Impedance Modulation Research Articles

Surface Impedance Modulation of FSS Composite Absorber for RCS Reduction at Normal and Grazing Incidence

Surface Impedance Modulation of FSS Composite Absorber for RCS Reduction at Normal and Grazing Incidence

Moving impedance profiles make one-way, spectrum-reshaping mirrors

We find a set of exact solutions to Maxwell's equations in spacetime-varying materials, where the refractive index is constant, while the impedance exhibits effective motion, i.e., it is a function of x−vt. We find that waves copropagating with the modulation are not reflected within the material, while counterpropagating waves are continually reflected by the changing impedance. For a finite section of such a material, we find analogs of transmission resonances, where specially shaped eigenpulses enter without reflection. We also find that there is a strong asymmetry in reflection from the medium when the impedance modulation is small but rapid, the material reflecting strongly from one side and negligibly from the other. Unlike stationary media, the spectrum of the reflected wave can be significantly different from the incident one. Published by the American Physical Society 2024

Износостойкость и коррозионное поведение Cu-Ti-покрытий в растворе SBF

Introduction. Currently, titanium and its alloys have become the most popular metal implantable biomaterials. However, the main disadvantage of titanium alloys is low wear resistance due to high viscosity. It is known that copper-titanium coatings effectively improve the antibacterial properties of titanium alloy and at the same time increase its wear resistance. Purpose of the work is to study the effects of a solution simulating body fluid on corrosion properties, friction coefficient and the wear of copper-titanium coatings obtained by electrospark deposition method of the Ti-6Al-4V alloy. Method. A non-localized electrode consisting of copper and titanium granules in various ratios was used to form copper-titanium coatings on a titanium alloy by electrospark deposition. The structure of the coatings was examined using a DRON-7 X-ray diffractometer in Cu-Kα radiation and an X-max 80 energy dispersive spectrometer. The antibacterial activity of the deposited Cu-Ti coatings was studied on a non-pathogenic gram-negative culture of Escherichia coli. Polarization tests in SBF solution were carried out using a P-40X potentiostat with an impedance measurement module. The metal content in the SBF solution after immersion of the samples was measured using an ICP-MS 2000 mass spectrometer. The tribological characteristics of the coatings according to the ASTM G99-17 standard using the “ball-on-disk” scheme with sliding friction in the SBF solution at loads of 10 and 25 N were examined. Results and discussions. It is shown that the bactericidal activity of Cu-Ti coated samples to a non-pathogenic culture of Escherichia coli increased monotonously with an increase in copper content. With copper concentration increasing, the corrosion current density of the coatings increased from 3.455 to 17.570 μA/cm2. It is shown that the SBF solution accelerates the wear of a titanium alloy many times over due to its interaction with the electrolyte via the oxidative wear mechanism. The use of Cu-Ti coatings allows reducing the friction coefficient and greatly decreasing the wear of Ti-6Al-4V alloy in the presence of an electrolyte.

Simple incorporation and calcination of Zn-Al LDH during PEO processing in near-neutral pH solutions

Plasma electrolytic oxidation (PEO) process was employed for preparing oxide coatings on AA2024 aluminum alloy in solutions containing Zn-Al layered double hydroxide (LDH) particles. Sodium hexametaphosphate aqueous solution was selected as the standard solution, based on its almost neutral pH value considered as important for the LDH stability. Different additives to the standard solution were examined including 2-mecaptobenzothiazole (MBT) and different Zn-Al LDH compounds. The formed coatings underwent characterization regarding their morphology, chemical and phase composition, as well as assessment of their photocatalytic and corrosion protection efficiency. Coating thickening and compactness evolution were noted for all coatings with LDH additions to the standard solution. Obtained coatings are well-crystallized featuring γ-Al2O3 and two Zn-containing crystalline phases, namely ZnO and NaZnPO4, originating mainly from the LDH addition to the solution. PEO coatings obtained in this study demonstrated very reasonable photocatalytic activity for immobilized photocatalyst, reaching 51 % after 6 h under UV irradiation. The inclusion of Zn-Al LDH substantially boosted the impedance modules at low frequencies by two orders of magnitude compared to bare AA2024 alloy when exposed to a 3.5 % NaCl solution.

