Passive Impedance Research Articles

A Closed-Loop Ear-Worn Wearable EEG System with Real-Time Passive Electrode Skin Impedance Measurement for Early Autism Detection

Autism spectrum disorder (ASD) is a chronic neurological disorder with the severity directly linked to the diagnosis age. The severity can be reduced if diagnosis and intervention are early (age < 2 years). This work presents a novel ear-worn wearable EEG system designed to aid in the early detection of ASD. Conventional EEG systems often suffer from bulky, wired electrodes, high power consumption, and a lack of real-time electrode–skin interface (ESI) impedance monitoring. To address these limitations, our system incorporates continuous, long-term EEG recording, on-chip machine learning for real-time ASD prediction, and a passive ESI evaluation system. The passive ESI methodology evaluates impedance using the root mean square voltage of the output signal, considering factors like pressure, electrode surface area, material, gel thickness, and duration. The on-chip machine learning processor, implemented in 180 nm CMOS, occupies a minimal 2.52 mm² of active area while consuming only 0.87 µJ of energy per classification. The performance of this ML processor is validated using the Old Dominion University ASD dataset.

Design and implementation of passive impedance adapter to damp resonances between VSC‐HVDC and AC systems

Design and implementation of passive impedance adapter to damp resonances between VSC‐HVDC and AC systems

The Design of the Dummy Arm: A Verification Tool for Arm Exoskeleton Development.

Motorised arm supports for individuals with severe arm muscle weakness require precise compensation for arm weight and elevated passive joint impedance (e.g., joint stiffness as a result of muscle atrophy and fibrosis). Estimating these parameters in vivo, along with the arm's centre of mass, is challenging, and human evaluations of assistance can be subjective. To address this, a dummy arm was designed to replicate the human arm's anthropometrics, degrees of freedom, adjustable segment masses, and passive elbow joint impedance (eJimp). This study presents the design, anthropometrics, and verification of the dummy arm. It successfully mimics the human arm's range of motion, mass, and centre of mass. The dummy arm also demonstrates the ability to replicate various eJimp torque-angle profiles. Additionally, it allows for the tuning of the segment masses, centres of mass, and eJimp to match a representative desired target population. This simple, cost-effective tool has proven valuable for the development and verification of the Duchenne ARm ORthosis (DAROR), a motorised arm support, or 'exoskeleton'. This study includes recommendations for practical applications and provides insights into optimising design specifications based on the final design. It supplements the CAD design, enhancing the dummy arm's application for future arm-assistive devices.

Self-Adaptive Resonance Technology for Wireless Power Transfer Systems to Eliminate Impedance Mismatches

Impedance mismatching can severely decrease the power transmission capacity or even invalid the control logic of wireless power transfer (WPT) systems. To eliminate the impedance mismatch caused by various factors, such as resonant parameter drift, coupling structure misalignment and control strategy, a self-adaptive mistuning correction circuit and corresponding parameter design rules are proposed to ensure the WPT system consistently operates under resonant state, accompanying the optimal power transfer ability. Moreover, a reactive compensation circuit that can create an auxiliary voltage source by the absorbed reactive power that is introduced by impedance mismatching is designed. This source can generate a new current on the coil to bring the mismatched input current back to the resonant state, according to the current superposition principle. Unlike passive impedance network that require high parameter precision and active impedance matching strategies equipped with detection and control circuits, the proposed approach can self-adaptively eliminate either undesired capacitive or inductive reactance with two additional switches and an energy-storage capacitor, improving impedance adjusting rate and providing better system robustness. The simulations and experiments are in good agreement with the theoretical analysis. This study has potential applications in harsh environments where the system impedance and coupling strength are continuously disturbed.

