Variations in the radiothermal radiation of the ice cover of Lake Arakhley as a geo-indicator of deformation and cracking

In January-March, 2020-2021, radiophysical studies were conducted of radiothermal radiation intensity for the testing site for Lake Arakhley, Transbaikalia, Russia. The set of equipment consisting of four microwave radiometers for the wavelengths from 0.3 to 2 cm was placed on the shore of the lake mounted on a stationary platform. The temperature and deformation of ice were simultaneously measured at the depth of 0.4 meters in two orthogonal directions: west-east and north-south. The temperature was measured with heat gauges in a vertical profile at the depths of 5, 10, 15, 20 and 40 cm. In the process of contact measurements in the period of cracking, signal impulses were recorded in the channel of the deformation sensor placed in the direction of the lake center (west-east). The measurement results were used in monitoring of the condition of the water body. It turned out that in the periods of registering the deformation impulses, changes in the radio brightness temperature and decrease in the ice temperature were observed. The microwave characteristics correlate with the temperature and deformation of the ice cover and may serve as an indicator of the meteorological conditions of the region.

Enhanced Tunability of BaTixSn1−xO3 Films on Dielectric Substrate

The structural properties of ferroelectric films of barium titanate-stannate on alumina substrates and the microwave characteristics of planar capacitive elements based on them are studied. It is established that the composition of the gas medium and the temperature of the substrate during the deposition of the film has a significant effect on the crystal structure, phase composition of the films and their electrical characteristics. Planar capacitors based on films subjected to high-temperature annealing after deposition exhibit 85% tunability at a frequency of 2 GHz, which is the best result for today.

Preparation of self-healing hydrogel toward improving electromagnetic interference shielding and energy efficiency

In this study, a self-healing hydrogel was prepared that is transparent to visible (Vis) light while absorbing ultraviolet (UV), infrared (IR), and microwave. The optothermal features of the hydrogel were explored by monitoring temperature using an IR thermometer under an IR source. The hydrogel was synthesized using sodium tetraborate decahydrate (borax) and polyvinyl alcohol (PVA) as raw materials based on a facile thermal route. More significantly, graphene oxide (GO) and graphite-like carbon nitride (g-C3N4) nanostructures as well as carbon microsphere (CMS) were applied as guests to more dissect their influence on the microwave and optical characteristics. The morphology of the fillers was evaluated using field emission scanning electron microscopy (FE-SEM). Fourier transform infrared (FTIR) attested that the chemical functional groups of the hydrogel have been formed and the result of diffuse reflection spectroscopy (DRS) confirmed that the hydrogel absorbs UV while is transparent in Vis light. The achieved result implied that the hydrogel acts as an essential IR absorber due to its functional groups desirable for energy efficiency and harvesting. Interestingly, the achieved results have testified that the self-healing hydrogels had the proper self-healing efficiency and self-healing time. Eventually, microwave absorbing properties and shielding efficiency of the hydrogel, hydrogel/GO, g-C3N4, or CMS were investigated, demonstrating the salient microwave characteristics, originated from the established ionic conductive networks and dipole polarizations. The efficient bandwidth of the hydrogel was as wide as 3.5 GHz with a thickness of 0.65 mm meanwhile its maximum reflection loss was 75.10 dB at 14.50 GHz with 4.55 mm in thickness. Particularly, the hydrogel illustrated total shielding efficiency (SET) > 10 dB from 1.19 to 18 and > 20 dB from 4.37 to 18 GHz with 10.00 mm in thickness. The results open new windows toward improving the shielding and energy efficiency using practical ways.

Breakdown Voltage Enhancement of Al0.1Ga0.9N channel HEMT With Recessed Floating Field Plate

In this paper, electrical and microwave characteristics of Al0.1Ga0.9N channel HEMTs was reported. The device performance were evaluated for conventional gate, field plate gate, and recessed floating field plate with Silicon nitride (SiN)/Hafnium oxide (HfO2) passivation. The recessed floating field plate HEMT with gate length LG = 0.8 µm, gate to drain distance LGD = 1 µm, and HfO2(SiN) passivation HEMT reports peak drain current density (IDS) of 0.282(0.288) A/mm at VGS = 0V, three terminal off-state breakdown voltage (VBR) of 677 (617) V, 6.38 Ω.mm of ON-resistance (RON), transconductance (gm,max) of 93(95) mS/mm, and FT/FMAX of 11.4/49 (12/22) GHz. The HfO2 (SiN) passivation device demonstrated the Johnson figure of merit (JFoM)) of 7.71 (7.404) THz.V and FMAX x VBR product of 33.173 (13.574) THz.V. The high JFoM along with high FMAX x VBR indicates the potential of the ultrawide bandgap AlGaN HEMTs for future power switching and high-power microwave applications. The proposed device DC characteristics are validated with reported expeimental work, which shows similar IDS and 54% and and 31% improvement in breakdown voltage on comparisons with conventional HEMT.

Architecting functionalized carbon microtube/carrollite nanocomposite demonstrating significant microwave characteristics

Biomass-derived materials have recently received considerable attention as lightweight, low-cost, and green microwave absorbers. On the other hand, sulfide nanostructures due to their narrow band gaps have demonstrated significant microwave characteristics. In this research, carbon microtubes were fabricated using a biowaste and then functionalized by a novel complementary solvothermal and sonochemistry method. The functionalized carbon microtubes (FCMT) were ornamented by CuCo2S4 nanoparticles as a novel spinel sulfide microwave absorber. The prepared structures illustrated narrow energy band gap and deposition of the sulfide structures augmented the polarizability, desirable for dielectric loss and microwave attenuation. Eventually, the architected structures were blended by polyacrylonitrile (PAN) to estimate their microwave absorbing and antibacterial characteristics. The antibacterial properties against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were scrupulously assessed. Noteworthy, the maximum reflection loss (RL) of the CuCo2S4/PAN with a thickness of 1.75 mm was 61.88 dB at 11.60 GHz, while the architected FCMT/PAN composite gained a broadband efficient bandwidth as wide as 7.91 GHz (RL > 10 dB) and 3.25 GHz (RL > 20 dB) with a thickness of 2.00 mm. More significantly, FCMT/CuCo2S4/PAN demonstrated an efficient bandwidth of 2.04 GHz (RL > 20 dB) with only 1.75 mm in thickness. Interestingly, FCMT/CuCo2S4/PAN and CuCo2S4/PAN composites demonstrated an electromagnetic interference shielding efficiency of more than 90 and 97% at the entire x and ku-band frequencies, respectively.

An Experimental and Systematic Insight into the Temperature Sensitivity for a 0.15-µm Gate-Length HEMT Based on the GaN Technology

Presently, growing attention is being given to the analysis of the impact of the ambient temperature on the GaN HEMT performance. The present article is aimed at investigating both DC and microwave characteristics of a GaN-based HEMT versus the ambient temperature using measured data, an equivalent-circuit model, and a sensitivity-based analysis. The tested device is a 0.15-μm ultra-short gate-length AlGaN/GaN HEMT with a gate width of 200 μm. The interdigitated layout of this device is based on four fingers, each with a length of 50 μm. The scattering parameters are measured from 45 MHz to 50 GHz with the ambient temperature varied from −40 °C to 150 °C. A systematic study of the temperature-dependent performance is carried out by means of a sensitivity-based analysis. The achieved findings show that by the heating the transistor, the DC and microwave performance are degraded, due to the degradation in the electron transport properties.