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Dielectric resonator antennas have been demonstrated to be an efficient radiator, especially with the possibility of fabricating it at low cost based on 3-D printing technologies. However, they have two main limitations which are: their relatively small gain (about 5dBi) and narrow bandwidth. To enhance the gain of DRA, higher-order mode excitation can be utilized; however, typically this has a limit of a few dB increments besides its negative effects on the bandwidth. This study employs a cavity-backed slot to provide an appropriate feeding method for a cylindrical dielectric resonator antenna (CDRA). This design effectively facilitates the excitation of higher-order modes, resulting in a significant gain of up to 15 dBi, which is essential for many wireless systems that are unable to support larger aperture sizes through the standard use of arrays. Additionally, two modes are excited to keep a relatively broadband of about 15 %. The proposed design consists of a cylindrical dielectric placed on top of a cavity-backed slot that is excited by a coaxial probe soldered to the top patch of the cavity. With this feeding, a good matching is achieved for different dielectric resonator heights, hence, the gain can be adjusted easily without the need of reoptimizing the antenna or the feed structures. The design process is explained in addition to performing a sensitivity analysis of fabrication tolerances which confirms that the 3-D printer provides enough accuracy with a negligible effect on the antenna's performance. Then a prototype with a medium length is fabricated and measured to provide high realized gain and impedance bandwidth of 11 dBi and 14.5 %, respectively. The measured data demonstrate the good performance of the antenna with great matching compared to the simulated ones. Furthermore, the antenna presents a good performance in terms of sidelobes and polarization. This proposed design outperforms other DRA designs based on higher-order modes. [ABSTRACT FROM AUTHOR]

Dielectric resonator antennas (DRAs) use dielectric material as a resonator to accomplish high radiation efficiency and avoid severe conductor loss. The dielectric material that behaves as a resonator is plagued by a number of limitations, including strong cross-polarised (XP) radiation and difficulties integrating with any development platform. Yet, it also offers a lot of benefits, including compact size, lightweight, affordable price, and diversity in form, including cylindrical, rectangular, conical, and ring. A discussion of DRAs, covering DRA propagation modes, geometries, feeding mechanisms, and different bandwidth augmentation approaches, is presented. A stacked arrangement with two or more DRs has achieved the widest impedance bandwidth (BW). The perforated topology is a straightforward alternative for increasing the DRA's bandwidth while maintaining a small, discrete size. [ABSTRACT FROM AUTHOR]

The application of ceramic for a circularly polarized (CP) filtering antenna is studied in this paper. The dielectric resonator (DR) of sintered aluminum oxide (Al 2 O 3) ceramic has a dielectric constant of 9.5 and low dielectric loss of 0.003, and excellent mechanical properties. The dielectric resonator antenna (DRA) consists of two parts, the upper part is a DR, and the lower part uses a feeding network containing two hairpin bandpass filters. The measured | S 11 | of the DRA is 48.0 % and the axial ratio (AR) bandwidth is 33.5 %. Meanwhile, the peak gain of the DRA is 6.13 dBi, and the suppression level across the stopband exceeds 15.2 dB. The DRA uses the hairpin bandpass filters to improve the filtering characteristics of the antenna and uses the corner-cutting processing of the DR to improve the AR, which can be implemented to reduce the cost of fifth-generation (5 G) communication. [ABSTRACT FROM AUTHOR]

(1– x)BaV 2 O 6 - x LiF (x = 0.025, 0.05, 0.10, 0.15) ceramics with an ultra-low sintering temperature of 475 °C were synthesized using the standard solid-state reaction method. The ceramics demonstrated a remarkable enhancement in the quality factor (Qf), reaching a maximum value of 16,800 GHz at x = 0.10, which is 5.6 times higher than that of pure BaV 2 O 6 ceramics obtained in this work. A near-zero temperature coefficient of resonant frequency (τ f = 1.44 ppm/°C) was simultaneously achieved, together with a dielectric constant ε r of 11.54. Additionally, the chemical compatibility between the present ceramics and the Al electrode was confirmed. Moreover, a millimeter-wave antenna with an excellent S 11 value of −50.3 dB, and a large bandwidth of 3.44 GHz was fabricated using the 0.9BaV 2 O 6 -0.1LiF ceramic as the dielectric resonator. These results highlight the potential application prospects of (1– x)BaV 2 O 6 - x LiF ceramics in the ultra-low temperature co-fired ceramic technology and 5 G millimeter-wave antennas. [ABSTRACT FROM AUTHOR]

A comprehensive design of an ultra-broadband circularly polarized (CP) dielectric resonator antenna (DRA) array operating in the C-band for fifth-generation (5G) communication systems is presented in this paper. The objective is to achieve a compact antenna size capable of receiving and transmitting CP electromagnetic waves over a wider bandwidth. The material chosen for the dielectric resonator (DR) is Alumina (Al 2 O 3) ceramic, known for its low dielectric loss and exceptional mechanical properties, making it an ideal candidate for the DR. The proposed design utilizes a 2 × 2 array of cross-shaped DRs, fed by a compact circular phase-shift feeding network with double-point feeding. This configuration results in a 3-dB axial ratio (AR) bandwidth of 48.7 % and an impedance matching bandwidth (IMB) of 53.2 %. The antenna's horizontal size is reduced to 1.17 × 1.17λ 0 2, and the gain is significantly enhanced by exciting multiple Mie resonances in the stacked DRs, yielding a measured peak gain of 12.48 dBic. These outstanding features position the CP DRA array as an excellent choice for 5G communication systems. [ABSTRACT FROM AUTHOR]

The impact of Cr3+ substitution on the electrical and dielectric properties of Y-type hexaferrites with composition Ba 2 Mg 2 Cr x Fe 12-x O 22 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) was synthesized by the sol-gel auto combustion technique. The lattice parameters 'a' and 'c' slightly increase with the substitution content of Cr3+, and some other physical parameters, including porosity, microstrain, dislocation density, specific surface area, and stacking fault coefficient, were determined from XRD data. FTIR spectra confirm the formation of iron oxide base material by the appearance of three signature bands at precisely 429, 474, and 499 cm-1 due to Fe–O vibrations at octahedral and tetrahedral sites. Substituting Cr3+ at the octahedral site enhanced the room temperature DC electrical resistivity from 6.89 × 109 to 2.27 × 1010 Ω-cm. Temperature-dependent DC electrical resistivity exhibits semiconducting behavior. There is a direct relation between resistivity and activation energy. The dielectric behavior of Cr3+ substituted samples in the frequency range of 1 MHz–6 GHz was understood based on the conduction mechanism through the hopping of electrons between Fe3+ and Fe2+ ions and the Maxwell-Wagner Model. In impedance spectroscopy studied using Cole-Cole plots, most dielectric response arises from the contribution of the grain boundary effect. With the substitution of Cr3+, dielectric losses decreased. A very high Q-value around 1 GHz was observed, suggesting that these hexaferrites are efficient materials for many high-frequency applications, such as multi-layer chip inductors (MLCI), dielectric resonators, and power applications. [ABSTRACT FROM AUTHOR]

