Characteristic Impedance Constant Research Articles

Recursive algorithm for the distribution of characteristic impedance of an elastic rod producing a prescribed impact force history on a given elastic rod

Axial impact between two elastic rods with piecewise constant characteristic impedance is considered. The distribution of characteristic impedance of the impacted rod and the impact velocity are given. By use of a 1D recursive algorithm, the characteristic impedances of the impacting rod are determined as long as they are all positive so that a prescribed impact force is realized. A condition for positivity of the characteristic impedance is derived in terms of transmission coefficients for wave energy. At the time from which positivity of all characteristic impedances cannot be maintained, or earlier, the characteristic impedance of the impacting body is continued, e.g., at the level of the last positive characteristic impedance or at level zero corresponding to cutting off the impacting rod. Examples of prescribed exponentially decreasing and linearly increasing impact forces are presented for a uniform impacted rod with constant characteristic impedance. In these examples, there is good agreement between the prescribed impact force and the impact force obtained from 3D FE simulation with a piecewise linear diameter of the impacting body that approximates the piecewise constant diameter obtained by use of the 1D recursive algorithm.

Continuously Tunable True-Time-Delay Phase Shifter Based on Transmission Lines With Simultaneously Reconfigurable Impedance and Phase Constant

This article reports on the design of continuously tunable true-time-delay (TTD) phase shifter using transmission lines with simultaneously reconfigurable impedance and phase constant. The reconfigurable transmission lines are designed with an independent control of equivalent series inductance and capacitance, which thus can achieve tunable phase constant (i.e., phase shift) while maintaining constant characteristic impedance. With the perfect matching property for all tuning states of phase constant, the proposed reconfigurable transmission-line units are cascaded to construct a tunable TTD phase shifter. For the proof-of-concept demonstration, three TTD phase shifters based on the proposed reconfigurable transmission lines with phase shifts of 45°, 90°, and 180° at center frequency of 1 GHz ( $f_{0}$ ) are designed and fabricated. The measured 2-unit phase shifter is tuned from −128° to −175° at $f_{0}$ while the insertion loss is better than 0.8 dB. The return loss is better than 15 dB from dc to $1.28f_{0}$ . For the 4-unit phase shifter, the phase shift tuning range is 93° at $f_{0}$ with insertion loss better than 1.4 dB. The return loss is better than 15 dB from dc to $1.03f_{0}$ for all states. The 8-unit phase shifter shows a measured tuning range of 183° at $f_{0}$ with insertion loss better than 2.0 dB. The return loss is better than 15 dB from dc to $1.03~ f_{0}$ for all states. The measured continuously tunable delay time is 507 ps. The measured 1-dB compression point is better than 12 dBm at $f_{0}$ for all states. As compared with the state-of-the-arts, the main merits of the proposed phase shifter are large phase shift/unit and wide matching bandwidth.

Influence of Milling Time on Structural and Electromagnetic Properties of Manganese Doped Cobalt Ferrite Nanoparticles

This paper reports on the electromagnetic properties of manganese doped cobalt ferrite nanoparticles, synthesized via solid state reaction route using the planetary ball milling technique at different milling time (8h and 12h)in order to tune the material for applications in high frequency as well as microwave devices. The XRD patterns show the cubic spinel structure of the material. The lattice constant along with other associated structural parameters are found to increase but the particle size to decrease with the milling time. The positive value of real part of permeability is found to increase with the increase of frequency for the sample of milling time 8h. But for the sample of milling time 12h, its negative value is observed below 2 kHz and after onwards it becomes positive. This negative value of real part is the signature of diamagnetic behavior at the low frequency regime, which is assumed to originate due to the dominance of antiferromagnetic effect of Mn2+ ions on the B site. The diamagnetic behavior may make this material suitable to be used in electromagnetic suppression or shielding devices. The real part e' of permittivity demonstrates the normal behavior for both the sample of milling time 8h and 12h below 2 kHz and 0.1 MHz respectively. The peaks at 8MHz for the sample of milling time 8h and at 1MHz for the sample of milling time 12h in the dispersion of its imaginary part e'' indicate the resonance condition for the respective sample at the higher frequency regime, which is assumed to be originated from the faster hoping of electrons between Fe2+ and Fe3+ in the B site. At the low frequency regime, the a.c resistivity decreases almost exponentially with the increase of frequency to a certain minimum value at 10 kHz and 1 kHz for the samples of milling time 8h and 12h respectively and after onwards it becomes almost independent of frequency. The structural correlation is analyzed with the Col-Cole plot where the single incomplete semicircle corresponds to the grain boundary resistance for 12h milled sample and double incomplete semicircles to both the grain boundary and grain resistances for 8h milled sample. Almost constant characteristic impedance implies that both the permeability and permittivity are of equal value for the sample of milling time 12h and its nearer-to-zero value of eddy current loss may make this material suitable to be used in the design of microstrip/patch antenna. However the linear variation of characteristic impedance with the frequency for the sample of milling time 8h implies the tuning effect of multilayer capacitance, which may make this sample to be integrated as tuner with the microstrip/patch antenna.

