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Gdańsk University of Technology

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Publications from the year 2021

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  • EXPERIMENTAL AND NUMERICAL INVESTIGATION ON SPECIMEN GEOMETRY EFFECT ON THE CTOD VALUE FOR VL-E36 SHIPBUILDING STEEL
    • Jakub Kowalski
    2021 Full text Polish Maritime Research

    There are special cases in the marine industry, where additional material tests, such as the fracture toughness test, must be performed. Additional fracture toughness tests, such as CTOD (Crack Tip Opening Displacement), are typically performed on three-point bend specimens. The dimension that defines all the specimen dimensions is the thickness of the material to be tested. It is recommended by classification societies (e.g. DNVGL) to test specimens that are twice as high as the material thickness. The width determines the length and, therefore, the weight of the specimen which, for a 100 mm plate is over 140 kg. Current ASTM E1820, BS7448-1 and ISO 12135 testing standards also allow for proportions other than those recommended. This results in a much smaller test piece. Reducing the specimen size allows the testing machine to achieve lower forces than a specimen with a width to thickness ratio of two. This paper presents the effect of changing the specimen geometry on CTOD test results. Research was performed for specimens with a height to thickness ratio of one and two. Abaqus software was used for numerical calculations. The numerical results were, at selected points, verified experimentally.

  • Experimental and numerical investigations of ultimate strength of degradated structures
    • Krzysztof Wołoszyk
    2021 Full text

    The presented work investigates the corrosion influence on the structural behaviour of structural elements. Nine welded large-scale stiffened plates, and 30 standard small specimens have been subjected to the accelerated marine immersed conditions. After corrosion testing, the specimens have been accurately measured in terms of surface characteristics. The coupon specimens were furtherly subjected to tensile loading to develop the mechanical properties conditional on the severity of corrosion degradation. The FE analyses employing the technique of random field modelling were developed and validated against experiments. The stiffened plates were subjected to the compressive loading, and the structural response has been analysed, accounting for initial imperfection, corrosion degradation, welding-induced residual stresses, and material nonlinearity. The numerical models of different accuracy of corrosion degradation models were validated with the experimental results showing that only when non-uniform thickness reduction with subsequent changes in mechanical properties is taken into account, the structural behaviour could be accurately simulated. An analytical formulation allowing for a fast estimation of the structural capacity of corroded stiffened plates and the reliability formulation taking into account the time-dependent development of corrosion degradation has been developed.

  • Experimental and theoretical investigation of conformational states and noncovalent interactions in crystalline sulfonamides with a methoxyphenyl moiety
    • Mateusz Kowalik
    • Jakub Brzeski
    • Małgorzata Gawrońska
    • Katarzyna Kazimierczuk
    • Mariusz Makowski
    2021 CRYSTENGCOMM

    Four sulfonamide derivatives with a methoxyphenyl moiety, namely N-{4-[(2-methoxyphenyl)sulfamoyl] phenyl}acetamide (1a), N-{4-[(3-methoxyphenyl)sulfamoyl]phenyl}acetamide (1b), 4-amino-N-(2- methoxyphenyl)benzenesulfonamide (2a) and 4-amino-N-(3-methoxyphenyl)benzenesulfonamide (2b), have been synthesized and characterized physiochemically by CHNS, MS, FT-IR, 1H NMR, 13C NMR, PXRD and TG methods. Crystal structures were determined by SC-XRD and their conformational and noncovalent interaction properties were examined by both experimental and theoretical (HS, MEPS, NBO, dimerization energy, QTAIM) methods. The conformational flexibility of the bridge connecting two phenyl rings was studied and minimum-energy conformations were theoretically found. The packing architecture and hydrogen bond networks were described by graph set notation. Hirshfeld surface analysis revealed regions of stronger contacts and allowed us to indicate the relative contributions of different noncovalent contacts in the crystal packing. MEPS calculations helped to distinguish the electron rich and electron poor regions and to find the best H-bond donors and acceptors. The use of the QTAIM method enabled us to explain the influence of functional groups and molecular arrangement on the strength of noncovalent interactions in the crystals and overall packing efficiency

