Microwave Dielectric Resonators Research Articles

Radio-Frequency Conductivity Characteristics and Corresponding Mechanism of Graphene/Copper Multilayer Structures.

High-radio-frequency (RF) conductivity is required in advanced electronic materials to reduce the electromagnetic loss and power dissipation of electronic devices. Graphene/copper (Gr/Cu) multilayers possess higher conductivity than silver under direct current conditions. However, their RF conductivity and detailed mechanisms have rarely been evaluated at the micro scale. In this work, the RF conductivity of copper-copper (P-Cu), monolayer-graphene/copper (S-Gr/Cu), and multilayer-graphene/copper (M-Gr/Cu) multilayer structures were evaluated using scanning microwave impedance microscopy (SMIM) and dielectric resonator technique. The results indicated that the order of RF conductivity was M-Gr/Cu < P-Cu < S-Gr/Cu at 3 GHz, contrasting with P-Cu < M-Gr/Cu < S-Gr/Cu at DC condition. Meanwhile, the same trend of M-Gr/Cu < P-Cu < S-Gr/Cu was also observed using the dielectric resonator technique. Based on the conductivity-related Drude model and scattering theory, we believe that the microwave radiation can induce a thermal effect at S-Gr/Cu interfaces, leading to an increasing carrier concentration in S-Gr. In contrast, the intrinsic defects in M-Gr introduce additional carrier scattering, thereby reducing the RF conductivity in M-Gr/Cu. Our research offers a practical foundation for investigating conductive materials under RF conditions.

Dielectric microwave resonator with large optical apertures for spin-based quantum devices

We demonstrate a low-loss dielectric microwave resonator with an internal quality factor of 2.30×104 while accommodating optical apertures with a diameter of 8 mm. The two seemingly conflicting requirements, high quality factor and large optical apertures, are satisfied, thanks to the large dielectric constant of rutile (TiO2). The quality factor is limited by radiation loss, and we confirmed by numerical simulation that this radiation loss can be suppressed by extending the enclosure height of the resonator; the resonator can potentially achieve a dielectric loss-limited quality factor, exceeding 106. Using this resonator, we performed both continuous-wave (cw) and pulse electron spin resonance (ESR) spectroscopy on 2,2-diphenyl-1-picrylhydrazyl (DPPH) crystalline powder and P1 centers in a diamond crystal in a dilution refrigerator. The cw ESR spectroscopy demonstrated high-cooperativity and strong spin-resonator coupling with the DPPH and P1 centers, respectively, while the pulse ESR spectroscopy successfully measured longitudinal and transverse relaxation times. This optically accessible low-loss microwave resonator enables the implementation of a spin-based quantum device, such as a microwave-optical photon transducer.

Recent development in reconfigurable dielectric resonator antenna and microwave filter: design and application

SummaryDeveloping wireless communication systems depends on reconfigurable microwave filters (MF) and dielectric resonator antenna (DRA) because the functionality of the various filters and antennas available for a wireless communication system is limited, and reconfigurable DRA and MF are utilized to overcome these limitations. The throughput of a multiantenna system can be achieved with reconfigurable DRA and filter. Various switching strategies and classifications of reconfigurable DRA and MF are presented. The electrical reconfiguration technique is most suitable for developing a reconfigurable DRA and filter among all the switching techniques. In this approach, reconfigurability may be accomplished by utilizing a PIN diode, a varactor diode, and a radio‐frequency microelectromechanical switch (RF‐MEMS). These switches are more reliable, highly efficient, and easily integrated with the microwave circuit. Reconfigurable DRA with machine learning is demonstrated. The application of reconfigurable DRA and filters in cognitive radio (CR) is also demonstrated. Also, the review article focused on the performance parameters, design, and challenges of reconfigurable antenna and MF.

