Showing papers on "Electrical impedance published in 2014"

Impedance Shaping of the Grid-Connected Inverter with LCL Filter to Improve Its Adaptability to the Weak Grid Condition

Abstract: The current-controlled grid-connected inverter with LCL filter is widely used in the distributed generation system (DGS), due to its fast dynamic response and better power quality features. However, with the increase of power injected into the grid, control performances of the inverter will be significantly influenced by the nonideal grid conditions. Specifically, the possible wide variation of the grid impedance challenges the system stability. Meanwhile, background harmonics of the grid can greatly distort the injected current. Therefore, the control of the inverter should be designed with strong stability-robustness and high harmonic-rejection-ability, both of which correlate closely with the inverter output impedance. However, it is difficult to shape the output impedance into the one with a desirable characteristic simply by adjusting the current loop gain. In this paper, an impedance shaping method is proposed with virtual impedances, and the current control loop can be designed independently. The implementation and parameter design of the virtual impedances are studied under the practical considerations. With this proposed method, the grid-connected inverter can work stably over a wide range of the typical inductive-resistive grid impedance and exhibit strong rejection ability of grid-voltage harmonics. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method.

Apparatus for providing a control signal for a variable impedance matching circuit and a method thereof

Abstract: An apparatus for providing a control signal for a variable impedance matching circuit comprises a control module configured to generate a control signal for adjusting an impedance of a variable impedance matching circuit coupled to an antenna module. The control module is configured to generate the control signal based on a sensor signal received from a sensor circuit located in proximity to the antenna module. The sensor signal comprises information related to a power of an electromagnetic signal radiated by the antenna module.

Polarization-Independent and Ultrawideband Metamaterial Absorber Using a Hexagonal Artificial Impedance Surface and a Resistor-Capacitor Layer

Abstract: A polarization-independent ultrawideband metamaterial absorber is proposed for X-band applications. High absorptivity over an ultrawide spectrum is achieved by the combination of an artificial impedance surface (AIS) and a resistor-capacitor (RC) layer. In addition, the unique hexagonal shape of an AIS and RC layer enables polarization insensitivity. A circuit analysis is introduced based on a transmission-line model and shows good agreement with the full-wave analysis. Fabrication tolerance issues are considered with parametric studies in the electromagnetic simulation. The proposed absorber is fabricated on low-cost FR4 substrates, and its absorption performance is experimentally demonstrated at different angles and polarizations of incident electric fields.

Strong environmental coupling in a Josephson parametric amplifier

Abstract: We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behavior using the “pumpistor” model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over the complexity of gain profiles through added variation in the environment impedance at a given frequency. With strong coupling to a suitable external impedance, we observe a significant increase in dynamic range, and large amplification bandwidth up to 700 MHz giving near quantum-limited performance.

A universal equivalent circuit for carbon-based supercapacitors

Abstract: A universal equivalent circuit is proposed for carbon-based supercapacitors. The circuit, which actually applies to all porous electrodes having non-branching pores, consists of a single vertical ladder network in series with an RC parallel network. This elegant arrangement explains the three most important shortcomings of present-day supercapacitors, namely open circuit voltage decay, capacitance loss at high frequency, and voltammetric distortion at high scan rate. It also explains the shape of the complex plane impedance plots of commercial devices and reveals why the equivalent series capacitance increases with temperature. Finally, the construction of a solid-state supercapacitor simulator is described. This device is based on a truncated version of the universal equivalent circuit, and it allows experimenters to explore the responses of different supercapacitor designs without having to modify real supercapacitors.

Calibrated complex impedance and permittivity measurements with scanning microwave microscopy.

Abstract: We present a procedure for calibrated complex impedance measurements and dielectric quantification with scanning microwave microscopy. The calibration procedure works in situ directly on the substrate with the specimen of interest and does not require any specific calibration sample. In the workflow tip‐sample approach curves are used to extract calibrated complex impedance values and to convert measured S11 reflection signals into sample capacitance and resistance images. The dielectric constant of thin dielectric SiO2 films were determined from the capacitance images and approach curves using appropriate electrical tip‐sample models and the"r value extracted at fD 19:81 GHz is in good agreement with the nominal value of"r 4. The capacitive and resistive material properties of a doped Si semiconductor sample were studied at different doping densities and tip‐sample bias voltages. Following a simple serial model the capacitance‐voltage spectroscopy curves are clearly related to the semiconductor depletion zone while the resistivity is rising with falling dopant density from 20 to 20 k. The proposed procedure of calibrated complex impedance measurements is simple and fast and the accuracy of the results is not affected by varying stray capacitances. It works for nanoscale samples on either fully dielectric or highly conductive substrates at frequencies between 1 and 20 GHz.

