Adjustable Impedance Research Articles

An adaptive power control method for soft open points based on virtual impedance

The fluctuations in power output from distributed power sources are rapid and dramatic, causing voltage fluctuations in the distribution network that threaten the safety of electricity consumption. Soft open points (SOPs) can replace traditional contact switches and are expected to suppress voltage fluctuations. However, traditional power regulation methods based on the reference values are unable to address rapid and large voltage fluctuations. Therefore, this paper proposes an adaptive power control method for SOPs based on virtual impedance. The SOP is modeled as a series link of adjustable impedance and a voltage source. Then, the voltage difference component is used to calculate the reference for the DQ domain to regulate the power flow in real time automatically. By doing so, the proposed method can smooth the voltage fluctuations in the distribution network. Additionally, the virtual impedance is also optimized to minimize the power loss. Finally, the method is validated through simulation and experiments, demonstrating that this method can automatically regulate power and significantly reduce voltage fluctuations.

Improved Design of a SiC MOSFET Gate Drive with Crosstalk Suppression Capability

For high-frequency switching applications, silicon carbide (SiC) devices are more suitable than silicon-based devices, which is conducive to improving the efficiency and power density of power electronic equipment. However, as the switching frequency increases, the influence of parasitic parameters on the switching characteristics of devices becomes increasingly apparent. When SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) are applied in bridge circuits, the crosstalk problem easily occurs with the complementary conduction of upper and lower transistors, which seriously limits the promotion of SiC MOSFETs. However, the existing crosstalk suppression drive circuit tends to increase the switching loss, switching delay, and control complexity; therefore, a gate drive with crosstalk suppression capability is proposed. In this paper, the gate drive has two features: a negative voltage to shut down the SiC MOSFET; and an adjustment of the gate-source equivalent impedance. To accomplish this goal, the mechanism of crosstalk voltage generation is analyzed. Furthermore, the operation principle of the gate drive is analyzed, and the parameters of the gate drive are designed. Eventually, the proposed gate drive is verified by an LTspice simulation and experimental platform. The results prove that the gate drive can suppress the crosstalk voltage without affecting the switching speed.

A 56-Gb/s,0.708 pJ/bit single-ended simultaneous bidirectional transceiver with hybrid errors cancellation techniques for die-to-die interface

This paper presents a low-power Simultaneous Bidirectional (SBD) transceiver with a power consumption of 0.708 pJ/bit, supporting a 56-Gb/s single-ended high-bandwidth density for die-to-die communication. To address the issue of separating signal amplitude mismatch in the SBD hybrid circuit, a transmitter driver with feed-forward equalization (FFE) is designed to realize adjustable impedance and amplitude. Instead of using a transconductance amplifier (TIA), the R-CTLE circuit is designed to compensate for insertion loss while improving the Signal Integrity (SI). Designed in a 28 nm standard CMOS process, the transceiver demonstrates 56 Gb/s/wire (28 Gb/s each direction) over a 21 mm on-chip channel. The energy efficiency is 0.708 picojoules per bit (0.708 pJ/bit) and a bit error rate (BER) ¡10e−12 with compensating insertion loss of −4.16 dB.

Optimal design of ultrasonic transducer based on multi-layer backing with adjustable impedance

Ultrasonic transducers, especially used in medical imaging, strike a balance between sensitivity and bandwidth to yield high-quality images. This challenge centers on the optimal transmission of acoustic energy across the layers of transducer. The backing layer stands as a critical component of transducers, orchestrating the conversion of acoustic impedance to enhance bandwidth. While traditional designs often utilize metal particle-polymer composites, issues arise from material limitations, complex fabrications, and deviations in sample properties. This study introduces an optimized multilayer backing (MLB) design using a metal-polymer structure. Implementing an equivalent circuit model, an MLB of epoxy-aluminum composite is designed. The ultrasonic transducer has an operating frequency of about 6 MHz, in which the backing layer is a stacking composite of 19.3 μm epoxy resin and 30 μm aluminum foil. Notably, this optimized design increased the -6dB bandwidth from 27.72 % to 33.44 % and verified its superior electro-acoustic performance based on ultrasonic imaging. Furthermore, this innovative design approach provides a wider range of acoustic impedance, improves the efficiency of ultrasonic energy transmission, and provides a streamlined approach to miniaturized transducer design.

