Impedance Results Research Articles

Magnetic field probes for use in radio frequency plasma

An impedance analyzer has been used in the characterization of a magnetic induction probe (B-dot probe) for use in plasma. The role of the impedance analyzer was to determine the frequency response of a B-dot probe up to 100 MHz. The probe was specifically designed to take measurements in rf plasma driven at 13.56 MHz. Probe sensitivity and calibration are considered based on the impedance values obtained when a B-dot probe is swept over a wide frequency range. Effects such as unbalanced loads based on transmission line inductances and termination impedance are shown to be limiting factors on the probes useful frequency range. The use of an impedance analyzer allows these effects to readily be characterized.

The Effects of Load Impedance, Line Length, and Branches in Typical Low-Voltage Channels of the BPLC Systems of Developing Countries: Transmission-Line Analyses

This paper presents the influence of line length, number of branches (distributed and concentrated), and terminal impedances on the performance of a low-voltage broadband power-line communication channel. For analyses, the systems chosen are typical low-voltage power-line networks found in Tanzania. The parameters varied were the network's load impedances, direct line length (from transmitter to receiver), branched line lengths, and number of branches. From the frequency responses of the transfer functions (ratio of the received and transmitted signal), it is seen that the position of notches and peaks in the amplitude responses are affected by the aforementioned network parameters and topology. As a result, the time-domain responses are attenuated and distorted. Time-domain responses of power-line channels under various conditions are also investigated for a given pulse input at the transmitter. The observations presented in this paper could be useful for suitable power-line communication system design.

Uncertainty of Free-Space Dipole Antenna Factor From 1 GHz to 2 GHz

The free-space antenna factor (AF) of a dipole antenna above 1 GHz using the three-antenna method (TAM) and associated uncertainty is presented. Theoretical site insertion loss containing antenna alignment and terminal impedances is newly given for the TAM and the uncertainty analysis. Higher order terms of Taylor series expansion are considered to include the effect of the alignment angle on uncertainty. Finally, the AFs are obtained with an expanded uncertainty of 0.4 dB (k = 2) in the entire frequency range.

A Comprehensive Analysis of AM–AM and AM–PM Conversion in an LDMOS RF Power Amplifier

In this paper, a Volterra analysis built on top of a normal harmonic balance simulation is used for a comprehensive analysis of the causes of AM-PM distortion in a LDMOS RF power amplifier (PA). The analysis shows that any nonlinear capacitors cause AM-PM. In addition, varying terminal impedances may pull the matching impedances and cause phase shift. The AM-PM is also affected by the distortion that is mixed down from the second harmonic. As a sample circuit, an internally matched 30-W LDMOS RF PA is used and the results are compared to measured AM-AM, AM-PM and large-signal S11.

Analysis and Design of Passive Polyphase Filters

Passive RC polyphase filters (PPFs) are analyzed in detail in this paper. First, a method to calculate the output signals of an n-stage PPF is presented. As a result, all relevant properties of PPFs, such as amplitude and phase imbalance and loss, are calculated. The rules for optimal pole frequency planning to maximize the image-reject ratio provided by a PPF are given. The loss of PPF is divided into two factors, namely the intrinsic loss caused by the PPF itself and the loss caused by termination impedances. Termination impedances known a priori can be used to derive such component values, which minimize the overall loss. The effect of parasitic capacitance and component value deviation are analyzed and discussed. The method of feeding the input signal to the first PPF stage affects the mechanisms of the whole PPF. As a result, two slightly different PPF topologies can be distinguished, and they are separately analyzed and compared throughout this paper. A design example is given to demonstrate the developed design procedure.

A 3–50 GHz Ultra-Wideband PHEMT MMIC Balanced Frequency Doubler

A novel configuration of ultra-wideband (UWB) GaAs PHEMT monolithic microwave integrated circuit balanced frequency doubler is presented. By using two different terminal impedances of the common-source/common-gate active balun, the doubler exhibits UWB characteristic with more than a four octave frequency range. From 3 to 50 GHz, the measured conversion gain and fundamental frequency suppression of the doubler are better than -4 dB and 15 dB.