Transversal Asymmetry in Periodic Leaky-Wave Antennas for Bloch Impedance and Radiation Efficiency Equalization Through Broadside

Abstract: This paper demonstrates that unit cell asymmetry with respect to the transversal axis -or transversal asymmetry- is an essential design parameter in periodic leaky-wave antennas (P-LWAs). Specifically, it shows that transversal asymmetry can be leveraged to fully and systematically solve the well-known radiation degradation of P-LWAs at broadside, where it provides both open-stopband closure and efficiency equalization. The problem is addressed via a generic equivalent circuit model composed of a series resonator, a shunt resonator and ideal transformers for modeling asymmetry by a single and simple parameter, namely the transformation ratio. Once the series and shunt frequencies have been balanced (frequency-balancing), equalization is ensured by adjusting the degree of asymmetry in the unit cell so to match the at-broadside Bloch impedance to the off-broadside Bloch impedance. This equalization condition is referred to as quality factor balancing ( Q-balancing) and it is related to the Heaviside condition (distortionless propagation) in homogeneous transmission lines. Based on this theory, optimization schemes for employing commercial fullwave eigenmode and drivenmode solvers are proposed to design unit cells with equalized efficiencies. Finally, two examples of P-LWAs are presented, a composite right/left-handed (CRLH) P-LWA and a series-fed coupled patch (SFCP) P-LWA, and verified to fully confirm the predictions of the theory obtained by circuit modeling.

18.4 A 4.9mΩ-sensitivity mobile electrical impedance tomography IC for early breast-cancer detection system

Abstract: A mobile electrical impedance tomography (EIT) IC is proposed for early breast cancer detection personally at home. To assemble the entire system into a simple brassiere shape, EIT IC is integrated via a multi-layered fabric circuit board which includes 90 EIT electrodes and two reference electrodes for current stimulation and voltage sensing. The IC supports three operating modes; gain scanning, contact impedance monitoring, and EIT modes for the clear EIT image. A differential sinusoidal current stimulator (DSCS) is proposed for injection of low-distortion programmable current which has harmonics less than $-$ 59 dBc at a load impedance of 2 kΩ. To get high sensitivity, a 6-channel voltage sensing amplifier can adaptively control the gain up to a maximum of 60 dB, and has low input referred noise, 36 nV/ $\surd$ Hz. The 2.5 × 5 mm chip is fabricated in a 0.18 µm 1P6M CMOS process and consumes 53.4 mW on average. As a result, a sensitivity of 4.9 mΩ is achieved which enables the detection of a 5 mm cancer mass within an agar test phantom.

Asymmetrical Grid Fault Ride-Through Strategy of Three-Phase Grid-Connected Inverter Considering Network Impedance Impact in Low-Voltage Grid

Abstract: This letter presents a new control strategy of three-phase grid-connected inverter for the positive sequence voltage recovery and negative sequence voltage reduction under asymmetrical grid faults. Unlike the conventional control strategy based on an assumption that the network impedance is mainly inductive, the proposed control strategy is more flexible and effective by considering the network impedance impact, which is of great importance for the high penetration of grid-connected renewable energy systems into low-voltage grids. The experimental tests are carried out to validate the effectiveness of the proposed solution for the flexible voltage support in a low-voltage grid, where the network impedance is mainly resistive.

High-Frequency Induction Machine Modeling for Common Mode Current and Bearing Voltage Calculation

Abstract: In this paper, several inverter-fed induction machines with rated powers between 1.5 and 240 kW are modeled for calculating the common mode (CM) stator ground current and the capacitive bearing voltage. Simple methods to extract the parameters of the high-frequency machine model from the measured CM and differential mode impedances are presented. Furthermore, the most significant parameters are given for five different machine sizes between 1.5 and 240 kW rated power. Calculation examples are provided in comparison to the experimental results.