Examining Energy Storage Potential in Weakly Polar Nematic Liquid Crystals Infused with Anthraquinone Dye: A Comprehensive Approach

The applications of liquid crystals in the field of renewable, clean and sustainable technologies of energy storage are of utmost importance at present. This paper delves into dielectric spectroscopic studies of a weakly polar nematic liquid crystal (NLC) enriched with an anthraquinone dye. The primary objective is to assess the impact of increasing dye concentrations on various properties. Anthraquinone dye has been found to increase the dielectric permittivity of weakly polar NLC, leading to a 4.7-fold increase in dielectric anisotropy. Simultaneously, a reduction of around 11% in threshold and operating voltages of the NLC has also been recorded after using dye as the guest material. The added dipolar contributions provided by dye molecules have been attributed to this surplus permittivity. The NLC has been found to have an approximately 54% faster response to the applied field. The intrinsic polarization field of dye molecules accelerates nearby LC molecule reorientation, leading to a 56.5% faster fall time and a 29.8% faster rise time in a 3.0 wt% dye-doped LC cell. These experimental results have been validated via computational studies as well. The simulation results about dipole moment and polarizability provide robust support for our experimental results. Such composites evince their potential for energy storage and 5G communication technologies with adjustable impedance and permittivity.

Impedance adjustment for learning human variable impedance skill

Impedance adjustment for learning human variable impedance skill

Simplified Analysis and Characterization of Dual Power Source Wireless Power Transfer System

Non-contact wireless power transfer systems require power regulation to ensure their proper operation at rated power due to the many degrees of freedom in non-contact coupling structures. Recently, a promising technology has been introduced for wireless power transfer systems, namely, the fractional-order technology with dual power sources to construct an equivalent impedance structure with both variable resistance and reactance. Unlike other impedance matching technologies, the fractional-order technology allows for the adjustment of the equivalent impedance of the resonant network without requiring precise selection of resonant parameters. However, this technology has not been widely adopted due to the abstract concepts involved in fractional calculus theory and control logic. In this study, we employed circuit theory to comprehensively analyze the electrical implications of fractional theory and to provide a detailed description of the inner features of Cα. This study reveals the underlying correlation between control variables and the order of Cα. Additionally, it is shown that the same fractional-order circuit can display both inductive and capacitive reactance, resulting in a significant extension of the impedance adjustment range of fractional-order components. A prototype was designed and constructed to validate the proposed approach, and the experimental results closely matched the theoretical calculations obtained from the proposed approach.

Magnetic field intensity suppression using communication-less impedance adjustment for inductive power transfer systems

This letter describes the effectiveness of magnetic field intensity suppression through communication-less impedance adjustment in an inductive power transfer (IPT) system. The impedance adjustment scheme comprises a circuit configuration design that enables adaptive reactance adjustment using a field-effect transistor (FET) bridge-based variable reactor, which includes a coupling-coefficient estimation method for adjusting load resistance. The experimental results show that the load impedance that minimizes the magnetic energy stored in the IPT system can suppress the magnetic field intensity by up to 16.5% with only a 4.8% decrease in power transfer efficiency compared to load impedance that maximizes the power transfer efficiency.

A Hybrid LCC-SP Compensation Network With Adjustable Impedance Angle Used for Single-Stage Wireless Power Transfer

In order to realize constant current output (CCO) and constant voltage output (CVO) in single-stage wireless power transfer (WPT), this paper proposes a hybrid LCC-SP compensation network with adjustable impedance angle. The switching between CCO and CVO could be realized by changing the parameters of the circuit rather than changing the structure of the circuit, which cause fewer influence on the circuit when the operation mode switches. Due to the structure of the proposed compensation network, the hybrid LCC-SP compensation network could isolate the DC component in single-stage WPT converter which is caused by asymmetric modulation strategy to ensure the loosely coupled transformer works normally. Zero voltage switching (ZVS) can be realized by adjusting the impedance angle. Moreover, the current of primary coil could keep constant which can be used to protect the primary converter when the secondary coil is moved accidentally. And the transfer gain of the proposed compensation network does not rely on the transformer parameters, more parameters design freedom can be realized. The few passive devices are used in this circuit for higher efficiency and lower cost. Finally, the superiorities of the proposed circuit are verified by experiments.