Technology important ferrites ceramic Sr 2 Ni 2 Ga x Fe 12-x O 22 (x = 0.00, 0.2, 0.4, 0.6, and 0.8) samples were produced using sol-gel auto combustion route. Structural, electrical, dielectric, and magnetic parameters were identified by substituting Ga3+ at the Fe3+ site. It was recognized that an increase of Ga3+ content in (Sr 2 Ni 2 Ga x Fe 12-x O 22) ceramic samples first decreased, then increased lattice parameters, and the density of samples was observed. This is because of the ionic radii and atomic weight of Ga3+ and Fe3+ cations. FTIR spectra show two characteristic absorption bands at 444-513 cm−1 caused by metal-oxygen vibrations. Due to the contribution of smaller grains of samples, the higher values of resistivity were observed, which vary from 3.78 × 1010 (Ω cm) to 1.13 × 1011 (Ω cm) by the substitution of Ga3+ ions at the octahedral site. The activation energy was measured between 0.20 and 0.61 eV. The dielectric response of Ga3+ substituted ferrite ceramic samples were studied in the 1 MHz-6 GHz frequency region. The Maxwell-Wagner bilayer model studied the effect of polarization with applied frequency on dielectric parameters. With the substitution of Ga3+, minimal losses in the range 0.34–0.44, about 6 GHz, and a high Q-value of about 10,000 were observed for each sample. In impedance spectroscopy analysis Cole-Cole plots confirm that the dielectric response is because of the influence of grain boundaries. The substitution of Ga3+ enhances saturation magnetization (68.20–71.78 emu/g) while coercivity decreases (655.86–507.86 Oe). In the present finding, the low dielectric loss, moderate permittivity, high value of the Quality factor, and very high value of resistivity of about 1.13 × 1011 that reduces the eddy current losses suggested that these materials are appropriate candidates for many high-frequency applications such as multilayer chip inductor, dielectric resonators, power applications, and microwave devices. [ABSTRACT FROM AUTHOR]

In this study, the Ba 3 P 2 O 8 and Mg 2 B 2 O 5 were fabricated by the solid-state reaction method separately, and the (1-x)Ba 3 P 2 O 8 -xMg 2 B 2 O 5 (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba 3 P 2 O 8 -xMg 2 B 2 O 5 composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE 01δ mode dielectric resonator method, respectively. The results revealed that the Mg 2 B 2 O 5 phase and Ba 3 P 2 O 8 phase could coexist well in the (1-x)Ba 3 P 2 O 8 -xMg 2 B 2 O 5 composite ceramics without formation of any new phases. The abnormal grain growth of Ba 3 P 2 O 8 grains was inhibited by the addition of Mg 2 B 2 O 5. In addition, through composition of Ba 3 P 2 O 8 and Mg 2 B 2 O 5 , the temperature coefficient of resonant frequency (τ f) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba 3 P 2 O 8 -0.2Mg 2 B 2 O 5 composite ceramic was achieved at a sintering temperature of 920 °C, τ f = −1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity ε r = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba 3 P 2 O 8 -0.2Mg 2 B 2 O 5 composite ceramic is a candidate LTCC material with wide application prospects. [ABSTRACT FROM AUTHOR]

In this paper, a laminated planar feed structure has been proposed to excite the omnidirectional radiation modes of a dielectric resonator (DR): TM 01δ , TM 011+δ and TM 012+δ. The resonant frequencies of the three modes are 2.44, 2.78 and 3.10 GHz respectively. By combining three resonant frequencies, the proposed band-notched dielectric resonator antenna (DRA) achieves a wide impedance bandwidth and stable omnidirectional radiation pattern in the whole passband. The simulated passbands of the proposed band-notched DRA are 2.23–2.56 GHz and 2.71–3.17 GHz. The laminated planar feed structure also can produce an adjustable radiation null (RN) at the upper edge of the passband, improving the skirt selectivity. To suppress in-band interference, four metal patches have been plated on the side walls of the DR and another adjustable RN (notched frequency) is generated within the passband. By changing the size of the metal patch, the notched band can be adjusted. In a word, the proposed DRA has numerous advantages such as wideband, stable omnidirectional radiation, filtering and band-notched functions. A prototype has been fabricated and measured for demonstration, and the measured results are coincided with the simulated ones. [ABSTRACT FROM AUTHOR]

In this paper, a bi-tunable metamaterial absorber comprising a subwavelength resonator of semiconducting material InAs and a metallic plane adhered to a dielectric layer has been proposed in the terahertz regime. Absorption of about 99.8 % is achieved at 4.446 THz with the application of magnetic field B = 0.4 T and a high tunability rate of 0.4 THz/T in the central resonance frequency due to the presence of a magnetostatically tunable H-shaped InAs resonator and polyimide dielectric layer. The same structure supports dual control over the resonance by replacing polyimide dielectric layer with InSb, as InSb possesses temperature- and magnetic field-dependent dielectric properties. The replacement of polyimide dielectric layer with InSb provides near unity absorption of 99.99 % at B = 0.4 T but when the effect of temperature on the absorption is taken, it provides a high absorptivity of 99.99 % at T = 285 K with a blue shift in the maximum resonance frequency, providing tunability of 0.016 THz/K on increasing the temperature from 280 K to 295 K. Thus, the proposed absorber not only provides dual control over the resonance spectrum but also progresses towards more practical applications in the sensing and detection of temperature variance. • Single controllable metamaterial absorber comprising indium arsenide (InAs) and polyimide. • Yields absorptivity of 99.8 % at B = 0.4 T, tunability of 0.4 T with the variation of magnetic field from 0.1T to 0.4 T. • Bi-controllable response is observed by replacing polyimide dielectric layer with indium antimonide (InSb) which supports magnetic as well as thermal control. • Maximum absorption of 99.99 % is achieved when magnetic action is taken in control where as 99.99 % of absorption is achieved when thermal action is considered as well as provides high temperature tunability of 0.016 THz/K on increasing the temperature from 280 K to 295 K. • The proposed absorber not only provides dual control over the resonance spectrum but also find its application in sensing [ABSTRACT FROM AUTHOR]

• Two important but overlooked problems during τ f measurements are discussed in detail. • Overlook on temperature denpendence of τ f may result in serious misunderstanding. • The as-measured τ f is for resonator but not sample, which causes measurement error. • Suggestions are given to ensure measurement reliability of τ f and avoid misleading. As a key parameter of microwave dielectric ceramics, the temperature coefficient of resonant frequency (τ f) determines the temperature stability of microwave dielectric ceramics and relevant microwave devices. The τ f of a microwave dielectric ceramic is typically calculated from the measured resonant frequencies of the system, consisting of the ceramic sample plus other dielectric elements, at two temperatures ∼60 – 70 °C apart. This measurement process assumes that τ f is a constant; however, it is generally temperature-dependent based on both theoretical and experimental results. Furthermore, the as-measured τ f is actually the τ f of the dielectric resonator system , which is different from that of the sample itself. In this paper, these two overlooked problems during τ f measurement are discussed in detail, and suggestions are given to avoid their possible misleading consequences and thus ensure the reliability of τ f measurements. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel self-multiplexing terahertz antenna with four tunable ports is proposed in this work. The configuration comprises four rectangular dielectric resonators (DRs) affixed to a substrate, which are excited through L-shaped microstrip-fed slots positioned beneath them. To guarantee efficient isolation among the tunable antenna components, periodic unit cells are introduced into the ground plane, forming a defective ground structure (DGS). Each L-shaped slot element is equipped with a graphene strip to regulate the tunability of each DR element. This antenna can operate in various modes with resonant frequencies at 4.01, 4.23, 4.37, and 4.57 THz. It holds potential for future terahertz wireless applications that require the utilization of adjacent channels with distinct communication frequencies. Furthermore, a four-port antenna design is implemented, offering tunable MIMO capabilities with self-quadruplexing ability. The MIMO parameters, specifically the envelope correlation coefficient (ECC) and diversity gain (DG), have been assessed and found to fall within acceptable limits across the operating frequency bands. Additionally, an equivalent circuit model (ECM) is analysed to shed light on the antenna's working principle and verify the obtained results. [ABSTRACT FROM AUTHOR]

In this paper, a circularly polarized rectenna is proposed for microwave energy transmission, which is composed of a broadband Substrate Integrated Waveguide (SIW) antenna and a rectifier circuit. A dielectric resonator is loaded on the SIW antenna, enhancing the impedance bandwidth. Circular polarization is achieved by chamfering the diagonal of the rectangular patch. Two sections of microstrip branches are employed for good impedance matching over the broadband operation. Measured results show that the proposed rectenna has a good impedance performance (|S 11 | < −10 dB) and high RF-DC conversion efficiency (>50 %) over a relative bandwidth of 22.9 % (29–36.5 GHz). The maximum conversion efficiency of 67.5 % is realized at the input power of 18 dBm. [ABSTRACT FROM AUTHOR]

