High-permittivity Dielectric Resonator Research Articles

Lower Bounds to the Q Factor of Electrically Small Resonators Through Quasistatic Modal Expansion

The problem of finding the optimal current distribution supported by small radiators yielding the minimum quality (Q) factor is a fundamental problem in electromagnetism. Q factor bounds constrain the maximum operational bandwidth of devices including antennas, metamaterials, and nanoresonators, and have been featured in seminal papers in the past decades. Here, we determine the lower bounds of Q factors of small-size plasmonic and high-permittivity dielectric resonators, which are characterized by quasi-electrostatic and quasi-magnetostatic natural modes, respectively. We expand the induced current density field in the resonator in terms of these modes, leading to closed-form analytical expressions for the electric and magnetic polarizability tensors, whose largest eigenvalue is directly linked to the minimum Q factor. Our results allow also to determine in closed form the corresponding optimal current density field. In particular, when the resonator exhibits two orthogonal reflection symmetries the minimum Q factor can be simply obtained from the Q factors of the single current modes with non-vanishing dipole moments aligned along the major axis of the resonator. Overall, our results open exciting opportunities in the context of nano-optics and metamaterials, facilitating the analysis and design of optimally shaped resonators for enhanced and tailored light-matter interactions.

Split Ring Antennas and Their Application for Antenna Miniaturization

This paper investigates the miniaturization capability of split ring array antennas embedded in a low-permittivity dielectric substrate, in comparison with the same-sized high-permittivity dielectric resonator antennas (DRAs). In order to understand the miniaturization performance, a size-fixed dielectric substrate with different split ring arrays is studied. The simulation results show that the miniaturization capability increases with decreased unit cell resonant frequency and/or increased unit cell induced permeability. Miniaturizations as high as 25.54 times that of a high-permittivity DRA are obtained with split rings, etched on a dielectric substrate having a low permittivity of 2.2. Furthermore, this excessive miniaturization does not come at the expense of excessive deterioration of the antenna impedance bandwidth, gain, and radiation efficiency. Consequently, the miniaturized split ring arrays still provide high gains over wider bandwidths. This inference is further verified by comparing the miniaturization and other antenna performance parameters with three other modified split ring configurations. To experimentally verify this work, a split ring antenna was fabricated and tested, and good agreement between the simulated and measured results was observed. The results of this study indicate that adding resonant metallic inclusions into low- permittivity DRAs significantly increases their miniaturization capability, without overly deteriorating the performance.

Near-field mapping of high permittivity dielectric microwave resonator modes via optically induced conductance.

In this paper, we demonstrate a straightforward, low-cost, and high resolution optical-based method to measure the three-dimensional relative electric field magnitude in microwave circuits without the need to monitor reflected laser beams or the requirement of photoconductive substrates for the device under test. The technique utilizes optically induced conductance, where a focused laser beam excites electron-hole-pairs (EHPs) in a semiconductor thin film placed in the near-field of a microwave circuit. The generated EHPs create localized loss in the resonator and modulate the transmitted microwave signal, proportional to the local microwave electric field. As a proof of principle, several different modes of a high permittivity (ɛ ∼ 80) cylindrical dielectric resonator are mapped.

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.

A Semi-Analytical Model of High-Permittivity Dielectric Ring Resonators for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is an imaging technique exploiting the magnetic resonance (MR) of specific nuclear spins, like protons. In this article, MR probes based on dielectric ring resonators are investigated from a theoretical approach. We take advantage of the high-permittivity and low-loss properties of the ceramic material used for manufacturing these probes for microscopy applications. Magnetic resonance microscopy (MRM) aims at imaging tiny samples with a sufficient resolution to distinguish small details. In this framework, compact resonators, called volume probes, contain the investigated sample and are used for both signal transmission and reception. The newly developed semi-analytical model enables the estimation of the frequency of the first transverse electric mode of a cylindrical resonator. It also provides a method to compute the corresponding magnetic field distribution, the dielectric losses contributions from the probe and the sample, and the signal-to-noise ratio (SNR). The proposed approach aims at providing design guidelines for dielectric probes.

Circularly polarized microwave antenna for nitrogen vacancy centers in diamond.

