Optimum Impedance Research Articles

A 50 W dual‐band high‐efficiency gallium nitride high electron mobility transistor power amplifier with three‐stage L‐type DC bias circuit at 1.8 and 2.6 GHz

AbstractA 50 W dual‐band high‐efficiency gallium nitride (GaN) high electron mobility transistor (HEMT) power amplifier with a three‐stage L‐type DC bias circuit capable of individually adjusting second‐harmonic impedances is proposed for 1.8 and 2.6 GHz frequencies. The output network of this power amplifier is composed of an output matching network comprising five‐stage transmission lines and a three‐stage L‐type DC bias circuit with three L‐type circuits and one transmission line. The one‐stage L‐type circuit comprises a series transmission line and a quarter‐wavelength open‐ended shunt stub. For the high‐efficiency performance of the power amplifier, the output matching network is matched to the optimum impedances of the fundamental frequencies, and the DC bias circuit optimizes the impedances individually at the second‐harmonic frequencies without affecting the matched fundamental frequency impedances in the output matching network. Measured results show that the proposed dual‐band GaN HEMT power amplifier achieved gains of 15.6 and 13.8 dB as well as maximum power‐added efficiencies of 70.5% and 66.3% with 47 dBm output power at 1.8 and 2.6 GHz, respectively.

Construction of Ni-Zn bimetal sulfides Heterostructured-hybrids for High-performance electromagnetic wave absorption

Utilizing the synergistic effect of multiple components in heterostructured composites has been regarded as a promising strategy for achieving high-performance electromagnetic wave absorption. Nonetheless, rationally collocate the components of absorbers in order to legitimately achieve synergy remains an intractable problem. By adjusting the NiS and ZnS composition ratios in the ZnS/NiS/C composites, the optimal impedance matching and dissipation capability can be obtained. The formation of a ZnS/NiS heterostructure is found to significantly enhance polarization relaxation, and the relative ratios of ZnS and NiS have a significant effect on the electromagnetic properties. The optimal performance was obtained on Z1N2, with a minimum reflection loss of –51.45 dB at 4.72 GHz and –56.69 dB at 11.12 GHz, respectively, and an effective absorption bandwidth of up to 3.68 GHz at 1.16 mm. The potential of heterogeneous bimetal sulfides as high-performance absorbers is demonstrated in this study.

Optimal interstage liner design: A parametric study

The current trends for next generation turbofan engines are towards shorter nacelles and increased distances between the fan and the outlet guide vanes. This leads to an overall reduction in lined surface areas as well as an increase in the relative importance of the interstage liner, which is the liner placed between the rotor blades and the stator vanes. So far most of the efforts have been on liners for intakes and bypass ducts. The interstage is different in that the liner is subject to a mean flow with a strong swirl component and shear. The focus of this paper is on the effect of swirling flow on optimal liner attenuation in the interstage region. A broadband source downstream at the Outlet Guide Vanes (OGV) consisting of all propagating modes with equal power in each mode is used. Optimum impedance plots are generated for approach and take-off mean flow conditions. The effect of swirl on liner optimum resistance and reactance and optimum insertion loss is observed for a frequency range characteristic of real turbofan engines.

A Yield-Improvement Method for Millimeter-Wave GaN MMIC Power Amplifier Design Based on Load—Pull Analysis

Process fluctuations can significantly affect the yield of millimeter-wave circuits based on submicrometer semiconductor processes. A yield-improvement design that incorporates passive circuits is well established. However, how to consider the process fluctuation in active circuit designs (e.g., power amplifiers) and improve yield is still a challenge. In this article, a yield-improvement load-pull design method, which can be used to find optimum load impedance accounting for high yield while maintaining good output performance, is presented. The yield-improvement load-pull theory is described using an analytical model of transistor large-signal performance considering the process fluctuation. A method of the yield-improvement load-pull for the practical microwave monolithic integrated circuit (MMIC) design is introduced in detail. For demonstration purposes, a high-performance Ka-band power amplifier MMIC is designed. The results show that with the proposed yield-improvement load-pull method, an obvious improvement of yield can be observed with only minimal sacrifice of the output power ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ) and the power added efficiency ( η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PAE</sub> ), respectively. As a result, the method of this article can be used to improve the yield of millimeter-wave/terahertz integrated circuits (ICs).

