Low-loss Materials Research Articles

All-Dielectric Dual-Band Anisotropic Zero-Index Materials

Zero-index materials, characterized by near-zero permittivity and/or permeability, represent a distinctive class of materials that exhibit a range of novel physical phenomena and have potential for various advanced applications. However, conventional zero-index materials are often hindered by constraints such as narrow bandwidth and significant material loss at high frequencies. Here, we numerically demonstrate a scheme for realizing low-loss all-dielectric dual-band anisotropic zero-index materials utilizing three-dimensional terahertz silicon photonic crystals. The designed silicon photonic crystal supports dual semi-Dirac cones with linear-parabolic dispersions at two distinct frequencies, functioning as an effective double-zero material along two specific propagation directions and as an impedance-mismatched single-zero material along the orthogonal direction at the two frequencies. Highly anisotropic wave transport properties arising from the unique dispersion and extreme anisotropy are further demonstrated. Our findings not only show a novel methodology for achieving low-loss zero-index materials with expanded operational frequencies but also open up promising avenues for advanced electromagnetic wave manipulation.

Super Low Profile 5G mmWave Highly Isolated MIMO Antenna with 360∘ Pattern Diversity for Smart City IoT and Vehicular Communication

This study introduces a planar folded super low profile 5G mmWave monopole antenna for small IoT devices with superior efficiency and gain. Low-loss Rogers RT-5880 substrate material has been utilized to achieve higher efficiency, gain, and diversity performance in a relatively compact size. The unit element planar monopole antenna has been designed within 6.15×5.13×0.8mm3 with a partial ground. Four unit element antenna was orthogonally arranged on alternating sides of the substrate plane with narrow inter-component spacing in the multiple input multiple output (MIMO) system. The integration of the double negative (DNG) metamaterial array on the antenna led to a cumulative improvement in the overall performance of the antenna, which includes gain, efficiency, and isolation. The minimum isolation of the antenna increased by 11 dB with substrate-loaded metamaterial. The proposed MIMO antenna model with substrate-loaded metamaterial demonstrates 8 GHz instantaneous bandwidth (33.1 GHz - 41.1 GHz), 0.001 envelope correlation coefficient (ECC), diversity gain (DG) greater than 9.99 dB, channel capacity loss (CCL) less than 0.2bits/s/Hz, and a total active reflection coefficient (TARC) of 25 dB, which suggests that the diversity characteristics of the MIMO antenna system is impressive. Moreover, a densely packed 12-element antenna model has been introduced in this study with 360∘ pattern diversity, capable of receiving signals from any direction. Three 4-element MIMO systems have been arranged in an architecture to develop the 12-element MIMO system, and the size of the 12-element MIMO architecture is 15×15×15mm3. Despite having this compact size and dense packing, the 12-element MIMO antenna model shows similar diversity performance as the 4-element antenna model. Analog equivalent circuit models or resistor-inductor-capacitor (RLC) equivalent systems for the antenna models were created. A concept of a 128-element massive MIMO antenna has been presented to support the end devices, creating an application scenario of an IoT-interconnected smart city.

Precision multi-mode microwave spectroscopy of paramagnetic and rare-earth ion spin defects in single crystal calcium tungstate

We present experimental observations of dilute ion spin ensemble defects in a low-loss single crystal cylindrical sample of CaWO4 cooled to 30 mK in temperature. Crystal field perturbations were elucidated by constructing a dielectrically loaded microwave cavity resonator from the crystal. The resonator exhibited numerous whispering gallery modes with high Q-factors of up to 3×107, equivalent to a loss tangent of ∼3×10−8. The low loss allowed precision multi-mode spectroscopy of numerous high Q-factor photon–spin interactions. Measurements between 7 and 22 GHz revealed the presence of Gd3+, Fe3+, and another trace species, inferred to be rare-earth, at concentrations on the order of parts per billion. These findings motivate further exploration of prospective uses of this low-loss dielectric material for applications regarding precision and quantum metrology, as well as tests for beyond standard model physics.