A novel siloxene@MoS2 heterostructure for improving the wear and corrosion resistance performance of epoxy coatings

Siloxene (Sic) flakes are two-dimensional silicon-based materials that have been extensively investigated in the domains of batteries, supercapacitors, and electrocatalysis, with essentially no research in the domain of corrosion and wear resistance performance of metal coatings. In this study, Sic sheets were prepared through topological chemical exfoliation and applied to epoxy (EP) resin systems for the first time. The effects of Sic sheets on the corrosion and wear resistance performance of the composite coatings were explored. To improve the enhancement effect of Sic on the tribological properties and corrosion resistance of the composite coatings, molybdenum disulfide (MoS2), which exerts a self-lubricating effect and an enhanced interfacial effect, was grown on the surface of Sic using a hydrothermal method. The corrosion resistance and tribological properties of the prepared composite coatings were characterized through electrochemical impedance spectroscopy, polarization curve analysis, and friction and wear tests. The results indicated that the composite coating containing 0.75 wt% siloxene@MoS2 (Sic@MS) has the best corrosion resistance and tribological properties. Compared with the pure EP coating, the wear rate of the Sic@MS coating with the aforementioned concentration was reduced by 67 %. Furthermore, the impedance module value at 0.01 Hz was increased by three orders of magnitude and the corrosion current density was reduced by three orders of magnitude after 60 days of immersion in NaCl solution. The above results provide a new idea for the application of Sic materials.

Reflective anomalous beam splitter (RABS) metasurface for millimeter-wave (mm-Wave) frequency

Metasurfaces have gained a considerable amount of interest in the past decade for their capabilities to manipulate electromagnetic (EM) waves in different manners. They have offered multiple functionalities in terms of wave control depending on the given application. In terms of wave control, particularly EM beam splitting, it can be challenging compared to the given literature review, to achieve a wide number of beam-splitting reflections and coverage for multiple incident angles simultaneously. In this paper, we focus on the design of a metasurface based on the methodology of high periodicity supercell design (5.76λ) and impedance modulation to achieve a various number of beam-splitting angles, while maintaining the same coverage at multiple incident angles for millimeter-wave (mm-Wave) frequencies. Following the generalized phase law of reflection alongside proper optimization of the surface impedance, the proposed reflective anomalous beam splitter (RABS) metasurface is designed to be polarization independent, and high reflection efficiency is achieved with a wave beam split into 11 different directions while operating for multiple incident angles simultaneously, making it a promising candidate to overcome challenges for various mm-Wave communication applications, especially in expanding 5G coverage in non-line of sight regions at a 28 GHz frequency band. The performance of the RABS metasurface is evaluated using both full-wave simulations and experimental measurements, which demonstrate its effectiveness in achieving 11 efficient reflective anomalous beams with a reflection efficiency of up to 96.65% and 97.36% in TE and TM modes at 28 GHz.

Potential diagnostic and distinguishing roles of microneedle‐based biosensors in bacterial and aseptic meningitis

AbstractMeningitis, which is defined by inflammation of the meninges, is a major cause of death and morbidity worldwide. Traditional diagnostic approaches, such as imaging procedures and the study of cerebrospinal fluid, are intrusive, time consuming and sometimes non‐specific. The suggested approach entails creating a biosensor based on microneedles that can detect in real time without the requirement for labels. The biosensor uses highly sensitive detection techniques to detect changes in ionic current and modulation of impedance in response to biomolecules that are of interest, such as proteins and nucleic acids, which are linked to meningitis infections. Initial studies have shown that the microneedle‐based biosensor for meningitis diagnosis is both feasible and effective. When it comes to identifying bacterial and aseptic meningitis biomarkers from blood and cerebrospinal fluid (CSF) samples, the biosensor showed excellent sensitivity and specificity. This novel technique has the potential to enhance patient outcomes by facilitating prompt intervention and tailored therapy by offering a quick, safe and accurate way to distinguish between bacterial and aseptic meningitis. To maximise the biosensor's performance and confirm its therapeutic usefulness in various contexts, more investigations and advancements are necessary.