High-performance passive impedance network model for grid-tie inverters in steady state

Nowadays, the high penetration of inverter-interfaced distributed energy resources (DERs) has raised a well-founded concern regarding the interaction of these devices with the upstream grid. The harmonic interaction phenomenon between these players can be described by time-domain simulations, using high computational effort switched and/or average models often impractical for large power systems. This paper proposes an innovative low-computational-burden model named passive impedance network (PIN), capable of accurately representing DERs in electric power systems (EPSs). Through passive RLC components, the PIN model can describe DER dynamic behavior at a certain frequency of interest, making it able to represent harmonic flow within the EPS nodes. The proposed model is compared with the switched model, average model, and an experimental setup under different grid distortions and injected current profiles. A comparison of the total demand distortion (TDD) between the proposed PIN model and the experimental results is carried out. The effect of DER parameter deviations on PIN model accuracy is addressed, in which the absolute error of the PIN model TDD values are 0.65% and 0.06% for the experimental and switched model, respectively. Besides, the PIN model presents an improved computational performance compared to the time-domain-based switching model, requiring 99% less computational burden.

Development of a passive wireless sensor for fluidic detection and characterization utilizing the PCB-based coplanar electrode (PCE) configuration

During the global economic development, there's a growing focus on healthcare, especially in the advancement of medical diagnostic technologies, with a significant emphasis on glucose level evaluation. Glucose biosensors, predominantly electrochemical, have evolved over four generations, with the first three being enzyme-based and known for sensitivity and cost-effectiveness, albeit with limitations due to environmental susceptibility and reliance on enzyme activity. Recent advancements in non-invasive blood glucose monitoring, utilizing optical, microwave, and electrochemical techniques, offer diverse benefits without tissue penetration. Among these, impedance sensing stands out due to its flexibility and integration capability in handheld devices. This study proposes a wireless passive impedance method leveraging the inductor-capacitor (LC) sensing technique and PCB (Printed Circuit Board)-based coplanar electrode (PCE) configuration for fluidic sample detection. The proposed system integrates a two-coplanar-electrode layout with a square spiral inductor to assess fluidic conductivity and characterize various fluid types within samples. The effectiveness of this configuration was validated through experiments with NaCl and glucose solutions, confirming the feasibility of integrating PCB-based coplanar electrodes into conventional LC passive wireless sensing designs for fluidic detection and characterization.

A novel cable configuration method for fully-actuated parallel cable-driven systems: Application in a shoulder rehabilitation exoskeleton

Cable-driven exoskeletons play a significant role in poststroke rehabilitation. Since cables can only pull but not push, conventional parallel cable-driven exoskeletons are usually over-actuated, leading to uncertain dynamics. This paper proposes a cable configuration method utilizing the antagonistic cable pair to achieve full-actuation. The antagonistic cable pair is formed by assigning a passive impedance cable corresponding to an active driving cable. This method is illustrated as feasible through force closure analysis based on screw theory, and is implemented in a shoulder rehabilitation exoskeleton. Subsequently, the dynamics model of the exoskeleton is formulated, and the isomorphic mapping between cable tension space and joint space is established. Additionally, the elastic fluctuation absorption mechanism is presented to absorb the length fluctuation produced by the antagonistic cable pair, through the deformation of elastic elements. The continuity of cable tension is evidenced through its finite and smooth partial derivatives. Finally, the experimental results of prototype validate that the fully-actuated parallel cable-driven exoskeleton can be achieved with the proposed method.

Optimized MMC passive impedance shaping method for high frequency oscillation suppression

Recent years, there have been several high-frequency oscillation events in modular multilevel converter (MMC) based DC current projects. Considering the wideband oscillation characteristics of this issue, passive MMC impedance shaping methods are superior solutions for their advantages over the active methods in enhancing the broadband damping level. However, the optimization of parallel passive devices mainly focused on reactive power compensation and the suppression of characteristic harmonics generated by low-level inverters, which is not applicable to MMC systems. To address the optimization design problem of passive damping devices, this paper proposes an optimized design method for passive filters by analyzing the relationship between the passive damping device and the impedance shaping effect of the inverter. The proposed method reduces the capacity of the passive damping device while ensuring system stability margin. Finally, the effectiveness of the proposed passive impedance shaping strategy is verified through time-domain simulations considering changes in AC side operating conditions and power reduction operation of the MMC.