Active Training Control Method for Rehabilitation Robot Based on Fuzzy Adaptive Impedance Adjustment

For lower limb rehabilitation robots, different patients or patients in different rehabilitation stages have different motion abilities, and the parameters of the traditional impedance control model are fixed and cannot achieve the best active suppleness training effect. In this paper, an active training control method based on the spring damping model (SDM) and the fuzzy adaptive adjustment of its parameters is proposed. The SDM offsets the target trajectory according to the patient interaction force to obtain a new desired trajectory, creating a controllable impedance environment for the patient. Fuzzy rules are established using coefficients reflecting the patient’s motion ability to adaptively adjust the stiffness and damping coefficients of the SDM. The virtual human–machine force interaction environment is changed to achieve the adaptive adjustment of the resistance training difficulty on the motion ability. The adaptive impedance control method proposed in this paper has achieved the expected goal through experimental verification, which can greatly mobilize the active participation of patients and help improve the rehabilitation effect of patients.

N-doped carbon hollow spheres supported N-doped carbon nanotubes for efficient electromagnetic wave absorption

Hierarchical and hollow heteronanostructures had attached wide attention in electromagnetic wave (EMW) absorption fields due to their adjustable impedance matching and loss property. However, fabrication of well-defined heteronanomaterials with hierarchical and hollow features is challenging. Here, we develop a simple method to prepare N-doped carbon hollow spheres supported by N-doped carbon nanotubes (Ni@NCNT/NCHSs). Due to the hierarchical and hollow features, the Ni@NCNT/NCHSs exhibit high-efficiency EMW absorption performance. With a thickness only 1.6 mm, the optimized heteronanostructure has an RLmin of −64.75 dB and an EAB of 4.17 GHz. The experimental results demonstrate that the hierarchical and hollow heteronanostructures have significantly enhanced dielectric loss and conductive loss of the Ni@NCNT/NCHSs as well as the impedance matching characteristics, which are responsible for their enhanced EMW absorption performances. This work presents an effective method to synthesize hierarchical and hollow heteronanostructures for high-performance EMW absorption.

Tunable elastic metasurface based on adjustable impedances for Gaussian beam manipulation

Different from the common tunable elastic metasurface (TEM), like piezoelectric active metasurface, in this paper, we propose a TEM composed of impedance-adjustable subunits (IASs) to realize tunable manipulations of flexural waves. Based on the impedance theory, the adjustable mechanism of the phase shift of the IAS is clarified according to the derivations for the relationship between the force/moment interface impedances and complex reflection coefficients. The boundary effect is considered, and the difference between the impedances of the flexural and acoustic waves is demonstrated for the subunits with free and clamped boundary conditions. By using the diffraction theory and coupled-mode theory, an analytical model is established for the metasurface subjected to a Gaussian flexural beam incidence, based on which, the total wavefield consisting of all propagating diffraction orders is solved. Its accuracy and the modulation function adjustability of the TEM are demonstrated by the finite element (FE) simulations and experiments. The proposed IAS possesses a flexible and reliable layout for TEM design and has potential engineering applications in vibration control, health monitoring, etc.

