Impedance Mismatch Problem Research Articles

Lightweight dielectric-magnetic synergistic necklace-shaped Co@NCP/carbon nanofiber composites for enhanced electromagnetic wave absorption

In order to solve the problem of impedance mismatch of carbon fiber absorbing materials, it is crucial to create a carbon-based absorbing material with a special structure, synergistic magnetic and dielectric properties. In this paper, necklace-shaped Co@N-doped carbon polyhedron /carbon nanofiber (Co@NCP/CNF) composites with synergistic magnetic and dielectric properties are successfully fabricated by electrospinning. Compared with Co@NCP and CNF, the optimal minimum reflection loss of Co@NCP/CNF composite is -66.14 dB at 2.89 mm and the maximum effective absorption bandwidth is 6.24 GHz (11.76-18.00 GHz) at 2.25 mm at a low filler load of 10 wt.%. The necklace-like structure, the coupling effect of dielectric and magnetic materials and the heterogeneous interface form multiple polarizations, conductive losses and multiple loss mechanisms to optimize impedance matching and attenuation performance, which is conducive to excellent absorption performance. More importantly, the radar cross section (RCS) reduction is as high as 24.02 dB·m2, which has proven to have a good absorption effect in actual application environments. This work combines the advantages of Co@NCP and CNF very well, which provides guidance for designing EM waves nanocomposite fiber absorbers with lightweight and strong absorbing properties.

An Energy Management System for Distributed Energy Storage System Considering Time-Varying Linear Resistance

As the proportion of renewable energy in energy use continues to increase, to solve the problem of line impedance mismatch leading to the difference in the state of charge (SOC) of each distributed energy storage unit (DESU) and the DC bus voltage drop, a distributed energy storage system control strategy considering the time-varying line impedance is proposed in this paper. By analyzing the fundamental frequency harmonic components of the pulse width modulation (PWM) signal carrier of the converter output voltage and output current, we can obtain the impedance information and, thus, compensate for the bus voltage drop. Then, a novel, droop-free cooperative controller is constructed to achieve SOC equalization, current sharing, and voltage regulation. Finally, the validity of the system is verified by a hardware-in-the-loop experimental platform.

Active damping control based bus voltage resonance suppression in electrolytic capacitorless PMSM application

Abstract The structure of electrolytic capacitorless in automotive electronic applications has the advantages of lower cost and better reliability. However, motor drive systems using this structure may experience unstable bus voltage. To this end, this paper proposes an active damping control strategy based on virtual impedance. By modelling the electric drive system and conducting stability analysis, the cause of bus voltage resonance due to the use of small capacitors is revealed. Based on the extracted DC bus voltage harmonic signal, additional voltage vectors are added in the d-axis and q-axis voltage vectors, eliminating the impedance mismatch problem in the drive system caused by the reduction of bus capacitance, effectively suppressing the voltage oscillation on the machine side of the drive system. Simulation data shows that under the condition of using small-capacity ceramic capacitors, the method proposed in this paper achieves a harmonic suppression capability similar to that of large-capacity electrolytic capacitors, effectively ensuring the application safety of automotive drivers with electrolytic capacitorless architecture.

Fabrication of MXene-encapsulated Co@C nanoparticles for efficient microwave absorption in the X-band

Two-dimensional MXene has structural advantages in electromagnetic wave scattering due to its layered structure, but MXene materials can lead to impedance mismatch problems due to their high dielectric constants, so it is still a challenge to design highly efficient wave-absorbing materials based on MXene with low reflection loss, thin thickness, and wide absorption frequency. In this study, composite wave-absorbing materials were fabricated from Co–Co PBA precursors and MXene using liquid nitrogen flash freezing and freeze-drying techniques. By treating MXene and the PBA precursor at a high temperature of 750 °C, a rich heterogeneous interface was formed between Co@C and MXene (CCM7), and the impedance matching was optimized to improve the reflection loss capability. The optimized sample has an effective absorption bandwidth of 4.1 GHz at 2.5 mm covering the entire X-band with a minimum reflection loss of −61.42 dB. It is also demonstrated that CCM7 is satisfactory for Radar Cross-Section of flat panels and unmanned aerial vehicles by CST calculations, and this work provides a fresh perspective on the use of effective MXene composites for microwave absorption.