Tailoring the structural, optical, and dielectric properties of nanocrystalline niobate ceramics for possible electronic application

In the past decades, magnesium niobate materials have been extensively inves- tigated due to their exceptional dielectric characteristics at microwave fre- quencies and are widely employed in microwave dielectric resonators. In present research, the nanocrystalline MgNb2O6 having an orthorhombic crys- tal structure with P b c n space group was successfully synthesized at 1000oC using a chemical route. X-ray diffraction (XRD), Raman spectroscopy, FESEM, impedance analyzer, and diffuse reflectance spectroscopy (DRS) were used to characterize the prepared phase. The average crystallite size, unit cell volume and the X-ray density of the prepared material were evaluated to be 52.55 nm, 407.65A˚ 3 and4.9865g/cm3,respectively.Themolecularbendingandstretch- ing vibrations of metal oxide bonds were examined by Raman spectroscopy, which ranged from 232 cm−1 to 1007 cm−1. FESEM analysis of the prepared ceramics revealed uniformly distributed grains with clear grain boundaries bearing the average grain size of 0.78 µm. A high direct band gap of 2.97 eV was investigated from DRS. The impedance analysis of the prepared phase revealed a decrease in the capacitance and dielectric constant between 40 Hz to 10 MHz. At 10 MHz frequency, the dielectric constant of the material was found to be 13.15. The loss tangent also displayed a systematic decrease with the increase in frequency from 40 Hz to 10 MHz.

Coherent control of electron spin qubits in silicon using a global field

Silicon spin qubits promise to leverage the extraordinary progress in silicon nanoelectronic device fabrication over the past half century to deliver large-scale quantum processors. Despite the scalability advantage of using silicon technology, realising a quantum computer with the millions of qubits required to run some of the most demanding quantum algorithms poses several outstanding challenges, including how to control many qubits simultaneously. Recently, compact 3D microwave dielectric resonators were proposed as a way to deliver the magnetic fields for spin qubit control across an entire quantum chip using only a single microwave source. Although spin resonance of individual electrons in the globally applied microwave field was demonstrated, the spins were controlled incoherently. Here we report coherent Rabi oscillations of single electron spin qubits in a planar SiMOS quantum dot device using a global magnetic field generated off-chip. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer.

Ternary compound MgTiO3 combined with graphene for solar-blind deep ultraviolet photodetection

Ternary materials have gained great popularity in the field of solar-blind ultraviolet (UV) photodetectors due to their diverse band gaps. Whereas, quality problems brought by lattice damage and phase separation appear frequently during preparation, which greatly limit the application of ternary solar-blind photoresponsive materials. MgTiO3 (MTO), a ceramic material, has extensive application in microwave capacitors and dielectric resonators but takes no place in the field of photodetectors. Faced with this situation, this study investigates the effect of annealing on the structure of MTO thin film, and fabricates a solar-blind UV detector through combining MTO with graphene, which expands the application of ternary compound MTO to the field of photodetectors. Under solar-blind UV illumination, this MTO-based detector exhibits excellent performance with an open circuit voltage as high as 1.7 V. At 0 V bias, the detector exhibits an ultrafast response speed with the rise and decay time as short as 30 ms and 25 ms, respectively. Besides, a responsivity up to 46.5 mA/W, an external quantum efficiency (EQE) up to 20.4%, and a specific detectivity (D*) up to 6.14 × 1011 Jones also prove the great performance this detector owns. All the results achieved in this work not only suggest the great potential of MTO in being applied to fabricating solar-blind UV detectors, but also provide some guidance for the development of photovoltaic detectors based on other ternary semiconductor materials.

Effects of Strontium on the Structural, Optical, and Microwave Dielectric Properties of Ba2Ti9O20 Ceramics Synthesized by a Mixed Oxide Route.

Solid solutions of Sr-doped barium nonatitanate (Ba2Ti9O20) ceramics were synthesized by a mixed oxide route, studied their structural, microstructural, optical, and microwave dielectric properties were studied. X-ray diffraction (XRD) has been used to reveal the structure and crystallite size of doped Ba2Ti9O20 ceramics. Rietveld refinements of XRD patterns revealed that all of the ceramics have a tetragonal structure with space group I4/m. The surface morphologies of all the samples were characterized by using scanning electron microscopy (SEM). Fourier transform infrared (FT-IR) studies gave the O–H and Ti–O modes of vibrations. The stretching modes of Ti–O and O–H were noted at 1400, 2960, 3700, and near to 440 cm–1, respectively. The band gap energy decreases with increasing Sr2+ contents, and a high value (2.12 eV) was observed in the base sample. The microwave dielectric properties of the ceramic samples were studied at different frequencies ranging from 1 to 2 GHz by using impedance spectroscopy. The obtained results showed the suitability of these samples for microwave dielectric resonator (antenna) applications.

Progress and Recent Strategies in the Synthesis and Catalytic Applications of Perovskites Based on Lanthanum and Aluminum.