Machine learning-based technique for directivity prediction of a compact and highly efficient 4-port MIMO antenna for 5G millimeter wave applications

Miniaturized Millimeter Wave (mm-wave) MIMO antenna arrays with an observed 10-dB impedance broad bandwidth of 3.7 GHz (25.785–29.485) are the focus of this study's design and analysis for a 5G application. Rogers RT/duroid 5880, a low-loss dielectric material, is utilized in the antenna's fabrication. For MIMO antenna design down to the lowest frequency, the substrate and ground must have dimensions of 3.3λ0 × 3.3λ0. Besides compact, the suggested design has a supreme gain of 8.9 dB, isolation greater than 29.24, and a maximum efficiency rating of 98.4 %. A Diversity Gain (DG) has a value that is greater than 9.99, whereas an Envelope Correlation Coefficient ECC) has a value that is less than 0.00005. The effectiveness of machine learning (ML) models can be estimated using a variety of different metrics, including the variance score, R square, mean square error (MSE), mean absolute error (MAE), and root mean square error (RMSE). Out of the five ML models, the one that has the greatest accuracy and has a low margin of error when predicting directivity is the Random Forest Regression model. In conclusion, the data from the CST and ADS modeling as well as the actual and expected outcomes from machine learning demonstrate that the recommended antenna is a potential candidate for use with 5G.

Continuously-tunable, compact, freespace notch-filter design using an all-dielectric metagrating capped with a low-loss phase change material

Abstract Active metasurfaces utilizing phase change materials (PCMs) are currently under investigation for applications in free-space optical communication, optical signal processing, neuromorphic photonics, quantum photonics, and compact LiDAR. Attention has now turned towards novel PCM like Sb2S3 which exhibit lower optical absorption and reasonable values of refractive-index contrast in comparison to traditional data-storage PCM. We propose and numerically study the class of all-dielectric metagratings capped with low-loss PCM and predict the possibility of continuously tunable resonances whose quality factors degrade gracefully during the amorphous-to-crystalline phase transition of the PCM. Specifically, we consider the CMOS-compatible silicon-nitride on silica substrate material platform for simple and asymmetric metagratings (in particular, the symmetric-broken dimerization) and Sb2S3 capping. Our numerical study predicts that notch-filters operating around the 1550 nm NIR wavelength window can be achieved with tuning range of over 76 nm with Q-factors ranging from 784 (amorphous-phase) to 510 (crystalline-phase) (a degradation in Q of about 35%) and insertion loss of about 0.9 dB. These performance figures are a significant improvement over previously published designs utilizing data-storage PCMs and other traditional notch-filter mechanisms. We examine the influence of grating dimerization and geometrical parameters on performance metrics of the notch-filter and predicts the possibility to trade-off rejection-band and in-band spectral transmission properties. Lastly, we perform a study of all-optical phase change mechanism. Our study is promising for the miniaturization of tunable notch-filter based optical systems.

Analysis of the influence of the parameters of a new low-loss magnetic material of the stator core on the efficiency of a high speed electric motor

Analysis of the influence of the parameters of a new low-loss magnetic material of the stator core on the efficiency of a high speed electric motor

Ultrasonic-assisted stripping of single-crystal SiC after laser modification

Laser stripping technology is an advanced processing method with high efficiency and low material loss, which can greatly reduce material loss in the production process of single-crystal SiC wafer, but the single-crystal SiC ingot still have a certain bonding force after laser modification. Ultrasonic vibration can reduce the bonding force and thus strip single-crystal SiC wafer. In order to investigate the effect of ultrasonic vibration on the reduction of the bonding force of single-crystal SiC internal modification layer, through the ultrasonic-assisted stripping of single-crystal SiC orthogonal experiment, the ultrasonic vibration parameters of ultrasonic frequency, vibration time and ultrasonic power of the three indexes of the reduction of the bonding force was analyzed. The results show that the bonding force of the modified layer decreased by 25 %–60 % after ultrasonic vibration. Variance analysis of the experiment results showed that the main factors influencing the bond strength reduction were vibration time and ultrasonic power in turn. When the vibration time is longer and the ultrasonic power is higher, the stripping force decreases more, and the stripping force of single-crystal SiC wafers decreases up to 60 % under the condition of vibration time of 5min and ultrasonic power of 700 W. Through analysis of the single-crystal SiC cross-section, distinct cleavage steps and cleavage channels are evident. The laser-modified region exhibits defect such as nano-pores, micro-cracks, and nano-particles.After the single-crystal SiC laser modification process was upgraded, the distance between the ultrasonic tool head and the single-crystal SiC was 1.5 mm can directly strip off the single-crystal SiC wafer. And eventually stripped 6-inch single-crystal sic wafers. Therefore, ultrasonic vibration can increase the internal defects in the single-crystal SiC modified layer, causing crack expansion to occur and ultimately stripping the single-crystal SiC wafer.