A Low-Noise and Fast-Settling UHF RFID Receiver With Digitally Controlled Leakage Cancellation

UHF RFID reader suffers from a strong transmitter (Tx) leakage signal coupled to a receiver (Rx), especially for an area-compact single-antenna implementation. Then, several Tx leakage cancellation schemes have been developed not to saturate the Rx and to minimize the performance degradation. This brief proposes a UHF RFID reader Rx with a low noise performance and a fast settling time by employing a digitally controlled leakage cancellation method in both passive and active realizations. A digitally-controlled passive vector reflector enhances the Tx to Rx isolation ratio by providing the optimum load impedance. An active anti-leakage feedback loop adaptively tracks the time-varying leakage and generate the phase-inverted leakage replica to suppress the leakage. The prototype chip is fabricated in a CMOS 55 nm process and the area of the chip is 2.1 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.8$ </tex-math></inline-formula> mm. The passive leakage cancellation (PLC) with a vector reflector endures the 1 dBm leakage with a low Rx noise figure of 12.5 dB and 35.7 mW power consumption. The active leakage cancellation (ALC) with an anti-leakage feedback loop covers 6 dBm leakage with a fast settling time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.6~\mu \text{s}$ </tex-math></inline-formula> and 58 mW power consumption.

A mathematical formulation for the optimal impedance of a curved axial microperforated panel in a duct bend.

Previous work [J. Acoust. Soc. Am. 145, 501-511 (2019)] showed that a micro-perforated panel (MPP) placed in a duct bend will couple to the separated air channels to constitute a resonant system. This coupling effect results in the vibration of air mass inside micropores and provides damping to the duct. However, only limited attenuation was obtained. To enhance the damping effect, a mathematical formulation for the optimal impedance of the MPP (or a thin structure that has continuous normal velocity and pressure jump boundary conditions) is derived based on the concept of Cremer impedance which is mathematically equivalent to finding the exceptional point of a non-Hermitian system. Validation of the proposed model is made by examining the mode merging phenomenon at the exceptional point. The optimal damping is also compared with a straight duct having one of its wall lined.

Facile fabrication of cobalt/nitrogen-doped graphite composites with high-performance microwave absorption

Magnetic metals are vital microwave-absorbing materials in alleviating electromagnetic (EM) pollution; however, in practical applications they are limited by their high density and relatively narrow absorption band. An effective strategy for addressing this issue is compounding magnetic metals with carbon materials. In this work, we fabricated the carbon/nitrogen-doped graphite (Co/NC) composites using a simple and low-cost method by directly calcining a dry mixture of melamine and Co powders in Ar gas. Part of Co/NC composite was calcined at 800 °C (Co/NC−800). The effects of variations in phase composition and morphology on the EM parameters and microwave-absorbing performance were investigated. Compared to pure Co, Co/NC−800 composite exhibits excellent microwave-absorbing performance such as strong absorption, better EM wave attenuation, and a lighter weight. Particularly, Co/NC−800 composite achieved the minimum reflection loss (RL) of −57.76 dB at 4.88 GHz and an effective absorption bandwidth (EABW, RL ≤ −10 dB) of 14.26 GHz (3.74–18.00 GHz) at a coating thickness d of 1.00–5.00 mm. Further, the maximum EABW of 5.50 GHz was attained at d = 1.86 mm. The optimal impedance matching, multiple scattering and reflections of EM waves on rough surfaces, and strong dielectric loss including conduction loss, interfacial and dipolar polarizations were noted as the main factors for the enhanced EM energy absorbance of Co/NC−800 composite. We believe our work may serve as a guideline for the fabrication of other light carbon-based magnetic metal composites as EM wave absorbers.

A breathable and flexible fiber cloth based on cellulose/polyaniline cellular membrane for microwave shielding and absorbing applications

High-performance electromagnetic (EM) wave absorption and shielding materials integrating with flexibility, air permeability, and anti-fatigue characteristics are of great potential in portable and wearable electronics. These materials usually prepared by depositing metal or alloy coatings on fabrics. However, the shortcomings of heavy weight and easy corrosion hamper its application. In this work, the cellulose nanofiber (CF) fabric was prepared by electrospinning technology. Then, conductive polyaniline (PANI) was deposited on the CF surface via a facile in-situ polymerization process. The interweaving cellulose/polyaniline nanofiber (CPF) composite constructs a conductive network, and the electrical conductivity can be adjusted by polymerization time. Benefiting from optimal impedance matching, strong conductive loss, as well as interfacial polarization, the CPF possesses excellent EM absorption performance. The minimum reflection loss (RLmin) value is −49.24 dB, and the effective absorption bandwidth (RL < −10 dB, fe) reaches 6.90 GHz. Furthermore, the CPF also exhibits outstanding electromagnetic interference (EMI) shielding capability with shielding efficiency (SE) of 34.93 dB in the whole X band. Most importantly, the lightweight CPF fabrics have the merits of mechanical flexibility, breathability and wash resistance, which is highly applicable for wearable devices.

