Frequency-independent Elements Research Articles

Multi-objective metaheuristic optimization for simplified modeling of soil-pile interaction systems under lateral and rocking motions

A consistent lumped-parameter model (LPM) is established to characterize the dynamic response of single and group piles in a homogeneous half-space subjected to coupled lateral-rocking vibrations. The proposed model comprises adjustable modules that can adapt to simulate a wide range of pile foundation configurations. This study utilizes a metaheuristic algorithm to solve a bicriteria optimization problem, aiming to determine both the layout and parameters of the optimal LPM. The optimal model is created to approximately reproduce the amplitude and phase angle of a soil-pile interaction (SPI) system undergoing harmonic loadings. Besides, the proposed model using frequency-independent elements allows for rapid computation of dynamic responses in the SPI system. Several analyses in the time and frequency domains validate the performance of the proposed model undergoing forced vibrations and seismic excitations. The analyzed results prove the capability and accuracy of the proposed model in approximating the dynamic responses of SPI systems. The results presented demonstrate the significant potential of the proposed model for dynamic structural analysis, particularly when accounting for structural nonlinearities in the time domain.

Dirac-Based Quantum Admittance of 2D Nanomaterials at Radio Frequencies

Starting from a rigorous finite mass, Dirac equation-based model, we investigate the R.F. quantum admittance of a monolayer 2D material under the action of an electromagnetic (e.m.) wave with axially directed vector potential. With some reasonable approximations, the analysis yields a relatively simple RLC-equivalent circuit with frequency-independent elements depending on the bias, temperature, effective mass, Fermi velocity and effective e.m. index of the material, losses and other relevant parameters.

A simplified model of layered soil for analyzing vertical vibration of loaded foundations

Numerous physical models using frequency-independent elements have been developed to reproduce impedance functions for the purposes of time-domain soil–foundation interaction analysis. Most of the models have been developed to simulate homogeneous soils. However, the physical models developed in past research for layered soils are mostly focused on surface foundations only. Accordingly, this study proposes a representative simplified model to simulate the three-dimensional layered soil for square foundations embedded in a non-uniform layer, overlying a uniform half-space, subjected to vertical forced vibrations. The non-uniform layer has shear-wave velocities linearly varying with depth. Non-dimensional charts are presented to determine the model parameters as per foundation embedment ratios, layer depth ratios, and shear-wave velocity ratios of layered soil. The capability of the proposed model is demonstrated through the analysis of frequency-response curves of the foundation to a constant-force type oscillator in the frequency domain and of the displacement history of the foundation to a non-periodic loading in the time domain. The proposed model is found to give results consistent with those obtained from a dynamic soil-structure interaction analysis program. The proposed model may be of practical value for analysis of dynamically loaded foundations.

High-Frequency Characterization and Parametrized Modeling of DC-Biased Surface-Mount Ferrite Beads for EMI Suppression Applications

Circuit models of ferrite beads used for electromagnetic (EM) noise filtering are important for prediction and effective reduction of EM noise on power or signal lines. A methodology for impedance characterization and modeling of surface-mount ferrite beads is proposed in this article. The presented methodology combines series and shunt characterization methods to extract the equivalent circuit model of ferrite beads. The extracted models consist of frequency-independent elements and they are valid up to 1 GHz, to cover the bandwidth required by the EM compatibility standards for measurements of EM emissions. The values of the lumped elements of the extracted model are optimized to fit the measured impedance characteristics for each ferrite bead at bias current levels up to 5 A. Finally, the values of the lumped elements are parametrized with respect to the bias current from 0 to 5 A and the normalized error of the model compared to the measurements is calculated and found to be less than 10 $\boldsymbol{^{\mathrm{-3}}}$ .

A Passive Equalizer Design for Shielded Differential Through-Silicon Vias in 3-D IC

This letter develops a simplified circuit model for the shielded differential through-silicon vias (SD-TSVs). The model is consisted of four frequency-independent elements and can accurately predict the insertion loss of the SD-TSVs up to 20 GHz. Based on the model, a parallel resistor–capacitor equalizer is proposed. The proposed passive equalizer achieves wide-band equalization and perfect compensation for high-speed differential signaling.