Low-loss Se-based phase-change materials for infrared photonics

The work presents the results of comprehensive studies of the optical and transport properties, phase transition heats, the X-Ray diffraction and Raman spectra of Ge2Sb2Se4Te1, Sb2Se3 and Bi2Se3 samples obtained by vacuum thermal deposition. We demonstrate a high contrast in the refractive index and extinction coefficient in the spectral range in wavelengths of 500–1800 nm and transmissivity and reflectivity spectra in the range in wavelengths of 500–3000 nm. The investigated materials show low optical losses and high figure of merit in much of the IR-spectrum. Changes in structural properties are analyzed by XRD and Raman methods. Features of phase transformations are described by thermogravimetry and differential scanning calorimetry.

Influence of the inner roughness of powder channels on the powder propagation behavior in laser metal deposition

The powder propagation behavior of powder nozzles for the laser metal deposition process has a significant influence on powder utilization rate and track geometry. A well-focused powder stream will lead to a higher process efficiency and lower material loss. Powder channels with different roughness and a constant diameter of 1.5 mm were placed by wire electrical discharge machining into a copper alloy printed by powder bed fusion. Nickel base powder with a size of −106 to +45 μm was delivered through the powder channels with varied carrier gas flow rates and varied powder mass flow rates. High-speed imaging was used to analyze the powder flow. From these recordings, the dispersion angle of the powder stream from single channels could be measured as well as the velocity of particles. Moreover, the relationship between individual particle velocity and individual particle flight angle was investigated. It was found that the inner roughness of powder channels has a major impact on powder propagation behavior. It could be shown that with a decrease in Ra from 2.16 to 0.27 μm the divergence angle decreased by around 61% while the particle velocity was increased by at least 28% for all varied parameters. Particles with a high velocity tend to have a lower particle flight angle.

Highly sensitive photonic crystal fiber chemical sensor for detecting carbon disulfide and bromoform in the THz regime

In this study, an innovative photonic crystal fiber (PCF) designed specifically for the detection of carbon disulfide and bromoform liquid chemicals within the THz frequency range was introduced. The PCF’s structural design was achieved using the Finite Element Method (FEM) and Perfectly Matched Layer (PML) boundary conditions within COMSOL Multiphysics, ensuring precision through appropriate numerical parameters. Six distinct configurations were developed, incorporating circular, square, rectangular slotted, benzene-shaped circular, and two elliptical core designs, as well as an eight-elliptical core design. The PCF models were constructed utilizing the dielectric material TOPAS for accurate simulation and analysis. Various crucial parameters of the proposed PCF were examined across a wide THz spectrum spanning from 0.2 to 1.2 THz. The PCF model exhibited a peak output at the operating frequency of 0.8 THz for the square-shaped core design, achieving a relative sensitivity of 96.891% for bromoform and 95.603% for carbon disulfide. Remarkably low material losses of 0.0081104 cm−1 for bromoform and 0.006703 cm−1 for carbon disulfide were observed, along with a core power fraction of 93.107% for bromoform and 94.263% for carbon disulfide. The effective area was determined to be 1.77 × 10−07 μm2 for bromoform and 1.70 × 10−07 μm2 for carbon disulfide, while the confinement loss measured 2.25 × 10−17 dB/cm for bromoform and 4.76 × 10−17 dB/cm for carbon disulfide. These superior attributes strongly suggest that this model will be crucial in applications like supercontinuum generation, sensing, and biomedical imaging.

A novel high hardness and low loss Mg5Ga2Sn2O12 ceramic with spinel-structure

Inorganic oxides with a spinel structure play an indispensable role in various applications because of their stability and exceptional performance. This study prepared Mg5Ga2Sn2O12 ceramics using the solid-state method. TEM analysis reveals that the ceramics show local lattice distortions. When the sintering temperature is 1480 °C, the relative density and Vickers hardness of Mg5Ga2Sn2O12 ceramics are 96.8 % and 12.58 GPa, respectively. The Mg5Ga2Sn2O12 ceramics exhibit optimum microwave dielectric properties, with εr = 8.57, Q × f = 138,769 GHz, and τf = −24.7 ppm/°C. Far-infrared fitting shows that the vibration mode in the low-wave number region has a significant influence on the dielectric properties of ceramics. The P–V−L theory indicates that the Sn–O bond has the most significant influence on εr and Q × f. Given these advantages, Mg5Ga2Sn2O12 ceramics hold promise for applications in low-loss dielectric materials.

