Search Results (296)

This systematic review explores recent advancements in antenna and rectifier systems for radio frequency (RF) energy harvesting within the gigahertz frequency range, aiming to support the development of sustainable and efficient low-power electronic applications. Conducted under the PRISMA methodology, our review filtered 2465 initial records down to 80 relevant studies, addressing three research questions focused on antenna design, operating frequency bands, and rectifier configurations. Key variables such as antenna type, resonant frequency, gain, efficiency, bandwidth, and physical dimensions were examined. Antenna designs including fractal, spiral, bow-tie, slot, and rectangular structures were analyzed, with fractal antennas showing the highest efficiency, while array antennas exhibited lower performance despite their compact dimensions. Frequency band analysis indicated a predominance of 2.4 GHz and 5.8 GHz applications. Evaluation of substrate materials such as FR4, Rogers, RT Duroid, textiles, and unconventional composites highlighted their impact on performance optimization. Rectifier systems including Schottky, full-wave, half-wave, microwave, multi-step, and single-step designs were assessed, with Schottky rectifiers demonstrating the highest energy conversion efficiency. Additionally, correlation analyses using boxplots explored the relationships among antenna area, efficiency, operating frequency, and gain across design variables. The findings identify current trends and design considerations crucial for enhancing RF energy harvesting technologies. Full article

The development of power engineering requires the introduction of new materials and technologies to improve the quality and durability of products. One promising direction is the creation of heat-protective coatings for the protection of working surfaces of turbine blades of gas turbine engines operating at temperatures up to 1000–1200 °C. Intermetallic coatings based on iron aluminides (Fe₃Al, FeAl) have high resistance to oxidation due to the formation of an oxide layer: Al₂O₃. However, their application is limited by brittleness due to the so-called third element effect, which can be reduced through alloying with chromium. In this study the processes of formation of Fe–Al–Cr intermetallic coatings produced by air plasma spraying and the mechanisms affecting their stability at high temperatures were investigated. Experimental studies included the analysis of the microhardness, wear resistance, and corrosion resistance of coatings, as well as their phase composition and microstructure. The results showed that the optimization of sputtering parameters, especially in the FrCrAl (30_33) mode, promotes the formation of a coating with improved tribological and anticorrosion characteristics, which is associated with its dense and uniform structure. These data have an important practical significance for the creation of wear-resistant and corrosion-resistant coatings applicable in power engineering. Full article

Fire-resistant coatings have emerged as crucial materials for reducing fire hazards in various industries, including construction, textiles, electronics, and aerospace. This review provides a comprehensive account of recent advances in fire-resistant coatings, emphasizing environmentally friendly and high-performance systems. Beginning with a classification of traditional halogenated and non-halogenated flame retardants (FRs), this article progresses to cover nitrogen-, phosphorus-, and hybrid-based systems. The synthesis methods, structure–property relationships, and fire suppression mechanisms are critically discussed. A particular focus is placed on bio-based and waterborne formulations that align with green chemistry principles, such as tannic acid (TA), phytic acid (PA), lignin, and deep eutectic solvents (DESs). Furthermore, the integration of nanomaterials and smart functionalities into fire-resistant coatings has demonstrated promising improvements in thermal stability, char formation, and smoke suppression. Applications in real-world contexts, ranging from wood and textiles to electronics and automotive interiors, highlight the commercial relevance of these developments. This review also addresses current challenges such as long-term durability, environmental impacts, and the standardization of performance testing. Ultimately, this article offers a roadmap for developing safer, sustainable, and multifunctional fire-resistant coatings for future materials engineering. Full article

The enthalpy of formation (dH_m) is a crucial parameter in evaluating the structural stability of organic semiconductors. In this study, we employed machine learning (ML) models to predict the dH_m of organic semiconductors. The current results show that Kappa2 and NumRotableBonds are highly correlated with the dH_m, indicating their importance in determining the stability of these materials. Using Gradient Boosting, Random Forest, and Extra Trees models, we achieved a high R² value of 0.68–0.70, demonstrating the effectiveness of these models in predicting the dH_m. Further analysis using SHAP values revealed that Kappa2 and fr_uncrch_alkane are the most important descriptors in determining the dH_m. These findings provide valuable insights into the structural evaluation and stability of organic semiconductors and highlight the potential of ML models in predicting key properties of these materials. Full article