Frequency and temperature dependence behaviour of impedance, modulus and conductivity of BaBi4Ti4O15 aurivillius ceramic

Abstract: In this work, we report the dielectric, impedance, modulus and conductivity study of BaBi 4 Ti 4 O 15 ceramic synthesized by solid state reaction. X-ray diffraction (XRD) pattern showed orthorhombic structure with space group A21am confirming it to be an m = 4 member of the Aurivillius oxide. The frequency dependence dielectric study shows that the value of dielectric constant is high at lower frequencies and decreases with increase in frequency. Impedance spectroscopy analyses reveal a non-Debye relaxation phenomenon since relaxation frequency moves towards the positive side with increase in temperature. The shift in impedance peaks towards higher frequencyside indicates conductionin material andfavouringof the longrangemotion of mobile charge carriers. The Nyquist plot from complex impedance spectrumshows only one semicircular arc representingthe grain effect in the electrical conduction. The modulus mechanism indicates the non-Debye type of conductivity relaxation in the material, which is supported by impedance data. Relaxation times extracted using imaginary part of complex impedance (Z ′′ ) and modulus (M ′′ ) were also found to follow Arrhenius law. The frequency dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of DC conductivity exhibits a negative temperature coefficient of resistance behaviour.

Transformation Electromagnetics Devices Based on Printed-Circuit Tensor Impedance Surfaces

Abstract: A method for designing transformation electromagnetics devices using tensor impedance surfaces is presented. The method is first applied to idealized tensor impedance boundary conditions (TIBCs), and later to printed-circuit tensor impedance surfaces (PCTISs). A PCTIS is a practical realization of a TIBC. It consists of a tensor impedance sheet, which models a subwavelength patterned metallic cladding, over a grounded dielectric substrate. The method outlined in this paper allows anisotropic TIBCs and PCTISs to be designed that support tangential wave vector distributions and power flow directions specified by a coordinate transformation. As an example, beam-shifting devices are designed, using TIBCs and PCTISs, that allow a surface wave to be shifted laterally. The designs are verified with a commercial full-wave electromagnetic solver. This work opens new opportunities for the design and implementation of anisotropic and inhomogeneous printed-circuit or graphene-based surfaces that can guide or radiate electromagnetic fields.

Y-source impedance network

Abstract: This paper introduces a Y-shaped impedance network for realizing converters that demand a high voltage gain while using a small duty ratio. To achieve that, the proposed network uses a tightly coupled transformer with three windings, whose obtained gain is presently not matched by existing networks operated at the same duty ratio. This capability has been demonstrated by mathematical derivation for the proposed network in comparison with other recently reported networks. To further prove the network performance, a single-switch dc-dc converter has been implemented with the network, before testing it experimentally. The results obtained clearly verify the network performance in addition to its higher power density that can generally be achieved by coupled magnetics.

Embedded 3D electromechanical impedance model for strength monitoring of concrete using a PZT transducer

Abstract: The electromechanical (EM) impedance approach in which piezoelectric ceramics (PZT) simultaneously act as both a sensor and an actuator due to their direct and inverse piezoelectric effects has emerged as a powerful tool for structural health monitoring in recent years. This paper formulates a new 3D electromechanical impedance model that characterizes the interaction between an embedded square PZT transducer and the host structure based on the effective impedance. The proposed formulations can be conveniently used to extract the mechanical impedance of the host structure from the electromechanical admittance measurements of an embedded PZT patch. The proposed model is verified by experimental and numerical results from a smart concrete cube in which a square PZT transducer is embedded. Subsequently, this paper also presents a new methodology to monitor the compressive strength of concrete based on the effective mechanical impedance. By extracting the effective mechanical impedances from the electromechanical admittance signatures, measuring the compressive strength of the concrete cubes at different ages and combining these measurements with the index of the correlation coefficient (CC), a linear correlation between the concrete strength gain and the CC of the real mechanical admittances was found. The proposed approach is found to be feasible to monitor the compressive strength of concrete by age.

Compact Hyper-Band Printed Slot Antenna With Stable Radiation Properties

Abstract: A compact hyper-band ( $>$ 10:1 impedance bandwidth) printed antenna design is investigated numerically and experimentally. It is based on an elliptical-slot antenna augmented with a parasitic oval patch and driven with a specially engineered microstrip-line-fed elliptical tuning fork element. The parasitic and driven elements are adjusted along with the elliptical slot to create additional resonance modes; adjust the coupling strengths among all of the design components; facilitate the overlap of adjacent resonance modes; and fine tune the input impedance. The total size of the final optimized antenna is only 30 $\times$ 40 ${\rm mm}^{2}$ . It exhibits a $-$ 10-dB impedance bandwidth from 2.26 to 22.18 GHz. Desirable radiation performance characteristics, including relatively stable and omni-directional radiation patterns, are obtained over this range. A prototype was fabricated and tested. The experimental results confirm the predicted input impedance bandwidth and radiation characteristics. While the hyper-band performance could be used for high fidelity short pulse applications, the antenna could also be used for multi-band operations from 3.1–10.6 GHz since it covers that entire ultra-wideband (UWB) spectral range.