  • Experimental and theoretical investigation of the reactivity of [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2}] towards selected ketones
    • Aleksandra Ziółkowska
    • Natalia Szynkiewicz
    • Łukasz Ponikiewski
    2021 DALTON TRANSACTIONS

    In this work, we report a new type of reactivity of [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2}] (1) towards ketones (BDI* = 2,6-diisopropylphenyl-β-methyldiketiminate ligand). In the reaction of 1 with acetone, cyclopentanone or cyclohexanone, a ketone moiety is inserted into Ti–Pphosphanyl or Ti–Pphosphido bonds to form complexes with a new C–P–P moiety, providing [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2-C(Me)2O}] (2a), [(BDI*)Ti(Cl){η2-OC(Me)2P(SiMe3)-PiPr2}] (2b), [(BDI*)Ti(Cl){η2-P(SiMe3)-P(iPr)2-{C(CH2)4}O}] (3a), and [(BDI*)Ti(Cl){η2-P(SiMe3)-P(iPr)2-{C(CH2)5}O}] (4a). Starting complex 1 reacts with cyclohexanone, yielding a monocrystalline complex [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)C(CH2)5O}Ti(Cl){PiPr2-P(SiMe3)C(CH2)5O}] (4d) with the insertion of two ketone molecules. Interestingly, we found that monoinserted complexes 2a and 3a may be oxidized via a reaction with AgCl, leading to elimination of the –SiMe3 group and oxidation of the titanium atom. This reaction led us to isolate the Ti(IV) complex [(BDI*)Ti(Cl){η2-P-P(iPr)2-{C(CH2)5}O}] (5) in crystalline form. To identify the kinds of products that may be formed and determine which products are the most energetically favoured ones, we conducted a thermodynamic DFT study of 1 towards acetone, cyclopentanone and cyclohexanone. Structures 2a, 2b, 3a, 3e, 4a, 4d, and 5 were characterized by X-ray crystallography, and complex 5 was also identified by NMR spectroscopy.

  • Experimental and theoretical study of a vertical tube in shell storage unit with biodegradable PCM for low temperature thermal energy storage applications
    • Rafał Andrzejczyk
    • Tomasz Kowalczyk
    • Przemysław Kozak
    • Tomasz Muszyński
    2021 Full text APPLIED THERMAL ENGINEERING

    This article presents the experimental investigations of the coconut oil-based TES module for HVAC applications in the ambient and-sub ambient temperature range. To properly study this problem modular experimental module and test loop were developed. Special attention has been paid to study the physical mechanism of the melting/solidification process for natural substance (coconut oil) which has perspectives to be used in thermal energy storage systems. It has been a highlight that the melting/solidification process is much more complex for non-eutectic mixtures and there are limited analytical models witch could be used to design TES working with such substances. Due to the limit of literature data for thermophysical properties of coconut oil own experimental data has been conducted. The article presents both visual and thermal characteristics of the melting and solidification process. It has been confirmed the strong influence of natural convection phenomena at the melting process. What is more, it has been observed that in the case of coconut oil it is better to talk about appearance melting temperature than melting temperature. The experimental analysis confirmed that appearance melting temperature is a function of radial distance from the heat source. In the case of solidification, the influence of natural convection is reduced quickly due to the increasing domination of the conduction heat transfer mechanism. For the solidification temperature profiles are characteristic of the occurrence of subcooling temperature. The level of temperature drop in sub cooling is a function of radial distance from the heat source. It has been also confirmed that in case of melting as well as solidification process the shape of the phase-change profile seems to form a truncated cone (in case of melting inverted). To validate the engineering approach to vast discrepancies in the literature data own experiment has been evaluated with a simple mathematical model to verify the applicability of the literature data in system behavior prediction. Based on the best-fit approach the parameters thermal resistance of the module R = 1.3 W/K was found. Additionally the latent heat of the coconut oil of 178 kJ/kg with Gaussian distribution for melting in temperature of 25 °C and solidification at 21 °C. The proposed correlation can be easily used to optimize latent thermal energy storage cooperated with the HVAC system.