Reconfigurable and polarization-dependent optical filtering for transflective full-color generation utilizing low-loss phase-change materials

All-dielectric metasurface, which features low optical absorptance and high resolution, is becoming a promising candidate for full-color generation. However, the optical response of current metamaterials is fixed and lacks active tuning. In this work, we demonstrate a reconfigurable and polarization-dependent active color generation technique by incorporating low-loss phase change materials (PCMs) and CaF2 all-dielectric substrate. Based on the strong Mie resonance effect and low optical absorption structure, a transflective, full-color with high color purity and gamut value is achieved. The spectrum can be dynamically manipulated by changing either the polarization of incident light or the PCM state. High transmittance and reflectance can be simultaneously achieved by using low-loss PCMs and substrate. The novel active metasurfaces can bring new inspiration in the areas of optical encryption, anti-counterfeiting, and display technologies.

A flow through coaxial cell to investigate high frequency broadband complex permittivity: Design, calibration and validation

This paper presents a new apparatus: a large flow through coaxial cell designed for broadband dielectric characterization of material under controlled hydraulic and chemical boundaries. The cell is calibrated with a single measurement made on a perfectly known dielectric liquid (deionized water) together with an optimization procedure. Then, two methods are proposed to compute the dielectric characteristics: an iterative solver and an optimization method. These two methods are systematically investigated for two reference liquids: a low loss dielectric material (ethylene glycol) and high loss dielectric liquid (saline solutions with different concentration). Tabulated data were used to perform a quantitative error analysis in terms of estimated complex permittivity. The results have shown high performance in terms of real part and good performance in terms of real part. The measurements on saline solution also highlight the impact of electrode polarization with dramatic effect in the lower part of the frequency range.

Numeral simulation of solution mixing effect and product preparation effect in the process of preparing cerium oxide by microwave heating

Microwave heating has the characteristics of simple control and high efficiency, in which electromagnetic force plays an important role. Using the UDF function and energy equation in FLUENT software, the electromagnetic force model in the tube is established. The mixing process of cerium chloride solution under different heating modes, the mixing effect of Lorentz force and the preparation process of cerium oxide under different inlet material velocities were numerically simulated. CFD-Post and MATLAB software are used to post-process the data of the whole fluid area. Through the above analysis, the best process conditions of numerical simulation and experiment are finally determined. The results show that microwave heating has better mixing effect and lower material loss compared with conventional heating, in which electromagnetic force plays a promoting role; Under the condition of microwave heating, the product conversion rate is high, and the concentration of cerium oxide is high and distributed evenly. The more appropriate mixing method of cerium chloride and preparation method of cerium oxide are microwave heating, and the more appropriate inlet velocity of materials is 0.15 m/s.

Anti-Resonant Hollow-Core Fibers with High Birefringence and Low Loss for Terahertz Propagation

A new type of anti-resonant hollow-core fiber for terahertz waveguides is proposed. By introducing central support pillars and an elliptical structure, the fiber achieves high birefringence while maintaining low confinement loss and low material absorption loss. The fiber structure is optimized through simulation using the finite element method. The optimized fiber exhibits a birefringence of up to 1.22 × 10−2 at a frequency of 1 THz, with a confinement loss of 8.34 × 10−6 dB/cm and a material absorption loss of 7.17 × 10−3 dB/cm. Furthermore, when the bending radius of the fiber is greater than 12 cm, the bending loss of the anti-resonant optical fiber at 1 THz is less than 1.36 × 10−4 dB/cm, demonstrating good bending resistance and high practical value. It is expected to play a significant role in optical communication systems.

Rewritable Photonic Integrated Circuit Canvas Based on Low-Loss Phase Change Material and Nanosecond Pulsed Lasers.

