-sphere band-pass filter is measured showing <5 dB insertion loss and 0.4% bandwidth at 170 GHz. A concept for mechanically tuning of a two-sphere band-pass filter is demonstrated for a filter operating around 105 GHz. The measured filter shows approximately 5 dB insertion loss and <0.5% bandwidth and its passband can be varied over 3 GHz of frequency, or 3%. Technological challenges are discussed.

Optical spherical dielectric resonator antenna for sensing and wireless communication

AbstractIn this article, Terahertz spherical dielectric resonator antenna (DRA) is mathematically formulated and simulated at 511 THz for LiDAR and retinal photoreceptor applications. Titanate DR element is used at optical design frequency. It is validated with good S11, radiation pattern and 5.6 dBi gain plots using HFSS simulator. Unique mathematical formulation on super directivity and radiated states is formulated for the first time. The proximity coupled feed is used with laser Gaussian beam excitation. The silver nano waveguides is used to provide feed mechanism to terahertz DRA. This DR design at optical frequency can be used for wireless sensing and communication applications. It has novel geometry.

Spherical Dielectric Resonator Antenna Operating at 180 GHz

The characteristics of different resonance modes of a dielectric sphere (Alumina ceramic, permittivity around 10) are investigated by Mie's theory and confirmed by field simulations and by measurements. Based on the dominant transverse magnetic resonance mode of the sphere, an on-chip antenna design is proposed. The antenna for operation at 180 GHz is using a spherical dielectric resonator of Alumina ceramic with diameter of 0.6 mm. The antenna design is characterized by small chip-area consumption, high gain, and excellent radiation efficiency. Measurements confirm the simulated results.

Conformal Subgridding and Application to One-Eighth Spherical Shell Dielectric Resonator Antenna Array

To model the object with concave and convex surfaces accurately, an economical conformal subgridding scheme is proposed in this article. Its double conforming procedure with coarse grid (CG) and fine grid (FG) guarantees the modeling accuracy. Fast linear interpolation effectively exchanges electromagnetic fields information on the interface between grids of two sizes. One-step leapfrog alternating direction implicit (ADI) finite-difference time-domain (FDTD) method overcomes the Courant stability condition in FG region; meanwhile, conventional FDTD ensures the efficiency of simulation in CG region. While we concern the unconditionally stable method, there is not any grid omitted in our irregularly profiled fine region and any extra time wasted in solving small-scale tridiagonal matrixes cell by cell. To verify our codes, a 2-D arc component has been simulated first. Then the performance of a probe-fed normal one-eighth spherical dielectric resonator antenna (DRA), a new designed conformal-microstrip-fed one-eighth spherical shell DRA, and a four-element array with the spherical shell DRAs connected by a T-shaped power divider has been calculated by our codes. Satisfactory performance of the antenna has been obtained in return loss and radiation patterns, which are verified by measured results. The shell antenna features smaller size, lighter weight, and more convenience in conforming to the corners of the instrument housing, even with different dimensions. Most particularly, the proposed conformal subgridding scheme and its hybrid FDTD implementation perform outstandingly in simulating the thin shell antenna in terms of computer memory, CPU time, as well as accuracy.

Millimeter-Wave Low-Loss Multifeed Superstrate-Based Antenna

A low-loss multifeed antenna with controlled polarization and beam steering is presented. A low-profile resonant cavity antenna is fed by multiple spherical dielectric resonators (DRs), demonstrating its multifeed capabilities. Each of the DRs are themselves fed from four different sides by microstrip resonators on a planar circuit board. The beam pointing direction and polarization of the antenna are controlled by the signal phases at the respective input ports. Several antennas with varying feed topology are investigated, showing the versatility of this method. A 16-way 34 GHz prototype is built and measured, demonstrating high overall efficiency (considering power combining loss and antenna loss) of 80%.