A method for improving broadband phase performance of CS/CG active balun

AbstractA method for improving broadband phase performance of common‐source/common‐gate (CS/CG) active balun is presented. By setting different terminal impedances and DC bias, the phase error of the balun can be controlled within 7° from 1 to 20 GHz in simulation. A fabricated 2–40 GHz balanced MMIC doubler using the designed active balun has the fundamental frequency suppression (FFS) of more than 16 dB. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2777–2780, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23793

Terminal Impedance and Antenna Current Distribution of a VLF Electric Dipole in the Inner Magnetosphere

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The current distribution and input impedance of an electric dipole antenna operating in a cold magnetoplasma at very low frequency (VLF) is determined through numerical simulation. A full wave solution of Maxwell's equations using a finite-difference frequency-domain (FDFD) method is implemented to simulate electromagnetic wave propagation in this highly anisotropic medium. The classical perfectly matched-layer (PML) boundary condition is found to exhibit instabilities in the form of nonphysical wave amplification in this environment. To circumvent these difficulties, a PML is developed that is tailored to the cold plasma environment at VLF frequencies. It is shown that the current distribution for antennas with length <formula formulatype="inline"> <tex>$≪$</tex></formula> 100 m is approximately triangular for magnetospheric conditions found at <formula formulatype="inline"><tex>$L = 2$</tex></formula> and <formula formulatype="inline"><tex>$L = 3$</tex></formula> in the geomagnetic equatorial plane. Calculated variations of input impedance as a function of drive frequency are presented for two case studies and compared with predictions of existing analytical work. </para>

Identification of airway characteristics using the input impedance

To understand how the input impedance determined at the throat correlates with changes in the dynamic characteristics of the airways, a simplified 5-lobe model is developed and simulated. The model takes into account some realistic conditions such as varying cross-sectional areas, flexible wall properties and branching. The lobe terminal impedances are implemented in the model to predict the input impedance at the throat. The effects of airway constrictions and wall elastance variations on this impedance are determined for a range of frequencies. It is concluded that the developed model is capable of predicting various physiological changes in the airway passages.

Multiterminal Three Phase Transformer Model With Balanced or Unbalanced Loading

A terminal model of a transformer is developed which permits balanced or unbalanced loading. After the terminal-loading problem is solved, currents within and voltages across the individual windings can be obtained. The method is general and allows for standard and complicated winding interconnections such as deltas and extended deltas, Y's and ungrounded Y's, series connections, zig-zag, phase shifters, etc. In addition, these connections can be performed successively to get an even greater variety of winding connections. Unbalanced loading includes a single or double line-to-ground fault. The method then enables the winding currents to be obtained for subsequent force and stress analysis. The method can also be used to obtain regulation effects and terminal to terminal impedances.

Current-mode multiphase sinusoidal oscillator using CDTA-based allpass sections

In this work, a current tunable current-mode multiphase sinusoidal oscillator (MSO) employing current differencing transconductance amplifier (CDTA)-based first-order allpass sections is presented. The proposed MSO circuit, which uses only two CDTAs and one virtually grounded capacitor for each phase, can generate arbitrary 2 n -phase current-output signals ( n = 2 , 3 , 4 , … ) equally spaced in phase, all at high output impedance terminals. The oscillation condition and the oscillation frequency can be controlled electronically and independently by adjusting the bias current of the CDTA. The oscillator has low-sensitivity performance. Simulation results are also given to verify the functionality of the proposed oscillator.