The sensing applications of nitrogen-vacancy color centers in a diamond require an efficient manipulation of the color center ground state over the whole volume of an ensemble. Thus, it is necessary to produce strong uniform magnetic fields of a well-defined circular polarization at microwave frequencies. In this paper, we develop a circularly polarized microwave antenna based on the excitation of hybrid electromagnetic modes in a high-permittivity dielectric resonator. The influence of the geometrical parameters of the antenna on the reflection coefficient and magnetic field magnitude is studied numerically and discussed. The Rabi frequencies and their inhomogeneity over the volume of a commercially available diamond sample are calculated. With respect to the numerical predictions, a Rabi frequency as high as 34 MHz with an inhomogeneity of 4% over a 1.2 mm × ∅2.5 mm (5.9 mm3 in volume) diamond sample can be achieved for 10 W of input power at room temperature. The antenna prototype is fabricated, and experimental investigations of its characteristics are performed in microwave and optical frequency domains. The circular polarization of the microwave magnetic field with an ellipticity of 0.94 is demonstrated experimentally. The Rabi oscillation frequency and its inhomogeneity are measured, and the results demonstrate a good agreement with the numerically predicted results.

Wireless Power Transfer System Based on Strapping Resonators

In this study, a kind of strapped resonator is proposed to deal with high power wireless power transfer (WPT) in microwave regimes. In many specific applications, such as high power microwave wireless power transfer system (WPT), a coil resonator is not suitable due to the frequency limitations. The high cost of the high-permittivity dielectric resonators also limits their application. As a high Q resonator, the strapped resonator is often used in the anode structure of a magnetron. The field distribution of π and π + 1 modes allow the system to operate in dual-frequency mode. Numerical simulation and experimental validation show that with a certain distance, the system provides power transfer efficiency of more than 80% and 70% at 630 MHz and 970 MHz, respectively. Compared to the system based on dielectric resonators, the proposed system has higher power capacity. The leakage and radiation loss of the system is also discussed using numerical methods.

Q-band cross-coupled dielectric resonator filter using TM mode for satellite application

AbstractA new structure of Q-band filter comprising rectangular high-permittivity dielectric resonators (DR) operating at TM11δ mode is introduced. The resonator shows high-quality factor (Q) and wide spurious free window compared with other technologies available at Q-band for realizing filters. Low permittivity ceramic material (quartz) is used as a support for holding DR at the center of the cavity. An eight-pole cross-coupled band-pass filter having a bandwidth of 225 MHz at 38.5 GHz was realized. Resonant coupling structure is introduced to realize cross-coupling in filter. The resonator assemblies were optimized precisely to achieve effective linear frequency drift over temperature of the order of 2 ppm/°C. The filter also survived severe sine and random vibration test for satellite application.

Wideband rectangular dielectric resonator antenna for low‐profile applications

A new wideband low-profile omni-directional dielectric resonator antenna (DRA) is presented. By joining back-to-back two thin identical rectangular high-permittivity dielectric resonators (DRs) and feeding the arrangement with a microstrip feed line inserted in-between the DRs, an impedance bandwidth covering the frequency range from 4.78 to 12.32 GHz, or ~88.2%, is achieved. Importantly, the measured results show that the proposed low-profile DRA also provides a stable omni-directional radiation pattern with low cross-polarisation. The proposed antenna size is 12 × 24 × 2 mm 3 or ~0.191 λ 0 × 0.384 λ 0 × 0.032 λ 0 at 4.8 GHz.

Switchable all‐dielectric frequency selective surface based on dielectric resonators

Here, the authors propose a switchable all-dielectric frequency selective surface (ADFSS), which is composed of two periodically placed high-permittivity dielectric resonator (DR) arrays. If the two DR arrays are laminated together, the FSS presents band-stop property; while if the two DR arrays are separated by a narrow gap, the FSS exhibits band-pass property. The switching characteristic of the device can be explained with DR theory and effective medium theory. The experimental results of the switchable ADFSS demonstrate a fractional bandwidth of 22.2% and a large field of view in a wide band (from 11.9 to 14.8 GHz), which is consistent with the simulated results. The method can be readily extended to the design of on/off ADFSS at other frequencies.