• New ULTCC glass-ceramic material fabricated at 470 °C for dwell time of 30 min. • Low porosity and low surface roughness, comparable to conventional LTCC materials. • Practically invariant dielectric constant over the microwave and THz frequency range. • Good repeatability of the thermal dependence of the dielectric constant. In this study, a new ultra - low - temperature co-fired ceramic (ULTCC) glass-ZnO-SiO 2 -B 2 O 3 CeO 2− MgO-Al 2 O 3 composite was developed and its applicability as a dielectric substrate in emerging high-performance communication technologies in the microwave and millimetre-wave frequency ranges was investigated. The novel material composition enables achieving good sinterability at a low fabrication temperature of 470 °C. Extensive studies have been conducted on the microstructure, porosity, water absorption, surface roughness, and thermal expansion coefficient. Following this analysis, the dielectric properties of the bulk glass-ceramic composites and the final ULTCC substrates were characterised. These measurements were conducted within a broad frequency range of 5 GHz–1.1 THz using split-post dielectric resonators, a Fabry-Perot open resonator, and a time-domain spectrometer, resulting in quasi-continuous frequency characteristics of the complex permittivity. Furthermore, the fabricated ULTCC substrates were subjected to surface-wise measurements, which provided 2D maps of the dielectric properties as qualitative and quantitative measures of the uniformity and quality of the material. [Display omitted] [ABSTRACT FROM AUTHOR]

A cylindrical dielectric resonator (CDRA) based 8-port Multiple Input Multiple Output (MIMO) antenna with multi-directional pattern diversity characteristics has been depicted in this communication. The proposed antenna comprised a box-shaped structure, formulated with the help of a two-port antenna system on each side of the structure, which consisted of two cylindrical dielectric resonators (CDRs) energized with the help of a rectangular ring aperture and microstrip feed line. A V-shaped defective ground structure (DGS) beneath the CDRs on each surface of the structure was introduced to achieve wideband and high isolation between two radiators. The multi-directional pattern diversity in the proposed antenna was attained by mounting each set (comprising two CDRs) of the radiating structure on the substrate in such a way as to produce spatially separated radiation beams in quad directions. The measured operating frequency for all eight ports covered the frequency range between 4.99 GHz to 5.94 GHz, while the isolation between CDRs of the proposed antenna was determined to be better than –22 dB, making the antenna appropriate for WLAN applications. [ABSTRACT FROM AUTHOR]

Cordierite-based dielectric ceramics with a lower dielectric constant would have significant application potential as dielectric resonator and filter materials for future ultra-low-latency 5G/6G millimeter-wave and terahertz communication. In this article, the phase structure, microstructure and microwave dielectric properties of Mg 2 Al 4–2 x (Mn 0.5 Zn 0.5) 2 x Si 5 O 18 (0 ≤ x ≤ 0.3) ceramics are studied by crystal structure refinement, scanning electron microscope (SEM), the theory of complex chemical bonds and infrared reflectance spectrum. Meanwhile, complex double-ions coordinated substitution and two-phase complex methods were used to improve its Q×f value and adjust its temperature coefficient. The Q×f values of Mg 2 Al 4–2 x (Mn 0.5 Zn 0.5) 2 x Si 5 O 18 single-phase ceramics are increased from 45,000 GHz@14.7 GHz (x = 0) to 150,500 GHz@14.5 GHz (x = 0.15) by replacing Al3+ with Zn2+-Mn4+. The positive frequency temperature coefficient additive TiO 2 is used to prepare the temperature stable Mg 2 Al 3.7 (Mn 0.5 Zn 0.5) 0.3 Si 5 O 18 - y wt%TiO 2 composite ceramic. The composite ceramic of Mg 2 Al 3.7 (Mn 0.5 Zn 0.5) 0.3 Si 5 O 18 - y wt%TiO 2 (8.7 wt% ≤ y ≤ 10.6 wt%) presents the near-zero frequency temperature coefficient at 1225 °C sintering temperature: ε r = 5.68, Q×f = 58,040 GHz, τ f = −3.1 ppm/°C (y = 8.7 wt%) and ε r = 5.82, Q×f = 47,020 GHz, τ f = +2.4 ppm/°C (y = 10.6 wt%). These findings demonstrate promising application prospects for 5 G and future microwave and millimeter-wave wireless communication technologies. [ABSTRACT FROM AUTHOR]

Metamaterials (MMs) have attracted intense attention owing to their unprecedented control over the propagation of electromagnetic waves. Researches on MMs usually concentrate on the metallic resonators layer, while the carbon materials-based resonators and the dielectric layer of MMs are relatively overlooked. Here, a novel and simple "metawall" perfect MM absorber based on carbon nanotube (CNT) is conducted, which enables ultra-wideband perfect absorption, showing three peaks with 99% absorption and yielding over 97% absorption in 5.6–11.0 GHz. A reproducible and cost-efficient fabrication method is proposed, using CNT paste as the resonator and the combination of lossy cement board and lossless ceramic fiberboard as the dielectric. Moreover, only one kind of one-dimensional gratings CNT pattern is required to achieve multi-band perfect absorption. Through the control experiments to investigate the roles of the components of the metawall structure, it is found that the wideband perfect absorption of the metawall can be attributed to its unique structure and the absorption performance of the cement board. The proposed metawall provides a new perspective for achieving wideband perfect absorption and may serve as a promising platform to combine carbon nanomaterials with practical load-bearing engineering components. We propose a novel and simple "metawall" perfect MM absorber based on CNT resonator and cement dielectric. A coatable CNT resonator and a simple fabrication method is presented. The metawall employees a special multilayer structure, achieving three peaks with near-unity absorption and yielding over 97% absorption in 5.6–11.0 GHz. A simple 1D CNT gratings pattern is required to achieve multi-band perfect absorption, which usually requires multiple resonators in traditional MMs. [Display omitted] [ABSTRACT FROM AUTHOR]

LaZn 1/2 Ti 1/2 O 3 is a double perovskite with promising microwave dielectric properties for applications towards dielectric resonators and antennas. Its dielectric properties can be enhanced through the substitution of suitable ions in either A- or B-sites. In this paper, we report a significant improvement in the quality factor (Q) by substituting Y3+ in the La site with a marginal reduction in dielectric constant (ε r). A single phase is confirmed in XRD indicating the formation of La 1- x Y x Zn 1/2 Ti 1/2 O 3 (0 ≤ x ≤ 0.25) solid solutions. The substitution results in an expansion of lattice along the b direction while there is a contraction in both a and c directions, leading to a reduction in unit cell volume. The dielectric constant, ε r , is observed to reduce from 33.4 to 29.6 due to the polarizability of A-site atoms. The temperature coefficient of resonant frequency (τ f) increases with an increase in x which does not appear to correlate with reducing tolerance factor (t). This non-conventional behaviour of τ f in this perovskite based solid solutions brings bond valence of O site (V O) into picture. V O appears to show competing effect on τ f. The non-monotonic behaviour is observed in Q × f with a maximum value of 41,400 GHz at x = 0.15 and a sharp decline for x > 0.15. This observation is correlated with variations in the A-site bond valence (V A) and a long-range ordering (LRO) of B-site ions. LRO is associated with A g mode at 710 cm−1 in the Raman spectra. The low frequency (< 250 cm−1) Raman modes shift to a higher frequency with the increase in Y3+. Y3+ substitution also induces lattice distortion which is discussed in terms of variations in FWHM and relative intensity of the Raman modes. • Improved Q × f of 41,400 GHz for x = 0.15 from 25,800 GHz for x = 0. • Long range ordering (LRO) of B-site ions is evident from Raman spectra only. • Drastic fall in Q × f for x > 0.15 is related with reduced LRO with x. • 2 mol% lower Zn in the parent compound enhances Q × f to 30,800 GHz. • Increased τ f does not correlate with enhanced octahedral tilt unlike in perovskites. [ABSTRACT FROM AUTHOR]