Substantiation of optimal characteristics of the device for electroodontodiagnostics based on the study of complex electrical resistance of tooth tissues

AIM. Aim of this work is to substantiate the optimal characteristics of the apparatus for electroodontodiagnostics on the basis of studying the complex electrical resistance of tooth tissues.MATERIALS AND METHODS. The study of complex tissue resistance during electroodontodiagnostics in 50 patients aged from 18 to 55 years was carried out. A total of 181 teeth were studied. All the teeth studied were with formed roots. 52 teeth were intact, 40 teeth had been previously treated for caries, 26 teeth had carious process, 21 teeth were diagnosed with pulpitis, 9 teeth were diagnosed with periodontitis, 33 teeth had been previously subjected to endodontic treatment.RESULTS. The results of studying the complex tissue impedance during electroodontodiagnostics showed that the impedance module can be in a wide range from 120 kOhm to 3500 kOhm. At that, the main contribution to the complex impedance is made by the state of hard tissues of teeth.CONCLUSION. The obtained results showed that the device for electroodontodiagnostics should automatically in a continuous mode to measure impedance and according to it to control the supply of the necessary exponentially increasing alternating sinusoidal current with a frequency of 50 Hz.

Parallel-coupled hierarchical and reconfigurable structure for broadband sound absorption

Conventional series-coupled or parallel-coupled sound absorbers can only work effectively in a fixed frequency range, of which the absorption spectra can not be allowed to divide. Here, a parallel-coupled hierarchical structure with two relatively independent frequency bands of sound absorption is proposed. The hierarchical structure is composed of two type subunits of embedding neck Helmholtz resonator (ENHR) and segmented neck Helmholtz resonator (SNHR). Sound energy in the high-frequency region is dissipated in the first layer by the multiple local resonances coupling of ENHRs. The second layer effectively captures and absorbs low-frequency energy through the coupling of multiple SNHRs with varying parameters. The comprehensive discussion on the effects of acoustic impedance and structural parameters highlights the superior capability of this structure in impedance modulation. To demonstrate its broadband absorption performance, a hierarchical structure consisting of 20 subunits is employed. Finally, a above 90% broadband quasi-perfect absorption over a frequency range from 450 Hz to 1750 Hz is achieved under a thickness of 48 mm. Furthermore, a dual-band modular design concept for frequency-selective absorption is presented based on the tunability and independence of the two absorption bands. Therefore, the proposed hierarchical structure achieves reconfigurability by replacing either the first or second layer, thereby breaking away from traditional parallel design methods and providing a practical approach to controlling noise sources whose spectral characteristics change with operating conditions.

Topological magnetic transition and impedance modulation based on rotational deformations

Topological magnetic transition and impedance modulation based on rotational deformations

Investigation of electromagnetic wave absorption and anti-corrosion mechanism of multifunctional Ni/AlN composite coatings with core-shell structure by laser cladding