Nesne Yönelimli Bir Yaklaşımla İş Verilerinin Yönetimi

Nowadays, managing data is so vital for companies in every sector to compete with competitors. Databases are the critical part of information systems to process raw data. Some of them are open source code and some of them are commercial ones. In this study, the main question is that how business data is managed based on the concept of persistence without a need to connect to a database management system to make a contribution for the problem of impedance mismatch. To find the answer of this question, a persistent object-oriented model has been proposed to establish an infrastructure for especially small companies to manage business data. When designing this model, the source of inspiration has been the concepts of persistence and delegation. Delegation contributes to diminish the effects of code scattering and code tangling problems and to increase modularity. It also plays an important role in the model in order to build an interface between users and the system. Serialization methodology has been applied to save data represented by persistent objects. C++ programming language was used for implementation of the model. The reliability of the proposed model has been proved based on Chidamber and Kemerer’s metric set to measure object-oriented programming. Consequently, the first version of the model has been implemented without needing any database management system. It has also provided valuable functionalities, i.e., saving or loading data, listing data, describing data, inserting data based on object-oriented concepts. In the future, the researchers of the same field can make contributions for developing this model by implementing new features to make it more powerful technically.

Equivalent transmission line characterization and multi‐layer material measurement analysis of the signal conversion process in the pulsed electro‐acoustic method

AbstractThis paper studies the equivalent transmission line model of the pulsed electro‐acoustic (PEA) method with its applications. Based on the consistency of acoustic wave behaviour inside lossy acoustic materials and voltage wave propagation in transmission line, an equivalent simulation model of the PEA system is developed, whose reliability is verified by the output from the transducer and amplifier models and the comparison with measured waveforms. For the problem of acoustic impedance mismatch between different modules, simulation indicates that the unequal impedances of semiconducting electrode and sample can affect the amplitude of the measured signal at the upper electrode side, and the reflected acoustic waves caused by the transducer can affect the charge waveform. Further simulation for multi‐layer materials finds that the reflected acoustic waves of different samples and sound absorbing module can superimpose on the charge signal. Accordingly, a selection criterion is proposed to avoid the effect of the reflected waves at the interface. As for the acoustic reflection caused by internal charge, it needs to be dealt with sequentially in calibration process, starting from the result inside the sample near ground electrode. The research can provide a foundation for analyzing the acoustic properties of the PEA method.

Multi-source excited travelling-wave bowtie antenna based on a meander series of YBCO bicrystal Josephson junctions

Series superconducting Josephson junctions (JJs), as terahertz (THz) mixers, have attracted increasing attentions due to their advantages in solving the saturation problem of superconducting mixers, achieving higher mixing harmonics and higher sensitivity in THz band. However, the normal-state resistances of the series JJs are so low that there exists an impedance mismatch between the coupled antenna and the JJs. In this paper, a meander embedding travelling-wave bowtie antenna is proposed for a series of bicrystal JJs. With this antenna, not only the problem of impedance mismatch can be solved, but also more series JJs can be inserted into the antenna. Five and even seven series JJs in the meander match the proposed antenna well. Furthermore, combined current distribution, far-field radiation patterns and parameter study are investigated in the numerical simulation to analyze this antenna.

Metal ions-assisted construction of SiO2/MXene/Fe3O4 aerogel as multifunctional electromagnetic wave absorbing material

Advanced electromagnetic wave absorbing materials are developing towards the directions of lightweight, thin thickness, broad absorption bandwidth, and multifunction. MXene, as a new type of two-dimensional material, has received widespread attention, but it is necessary to address the impedance mismatch problem caused by its high conductivity. In this work, Fe3O4/MXene composite aerogel is prepared by metal ion-assisted crosslinking method without adding additional crosslinking agents. And a layer of hydrophobic fumed silica is further sprayed on the aerogel. Benefiting from the magneto-electric synergistic effect and the porous structure, SiO2/MXene/Fe3O4 aerogels shows excellent electromagnetic wave absorption performances, achieving a quite broad absorption bandwidth up to 8.8 GHz at an extremely thin thickness of 1 mm. The hybrid aerogel also shows superhydrophobic and thermal insulation properties, which are conducive to improving the resistance to harsh environments and thus endow the absorbers with a long service time.