Block Diagram Representation of Controller Components of Distributed Power Flow Controller

In this paper, an attempt is made to present the controllers used for a power flow controller, termed as Distributed Power Flow Controller (DPFC). This comes under the category of Flexible AC Transmission Systems (FACTS) devices. DPFC emerges from the unified power flow-controller (UPFC), a most powerful FACTS device which can be used for both shunt and series control. So DPFC inherits the same control capability of simultaneous adjustment of line impedance, transmission angle and the bus voltage magnitude, which are the dynamic control parameters. The DPFC control and the functions of the different components for shunt and series controllers of DPFC are presented. These components can be obtained from Simulink Library of MATLAB environment and simulation model is obtained in this paper to check the dynamic response of DPFC.

Impedance Learning-Based Adaptive Control for Human–Robot Interaction

In this article, a new learning-based time-varying impedance controller is proposed and tested to facilitate an autonomous physical human–robot interaction (pHRI). Novel adaptation laws are formulated for online adjustment of robot impedance based on human behavior. Two other sets of update rules are defined for intelligent coping with the robot’s structured and unstructured uncertainties. These rules ensure stability via Lyapunov’s theorem and provide uniform ultimate boundedness (UUB) of the closed-loop system’s response, without a need for HRI force/torque measurement. Accordingly, the convergence of response signals, including errors in tracking, online impedance learning, robot parameter adaptation, and controller gain variation, is proven to operate in a bounded region (compact set) in the presence of robot and human uncertainties and bounded disturbances. The performance of the developed intelligent impedance-varying control strategy is investigated through comprehensive experimental studies in a repetitive following task with a moving target.

Compact Wideband and Variable Impedance Transformation Ratio Balun for Folded Dipole

Aiming at dipoles with different impedances, a wideband balun with adjustable impedance for the balanced port is proposed in this communication. The balun is directly connected to the dipole to form an antenna element, so it also needs to meet: no connection line is required; the overall size is less than a quarter of the wavelength. The proposed balun realizes balanced–unbalanced conversion through aperture coupling, and dual slot ensures its wide-band characteristics. Due to the high-impedance characteristics of the folded dipole (FD), the balun has achieved impedance conversion ratios of 6:1, 8:1, 10:1, and 12:1, and the corresponding bandwidths are 82.1%, 67.1%, 53.7%, and 44.4%, respectively. Finally, three types of wideband dipoles with different characteristic impedances are fabricated to verify the versatility of the balun.

Asymmetrically Enhanced Coplanar-Electrode Electroluminescence for Information Encryption and Ultrahighly StretchableDisplays.

Traditional alternating-current-driven electroluminescent (AC-EL) devices adopting a sandwich structure are commonly used in solid-state lighting and displays, while the emerging coplanar-electrode alternating-current-driven light-emitting variants manifest excellent application prospects in intelligent, multifunctional, and full-color displays, and sensing purposes. In this work, an asymmetricallyenhanced coplanar-electrode AC-EL device with a universal and straightforward architecture is designed based on the impedance adjustment strategy. This newly devised asymmetric structure extends the functionalities of the coplanar-electrode AC-EL devices by overcoming the bottlenecks of complicated patterning procedures and high driving voltages of symmetric configuration. The developed device design enables a new type of information encryption and ultrahighly stretchable patterned displays. Notably, the novel encryption appliances demonstrate feasible encryption/decryption features, multiple encryptions, and practical applicability; the biaxially stretchable display devices achieve the highest tensile performance in the field of stretchable electroluminescent pattern displays, and outperform the ultrahighly stretchable sandwich devices in terms of simple patterning process, higher brightness, wider color gamut, and long-term stability. The proposed configuration opens up new avenues for AC-EL devices toward a plethora of smart applications in wearable electronics with intelligent displays, dynamic interaction of human-machine interface, and soft robotics.

Multi-Input Variable Structure Converter With Optimal Power Extraction Strategy for Energy Harvesting

Multi-input converter combining various ambient sources, is considered as an effective approach to solving the problem of the sporadic and intermittent exist in energy harvesting. This paper proposes a multi-input variable structure to harvest vibration energy, which can work in dual sources parallel mode (DIPM), dual input series mode (DISM), and single source mode (SIM). In this work, GaN is adopted to eliminate power loss caused by body diodes of MOSFETs. The steady-state performance and input power of three modes are derived, it concludes that DIPM has the highest power which is different from traditional applications and DISM provides a wider working range. Due to the range of voltage variations in the energy harvesting process, the change of three modes can match the input and output power dynamically. Otherwise, the optimal power extraction strategy and energy management method based on impedance adjustment in discontinuous conduction mode (DCM) is used to improve the energy harvesting efficiency. An experimental prototype with simple control is built to verify the feasibility and performance of the proposed variable structure.