Developing efficient microwave absorbing materials (MAMs) suitable for prolonged use in marine environments is of great importance. Laser cladding serves as one of the new techniques for the material of surface modification and microwave-absorbing materials in the 3D printing. However, it is usually challenging to prepare materials that combine desirable printability, corrosion resistance, and microwave absorption properties using this technology. To enhance the microwave absorption of laser-clad Ni-based alloys, the method of impedance modulation was employed by incorporating ceramic powders with varying AlN content. The results show that Ni/AlN/MWCNTs composite functional materials with core-shell heterostructures were prepared under optimized laser processing parameters. This unique core-shell structure optimizes impedance matching increased polarization loss and multiple scattering to boost microwave absorption. The optimized 20wt% AlN content resulted in a minimum RL of -13.24dB at 13.86GHz, in addition, electrochemical tests showed that AlN enhanced the resistance to the corrosion medium transfer during the corrosion process, and the corrosion resistance of the Ni/AlN/MWCNTs composites material (self-corrosion current density (8.52 × 10-8), the charge transfer resistance (1.55 × 10-5)). Therefore, this work provides innovative theoretical and practical insight for the design and manufacture of advanced microwave-absorbing materials for harsh environments by laser melting technology.

On the use of aromatic-functionalized reduced graphene oxide to confine corrosive ions in nanocomposite coatings

A simple and fast chemical methodology to obtain reduced graphene oxide (GO) nanoplatelets functionalized with aromatic groups and their anticorrosive performance in an epoxy resin matrix is disclosed for the first time. Through a microwave-assisted method, GO was functionalized with triethoxyphenylsilane (TEPS) within 10 min to obtain Phenyl-GO nanoplatelets. The remaining oxygen-centered groups of the nanoplatelets were removed in a second step under a microwave-assisted reduction for 10 min to obtain Phenyl-rGO nanoplatelets. The proposed methodology produced highly exfoliated, hydrophobic, and thermally stable functionalized graphene nanoplatelets. Phenyl-rGO nanoplatelets were used as an additive (0.5 wt%) within an epoxy resin, resulting in Epoxy Resin/Phenyl-rGO nanocomposite, which was used as an anti-corrosive coating on A36 mild steel. The physicochemical properties of the epoxy resin were improved by the Phenyl-rGO addition, such as density, hardness, adhesion, hydrophobic behavior, and anticorrosive performance. The impedance module was increased up to 5 magnitude orders, reaching up to 1.0 × 106 Ω·cm2, and the corrosion rate (CR) was decreased down to 2 magnitude orders (from 1.67 down to 0.01 mm/year). Moreover, the non-polar character of the Phenyl-rGO, allowed the migration of the reduced nanoplatelets to the interphase and surface of the coating, resulting in nanoplatelets densely packed. The tortuous pathway of the corrosive species, generated by the interaction between nanoplatelets, results in a nanocomposite coating that is able to confine such species and prevent corrosion of the metallic surface.

A circulating current suppression strategy of VSG based on adaptive virtual complex impedance

By adding inertia and damping elements in droop control, virtual synchronous generators (VSG) can simulate the output characteristics of synchronous generators and effectively reduce the impact of power electronic equipment connected to the power grid. Since the capacity and spatial distribution of each VSG is random, the output impedance of VSG and line impedance are mismatched, which will cause circulating current between VSGs. Considering the influence of line resistance, the traditional dynamic virtual inductance control strategy can be enhanced. A circulating current suppression strategy based on adaptive virtual complex impedance is proposed after analyzing the composition and causes of the circulating current between VSGs. The proposed strategy compensates the line impedance adaptively according to VSG's output reactive power, thus to reduce the reactive power sharing errors and suppress the circulating current between VSGs. The scheme is reliable and robust under fault as there is no need for measurement of line impedance or communication modules. The simulation results are presented to verify the effectiveness of the proposed strategy.

Enhanced anti-corrosive capability of waterborne epoxy coating by ATT exfoliated boron nitride nanosheets composite fillers