Passive Model-Predictive Impedance Control for Safe Physical Human–Robot Interaction

Various cognitive systems have been designed to model the position and stiffness profiles of human behavior and then to drive robots by mimicking the human’s behavior to accomplish physical human-robot interaction tasks through a properly designed impedance controller. However, some studies have shown that variable stiffness parameters of the impedance controller can cause the violation of the passivity constraint of the robot states, and make the robot’s stored energy exceed the external energy injected from the human user, thus leading to the unsafe human-robot interaction. To solve this problem, this paper proposes a novel passive model predictive impedance control method including two control loops. In the bottom-loop of the proposed controller, the robot is driven by a variable impedance controller to achieve the desired compliant interaction behavior. In the top-loop of the proposed controller, the model predictive control (MPC) is used to ensure that the robot states satisfy the passivity constraint by calculating a complementary torque to limit the stored energy of the robot. The passivity of the closed-loop robot system and the feasibility of MPC are guaranteed by theoretical analysis, ensuring the safety of the robotic movement in the human-robot interaction. The effectiveness of the proposed method is demonstrated by the simulation and experiment on the Franka Emika Panda robot.

Design and measurement of a tunable metasurface low-frequency radar absorber

At the turn of the millennium, developments on metasurfaces lead to a significant step forward in the design of radar absorbing structures, especially at lower frequencies, thanks to a reduced thickness. Still, as with other passive impedance matching systems, they remain constrained in their bandwidth-to-thickness ratio. Fortunately, the recent integration of active electronic components onto metasurfaces has multiplied their functionalities, unlocking new ways to overcome these limitations. For instance, using varactor diodes, which act as variable capacitors, an absorbing metasurface can be rendered tunable to cover a frequency range wider than would any passive system of similar thickness. This is a valuable feature when facing modern frequency-hopping radars. However, the bias-dependent resistance introduced by the varactor diodes can compromise the impedance matching throughout the tunable frequency range. This work, therefore, focuses on the design and measurement of a tunable radar absorbing metasurface using varactor diodes, highlighting the necessity for a joint tuning of capacitance and resistance to grant near-perfect absorption over a wide frequency range.

Research on online passive electrochemical impedance spectroscopy and its outlook in battery management

Current lithium-ion battery (LIB) management technique relying solely on the limited time-domain measurements appears to reach its limit, and incorporating new sensing information, particularly the impedance of LIB, offers a promising path for improvement. Using the non-stationary random driving profile of electric vehicle (EV), a method to extract online passive electrochemical impedance spectroscopy (OPEIS) is proposed and validated, with relevant factors influencing its efficacy also investigated. The particularity of actual driving profile is revealed both theoretically and experimentally, and beyond expectation, the highly differentiated driving profiles yield a similar spectral pattern, which facilitates the acquisition of OPEIS. Continuous OPEIS characterized by the distribution of relaxation time (DRT) ranging from 0.2 Hz to 3 kHz are analyzed in detail under different battery conditions. Compared with offline reference EIS, most of the measurement errors are <3%. Based on the acquired spectral information and OPEIS, a safety-relevant detector and an internal temperature estimator for LIB are presented, and they can both realize a near instant electrochemical sensing up to 1 Hz. As the underlying opportunities of OPEIS are outlined, challenges in its reliable acquisition and engineering implementation are evaluated as well. By comprehensively discussing the realization of OPEIS, research in this paper is expected to provide valuable references for a more effective battery management.

Adjustable Phase-Amplitude-Phase Acoustic Metasurface for the Implementation of Arbitrary Impedance Matrices.

Impedance metasurfaces enable accurate regulation of acoustic fields. However, they can hardly supply a flexible response as such perfect operation is accompanied by stringent requirements on the design of unit cells. Actually, an arbitrary lossless and passive target impedance matrix requires the tuning of 3 independent real parameters. The set composed of a reflection phase, a transmission amplitude, and a transmission phase, enables the representation of an arbitrary impedance matrix, possibly possessing singular elements. In this paper, a mechanism of phase-amplitude-phase modulation (PAP modulation) is developed for the generic design of the unit cells of acoustic impedance metasurfaces. Adjustable acoustic impedance metasurfaces are further available under this framework. An impedance unit with 3 mobile parts is designed based on this idea. The assembled metasurface can handle different incidences for acoustic field manipulation at a given frequency. Beam steering and beam splitting are considered as demonstration examples and are verified by numerical simulation and experiment. PAP modulation enriches the design of acoustic impedance metasurfaces and extends the range of application of impedance theory.