All-dielectric frequency selective surface design based on dielectric resonator**Project supported by the National Natural Science Foundation of China (Grant Nos. 61201030, 61372045, 61472045, and 61401229), the Science and Technology Project of Jiangsu Province, China (Grant No. BE2015002), the Open Research Program of the State Key Laboratory of Millimeter Waves, China (Grant Nos. K201616 and K201622), and the Nanjing University of

In this work, we propose an all-dielectric frequency selective surface (FSS) composed of periodically placed high-permittivity dielectric resonators and a three-dimensional (3D) printed supporter. Mie resonances in the dielectric resonators offer strong electric and magnetic dipoles, quadrupoles, and higher order terms. The re-radiated electric and magnetic fields by these multipoles interact with the incident fields, which leads to total reflection or total transmission in some special frequency bands. The measured results of the fabricated FSS demonstrate a stopband fractional bandwidth (FBW) of 22.2%, which is consistent with the simulated result.

Investigations on Photoresist-Based Artificial Dielectrics With Tall-Embedded Metal Grids and Their Resonator Antenna Application

Novel photoresist-based artificial bulk dielectrics with tall-embedded metal grids are investigated and their radiation characteristics are studied in detail. The embedded metal grid substantially increases (around six times) the effective permittivity of the low permittivity base photoresist material, and enables excitation with a simple direct microstrip feed to radiate effectively at frequencies similar to a high-permittivity dielectric resonator antenna (DRA). Moreover, the grid changes the near fields inside the resonator and introduces novel modes that are completely different than those of usual DRAs. A set of artificial resonator antennas is designed, lithographically fabricated, and measured to demonstrate the new modes resonating at 17 and 19 GHz with 2% and 6% bandwidth and 7.6 and 6.6 dB broadside gain, respectively, with suitable cross-polarization levels of better than $- {20}\;\text{dB}$ . These new modes do not appear simultaneously, and can be excited separately by varying the length of the microstrip feed.

A band enhanced metamaterial absorber based on E-shaped all-dielectric resonators

In this paper, we propose a band enhanced metamaterial absorber in microwave band, which is composed of high-permittivity E-shaped dielectric resonators and metallic ground plate. The E-shaped all-dielectric structure is made of high-temperature microwave ceramics with high permittivity and low loss. An absorption band with 1 GHz bandwidth for both TE and TM polarizations are observed. Moreover, the absorption property is stable under different incident angles. The band enhanced absorption is caused by different resonant modes which lie closely in the absorption band. Due to the enhanced localized electric/magnetic fields at the resonant frequencies, strong absorptions are produced. Our work provides a new method of designing high-temperature and high-power microwave absorbers with band enhanced absorption.

A Low-Profile and High-Permittivity Dielectric Resonator Antenna With Enhanced Bandwidth

A dielectric resonator antenna of very high permittivity has been proposed. The antenna is designed based on a multilayered structure. To realize low profile and relatively large impedance bandwidth simultaneously, two separate dielectric resonators of high permittivity are placed symmetrically on top of the antenna structure. A low-permittivity dielectric substrate is inserted between the resonators and the ground. The total height of the antenna is 1.57 mm or 0.039λ (λ is the wavelength at the center frequency.) An enhanced bandwidth of 10.49% has been realized. The proposed antenna has stable radiation patterns across the whole operating band. Relatively high antenna gains over 6 dBi and a low cross-polarization level of -25 dB are also achieved.

A low-loss dielectric using CaTiO&lt;sub&gt;3&lt;/sub&gt;-modified Mg&lt;sub&gt;1.8&lt;/sub&gt;Ti&lt;sub&gt;1.1&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; ceramics for applications in dielectric resonator antenna