This study investigates the shell hydroforming of 1.2 mm-thick AA5052 aluminum alloy sheets to produce hemispherical domes which possess inherent spatial symmetry about their central axis. Shell hydroforming is widely used in fabricating lightweight, high-strength components for aerospace, automotive, and energy applications. The forming process was driven by a spatially symmetrical internal pressure distribution applied uniformly across the blank to maintain balanced deformation and minimize geometrical distortion. Experimental trials aimed at achieving a dome depth of 50 mm revealed wrinkle formation at the blank periphery caused by circumferential compressive stresses symmetrical in nature with respect to the dome’s central axis. To better understand the forming behavior, a validated 3D finite element (FE) model was developed, capturing key phenomena such as material flow, strain rate evolution, hydrostatic stress distribution, and wrinkle development under symmetric boundary conditions. The effects of the internal pressure (IP), blank holding force (BHF), coefficient of friction (CoF), and flange radius (FR) were systematically studied. A strain rate of 0.1 s⁻¹ in the final stage improved material flow, while a symmetric tensile hydrostatic stress of 160 MPa facilitated dome expansion. Although tensile stresses can induce void growth, the elevated strain rate helped suppress it. An optimized parameter set of IP = 5.43 MPa, BHF = 140 kN, CoF = 0.04, and FR = 5.42 mm led to successful formation of the 50 mm dome with 19.38% thinning at the apex. Internal pressure was identified as the most critical factor influencing symmetric formability. A process window was established to predict symmetric failure modes such as wrinkling and bursting. Full article

In this study, a novel improved ultra-wideband (UWB) antipodal Vivaldi antenna suitable for breast cancer detection via microwave imaging was designed. The antenna was made more directional by adding three pairs of nestings to the antenna fins by adding elliptical patches. The frequency operating range of the proposed antenna is UWB 3.6–13 GHz, its directivity is 11 dB, and its gain is 9.27 dB. The antenna is designed with FR4 dielectric material and dimensions of 34.6 mm × 33 mm × 1.6 mm. It was demonstrated that the bandwidth, gain, and directivity of the proposed antenna meet the requirements for UWB radar applications. The Vivaldi antenna was tested on an imaging system developed using the CST Microwave Studio (CST MWS) program. In CST MWS, a hemispherical heterogeneous breast model with a radius of 50 mm was created and a spherical tumor with a diameter of 0.9 mm was placed inside. A Gaussian pulse was sent through Vivaldi antennas and the scattered signals were collected. Then, adaptive Wiener filter and image formation algorithm delay-multiply-sum (DMAS) steps were applied to the reflected signals. Using these steps, the tumor in the breast model was scanned at high resolution. In the simulation application, the tumor in the heterogeneous phantom was detected and imaged in the correct position. A monostatic radar-based system was implemented for scanning a breast phantom in the prone position in an experimental setting. For experimental measurements, homogeneous (fat and tumor) and heterogeneous (skin, fat, glandular, and tumor) breast phantoms were produced according to the electrical properties of the tissues. The phantoms were designed as hemispherical with a diameter of 100 mm. A spherical tumor tissue with a diameter of 16 mm was placed in the phantoms produced in the experimental environment. The dynamic range of the VNA device used allowed us to image a 16 mm diameter tumor in the experimental setting. The developed microwave imaging system shows that it is suitable for the early-stage detection of breast cancer by scanning the tumor in the correct location in breast phantoms. Full article

Enhanced demand for the development of sustainable materials has generated significant research interest in products containing biomass-derived fibers, such as the fibers extracted from the energy crop Sida hermaphrodita (SH). Green chemicals and green methods, such as microwave treatment, have been used for the isolation of fibers from biomass waste. In this study, long extracted fibers were used as a reinforcement of the PLA matrix to give them high strength, which is required for high-performance biocomposites. To enable composite usage in automotive industry, several additives were applied to enhance their mechanical, thermal, and antimicrobial properties. Therefore, vegetable drying oil, montmorillonite nanoclay (MMT), and milled cork were used to improve their mechanical and thermal properties. Zinc oxide (ZnO) was applied to enhance the biocomposite’s antimicrobial properties, which were confirmed through significant bacterial reduction across all tested biocomposite variants, particularly in samples functionalized with ZnO, cork, and montmorillonite. Additionally, X-ray microtomography provided detailed insight into fiber dispersion and internal structural heterogeneity, which is crucial for evaluating mechanical performance and flame-retardant behavior. All characterization methods, including mechanical ones, lead to the conclusion that green and sustainable biocomposites based on PLA and Sida hermaphrodita fibers treated with antimicrobial (AM) and flame-retardant (FR) agents can be successfully applied for a wide variety of antimicrobial and flame-retardant products. Full article