  • Experimental Investigation of Free Convection Heat Transfer from Horizontal Cylinder to Nanofluids
    • Dorota Sawicka
    • Janusz Cieśliński
    • Slawomir Smolen
    2021 Full text ENERGIES

    The results of free convection heat transfer investigation from a horizontal, uniformly heated tube immersed in a nanofluid are presented. Experiments were performed with five base fluids, i.e., ethylene glycol (EG), distilled water (W) and the mixtures of EG and water with the ratios of 60/40, 50/50, 40/60 by volume, so the Rayleigh (Ra) number range was 3 104 Ra 1.3 106 and the Prandtl (Pr) number varied from 4.4 to 176. Alumina (Al2O3) nanoparticles were tested at the mass concentrations of 0.01, 0.1 and 1%. Enhancement as well as deterioration of heat transfer performance compared to the base fluids were detected depending on the composition of the nanofluid. Based on the experimental results obtained, a correlation equation that describes the dependence of the average Nusselt (Nu) number on the Ra number, Pr number and concentration of nanoparticles is proposed.

  • Experimental investigation of performance and emission characteristics of a miniature gas turbine supplied by blends of kerosene and waste tyre pyrolysis oil
    • Tomasz Suchocki
    • Łukasz Witanowski
    • Piotr Lampart
    • Paweł Kazimierski
    • Katarzyna Januszewicz
    • Bartosz Gawron
    2021 ENERGY

    Fossil fuels are non-renewable sources of energy that could be depleted in the near future, giving rise to amajor energy crisis. Scientists from all over the world are working on new technologies to produce fuelnot only from renewable sources but also from waste. This article is concerned with: (i) waste tyremanagement by means of the pyrolysis process, (ii) investigation of physico-chemical parameters ofwaste tyre pyrolysis oil (TPO), and (iii) investigation of performance and emission characteristics of aminiature GTM-140 turbine engine supplied by blends of kerosene and waste tyre pyrolysis oil. Thefinalaim of the research is to determine the influence of the applied blend composition (between 10 and 50%of TPO in the blends) on the performance and emission parameters of a small gas turbine. Turbine inletand outlet temperatures, fuelflow, static thrust, thrust specific fuel consumption (TSFC) and emissionsindex of NOx, CO, SO2are measured in a wide range of turbine load. The differences are the largest for thehighest rotational speeds, where the temperatures, TSFC and emissions of NOxespecially tend to increasewith the increasing fraction of pyrolytic oil in the blends, as compared to those of kerosene. However,emissions of SO2are lower for the all blends in the entire range of load.

  • Experimental Research of an Axial Piston Pump with Displaced Swash Plate Axis of Rotation
    • Paweł Załuski
    2021

    The article describes the influence of displacement of the swash plate rotation axis on the efficiency of axial piston pumps. The dead space volume was defined as the volume of the working chamber in the extreme position of the piston at the end of the pumping phase and its variability was determined as a function of the position of the axis of rotation of the swash plate and the swing angle of swash plate. The influence of swash plate rotation axis displacement on leaks between piston and cylinder was determined. It has been proven that displacement of the swash plate rotation axis reduces the dead space volume and leaks, thus improving the volumetric efficiency visible at small swash plate swing angles. The results of a comparative study of the volumetric and total efficiency of a modified design of a pump that allows the rotation axis to be repositioned are presented. The efficiency curves for the swash plate rotation axis crossing the shaft rotation axis and for the displaced swash plate axis of rotation are compared. The article also presents the author’s construction of an axial piston pump with displaced swash plate rotation axis with a follow-up mechanism of capacity change controlled by a stepper motor. The diagram and view of the test stand are shown, as well as the results of tests of volumetric and hydromechanical pump efficiency.

  • Experimental research of the effect of face milling strategy on the flatness deviations
    • Michał Dobrzyński
    • Daniel Chuchała
    • Kazimierz Orłowski
    • Mateusz Kaczmarczyk
    2021 Full text MATERIALS AND MANUFACTURING PROCESSES

    In this paper the dependencies between face milling strategy of EN AW6082-T6 aluminum alloy samples, with difference thicknesses (6, 8, and 12 mm) and two cold rolling directions, and flatness deviations were presented. Three strategies of milling included different proportions of material removed from both sides of the plates. This approach allowed to control the proportions of residual surface stresses on both sides of the specimens, which were created by the cold rolling process. The face milling strategy involving the symmetrical removal of material from both sides of the sample resulted in the best results of flatness deviations. This strategy was most effective for both rolling directions. It has been observed that the use of an appropriate face milling strategy is particularly important for thin sheets (6 mm thick). In the case of thicker plates (12 mm thick), the selected strategy has less impact on the final values of flatness deviations.