A magnetic-field-driven neuristor for spiking neural networks

Artificial intelligence has been widely deployed in many fields with remarkable success. Among various artificial neural network structures in artificial intelligence, the spiking neural network, as the next-generation artificial neural network, closely mimics the natural neural networks. It contains the all-or-nothing and diverse periodic spiking, which is an analogy to the behavior of natural neurons. Artificial devices that perform the function of neurons are called neuristors. Most existing neuristors are driven by electrical signals, which suffer the problem of impedance mismatch between input and output neuristors. By exploiting the S-shape negative differential resistances element that is sensitive to the external magnetic field, we constructed a magnetic-field-driven neuristor. Magnetic fields can stimulate all-or nothing spiking, and its shape and frequency can be modulated through capacitances in the circuit. As magnetic fields serve as the information carrier, the cascading of our neuristors can get rid of the electrical impedance mismatch, promising a scalable hardware platform for spiking neural networks.

Expanded graphite and thermally reduced graphene oxide filled with NiCo2O4 for improve microwave absorption

Three-dimensional porous carbon materials provide an effective way for electromagnetic wave absorbers that are lightweight and effective. We explore the effects of different three-dimensional porous expanded graphite (EG) and thermally reduced graphene oxide (TERGO) on wave absorption performance in this study. NiCo2O4-EG and NiCo2O4-TERGO three-dimensional wave-absorbing materials were prepared by an in situ self-assembly hydrothermal process. To address the problem of impedance mismatch and improve the attenuation capability, the microstructure of EG and TERGO were designed to control the conductivity loss and polarization loss. After heat treatment at 800 °C to form a regular honeycomb pore distribution, TERGO composites have moderate conductivity and conductive losses, as well as multiple polarization loss mechanisms. Consequently, the NiCo2O4-TERGO800 composite with a lower filling ratio displayed excellent microwave absorption, with the bandwidth of reflection loss ≤−10 dB coved 4.05 GHz. These findings provide valuable insights for fabrication and research of three-dimensional porous carbon material microwave absorbers.

Study on matching layer of ultrasonic transducer for defect detection of stainless steel

To solve the impedance mismatch problem between the piezoelectric wafer and the tested material when ultrasonic testing is used to detect the internal defects of materials, alumina powder and epoxy resin are compounded to prepare the matching layer material. Then the matching layer of the ultrasonic transducer is designed according to the quarter wavelength theory. The pulse-echo signal of the developed matching layer is tested and analyzed. The results show that the sound velocity of the matching layer is consistent with the changing trend of the acoustic impedance. That is, the acoustic impedance increases with the increase of the alumina mass fraction, and the density is 1080.73kg/m³. The ultrasonic transducer was designed by matching layer with a sound velocity of 1059.49m/s, with an acoustic impedance of 1.14mryal and acoustic attenuation coefficient of 0.1279dB/mm has good bandwidth and sensitivity.

Expanded graphite/Co@C composites with dual functions of corrosion resistance and microwave absorption

The development of microwave absorption materials with good environmental adaptability is a hot topic in the electromagnetic protection field. In this research, Expanded graphite (EG)/ZIF-67 nanocubes-derived (Co@C) composites were successfully fabricated by electrostatic assembly and subsequent heat treatment. The results show that the involvement of an appropriate content of Co@C not only overcomes the problem of single EG impedance mismatch but also introduces additional magnetic loss for the absorber. At the thicknesses of 1.6 mm and 1.5 mm, an effective absorption bandwidth (EAB) of 4.52 GHz and a minimum reflection loss (RLmin) of −48.4 dB were achieved for the Z2-700 sample with a low filling ratio (20 wt%). The enhancement of EMW-absorption performance is attributed to the optimization of impedance matching and the synergistic action between multiple loss mechanisms. Electrochemical corrosion test showed that graphite nanoflakes of EG enhanced the transfer resistance during corrosion, and the corrosion resistance of pure Co@C was enhanced with the protection of EG. This work provides a reasonable attempt to design and fabricate efficient microwave absorption materials suitable for harsh environments.