A PCB stator axial flux permanent magnet (AFPM) motor is presented that overcomes the manufacturing challenges associated with the complex geometry of conventional stators by employing a PCB substrate. Traditionally, AFPM motors are produced by winding coils around the stator teeth, a process that requires specialized winding machinery and is both labor intensive and time consuming, ultimately incurring considerable manufacturing costs and delays. In contrast, PCB substrates offer significant advantages in manufacturability and mass production, effectively resolving these issues. Furthermore, the primary material used in PCB substrates, FR-4, exhibits a permeability similar to that of air, resulting in negligible electromagnetic cogging torque. Cogging torque arises from the attraction between permanent magnets and stator teeth, creating forces that interfere with motor rotation and generate unwanted vibration, noise, and potential mechanical collisions between the rotor and stator. In the PCB stator design, the conventional PCB circuit pattern is replaced by the motor’s coil configuration, and the absence of stator teeth eliminates these interference issues. Consequently, a slotless motor configuration with minimal vibration and noise is achieved. The PCB AFPM motor has been applied to a vehicle-mounted electric water pump (EWP), where mass production and space efficiency are critical. In an EWP, which integrates the impeller with the motor, it is essential that vibrations are minimized since excessive vibration could compromise impeller operation and, due to fluid resistance, require high power input. Moreover, the AFPM configuration facilitates higher torque generation compared to a conventional radial flux permanent magnet synchronous motor (RFPM). In a slotless AFPM motor, the absence of stator teeth prevents core flux saturation, thereby further enhancing torque performance. AC losses occur in the conductors as a result of the magnetic flux produced by the permanent magnets, and similar losses arise within the PCB circuits. Therefore, an optimized PCB circuit design is essential to reduce these losses. The Constant Trace Conductor (CTC) PCB circuit design process is proposed as a viable solution to mitigate AC losses. A 3D finite element analysis (3D FEA) model was developed, analyzed, fabricated, and validated to verify the proposed solution. Full article

Light is essential for vegetable growth, with varying combinations of light quality affect differently on plant growth and development. In order to clarify the optimal light quality combination of celery LEDs, under hydroponic and full LED light conditions, this study investigated distinct combinations of light quality have various impacts on the growth and quality of celery using “Hongcheng Red Celery” as test material. Red-blue (R:B = 3:1, control), red-blue-purple (R:B:P = 3:1:1, purple (P)), red-blue-green (R:B:G = 3:1:1, green (G)), red-blue-yellow (R:B:Y = 3:1:1, yellow (Y)), and red-blue-far-red (R:B:FR = 3:1:1, far-red (FR)) light conditions were set up in the experiment, and plants were treated for 45 days. The findings indicated that the best growth in celery was achieved under the RBP, while RBG inhibited the growth of celery. The chlorophyll a and total chlorophyll contents of celery leaves were increased significantly by the RBP treatments compared to RB. In addition, net photosynthetic rate, stomatal conductance, and transpiration rate were highest in RBP. In RBP treatment, soluble protein, vitamin C, total phenols, total flavonoids, Ca, Fe, Zn in leaves and petioles of celery were higher than in other treatments. And the anthocyanins content in celery petioles was higher than other treatments. The RBP and RBG treatments reduced nitrate content. The RBP treatment increased the activities of apigenin synthesis-related enzymes CHS, FNS, ANS, and up-regulated expression of related genes CHS, FNS, and ANS, and increased apigenin content. In summary, the RBP is more favorable for celery growth and nutrient synthesis. Full article