An impedance matching technique for active-passive vibration control

Impedance matching techniques have shown potential for active vibration control of structures in bending. Such structures are commonly described by Euler-Bernoulli theory. Previous studies concerning impedance matching of these structures have only considered scalar quantities. However, for an Euler-Bernoulli beam four field variables are involved which implies that a scalar impedance is insufficient. The purpose of this study is therefore to expand the technique to include full 2x2 matrices. This is achieved by first deriving the reflection matrix as a function of the characteristic impedance matrices of an Euler-Bernoulli beam and an arbitrary termination impedance. An active impedance load is then introduced in order to manipulate the reflection matrix. A theoretical example is given where the approach is utilized to match the junction between an Euler-Bernoulli beam and a sandwich composite. This proposed active-passive damping configuration employs active control to enclose all incident power in the sandwich composite. Results show that the active impedance load is responsible for the main part of the power absorption over a broad frequency range.

Toward Integrated Circuit Size Reduction

In this article, voltage-basis, current-basis, and normalized scattering matrices were introduced and it was shown that three different scattering matrices are the same only with equal termination impedances but only the normalized scattering matrix is correct with arbitrary termination impedances. The scattering matrices can be calculated from impedance, admittance, or ABCD matrices characterizing a network. However, if the network has more than three ports, the calculation process from the admittance or impedance matrices is not simple. For this, conversion formulas of the ABCD parameters into the normalized scattering parameters were presented for the impedance-transforming directional couplers. If one can have any choice of the termination impedances of the directional couplers as shown in this article, the total size of a microwave integrated circuit can be reduced.

Current-Mode Multiphase Sinusoidal Oscillator Using Current Differencing Transconductance Amplifiers

This paper describes a simple current-controlled current-mode multiphase sinusoidal oscillator based on current differencing transconductance amplifiers (CDTAs) as active components. The proposed oscillator circuit, which employs only one CDTA and one grounded capacitor for each phase, can generate arbitrary n current-output signals (n being even or odd) equally spaced in phase, all at high output impedance terminals. The oscillation condition and the oscillation frequency can be controlled electronically and independently through the bias current of the CDTA. The oscillator has low-component count, low-sensitivity performance, and is highly suitable for monolithic implementation. PSPICE simulation results are given to confirm the operation of the proposed oscillator.

Low-power variable impedance load/tuning unit

An impedance tuner is presented which operates over the range 1.8 to 3 GHz. The tuner is suitable for use as either a one-port variable impedance termination or as a two-port tuning element. It employs a broadside coupler and a varactor diode tuned phase shifter and can yield |Gamma MAX | of nearly 0.9 giving near total coverage of the Smith chart. The power consumption of the whole unit is less than 800 mW, making it suitable for low-power applications. The size of the unit is 23 times 5 mm. Representative tuning and reflection variation are given for 2.2 GHz operation.

State-of-Charge Determination From EMF Voltage Estimation: Using Impedance, Terminal Voltage, and Current for Lead-Acid and Lithium-Ion Batteries

State-of-charge (SOC) determination is an increasingly important issue in battery technology. In addition to the immediate display of the remaining battery capacity to the user, precise knowledge of SOC exerts additional control over the charging/discharging process, which can be employed to increase battery life. This reduces the risk of overvoltage and gassing, which degrade the chemical composition of the electrolyte and plates. The proposed model in this paper determines the SOC by incorporating the changes occurring due to terminal voltage, current load, and internal resistance, which mitigate the disadvantages of using impedance only. Electromotive force (EMF) voltage is predicted while the battery is under load conditions; from the estimated EMF voltage, the SOC is then determined. The method divides the battery voltage curve into two regions: 1) the linear region for full to partial SOC and 2) the hyperbolic region from partial to low SOC. Algorithms are developed to correspond to the different characteristic changes occurring within each region. In the hyperbolic region, the rate of change in impedance and terminal voltage is greater than that in the linear region. The magnitude of current discharge causes varying rates of change to the terminal voltage and impedance. Experimental tests and results are presented to validate the new models.

Verification of Multipair Copper-Cable Model by Measurements

Analysis, assessment, and design of advanced wireline transmission schemes over multipair copper cables require accurate knowledge of the channel properties. This paper investigates modeling of multiconductor cables based on interpair impedance measurements. A unified approach to the application of the model is introduced. The direct measurement approach of the underlying interpair impedances yields a good match with the alternative approach suggested in the recent study of Cioffi et al. Crosstalk coupling functions derived from the model exhibit a good match with the corresponding direct measurements in the case in which the modeled length is close to the length of the interpair impedance measurements. However, the prediction power of this model with respect to termination impedance is limited.