  • Experimental Study of the Resistance to Influence of Aggressive Liquids on Lightweight Concrete
    • Marzena Kurpińska
    • Elżbieta Haustein
    2021 Full text Materials

    In light of the scientific research, the corrosion of concrete structures is one of the main problems that may reduce their durability due to the negative impact of the natural environment. The paper analyzes the influence of the type of component on the selected properties of lightweight concrete subjected to the influence of aggressive liquids. Four concrete mixes were prepared with a granular aggregate made of foamed glass (GEGA) and aggregate made of sintered fly ash (GAA) with the use of a mineral additive: silica fly ash. The prepared lightweight concrete after one year was exposed for 60 days to the following environments: strong acid—HCl, 1% and 2% concentration, weak acid—CH3COOH, 1% and 2% concentration, and an aqueous salt solution of Na2SO4 , 1% and 2% concentration. Then, the compressive strength was tested, and the microstructure analysis of the ready-made lightweight concrete (LWC) was performed. The degree of penetration of aggressive solutions into the cracks of the samples was assessed by means of applying 1% phenolphthalein solution. Changes in the weight of lightweight concrete samples after the test period were estimated. The obtained test results indicate that the decrease in the durability of lightweight concrete can be classified as a long-term process. Concrete with GEGA and GAA showed high resistance to aggressive environments. Moreover, the environment containing chlorides turned out to be the most aggressive, while the environment containing sulfates proved to be the least aggressive. The higher the concentration of the destructive factor was, the faster the corrosion process went. This has been proven by measuring the pH using phenolphthalein and carrying out microscopic examination. Concretes containing aggregates made of foamed glass and sintered fly ash are suitable for use both in traditional construction and in facilities exposed to an aggressive environment (e.g., in the chemical industry and at gas stations.

  • Experimental tuning of AuAg nanoalloy plasmon resonances assisted by machine learning method
    • Robert Kozioł
    • Marcin Łapiński
    • Paweł Syty
    • Wojciech Sadowski
    • Józef Sienkiewicz
    • Bartosz Nurek
    • Valentin Maraloiu
    • Barbara Kościelska
    2021 Full text APPLIED SURFACE SCIENCE

    Plasmonic nanostructures based on AuAg nanoalloys were fabricated by thermal annealing of metallic films in an argon atmosphere. The nanoalloys were chosen because they can extend the wavelength range in which plasmon resonance occurs and thus allow the design of plasmonic platforms with the desired parameters. The influence of initial fabrication parameters and experimental conditions on the formation of nanostructures was investigated. For the surface morphology studies, chemical composition analysis and nanograin structure, Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-Ray Spectroscopy (EDS) and High-Resolution Transmission Electron Microscopy (HR TEM) measurements were performed. The position of the resonance band was successfully tuned in the 100 nm range. The EDS together with the XPS analysis confirmed the formation of an alloy with the aspect ratio of individual metals in a single nanoisland similar to the ratio of the thicknesses of the initially sputtered layers. The experimental research was complemented by the neural network model, which enables the calculation of the absorbance peak depending on the thickness of Au and Ag layers and the annealing time. The proposed model of machine learning makes it possible to fine-tune the desired position of the plasmon resonance.