Background and Objectives: This study aimed to evaluate the safety, efficacy and outcomes of ultramini percutaneous nephrolithotomy (UM-PNL) in preschool-aged children with kidney stones. Materials and Methods: A retrospective analysis was conducted on 711 renal units of 676 paediatric patients aged 0–6 years who underwent UM-PNL between April 2014 and July 2024. The children’s demographic data, stone characteristics, operative details and postoperative outcomes were analysed. The procedure was performed using a 9.5 Fr sheath and a 7.5 Fr nephroscope, with laser lithotripsy applied. Postoperative follow-up included imaging and a clinical assessment of complications. Results: The mean patient age was 34.2 months (range: 5–72 months). Haematuria (36.8%) and urinary tract infections (24.5%) were the most common presenting symptoms. The mean stone size was 16.2 mm, and the stone-free rate was 89.2% after the first session, increasing to 96.4% with additional interventions. The mean operative time was 38 min. No major complications were observed; 8.4% of cases had Clavien grade 3b complications, most of which were managed conservatively. Blood transfusion was required in 2.6% of the cases. Conclusions: UM-PNL is a safe and effective treatment method for kidney stones in preschool-aged children, characterized by high stone-free rates and a low risk of complications. With proper patient selection and experienced surgical teams, UM-PNL can be considered a first-line option in paediatric stone management. Full article

Objectives: Trauma to maxillary incisors is frequent, and requires timely, conservative management for optimal prognosis. This in vitro study evaluated the fracture resistance (FR) and orthodontic bracket bond strength (BS) of incisors following incisal fragment reattachment using various restorative techniques. Materials and Methods: Two independent tests—FR testing (Newtons) and BS testing (megapascals)—were conducted. Eighty intact human maxillary central incisors (n = 40/test), standardized in size and shape using a digital caliper (Mitutoyo, ±0.01 mm), were embedded in acrylic resin and numbered. An uncomplicated crown fracture was induced in 64 teeth (n = 32/test), and the teeth were randomly assigned (simple randomization using Excel’s RAND function) to five groups (n = 8/group/test): (1) intact teeth (negative control, NC); (2) nanohybrid composite buildup using Filtek Z250 and Single Bond 2 (positive control, CB); (3) fragment reattachment using flowable composite (Filtek Supreme, FL); (4) reattachment with a palatal veneer using a nanohybrid composite (PV); and (5) reattachment reinforced with a polyethylene fiber band (Ribbond Inc., RB). In BS testing groups, stainless steel orthodontic brackets (PINNACLE) were bonded using Transbond XT, centered over the fracture line. Light curing was performed using an LED unit (Mini LED Standard, Acteon, 1250 mW/cm², 20 s/bond, 40 s/composite, 2 mm curing tip distance). Specimens were stored in distilled water at room temperature for 24 h before reattachment. FR and BS were evaluated using a universal testing machine (Instron) until failure. Failure modes were analyzed, and data were statistically evaluated using one-way ANOVA, Tukey’s post hoc test, and Pearson’s correlation analysis. Results: Significant differences were observed among groups for both FR and BS (p < 0.05). The NC group exhibited the highest FR (514.4 N) and BS (17.6 MPa). The RB group recorded the second-highest FR (324.6), followed by the PV (234.6), CB (224.9), and FL (203.7) groups. The CB group demonstrated the second-best BS (16.6), followed by the RB (15.2), FL (13.4), and PV (6.5) groups. FR and BS were negatively correlated. Mixed failures predominated in the reattachment groups, except for the PV group, which showed mainly adhesive failures. In BS testing, mixed failures dominated in the NC and CB groups, while adhesive failures predominated in the PV and FL groups. Conclusions: Ribbond reinforcement improves the mechanical performance of reattached incisal fragments, and composite buildup may provide more reliable bracket bonding than fragment reattachment. Clinical Relevance: In cases where biomimetic, minimally invasive reattachment is indicated, Ribbond fiber reinforcement appears to offer a reliable restorative solution. Full article

This study presents a novel approach to manufacture a rigid printed circuit board (PCB) using sustainable polymers. Current PCBs use a fossil-fuel-based substrate, like FR4. This presents recycling challenges due to its composite nature. Replacing the substrate with an environmentally friendly alternative leads to a reduction in negative impacts. Polylactic acid (PLA) and Polyhydroxybutyrate (PHB) biopolymers are used in this study. These two biopolymers have low melting points (130–180 °C, and 170–180 °C, respectively) and cannot withstand the high temperature soldering process (up to 260 °C for standard SAC (SnAgCu, tin/silver/copper) lead free solder processes). Our approach for replacing the PCB substrate is applying the PLA/PHB carrier substrate at the end of the PCB manufacturing process using injection molding technology. This approach involves all the standard PCB processes, including wet etching of the Cu conductors, and component assembly with SAC solder on a thin flexible polyimide (PI) foil with patterned Cu conductors and then overmolding the biopolymer onto the foil to create a rigid base. This study demonstrates the functionality of two test circuits fabricated using this method. In addition, we evaluated the adhesion between the biopolymer and PI to achieve a durable PCB. Moreover, we performed two different end-of-life approaches (debonding and composting) as a part of the end-of-life consideration. By incorporating biodegradable materials into PCB standard manufacturing, the CO₂ emissions and energy consumption are significantly reduced, and installation costs are lowered. Full article

