Attenuation Loss Research Articles

Electromagnetic wave absorption performance of porous geopolymer: Dual effects of fly ash on alkali activation and microwave dissipation

The simultaneous occurrence of aggregation reactions in fly ash (FA) facilitates the uniform dispersion of internal ferrite into the geopolymer. Considering the excellent impedance matching and multiple reflection effects of foam concrete, this paper develops a ‘zero-absorber’ foam geopolymer-based electromagnetic absorbing material. The effects of different densities (400, 600, 800, 1000, 1200 kg/m3) and FA contents (40 %, 50 %, 60 %, 70 %, 80 %) on the electromagnetic absorption performance of foam geopolymer are investigated, respectively. Combined with the iron element distribution and 3D pore structure by SEM and X-CT analysis, the dissipation mechanism of electromagnetic energy by FA and pore structure in foam geopolymer are further explored. Experimental results show that FA can uniformly disperse inherent ferric ions from the matrix into the geopolymer during the polymerization reaction, leading to excellent magnetic losses through magnetic moment orientation adjustment and intermolecular friction interactions without adding external absorber. Additionally, the uniformly dispersed porous structure consumes incident electromagnetic energy through reflection, scattering, coherent attenuation, and interference resonance loss effects. It shows multi-scale electromagnetic absorption effects in the ‘zero-absorber’ foam geopolymer-based electromagnetic absorbing material, including pore structure multiple reflections (millimeter scale), inter-pore wall interference resonance (micrometer scale), and ferric ion magnetic loss (nanometer scale). For the foam geopolymer with 1000 kg/m3 density and 50 % FA, it achieves the optimal electromagnetic absorbing performance with the minimum reflection loss (RL) of −34.9 dB and the effective absorption bandwidth of 14.1 GHz (RL below −10 dB) in 2–18 GHz range.

An advanced fabrication method for Yb3+-Doped optical fibers featuring AlPO4 core glass

Ytterbium (Yb)-doped fibers using aluminophosphosilicate (Yb-APS) host glass offer significant advantages over conventional aluminosilicate (Yb-AS) fibers, such as strong photodarkening resistance, higher RE-ion solubility and lower Numerical Aperture (NA), making them ideal for high-power laser applications. However, achieving optimal performance in Yb-APS fiber fabrication poses various challenges, including maintaining a precise Al3+/P5+ ratio (1:1), minimizing the central dip in the refractive index profile (RIP), ensuring proper dopant distribution, and reducing background loss. We introduce a new fabrication method for Yb-APS fiber to address these challenges. This approach entails first synthesizing amorphous Yb³⁺: AlPO4 particles, then incorporating them into the fiber core using a hybrid technique that merges Vapor Phase Delivery (VPD) with solution doping (SD). We extensively utilized various materials and optical characterizations, including XRD, FTIR, Raman spectroscopy, FESEM, and XPS, to fine-tune the composition of Yb³⁺: AlPO4. The optical characterization of the developed preform sample, including absorption, emission, and luminescent lifetime measurements, was conducted to assess the fabrication technique's suitability. The results confirmed the successful incorporation of Yb-ions into the preform core, with peaks consistent with reported values. The fiber's attenuation loss was measured, showing approximately 10 dB/km at 1200 nm. This indicates that the particles dissolved smoothly during preform and fiber processing, resulting in minimal scattering loss in the fiber core. The developed fiber demonstrated NA of 0.1, uniform RIP along the preform length with significant reduction of the central dip formation and improved spectral performance (∼1.7X broader bandwidth) compared with an equivalent Yb-AS fiber. These findings suggest the Yb-APS fiber's overall effectiveness and structural robustness, highlighting the potential of the proposed fabrication method for high-power fiber laser applications.