An Analytical Design Method for a Novel Dual-Band Unequal Coupler With Four Arbitrary Terminated Resistances

Abstract: A new design concept of a generalized dual-band branch-line coupler with unequal power division and four arbitrary terminated resistances is proposed in this paper. By using an external frequency-dependent impedance transformer, a novel dual-band branch-line coupler is obtained with a detailed analytical design method. For ease of design, maximum power-dividing ratio with varying frequency ratio for different terminated impedance values is provided. Owing to the additional design freedom, the calculation of parameters becomes much more flexible. Finally, for experimental validation and convenient measurement, a dual-band unequal microstrip branch-line coupler with four standard ports is designed, fabricated, and measured. Good agreement between the simulated and measured results can be observed.

A short footnote: Circuit design for faradaic impedimetric sensors and biosensors

Abstract: Electrochemical impedance spectroscopy (EIS) is an electrochemical surface characterization technique and has been widely used in biosensor and chemical sensors, also provides label free detection. This technique is used as faradaic and non-faradaic measurement. The advantage of the sensitivity of faradaic impedance spectroscopy becomes useful and preferred technique. In this review we tried to answer these questions: how Nyquist plots are fitted in proper circuit and how a proper circuit element is chosen in fitting and impedance calculation steps. Nyquist plot can become very confusing to fit on a proper circuit modal and calculation of impedance (Z). Z is called in other word as electron transfer resistance (Ret), additionally electrolyte interface impedance (Rs), capacitance (C) and Warburg impedance (W) are the other elements. These all circuit elements must be constructed in a proper order to fit Nyquist plot into a good circuit model. Therefore it is very important to examine Nyquist plot for accurate calculation.

Control of Inverters Via a Virtual Capacitor to Achieve Capacitive Output Impedance

Abstract: Mainstream inverters have inductive output impedance at low frequencies (such inverters are called L-inverters). In this paper, a control strategy is proposed to make the output impedance of an inverter capacitive at low frequencies (such inverters are called C-inverters). The proposed control strategy involves the feedback of the inductor current through an integrator, which is actually the impedance of a virtual capacitor. The gain of the integrator or the virtual capacitance is first selected to guarantee the stability of the current feedback loop and then optimized to minimize the total harmonic distortion (THD) of the output voltage. Moreover, some guidelines are developed to facilitate the selection of the filter components for C-inverters. Simulation and experimental results are provided to demonstrate the feasibility and excellent performance of C-inverters, with the filter parameters of the test rig selected according to the guidelines developed. It is shown that, with the same hardware, the lowest voltage THD is obtained when the inverter is designed to be a C-inverter. A by product of this study is that, as long as the current ripples are kept within the desired range, the filter inductor should be chosen as small as possible in order to reduce voltage harmonics. This helps reduce the size, weight, and volume of the inductor and improve the power density of the inverter.

Blackbox quantization of superconducting circuits using exact impedance synthesis

Abstract: We propose a new quantization method for superconducting electronic circuits involving a Josephson-junction device coupled to a linear microwave environment. The method is based on an exact impedance synthesis of the microwave environment considered as a blackbox with impedance function $Z(s)$. The synthesized circuit captures dissipative dynamics of the system with resistors coupled to the reactive part of the circuit in a nontrivial way. We quantize the circuit and compute relaxation rates following previous formalisms for lumped element circuit quantization. Up to the errors in the fit our method gives an exact description of the system and its losses.

Systems and methods for arc detection and drag adjustment

Abstract: The systems and methods of the present disclosure detect arcing patterns or impedance changes and adjust the level of electrosurgical energy provided to tissue based on the detected arcing patterns or impedance changes. In embodiments, the drag force imposed on the electrode or blade of an electrosurgical instrument may be controlled by adjusting the level of electrosurgical energy based on the detected arcing patterns or impedance changes. The arcing patterns or impedance changes may be detected by sensing voltage and/or current waveforms of the electrosurgical energy and analyzing the sensed voltage and/or current waveforms. The current and/or voltage waveform analysis may involve calculating impedance based on the sensed voltage and current waveforms and calculating changes in impedance over time. The waveform analysis may involve detecting harmonic distortion using FFTs, DFTs, Goertzel filters, polyphase demodulation techniques, and/or bandpass filters. The waveform analysis may involve determining a normalized difference or the average phase difference between the voltage and current waveforms.