Metallic reflectors with notched RCS spectral signature using dielectric resonators

Dielectric resonators are placed in front of the metallic plane plate and corner reflectors. Excitation of the resonant mode produces strong scattering of an incident plane wave which shows up as narrow notch in the mono-static radar cross section (RCS) spectral signature at the resonance frequency. Experimental proof at V-band is given with a corner reflector of centimetre size with spherical dielectric resonators of 0.8 mm diameter showing a notch at 64 GHz.

High directivity of the dielectric spherical antennas in 0.2-0.35 THz range

The article presents the results of numerical simulation by the finite element method of a spherical dielectric resonator with a dipole antenna placed inside. The directional properties of this type of antenna in the 2–4 GHz and 0.2–0.35 THz bands are calculated. It is shown that in a narrow band due to high order Mie resonances, the peak directivity of the antenna can reach values of 12.5 dBi with radiation efficiency of 0.9 and a sphere size of the order of 1.2 λ. A variant of the antenna for the 0.2–0.35 THz range with its placement on a dielectric substrate is proposed, and the dimensional ratios of the structural elements for the narrow-band mode with maximum gain are presented.

Design of One-Eighth Spherical Dielectric Resonator Antenna for 5G Applications

A one-eighth spherical surface dielectric resonator antenna (OESS-DRA) is proposed first time. To analyze this thin shell structure, electromagnetic fields distribution is discussed by using the Hertz vector and boundary conditions. We simplify the solution of Maxwell equations by using Hertz vector because the polarization current is primary in the OESS-DRA. The Hertz vector can be expressed the current better. This proposed antenna is composed of one-eighth spherical dielectric shell fed by coaxial probe; and the ground with metal-corner-reflector makes the antenna with high gain and directional radiation properties. To verify this design, a fabricated sample is tested; results show the antenna covering bandwidth 4.56-6.88GHz, a high gain greater than 9.5dBi (peak gain 11.8dBi at 5.0GHz), and a high radiation efficiency over 85% in the entire working frequency band, as well. The OESS-DRA can be a good candidate in 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> generation communication applications.

High Directivity in the Narrow Band of Spherical Dielectric Antennas in GHz and THz Ranges

The article presents the results of numerical simulation by the finite element method of a spherical dielectric resonator with a dipole antenna placed inside. The directional properties of this type of antenna in the 2–4 GHz and 0.2–0.35 THz bands are calculated. It is shown that in a narrow band due to high order Mie resonances, the peak directivity of the antenna can reach values of 12.5 dBi with radiation efficiency of 0.9 and a sphere size of the order of 1.2λ. A variant of the antenna for the 0.2–0.35 THz range with its placement on a dielectric substrate is proposed, and the dimensional ratios of the structural elements for the narrowband mode with maximum gain are presented.

High-Gain Low-Profile Chip-Fed Resonant Cavity Antennas for Millimeter-Wave Bands

This letter demonstrates a novel integration approach to design high gain chip-fed antennas in V -band and W -band. An on-chip spherical dielectric resonator is integrated with a resonant cavity antenna, which resulted in high radiation efficiency and increased gain. The proposed approach minimizes the use of chip area and provides several advantages, such as, low profile and ease of assembly in comparison to similar antennas, reaching 17.8 dBi and 18.4 dBi gain for V -band and W -band, respectively.

Coherently Driven and Superdirective Antennas

Antennas are crucial elements for wireless technologies, communications and power transfer across the entire spectrum of electromagnetic waves, including radio, microwaves, THz and optics. In this paper, we review our recent achievements in two promising areas: coherently enhanced wireless power transfer (WPT) and superdirective dielectric antennas. We show that the concept of coherently enhanced WPT allows improvement of the antenna receiving efficiency by coherent excitation of the outcoupling waveguide with a backward propagating guided mode with a specific amplitude and phase. Antennas with the superdirectivity effect can increase the WPT system’s performance in another way, through tailoring of radiation diagram via engineering antenna multipoles excitation and interference of their radiation. We demonstrate a way to achieve the superdirectivity effect via higher-order multipoles excitation in a subwavelength high-index spherical dielectric resonator supporting electric and magnetic Mie multipoles. Thus, both types of antenna discussed here possess a coherent nature and can be used in modern intelligent antenna systems.