Constructing multi-layer heterogeneous interfaces in liquid metal graphite hybrid powder: Towards microwave absorption enhancement

Carbon based materials are widely used in the preparation of microwave absorption materials due to their low density, high attenuation loss and large specific surface area. However, their high conductivity usually leads to high reflection loss. In this study, multi-layer heterogeneous interfaces were constructed in liquid metal graphite hybrid powder to reduce reflection loss and enhance microwave absorption performance. Gallium oxide (Ga2O3) layer was formed in Ga coated graphite powder to improve impedance matching and attenuation constant via an annealing treatment. Specifically, the hybrid particles with 50 wt% Ga and being annealed at 120 °C for 2 h have a minimum reflection loss (RLmin) value of −42.68 dB and a maximum effective absorption bandwidth (EAB) of 4.11 GHz at a thickness of 3.3 mm. The hybrid particles not only have multi-layer structures with different electrical conductivity, but also form heterojunctions between different interfaces, which can further enhance dipole and interfacial polarization.

Outage probability minimization by optimal beamwidth selection for UAV-to-HAP FSO links under pointing inaccuracies

The design of a free-space optical (FSO) link between an unmanned aerial vehicle (UAV) and a high-altitude platform (HAP) in the practical scenario of generalized pointing errors (PE) and beam wandering (BWAN) is addressed. We propose to select appropriately the system parameters such as optical beamwidth at the UAV and its flight altitude so as to minimize the outage probability. First, we characterize the channel statistics by taking into account the joint influence of attenuation loss, weak atmospheric turbulence and generalized PE particularly impaired by BWAN. Second, we formulate the closed-form expressions for outage probability, where we also derive an asymptotic expression at high signal-to-noise ratios (SNR)s. Third, we derive the optimum beamwidth at the UAV leading to the instantaneous minimum outage probability under generalized PE and BWAN. Finally, we address the optimal flight altitude of the UAV to avoid strong turbulence in order to ensure efficient data transmission. Our simulation results validate both the effectiveness and the accuracy of the derived asymptotic outage probability and the adequate choice of beamwidth and flight altitude to minimize the average outage performance. For instance, our results show that at an SNR of 20 dBm, the link availability is increased from 20% (with nominal beamwidth) to more than 70% by adopting the proposed beamwidth optimization.

A novel FAM83G variant from palmoplantar keratoderma patient disrupts WNT signalling via loss of FAM83G-CK1α interaction.

Palmoplantar keratoderma (PPK) is a multi-faceted skin disorder characterized by the thickening of the epidermis and abrasions on the palms and soles of the feet. Among the genetic causes, biallelic pathogenic variants in the FAM83G gene have been associated with PPK in dogs and humans. Here, a novel homozygous variant (c.794G>C, p.Arg265Pro) in the FAM83G gene, identified by whole exome sequencing in a 60-year-old female patient with PPK, is reported. The patient exhibited alterations in the skin of both hands and feet, dystrophic nails, thin, curly and sparse hair, long upper eyelid eyelashes, and poor dental enamel. FAM83G activates WNT signalling through association with ser/thr protein kinase CK1α. When expressed in FAM83G-/- DLD1 colorectal cancer cells, the FAM83GR265P variant displayed poor stability, a loss of interaction with CK1α and attenuated WNT signalling response. These defects persisted in skin fibroblast cells derived from the patient. Our findings imply that the loss of FAM83G-CK1α interaction and subsequent attenuation of WNT signalling underlie the pathogenesis of PPK caused by the FAM83GR265P variant.

MCML-BF: A Metal-Column Embedded Microstrip Line Transmission Structure with Bias Feeders for Beam-Scanning Leakage Antenna Design.

This article proposes a novel fixed-frequency beam scanning leakage antenna based on a liquid crystal metamaterial (LCM) and adopting a metal column embedded microstrip line (MCML) transmission structure. Based on the microstrip line (ML) transmission structure, it was observed that by adding two rows of metal columns in the dielectric substrate, electromagnetic waves can be more effectively transmitted to reduce dissipation, and attenuation loss can be lowered to improve energy radiation efficiency. This antenna couples TEM mode electromagnetic waves into free space by periodically arranging 72 complementary split ring resonators (CSRRs). The LC layer is encapsulated in the transmission medium between the ML and the metal grounding plate. The simulation results show that the antenna can achieve a 106° continuous beam turning from reverse -52° to forward 54° at a frequency of 38 GHz with the holographic principle. In practical applications, beam scanning is achieved by applying a DC bias voltage to the LC layer to adjust the LC dielectric constant. We designed a sector-blocking bias feeder structure to minimize the impact of RF signals on the DC source and avoid the effect of DC bias on antenna radiation. Further comparative experiments revealed that the bias feeder can significantly diminish the influence between the two sources, thereby reducing the impact of bias voltage introduced by LC layer feeding on antenna performance. Compared with existing approaches, the antenna array simultaneously combines the advantages of high frequency band, high gain, wide beam scanning range, and low loss.