  • Explicit Size-Reduction of Circularly Polarized Antennas through Constrained Optimization with Penalty Factor Adjustment
    • Marzieh Mahrokh
    • Michał Kozieł
    2021 Full text IEEE Access

    Modern communication systems of high data capacity incorporate circular polarization (CP) as the preferred antenna radiation field configuration. In many applications, integration of the system circuitry with antennas imposes size limitations on CP radiators, which makes their development process a challenging endeavor. This can be mitigated by means of simulation-driven design, specifically, constrained numerical optimization. Majority of the performance-related constraints are expensive to evaluate, i.e. require full-wave electromagnetic (EM) analysis of the system. Their practical handling can be realized using a penalty function approach, where the primary objective (antenna size reduction) is complemented by contributions proportional to properly quantified constraint violations. The coefficients determining the contribution of the penalty terms are normally set up using designer’s experience, which is unlikely to render their optimum values in terms of the achievable miniaturization rates as well as constraint satisfaction. This letter proposes a procedure for automated penalty factor adjustment in the course of the optimization process. Our methodology seeks for the most suitable coefficient levels based on the detected constraint violations and feasibility status of the design. It is validated using two CP antenna structures. The results demonstrate a possibility of a precise constraint control as well as superior miniaturization rates as compared to the manual penalty term setup.

  • Exploring DAD and ADD Methods for Dealing with Urban Heat Island Effect
    • Julia Kurek
    • Justyna Martyniuk-Pęczek
    2021 Full text Sustainability

    The Urban Heat Island (UHI) effect in the context of climate change and temperature fluctuations is an increasing challenge for contemporary cities. Numerous activities focus on mitigation and adaptation to the UHI effect using both appropriately selected design strategies and technological solutions. However, not all of these technologies support the postulates of ecological and low-carbon cities. Their design, implementation, and operation process sometimes causes conflicts or misunderstandings among designers, industry engineers, and residents. The aim of the research was to examine the relationship between UHI effect mitigation, adaptation, and energy efficiency strategies. A further goal was to build a matrix of synergistic elements and conflicts for respective actors and stakeholders, and an analysis of the elitist DAD (Decide-Announce-Defend) method and participatory ADD (Announce-Discuss-Decide) or EDD (Engage-Deliberate-Decide) in dealing with the UHI effect. The literature review and case study analysis methods were applied. In the study, the strategies of five chosen European capitals (Berlin, London, Paris, Vienna, and Warsaw) experiencing a UHI problem were analyzed. As result, a matrix of the most common goal differences of respective stakeholders in dealing with the UHI effect was developed. One of the main conclusions is the necessity of undergoing synergic collaboration between actors that are not cooperating yet, combined with risk analysis and appropriate education at different levels for a successful and socially equal mitigation and adaptation to the UHI effect.

  • Exploring multi-step glucose oxidation kinetics at GOx-functionalized nanotextured gold surfaces with differential impedimetric technique
    • Wiktoria Lipińska
    • Jacek Ryl
    • Paweł Ślepski
    • Katarzyna Siuzdak
    • Katarzyna Grochowska
    2021 Full text MEASUREMENT

    For a few past years, we can observe the enormous growth of investigations related to ultrasensitive electrochemical sensors capable of reliable determination of important body parameters and analytes. Utilized procedures rely on standard electrochemical methods, demanding electrode polarization, and information about the initial characteristics of the working electrode. More and more complex electrode materials are characterized however their electrochemical response is not fully understood or defined, affecting data reproducibility. Herein, we propose a novel protocol utilizing dynamic electrochemical impedance spectroscopy in galvanostatic mode (g-DEIS) to verify the sensor performance. The protocol was applied to study the response of Ti-Au nanotextured electrode depending on glucose concentration changes. The g-DEIS allowed to monitor complex mechanism occurring at the electrode/electrolyte interface with the continuously dosed glucose through electric parameters derivatives in analyte content. Our studies revealed a visible increase in electrode electric heterogeneity above 1.9 mM of glucose and gold nanoparticles’ oxidation above 3.8 mM, both influencing electrode kinetics. The results were confirmed using supporting cyclic voltammetry and x-ray photoelectron spectroscopy studies. The proposed protocol’s unique features could significantly spread further application of targetable biosensors for real-time diagnostics.