Lanthanum aluminate-based perovskite (LaAlO3) has excellent stability at high temperatures, low toxicity, and high chemical resistance and also offers wide versatility to the substitution of La3+ and Al3+, thus, allowing it to be applied as a catalyst, nano-adsorbent, sensor, and microwave dielectric resonator, amongst other equally important uses. As such, LaAlO3 perovskites have gained importance in recent years. This review considers the extensive literature of the past 10 years on the synthesis and catalytic applications of perovskites based on lanthanum and aluminum (LaAlO3). The aim is, first, to provide an overview of the structure, properties, and classification of perovskites. Secondly, the most recent advances in synthetic methods, such as solid-state methods, solution-mediated methods (co-precipitation, sol–gel, and Pechini synthesis), thermal treatments (combustion, microwave, and freeze drying), and hydrothermal and solvothermal methods, are also discussed. The most recent energetic catalytic applications (the dry and steam reforming of methane; steam reforming of toluene, glycerol, and ethanol; and oxidative coupling of methane, amongst others) using these functional materials are also addressed. Finally, the synthetic challenges, advantages, and limitations associated with the preparation methods and catalytic applications are discussed.

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.

Dispersive readout of room-temperature ensemble spin sensors

We demonstrate dispersive readout of the spin of an ensemble of nitrogen-vacancy centers in a high-quality dielectric microwave resonator at room temperature. The spin state is inferred from the reflection phase of a microwave signal probing the resonator. Time-dependent tracking of the spin state is demonstrated, and is employed to measure the T 1 relaxation time of the spin ensemble. Dispersive readout provides a microwave interface to solid state spins, translating a spin signal into a microwave phase shift. We estimate that its sensitivity can outperform optical readout schemes, owing to the high accuracy achievable in a measurement of phase. The scheme is moreover applicable to optically inactive spin defects and it is non-destructive, which renders it insensitive to several systematic errors of optical readout and enables the use of quantum feedback.

Machine learning analysis of microwave dielectric properties for seven structure types: The role of the processing and composition

During recent decades the rapid growth of wireless communications technologies has resulted in developing new dielectric ceramics for different applications. Materials for the microwave dielectric resonators have to meet three main requirements: controllable permittivity value for possible device miniaturization or fast signal transmission, high quality factor (low dielectric loss) for frequency selectivity and near-zero temperature coefficient of resonant frequency for temperature stability. In this study, the machine learning-based analysis of the experimental data was performed to distinguish the parameters responsible for the microwave dielectric characteristics and to analyze their relative contribution to the functional properties for considered compounds of several structure types: aeschynites, euxenites, columbites, ixiolites, wolframites, fergusonites and scheelites. New descriptors encapsulating the information on the constituent building blocks, their number and the point group symmetry as well as the connectivity of the building blocks have shown good prospects for use as robust parameters describing the structure of the inorganic crystalline compounds. The impact of the synthesis route and composition on the microwave dielectric characteristics was analyzed. The role of the grain boundaries and the recrystallization processes is discussed. For the considered classes of compounds, the values of the microwave dielectric parameters can be predicted with Root Mean Square Error (RMSE) of 4.84 for the dielectric constant and 21.86 for the temperature coefficient of resonant frequency.

Microwave Dielectric Ceramic Materials and Their Industry Development Overview and Future Prospects

Nowadays, microwave dielectric ceramics are widely used in all kinds of modern communication equipment, becoming the key material for manufacturing microwave dielectric filters and resonators. With the rapid development of related fields, the scope of application of microwave dielectric ceramics has been further expanded. On this basis, this paper explores the development history of microwave dielectric ceramics and the situation and future outlook of its industry. By combining historical events and data, the development history of microwave dielectric ceramics is described. The situation is also analysed and discussed in the context of the times and current events to provide an objective evaluation and forecast of the industry. The final results show that in the context of the new era of 5G, the microwave dielectric ceramics industry has entered a brand new stage of development and it presents a huge potential for innovation and development.

