Optimum Impedance Research Articles

Achieving Superior Electromagnetic-Absorbing Performances in the Hexagonal Flake BaFe12O19@PVDF Composites.

Combining magnetic and dielectric materials to form a composite can significantly improve its impedance matching and electromagnetic wave absorption performance. Furthermore, composite materials with a core-shell structure hold promise in meeting the demand for lightweight and highly electromagnetic-absorbing properties. In this study, uniform hexagonal flake barium ferrite (BaFe12O19) was prepared using the hydrothermal method. Subsequently, BaFe12O19@PVDF composites were synthesized by the sol-gel method. By adjusting the mass ratio of BaFe12O19 and PVDF, the shell size of the BaFe12O19@PVDF composite material was controlled, and its electromagnetic absorption performance was enhanced. The shell thickness of BaFe12O19@PVDF is 19.64 nm when the BaFe12O19: PVDF mass ratio is 1:1.0, and the optimal impedance matching is obtained at 13.4 GHz. Meanwhile, at a thickness of 1.5 mm, the minimum reflection loss (RLmin) reached -58.04 dB, and an effective absorption bandwidth (EAB) (RL ≤ -10 dB) of 5.53 GHz was achieved within the frequency range of 11.65 to 15.63 GHz and from 16.36 to 17.91 GHz. Besides, the composites with a matching thickness of 3.5 mm show a maximum EAB of 15.90 GHz when the mass ratio of BaFe12O19 to PVDF is 1:1.2. Within the frequency range of 2-18 GHz, the coverage of reflection loss less than -10 dB is 99.38%, almost achieving full coverage. These results demonstrate that BaFe12O19@PVDF composites exhibit excellent electromagnetic-absorbing performances, making them an excellent candidate for electromagnetic wave absorption in 5G communications.

Thermally-driven contraction asymmetric yolk-shell MnSe@C microsphere with boosted dielectric behaviors and microwave absorption

The conventional selective template etching method to fabricate yolk-shell microwave absorbers is inconvenient and inefficient, so the thermally-driven contraction strategy was used to prepare asymmetric yolk-shell MnSe@C microsphere microwave absorbers via self-template directed transformation. The self-templated oriented transformation enables compositional customization and enhances the template utilization. The confinement effect of the carbon shell is crucial for realizing the thermally-driven contraction strategy and contributes to the strong conduction loss to MnSe@C. On the other hand, the enhanced polarization loss benefits from the abundant heterogeneous interfaces and defects in the asymmetric yolk-shell MnSe@C microspheres. The rich cavities in the yolk-shell structure not only facilitate optimal impedance matching, but also promote the enhancement of multiple reflection loss (RL). As a result, the asymmetric yolk-shell MnSe@C microspheres obtain excellent microwave absorption performance, the minimum RL (RLmin) and the maximum effective absorption bandwidth (EAB) reaching –54.4 dB and 5.1 GHz, respectively, at a thickness of 1.9 mm. The successful obtainment of the asymmetric yolk-shell MnSe@C microspheres paves the way for the convenient synthesis of the yolk-shell transition-metal selenides (TMSs) microwave absorbers.

Microwave absorption enhancement by SiC nanowire aerogels through heat treatment-based oxidation modulation

SiC nanowire aerogels (SNWA) emerge as a promising category of electromagnetic wave absorbers (EMA) that can be applicable to extreme environments since they possess exceptional dielectric loss properties and superior ceramic characteristics. However, obtaining high-performance microwave absorption (MA) with a single SiC nanowire component poses a formidable challenge, such that the intrinsic MA potential in SNWA should be analyzed in depth. In this study, SNWAs were synthesized as a foundational matrix, of which the nanowire diameters were uniformly distributed, by adopting a straightforward and simple chemical vapor deposition (CVD) method. Subsequently, the SiO2 sheath thickness on the external surface of SiC nanowires was modified through controlled oxidation modulation. Noteworthily, the above-described precise control over the SiO2 sheath thickness served a dual purpose: it enables optimal impedance matching in the SNWA while substantially augmenting its dielectric loss capacity. To the best of our knowledge, this study has underscored the significance of optimizing the SiC/SiO2 heterointerface for enhancing MA in SNWA for the first time. Such optimization is promising to significantly facilitate the design and synthesis of SiC nanowire-based EMA.