A Compact Passive Equalizer Design for Differential Channels in TSV-Based 3-D ICs

In this paper, a compact passive equalizer for differential transmission channel is designed in TSV-based three-dimensional integrated circuits (3-D ICs). The compact size of the equalizer is achieved by a square shunt metal line. Three simplified odd-mode half circuit models are proposed for ground-signal-signal-ground (G-S-S-G) type TSVs, differential on-interposer interconnects, and differential channels, respectively. Those simplified models merely consist of frequency-independent elements and can accurately predict the differential insertion losses up to 20 GHz. Moreover, the electrical parameters of the proposed serial resistance-inductance ( RL ) type equalizers are derived from the system transfer functions and optimized by virtue of the time-domain inter-symbol interference cancellation technique. Further, the geometrical parameters of the RL equalizers are calculated by using a genetic algorithm based multi-objective optimization method. Finally, the performance of the designed RL equalizer is validated by both frequency- and time-domain simulations for 20 Gb/s high-speed differential signaling.

Experimental and theoretical methods on determination of stress-dependent natural frequency of marine sedimentary clay

ABSTRACTExcited by the vibration sources in dynamic engineering, the natural frequency and damping factor of the saturated marine sedimentary clay are key dynamic parameters that influence the responses under cyclic loads. Experimental and theoretical methods are proposed in this paper to analyze the natural frequency and the stress-dependent nonlinearity. The experimental method shows that the natural frequency of soils with specific stress state subjected to large cyclic shear strain can be estimated from the data of dynamic triaxial tests based on the amplitude–frequency response curve. Trial and error by the criterion from the half-power bandwidth method is used to determine the optimal fitting. The results of a theoretical study on the free vibration of soil layers are then presented to derive the analytic solution of natural frequency. In addition to the two frequency-independent elements (a lumped mass matrix and a stiffness matrix), the system’s equivalent damping coefficient matrix is iteratively determined based upon the forced vibration experimentally. Finally, the impacts of the resonance phenomenon on the dynamic shear modulus and hysteretic loop are discussed.

An Improved Millimeter-Wave General Cascade De-Embedding Method for 110 GHz On-Wafer Transistor Measurements

In this paper, impact of parasitic ground plane and via stack on device parameters is investigated at millimeter-wave frequencies and further addressed by an improved general cascade procedure with an additional short dummy up to 110 GHz for the first time. The ground inductance is extracted accurately up to millimeter-wave range by applying a generalized two-port network for adapters and the determined ground inductance value is verified by analytical results. The generalized black-box model is utilized in order to take the distributed effects of adapters into account at millimeter-wave frequencies. This modified method can obtain frequency-independent intrinsic elements in the millimeter-wave range, verifying the presented approach.

Equivalent circuit model of a coaxial excited microstrip‐fed quasi‐lumped element resonator antenna array

An approximate lumped-parameter equivalent circuit model of the quasi-lumped element resonator antenna array is presented. The array consists of six series resonant circuits of frequency-independent elements, each with an interdigital finger capacitor (IDC), and shorted across by a parallel narrow strip inductor. Each resonator exhibits an aperture size of 0.207λg × 0.2λg at a centre frequency of 5.8 GHz, with entire array size of 2.857λg × 1.07λg . The resulting design is fed by a microstrip line and excited by a coaxial feed probe. A simple equivalent circuit model representing the six resonant circuits as well as the coaxial feed probe circuit, using the magnetic-frill model approach but with the simplest uniform-current model is described to predict the characteristics of the proposed resonator (and by extension, the proposed array), the effects of the coaxial probe and the microstrip feed line. Simulated data obtained from a full wave analysis using finite integration technique commercial solver is compared with the Agilent advanced design system results of the equivalent circuit. The derived equivalent circuit model was validated both analytically and by numerical simulations.