A simple decoupling technique by using conformal metal strips is investigated for isolation enhancement of terahertz (THz) multi-input–multi-output (MIMO) dielectric resonator (DR) antennas (DRAs) in this paper. Metal strips with proper dimensions are symmetrically printed on both sides of the upper surface of DRs. The introduction of metal strips can cause disturbance to the electromagnetic (EM) fields inside the DRs by introducing the induced fields, thereby suppressing the diffusion of EM fields and rearranging the EM fields, ultimately reducing the level of coupling and enhancing the isolation between ports. Two kinds of MIMO antennas, i.e., using two DRs and sharing one DR, are used as implementation examples to verify the effectiveness of the proposed technique. Corresponding results show that by optimizing the dimensions of the metal strips reasonably, the isolation for antenna containing two DRs increased from 14.7 to 59.2 dB at 2.98 THz, while the isolation for another sharing one DR increased from 7.1 to 40 dB at 3.64 THz. Excellent improvement of isolation has been achieved through the proposed technique and the proposed MIMO antennas are expected to be applied in future THz communication. [ABSTRACT FROM AUTHOR]

The superior performance of metamaterial-inspired sensors has enabled their application in various material characterization tasks, such as dielectric constant measurement, concentration determination, composition quantification, and impurity or defect detection. This article provides a comprehensive review of recent advancements in metamaterial-inspired sensors, with a specific focus on their design aspects. The applications, working principles, and classifications of these sensors are systematically introduced. A novel classification system for metamaterial-based sensors is proposed to categorize them based on their measurement systems, which are planar transmission lines, cavity waveguides, and free-space measurements. Each metamaterial-loaded measurement system is analysed, considering excitation techniques for resonators and the loading configuration of samples under test. Design strategies, including resonator and sensor topology optimization, appropriate material selection, advanced fabrication and data processing techniques, and simplified operations, are reviewed. Lastly, current challenges, encompassing instrumental, sample-related, and application challenges, are addressed. It is envisioned that the design strategies are useful in the development of microwave sensors with enhanced sensitivity, selectivity, accuracy, and robustness. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel rapid moisture test for oil-paper insulation. • Microstrip ring resonator analyzes dielectrics properties. • Precise moisture level distinction found. • New model assesses the moisture content accurately. Moisture ingress significantly accelerates the aging of oil-paper insulated equipment, making accurate assessment of moisture content critical for the operation and maintenance of oil-immersed insulated power equipment. In this paper, a novel method for rapid moisture content evaluation is proposed based on a microstrip ring resonator (MRR) designed with a fundamental frequency of 1.16 GHz. A calculation model for the dielectric response analysis using MRR is established to characterize dielectric properties of the material layered on the substrate. ANSYS HFSS electromagnetic simulation software was used to study the impact of dielectric material thickness and the substrate on the MRR test results. Experimental measurement demonstrated that the maximum deviation in resonance frequency was merely 0.542 %. The dielectric properties of uniformly and non-uniformly damp insulating pressboard were analyzed across the frequency band from 1 to 6 GHz. The MRR test results were compared with those of the standard resonant cavity method and frequency domain dielectric spectroscopy (FDS) test. Using the regression algorithm and curve analysis, moisture assessment models for both uniformly and non-uniformly damp oil-paper insulation were established. The experimental results show that the MRR test can clearly distinguish between the pressboard samples with varying moisture levels under uniform conditions, with a maximum moisture evaluation error of 8.19 %. The results demonstrate that the MRR test method, requiring only 56 s, can quickly and effectively evaluate the moisture content of insulating pressboard. [ABSTRACT FROM AUTHOR]

In this article, an approach to realizing a dielectric resonator based bow-tie shaped antenna for the sub-6 GHz, 5G and IoT applications is discussed that utilizes droplet-shaped radiators for its two arms. The droplet-shaped radiating element is systematically derived to obtain a wider bandwidth response by truncating the sides of an aperture-coupled cylindrical DRA operating at H E 11 δ mode. The proposed bow-tie dielectric resonator antenna (DRA) is a modified dipole structure that uses a balanced line to differentially feed the two radiating segments to attain an overall wideband characteristics. A wideband matching balun circuit facilitates the antenna feeding which produces equal amplitude signals with 180 ° phase difference at its two output ports throughout the band of interest. The measurement of the proposed antenna confirms that it can serve several 5G bands like n77 (3300–4200 MHz), n78 (3300–3800 MHz), n48 (3550–3700 MHz) and n79 (4400–5000 MHz) with an overall wide bandwidth of 42.7% in the sub-6 GHz range. This planar configuration has a realized gain value ≥ 7.5 dBi within 3.37–3.91 GHz and it remains higher than 6 dBi almost throughout the working bandwidth of 3.18–4.91 GHz with considerably wide beamwidth. This broadband DRA has a consistent broadsided radiation pattern with cross-polarization discrimination (XPD) > 20 dB and its radiation efficiency varies between 60%–70% within 3.2–4.8 GHz. The antenna occupies a volume 1.2 λ × 1. 2 λ × 0. 1 λ corresponding to its lower frequency of operation and it can support many more significant applications including WiMAX (3.3–3.8 GHz), Citizens Broadband Radio Service (CBRS) (3.55–3.7 GHz) and LTE (3.41–3.5 GHz uplink/3.51–3.6 GHz downlink). All these characteristics make this antenna a suitable candidate for use in transceiver modules for indoor communication, base stations, and vehicular communication. • A bow-tie dielectric resonator antenna is designed for the sub-6 GHz, 5G, and IoT. • It is low profile (0.1 λ g) and has a wide bandwidth of 42.7% (3.18-4.91 GHz). • It can support n77, n78, n48, and n79 5G bands and has a maximum gain of 9.2 dBi. • Applications: LTE (3.41-3.5/3.51-3.6 GHz), WiMAX (3.3-3.8 GHz) and CBRS (3.55-3.7GHz). • Its single balance feed makes it easily integrable to the RF front-ends. [ABSTRACT FROM AUTHOR]

This paper presents a design for a low-coupling multiple-input multiple-output (MIMO) antenna with two antenna elements. There is a dielectric resonator centrally and four inverted-F slots around on each element. This dielectric resonator consists of a dielectric block with an I-shaped metal pattern and is encircled by a metal ring with air holes. The use of inverted-F slots and the dielectric resonator effectively reduces the mutual coupling between the two antenna elements. Simulation and measurement results indicate that the designed MIMO antenna achieves a high level of isolation, maintains a low envelope correlation coefficient, and possesses a relatively high overall active reflection coefficient efficiency within the bandwidth of 6.41 GHz–6.62 GHz. These characteristics make the MIMO antenna perform exceptionally well in enhancing communication system performance, particularly in terms of signal quality, channel capacity, and system efficiency. [ABSTRACT FROM AUTHOR]

Niobate-based microwave ceramics with low loss are expected to be used in 5G communication devices such as antennas, resonators and dielectric filters. In order to obtain a thermally-stable dielectric ceramic, (1- x)Li 3 Mg 2 NbO 6 - x CaTiO 3 -4wt%LiF system were fabricated. The results of crystal structure and microstructure showed specimens possessed a two phase system with Li 3 Mg 2 NbO 6 and CaNbO 3. The microstructure and dielectric performances of niobate-based ceramics are closely related to the amount of CaTiO 3 added. An optimum dielectric property of ε r ∼15.8, Q × f ∼84430 GHz and τ f ∼6.5 ppm/°C was obtained at 1050 °C for 0.925Li 3 Mg 2 NbO 6 -0.075CaTiO 3 -4wt%LiF ceramic. • Temperature stable of Li 3 Mg 2 NbO 6 -based ceramics was fabricated. • The sintering temperature is 1050 °C. • CaTiO 3 additives improved dielectric properties. • Optimal properties of ε r ∼15.8, Q×f ∼84430 GHz, and τ f ∼6 ppm/°C were acquired. • Which is an alternative material for communication components. [ABSTRACT FROM AUTHOR]