Numerical Modeling and De-Embedding of Non-Planar Periodic Guided-Wave Structures via Short-Open Calibration in 3-D FEM Algorithm

In this paper, a numerical short-open calibration (SOC) technique is presented to numerically model and de-embed a variety of non-planar periodic guided-wave structures based on the 3-D full-wave finite element method (FEM). A simple current source or lumped-port model is introduced in formulation of a determinant FEM algorithm. By incorporating the SOC in the FEM solver, the intrinsic port discontinuity caused by this port model is then fully removed or calibrated out of the core non-planar periodic guided-wave structure during the calibration process. Because of the 3-D nature of FEM, the effective per-unit-length parameters of the core periodic guided-wave structure, i.e., effective propagation constant and effective characteristic impedance, are extracted successfully. Two numerical examples, including microstrip line with periodical loading of shorting pins and metal–insulator–metal composite right/left handed structure, are numerically modeled for demonstration and verification. Extracted results have validated the feasibility and accuracy of the presented FEM-SOC, thereby exhibiting its advanced capability in numerical modeling and de-embedding of non-planar structures with complicated configurations.

Experimental Evaluation of the Inverse Scattering Method for Electrical Cable Fault Diagnosis

Recently published theoretic and experimental results have shown the ability of inverse scattering-based methods to detect and to locate soft faults in electric cables, in particular, faults implying smooth spatial variations of cable characteristic parameters. The purpose of the present paper is to further experimentally evaluate the inverse scattering method for retrieving spatially distributed characteristic impedance from reflectometry measurements. With high quality coaxial cables connected in parallel, composite cables of piecewise constant characteristic impedance profiles are built in order to evaluate the accuracy of the inverse scattering method and its robustness in the presence of impedance discontinuities.

High frequency characterization of graphene nanoribbon interconnects

Interconnects and nanoscale transmission lines are critical components in the design of nanoelectronic systems. In this letter, we study the high frequency characteristics of chemical vapor deposition (CVD) graphene nanoribbon (GNR) interconnects and radio frequency propagation in GNRs embedded in a coplanar waveguide structure up to 20 GHz. An equivalent transmission line model is proposed to characterize the GNRs in high frequency regime. The strong agreement between fitting circuit parameters and measured data suggests that our model can be used in the design of nanoscale circuits in which GNRs are used to interconnect elements in the circuits. The fabricated GNRs show fairly constant characteristic impedance at high frequencies which could be useful for radio frequency interconnect applications. Our study provides an insight into microwave behavior of GNRs for developing high speed graphene devices.

COMPARISON AND OPTIMIZATION OF DISPERSION, AND LOSSES OF PLANAR WAVEGUIDES ON BENZOCYCLOBUTENE (BCB) AT THZ FREQUENCIES: COPLANAR WAVEGUIDE (CPW), MICROSTRIP, STRIPLINE AND SLOTLINE

This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Zc flxed at 100› and a constant efiective width Wefi flxed at 30m. The best waveguides are microstrip (fiT = 2:52dB/mm for Zc = 100› and for W=H = 35=50m (with W the strip width and H the substrate height) and fiT = 2:29dB/mm for Wefi = 30m at 1THz with H = 30m) and stripline (with quasi-null radiation losses and the best quality factor QT = 63 for Zc = 100›). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low QT problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, ampliflers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.

A Miniaturized and Broadband Balun Using Artificial Coupled Line With Imaginary Even-Mode Impedance

A broadband and miniaturized balun is proposed using the artificial coupled line with the imaginary even-mode impedance. The artificial coupled line is a metamaterial transmission line with zero electrical length for the even-mode excitation, whereas it behaves like a TEM transmission line with approximately constant characteristic impedance for the odd-mode excitation. Based on the artificial coupled line, a new concept to design a broadband balun is presented. The broadband characteristic of the balun is explained by the odd- and even-mode analysis. A balun is realized using low-temperature co-fired ceramic fabrication technology, simulated by a full-wave tool, and measured in the three-port vector network analyzer system. It exhibits good amplitude imbalance of 0.3 dB and phase imbalance of 179°±3° with the return loss greater than 10 dB from 3.3 to 7.1 GHz with 73% of fractional bandwidth. Its electrical size is only 0.063×0.44λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and its physical size is 1.6×11.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Compared with previous works, the proposed balun possessing good balance has a more compact size with broadband operation.