Design of 0.6–0.8-GHz and 1.6–1.9-GHz Dual-Band PA With Peak PAEs of Over 70% by NPE Method With Dynamical Continuous-Mode Criteria

A high-efficiency concurrent dual-band GaN power amplifier (PA) is designed and fabricated based on the network parameter extraction (NPE) method, where the expanded optimum load impedance spaces of continuous modes are applied to construct the NPE criteria to facilitate harmonic tuning. A swallow-spit process is proposed to improve the effectiveness of NPE by dynamically changing the criteria. The prototype design process verified that the proposed algorithm is easy to be implemented, which avoids the cumbersome tunings and complex numerical derivations on the parameters of the dual-band output matching networks. Measurement results demonstrate that the fabricated GaN PA achieves saturated output powers of 40.5 dBm ± 0.4 dBm and 41 dBm ± 0.3 dBm over dual bands of 0.6-0.8 GHz and 1.6-1.9 GHz with peak PAEs of 71%-74% and 68%-73%, respectively.

Evolution from core-shell, yolk-shell to hollow structure of hierarchical SiO2@MoSe2@FeNi3 for enhanced electromagnetic wave absorption

In the design of advanced electromagnetic wave absorbing materials, composition and microstructure are critical to affect interactions between the incident waves with the absorbers. Here hierarchical SiO2@MoSe2@FeNi3 has been developed and impacts of evolution from core-shell, yolk-shell to hollow structures on the absorption performance has been investigated. Combination of the magnetic FeNi3 and the dielectric MoSe2 and SiO2 gives rise to synergistic and effective dissipation of the incident waves, whereas the impedance can be tuned by the size of the void during the microstructural evolution. Among the designed hierarchical SiO2@MoSe2@FeNi3, the yolk-shell composite exhibits enhanced absorption with a minimum reflection loss of − 45.25 dB over a wide effective absorption bandwidth of 6.80 GHz at a thickness of 1.4 mm due to optimal attenuation and impedance matching.

Impedance Optimization for Uncertain Contact Interactions Through Risk Sensitive Optimal Control

This letter addresses the problem of computing optimal impedance schedules for legged locomotion tasks involving complex contact interactions. We formulate the problem of impedance regulation as a trade-off between disturbance rejection and measurement uncertainty. We extend a stochastic optimal control algorithm known as Risk Sensitive Control to take into account measurement uncertainty and propose a formal way to include such uncertainty for unknown contact locations. The approach can efficiently generate optimal state and control trajectories along with local feedback control gains, i.e. impedance schedules. Extensive simulations demonstrate the capabilities of the approach in generating meaningful stiffness and damping modulation patterns before and after contact interaction. For example, contact forces are reduced during early contacts, damping increases to anticipate a high impact event and tracking is automatically traded-off for increased stability. In particular, we show a significant improvement in performance during jumping and trotting tasks with a simulated quadruped robot.

Fabrication of binary MOF-derived hybrid nanoflowers via selective assembly and their microwave absorbing properties

In recent years, carbon materials derived from metal-organic frameworks (MOFs) have attracted much attention in the field of microwave absorption. It is challenging to prepare composite absorbers with a controllable binary MOF-on-MOF heterostructure. Here, we construct two binary hybrid MOF heterostructures through selective assembly strategies, and realizes their conversion to magnetic porous carbon materials through a simple carbonization process. The special hybrid structure of hexagonal pyramid column and octahedron depends on the selective growth of the guest MOF on the specific crystal facet of the host MOF. The microwave absorbing properties of carbonized UIO-66@Co-doped MIL-88B (UM) and DUT-52@Co-doped MIL-88B (DM) are systematically studied. The selectively combined heterogeneous components endow the absorber with hierarchical pore structures, optimal impedance matching and excellent electromagnetic attenuation capabilities. The products carbonized at 700 °C (UM-700 and DM-700) exhibit superior microwave absorbing properties. It is worth noting that only with a matching thickness of 2 mm, the minimum reflection loss (RLmin) of DM-700 exceeds −65.2 dB, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 4.8 GHz. This work might provide a new strategy for rational design of absorbers with exquisite MOF-on-MOF heterostructures.