In next-generation mobile and wireless communication systems, low sintering temperature and excellent dielectric properties are synergistic objectives in the application of dielectric resonators/filters. In this work, Li 2 Ti 0·98 Mg 0·02 O 2·96 F 0.04 –1 wt% Nb 2 O 5 (LTMN) ceramics were fabricated, and their sintering temperature was successfully lowered from 1120 °C to 750 °C by adjusting the mass ratio of B 2 O 3 –CuO (BC) additive. The optimum dielectric properties (ԑ r ~ 24.44, Q × f ~ 60,574 GHz and τ f ~ 22.8 ppm/°C) were obtained in BC-modified LTMN ceramics sintered at 790 °C. Even if their sintering temperature was lowered to 750 °C, the lowest temperature among the Li 2 TiO 3 -based dielectric ceramics currently used for LTCC technology, excellent dielectric properties (ԑ r ~ 23.77, Q × f ~ 51,636 GHz) were still maintained. Additionally, no extra impurity phase was detected in BC-modified LTMN ceramics co-fired with Ag at 790 °C, indicating that BC-modified LTMN ceramics have a bright prospect in high-performance LTCC devices for 5G applications. [ABSTRACT FROM AUTHOR]

In this study, MgAl 2 O 4 -based ceramics with high quality factor (Qf) and low dielectric constant (ε r ≤ 10) were obtained by fabricating MgAl 2- x (Zn 0.5 Ti 0.5) x O 4 (x = 0–0.5) ceramics via conventional solid-state reaction method. Excellent microwave dielectric properties were achieved for samples at x = 0.5 and sintered at 1550 °C, i.e., ε r = 9.86, Qf = 263 900 GHz (five times better than that for x = 0 sample) and τ f = −92 ppm/°C. The X-ray diffraction (XRD) patterns displayed characteristic peaks of MgAl 2 O 4 with spinel structure. MgTi 2 O 5 and MgTiO 3 were considered as secondary phases. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and relative density analysis indicated that ultra-high Qf values were dominated by dense microstructure, secondary phase and cation vacancies; whereas ε r values were mainly affected by secondary phase and ionic polarizability. MgAl 2- x (Zn 0.5 Ti 0.5) x O 4 ceramics with excellent microwave dielectric properties have potential application in millimeter-wave communication, dielectric filters, dielectric antennas and resonators. [ABSTRACT FROM AUTHOR]

In this paper, a novel metamaterial absorber-based sensor design in the S-band region is proposed for the characterization of solid and liquid samples. Unlike typical microwave sensor structures, where the sensing and resonator layers are manufactured separately, the proposed sensor design has a monolithic structure with a cavity in the dielectric substrate on which the samples can be placed. Thanks to this structure, which can be easily manufactured precisely with 3D printing technology, both solid and liquid sample tests can be performed without the need for additional processing. The absorber of the proposed sensor design consists of an electric-field-coupled (ELC) resonator placed on the cavity-loaded substrate with the other side fully grounded. To ensure a strong interaction between the ELC resonator and sample materials, the resonator is aligned just on the cavity. In the design process, the absorption behavior of the monolithic structure depending upon the ELC resonator and dielectric environment was predicted with an equivalent analytical model. Moreover, many parametric analyses were carried out to achieve high absorbency and sensitivity properties. To validate the numerical design, a fabricated prototype was measured using two solid and three liquid samples. According to the simulation and measurement results, the proposed design with novel configuration exhibits high sensitivity performance compared with recently reported microwave sensor designs. [Display omitted] • A novel metamaterial absorber-based sensor design in the S-band region. • Both solid and liquid sample tests can be performed without additional processing. • The proposed sensor design has a monolithic structure with the sensing layer. • This structure can be easily manufactured precisely with 3D printing technology. • It can distinguish both solid and liquid samples with the highest sensitivity. [ABSTRACT FROM AUTHOR]

• The coupling effect of the parametric and forced resonance phenomena of GPLRDP arches is investigated. • Increasing porosity makes the coupled dynamic instability region wider. • The critical excitation frequency is sensitive to the GPL weight fraction under a high level of DC voltage. • The critical excitation frequency is also affected by AC frequency at a certain range. Graphene platelet-reinforced dielectric porous (GPLRDP) arches are a kind of multifunctional structures, which can be used to design various dielectric resonators and soft robotic components. This work studies the coupled dynamic instability of GPLRDP arches under electromechanical loading. It is assumed that the presence of voids is uniformly distributed in the arch structure, while graphene platelets (GPLs) are uniformly dispersed inside the skeleton of such voids. The effective medium theory (EMT) is used to determine the effective dielectric permittivity and Young's modulus of such structures. Based on the Hamilton principle, the governing equations of this problem are formulated. The differential quadrature method (DQM) and the Bolotin method are then used for solving the arch system to identify the coupled dynamic instability region. In this study, we observe the coupling effect of parametric and forced resonance phenomena. A series of numerical experiments are also carried out to examine the influence of porosities, GPL weight fractions, boundary conditions, and electrical voltage levels on the critical excitation frequency and coupled dynamic instability behavior of GPLRDP arches. It is found that the coupled dynamic instability region becomes wider and shifts to low frequency as the effect of porosity increases. When the signal amplitude of AC frequency is within a certain range, there is an abrupt increase of the critical excitation frequency under a high level of DC voltage. The numerical results of this work demonstrate that the location and size of the coupled dynamic instability region can be actively controlled by adjusting the material and structural parameters. [ABSTRACT FROM AUTHOR]

The microstructure and solvation mechanics of binary liquids are key for predicting mixture permittivity. However, since traditional mixing rules do not consider this complexity, they must be modified to address the mixture characteristics through an interaction factor (k i n t). This paper evaluates this parameter for several mixing rules, applying Support Vector Regressor models trained with glycerin-water reflective signals acquired with a Dielectric Resonator sensor. The regression error of these models indicates both the optimal interaction factor and the mixing rule that fits the most with experimental permittivity values. Kraszewski and Hashin-Shtrikman mixing rules achieved the best performance with an RMSE of around 1. In addition, this paper suggests that the interaction factor can be estimated through the molar volume and the dielectric contrast between liquids (k i n t = 2.67) without acquiring experimental data. Moreover, after analyzing the physical limitations of a linear modification formula, this paper proposes an alternative based on a Gaussian function that avoids unrealistic volume fractions. Both contributions enhance mixing rule accuracy and improve the flexibility to model mixture dielectric behavior. • Machine Learning models trained with a specific mixture data can validate any permittivity characterization from any mixture. • A novel estimation formula to calculate the interaction factor through the molar volume ratio and the dielectric contrast. • A Gaussian formula provides physically realistic volume fraction modifications to model the mixture dielectric behavior. • Multiparametric fraction volume modification enhances the fitting between mixing rule estimations and experimental values. [ABSTRACT FROM AUTHOR]

A Fabry-Pérot (FP) cavity derived from a transformational medium is reported. The proposed coordinate transformation provides spatial gradient dielectric profiles to confine the electromagnetic (EM) waves in the form of FP modes. The quality factor, free spectral range, and finesse of the proposed transformation optics (TO)-based cavity are calculated and compared with a conventional dielectric resonator. It is observed that a pencil-like directional EM beam is emitted for a line source placed inside the TO cavity and the beam's profile shape is strongly dependent on the width of the line source. By cascading several TO cavities, a directional EM power divider is demonstrated numerically. The frequency-dependent EM beam steering by the proposed cascaded TO cavities with 0⸰ and 90⸰ beam directionalities is useful for selective power coupling requirements in RF and optical domains. The 2- dimensional results were cross-checked with the 3-D design using unit cell approximation method and the fabrication issues associated with the proposed TO slab are further addressed. [ABSTRACT FROM AUTHOR]

This work presents an easy-to-use microwave split dielectric resonator (MSDR) for X-band dielectric measurements of free-standing unpolished poly-crystalline diamond (PCD). PCD grown with varying CH 4 /H 2 and O 2 / CH 4 /H 2 in the gas phase show stark differences in dielectric loss. Low microwave dielectric loss PCD is found for CH 4 /H 2 concentrations of less than 5% while PCD grown with O 2 show very high loss tangents. Vacuum annealing introduces non-diamond carbon (NDC) impurities which increases the loss, however, even after significant discolouration the loss is still lower than the O 2 grown PCD. The loss mechanism of O 2 grown PCD is likely due to a high concentration of grain boundaries and grain boundary hopping conduction mechanisms as opposed to high concentrations of NDC impurities. [Display omitted] [ABSTRACT FROM AUTHOR]