  • Exploring the Institutional and Bottom-Up Actions for Urban Air Quality Improvement: Case Studies in Antwerp and Gdańsk
    • Joanna Badach
    • Małgorzata Dymnicka
    • Jarosław Załęcki
    • Maciej Brosz
    • Dimitri Voordeckers
    • Maarten Van Acker
    2021 Full text Sustainability

    The article presents the results of qualitative studies concerning the presence of air quality management in the process of urban planning and in the public discourse in Antwerp, Belgium, and Gdańsk, Poland. We focused on the way urban planners, environmental experts, and stakeholders perceive the problem of air pollution, especially with respect to urban development policy, and whether they consider it one of the major factors determining the quality of the urban built environment. The analysis was empirically based on free, partially structured interviews with experts. With that aim, we referred to certain assumptions of the multidimensional concept of environmental protection and integrated urban planning, highlighting the knowledge gained through interview analysis, literature review, and comparative case study research. The approach brings to light the difference between the perceived and measured air quality and to what extent it is affected by the spatial conditions. The research reveals how the range of perceptions of air pollution is embedded in several sociological, urban planning, and cultural perspectives and how these perceptions differ between the different profiles of the stakeholders and experts.

  • Exposure to Bisphenol A Analogs and the Thyroid Function and Volume in Women of Reproductive Age—Cross-Sectional Study
    • Justyna Milczarek-Banach
    • Dominik Rachoń
    • Tomasz Bednarczuk
    • Katarzyna Myśliwiec-Czajka
    • Andrzej Wasik
    • Piotr Miśkiewicz
    2021 Full text Frontiers in Endocrinology

    Bisphenols (BPs) are commonly known plastifiers that are widely used in industry. The knowledge about the impact of BPs on thyroid function is scarce. Proper thyroid functioning is especially important for women of reproductive age, as hypothyroidism affects fertility, pregnancy outcomes and the offspring. There are no studies analyzing the influence of BPs on thyroid function and volume in non-pregnant young women. The aim of this cross-sectional study was to evaluate the relationship between bisphenol A and its 10 analogs (BPS, BPC, BPE, BPF, BPG, BPM, BPP, BPZ, BPFL, and BPBP) on thyroid function and volume in women of reproductive age. Inclusion criteria were: female sex, age 18–40 years. Exclusion criteria were history of any thyroid disease, pharmacotherapy influencing thyroid function, pregnancy or puerperium, and diagnosis of autoimmune thyroid disease during this study. Venous blood was drawn for measurement of thyrotropin (TSH), free thyroxine, thyroid peroxidase antibodies, thyroglobulin antibodies, BPs. Urine samples were analyzed for: ioduria and BPs. Ultrasound examination of thyroid gland was performed. One hundred eighty participants were included into the study. A negative correlation was found between urine BPC and the thyroid volume (R = −0.258; p = 0.0005). Patients with detected urine BPC presented smaller thyroid glands than those with not-detected urine BPC (p = 0.0008). A positive correlation was found between TSH and urine BPC (R = 0.228; p = 0.002). Patients with detected urine BPC presented higher concentrations of TSH versus those with not- detected urine BPC (p = 0.003). There were no relationships between any of serum BPs as well as the other urine BPs and thyroid function and its volume. The only BP that demonstrated the relationship between thyroid function and its volume was BPC, probably because of its chemical structure that most resembles thyroxine. Exposure to this BP may result in the development of hypothyroidism that could have a negative impact on pregnancy and the offspring.

  • Extended Newmark method to assess stability of slope under bidirectional seismic loading
    • Aleksandra Korzec
    • Robert Jankowski
    2021 SOIL DYNAMICS AND EARTHQUAKE ENGINEERING

    The paper concerns the dynamic behavior of a simple slope model subjected to simultaneous horizontal and vertical excitations. The proposed method is based on Newmark’s sliding block concept, however, four new features are introduced. The most important assumption is that the normal component of dynamic excitations affects the resisting force both before and after the initiation of the relative slope motion, making it time-dependent. The proposed formula and solution method is validated by experiments conducted on the shaking table and the bidirectional oscillatory device. The block displacement and acceleration time-histories are measured and analyzed. Experiments results conducted for bidirectional cyclic motion showed that the influence of vertical acceleration on the stability of the slope can be both negligible and significant (up to 57%). The numerical tests results, performed for thirty-five European seismic records, showed the underestimation of permanent displacement can reach up to 19% if the vertical excitation is neglected.