The efficacy of different torque profiles for weight compensation of the hand.

Orthotic wrist supports will be beneficial for people with muscular weakness to keep their hand in a neutral rest position and prevent potential wrist contractures. Compensating the weight of the hands is complex since the level of support depends on both wrist and forearm orientations. To explore simplified approaches, two different weight compensation strategies (constant and linear) were compared to the theoretical ideal sinusoidal profile and no compensation in eight healthy subjects using a mechanical wrist support system. All three compensation strategies showed a significant reduction of 47-53% surface electromyography activity in the anti-gravity m. extensor carpi radialis. However, for the higher palmar flexion region, a significant increase of 44-61% in the m. flexor carpi radialis was found for all compensation strategies. No significant differences were observed between the various compensation strategies. Two conclusions can be drawn: (1) a simplified torque profile (e.g., constant or linear) for weight compensation can be considered as equally effective as the theoretically ideal sinusoidal profile and (2) even the theoretically ideal profile provides no perfect support as other factors than weight, such as passive joint impedance, most likely influence the required compensation torque for the wrist joint.

Passive Impedance-Matched Neural Recording Systems for Improved Signal Sensitivity.

Wireless passive neural recording systems integrate sensory electrophysiological interfaces with a backscattering-based telemetry system. Despite the circuit simplicity and miniaturization with this topology, the high electrode-tissue impedance creates a major barrier to achieving high signal sensitivity and low telemetry power. In this paper, buffered impedance is utilized to address this limitation. The resulting passive telemetry-based wireless neural recording is implemented with thin flexible packages. Thus, the paper reports neural recording implants and integrator systems with three improved features: (1) passive high impedance matching with a simple buffer circuit, (2) a bypass capacitor to route the high frequency and improve mixer performance, and (3) system packaging with an integrated, flexible, biocompatible patch to capture the neural signal. The patch consists of a U-slot dual-band patch antenna that receives the transmitted power from the interrogator and backscatters the modulated carrier power at a different frequency. When the incoming power was 5-10 dBm, the neurosensor could communicate with the interrogator at a maximum distance of 5 cm. A biosignal as low as 80 µV peak was detected at the receiver.

Selective Harmonic Voltage Control for STATCOMs in Wind Power Plants

This paper proposes a selective harmonic voltage control approach for the static synchronous compensator (STATCOM) deployed in wind power plants (WPPs). The method enables STATCOM to mitigate voltage harmonics at the point of interconnection of WPP without using the high-voltage sensor. Further, a passivity-based design of the proposed control method is developed to eliminate the negative resistances around the concerned harmonic components, which allows robust harmonic voltage damping under the different passive grid impedances. The effectiveness of the approach is elaborated by theoretical analysis and validated by electromagnetic simulations.

Printed Metasurface Leaky Wave Antennas Based on Penetrable Aperture Field Synthesis

A design methodology for 1-D modulated printed metasurface leaky-wave antennas (LWAs) with a pattern synthesis capability in 2-D TE polarization is presented. For a desired radiation pattern, complete tangential fields on the surface of a grounded dielectric substrate are constructed and optimized to find a pointwise passive surface impedance distribution. Dielectric and conductor losses are taken into account in the field synthesis process via a design curve obtained using analysis of a physical unit cell with lossy constituents. It enables accurate prediction of the aperture field distribution when practical lossy materials are used. A spatially modulated impedance can be realized using an array of printed copper strips. Three 10-wavelength-long LWA designs are demonstrated numerically for broadside, two-beam, and sector patterns. The LWA for broadside radiation is fabricated and measured, showing a good agreement with the simulation results.