In Vivo Validation of an In Situ Calibration Bead as a Reference for Backscatter Coefficient Calculation

ObjectiveThe study described here was aimed at assessing the capability of quantitative ultrasound (QUS) based on the backscatter coefficient (BSC) for classifying disease states, such as breast cancer response to neoadjuvant chemotherapy and quantification of fatty liver disease. We evaluated the effectiveness of an in situ titanium (Ti) bead as a reference target in calibrating the system and mitigating attenuation and transmission loss effects on BSC estimation. MethodsTraditional BSC estimation methods require external references for calibration, which do not account for ultrasound attenuation or transmission losses through tissues. To address this issue, we used an in situ Ti bead as a reference target, because it can be used to calibrate the system and mitigate the attenuation and transmission loss effects on estimation of the BSC. The capabilities of the in situ calibration approach were assessed by quantifying consistency of BSC estimates from rabbit mammary tumors (N = 21). Specifically, mammary tumors were grown in rabbits and when a tumor reached ≥1 cm in size, a 2 mm Ti bead was implanted in the tumor as a radiological marker and a calibration source for ultrasound. Three days later, the tumors were scanned with an L-14/5 38 array transducer connected to a SonixOne scanner with and without a slab of pork belly placed on top of the tumors. The pork belly acted as an additional source of attenuation and transmission loss. QUS parameters, specifically effective scatterer diameter (ESD) and effective acoustic concentration (EAC), were calculated using calibration spectra from both an external reference phantom and the Ti bead. ResultsFor ESD estimation, the 95% confidence interval between measurements with and without the pork belly layer was 6.0, 27.4 using the in situ bead and 114, 135.1 with the external reference phantom. For EAC estimation, the 95% confidence intervals were –8.1, 0.5 for the bead and –41.5, –32.2 for the phantom. These results indicate that the in situ bead method has reduced bias in QUS estimates because of intervening tissue losses. ConclusionThe use of an in situ Ti bead as a radiological marker not only serves its traditional role but also effectively acts as a calibration target for QUS methods. This approach accounts for attenuation and transmission losses in tissue, resulting in more accurate QUS estimates and offering a promising method for enhanced disease state classification in clinical settings.

Hidden schematics of EMI filters

The paper presents the lumped parameters of EMI filters that must be used in the design process. In order to obtain consistent results, apart from the conventional parameters and stress de-rating factors (power dissipation, limiting voltage and current, operating temperature range, etc.), one should think also in terms of nonideal behaviour of the circuit elements in the equivalent model. Following this conduct the calculated filter characteristics (attenuation or insertion loss) will gain in accuracy.

Phase transition enhanced electromagnetic wave absorption in Cs(Pb,Fe,Co,Ni,Mn)Br3‐based high‐entropy compounds

AbstractTo address challenges such as signal interference and crosstalk, the development of novel materials with the ability of electromagnetic absorption (EMA) is imperative. In this study, the composition of the B‐site of CsPbBr3 was fixed for all samples Pb0.2Fe0.2Co0.2Ni0.2Mn0.2 with varying A/B ratios of 1:1, 1:2, and 1:3. We achieved good EMA properties for the Cs1(Pb0.2Fe0.2Co0.2Ni0.2Mn0.2)3O3, including a minimum reflection loss of 75 dB at 10.2 GHz and a 2.5 mm thickness, accompanied by an exceptionally wide effective bandwidth of 8.8 GHz. X‐ray diffraction, transmittance electron microscopy, and X‐ray photoelectron spectroscopy, etc. were used to characterize the structure, morphology, and EMA‐associated properties of CsMBr3. The presence of high entropy was validated through meticulous analysis using Rietveld and grazing‐incidence wide‐angle scattering patterns. The magnetic permeability, dielectric constant, polarization, and attenuation loss were improved with a high‐entropy ratio of 3 within the 30–50 nm crystals. Notable lattice distortion within PbBr6 and phase transition within high‐entropy alloying are the driving forces behind these enhanced EMA characteristics.