High- Q antennas are highly sought after for their narrow bandwidth and compact size, enabling them to occupy minimal volume in a given structure. In this paper, we present a new ultra-narrow band filter/antenna designed for LoRa applications. The filter/antenna consists of an elliptical slot loaded with a high permittivity rectangular dielectric resonator, excited by a coupled microstrip line. The proposed antenna serves not only as a radiating element but also as a filter, offering the significant benefit of eliminating loss between the filter and the antenna. To assess the influence of the SMA power cable on miniature antennas, we conducted a comparison of the antenna with and without a radio frequency (RF) module, focusing on radiation pattern. Our proposed filter/antenna provides a compact profile of 25 × 40 mm 2 (λ / 13 × λ /8), an omnidirectional radiation pattern, and remarkable rejection in the stop-band. The validity of the proposed design is accomplished by comparing the electromagnetic simulation with fabrication and measurement results, achieving a high level of agreement between simulation and measurement. Thanks to its exceptional performance, small size, low cost, and low-power characteristics, this innovative structure is suitable for IoT applications at UHF band with a stop-band outside this frequency to avoid potential interference from adjacent bands. [ABSTRACT FROM AUTHOR]

In this paper, a multi parallel CSRR (MP-CSRR) sensor for non-invasive blood glucose monitoring is introduced. The sensor divides six CSRR units into two parallel circuits, forming 2 × 3 CSRR matrix to expand the sensing area of the sensor. This sensor can adjust the resonant frequency of the sensor itself by adjusting the spacing between the horizontal or vertical CSRR units. In this paper, the sensor is achieved a resonance frequency of 2.5–3.5 GHz after loading glucose solution. When the concentration of the solution changes, the resonance frequency and S 21 depth of the resonator changes with the dielectric parameters of the solution. Thus, non-invasive monitoring of glucose concentration is achieved. The variation relationship between resonant frequency and CSRR unit spacing and the feasibility of using it for solution detection are verified through simulation. The experimental results are showed that the resonant frequency sensitivity of the sensor is 9.59 × 10−2 MHz/(mg/dL), and the |S 21 | sensitivity is 7.47 × 10−3 dB/(mg/dL). [Display omitted] • Multiple CSRR parallel structures for non-invasive blood glucose monitoring. • Adjusting the distance between adjacent CSRRs can adapt to different detection frequencies and environments. • The sensor achieves detection within the range of 2.5 GHz to 3.5 GHz. • The resonant frequency of the sensor shows high sensitivity to changes in glucose concentration. [ABSTRACT FROM AUTHOR]

Tri-layer ZnTi 0.97 Ge 0.03 Nb 2 O 8 -TiO 2 -ZnTi 0.97 Ge 0.03 Nb 2 O 8 ceramics with different mass fractions of TiO 2 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 ZnTi 0.97 Ge 0.03 Nb 2 O 8 -TiO 2 , 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 Zn 2 GeO 4. After sintering at 1120 ℃ for 6 h, ZnTi 0.97 Ge 0.03 Nb 2 O 8 -TiO 2 -ZnTi 0.97 Ge 0.03 Nb 2 O 8 tri-layered ceramics exhibited excellent dielectric properties (ε r = 42.1, Q× f = 51,477 GHz and τ f = +1.9 ppm/℃) with 0.04 wt% TiO 2 , 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. [ABSTRACT FROM AUTHOR]

Light scattering properties of dielectric nanostructures (DNSs) have been recently applied for biosensing. It is worth noting that, however, the application of dielectric materials as light scattering probes in the field of analysis and detection has rarely been reported, especially at the single particle level. Herein, for the first time, we use ZnO micron rods (ZnOMRs) as dark field microscope (DFM) imaging probes for single particle level optical sensing. It was found that a drastic reduction of scattering intensity of the ZnOMRs with increase of the surrounding medium's refractive index (RI), especially when illuminated by transverse electric (TE) polarized light, showing polarization-dependent RI sensitivity properties. In addition, the scattering color of the ZnOMRs gradually blue-shifted with the increase of solvents' RI, this can avoid the problem of low sensitivity of the probe with a red scattering color in the previous reports. The characteristic scattering properties and polarization-dependent RI sensitivity properties of ZnOMRs provide more possibilities for the development of new single-particle optical analytical methods. We demonstrated that the scattering color of ZnOMRs could be manipulated by adjusting the structure size, dielectric environment and lighting illumination conditions. Based on this, we for the first time used it as dark-field microscopy (DFM) imaging probes for refractive index (RI) sensing at the single particle level. A drastic reduction of scattering intensity of the ZnOMRs with increase of the surrounding medium's RI, especially when illuminated by transverse electric polarized light was discovered, showing polarization-dependent RI sensitivity properties. Image 1 • Polarization-dependent refractive index sensitivity. • The RGB values are used as the sensing parameters, which greatly reduces the technical requirements and costs. • Broadens the choice of light scattering analysis probes no longer limited to noble metal plasmonic materials. • There is no plasmonic photothermal problem in dielectric materials, which is beneficial to to practical application. [ABSTRACT FROM AUTHOR]

In this study, the sol-gel method was employed for the preparation of M-type hexaferrites Sr 1-x Al x Fe 12-y Co y O 19. Annealing of these samples was done at 1200 °C for 4 h. The single phase structure of all the prepared samples of M-type hexaferrites was observed by the X-ray diffraction (XRD) plots. The changes were examined in lattice parameters (a and c), cell volume, as well as in c/a ratio. The variations in c/a ratio were attributed to the changes in lattice parameters. The volume of the cell was found within the range 676.822–667.036 Å3. Debye Scherrer's formula was used for the measurement of crystallite size, which was found in the range of 26.026 to 22.634 nm. The variations were also perceived in bulk density (δ b) and porosity (%) with the incorporation of Al–Co concentration. There was reduction in X-ray density (δ x), due to the increment in substitution concentration. Fourier transform infrared spectroscopy (FTIR) was performed in the range 400–3000 cm−1, which displayed specific absorption bands regarding hexagonal ferrites. Dielectric parameters including dielectric constant, dielectric loss, tan loss, and AC-conductivity revealed decreasing behavior, due to Al–Co substitution. The slope "n" was measured from graph of log(σ ac) as a function of log(ω), and found within the range 0.697–0.972. The grain boundary contribution of all the synthesized samples was evidenced via Cole-Cole plots, and extraordinary contribution of grain boundaries in conduction phenomenon was established by the presence of only one semi-circle in Cole-Cole plots. Therefore, the smaller dielectric parameters of the investigated M-type hexaferrites recommended their feasible role in large frequency applications (e.g., dielectric resonators, microwave absorbers, phase shifters, and stealth technology). [ABSTRACT FROM AUTHOR]