Design of Ku-band power amplifier for satellite applications using neural network

Power amplifier one of the most important part of a transmitter. For the proposed power amplifier, the optimum load and source impedances have been calculated by source and load-pull analysis. The device selected is Cree CGHV1J006D, and the substrate chosen is alumina. With help of neural network algorithm the optimum matching architecture design of input and output network are calculated and the value is validated through Keysight ADS. At frequency range of 13.75 GHz-14.5 GHz maximum drain efficiency of 32.434% and the gain of 4.236 dB is achieved. The proposed power amplifier(PA) have dimension of 22 mm × 4 mm. With an output power of more than 35 dBm, these results represent state-of-the-art performance in terms of power efficiency in the Ku-band.

Uncertainty-oriented optimal impedance control for EPS-human system with reliability evaluation

This study proposes an interval optimal impedance control method for the electric power steering- human (EPS-H) system with reliability constraints. Considering the relationship between the lateral control using electric power steering of the vehicle and the human, a position-based impedance control model for the integrated EPS-H system is first developed. Polynomial chaos expansion in the surrogate model is employed to establish the interval state-space equation to obtain the bounded responses of the impedance control system using the interval dimensional analysis method. Moreover, the influence of uncertain parameters on the overall control system is obtained by deriving the interval optimal control law consisting of the interval linear quadratic tracking (LQT) inner loop and the interval impedance control outer loop through the interval uncertainty analysis. Furthermore, a non-probabilistic time-varying reliability method is proposed to evaluate the safety of the whole impedance system using the partial derivatives with respect to the uncertain parameters derived from the interval state-space equation. Regarding the nominal cost function and steady-state error of nominal responses as two optimization objectives, the multi-objective reliability-based design optimization is built and solved. Finally, a numerical example of the impedance control model for the EPS-H system is applied to verify the effectiveness of the proposed method.

RF Characterization of GaAs HBT under Load Mismatch with Reverse Wave Injection Technique.

RF PAs need to be reliable enough to protect them from damage under load mismatch conditions. This paper investigated the characteristics of GaAs heterojunction bipolar transistors (HBTs) under load mismatch conditions using a novel reverse wave injection technique to realize large VSWR ruggedness measurement with the circle centered at 50 Ohm and optimal impedance separately to analyze the device in real applications. With a real-time waveform measurement system, the RF voltage and current waveform information can be acquired, which provide a more-accurate view of what is occurring at the current generator plane of the HBT device. Thereby, the potential failure mechanisms and load impedance can be identified to design the most-suitable PA circuits in communication systems.

Ultra-flexible silver/iron nanowire decorated melamine composite foams for high-efficiency electromagnetic wave absorption and thermal management

Nowadays, functional electronic devices with excellent flexibility and thermal management capability for effective electromagnetic wave absorption are urgently in demand. Herein, a novel and highly flexible silver nanowire (AgNW)/iron nanowire (FeNW) decorated melamine composite foam (AgFe-MF) was prepared via simple dip-coating process. Owing to optimal impedance matching, synergistic dielectric and magnetic losses as well as three-dimensional porous structure, the AgFe-MF with an ultra-low filler content (0.22 vol%) exhibited an outstanding minimum reflection loss of −69.61 dB, and the best effective absorption bandwidth (EAB) could reach up to 6.37 GHz. Importantly, the EAB of long-time working AgFe-MF was enhanced to 7.01 GHz after 1000 compress-release cycles under 40 % strain. Besides, it also featured considerate Joule heating capacity and achieved a saturation temperature of over 85.7 ℃ under 2.6 V voltage. The impressive thermal isolation and long-term stability ensured the safety used as portable heater. Therefore, this work will provide a vital slight for fabricating smart wearable electronic devices with integrated anti-electromagnetic radiation and personalized thermal management performances towards potential thermal and health threats.