  • Extending the Frequency Limit of Microstrip-Coupled CSRR Using Asymmetry
    • Abhishek Kumar Abhishek
    • Adam Lamęcki
    • Roberto Gómez-García
    • Michał Mrozowski
    2021 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES

    Abstract— This article explains the frequency limitation in designing microstrip circuits based on a complementary split-ring resonator (CSRR) and reports a novel technique for increasing its operating frequency, which makes the CSRR suitable for high-frequency applications. This study helps in synthesizing the dimensions of symmetric CSRR (SCSRR) and asymmetric CSRR (ACSRR) circuits, which shows the applicability of the proposed technique in designing mm-wave circuits. It is observed that the upper frequency limit of the microstrip-coupled SCSRR is mainly due to weak electric coupling. The weak coupling implicates radiation loss in the structure, and the frequency at which the SCSRR has maximum loss due to radiation is found to be much less than the cutoff frequency of the higher order mode of the microstrip line, thus effectively limiting the operating frequency range of the circuit. In this article, the type of coupling and associated electrical parameters, e.g., reflected power, transmitted power, radiated power, losses, quality factor, voltage standing wave ratio, and gain, are investigated in detail. The allowable bandwidth of the fundamental mode of the microstrip line can be utilized to design CSRR with improved coupling. It is found that the ACSRR enhances the coupling coefficient using the cross-coupling effect. At higher frequencies, where the electric coupling is becoming too weak for the SCSRR, it is possible to design a magnetically coupled ACSRR of the same dimensions as the SCSRR. Finally, the design profile for both the SCSRR and ACSRR is studied in detail, and the radiating condition is discussed as a function of the height and dielectric constant of the substrate. For practical-verification purposes, two circuit prototypes are fabricated on a 1.5-mm-thick Rogers RT5880 substrate, and the measured results are found to be in good agreement with the proposition. It is found that, for a given microwave substrate, the maximum allowable resonating frequency of the ACSRR structure is nearly twice that of the SCSRR structure.

  • Fabrication of toughened plastic using styrene butadiene rubber-poly (methyl methacrylate) interpenetrating polymer networks
    • J. James
    • G.v. Thomas
    • D Rouxel
    • Michał Strankowski
    • N. Kalarikkal
    • Sabu Thomas
    2021 Materials Today Chemistry

    A standard set of interpenetrating polymeric networks (IPNs) has been contrived using an elastomerstyrene butadiene rubber and a thermoplastic poly (methyl methacrylate) through sequential polymerization protocol. This low-cost material can be hopefully engaged as a toughened plastic with cocontinuous morphology. Different morphological protocols including Raman imaging are effectively utilized to envisage the effect of blend ratio in IPN fabrication. The different mechanical properties of IPNs revealed that the cross-linking in phases have their own impact. Thermogravimetric analysis is used as an efficient tool to prove the extra thermal stability of IPNs. Of seven different composites theoretical models, the Davies model showed better fit to the experimental data. The etiquette of characterization adopted in this work including mechanical, morphological, and thermal protocols and their correlation with theoretical predictions can definitely be act as a platform for the synthesis of low-cost toughened plastic.

  • Face with Mask Detection in Thermal Images Using Deep Neural Networks
    • Natalia Głowacka
    • Jacek Rumiński
    2021 Full text SENSORS

    As the interest in facial detection grows, especially during a pandemic, solutions are sought that will be effective and bring more benefits. This is the case with the use of thermal imaging, which is resistant to environmental factors and makes it possible, for example, to determine the temperature based on the detected face, which brings new perspectives and opportunities to use such an approach for health control purposes. The goal of this work is to analyze the effectiveness of deep-learning-based face detection algorithms applied to thermal images, especially for faces covered by virus protective face masks. As part of this work, a set of thermal images was prepared containing over 7900 images of faces with and without masks. Selected raw data preprocessing methods were also investigated to analyze their influence on the face detection results. It was shown that the use of transfer learning based on features learned from visible light images results in mAP greater than 82% for half of the investigated models. The best model turned out to be the one based on Yolov3 model (mean average precision—mAP, was at least 99.3%, while the precision was at least 66.1%). Inference time of the models selected for evaluation on a small and cheap platform allows them to be used for many applications, especially in apps that promote public health.