Constant Impedance TEM Horn Antenna: Aperture and Characteristic Impedance’s Impacts on Axial Electric Field

TEM horn antenna with constant characteristic impedance (CCI TEM horn antenna) is a widely used ultra-wideband (UWB) antenna. Considering the peak-to-peak value of the axial electric field (Vpp), how to design such antenna’s characteristic impedance (Z c) has not been involved in previous research. The relationship between Vpp and antenna aperture as well as characteristic impedance is numerical analyzed. The simulation and experimental results show that the optimal aperture is existed to maximize Vpp when the antenna’s length is fixed at the axis. More over, Vpp of the antenna with optimal aperture reaches the maximum value when the characteristic impedance is 280 ohm.

Evaluation of EMI Reduction Effect of Guard Traces Based on Imbalance Difference Model

Placing a guard trace next to a signal line is the conventional technique for reducing the common-mode radiation from a printed circuit board. In this paper, the suppression of common-mode radiation from printed circuit boards having guard traces is estimated and evaluated using the imbalance difference model, which was proposed by the authors. To reduce common-mode radiation further, a procedure for designing a transmission line with guard traces is proposed. Guard traces connected to a return plane through vias are placed near a signal line and they decrease a current division factor (CDF). The CDF represents the degree of imbalance of a transmission line, and a common-mode electromotive force depends on the CDF. Thus, by calculating the CDF, we can estimate the reduction in common-mode radiation. It is reduced not only by placing guard traces, but also by narrowing the signal line to compensate for the variation in characteristic impedance due to the guard traces. Experimental results showed that the maximum reduction in common-mode radiation was about '14 dB achieved by placing guard traces on both sides of the signal line, and the calculated reduction agreed with the measured one within 1 dB. According to the CDF and characteristic impedance calculations, common-mode radiation can be reduced by about 25 dB while keeping the characteristic impedance constant by changing the gap between the signal line and the guard trace and by narrowing the width of the signal line.

Ferromagnetic Thin Films for Loss Reduction in On-Chip Transmission Lines

Microstrip transmission lines fabricated on standard silicon wafers are shown to benefit from the incorporation of thin ferromagnetic Ni-Fe films when compared to control devices without Ni-Fe. At 1 GHz, inductance and quality factor of the microstrip lines are enhanced by factors of 6 and 3, respectively, while the characteristic impedance of a 20 mum wide line is increased by 85%. For constant characteristic impedance, a 200 nm thick Ni-Fe film reduces attenuation from 1.6 to 0.7 dB/cm at 500 MHz

Analytical Calculation of Resonances in Tapered Double-Port TEM Waveguides

This contribution presents an analytical method for the calculation of resonances of higher order modes valid for tapered double-port TEM waveguides with constant characteristic impedance. Because these resonances determine the usable bandwidth of the waveguide, their precise knowledge is essential. The accuracy of the proposed method has been proven using TEM waveguides with either rectangular or circular cross section.

Guided‐wave characteristics of periodic microstrip lines with inductive loading: Slow‐wave and bandstop behaviors

AbstractGuided‐wave characteristics of planar periodic microstrip lines with inductive loading are investigated by resorting to the unit‐length transmission parameters of an equivalent transmission line. By applying the SOC de‐embedding technique, the above two quantities are effectively extracted from the full‐wave MoM modeling of a microstrip line with finite periodic cells. Extensive results at first confirm the slow‐wave behavior such that both real parts of such two quantities rise up slowly and then rapidly with frequency. Further, they demonstrate, for the first time, the guided‐wave bandstop characteristic with non‐zero attenuation constant and imaginary characteristic impedance. Five‐cell periodic microstrip circuits are then designed and fabricated for theoretical and experimental verification. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 77–79, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20052

Characteristic impedance and propagation of the first higher order microstrip mode in frequency and time domain

This paper experimentally and theoretically confirms the validity of the definition proposed by Das (1996) for computing the complex characteristic impedance of the first higher order (EH/sub 1/) microstrip mode. The normalized complex propagation constant and complex characteristic impedance of the microstrip obtained by the rigorous full-wave integral-equation method are also presented. To better understand the circuit behavior of the leaky mode at the respective frequencies, the results are analyzed in both frequency and transformed steepest descent plane. A differential time-domain reflectometry (TDR) experiment shows that the experimental results are in excellent agreement with the time-domain plots obtained theoretically by the inverse discrete Fourier transform of the transmission line modeled by the dispersive characteristic. The propagation characteristics of the echoed signals in the time domain, which are reflected from the open end of the leaky line, are analyzed in detail using the corresponding group velocity of the EH/sub 1/ mode. The time-to-frequency conversion of the measured TDR data reveals that the reflection, leaky, and propagation zones coexist simultaneously for the EH, mode propagation. The conversion also accurately assesses the attenuation constant of the EH, mode if the attenuation is not too high. The Fourier transform of the TDR responses also simultaneously yields the input reflection coefficient (S/sub 11/) and the complex characteristic impedance. The complex characteristic impedance extracted from the TDR responses also agrees closely with the theoretical data.