Design and Development of High Voltage High Pulse Power Supply using FPGA for Dynamic Impedance Matching

High Voltage High Pulse Power Supply (HVHPPS) is designed with the goal to match fixed load, so thatprecise pulse output can be achieved. Generally the loads involve magnetron, klystron, and particle accelerators etc. The HVHPPS output pulse shape changes with load impedance variation due to various reasons. Due to changes in impedance, the performance of Pulse Power Supply degrades and reflects the power at the source end which causes component failure and system shut down. To overcome such problems, a scale down High Voltage High Pulse Power is designed and developed to match the dynamic impedance variations upto 25 % of mismatch. In earlier days, all HVHPPS were designed using microcontrollers where the problem of pulse to pulse monitoring and computational speed was compromised. The availability of variable and self-defined, Field Programmable Gate Array (FPGA) controller, which provided flexibility to design the pulse to pulse shaping and various vital parameter monitoring, made it possible. This paper presents the design and implementation of HVHPPS over an FPGA platform to meet the fast response requirement. This paper provides a solution for impedance mismatch problems associated with such types of power supply, and also presents specifications for major components in a high voltage pulse power system for various types of load ranges. An experimental test hardware was designed and developed for HVHPPS to implement dynamic impedance algorithm and validate the results.

T-ZnOw/FCIPs with vertical-orientated structure achieving temperature-stable broadband microwave absorption

Currently, most magnetic high-temperature microwave absorbing materials (MAMs) suffer from the problem of impedance mismatch caused by sudden increase in conductivity along with the changing temperature. Herein, the tetra-needle zinc oxide whisker (T-ZnOw) is used as a structural template to manage the spatial distribution of flake carbonyl iron powders (FCIPs), achieving temperature-stable broadband microwave absorption in the range of 30–350 °C. By adjusting the filling content of T-ZnOw makes FCIPs change from random distribution to a vertically oriented distribution. This distribution provides more stable conductive paths and facilitates low temperature-sensitivity conductance loss. At the same time it provides more transmission channels for the incidence of electromagnetic waves (EMW) and achieves excellent impedance matching. Compatibility of conductance loss and impedance matching is thus achieved. The effective absorption bandwidth (reflection loss (RL) < −10 dB) of T-ZnOw/FCIPs in the range of 30–350 °C could cover entire X-band (8.2–12.4 GHz). This work proposes a simple method to adjust the spatial distribution of absorbers and provides a valuable inspiration for the preparation of temperature-stable broadband MAMs.

Analysis Method of Bending Effect on Transmission Characteristics of Ultra-Low-Profile Rectangular Microstrip Antenna.

With the advent of wearable communication devices, microstrip antennas have developed multiple applications due to their ultra-low-profile properties. Therefore, it is essential to analyze the problem of frequency shift and impedance mismatch when the antenna is bent. For the case of a rectangular patch antenna E-plane bent on the cylindrical surface, (1) this paper introduces the effective dielectric constant into the cavity model, which can accurately predict the resonance frequency of the antenna, and (2) according to the equivalent circuit model of the antenna resonance mode, the lumped element parameters are calculated based on the above effective dielectric constant, so that impedance characteristics and the S-parameter matching the port can be quickly constructed. From the perspective of circuit frequency characteristics, it explains the change in the transmission performance of the curved antenna. The experimental results show that the maximum difference between the experimental and theoretical calculation frequencies is less than 1%. These results verify the validity and applicability of the theory in the analysis of ultra-low-profile patch antennas and wearable electronic communication devices. It provides a theoretical basis for the fast impedance matching of patch antennas under different working conditions.

Suppression of spin rectification effects in spin pumping experiments

Spin pumping (SP) is a well-established method to generate pure spin currents allowing efficient spin injection into metals and semiconductors avoiding the problem of impedance mismatch. However, to disentangle pure spin currents from parasitic effects due to spin rectification effects (SRE) is a difficult task that is seriously hampering further developments. Here we propose a simple method that allows suppressing SRE contribution to inverse spin Hall effect (ISHE) voltage signal avoiding long and tedious angle-dependent measurements. We show an experimental study in the well-known Py/Pt system by using a coplanar waveguide (CPW). Results obtained demonstrate that the sign and size of the measured transverse voltage signal depends on the width of the sample along the CPW active line. A progressive reduction of this width evidences that SRE contribution to the measured transverse voltage signal becomes negligibly small for sample width below 200 μm. A numerical solution of the Maxwell equations in the CPW-sample setup, by using the Landau-Lifshitz equation with the Gilbert damping term (LLG) as the constitutive equation of the media, and with the proper set of boundary conditions, confirms the obtained experimental results.