A switchable graphene-based terahertz metamaterial absorber is proposed by using nonstructured graphene loaded with simple dielectric resonators, which can achieve both the broad and dual-band absorption with polarization-independent and wide-angle characteristics. The relative bandwidth of the two bands above 80% absorption reaches 97.8% and 31% in the frequency range of 0.473–1.407 THz and 2.273–3.112 THz, respectively. By changing the chemical potential of graphene, the state of the absorber can be switched from absorption (>80%) to reflection (>91%) over the two broad bands. Physical mechanisms of the broad dual-band switchable absorber are investigated by the impedance matching theory and the coupled-mode theory. The dual bands are caused by the Fabry-Perot resonance of dielectric substrate, the broad and high absorption originates from the appropriate impedance match between the absorber and free space. As the absorber is based on a monolayer nonstructured graphene loaded with simple dielectric resonators, the processing difficulty will be reduced greatly and it is easy to tune it through the bias voltage. This structure provides a new perspective to design broad multi-band absorbers and would have promising applications in multiple amplitude modulators, imaging and sensing. Fig. 1. (a) Schematic view of the broad dual-band metamaterial absorber consisting of 5 × 5 unit cells. (b) Reflection, transmission and absorption of the structure.As is shown in Fig. 1 (a), a switchable graphene-based terahertz metamaterial absorber is proposed based on the dielectric-graphene-dielectric-metal structure, which can achieve both the broad and dual-band absorption with polarization-independent and wide-angle characteristics. By changing the chemical potential of graphene μ c , the state of the absorber can be switched from absorption (>80%) to reflection (>91%) over the two broad bands. Fig. 1 (b) shows that the relative bandwidths of the two bands over 80% absorption can reach 97.8% and 31% in the frequency range of 0.473–1.407 THz and 2.273–3.112 THz for μ c = 1 eV. Physical mechanisms of the broad dual-band switchable absorber are investigated by the impedance matching theory and the coupled-mode theory. The dual bands are caused by the Fabry-Perot resonance of dielectric substrate, the broad and high absorption originates from the appropriate impedance match between the absorber and free space. As the absorber is based on a monolayer nonstructured graphene loaded with simple dielectric resonators, the processing difficulty will be reduced greatly and it is easy to tune it through the bias voltage. This structure provides a new perspective to design broad multi-band absorbers and would have promising applications in multiple amplitude modulators, imaging and sensing. Image 10428 [ABSTRACT FROM AUTHOR]

We report the effect of precursor's purity and heterovalent substitution on the microstructure and dielectric properties of BaZrO 3 ceramics. We find that independent of the purity or raw materials, the dielectric loss of BaZrO 3 at microwave frequencies is rather high with a Q factor in the range of 1000–3000 at 10 GHz. All stoichiometric ceramics studied show up to three types of low- T dielectric relaxations in the 2–250 K range. All these dielectric anomalies can be suppressed by partial substitution of Zr for Nb. By alloying of BaZrO 3 with a hypothetical BaGa 1/2 Nb 1/2 O 3 phase the Q × f value of ceramics at microwave frequency can be improved significantly. The origin of this remarkable improvement is attributed to the effect of the donor ions on the random electric fields and antiferrodistortive instability. Ceramic with a chemical composition of BaZr 0.96 Ga 0.02 Nb 0.02 O 3 sintered at 1600 °C shows dielectric constant, ε ′ = 36.7, temperature coefficient of the resonance frequency, τ f = +110 ppm/°C and Q × f = 172 THz. [ABSTRACT FROM AUTHOR]

In this paper, a new self-oscillating mixer (SOM) including a dielectric resonator (DR) antenna fed by a half-mode substrate integrated waveguide (HMSIW) has been proposed using hybrid integrated circuit technique on an FR4 epoxy substrate. The HMSIW resonator with high quality factor and the DR radiator with higher order HEM 13δ mode excitation are responsible for the excellent phase noise performance of the oscillator and the high directivity of the antenna, respectively. The phase noise, estimated LO power, and conversion gain were obtained as −102.5 dBc/Hz at 1 MHz offset, 8.74 dBm at an oscillation frequency of 24.15 GHz, and 8.5 dB, respectively. The figure-of-merit for the oscillator was obtained −172.8 dBc/Hz. [ABSTRACT FROM AUTHOR]

The comprehensive properties and sintering temperature of microwave dielectric ceramics are the key factors limiting their practical application. In this work, a novel strategy of complex (Co 1/3 Nb 2/3)4+ ions substituted and adding glass (Li 2 O-B 2 O 3 - SiO 2 -CaO-Al 2 O 3 : LBSCA) was proposed to greatly enhance the microwave dielectric properties of Ba 3 Ti 4- x (Co 1/3 Nb 2/3) x Nb 4 O 21 (0 ≤ x ≤ 12 mol%, x CN-BTN) ceramics. A new ceramic of (Co 1/3 Nb 2/3)4+ substitution improved hexagonal phase BTN was successfully fabricated and systematically investigated. As the increased of (Co 1/3 Nb 2/3)4+ ions concentration, the Q× f was greatly increased because of higher packing fraction, and the reduction in the [Nb1/Ti1O 6 ] octahedral distortion caused great changes of τ f. Besides, the P-V-L theory revealed that the Ti/Nb ratio greatly contributed in permittivity ε r , and the Nb-O bonds mainly affected dielectric loss, especially in Nb(1)-O2(1) bond. As a result, the superior microwave dielectric properties were obtained in 6CN-BTN ceramic sintered at 950 °C: ε r ∼40.99 ± 0.48, Q× f ∼17,310 ± 565 GHz, and τ f ∼8.62 ± 4.34 ppm/°C. More encouragingly, 6CN-BTN showed good compatibility with silver, making it a promising K 40 LTCC material for filter and dielectric resonators. This study presented a new strategy to improve the properties of BTN-based materials by complex ions substitution, which was expected to provide a general approach for the design of advanced microwave dielectric ceramics for other material systems. • A novel strategy of (Co 1/3 Nb 2/3)4+ substituted was proposed to greatly enhance the microwave performance of BTN ceramics. • (Co 1/3 Nb 2/3)4+ ions can greatly change the [Nb/TiO 6 ] octahedral distortion, thus greatly improving the Q× f and τ f. • 6CN-BTN ceramic with high performance, low sintering temperature and temperature stable. • 6CN-BTN ceramics is expected to be a candidate material for K 40-LTCC ceramics. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of a single-layer, horizontally polarized, dual-band, omni- and multi-directional hybrid dielectric resonator antenna (DRA) feeding through a 50 Ω coaxial connector. The proposed antenna consists of an FR4 substrate, a regular ground plane and a cross-shaped patch. The connector is placed at the middle point of the square ground plane. Above the microstrip patch, four similar solid dielectric resonator elements are placed diagonally. These DRA structures generate the TE 111 , hybrid HEM 22δ modes and put up an ideal magnetic dipole and an electric quadrupole far-field radiation pattern. To verify the idea, an optimized antenna model is fabricated and tested. A reasonable agreement between the measured and simulated results is obtained. The measured impedance bandwidths of the TE 111 and HEM 22δ modes are 4.26 % (2.9–3.2 GHz) and 4.34 % (4.4–4.6 GHz), respectively. The proposed antenna has a stable omnidirectional radiation pattern at the first resonance frequency and a directional radiation pattern at the second resonance frequency and provides volume reduction. [ABSTRACT FROM AUTHOR]

A dual-broadband and high-efficiency polarization conversion metasurface based on asymmetric transmission is proposed, which is composed of two orthogonal metal gratings, metal resonator and FR-4 dielectric spacer. The simulated results show that the designed metasurface can convert x -polarized incident waves into y -polarized waves in the frequency ranges of 4.64–14.37 GHz and 17.02–37.23 GHz, and the corresponding polarization conversion ratio (PCR) exceeds 90%. The relative bandwidths of the two bands are 102.37% and 74.51%, respectively. The influence of structural parameters on the transmissive polarization conversion performance is studied. The bandwidths of the two bands can be easily modulated by varying the structural parameters of l , n , m and w. The excellent performance of dual-broadband and high-efficiency covers C, X, Ku, K and Ka bands, which can also be well maintained in the oblique incidence range of 0°–50°. Moreover, the mechanism of transmissive polarization conversion is analyzed. The prototype is fabricated and the experimental results are basically consistent with the numerical simulation. The proposed metasurface has potential application value in polarization imaging radar or radiometer, radar, transmission array antennas and filter. • The proposed polarization converter is a dual-broadband transmissive linear polarization conversion metasurface. • The relative bandwidths of PCR greater than 90% are 98.08% and 73.82%, respectively. • The excellent transmissive polarization conversion performance covers C, X, Ku, K and Ka bands. [ABSTRACT FROM AUTHOR]