In this work, 2-amino-5 mercapto-1, 3, 4-thiadiazole/boron nitride nanosheets (ATT/BNNS) nanofillers were prepared via using ATT as intercalating agent to exfoliate BNNS by a liquid-phase assisted ultrasound method. The FTIR and the XPS consequences testify that the corrosion inhibitor ATT is successfully grafted onto BNNS. TEM results indicate that BNNS is adequately exfoliated by ATT and the agglomeration phenomenon is alleviated. BNNS, ATT and ATT/BNNS nanofillers were processed into the waterborne epoxy (WEP) respectively, and WEP composite coatings were then fabricated by a spraying method on the copper electrode. The EIS measurements demonstrate that WEP ATT/BNNS coating displays the best protective performance in combination with optical morphology observation under saline immersion, compared with other three coatings. It is mainly attributed to the combined action of active protection from ATT inhibitor and physical barrier from BNNS. The two-dimensional BNNS nanofiller dispersed in the WEP coating plays the role of physical barrier, forms a “labyrinth effect”, extends the invasion way of corrosive media, thus enhancing the physical barrier effect in the composite coating. Furthermore, ATT inhibitor can also diffuse through the coating to the copper substrate and build a safety shield to hold back further corrosion. Importantly, after 40 days immersion in 3.5 wt% NaCl solution, the value of impedance module at 0.01 Hz of WEP ATT/BNNS coating is about 2 orders of magnitude larger than that of pure WEP coating, revealing superior long-term anticorrosion performance.

Highly effective inhibition of steel corrosion in 1.0 M HCl solution using a novel non-ionic surfactant with coumarin moiety: Practical and computational studies

A new non-ionic organic coumarin-based surfactant was synthesized and applied to the surface of the steel in 1.0 M HCl solution. The response of the steel surface to the corrosion suppression was probed by measuring polarization, impedance, and frequency modulation in different concentrations (0.5 × 10−4 M to 7.5 × 10−4 M). While fitting the experiments to different adsorption isotherms, the steel-inhibitor interface interacted according to the Langmuir model. The maximum efficiencies of 84.18 % and 97.93 % were obtained for the inhibitor's lowest and highest concentrations, respectively based on the impedance spectroscopy measurements. The inhibitor was able to combat the anodic and cathodic reactions simultaneously showing a mixed-type inhibition ability. The free energy ΔGads was calculated to be from −36.75 to – 38.62 kJ/mol based on the Langmuire model, indicating chemical adsorption on steel surface. A narrow energy gap of 3.012 eV was predicted by DFT calculations in consistency with high inhibition efficiency. The molecular reactivity was attributed to the contiguous system of many π orbitals on naphthalene, chromone, thiazole, and diazene entities. In turn, the p-electrons of the oxaheptadecane chains exhibit a lower contribution to the adsorption of the surfactant on the metal surface. New experimental and theoretical insights were derived and related to corrosion inhibition.

Broadband sound absorption based on impedance decoupling and modulation mechanisms.

In sound absorbers, acoustic resistance and reactance are usually coupled together and affect each other, which brings difficulties to impedance matching. An impedance decoupling method is proposed to make acoustic resistance and acoustic reactance vary independently. For the same thickness and perforation rate, acoustic reactance of the perforated panel with tube bundles (PPTBs) varies with the diameter of the tube, but acoustic resistance remains constant. Theoretical and simulated results show that a PPTB absorptive unit can exhibit resonance modes with varying damping states through impedance decoupling. It is found that through well-modulation, the PPTB unit in a slightly over-damped state cannot only maintain high sound absorption coefficients, but also expand the absorption peak bandwidth. Utilizing the mechanism of impedance decoupling, a broadband absorber is designed and evaluated by comprising the PPTB and microperforated panel (MPP). Measurement results indicate that it possesses an average absorption coefficient of 85% spanning more than a 3-octave bandwidth from 160 Hz to 1400 Hz with a deep sub-wavelength thickness. The impedance decoupling method helps to implement sound absorbers with highly efficient low-frequency broadband absorption.