Performance improvement and thermomechanical analysis of a novel asymmetrical annular thermoelectric generator

Enhancing thermoelectric performance hinges on optimizing the geometry of thermoelectric legs. In this study, we present a novel asymmetrical annular thermoelectric generator (ATEG) in which the proportions of P-type and N-type legs are meticulously balanced. We construct a one-dimensional analytical model tailored to this ATEG. Utilizing this model, we derive the relationship governing thermal-electrical impedance matching in an asymmetrical ATEG and formulate a general expression for optimizing the asymmetry coefficient. We explore the influence of various thermal boundary conditions on optimal impedance matching, ideal annular leg parameters, and the optimal asymmetry coefficient. Our findings reveal that thermal boundary conditions significantly affect the optimal load ratio. Furthermore, in comparison to traditional ATEGs, our proposed asymmetrical ATEG with the optimized structure exhibits a remarkable 16.2 % increase in output power while maintaining the same material volume. Additionally, we perform a three-dimensional numerical analysis of the asymmetrical ATEG using Comsol. Our research findings indicate that introducing the asymmetric structure leads to higher maximum thermal stress on the legs. Interestingly, the study of asymmetric thermal boundary conditions highlights that improving heat transfer between the ATEG and the cooler yields higher mechanical reliability compared to enhancing heat transfer between the ATEG and the heat source.

Research on fuzzy impedance control of upper-limb rehabilitation robot based on membership functions online optimization learning strategy

PurposeTo improve the position tracking efficiency of the upper-limb rehabilitation robot for stroke hemiplegia patients, the optimization Learning rate of the membership function based on the fuzzy impedance controller of the rehabilitation robot is propose.Design/methodology/approachFirst, the impaired limb’s damping and stiffness parameters for evaluating its physical recovery condition are online estimated by using weighted least squares method based on recursive algorithm. Second, the fuzzy impedance control with the rule has been designed with the optimal impedance parameters. Finally, the membership function learning rate online optimization strategy based on Takagi-Sugeno (TS) fuzzy impedance model was proposed to improve the position tracking speed of fuzzy impedance control.FindingsThis method provides a solution for improving the membership function learning rate of the fuzzy impedance controller of the upper limb rehabilitation robot. Compared with traditional TS fuzzy impedance controller in position control, the improved TS fuzzy impedance controller has reduced the overshoot stability time by 0.025 s, and the position error caused by simulating the thrust interference of the impaired limb has been reduced by 8.4%. This fact is verified by simulation and test.Originality/valueThe TS fuzzy impedance controller based on membership function online optimization learning strategy can effectively optimize control parameters and improve the position tracking speed of upper limb rehabilitation robots. This controller improves the auxiliary rehabilitation efficiency of the upper limb rehabilitation robot and ensures the stability of auxiliary rehabilitation training.

Design of an optimized load-resilient conjugate T for the ICRH system in the LHD using a novel hybrid circuit/3DLHDAP code and experimental results

It is crucial to correctly predict the S-matrix with plasma and set the optimal impedance matching device in the ion cyclotron resonance heating (ICRH) antenna system design. In this paper, a hybrid circuit/3DLHDAP code to verify the S-matrix measurements in the presence of plasma and optimize the load-resilient conjugate-T circuit for Large Helical Device (LHD) ICRH antennas has been developed and benchmarked. The variation of S-matrices for handshake form (HAS) and field-aligned-impedance-transforming (FAIT) antenna systems with density, magnetic field and coupling distance during heating obtained by the code’s simulations agrees with that of with the LHD ICRH experiments. The mutual coupling of toroidally aligned HAS antennas is larger than that of poloidally aligned FAIT antennas over a wide range of densities. When the density and coupling distance increase, under a magnetic field on the magnetic axis of 2.75 T and 1.0 T, within a certain density change range, at the minimum voltage position with vacuum injection, the change rule of the antennas’ Sa_minV_ 11 and Sa_minV_ 22 with density is opposite to that with coupling distance, which means that under certain conditions, adjusting the coupling distance may make up for the S-parameters changes caused by plasma density variation, keeping the minimum voltage position fixed, and may make impedance matching easier to achieve during long-pulse operation. Based on obtaining the S parameters, conjugate-T circuits for the HAS and FAIT antennas are designed with the hybrid circuit/3DLHDAP code, which can keep the reflection coefficients low without controlling impedance matching device over a wide range of plasma parameters region. The related results in this paper may provide some guidance for the high-power long-pulse operation of the ICRH antenna system on the fusion device.