A Case Study: Influence of Circuit Impedance on the Performance of Class-E2 Resonant Power Converter for Capacitive Wireless Power Transfer

The evolution of power electronics led to rapid development in wireless charging technology; as a result, a single active switch topology was introduced. The present market utilizes inductive wireless power transfer (IPT); because of the disadvantages of cost, size, and safety concerns, research on wireless power transfer was diverted towards capacitive wireless power transfer (CPT). This paper studies the optimal impedance tracking of the capacitive wireless power transfer system for maximum power transfer. Compared to prior methods developed for maximum power point tracking in power control, this paper proposes a new approach by means of finding impedance characteristics of the CPT system for a certain range of frequencies. Considering the drone battery as an application, a single active switch Class-E2 resonant converter with circular coupling plates is utilized. Impedance characteristics are identified with the help of equations related to the input and resonant impedance. The impedance tracking is laid out for various resonant inductors, and the difference in current peak is observed for each case. Simulations verify and provide additional information on the reactive type. Additionally, hardware tests provide the variation of input current and output voltage for a range of frequencies from 70 kHz to 300 kHz. Efficiency at the optimal impedance points for a resonant inductor with 50 μH and 100 μH are tested and analyzed. It is noted that the efficiency for a resonant inductor with 50 μH is 8% higher compared to the CPT with a 100 μH resonant inductor. Further hardware tests were performed to investigate the impact of frequency and duty cycle variation. Zero-voltage-switching (ZVS) limits have been discussed with respect to both frequency and duty cycle.

Design of a single degree of freedom acoustic liner for a fan noise test rig

Acoustic liners are an essential part of noise reduction technologies commonly applied in aircraft turbofan engines. Fan noise suppression can be achieved by selecting an appropriate liner design with optimal acoustic impedance at the blade passing frequency. Great efforts have been made not only to improve experimental characterization and numerical methods for acoustic liners, but also to understand noise generation mechanisms, which ultimately impacts on the liner design itself. To gain confidence in the liner design process, a liner barrel was developed and fabricated for the Fan Noise Test Rig located at the University of São Paulo. To this end, analytical methods were used to determine the optimal acoustic impedance for the Fan Noise Test Rig, and a flat test sample was fabricated for experimental characterization with flow using both in-situ and impedance eduction techniques at the Federal University of Santa Catarina. A liner barrel of same nominal geometry was fabricated and placed at the Fan Noise Test Rig, and a modal decomposition indicated that the Tyler-Sofrin mode has been successfully suppressed at the first blade passing frequency. Numerical predictions of liner transmission loss considering the flat sample impedance showed good agreement with experimental results.

Compact Wideband Coplanar Stripline-to-Microstrip Line Transition Using a Bended Structure on a Two-Layered Substrate

A design of a compact coplanar strip (CPS)-to-microstrip line (MSL) transition using a bended structure on a two-layered substrate is presented. The proposed transition consists of a CPS taper and a bended CPS-to-MSL transition on a two-layered substrate. The CPS taper is formed on the lower substrate with low permittivity (εr = 3.38), and the bended CPS-to-MSL transition is formed on the upper substrate with high permittivity (εr= 10.2). The proposed transition is designed with analytical formulas obtained by applying EM-based conformal mapping without parametric tuning trials. The conductor shape of the bended CPS-to-MSL transition is adjusted to form an optimal Klopfenstein impedance taper. The proposed CPS-to-MSL transition optimally connects between a high impedance CPS line (~160 Ω) and a 50 Ω MSL, which typically results in a long transition length for ultra-wideband performance. The implemented transition bended in a sinusoid shape on the two-layered substrate provides good performance from 2 GHz to 17 GHz with the maximum 2 dB insertion loss per transition, and the horizontal length of the bended transition is reduced to 42.9% of the straight transition length. This bended transition is developed for use in mm-wave balanced antenna/detector feeds but can be applied to a variety of wideband balanced circuit modules, where compact circuit size is critical.

Automatic Methodology for Wideband Power Amplifier Design

This letter presents an automatic power amplifier (PA) design methodology that uses a multidimensional search algorithm to find the best compromise between fundamental and harmonic impedance terminations for a specified bandwidth. In conventional design methodologies, PA designers need to preselect the optimum impedances, which normally follow non-Foster trajectories, and are thus impossible to achieve with passive matching networks (MNs) for a wide frequency range. Instead, the proposed automatic design method directly synthesizes the MNs to achieve the desired output power, efficiency, and gain performance, without forcing any impedance profiles. For that, load-pull data are interpolated using artificial neural networks and an algorithm based on the simplified real frequency technique is used to obtain the MNs. Finally, the method is validated with a single-ended PA implementation.