A Hybrid Impedance Matching Network for Underwater Acoustic Transducers

The underwater acoustic transducer (UAT) is an electro-acoustic conversion device, which is a nonlinear reactive load. An impedance matching network is usually added between the power amplifier and the UAT. This paper proposes a hybrid impedance matching network (HIMN) combining passive impedance matching and active impedance matching. Compared with the conventional matching, this method can improve the matching frequency range and reduce matching delay. Firstly, the impedance model of the UAT is proposed, and the matching principle of the HIMN is analyzed. On this basis, the parameter design method is given within the required frequency range. Then, to reduce the matching delay of the system, a control method based on reference signal synchronization is proposed, including the reference compensation voltage calculation method and model prediction control (MPC) with two-step prediction. Finally, the simulation and experimental hardware in loop (HIL) results are given, which verify the effectiveness of the proposed HIMN and control algorithm proposed in this paper. The results show that the proposed HIMN can achieve a wider matching frequency range and shorter matching delay.

A discussion on the characterization of grid emulators by apparent power rating and short-circuit power

Wind turbines are a driving force in the change towards renewable energies today. Offshore wind turbines have reached power ratings around 15 MW, and the growth continues. Grid emulators have become inevitable for the test and validation of wind turbines and subsystems at full scale. Yet, large investments for new installations present major challenges.Therefore, the following discussion outlines basic design aspects for the grid emulator main components: converter, transformer, and filter. The aim is to clarify the implications of requirements on the design to exhaust ratings for minimum investments, and to satisfy testing against the most recent standards and grid codes. Appropriate ratings are derived based on steady-state and transient test needs. It is shown how much overrating is specifically needed and why the converter is usually rated a multiple compared to the device under test. Further dimensioning criteria such as power quality, switching frequency, and filter size are discussed in this context.Finally, the capacity of grid emulators is often characterized by the short-circuit power. Two essentially different variants of short-circuit power are introduced, either being dependent on the converter peak current or the passive components impedance. While the first one reveals the overload capability, the latter represents a proper measure for grid strength. However, the emulated grid strength can be adjusted in a limited bandwidth using impedance control. The concept might be confusing at first glance, but it effectively decouples the virtual short-circuit power from the ratings of the power hardware.

Enhancing active reconfigurable intelligent surface

A Reconfigurable Intelligent Surface (RIS) panel comprises many independent Reflective Elements (REs). One possible way to implement an RIS is to use a binary passive load impedance connected to an antenna element to achieve the modulation of reflected radio waves. Each RE reflects incoming waves (incident signal) by using on/off modulation between two passive loads and adjusting its phase using a Phase Shifter (PS). However, this modulation process reduces the amplitude of the reflected output signal to less than unity. Therefore, recent RIS works have employed Reflection Amplifiers (RAs) to compensate for the losses incurred during the modulation process. However, these systems only improve the reflection coefficient for a single modulation state, resulting in suboptimal RE efficacy. Thus, this paper proposes a strategy for optimising RE by continuously activating the RA regardless of the switching load state. The performance of the proposed scheme is evaluated in two scenarios: (1) In the first scenario (Sc1), the RA only operates to compensate for high-impedance loads, and (2) in the second scenario (Sc2), the RA runs continuously regardless of the RE loads. To benchmark the performance of Sc1 and Sc2, various metrics are compared, including signal-to-noise ratio, insertion loss, noise figure, communication range, and power-added efficiency. Numerical examples are provided to demonstrate the effectiveness of the proposed scheme. It is found that the proposed system in Sc2 leads to better overall performance compared to Sc1 due to the increased gain of the RIS reflection.

Antenna Loading by Passive Impedance for Linear-to-Circular Polarization Conversion

Many passive and wireless devices, such as RFID tags or batteryless wireless sensors, are designed to control electromagnetic field backscattered by the devices, in order to maximize the interrogation range (or the device-to-reader separation distance) and/or to mitigate the electromagnetic clutter. In this letter, we show that a linearly polarized (LP) electromagnetic field can be converted into a circularly polarized field by using a passive and chipless device. The device, also called tag, consists of a one-port antenna loaded by a passive impedance, whose value is derived from a rigorous electromagnetic model including structural and antenna scattering modes. The experimental validation of predicted linear-to-circular polarization conversion is reported in the case of a patch antenna illuminated by a LP field. At the operating frequency of 2.6 GHz, the measured axial ratio of the electric field backscattered by the tag is lower than 1 dB.