Toward a Novel Thermal-Based Variable Impedance Module Through Adjusting Viscoelastic Properties of a Thermoresponsive Polymer

Toward a Novel Thermal-Based Variable Impedance Module Through Adjusting Viscoelastic Properties of a Thermoresponsive Polymer

Assessment of freeze damage in tuber starch with electrical impedance spectroscopy and thermodynamic, rheological, spectrographic techniques

In this study, we aimed to use electrical impedance spectroscopy (EIS) to assess the freeze-damage level of starches from potato tubers treated with multiple freezing-thawing (FT) cycles. The results showed that the relationship between the physicochemical properties of starches and the impedance characteristics of starch paste is temperature-dependent. As the temperature rises to 70–90 °C, the impedance modules show a significant correlation with the amylose and mineral contents, gelatinization and pasting properties, short-range ordered structure, relative crystallinity, and damage level within the range of 10–1 MHz (p < 0.01). This could be because FT leads to a reduction in amylose and ion content. Compared to a high level of freeze-damaged starch (FDS), a low level of FDS has less amylopectin and more amylose. Additionally, the ions could be typically evenly distributed throughout the unbranched linear amylose structure in starch paste. At the peak gelatinization temperature, the starch paste made from a low level of FDS exhibits a weakened network structure, allowing more unbound water for ion movement and enhancing electric conduction. In conclusion, EIS can predict the damage level and properties of FDS, which can benefit the frozen starchy food industry.

Using the stm32f407vg microcontroller to study the amplitude-frequency characteristics of biological tissues

The electrical properties of biological tissues of a plant origin are studied using the microcontroller STM32f407vg. The formulation of the problem of identifying informative signs of the viability of biological tissues when using the method of impedance measurement is given. It is shown that since currently in medical diagnostic practice there is no instrument base that would allow in an operational setting to diagnose the ability of biological tissue to self-heal after injury and damage as a result of thermal exposure, a gunshot wound or prolonged compression, the development of methods and means of instrumental diagnostics in this area of knowledge is an important modern task.&#x0D; The results of experimental measurements of impedance characteristics in the frequency range of 20 Hz – 2.0 MHz are presented. The frequency dependences of the stress modulus of a biological tissue of a plant origin are analyzed in its intact state, as well as after exposure of samples of a biological tissue in a freezer.&#x0D; A comparative analysis of the obtained frequency dependences is carried out. A significant difference between the frequency dependences of the stress modulus on a biological tissue and the frequency dependence of the stress modulus on an isotonic solution is shown. The idea was proposed that the degree of difference in the frequency distribution of the impedance module of the biological tissue from the impedance module of the isotonic solution can serve as a criterion for assessing the degree of damage to the biological tissue.

Методы и особенности измерения теплового сопротивления интегральных СВЧ-усилителей на гетеропереходных биполярных транзисторах

The method of measuring the thermal resistance (TR) of semiconductor devices (SD) according to OST 11 0944-96 and the original modulation method implemented in the hardware and software package developed by the authors are described. In both methods, the SD is heated by pulsed power, and the temperature of its active region (transition) is determined by a change in the temperature–sensitive parameter (TSP) - the voltage at the SD at a low current passed through the SD in the pauses between the pulses of the heating current. The measurement error of the vehicle by the standard method strongly depends on the choice of the duration of the heating current pulses and the delay time when measuring the voltage at the SD after switching off the heating current. In the modulation method, the duration of the heating current pulses is changed according to the harmonic law, and according to the results of measuring the voltage at the SD during the passage of the heating and measuring current, the modulus of the thermal impedance of the SD is determined as the ratio of the first harmonic of the transition temperature to the first harmonic of the heating power. According to the frequency dependence of the thermal impedance module, the components of the vehicle of the object are determined, while the requirements for maintaining the temperature of the device body are significantly reduced and, as a result, the measurement error of the vehicle is reduced. The results of comparative measurements of the TR of integrated microwave amplifiers (amplifying cascades) on InGaP/GaP HBT by the standard and modulation method at different values of the amplitude of the heating current are presented. It is shown that the results of measuring the TR of integrated microwave amplifiers by both methods are in good agreement with each other. It is established that with an increase in the amplitude of the heating current, the TR junction-case of integrated microwave amplifiers decreases, which is due to the alignment of current distribution in the structure of the GBT during heating.