Impedance Modulation Research Articles

Extended state observer-based pressure control for pneumatic actuator servo systems

A pneumatic actuator is a fast and economical tool that converts compressed air into mechanical motion. In this paper, an extended state observer (ESO)-based sliding mode controller (SMC) is developed to adjust the air pressure of the actuator for accurate position control. Specifically, an impedance control module is established to produce desired air pressure based on the relationship between forces and desired positions. Then, the ESO-based SMC is implemented to adjust the air pressure to the required level despite the presence of system uncertainties and disturbances. As a result, the position of the actuator is controlled to a setpoint through the regulation of pressure. The performance of ESO-based SMC is compared with that of a classic active disturbance rejection controller (ADRC) and a SMC. Simulation results demonstrate that the ESO-based SMC shows comparable performance to ADRC in terms of precise pressure control. In addition, it requires the least control effort necessary to excite valves among the three controllers. The stability of ESO-based SMC is theoretically justified through Lyapunov approach.

Impedance Control of Human Ankle Joint With Electrically Stimulated Antagonistic Muscle Co-Contraction.

Functional electrical stimulation (FES) is often used, typically in an open-loop manner, to restore paralyzed motor function for daily living activities. Several feedback control strategies have been developed to improve the performance and usability of FES-evoked movement. However, most of them have been position controllers, while the control strategy for human movement has been known as impedance modulation. Moreover, few studies have attempted to use antagonistic co-contraction for FES feedback control despite its expected benefits, such as enhanced stability and performance and better rehabilitation outcome. In this paper, we propose a robust impedance controller for FES that can adjust the intrinsic joint stiffness using co-contraction. It consists of an impedance control law based on time-delay estimation to compensate for the nonlinear uncertain joint dynamics and an antagonistic muscle co-contraction allocator to address the intrinsic joint stiffness caused by the co-contraction. The proposed controller was implemented on the ankle joints of five healthy subjects to simulate a standing balance situation. The results verified that the proposed controller can achieve desired impedance accurately by adjusting the intrinsic stiffness that stems from the change in the amount of co-contraction (up to 48.4% better impedance achievement with high desired stiffness).

Investigation of frequency characteristics of biological tissues impedance

The problem of identifying informative signs of biological tissues viability using the impedance measurement method is formulated. At present there is no instrumental base that makes it possible in an operational setting to diagnose the ability of biological tissue to heal itself after injury and damage as a result of thermal exposure, gunshot wound or prolonged compression. It is shown in this article that development of methods and tools for instrumental diagnostics in medical diagnostic practice is an important modern challenge.
 The results of experimental measurements of impedance characteristics in the frequency range of 20 Hz – 2.0 MHz are presented. The frequency dependences of the modulus of voltage on biological tissues of plant origin are analyzed in its intact state, as well as after exposure of biological tissue samples in a freezer at time intervals from 15 minutes to 2 hours.
 A comparative analysis of the obtained frequency dependences is carried out. A significant difference between the frequency dependences of the voltage modulus on biological tissues and the frequency dependence of the voltage modulus on an isotonic solution is shown. The concept is introduced that the degree of difference between the frequency distribution of the biological tissue impedance module from the impedance module of an isotonic solution can serve as a criterion for assessing the degree of damage to biological tissue.
 A conclusion is made about the advisability of developing the impedance measurement method as a method for diagnosing the viability of biological tissue; it is shown that the most promising approach to the development of impedance measurement methods is the analysis of transient processes when biological tissue is disturbed by small electric current pulses.

Graphene Oxide/Polyaniline Nanocomposites Used in Anticorrosive Coatings for Environmental Protection

In recent years, metal corrosion causes serious threats to the economy of the world and the living environment. Hence, it is very important to seek non-toxic and environmentally friendly materials with metal anti-corrosion properties for the sustainable development of society. The barrier properties of graphene oxide (GO) and the special electrochemical property of polyaniline (PANI) can significantly improve the corrosion resistance of metals. Herein, we developed an in-situ polymerization method to prepare graphene oxide/polyaniline (GO/PANI) nanocomposites with unique anti-corrosion properties. The obtained GO/PANI nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermalgravimetric analysis, UV–vis spectroscopy and scanning electron microscopy. The as-prepared composite materials were uniformly dispersed in epoxy resin to prepare anticorrosive coatings and coated on the surface of steel. The anti-corrosion performance of the coatings was measured by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique. The EIS results showed that the total impedance of epoxy/GO/PANI coatings is greater than epoxy/PANII coatings, and the impedance module value can reach 8.67 × 108 Ω·cm2. In general, it is concluded that the anti-corrosion performance of GO/PANI coating is significantly higher than PANI coating and pure GO coating.