Free space optical communication system in the presence of atmospheric losses

<span>Free space optical communication is gaining importance in the field of optical communication due to its high speed and high bandwidth applications. Free space optical communication system (FSOCS) provides many benefits as compared to traditional wireless communication system and fiber optic cables. This makes this technology the reasonable extension of metropolitan area network and also provides the quick recovery during natural disaster. This system performance is limited due to the atmospheric turbulence effect and various atmospheric losses such as rain, and fog. Gamma gamma atmospheric turbulent model is used to analyze the system performance in the presence of moderate to strong atmospheric turbulence. We have designed the FSO gamma <span>gamma turbulent model with non-return to zero (NRZ) modulation format employing wavelength division multiplexing (WDM), spatial diversity multiple input multiple output (MIMO) (8×8) at various atmospheric turbulence levels and attenuation loss of 10 dB/km at the distance of 2-4 km. Using the proposed model, the link distance is enhanced up to 4km in the presence of turbulence and atmospheric losses with minimum laser transmitted power.</span></span>

Differential effect of atorvastatin and pravastatin on thoracic spine attenuation: A sub-analysis of a randomized clinical trial

BackgroundStatins reduce cardiovascular events and may improve bone mineral density. MethodsWe conducted a sub-analysis of a randomized clinical trial that investigated the differential effect of moderate vs intensive low-density lipoprotein cholesterol (LDL-C) lowering therapies on coronary artery calcium (CAC) scores, and used the acquired images to assess the change in radiological attenuation of selected thoracic vertebrae. Baseline and 12-month unenhanced chest CT scans were performed in 420 hyperlipidemic, postmenopausal women randomized to atorvastatin (ATV) 80 mg/day or pravastatin (PRV) 40 mg/day in the Beyond Endorsed Lipid Lowering with Electron Beam Tomography Scanning (BELLES) trial. Bone attenuation was measured in three contiguous thoracic vertebrae at baseline and 12 months. ResultsThere were no differences in baseline demographic and clinical characteristics between treatment arms. The median percent lowering (interquartile range) in LDL-C was significantly greater with ATV than PRV [-53 (-69 to 20)% vs −28 (-55 to 74)%, p < 0.001], although the CAC score change was similar [12 (-63 to 208)% vs 13 (-75 to 358)%; p = 0.44]. At follow-up, the median bone attenuation loss was significantly greater with PRV than with ATV [-2.6 (-27 to 11)% vs 0 (-11 to 25)%; p < 0.001]. The attenuation loss in the PRV group was comparable to that of a historical untreated general population sample. In the entire cohort, the changes in LDL-C and total cholesterol were inversely correlated with bone attenuation change (p < 0.01). In adjusted multivariable linear regression analyses, race and percent change in LDL-C were independent predictors of bone attenuation change. Age, body mass index, history of smoking, diabetes mellitus, hypertension, peripheral vascular disease, or hormone replacement therapy did not affect percent change in BMD. ConclusionsThese findings support the hypothesis that there is an interaction between bone and cardiometabolic health and that intensive lipid lowering has a beneficial effect on bone health.

Slowdown of group velocity of light in dual 1480 nm hybrid pump cascade structure of Er3+-doped optical fiber at room temperature

In this paper, a general theory of slow light transmission in dual 1480nm hybrid pump cascade structure of Er3+-doped optical fiber at room temperature is presented. Our objective is to compare the dual 1480nm hybrid pump cascade structure with the 1480nm and 980nm hybrid pump cascade structure in relative modulation attenuation, time delay, fractional delay, group velocity, refractive index, and signal optical loss. Through theoretical calculation, the maximum time delay is increased by 1.111 times and 1.162 times, and the maximum fractional delay is increased by 1.091 times and 1.132 times when the pump power ratio M=0.5 and 0.75. The loss coefficient is reduced to 0.1 when M=1. The results show that compared with the previous research methods, the dual 1480nm hybrid pump cascade structure can obtain larger time delay, fractional delay and smaller loss, which may have important applications for the optimization of optical communication systems.