임의의 종단 임피던스를 갖는 DC Block의 완전 정합

Design equations of DC blocks terminated in arbitrary impedances are newly suggested and a microstrip DC block is tested for the perfect matching. The DC block is a two-port passive component and the power excited at a port is transmitted into another port. However, all the excited power at the input can not be delivered to the output and therefore most of the conventional DC blocks can not be perfectly matched with arbitrary termination impedances. To solve the matching problem, its one-port equivalent resonant circuit model, from which design equations can be derived, is newly suggested. Using the derived design equations, any DC block can be designed, perfectly matched without any restriction of coupling coefficients. To verify the derived design equations, measurements were carried out and the results are in good agreement with prediction, showing insertion and return losses at 4.1 ㎓ are 0.82 ㏈ and －31 ㏈, respectively.

Characterization of the Upper Limb Arterial Properties during Reactive Hyperemia

The radial artery (RA) pressure waveform is commonly used to reconstruct the central aortic pressure waveform. Because the RA pressure waveform has been used as input to this process, its features that are dependent on the local arterial properties can influence the final reconstructed aortic waveform. In this study, we determined the effects of altered upper limb pulse wave velocity (PWV) and local wave reflection parameters on RA pressure waveform augmentation (RA-AIx). Twenty healthy volunteers (10 men) between the ages of 18 and 35 years of age were recruited. Simultaneous pressure waveforms were acquired using arterial tonometers from the right carotid and the radial arteries, prior to and following tourniquet induced hyperemia. The phase velocities from the pressure wave transfer function were used to estimate the pulse wave velocity (PWV(infinity)), the local reflection coefficient (Gamma) and an estimate of the terminal impedance of the upper limbs, PWV(0+). The RA-AIx was represented as a linear, three-parameter model that included the input (the AIx of the carotid artery pressure waveform, CA-AIx), the Gamma and PWV(infinity) of the arm. Tourniquet induced hyperemia did not alter Gamma but reduced PWV(infinity), and PWV(0+) and increased RA-AIx. Multiple linear regression analysis indicated that RA-AIx was increased by high levels of CA-AIx and PWV(infinity) and decreased by elevated Gamma. The relative weighing of CA-AIx, Gamma and PWV(infinity) on RA-AIx were 3:2:1, respectively. The AIx of RA is determined to an equal extent by the input and local factors. Interpretation of the AIx of the RA and the reconstructed central aortic waveform should be made in the context of this relationship.

Comparison of Time-Domain Impedance Boundary Conditions for Lined Duct Flows

impedance of liners. This part of the model, however, is limited to single frequency sound source in its present form. The EHR is based on the z‐transformation of the corresponding impedance function for the Extended Helmholtz Resonator in the frequency‐domain. The implementations of the two models in the numerical simulation tool with the DRP scheme are discussed in details. The results from the both models in general agree notably well with each other. However, in one case, the results from the two models dier significantly due to the presence of strongly attenuated modes, which renders the approximations of the EFI invalid. The validation and verification of both models are carried out for the latest NASA impedance tube experiment and the generic aero‐engine frequency domain results of Rienstra and Eversman. In addition, an impedance eduction technique based on the EHR and the optimization process has been developed. This further extends applications of the time‐domain models. The simultaneous optimization of all frequencies considered in the NASA’s impedance tube experiments results in a physically reasonable set of parameters for the EHR. The fitted terminal impedances and the measured mean flow profiles are used for the impedance eduction. The numerical results of both models for the generic aero‐engine inlet test case with higher azimuthal modes also compare well if the same flow assumptions and eigenvalues are used as for the frequency domain methods. Overall both models give a similar physical behavior, but the EHR requires smaller time steps in the case of small face sheet reactances.