PID-like active impedance control for electroacoustic resonators to design tunable single-degree-of-freedom sound absorbers

Sound absorption at low frequencies still remains a challenge in both scientific research and engineering practice. Natural porous materials are ineffective in this frequency range, as well as acoustic resonators which present too narrow bandwidth of absorption, thus requiring alternative solutions based on active absorption techniques. In the present work, we propose an active control framework applied on a closed-box loudspeaker to enable the adjustment of the acoustic impedance at the loudspeaker diaphragm. More specifically, based on the proportionality between the pressure inside the enclosure and the axial displacement of the loudspeaker diaphragm at low frequencies, we demonstrate both analytically and experimentally that a PID-like feedback control approach allows tuning independently the compliance, the resistance and the moving mass of the closed-box loudspeaker to implement a prescribed impedance of a single-degree-of-freedom resonator. By considering different control combinations to tailor the resonator characteristics, a perfect absorption (with absorption coefficient equal to 1) is achievable at the target resonance frequency, while enlarging the effective absorption bandwidth. Moreover, the proposed feedback control strategy shows an excellent control accuracy, especially compared to the feedforward-based control formerly reported in the literature. The mismatches between the performance of experimental prototype and the model, likely to result from the control time delay and the inaccuracy in estimating the loudspeaker parameters, can be compensated directly by tuning the control parameters in the control platform. The active resonators implemented through the reported control scheme can be used to build more complex acoustic devices/structures to enable high-efficiency broadband sound absorption or other types of acoustic phenomena such as wavefront shaping.

Facile synthesis of Co/SC microwave absorbents by recycling coal hydrogasification residue

A coal hydrogasification residue, semi-coke (SC), was recycled to prepare SC-based composites for microwave absorption by a facile method. This mainly involved loading an ethanol solution of cobalt nitrate onto SC and then conducting in-situ carbothermal reduction. The results showed that, a Co/SC composite could be obtained at a carbothermal temperature of 700 ℃ (denoted by CoSC700). The CoSC700 composite exhibited excellent performance with a minimum reflection loss value of − 40.1 dB and an effective absorption bandwidth of 5.0 GHz at a coating thickness of 2 mm. This is the combined effect of good impedance matching and strong intrinsic dissipation capacity, which benefit from the effective adjustment of input impedance by Co as well as strong conduction and interfacial polarization relaxation losses caused by the effects of graphite carbon and SC-Co interfaces.

Path Planning and Impedance Control of a Soft Modular Exoskeleton for Coordinated Upper Limb Rehabilitation.

The coordinated rehabilitation of the upper limb is important for the recovery of the daily living abilities of stroke patients. However, the guidance of the joint coordination model is generally lacking in the current robot-assisted rehabilitation. Modular robots with soft joints can assist patients to perform coordinated training with safety and compliance. In this study, a novel coordinated path planning and impedance control method is proposed for the modular exoskeleton elbow–wrist rehabilitation robot driven by pneumatic artificial muscles (PAMs). A convolutional neural network-long short-term memory (CNN-LSTM) model is established to describe the coordination relationship of the upper limb joints, so as to generate adaptive trajectories conformed to the coordination laws. Guided by the planned trajectory, an impedance adjustment strategy is proposed to realize active training within a virtual coordinated tunnel to achieve the robot-assisted upper limb coordinated training. The experimental results showed that the CNN-LSTM hybrid neural network can effectively quantify the coordinated relationship between the upper limb joints, and the impedance control method ensures that the robotic assistance path is always in the virtual coordination tunnel, which can improve the movement coordination of the patient and enhance the rehabilitation effectiveness.