Effect of La3+ cation solubility on the structural, magnetic and electrical properties of barium hexaferrite

In the present work, was studied the effect of the La3+ cation solubility on the structural, magnetic and electrical properties of M-type barium hexaferrite (BaM). The Rietveld refinement revealed changes in the lattice parameters with increasing the La3+ concentration. Variations in the bond length and the distortion index of 2b, 4f2 and 12k oxygen polyhedral were observed with the La3+ insertion in the BaM structure. In addition to the BaM phase, secondary phases Fe2O3 and LaFeO3 arise, whose concentrations depend on the La3+ solubility. The magnetic properties are strongly affected by the La3+ incorporation in the structure, as well as by the secondary phases. Changes in the oxidation state of Fe3+ to Fe2+ decreases the exchange interaction, resulting in the magnetic moments disturbance. The electrical properties are dependent on the La3+ content and the secondary phase concentration. Undoped sample present the highest impedance values, decreasing linearly in all frequency range. For doped samples, the resistivity decreases in several orders due to the La3+ incorporation, while the ac-conductivity remains constant at low frequencies and presents dispersion at high frequencies. The dielectric permittivity present space charge polarization mechanism generated by electron hopping from Fe3+ to Fe2+ ions. The Non-Debye-type relaxation and the conductivity transition of long and short range are suggested from the results of imaginary impedance and electric module. The bond valence model revealed that the most affected crystallographic sites are 2b, 4f2 and 12k, where the exchange of valence of Fe3+ by Fe2+ ions should take place.

Flat Gain Broadband Metasurface Antennas

Modulated metasurface (MTS) antennas can provide a broadside pencil beam at the frequency where the cylindrical surface wave (SW) wavelength matches the period of the impedance modulation. For modulations with constant period, the mismatch between the SW wavelength and the period imposes a limitation on the gain-bandwidth product. However, this limitation can be overcome by shaping the local period as a function of the radial distance. Doing so, we generate an annular active region on the antenna aperture, where the SW-to-impedance interaction mainly occurs. Such active region moves from the antenna center to the circular rim as the frequency decreases. This article shows that one can optimize the profile of the local periodicity function to obtain broadside pencil beams over large bandwidths, while preserving the flatness of the gain versus frequency response and a good stability of the phase center. The antenna performances so obtained are really unique for flat antennas based on printed technology. Finally, we present a simple formula for the product between average gain and bandwidth, which gradually blends into the already known expression for modulations with constant period. This formula establishes an absolute limit of the gain-bandwidth product, which only depends on the wavelength-normalized antenna radius at the central frequency.

A Wearable CMOS Impedance to Frequency Sensing System for Non-Invasive Impedance Measurements.

In this paper, we demonstrate a novel non-invasive, wearable impedance sensor. The impedance sensor, using an impedance to frequency measurement, with two modes of resistance and capacitance measurement is implemented in CMOS 130nm technology. The sensor consisting of current and voltage comparators for different mode of measurement, has a low power consumption of 30 μW per channel. The sensor is demonstrated in two applications, thoracic impedance and hand gesture recognition. Thoracic impedance is based on impedance modulation through fluid accumulation. Hand gestures are detected through tissue impedance sensing. The full thoracic impedance sensing system is smaller than a credit card, low cost, and consumes 3mW which includes the sensor, transmitter, and power control unit. Data received by this sensor can be easily transferred for further processing and, eventually, detection of heart failure. The electrodes were implemented using conductive paint, and the system was validated using passive loads to represent human tissue models and test subjects. The hand gesture system operates on 600 μW with the maximum number of electrodes, and uses adhesive copper with electrical paint as electrodes.

Fixed-Frequency Beam-Steering Leaky-Wave Antenna With Switchable Beam Number

This letter presents a fixed-frequency beam-steering leaky-wave antenna (LWA) with switchable beam number. The proposed LWA consists of an impedance modulation surface (IMS) and dc bias circuit. A three-strip structure is designed as the unit cell of the IMS. In this design, varactor diodes are inserted in the unit cell and the impedance characteristics of every unit cell can be controlled independently. Both average reactance and modulation periodicity of the IMS can be tuned for leaky-wave radiation with different beam angle. The proposed LWA can be configured to work in single-beam mode or dual-beam mode. A prototype of the proposed LWA operating at 8 GHz is fabricated and measured. By controlling the dc voltages of varactor diodes, a scanning range of 118° can be achieved.