Programmable photonic integrated circuits (PICs) are an increasingly important platform in optical science and engineering. However, current programmable PICs are mostly formed through subtractive fabrication techniques, which limits the reconfigurability of the device and makes prototyping costly and time-consuming. A rewritable PIC architecture can circumvent these drawbacks, where PICs are repeatedly written and erased on a single PIC canvas. We demonstrate such a rewritable PIC platform by selective laser writing a layer of wide-band-gap phase change material (PCM) Sb2S3 with a low-cost benchtop setup. We show arbitrary patterning with resolution up to 300 nm and write dielectric assisted waveguides with a low optical loss of 0.0172 dB/μm. We envision that using this inexpensive benchtop platform thousands of PIC designs can be written, tested, and erased on the same chip without the need for lithography/etching tools or a nanofabrication facility, thus reducing manufacturing cost and increasing accessibility.

Crystal structure and dielectric properties of Ln2Ti2SiO9 (Ln = Pr and Nd)

Low loss and high dielectric constant materials are essentially desired for wide varieties of applications in electronics and communication technology. Herein the structure and dielectric properties of two titanosilicates, Ln2Ti2SiO9, for Ln = Pr3+ and Nd3+ are reported. Both materials are isostructural and have layered structure with layers of [LnTi2SiO9]3- and Ln3+ ions. Electrical properties of both have been analyzed by using the temperature and frequency dependent permittivity, loss, conductivity and modulus data. At room temperature, appreciable relative permittivity (35 for Nd2Ti2SiO9 and 22 for Pr2Ti2SiO9 over the frequency range of 100 Hz to 5 MHz) and low dielectric loss (like 0.007–0.03 at 100 Hz and 10−4-10−3 at 1 MHz). Analysis of dc-conductivity data of both compounds indicate that the conduction in both materials is due to the correlated barrier hopping (CBH) of polarons. The relaxation peak of modulus spectra indicates more non-Debye like relaxation in Pr2Ti2SiO9 than that in Nd2Ti2SiO9, and that is possibly due to increased correlation in the dynamics of hopping polarons in Pr2Ti2SiO9.

Thermal characterization of ceramic pills at millimeter waves with a TE01δ cavity resonator

The progress in 5G/6G technology prompts a demand for new materials operating at millimeter waves that can be exploited as substrates for electronic devices or antennas. In particular, a rapid development of millimeter wave band communication technology demands ceramic materials, which could be applied in low temperature cofired ceramic (LTCC) techniques. This kind of ceramics should possess a low dielectric constant (εr), a low loss tangent (tanδ) and a near-zero temperature coefficient. In the view of above, there is an urgent need for accurate and reliable material microwave characterization techniques that can operate at frequencies well above 15 GHz. Due to the fact that the majority of LTCC ceramic materials can be produced in a cylindrical shape, a suitable characterization method exploits a cylindrical resonator operating at a TE01δ mode, which is dedicated to the characterization of low-loss materials also as a function of temperature.

Analytic ellipsometric measurement for materials under bulk encapsulation

Accurate measurement of the dielectric functions of emerging optical materials is of great importance for advancements in solid-state physics. However, it is rather challenging since most materials are highly active in ambient conditions, which makes in-situ measurements tough. Here, we report an analytical ellipsometry method (AEM) accessible in ambient conditions for measuring the dielectric functions of chemically reactive materials under bulk encapsulation. Taking the highly pursued low-loss plasmonic materials, such as sodium films, as an example, the effectiveness and measuring errors of the proposed AEM have been systematically demonstrated. This verifies AEM’s superiority in overcoming the limitations of traditional spectroscopic ellipsometry methodologies, which include complex multi-parameter fitting procedures and the issue of potentially unphysical results, especially in newly developed low-loss materials. Our results will provide a generalized and convenient ellipsometric measurement strategy for sensitive materials under bulk encapsulation.

Extension of the method of images in electromagnetism at an interface between two lossless dielectric media

The method of images is well-known in electrostatics and electromagnetic radiation problems, like currents on a metallic ground plane to replace the original problem. This paper extends the method of images to the case of a dipole antenna on a dielectric ground plane, like concrete, considering that from 1 GHz to 40 GHz is a low-loss dielectric material. The contribution of this work is the model that expresses the electric and magnetic fields through the method of imaging for a dipole on a dielectric ground plane, for vertical and horizontal polarization. These results can be applied to propagation models to the mobile communications like 5G and 6G technologies. The wave impedance of the electromagnetic wave obtained has been discussed. This work allows replacing the treatment of Sommerferld's of a dipole antenna on a dielectric ground with losses with the extension of the image method.