Ultrastable eddy current displacement sensor working in harsh temperature environments with comprehensive self-temperature compensation

Abstract: This paper proposes a method of self-temperature compensation for eddy current sensors (ECSs) during rapid temperature changes. The temperature drift of the sensor impedance caused by the probe coil and target temperature variations was discussed and analyzed. The proposed impedance measurement method can distinguish the temperature drift caused by the sensor coil and the eddy currents in the target, and eliminate both of them in real time. A prototype ECS was manufactured and tested. The temperature coefficients of the probe's inductance and resistance caused by the target and the coil were measured by a designed setup. The results show that the temperature drift of the inductance is mainly caused by the target, and that of the resistance is mainly from the coil itself which is much larger than the inductance's drift. The prototype ECS that uses this new comprehensive self-temperature compensation method achieved an ultra-low temperature drift of 4 nm/°C without any additional hardware or temperature sensor. It can work effectively even the environment temperature changes as fast as 10 °C/h.

A systematic approach to modeling impedances and current distribution in planar magnetics

Abstract: Planar magnetic components using printed-circuit-board windings are attractive due to their high repeatability, good thermal performance and usefulness for realizing intricate winding patterns. To enable higher system integration at high switching frequency, more sophisticated methods that can rapidly and accurately model planar magnetics are needed. This paper develops a lumped circuit model that captures the impact of skin and proximity effects on current distribution and electromagnetic fields in planar magnetics. This enables accurate predictions of impedances, losses, stored reactive energy and current sharing among parallel windings. This lumped model is also a circuit domain representation of electromagnetic interactions. It can be used to simulate circuits incorporating planar magnetics, to visualize the electromagnetic fields, and to extract parameters for magnetic models by simulations. The modeling results match with previous theories and finite-element-modeling results. A group of planar magnetic devices, including transformers and inductors with various winding patterns, are prototyped and measured to validate the proposed approach.

Electrical transport properties of Mn–Ni–Zn ferrite using complex impedance spectroscopy

Abstract: Polycrystalline Mn0.45Ni0.05Zn0.50Fe2O4 was prepared by a standard solid state reaction technique. We report the electrical properties of this ferrite using ac impedance spectroscopy as a function of frequency (20 Hz–10 MHz) at different temperatures (50–350 °C). X-ray diffraction patterns reveal the formation of cubic spinel structure. Complex impedance analysis has been used to separate the grain and grain boundary resistance of this ferrite. The variation of grain and grain boundary conductivities with temperature confirms semiconducting behavior. The dielectric permittivity shows dielectric dispersion at lower frequency and reveals that it has almost the same value on the high-frequency side. The non-coincidence of peaks corresponding to modulus and impedance indicates deviation from Debye-type relaxation. A similar value of activation energy is obtained from impedance and modulus spectra, indicating that charge carriers overcome the same energy barrier during relaxation. Electron hopping is responsible for ac conduction in this ferrite. The electron hopping shifts toward higher frequency with increasing temperature, below which the conductivity is frequency independent. The frequency-independent ac conductivity has been observed at and above 300 °C in the frequency range 20 Hz–1 MHz. This frequency-independent ac conductivity is due to the long-range movement of the mobile charge carriers.

Ring-Shaped Substrate Integrated Waveguide Wilkinson Power Dividers/Combiners

Abstract: This paper proposes and presents a class of substrate integrated waveguide (SIW) power dividers/combiners based on a modified Wilkinson architecture. The proposed design consists of a ring-type circuit of 1.5 λ g length with three waveguide ports. Impedance variation without affecting cutoff frequency and integration of isolation resistance are the two major limitations in connection with the design of SIW Wilkinson structures. Central ring part with different thickness ensures different impedance in the first proposed scheme while the half-mode SIW in the second option. As for the second limitation, the optimal configuration of integrating the isolation resistance is studied. A version without resistance is also examined using a broad-wall series slot. To validate the proposed concept, a bilayered circuit with standard Printed circuit board prototype was fabricated and measured. A table summarizing performances of all the proposed circuits shows a bandwidth of around 25% at the 10 dB reference. A negligible additional insertion loss is observed. The proposed design techniques are found useful at millimeter-wave frequencies where reduced physical dimensions make a circuit configuration suitable for low-cost implementation. This concept is also valid for rectangular waveguide counterparts.