Dielectric Resonator-Based Passive Chipless Tag With Angle-of-Arrival Sensing

Passive chipless tags based on dielectric resonators (DRs) have been proposed for a novel millimeter-wave indoor self-localization system to mark fixed reference nodes. The tags employed in the system provide a unique spectral signature (resonance peaks) with much-increased radar cross section (RCS) by placing several identical DRs at the focal line of a spherical dielectric lens. Resonators of optimized geometry allow a modification of this original DR-lens tag by combining the lens with different size DRs which exhibit resonant frequencies separated by large frequency gaps. For easier manufacturing and testing, a demonstrator tag was designed for a “scaled” frequency range of 5–6 GHz with this configuration and is shown to produce spectral signatures of the monostatic RCS which are uniquely related to the angle of arrival (AoA) of the incident wave from a reader. Simulated signatures of a lens of 120-mm diameter with seven spherical DRs are presented and results are supported by experiment. Correlation processing of the signatures can give a resolution of few degrees in AoA while the bistatic RCS half-power beamwidth is on the order of 20°, and RCS levels of resonant peaks are produced between 0 and −6 dBm2.

Pattern Reconfigurable High Gain Spherical Dielectric Resonator Antenna Operating on Higher Order Mode

This letter proposes a pattern reconfigurable high gain spherical dielectric resonator antenna (DRA) operating on higher order mode. Two microstrip patches were used to excite $\text{TE}_{301}$ mode in the different direction. A reconfigurable switch network was designed and it has three switching modes for selecting each patch alone or selecting them simultaneously. The proposed antenna can reconfigure its radiation pattern by using a feeding structure, which is consist of two microstrip patches and the reconfigurable switch network. A prototype antenna operating on $\text{TE}_{301}$ mode at 5.8 GHz was fabricated by ceramic material. By experiment, we validated the new concept of pattern reconfigurable spherical DRA.

On-Chip Dual-Polarized Dielectric Resonator Antenna for Millimeter-Wave Applications

This letter describes the design of a dual-linear polarized on-chip millimeter-wave radiator based on a dielectric resonator. The dielectric resonator is a sphere of 1 mm diameter made of alumina ceramic material. The dielectric resonator antenna is excited by a microstrip resonator and fed with a 50 Ω microstrip feed line. The microstrip feed line and the excitation resonator are fabricated on a thin on-chip benzocyclobutene (BCB) dielectric. The spherical dielectric resonator self-aligns on-chip with high accuracy by means of an etched shallow cutout in the BCB layer. The chip area occupied by the dual-linear polarized antenna is small. The antenna is impedance matched to better than -10 dB over a frequency bandwidth of 8% around 105 GHz. The simulated radiation efficiency is reaching 80%.

Scattering of Electromagnetic Waves on Different Dielectric Resonators of the Microwave Filters

The theory of scattering of electromagnetic waves by systems of various coupled the different shape and variant permittivity dielectric resonators is expanded. A new definition of the coupling coefficients of different dielectric resonators is given. The analytical expressions of coupling coefficient of different cylindrical and spherical dielectric resonators made from different dielectrics are obtained. The main regularities of the change in the coupling with the variation of the structure's parameters are considered. The results of calculation of the transmission and the reflection coefficients for bandpass and bandstop filters on various dielectric resonators in the rectangular and circular waveguides are presented. Most optimal configurations, allowing to achieve the best scattering characteristics are determined.

High gain spherical DRA operating on higher-order mode excited by microstrip patch

This paper proposed a high gain spherical dielectric resonator antenna (DRA) operating on higher-order mode excited by microstrip patch. A microstrip patch was used to excite TEn01 mode on a dielectric sphere. The excited dielectric sphere operates as higher-order mode spherical DRA with high gain. Impedance matching method for conventional microstrip patch could be applied to the proposed antenna. Size minimization method for the excitation microstrip patch was also described on this paper. A prototype antenna operating on TE301 mode at 5.8 GHz was fabricated by a ceramic dielectric material, which dielectric constant is 13, and showed the peak gain of 9.03 dBi.