Design and optimization of intelligent orchard frost prevention machine under low-carbon emission reduction

In this paper, a self-heating small frost prevention machine is designed according to the agricultural frost prevention demand in mountainous and hilly areas. Firstly, the frost prevention machine's overall structure and key components are meticulously designed and modeled using UG 3D modeling software, tailored to the specific characteristics of the stepped planting environment in the mountainous area. At the same time, the flow field of the frost prevention machine is calculated and analyzed using jet diffusion theory and thermodynamic theory. The frost prevention machine's wind speed and temperature attenuation models are established, and subsequently fine-tuned and validated using Fluent to optimize its attenuation performance and operational range. To enhance frost prevention performance, a multi-objective bionic optimization strategy is applied to systematically optimize the structural and working parameters of the machine. Moreover, an adaptive mutation hybrid frog jump algorithm is introduced to further enhance the optimization accuracy. The simulation experimental results show that structural improvements can reduce axial speed and temperature attenuation loss by approximately 45%, while slightly increasing the machine's power consumption. On the other hand, optimizing working parameters enhances wind resistance and reduces overall power consumption. The actual experimental results show that the optimized frost prevention machine achieves a frost prevention coverage radius of 10 m within the orchard, even under maximum ambient wind speeds of 2 m/s, and it dynamically adapts to environmental changes. Additionally, the synergy of multiple frost prevention machines, powered by solar panels, enhances the overall frost prevention efficiency, leading to improved economy and reduced energy consumption.

Sleeved waveguide ultrasonic sensor for monitoring concrete health

This article reports the development of a novel embedded waveguide ultrasonic sensor for detecting the onset of damage in reinforced concrete structures. A sleeved waveguide is proposed to confine guided ultrasonic waves in one-dimension, with leakage to the surrounding media only through specially created openings, thus reducing attenuation losses and enhancing the capability to inspect large structures from a single transducer location. The test frequency and mode are identified through modelling, and the interaction of leaky guided ultrasonic waves with delamination within the concrete volume is studied. Numerical simulations validated by experiments are used to study the changes in wave features such as mode velocity, wavelength and wave reflection in the delamination region, helping to estimate its location. Further simulation studies are carried out to demonstrate the possibility of using multiple waveguide sensors and sleeve openings to provide a full view of the concrete volume. The results are encouraging for practical long-range and large-scale monitoring of concrete volumes using the proposed sleeved waveguide ultrasonic sensors.

Installation and Activation of Fiber To The Home (FTTH) Networks and Macrobending Problems in the Feeder Cable Segment

Macrobending is a form of disturbance in Fiber To The Home (FTTH) networks that occurs due to macro-level bending of the cable caused by damage to the fiber optic. Macrobending frequently occurs in FTTH networks within the feeder cables. Feeder cables serve as connectors between the Optical Line Terminal (OLT) and Optical Distribution Cabinet (ODC) in the FTTH system. The occurrence of macrobending in feeder cables affects the quality of the FTTH network. In this study, the impact of macrobending is analyzed based on curvature diameters of 50 cm, 25 cm, and 5 cm on feeder cables before and after FTTH network activation. Before FTTH network activation, the High Super Luminescent Diode (HSL) is used as the input power source, whereas after activation, the input power source comes from the OLT using Small Form-factor Pluggable (SFP) modules. The attenuation (loss) before activation due to macrobending, with curvature diameters of 50 cm, 25 cm, and 5 cm, is found to be 0.02 dB, 0.05 dB, and 0.26 dB, respectively. After activation, the attenuation with the same curvature diameters is measured as 0.01 dB, 0.02 dB, and 0.20 dB, respectively. It is observed that as the curvature diameter decreases, the attenuation increases. The comparison of attenuation before and after network activation doesn't show a significant difference because the input power doesn't affect macrobending, rather it is influenced by the curvature diameter.