• First Ferrite Resonator Antenna (FRA) manufactured directly from in natura ores. • Experimental data of dielectric characterization and FRA performance. • Resonance results compared with analytical formula. • Analysis of directivity, gain and efficiency of FRA. We present the evaluation of a ferrite resonator antenna designed from MnFe 2 O 4 -SiO 2 composite. The composite was synthesized from in natura ores, extracted in the state of Rio Grande do Norte, by solid state reaction. Two pellets were manufactured using 370 MPa and 740 MPa. Dielectric characterizations were performed previously, and new results are presented. Pressure increment led to a growth in MnFe 2 O 4 phase, from 88.7% to 90.1%, and a decrease in ferrite and cristobalite crystallite size. Dielectric constant presented well-defined behavior close to 5.0 and agreement with morphological characteristics. Ferrite resonator was simulated according to the dielectric characterizations and magnetic properties estimative. TM 110 theoretical results are presented and compared with the presented resonator. Reflection coefficient measurements are presented and compared to simulations. The error achieved in resonance frequency was lower than 0.15%, simulated radiation patterns presented low cross-polarization, below −55.33 dB. Simulated directivity, gain and efficiency are presented and discussed. [ABSTRACT FROM AUTHOR]

Stripline high frequency resonators or transmission line resonators (TLRs) manufactured as concentric RF coils at the opposite sides of a dielectric sheet serve as wireless self-resonant transmitters-receivers in MRI. Owing to their high quality factor relative to traditional RF coils composed of bulk inductor and capacitors, frequency selectivity of TLRs is high, making them promising elements for single-nucleus MRI. However, the computation of their resonance frequencies is cumbersome, and numerous mathematical mistakes and typos in publications lead to incorrect results. The present publication is the first to summarize the corrected formulas for computations and presents comparison of such computations to real measurements. [ABSTRACT FROM AUTHOR]

Abstract A polarization-independent perfect graphene absorber is numerically demonstrated. The novel absorber is composed of an array of dielectric square resonators and a graphene monolayer on a Bragg reflector. An absorption peak at a wavelength of 1550 nm with an absorbance of up to ∼ 99 % is achieved, owing to the critical coupling effect. Moreover, the designed graphene absorber exhibits an ultra-narrow spectrum bandwidth with an ultra-high quality factor, owing to the combined effects of the guided mode resonance achieved with the dielectric square resonators and photonic band gap with the Bragg reflector. In addition to the numerical results, an analysis model based on the coupled-mode theory is presented. Moreover, the electromagnetic field intensity distributions are plotted to provide a physical interpretation of the complete absorption. This study paves the way for the development of a perfect ultra-narrow spectrum-selective graphene absorber. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a modified class-F power-amplifier (PA) for GSM applications is designed, simulated and tested. In this design, novel symmetrical meandered lines compact microstrip resonant cell (SMLCMRC), is proposed as a new harmonics control circuit (HCC), which resulted in size compression, power added efficiency (PAE) enhancement, power gain improvement, and better linearization in the PA. In this work both of the conventional class-F amplifier and proposed amplifier with SMLCMRC is designed at 1.8 GHz. The measurements show that the proposed PA with SMLCMRC has 72.54% maximum PAE, 17.13 dB gain and the 1 dB compression point (P1dB) is about 35.1 dBm. These results show, 16.5% improvement in PAE, 1.33 dB increment in gain and 1.1 dB improvement in linearity operating range of proposed amplifier compared to the conventional PA. [ABSTRACT FROM AUTHOR]

Abstract Context Microwave sensing appears to be an open wide field to investigate medical applications, such as monitoring of vital signs (temperature, arterial pressure, ...), following different kinds of pathologies (cancer, glucose level ...) and aid for medical diagnosis. It offers an alternative to determine the dielectric properties of biological tissues through the development of local non-invasive and/or embedded sensors, giving thus a kind of imaging by the dielectric contrast. Moreover, RF communications links between several sensors can be developed to realize "Body Area Networks". Methods Biological tissues having high dielectric permittivity and losses in the microwave frequency domain (around 1 GHz), a resonant dielectric characterization method is used to obtain a good sensitivity. The experimental setup is based on the measured changes of electrical characteristics of the resonator (resonance frequency and its shift and broadening) when a biological tissue is applied on it. In our case, the sensor is a microstrip ring resonator operating in a two-port configuration at a fundamental frequency of 1 GHz. It consists of a meander loop in order to reduce its dimensions. Besides, an original excitation is proposed leading to small perturbation of the resonator when high dielectric losses material is characterized. This increased greatly the sensitivity of the method to obtain the dielectric properties of the samples. Dielectric parameters are determined by fitting S parameters measurements results with those of simulations using electromagnetic software's (HFSS, CST). Results Several biological tissues of animal origin were measured ex-vivo in the frequency range 0.5–5 GHz. The dielectric parameters obtained by this method are consistent with values proposed in databases or obtained by other researchers. A very good agreement between simulations and measurements is obtained leading to a good extraction of permittivity and losses of the tissues. Conclusions This paper presents an improved microwave sensor, either for reduced dimensions as for sensitivity, able to perform dielectric characterization of material having high complex permittivity such as biological tissues. Experiments and electromagnetic simulations have been achieved on several animal tissues (chicken, beef, pork ...), and results are in good agreement with literature. Works are in progress to optimize this sensor as an applicator for medical applications. Graphical abstract Highlights • A ring resonator for non-invasive microwave dielectric characterization is proposed. • A CPW feeding structure is investigated to provide better coupling. • The distributed resonator has been miniaturized with a meander shape. • The sensor has a good accuracy even for high dielectric loss materials. • Dielectric parameters of several animal biological tissues have been extracted by ex-vivo measurements. [ABSTRACT FROM AUTHOR]

All-dielectric resonant waveguide based quantum well infrared photodetectors with high responsivity, fine spectral resolution and a wide spectral range are proposed. Without ohmic loss, the guided mode resonances lead to highly efficient absorption of the field power by the quantum wells and high Q factors for narrow spectral widths. Close to 100% resonant absorption with spectral resolution finer than 100 nm could be achieved in the long wavelength infrared region. When the incident wavelengths deviate from the intrinsic absorption range of the quantum wells, a decrease in absorption coefficient causes an increase in Q factor and in mode intensity that would compensate the absorption power. As a result, a three-fold extension of the absorption range is demonstrated. The infrared detectors with these advances simultaneously are well suited for hyperspectral detection. Further, the device could be either polarization discriminative or insensitive by using anisotropic or isotropic in-couple gratings. The good tolerance to structural deviation could facilitate the fabrication process. [ABSTRACT FROM AUTHOR]

Non-radiating wireless power transfer (WPT) systems have found extensive applications in science and technology. This paper reports the design, simulation, and implementation of a compact single-port (DC to RF) WPT system composed of two coupled dielectric resonators (DR). The DR on the transmitter side, in combination with a transistor amplifier and a series feedback circuit, forms a dielectric resonator oscillator for microwave power generation. The DR on the receiver side is coupled to the transmitter DR such that the circuit can be considered as a dual-dielectric resonator oscillator or DDRO. The DDRO is designed for optimum power transfer to the output port. The measured RF output power of the proposed WPT system at 7.5 GHz for a 10 mm spacing between the transmitting and receiving DR is measured to be 13.07dBm at a DC voltage of 3.3 V and a supply current of 32.3 mA, which shows a good agreement with our proposed method of analysis. The available bandwidth at the operating frequency of 7.5 GHz is measured to be 150 MHz which provide a relatively wide bandwidth for simultaneous data transmission. [ABSTRACT FROM AUTHOR]

In this paper, a tunable wideband circularly polarization (CP) dielectric resonator antenna (DRA) is designed and simulated. The antenna is fed by slot coupling and circular polarization is achieved by the design of the slot configuration and by the excitation of different modes. The tunable response is provided by coating graphene on the top of the radiating dielectric resonator. The proposed antenna provides a wide 10 dB impedance bandwidth of 49% (2.7–4.46 THz) and an overlapped axial ratio bandwidth of 17.34% (2.87–3.43 THz). [ABSTRACT FROM AUTHOR]