Effect of yttrium on the wave absorption properties of Fe95Si1B2P0.5Cu1.5 alloy powders in the S-band and C-band

In this paper, the effect of rare earth Y on the wave absorption properties of Fe95Si1B2P0.5Cu1.5 alloy powders was investigated, regarding its problem of impedance mismatch in the S-band and C-band. The results show that the introduction of Y induces B atoms into the lattice of α-Fe, causing lattice distortion, while producing Fe2B and Y2Fe13.725Si0.275B. The content of Y affects the powders morphology, and the powders particles change from flake to bulk as the Y content increases. The addition of Y increases the real and imaginary parts of the magnetic permeability, while decreasing the real and imaginary parts of the dielectric constant. Furthermore, the main dielectric loss of the alloy powders turns from conduction loss to relaxation polarization, but the magnetic loss of the alloy powders remains the same as eddy current loss and natural resonance. Meanwhile, the dielectric loss is drastically reduced with little change in the magnetic loss of the alloy powders, which provided the conditions for improving the impedance matching of the material. The addition of Y substantially improves the effective absorption bandwidth and impedance matching of the alloy powders. Among the powders, Fe94.5Si1B2P0.5Cu1.5Y0.5 alloy powders shows superior absorption performance in the S-band and C-band: the minimum reflection loss (RLmin) can reach −42.405 dB at 3.5 mm, and in the thickness range of 1–5 mm, it can achieve full-band absorption in the S-band and C-band, including a maximum effective absorption bandwidth (EAB, RL ≤ 10 dB) of 4.25 GHz at a thickness of 2.4 mm and a EAB of 4.05 GHz at a thickness of 2.5 mm, which encapsulates the entire C-band.

Analysis of impedance matching for a spherical multi-degree-of-freedom ultrasonic motor.

A novel spherical multi-degree-of-freedom ultrasonic motor is designed, which can achieve three-degree-of-freedom motion through the cooperative drive of three built-in traveling wave stators. The novel ultrasonic motor has the characteristics of compact structure and high power density. Additionally, in order to solve the problem of impedance mismatch between the ultrasonic motor and the driving power supply, a semi-analytical method of impedance matching based on parallel resonance is proposed according to the impedance characteristics of ultrasonic motor. Through the combination of theoretical derivation and finite element simulation, the ultrasonic motor impedance matching on the impedance circle is analyzed. By this method, the optimum matching inductor of the motor is determined. After matching, the motor obtains a larger vibration amplitude and higher transmission efficiency. Finally, the reliability of the method is verified by simulation and experiment, which provides a reference for further improving the motor performance.

Investigating the Effects of Object-Relational Impedance Mismatch on the Efficiency of Object-Relational Mapping Frameworks

The object-relational impedance mismatch (ORIM) problem characterises differences between the object-oriented and relational approaches to data access. Queries generated by object-relational mapping (ORM) frameworks are designed to overcome ORIM difficulties and can cause performance concerns in environments which use object-oriented paradigms. The aim of this paper is twofold, first presenting a survey of database practitioners on the effectiveness of ORM tools followed by an experimental investigation into the extent of operational concerns through the comparison of ORM-generated query performance and SQL query performance with a benchmark data set. The results show there are perceived difficulties in tuning ORM tools and distrust around their effectiveness. Through experimental testing, these views are validated by demonstrating that ORMs exhibit performance issues to the detriment of the query and the overall scalability of the ORM-led approach. Future work on establishing a system to support the query optimiser when parsing and preparing ORM-generated queries is outlined.

Modeling and validation of a new reconfigurable patch antenna through equivalent lumped circuit‐based design for minimum tuning effort

AbstractThis study presents a modeling of a new reconfigurable patch antenna with equivalent lumped circuit. Instead of intuitive approaches, including structural changes used in the literature, the proposed reconfigurable antenna design is based on minimum tuning effort using only capacitance adjustments. The proposed design resolves impedance mismatch problem, which occurs due to the nature of using several frequencies by only capacitance adjustments rather than physical structure adjustments. Reconfigurable patch antenna for 2.45 GHz (Wi‐Fi), 3.6 GHz (Wi‐max and 5G), 5.4 GHz (WLAN and 5G) was considered for novel design strategy. A complete equivalent circuit model is configured and validated through AWR software. Full wave analysis of the proposed antenna is performed using CST software. A prototype of the proposed antenna is also fabricated on a FR4 substrate with the dimensions of 48.19 x 38.36 x 1.53 mm3 and measured to validate the full wave analysis and circuit theory solution results. It is shown that the equivalent circuit model, full wave analysis, and measurement results are in good agreement.