Equivalent Circuit for Dipole Antennas in a Lossy Medium

A lumped-parameter equivalent circuit for an uninsulated antenna in a lossy medium is derived from the impedance of the same antenna in air. Consisting of four frequency-independent elements and four elements related to loss tangent and frequency, the equivalent circuit is sufficiently accurate for a broadband simulation including the resonant frequency at which antennas are generally designed to operate. Acceptable relative errors are demonstrated by comparing the results of the equivalent circuit with simulated data obtained from a full wave analysis. The equivalent circuit can be used to replace complex antenna models in lossy media and quantify the effect of the loss on antenna performance.

단락 개방 Calibration 방법을 이용한 분포 정수 소자의 기생 소자 추출 및 대역 통과 필터에의 응용

본 논문에서는 단락 개방 calibration(SOC) 방법을 이용하여 결함 접지 면을 갖는 전송 선로(DGS)와 short-circuited comb line section의 기생 소자 값들을 추출하였다. Microstrip 선로들로 구성된 단락, 개방, 분포 정수 소자의 산란 파라미터 행렬들은 전자기 시뮬레이터 및 벡터 네트웍 분석기를 이용하여 측정하였다. 제안된 구조의 전자기 영향들은 주파수 독립적인 소자들로 구성된 II형 또는 T형 등가 회로로 각각 표현하였고, 2 포트 네트웍 해석을 수행함으로써, 측정된 산란 파라미터들과 등가회로 소자들 간의 관계를 보였다. 또한, 2차 버터워스 프로토 타입을 갖는 2.4 GHz 대역 통과 필터 설계에 이를 적용하였다. 그 결과, 중심 주파수에서 측정된 <TEX>$S_{11}$</TEX>과 <TEX>$S_{21}$</TEX>은 각각 -20 dB, -1.3 dB 이고, <TEX>$0.5{\sim}5\;GHz$</TEX>에서 예상했던 결과와 5 % 이내의 오차를 보였다. In this paper, we extract the parasitic elements of the transmission line with the defected ground structure(DGS) and the short-circuited comb line section using the Short-Open Calibration(SOC). The scattering matrixes of short, open and the distributed elements in microstrip line are measured by full electro-magnetic(EM) simulator and Vector Network Analyser(VNA). The electro-magnetic effects of the proposed structures are considered by the II and T equivalent circuits with frequency independent elements, and the relations between the measured scattering parameters and the elements in the circuits are shown by performing 2 port network analysis. Moreover, to design the 2.4 GHz bandpass filter with second order butterworth prototype, the proposed methods are applied. As results, the measured <TEX>$S_{11}$</TEX> and <TEX>$S_{21}$</TEX> indicate -20 dB and -1.3 dB at center frequency, and these are shown within 5 % error compare to the predicted results at <TEX>$0.5{\sim}5\;GHz$</TEX>.

Microwave Impedance Spectroscopy of Dense Carbon Nanotube Bundles

We have performed impedance spectroscopy of dense carbon nanotube (CNT) bundles in the broad frequency range from 10 MHz to 67 GHz. Dense CNT bundles were formed on sharp tips from aqueous suspension by ac dielectrophoresis and incorporated into on-wafer test structures. The frequency response of the bundles can be fit to a model with frequency-independent elements in the entire frequency range up to 67 GHz strongly suggesting that CNT properties do not depend on the frequency throughout the whole frequency range. The measurements at microwave frequencies allowed separate characterization of the bundle/metal electrode contacts and the bundle bulk. Effects of different CNT fabrication and suspension processing routes on bundle characteristics were identified. We have also made a preliminary estimation of the average inductance per current carrying shell in the bundles. For good quality nanotube bundles, the inductance has been found to fall within the range from approximately 3.5 to 40 nH/microm. With decreasing nanotube quality, the implemented estimation procedure yields higher values with a large uncertainty. Systematic measurements of devices with individual nanotubes are required to provide more accurate data.