Development of a 500-kV All Solid-State Linear Transformer Driver

A solid-state repetition linear transformer driver (LTD) for a high-power microwave (HPM) driver is constructed, comprising a total of 50 stage-series structures, with each stage possessing eight parallel bricks. This article describes the primary and secondary circuit differences between a driving source and a modern LTD, as well as analyzing the influence of load impedance on system efficiency in a simplified circuit of the LTD using a Laplace transform. This article also examines the optimum load impedance for a given magnetic core and primary circuit. The current load impedance of one stage is 2 Ω, and the corresponding system efficiency is 95%. A real-time control and triggering system are developed. A trigger transformer with a 100-channel pulse output is designed. The output voltage of the constructed driving source is about 500 kV, the current is 5 kA, the pulsewidth is about 125 ns, and the output power is 2.5 GW. The driving source can work at a repetition rate of 50 Hz. The driving source will drive a low magnetic field relativistic backward-wave oscillator to generate HPMs.

Design of bandwidth‐enhanced power amplifier based on class‐EF modes

AbstractThis article describes a methodology for designing broadband high‐efficiency GaN HEMT power amplifier (PA) which is suitable for base stations and modern wireless communication based on the Class‐EF mode. To achieve both efficiency enhancement and bandwidth extension for the PA, the load‐pull technique is employed to acquire the optimum impedance regions of the second harmonic. Especially, considering the influences of the harmonic control network on the accuracy of obtaining the fundamental impedance, the load‐pull technique is performed to obtain the optimal fundamental impedance again after the harmonic control circuit is determined. In addition, the theory of multiple frequencies matching is also employed to manipulate six desired fundamental frequency points concurrently. Based on the proposed theory, the Class‐EF PA prototype is designed and fabricated. The measurement results exhibits a drain efficiency (DE) of 60%–75% in the range of 2.1–3.6 GHz while having an output power of 38–40.5 dBm and gain of larger than 8 dB.

Multiple Input Multiple Output Resonant Inductive WPT Link: Optimal Terminations for Efficiency Maximization

In this paper a general-purpose procedure for optimizing a resonant inductive wireless power transfer link adopting a multiple-input-multiple-output (MIMO) configuration is presented. The wireless link is described in a general–purpose way as a multi-port electrical network that can be the result of either analytical calculations, full–wave simulations, or measurements. An eigenvalue problem is then derived to determine the link optimal impedance terminations for efficiency maximization. A step-by-step procedure is proposed to solve the eigenvalue problem using a computer algebra system, it provides the configuration of the link, optimal sources, and loads for maximizing the efficiency. The main advantage of the proposed approach is that it is general: it is valid for any strictly–passive multi–port network and is therefore applicable to any wireless power transfer (WPT) link. To validate the presented theory, an example of application is illustrated for a link using three transmitters and two receivers whose impedance matrix was derived from full-wave simulations.

Thermal phase transition controlling electromagnetic wave absorption behavior of PAN fiber derived porous magnetic absorber

The increasing excess electromagnetic wave (EMW) energies causes potential electromagnetic radiation pollution. It gives rise to more and more attention on designing environmentally friendly, efficient and suitable for large-scale industrial production of daily EMW absorbers. Carbon matrix composites modified with magnetic particles occupy the majority of these candidate absorbers. However, the preparation is still in its infancy. Here, we creatively mixed Fe(acac)3 with polyacrylonitrile (PAN) spinning solution, and then prepared magnetic carbon-based composites by in-situ pyrolysis of the obtained electrospun fibers (Fe(acac)3/PAN) at different temperatures. The SEM images display a fractured fibrous material with porous structure and uniform distribution of magnetic particles on the outer surface and inside. The XRD and XPS results indicate the composites consist of Fe3O4, Fe3C and carbon matrix. Besides, the thermal phase transition occurs with the pyrolysis temperature increasing from 300 to 1000 °C, and the formed Fe3O4 reacts with the carbon matrix to form Fe3C. As a result, the corresponding magnetic properties and electromagnetic properties improve. MCF-1000 exhibits enhanced EMW absorption performance with a minimum RL ( $${RL}_{\mathrm{min}}$$ ) value of − 29.27 dB at a matching frequency ( $${f}_{m}$$ ) of 11.68 GHz, a matching thickness ( $${t}_{m}$$ ) as low as 1.50 mm, and an effective frequency bandwidth as broad as 4.50 GHz from 13.50 to 18.00 GHz at a fixed thickness as thin as 1.13 mm. Further investigations indicate that such good EMW absorption behavior is attributed to the optimal impedance matching and the weakened eddy current effect which are both benefited by the thermal phase transition effect. The results provide theoretical and practical experience for the industrial large-scale preparation of a kind of EMW absorbers.