Enhanced structural and dielectric properties of calcium and chromium based M-type hexagonal ferrites

M-type hexaferrites with composition Ca1−xCrxFe12O19 were synthesized by the sol–gel auto-combustion method. Structural, morphological and dielectric properties were explored. Annealing of the samples was done at 1200 °C for 8 h. XRD pattern reveals single-phase magnetoplumbite structure. The structural properties as lattice parameters, crystallite size and cell volume of Ca1−xCrxFe12O19 hexaferrites were evaluated. Crystallite size of the particle varied from 45.85 to 42.96 nm. Morphology of the samples observed by scanning electron microscopy reveals regular platelet hexagonal structure and all the grains were distributed homogeneously. Dielectric parameters such as dielectric loss, dielectric constant, tangent loss, electric modulus, ac conductivity and Q values of the prepared samples were also discussed. These measured dielectric parameters are appropriate for high-frequency applications such as microwave absorber, phase shifter, dielectric resonator and stealth technology.

Coupled Resonator Calorimeter for Particle Detection

We describe a novel coupled microwave dielectric resonator system (an unusual form of parametric amplifier), which is under development, aimed at realizing a high-resolution single X-ray photon energy detector. Unlike other high-resolution detectors, it operates at a relatively high cryogenic temperature in the range of 7-30 K. Construction of the cooler system and thermal characterization system is completed. All aspects of the novel calorimeter performance have been evaluated, including demonstration of single-particle detection, the required rapid thermal time constant of a coupled resonator, a high df/dT response, and promising development of a low-noise microwave detection system.

Improved tri-layer microwave dielectric ceramic for 5 G applications

Tri-layer ZnTi0.97Ge0.03Nb2O8-TiO2-ZnTi0.97Ge0.03Nb2O8 ceramics with different mass fractions of TiO2 were initially prepared. The advantages of the multilayer architecture were fully demonstrated, and the microwave dielectric properties were controlled by the components of each dielectric layer. In contrast to the random distribution-type ZnTi0.97Ge0.03Nb2O8-TiO2, this tri-layer architecture could achieve a nearly 50 % increase in the Q×f value. Meanwhile, based on the parallel distribution mode, a 10 % increase in the dielectric constant could be obtained due to the existence of Zn2GeO4. After sintering at 1120 ℃ for 6 h, ZnTi0.97Ge0.03Nb2O8-TiO2-ZnTi0.97Ge0.03Nb2O8 tri-layered ceramics exhibited excellent dielectric properties (εr = 42.1, Q×f = 51,477 GHz and τf = +1.9 ppm/℃) with 0.04 wt% TiO2, and the cooperative optimization of microwave dielectric properties was achieved. This research provides a direction for the preparation of high-performance microwave dielectric resonators for application in 5 G wireless communication technologies.

DIELECTRIC RF RESONATORS WITH OPEN BOUNDARIES FOR STUDYING RADIATION EFFECT ON ELECTRODYNAMIC CHARACTERISTICS OF SOLID DIELECTRICS

The use of dielectric materials in the charged particles accelerators requires investigation of changes in the electrodynamic properties of these materials under the influence of ionizing radiation. First of all it is necessary to study the effect of radiation on the complex dielectric permittivity (ꜫ and tgδ) of these materials. The actual task is to measure very small relative changes in the dielectric constant, for example, ∆ꜫ/ꜫ~10-4. Such accuracy can be provided by resonator methods. In the present work results of theoretical and experimental research of microwave dielectric resonators with open boundaries are given. It is shown, that they can be used to measure dielectrics during irradiation by gamma radiation or charged particles beam. The analysis of factors that affect the accuracy of measurements is carried out.

The Use of Liquid Mixing Method to Prepare Ilmenite Structure-Based Ceramic Powders

Ilmenite structure-based ceramics such as MgTiO3, ZnTiO3 and FeTiO3 have become important materials in ceramic industries. One of them is for microwave dielectric resonator and oscillator applications on radar systems for MgTiO3 and ZnTiO3, and for spintronic device applications for the wide band gab antiferromagnetic semiconductor FeTiO3. The conventional solid-state reaction method has been widely utilized to prepare the ilmenite ceramic powders due to its practicability in industrial applications. In spite of its recognition, this method still has some shortcomings. Some of these are requiring high calcination temperatures (> 1000 °C), the use of very intensive milling causes granules of powder to coagulate with varying sizes in several micro meters that gives rise to inhomogeneity in the final product. The co-presence of intermediate phases such as Mg2TiO4, MgTi2O5, and Zn2TiO4 on the calcined MgTiO3 and ZnTiO3 powders may inhibit the dielectric properties of the ceramics, thus detrimental in industrial applications. As an alternative, a facile route of liquid mixing method was introduced to synthesize the ilmenite MgTiO3, FeTiO3 and ZnTiO3 powders at much lower calcination temperatures, i.e.340 and 500-550 °C and that of free of intermediate phase presence. This paper reports the performance of liquid mixing method on synthesis of the above three ilmenite ceramic powders as examined using TGA-DTA and XRD data.