Computer aided design automation for triboelectric nanogenerators

For application of triboelectric nanogenerators (TENG), it is essential to design TENG with high energy conversion efficiency, and it is one of the crucial parts to obtain TENG designs with optimal output impedance to match with that of application systems. Current design processes are incapable of optimizing TENGs with complex structures effectively, which greatly prolongs the research and development process and hinders application of TENGs. Here, a universal computer aided design automation is proposed to generate the structural and material design of TENG for optimal power output under designated matching resistance. A semi-analytical method and a non-dominated sorting genetic algorithm (NSGA-II) are used for the design automation. For demonstration, design automation for freestanding rotational TENG (FR-TENG) is carried out. An acceleration factor of up to ∼900 is obtained with systematical simulation acceleration. A group of designs with optimal powers and matching resistances are obtained, from which different input impedances of power management units can be obtained for applications. For verification, a FR-TENG with an optimal average output power over 88 mW is designed and fabricated, the output impedance is intentionally chosen from pareto-optimal front to match the input impedance of the subsequent power management unit. This is used to develop a fully self-powered wireless humidity/temperature/ultraviolet environmental monitoring system. This system can transmit the sensing information every ∼ 7 s and display on a remote terminal, validating the effectiveness of the proposed design automation method.

Multimodal-based shape optimization of a rectangular horn mounted in an enclosure for optimum impedance matching

This study presents a multimodal-based method to optimize the boundary shape of a rectangular horn for optimum impedance matching, assuming that the horn is mounted in an enclosure to adapt to practical applications. An infinite rectangular waveguide with a perfectly matched layer is introduced to solve the multimodal radiation impedances of the horn. The throat impedance of the horn is then calculated using the mode matching method. The optimum impedance matching properties over a wide frequency range are obtained by performing gradient-based shape optimization. The results show that the choice of target frequency band can significantly affect the optimization results. The numerical model is verified by the finite element method. The impedance matching performance of an optimal horn design is also experimentally validated.

Multifunctional ultralight magnetic CNFs/MXene/Fe3O4 nanodiscs aerogel with superior electromagnetic wave absorption performance

The design of innovative microstructures and the implementation of an appropriate multi-component strategy remain challenging in the development of advanced electromagnetic wave (EMW) absorbing materials. Achieving strong absorption and a wide effective absorption bandwidth while maintaining a thin sample thickness and low filling level is particularly demanding. Herein, a three-dimensional (3D) dielectric cellulose nanofiber (CNF)/Ti3C2Tx MXene carbon aerogel, incorporating magnetic Fe3O4 nanodiscs (NDs), was fabricated using a directional-freezing technique followed by reduction. Surprisingly, the reduction process activates the multifunctional application of aerogel with better elasticity and greatly improved electromagnetic properties, killing two birds with one stone. The structured cellular arrangement and the presence of diverse dielectric/magnetic interfaces contribute to the exceptional absorption capabilities by facilitating optimal impedance matching, enabling multiple polarization modes, and fostering electric/magnetic coupling phenomena. The aerogel exhibits excellent microwave absorption properties, characterized by its ultra-lightweight (3 % of filling ratio and 4.65 mg cm−3 of density), ultra-thin (2.18 mm), ultra-wide frequency band (6.68 GHz) and strong absorption (-56.8 dB). Additionally, the aerogel provides attractive functions such as thermal insulation and great mechanical properties (100 % recovery after 1000 cycles under 50 % strain). This study lays the groundwork for the advancement of microwave-absorbing materials, showcasing their vast potential for multifaceted applications.