The microwave dielectric properties of (1-x)Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.1</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -xCaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramics prepared by the mixed oxide route have been investigated. Spinel-structured Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.1</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , ilmenite-structured MgTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and perovskite-structured CaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were coexisted and the three-phases system was confined by X-ray diffraction patterns, EDX analysis and it also leads to near-zero τf. The microstructures of the ceramics were characterized by SEM. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a fine combination of microwave dielectric properties (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ~ 19.61, Q×f~ 72,700 GHz at 9.03 GHz, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ~ -3.7 ppm/°C) was achieved for 0.91Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.1</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -0.09CaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramics sintered at 1330°C for 4 h, which makes it is a very promising candidate material for applications in dielectric resonator antenna. A new triple-band dielectric resonator antenna fed by a coplanar waveguide is presented. The proposed antenna, composed of a high permittivity dielectric resonator and printed on FR4 substrate, is fed by a 50 Ω coplanar waveguide transmission line. In order to achieve wideband applications, the antenna with two parasitic inverted-L strip is demonstrated to generate two resonant frequencies covering 3.5 and 5.2 GHz. The measured results show that the antenna covers the frequency bands 2.30-2.72, 3.45-3.61, and 5.05-6.23 GHz with less than -10 dB of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> . The frequency response of the simulation results shows good agreement with the measured data. Good antenna gain, radiation efficiency and radiation patterns of the proposed antenna have also been observed across the operation band. Details of the proposed antenna design and experimental results are presented and discussed.

Experimental demonstration of a broadband all-dielectric metamaterial perfect reflector

All-dielectric metamaterials utilizing Mie resonances in high-permittivity dielectric resonators offer a low-loss alternative to plasmonic metamaterials. Here we present the demonstration of a single-negative all-dielectric metamaterial, comprised of a single layer of cylindrical silicon resonators on a silicon-on-insulator substrate, that possesses peak reflectance over 99% and an average reflectance over 98% across a 200 nm wide bandwidth in the short-wavelength infrared region. The study is also extended to disordered metamaterials, demonstrating a correlation between the degree of disorder and the reduction in reflectance. It is shown that near-unity reflection is preserved as long as resonator interaction is avoided. Realization of near-unity reflection from disordered metamaterials opens the door to large-area implementations using low-cost self-assembly based fabrication techniques.

Higher-Order Modes in High-Permittivity Cylindrical Dielectric Resonator Antenna Excited by an Off-Centered Rectangular Slot

In this letter, we study the higher-order modes excited in a high-permittivity cylindrical dielectric resonator antenna (DRA), situated asymmetrically on top of a rectangular slot in the ground plane of a microstrip line. Besides the modes excited by a symmetric positioning of the DRA above the feeding slot, we identified five new modes: <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TEme}_{010}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TEme}_{011}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TEme}_{210}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TEme}_{020}$</tex></formula> , and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TM}_{212}$</tex></formula> , respectively. The higher-order modes offer to the DRA antenna some interesting features: They have different radiation patterns for different operating modes; modes with close resonance frequency give wideband capabilities; and sometimes, when a mode has poor performance in one polarization, it is possible that another mode with close frequency can compensate it.

Circularly Polarized Cross-Slot-Coupled Stacked Dielectric Resonator Antenna for Wireless Applications

This paper presents a stacked cylindrical dielectric resonator antenna with wide circular polarization (CP) bandwidth (axial ratio < 3dB) of 16.0%. This wide CP bandwidth is achieved by stacking low permittivity dielectric (9.2) resonator on high permittivity dielectric (9.8) resonator to obtain improved impedance and axial ratio bandwidths as compared to conventional DRA. It is also shown that the asymmetrical structure used in the geometry results in a very high impedance bandwidth (more than 100%) in the frequency range of 2.1 GHz-12.0 GHz but at the expense of distorted CP operation on the off-broadside. This essentially covers the FCC band of operation (3.1GHz to10.6 GHz).

Hybrid Dielectric Resonator Antenna Composed of High-Permittivity Dielectric Resonator for Wireless Communications in WLAN and WiMAX

The-hybrid dielectric resonator antenna consisted of a cylindrical high-permittivity dielectric resonator, a rectangular slot, and two-rectangular patches were implemented. The hybrid dielectric resonator antenna had three resonant frequencies. The lower, middle, and higher resonant frequencies were associated with the rectangular slot, rectangular patches, and dielectric resonator, respectively. Parametric investigation was carried out using simulation software. The proposed hybrid dielectric resonator antenna had good agreement between the simulation results and the measurement results. The hybrid dielectric resonator antenna was implemented successfully for application in 2.4/5.2/5.8 GHz of WLAN and 2.5/3.5/5.5 GHz of WiMAX simultaneously.