This paper presents research findings on the turning of AZ31B magnesium alloy using ceramic-coated tungsten carbide tool inserts in a dry environment. Fifteen experiments were conducted according to the Box–Behnken design (BBD) for the straight turning of AZ31B magnesium alloy to investigate the variations in two important machinability indicators, i.e., material removal rate ‘MRR’ and mean roughness depth ‘R_Z’, with variations in cutting speed ‘C_S’, feed rate ‘f_r’, and depth of cut ‘DoC’. The cutting speed and feed rate had the maximum influence on the mean roughness depth and material removal rate, respectively. To address the challenge of optimizing conflicting machining responses, desirability function analysis (DFA) and grey relational analysis (GRA) were employed to identify the optimal turning parameters for conflicting machinability indicators or responses. These techniques enabled the simultaneous maximization of the material removal rate and the minimization of the mean roughness depth, ensuring an effective balance between productivity and surface quality. The optimal turning conditions—cutting speed of 90 m/min, feed rate of 0.2 mm/rev, and depth of cut of 1.0 mm—yielded the best multiperformance results with an MRR of 18,000 mm³/min and an R_Z of 2.21 µm. Scanning electron microscope (SEM) analysis of the chip and flank surface of the cutting tool insert used in the confirmation tests revealed the formation of band-saw-type continuous chips and tool wear caused by adhesion and abrasion. Full article

Background and Objectives: We aimed to assess the outcomes of upfront Optilume drug-coated balloon (DCB) dilation in patients after failed treatment for complex recurrent urethral stricture disease. All patients presented with acute urinary retention and were treated with DCB dilation regardless of stricture site and length. Materials and Methods: We retrospectively evaluated patients with acute urinary retention and known complex recurrent urethral strictures. Patients presented at the urology emergency room of our tertiary centre with an inability to void or a post-void residual (PVR) volume exceeding 400 mL between August 2021 and February 2024. Urethrography and/or endoscopic imaging confirmed the diagnosis. Patients with urinary tract infection/sepsis and those with neurological disease were excluded. Urethral dilation to 20 Fr was performed, followed by DCB dilation (30 Fr, 10 bar, 10 min). The primary endpoints were anatomical success (≥14 Fr by cystoscopy/calibration) at 12 months and freedom from repeat interventions. Results: Thirty-one consecutive male patients were evaluated, with twenty-six patients followed for ≥12 months (mean age 65 ± 16.8 years). The stricture sites included seven bulbopenile, seven bulbomembranous, seven anastomotic, three bladder neck, one penile, and one panurethral stricture. The median number of prior urethral/surgical interventions was 2 [IQR: 1–3] (range: 1–31). The median stricture length was 3 [IQR: 2–4] cm (range: 1–8). At 12 months, 65.4% (17/26) of subjects voided satisfactorily and were free of recurrence and reoperation. Conclusions: Timely DCB dilation may offer a viable treatment option for patients with complex recurrent urethral strictures and urinary retention, particularly those who are unable or unwilling to undergo surgical reconstruction and prefer to avoid indwelling catheters. Full article

In this study, we investigate the potential of using acrylonitrile–butadiene–styrene flame-retardant (ABS FR) plastic obtained from electronic waste to create a new composite material through the addition of fly ash microspheres obtained from the combustion of thermal coal at Ekibastuzskaya GRES 1, with the resulting material being suitable for the manufacturing of housings and other elements of electronic equipment. For this purpose, five composite compositions with microsphere/plastic ratios of 10/90, 20/80, 30/70, 40/60, and 50/50 were developed, which were then processed in an extruder at 250 °C to obtain test specimens. The thermal and mechanical properties of the specimens were compared with a control sample developed using ABS FR plastic from electronic waste without the addition of microspheres. The obtained materials, up to a microsphere/plastic ratio of 20/80, demonstrate increased mechanical properties and thermal stability with a simultaneous decrease in material density, while a further increase in the concentration of microspheres leads to a gradual decrease in mechanical properties. These properties make it possible to use the obtained composite for producing housings and other elements of electronic equipment. Full article