ZIF-67@carbon fiber derived magnetic-dielectric synergistic heterostructure for excellent microwave absorption under ultrathin thickness

Aiming to solve the aggravating electromagnetic radiation issues, high-performance electromagnetic wave (EMW) absorbers are urgently required. Recently, integrating carbonaceous and magnetic materials to obtain dielectric-magnetic double EMW loss has been intensively explored. Here, Co3O4/Co@carbon nanofibers/carbon nanotubes anchored on carbon fiber (Co3O4/Co@CNFs/CNTs/CF) hybrids (CFFs) with distinctive heterostructure were synthesized by annealing ZIF-67@CF and catalytic chemical vapor deposition, and deliver great superiorities in microwave dissipation. Specifically, when at a low filling ratio of 25 wt% in paraffin wax, CFF650 acquires a superb minimum reflection loss up to −60.85 dB at only 1.22 mm together with a broad effective absorption bandwidth of 4.24 GHz at merely 1.38 mm. Remarkably, the specific reflection loss of CFF650 achieves an unexpected value, comparable to many distinguished carbon-based composites previously reported. Besides, the simulation of radar cross section values ascertains the fulfilling stealth ability of CFFs under radar detection. These excellent characteristics benefit from the diverse components and unique heterostructures, which form rich conductive networks, plentiful heterogeneous interfaces, appropriate defect polarization and dipole polarization, sufficient magnetic loss as well as optimal impedance matching. Combined with the feasible and efficient fabrication method, this work offers a significant promise of CF-based composites for practical applications in EMW absorption.

Encapsulated prussian blue analogs derived nanocubes with tunable yolk-shell structure enabling highly efficient microwave absorption

Pyrolytic Prussian blue analogs (PBAs) have attracted much attention in the field of microwave absorption (MA) because of their outstanding magnetic-carbon synergism effect. However, pure PBAs are prone to collapse and aggregate during pyrolysis, resulting in impedance mismatch that weaken the MA performance. Herein, the amorphous carbon layer with adjustable dielectric constant as the encapsulated layer, together with pyrolytic PBAs enables remarkable optimized performance via forming the classic yolk-shell structure. Specifically, the amorphous carbon obtained by quantitatively carbonizing phenolic resin, can not only avoid the collapse of pyrolytic PBAs but also optimize electromagnetic parameters to achieve optimum impedance matching by varying thickness. The NiFe alloys/graphite carbon core derived from pyrolytic NiFe–PBAs also enhance synergistic attenuation in the YS-NiFe/GC@C absorbers. According to experimental results, all YS-NiFe/GC@C absorbers exhibit impressive MA properties. When the thickness of the amorphous carbon shell is 50 nm, the minimum reflection loss value is as low as −56.3 dB and the maximum effective absorption bandwidth reaches 5.64 GHz, indicating that optimizing impedance matching via hierarchical and quantitative design can maximize the MA capability. The result is then verified by simulation calculations. Therefore, this promising work provides guidance for the sophisticated construction of tunable PBA-based MA materials.

Optimal Impedance Design for Dual-Branch High-Frequency Inverter Based on Active Regulation and Passive Projection

Optimal Impedance Design for Dual-Branch High-Frequency Inverter Based on Active Regulation and Passive Projection

Low-Cost Manufacturing of Monolithic Resonant Piezoelectric Devices for Energy Harvesting Using 3D Printing.

The rapid increase of the Internet of Things (IoT) has led to significant growth in the development of low-power sensors. However; the biggest challenge in the expansion of the IoT is the energy dependency of the sensors. A promising solution that provides power autonomy to the IoT sensor nodes is energy harvesting (EH) from ambient sources and its conversion into electricity. Through 3D printing, it is possible to create monolithic harvesters. This reduces costs as it eliminates the need for subsequent assembly tools. Thanks to computer-aided design (CAD), the harvester can be specifically adapted to the environmental conditions of the application. In this work, a piezoelectric resonant energy harvester has been designed, fabricated, and electrically characterized. Physical characterization of the piezoelectric material and the final resonator was also performed. In addition, a study and optimization of the device was carried out using finite element modeling. In terms of electrical characterization, it was determined that the device can achieve a maximum output power of 1.46 mW when operated with an optimal load impedance of 4 MΩ and subjected to an acceleration of 1 G. Finally, a proof-of-concept device was designed and fabricated with the goal of measuring the current passing through a wire.