Contributions of joint mechanics and neural control to the generation of torque during movement.

Completing motor tasks that require contact is dependent on an ability to regulate the relationship between limb motions and interaction forces with the environment. This can be achieved by exploiting the mechanical properties of a limb or through active regulation of joint torques through changes in muscle activation. Leveraging the mechanical properties of a joint might simplify neural control when they are matched to the functional requirements of a task. The purpose of this study was to determine if humans change their control strategy, relying on limb mechanics rather than regulated muscle activation, when feasible. This was accomplished by measuring ankle impedance and muscle activation strategies in three tasks requiring joint torques to: oppose movement, assist movement, or remain constant during movement. We found that subjects produced more torque due to impedance and less torque due to muscle activation in the torque-oppose task, the only task that could feasibly be completed through impedance modulation. These results demonstrate that people do leverage the mechanical properties of a joint to complete certain task, lessening the need for precisely timed muscle contractions.

Analyzing the Output of Bundle-Controlled Line Impedance Modulator (LIM) based Power Control and Line De-icing using MATLAB

Analyzing the Output of Bundle-Controlled Line Impedance Modulator (LIM) based Power Control and Line De-icing using MATLAB

An unusual frequency dispersion of the dielectric permittivity maxima at temperatures around the tetragonal–cubic phase transition of methylammonium lead iodide

We report studies on the unusual frequency dispersion of the dielectric permittivity maxima of methylammonium lead iodide pellets at temperatures around the tetragonal–cubic phase transition. The origin of this observed permittivity response was studied in terms of grains and grain boundaries’ contributions in impedance, electric modulus, dielectric permittivity, and electrical conductivity. From theoretical fits of impedance and electric modulus measurements at different temperatures over a frequency range of 103–10 Hz, the reconstructed contributions of the grain boundary and grain permittivities show peaks around 339 K and 384 K, respectively. The origin of the grain boundary permittivity peak is discussed in terms of heterogenic ionic conduction associated with I− and MA+ ions in MAPbI3, while the peak in grain permittivity at high temperature is in terms of ionization of intrinsic carriers. The high value of the grain dielectric permittivity (εg=1193), compared to the reconstructed grain boundary permittivity (εgb=53), suggests a possible relaxor ferroelectric behavior with a diffuse phase transition for methylammonium lead iodide. The difficulties in confirming the ferroelectric nature of this halide perovskite based on impedance and electrical module data are also discussed.

Local tissue electrical parameters predict oral mucositis in HNSCC patients: A diagnostic accuracy double-blind, randomized controlled trial

Oral Mucositis (OM) is a common adverse effect of head and neck squamous cell carcinoma (HNSCC) treatment. The purpose of this study was to investigate the significance of early changes in tissue electrical parameters (TEPs) in predicting the development of OM in HNSCC patients receiving radiation therapy (RT). The current study combined two study designs. The first was a case-control study. The control group comprised of RT patients who did not receive head and neck RT, and patients with HNSCC who received RT comprised the case group. In the second part of the study, the case group was included in a parallel cohort. A total of 320 patients were assessed for eligibility, and 135 patients were enrolled. Double blinding was performed, and neither the patients nor the care providers knew the measured parameters. The primary outcome was the detection of between-group changes in local TEPs over the follow-up period. The secondary outcome was the appearance of OM grades II, III, or IV and the predictive value of local TEPs in determining the incidence of OM after RT. The variables, impedance module, resistance, reactance, phase angle, and capacitance, were analyzed by the receiver operator curves (ROC). The case and control groups did not differ in demographic and clinical characteristics. Radiation therapy increased the local impedance module, resistance, reactance, and phase angle and reduced the local tissue capacitance in both groups. Evaluation of TEPs in the first week of RT correlated with the development of OM lesions during cancer therapy. ROC analysis showed that local impedance module and resistance presented higher specificity than did other parameters in predicting OM. In conclusion, local tissue electrical parameters measured at the first RT week can be useful tools to predict oral mucositis.