Cross-scale construction of SiC–Si3N4 porous ceramics with superior electromagnetic wave absorption performance

A unique ceramic structure, which comprises whiskers in its pores and is capable of high-performance microwave absorption, has been designed by comnlining a sacrificial template method with catalytic nitriding. The influence of α-Si3N4 whisker content on the composition, structure, electromagnetic properties, and absorption properties of ceramics is also studied. The α-Si3N4 whisker content is controlled by changing the catalyst amount (FeCl2·4H2O). After adding 5 wt% FeCl2·4H2O, the highest α-Si3N4 whisker content is 78.06 %. The minimum reflection loss value of SiC–Si3N4 porous ceramics with thickness of 2.7 mm is −74.09 dB, rendering it superior than that of previously reported SiC-based absorbing ceramics. The supreior absorption performance is attributed to the reasonable structural design. The unique “whiskers in its pores” structure optimizes impedance matching, enhances attenuation loss and interference cancellation at three scales. This work provides new insights and ideas for the design and development of high-performance ceramic-based absorbing materials.

Performance analysis of underwater vertical wireless optical communication links using selection combining.

In this paper, we have investigated the performance of underwater vertical wireless optical communication (UVWOC) links employing on-off key modulation for selection combining based receive diversity schemes in the presence of underwater turbulence, pointing errors, and attenuation losses. Due to variations in temperature and salinity along the ocean's depth, turbulence-induced fading affects the performance of the underwater vertical wireless optical link. The vertical link of the underwater medium influenced by a strong turbulence regime is modeled using cascaded gamma-gamma distribution considering multiple non-identical layers along with attenuation losses and pointing errors. We have derived closed-form expressions for the average bit error rate (BER) and outage probability (OP) for the link employing multiple detectors at the receiving end. The accuracy of all of the closed-form expressions derived in this paper has been validated using Monte Carlo simulations.

Power allocation algorithm for capacity maximization in 5G MIMO systems

The multiple input - multiple output (MIMO) systems have sparked a lot of research interest because of their ability to increase the system capacity without using much bandwidth. The High-Speed Train (HST) communication system's capacity was calculated by assuming that the SNR is unaffected by variations in attenuation and channel losses. Here, considering this optimization problem, a power allocation algorithm using the Water-Filling technique is proposed for the MIMO system with known Channel Side Information (CSI) at the transmitter and receiver. The presented algorithm may be efficiently optimized for improving channel capacity to achieve spectral efficiency (SE).

A review of link budget analysis of satellite communication systems

At present, the link budget of satellite systems has become an essential part of the engineering design of satellite communication systems. Through the link budget, the performance of communication equipment and the loss of signal attenuation and interference during transmission can be comprehensively analysed, and the equipment resource configuration and device parameters can be continuously optimised to meet the user's communication capacity and quality requirements while leaving appropriate margins. This study aims to explore the link budget of the satellite system, study the parameters, channel characteristics and application of the satellite link budget, and provide a theoretical basis and practical reference for the design and performance optimisation of the satellite communication system. Firstly, the research background and significance of satellite communication links are introduced, and the characteristics and advantages of other communication systems are analysed and compared from multiple dimensions. The main factors affecting the link budget, such as path loss, related atmospheric attenuation, and carrier-to-noise ratio, were mainly discussed using the parameter estimation method and comparative analysis. Then, from the perspective of channel characteristics, the critical issues of satellite link budget, including signal-to-noise ratio, code rate and other factors, are discussed. Based on the above research, this paper summarises the performance evaluation of satellite communication systems and provides a reference for practical applications.

Data-driven based ultrasonics analysis for evaluating the bond strength of concrete layers

In accelerated bridge constructions, the 3D printing process, and structural retrofitting, the bond condition between concrete layers considerably affects their structural safety and functionality. Nondestructive tests can effectively and efficiently monitor these structures' bond conditions. This paper used the convolutional neural network (CNN) and multilayer perceptron (MLP) to estimate the bond strength of concrete layers based on vital ultrasound parameters. In this regard, ultrasound pulse velocity, attenuation, maximum amplitude, and energy loss of the ultrasound wave were assessed as the inputs of the machine learning models. The target was the bi-surface shear strength of the specimens. Two different approaches were considered to evaluate the energy loss of the wave 1) in the whole specimen and 2) at the bond zone, and the models based on each dataset's accuracy were compared. Parameters resulting from the second approach were more reliable and had better consistency with bond strength variation than the first one. Moreover, the ultrasonic parameters were investigated to determine the most sensitive ultrasound factor to the different bond treatments. Accordingly, attenuation was the most susceptible parameter toward the change of bond strength.