Attenuation Characteristics and Sensitivity Analysis for Coplanar Waveguide

The behaviour of attenuation losses in Coplanar waveguides (CPW) is studied for quasi-planar transmission lines with constant characteristic impedance (Z0) and resistivity, having different geometry's. This behavior helps in making a suitable choice of the type of structure and its dimensional parameters depending upon the application. Minimization of loss for a chosen substrate thickness, conductivity and impedance is analyzed. Dispersion characteristics of CPW have been plotted for various metallization thicknesses. A sensitivity analysis for effective dielectric constant with respect to various dimensional parameters of CPW is presented.

Loss minimisation and sensitivity analysis for coplanar waveguide

This paper presents a description of propagation and losses for coplanar waveguide (CPW) structures using quasi - static analysis, based on the approximate conformal technique. The behaviour of attenuation losses in CPWs is studied for quasi planar transmission lines with constant characteristic impedance and resistivity, having different geometries. Minimisation of loss for a chosen substrate thickness, conductivity and characteristic impedance is analysed. Effective dielectric constant has also been computed for various coplanar waveguide structures. A sensitivity analysis for effective dielectric constant with respect to gap width, strip width and substrate height, is presented. Analytical formulations are presented for all calculations.

EVALUATION OF FORCE AND PARTICLE VELOCITY AT THE HEATED END OF A ROD SUBJECTED TO IMPACT LOADING

A method to evaluate the force and particle velocity at the heated end of a rod subjected to impact loading is presented. The method is based on a characteristic impedance function determined by a set of parameters. With a given characteristic impedance function the force and particle velocity at the heated end can be evaluated from measured strains at two cross-sections of the rod. In order to evaluate the characteristic impedance function the rod is impacted by a hammer at one end and the heated end is free. The optimal set of parameters is determined by a procedure which minimizes the error, i. e. the evaluated force at the free end of the rod. The results show that the error obtained with the constant characteristic impedance function is considerable, whereas the error obtained with the evaluated characteristic impedance function is of the same magnitude as the error obtained for a test at constant temperature. Thus, with this method it is possible to evaluate the force and particle velocity at the heated end of a rod with the same accuracy as for a uniform rod at room temperature.

The modelling of networks with frequently changing topology whilst maintaining a constant system matrix

AbstractThis paper describes a novel technique with which a system with changing topology can be modelled whilst maintaining a constant system matrix. This technique employs a new transmission‐line switch model which has a constant characteristic impedance, irrespective of its state. The method is explained, compared with the switched‐resistance method and demonstrated by two examples. It has been found that the proposed method offers substantial advantages in the formulation of the problems and in the efficiency of computation.

Analysis of elastic waves in non-uniform rods from two-point strain measurement

A method is established which permits evaluation of the histories of normal force and particle velocity at an arbitrary cross-section E of a non-uniform linearly-elastic rod from measured strain histories at two different cross-sections, A and B. Other quantities at E, such as stress, strain, displacement, acceleration and power transmission, can be determined in terms of the evaluated normal force and particle velocity. The method is an extension of that developed by Lundberg and Henchoz for uniform rods. Theoretical results, based on one-dimensional elastic wave theory, are provided for the general case as well as for cases of piecewise constant characteristic impedance. Experimental tests with different configurations of non-uniform rods and strain gauges show that the normal force histories determined at E with the present method (from measured strains at A and B) agree well with those obtained through direct strain measurement at E.

Some fundamental transmission properties of impedance transitions

Reflection and transmission of waves by impedance transitions from a constant input to a constant output characteristic impedence are considered. Several fundamental properties are explored, primarily for impedance transitions with piece-wise constant characteristic impedance in an arbitrary number N of intervals of equal length. For example, the following properties are shown: (i) The relative momentum transmission depends only on the ratio of output to input characteristic impedance. (ii) For a given impedance transition there are at most, and generally exactly, 2 N different transitions, including the original one, with identical transmission properties. (iii) For monotoneous impedance transitions the efficiency of energy transmission is minimized by one with an abrupt change in characteristic impedance. (iv) There exists an optimal impedance transition, with a certain antisymmetry, which maximizes the efficiency of energy transmission for a given incident wave of finite duration and energy. Several of the results can be extended to more general classes of impedence transitions. Simple illustrative examples are given.