Application of electromechanical impedance technique in the monitoring of sigma phase embrittlement in duplex stainless steel

Duplex stainless steels (DSS) have a structure composed of austenite and ferrite in approximately equal volume fractions which provides an excellent integration between mechanical properties and corrosion resistance. However, the formation of intermetallic phases, such as sigma (σ) phase could become a major problem, once a small percentage of this phase originates a drastic deterioration of toughness and ductility, phenomenon known as σ phase embrittlement. In the present work, the effect of the isothermal aging treatment at 800 °C (temperature in which σ phase can be formed) on the degradation of mechanical properties of UNS S31803 DSS was investigated. The results showed that σ phase precipitation occurred regularly and by eutectoid decomposition. The effect of sigma phase on the mechanical properties was analyzed by the microhardness and impact tests at room temperature. The assessment of DSS also includes an σ phase embrittlement monitoring alternative method based on the electromechanical impedance (EMI), using piezoelectric sensors. The basic idea of the σ phase embrittlement monitoring method is that the increase in the hardness and the decrease in the impact toughness will leads to the variation in the EMI signatures by modifying structural stiffness. The proposed methodology is evaluated using the impedance module (|Z|), resistance (R), reactance (X) and by the statistical indexes: Relative Variation of Natural Frequencies (RVNF) and Root Mean Square Deviation (RMSD). This method is considered a nondestructive test, presents accurate results with high sensitivity and reliability providing capacity of determining sigma phase embrittlement and has promising application potential in this and other materials.

Retrodirective metasurfaces from non-reciprocal to reciprocal using impedance modulation for high-super-cell-periodicity designs

The growing popularity of metasurfaces and their exceptional physical phenomena has gained remarkable interest in terms of propagation and electromagnetic wave control. Particularly, for the case of retroreflection, retrodirective gradient metasurfaces are well known for their reciprocal responses in terms of retroreflection specially for subwavelength super-cell periodicity designs. Recently, we have observed that for metasurfaces with high super-cell periodicities greater than $$2\lambda $$ , the retrodirective metasurface loses its reciprocal response in terms of retrodirectivity. The main challenge in this case is to retain the reciprocal response, as well as achieving efficient responses for retroreflection at the higher orders of diffraction that exist at these periodicities. Thus, in this paper we demonstrate the design of a retrodirective metasurface from non-reciprocal to reciprocal following the generalized phase law of reflection and introducing the impedance modulation technique, for a metasurface operating at 14.7 GHz with a super-cell periodicity of $$2.88 \lambda $$ . On the other hand, with a well-engineered surface impedance of a super-cell at these periodicities, efficient responses of retroreflection can be achieved at the higher orders of diffraction, giving rise to a retrodirective metasurface design operating simultaneously for multiple incident angles. Retroreflection has been achieved at eleven angles simultaneously, and the reciprocal property was retained at the desired angle of incidence $$10^{\circ }$$ .

Detecting spots of garden strawberry by impedance spectroscopy method

The study was conducted to identify eight informative parameters of the electrical impedance of strawberry leaf tissue: active and reactive resistance in series and parallel circuits of the measurement object electrical model, phase shift, capacitance, loss tangent, impedance module. These parameters are associated with the action of fungi pathogens of garden strawberry spots Ramularia tulasnei Sass, Marssonina potentillae (Desm), Dendrophoma obscurans (Ell. & Ev.) Anderson). Diagnosis of diseases was carried out by visual analysis of symptoms and microscopic analysis of the sporulation of fungi pathogens. The study was carried out using a precision impedance analyzer WK 6505B in accordance with the developed technique. The bio-impedance parameters of the strawberry leaf tissue were measured using sensor electrodes placed on the upper side of the leaf with a constant clamping force. Each parameter of the tissue bio-impedance on the leaf surface was measured when electrodes were installed to the right and left of the central leaf vein. To reduce the contact resistance between the electrodes and the leaf surface, the electrodes were lubricated with a special electrode gel. There were 2624 dependences obtained of the bio-impedance parameters of healthy leaves and the ones affected with white, brown, and angular spots of three varieties of garden strawberry (Eliani, Tanyusha, and Darenka). The variance analysis of the average values of the data revealed that the most informative part of the changes in all parameters lies in the low-frequency region of α-dispersion of bio-impedance: from 20 Hz to 10 kHz. It is proposed to use reactive impedance measured in the low-frequency region of α-dispersion of bioimpedance as the main informative parameter of bio-impedance for detecting spots. With this reactive impedance, extreme values of its change appear for healthy leaves of garden strawberries and the diseased ones. The results of the research will be used to create a device for the early diagnosis of spots of wild strawberries.