Design of a 0.4–3.9-GHz Wideband High-Efficiency Power Amplifier Based on a Novel Bandwidth Extended Matching Network

The design of a multi-octave power amplifier (PA) is presented based on extended continuous Class-B/J (ECB/J) modes in this paper. The wide design space provided by the ECB/J modes has been used as the goal for the design. A unique bandwidth extended matching network that can achieve a broadband impedance matching in the appropriate impedance region by simultaneously manipulating six frequency points is proposed to compensate for the impedance dispersion effect caused by the change of the optimal impedance with the operating frequency in the design of the matching network. To verify the proposed methodology, a wideband PA is designed and fabricated by using a commercial 10-W gallium nitride (GaN) device. The implemented PA achieves a bandwidth of 163% from 0.4 to 3.9 GHz while exhibiting excellent performance of 38-42.3 dBm output power, 57-68% drain efficiency, and 10-13 dB gain. The measured adjacent channel power ratio (ACPR) is lower than -26 dBc at 0.8, 1.5, 2.0, 2.5, 3.0, and 3.5 GHz when the output power is lower than 36 dBm.

Load Mismatch Compensation of Doherty Power Amplifier Using Dual-Input and Mode Reconfiguration Techniques

Doherty power amplifier (DPA) has shown great potentials in wireless communication systems. However, the output power and efficiency of a DPA are very susceptible to load mismatch. This paper presents the load mismatch analysis and compensation of coupler-based DPAs leveraging on dual-input and mode reconfiguration techniques. A comprehensive analysis, which takes voltage clipping into consideration, is conducted on a coupler-based dual-input DPA (CBDI-DPA) under load mismatch condition. It is illustrated that the parallel Doherty mode could recover the saturation and back-off drain efficiencies (DEs) for the load mismatch in the left and right half parts of the Smith chart, respectively. And the serial Doherty mode could recover the back-off and saturation DEs for the load mismatch in the left and right half parts of the Smith chart, respectively. As a validation, a CBDI-DPA operating at 2.4 GHz is fabricated and measured in this paper. Under the optimal load impedance condition, the fabricated CBDI-DPA delivers a saturation power of more than 43.5 dBm, a saturation DE of more than 70% and a 6 dB back-off DE of more than 60% in both the parallel and the serial Doherty modes. Meanwhile, the simulation and experimental results demonstrate the proposed method can recover the output power and efficiency of a DPA when the load mismatch is inside the 2:1 VSWR circle.

Switchless Dual-Power-Mode Fully Differential HBT Power Amplifier for Mobile Applications

This study proposes a switchless dual-power-mode (DPM) power amplifier (PA), which operates independently in high-powermode (HPM) and low-power mode (LPM) to improve the efficiency. The DPM PA optimizes the output impedances using bias control of the PA and the proposed bidirectional output matching structure with a transformer (TF) for each power mode with no switches for isolation between the LPM and the HPM with high passive efficiency. The proposed output structure realizes a high impedance in the nonoperating mode network to ensure that the operating mode network realizes the optimal impedance by utilizing bidirectional matching of the off characteristics of transistors and TF output for each mode. The differential DPM PA is implemented using a 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \mathrm{m}$</tex-math> </inline-formula> InGaP/GaAs heterojunction bipolar transistor (HBT) process on a nine-layer printed circuit board with low insertion loss to demonstrate the proposed structure. The HPM and LPM, operating independently, achieved the gains of 24–25.5 and 11.4–12.9 dB and the saturated output power of 34.2–34.8 and 23.2–23.5 dBm, with a peak power-added efficiency (PAE) of 44.4%–49% and 32%–34.4%, respectively, under a continuous-wave (CW) signal test of over 5.15–5.925 GHz. The proposed PA error vector magnitude (EVM) is tested with 160 MHz of a 64-quadrature amplitude modulator (QAM) signal and achieves the average output powers of 24.5 and 14 dBm (EVM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ -$</tex-math> </inline-formula> 32 dB) and a PAE of 10.5% and 10.1% for HPM and LPM with digital predistortion, respectively.