A new method for identifying TE&lt;sub&gt;01δ&lt;/sub&gt; mode during microwave dielectric measurements of low-loss materials

The metal resonant cavity method working with TE&lt;sub&gt;01δ&lt;/sub&gt; mode is a universal method for evaluating the microwave dielectric properties of low-loss materials. All the microwave dielectric resonators are multi-mode resonators, so the correct identification of TE&lt;sub&gt;01δ&lt;/sub&gt; mode is the basis for the microwave dielectric measurements. The TE&lt;sub&gt;01δ&lt;/sub&gt; mode can be identified by predicting the resonant frequency and its variation with resonator size, expelling the spurious modes according to the exciting conditions, etc., while these methods are relatively complex and sometimes unreliable. In the present work, a simple method for accurately identifying the TE&lt;sub&gt;01δ&lt;/sub&gt; mode is developed. A low-loss reference sample with known dielectric properties is introduced and placed in the cavity for the first step, and the to-be-measured sample is placed on the reference sample for the second step. The rough permittivity of the to-be-measured sample can be calculated from the TE&lt;sub&gt;01δ&lt;/sub&gt;-mode resonant frequencies in the two steps through the finite element analysis, and is used to predict the resonant frequency for TE&lt;sub&gt;01δ&lt;/sub&gt; mode when only the to-be-measured sample is placed in the cavity. The difference between the predicted and measured TE&lt;sub&gt;01δ&lt;/sub&gt;-mode resonant frequencies for the to-be-measured sample is less than 1%, so that the TE&lt;sub&gt;01δ&lt;/sub&gt; mode can be easily distinguished from the spurious modes and accurately identified.

Electrically Small Water-Based Hemispherical Dielectric Resonator Antenna

Recently, water has been proposed as an interesting candidate for use in applications such as tunable microwave metamaterials and dielectric resonator antennas due to its high and temperature-dependent permittivity. In the present work, we considered an electrically small water-based dielectric resonator antenna made of a short monopole encapsulated by a hemispherical water cavity. The fundamental dipole resonances supported by the water cavity were used to match the short monopole to its feed line as well as the surrounding free space. Specifically, a magnetic (electric) dipole resonance was exploited for antenna designs with a total efficiency of 29.5% (15.6%) and a reflection coefficient of −24.1 dB (−10.9 dB) at 300 MHz. The dipole resonances were effectively excited with different monopole lengths and positions as well as different cavity sizes or different frequencies in the same cavity. The overall size of the optimum design was 18 times smaller than the free-space wavelength, representing the smallest water-based antenna to date. A prototype antenna was characterized, with an excellent agreement achieved between the numerical and experimental results. The proposed water-based antennas may serve as cheap and easy-to-fabricate tunable alternatives for use in very high frequency (VHF) and the low end of ultrahigh frequency (UHF) bands for a great variety of applications.

Microwave Impedance of Thin-Film Superconductor–Normal Metal Hybrid Structures with a High Conductivity Ratio

The temperature dependence of the linear electrodynamic response of thin-film superconductor (MoN)–normal metal (Al) hybrid structures with a high conductivity ratio in the normal state has been theoretically and experimentally investigated. Low-frequency measurements of the coefficient of mutual induction of two coils with a sample placed between them indicate an increase in the magnetic screening of the superconductor–normal metal (SN) structures with an increase in the Al layer thickness dAl near liquid-helium temperatures. Measurements of the frequency shift δf of a microwave dielectric resonator, brought into contact with the sample, as a function of temperature and dAl showed that (i) the character of the dependence δf(T) depends strongly on dAl and (ii) the resonance frequency shift of SN structures at temperatures close to the critical temperature Tc is not described by dependence const/(1 – T/Tc), which is typical of thin superconducting films. Numerical calculations performed within the Usadel model well describe the observed effects. Thus, these anomalies of the electrodynamic properties of SN structures can be explained by the presence of a minigap in the spectrum of quasiparticles due to the proximity effect in a normal-metal layer, which depends on dAl, and by the high conductivity of the Al layer.