Tunable Matching Networks Based on Phase-Switched Impedance Modulation1

The ability to provide accurate, rapid, and dynamically controlled impedance matching offers significant advantages to a wide range of present and emerging radio-frequency (RF) power applications. This article develops a new type of tunable matching network (TMN) that enables a combination of much faster and more accurate impedance matching than is available with conventional techniques and is suitable for use at high power levels. This implementation is based on a narrow-band technique, termed here phase-switched impedance modulation (PSIM), which entails the switching of passive elements at the RF operating frequency, effectively modulating their impedances. The proposed approach provides absorption of device parasitics and zero-voltage switching (ZVS) of the active devices, and we introduce control techniques that enable ZVS operation to be maintained across operating conditions. A prototype PSIM-based TMN is developed that provides a 50-Ω match over a load impedance range suitable for inductively coupled plasma processes. The prototype TMN operates at frequencies centered around 13.56 MHz at input RF power levels of up to 200 W.

Reinforcement Corrosion Research Based on Electrochemical Impedance Spectroscopy for Coral Aggregate Seawater Concrete in a Seawater Immersion Environment

Abstract The use of electrochemical impedance spectroscopy (EIS) method, Nyquist plots, and Bode impedance module plots of coral aggregate seawater concrete (CASC) at different exposure times in a seawater immersion environment was tested. The most suitable equivalent electric circuit (EEC) for fitting reinforcement corrosion of CASC in a seawater immersion environment was investigated. The reinforcement corrosion electrochemical parameters were calculated. The factors affecting reinforcement corrosion of CASC were researched. The results showed that in order to reduce reinforcement corrosion risk, the concrete cover thickness should be thicker than 5.5 cm. As exposure time increased, the decrease rate of anticorrosion effectiveness for the calcium nitrate inhibitor was higher than that for the amino alcohol inhibitor. Corrosion resistance would improve if the inhibitor was preabsorbed. Corrosion resistance of different types of reinforcements followed the rule: 2205 duplex stainless steel > 316 stainless steel > new organic coated steel > zinc–chromium coated steel > common steel.

Overview of Modulation Strategies for LLC Resonant Converter

In this article, based on the LLC resonant converter fundamental harmonic analysis model, the modulation strategies for LLC resonant converter can be categorized into the following three groups: 1) input voltage fundamental harmonic modulation; 2) resonant tank elements modulation; and 3) secondary equivalent impedance modulation. Operational principles and control diagrams for different modulation strategies are given. Comprehensive comparisons between these modulation strategies in terms of topology complexity, control complexity, and voltage gain range are presented with respect to the same system specifications. The advantages and disadvantages for each modulation strategy are summarized to provide guidance for engineers when analyzing and designing an LLC resonant converter. The hybrid modulation strategies are categorized into different groups based on the specific applications. Brief introductions of these hybrid modulation strategies are presented. Future trends regarding the modulation strategies of LLC resonant converters are presented.

Effect of AC interference on hydrogen evolution reaction of x80 steel

PurposeThe purpose of this paper is to quantify the influence of alternating current (AC) interference on hydrogen evolution reaction of X80 steel.Design/methodology/approachThe hydrogen evolution potential was obtained by cathodic potentiodynamic polarization curve. The instantaneous potential under AC interference was obtained by high-frequency acquisition with three-electrode system. Electrochemical impedance spectroscopy and Tafel polarization curves were used to study the influence mechanism of AC interference on instantaneous potential.FindingsIt was concluded that the hydrogen evolution reaction could occur on X80 steel under AC interference. There were critical AC current densities of about 100 to 200 A/m2, beyond which the cathode reaction of X80 steel changed from oxygen absorption to hydrogen evolution. Besides the pH value, the initial polarization potential EZ and impedance module of the steel/electrolyte interface under AC interference were also the factors that affected the critical AC densities in different solutions.Originality/valueThis research quantified the hydrogen evolution capacity of X80 steel under AC interference, which could be applied to clear the effect of AC interference on hydrogen evolution reaction.

56/28-Gb/s PAM4/PAM2 Impedance-Modulated Transmitter Enabling 44-dB/58-dB Loss Compensation at 14 GHz in a 7-nm FinFET Transceiver

This letter reports a 56-Gb/s PAM4, 28-Gb/s PAM2 transmitter that utilizes impedance modulation to implement pre-emphasis postcursor and precursor and low impedance postcursor modes. Implemented as part of a 7-nm FinFET transceiver, the multimode impedance modulated transmitter can compensate for 44- dB/58-dB channel loss in PAM4/PAM2 which is the highest loss compensation reported to date @56 Gbps. The transmitter achieves an impressive figure-of-merit of 0.86-pJ/bit per volt of differential output swing and surpasses its current mode logic based counterpart by a wide margin in terms of power and performance.