Admittance of planar two-terminal quantum systems

We develop an approach to calculate the admittance of effectively one-dimensional open quantum systems in random phase approximation. The stationary, unperturbed system is described within the Landauer-B\"uttiker formalism taking into account the Coulomb interaction in the Hartree approximation. The dynamic changes in the effective potential are calculated microscopically from the charge-charge correlation function resulting from the stationary scattering states. We provide explicit RPA-expressions for the quantum admittance. As a first example the case of a quantum capacitor is considered where we can derive a small-frequency expansion for the admittance which lends itself to an experimental testing of the theory. A comparison of the low-frequency expansion with the complete RPA-expression shows that for a quantum capacitor a simple classical equivalent circuit with frequency-independent elements does not describe satisfactorily the quantum-admittance with increasing the frequency.

Inhomogeneous transport property of Alq 3 thin films: Local order or phase separation?

Steady-state current–voltage ( I– V) and impedance–voltage ( Z– V) measurements were performed on in situ (UHV) prepared metal (Ag, Al)/Alq 3/indium-tin oxide (ITO) devices after exposure to air. When increasing the positive bias on the top metal electrode to a relatively well-defined critical value, a transition from semiconducting to semi- or even insulating behavior of the contacted Alq 3 thin film is observed by means of I– V measurements. The final insulating state remains stable when applying negative bias to the Ag electrode. In the case of the Al electrode, there is a voltammetric current wave under a well-defined negative bias indicating a redox reaction of mobile ions at the Al electrode. The Z– V measurements reveal a peculiar feature of ac transport through the Alq 3 thin films, namely the equivalent series capacitance is equal to its parallel counterpart in the frequency range from 100 to 1 MHz and amounts to only a fraction (0.3–0.5) of the expected geometrical capacitance of the device. An equivalent electrical circuit has been developed, based on the existence of two parallel transport paths: an insulating (amorphous) Alq 3-phase shunted by a semiconducting (semi-insulating) one, both running into the impedance of the back contact. The equivalent circuit model composed exclusively of frequency independent elements is useful for predicting the maximum frequency for retaining the full geometrical capacitance. Even though the model is capable of describing the bias dependence of the impedance correctly, it does not shine light on the nature of the (ordered) phase or domain responsible for the dielectric loss. The possibility of local order connected with dipole–dipole interaction in the metal/Alq 3 interface zone is discussed. In any case, the ordered portion of the organic material seems to form the huge interface dipole of about 1 eV with Ag or Al [M.A. Baldo, S.R. Forrest, Phys. Rev. B 64 (2001) 085201], the direction of the dipole promoting electron injection to Alq 3. Then the semiconductor-to-insulator transition could be initiated by a damage of the interface dipole under a critical positive dc bias of the metal, preventing the flow of both dc and the real component of low-frequency ac current. The transition is not accompanied by any significant change in the impedance of the back contact common to both phases.

A derived physically expressive circuit model for multilayer RF embedded passives

In this paper, a derived physically expressive circuit model is presented for automatically deriving an equivalent-circuit model of a multilayered embedded RF passive. The scheme is based on the partial-element equivalent-circuit (PEEC) model and a simple circuit transformation. By defining an appropriate cutoff criterion that is related to the highest frequency of interest, most of the internal nodes in the coupling circuit generated by the PEEC model can be approximately absorbed by the remaining frequency-independent LC elements progressively. The model is very simple to implement and has apparent physical meaning. Mathematically, this model progressively recombines the least significant system pole with other less significant poles. The resultant physically expressive circuit model will be very useful in designing multilayer embedded RF circuits. Four examples are given for demonstrating the validity and effectiveness of the scheme.

An Efficient Numerical Model for Planar Spiral Inductor On-Chip

In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range.

A simple wide-band on-chip inductor model for silicon-based RF ICs

In this paper, we developed a simple wide-band inductor model that contains lateral substrate resistance and capacitance to model the decrease in the series resistance at high frequencies related to lateral coupling through the silicon substrate. The model accurately predicts the equivalent series resistance and inductance over a wide-frequency range. Since it has frequency-independent elements, the proposed model can be easily integrated in SPICE-compatible simulators. The proposed model has been verified with measured results of inductors fabricated in a 0.18-/spl mu/m six-metal CMOS process. We also demonstrate the validity of the proposed model for shielded inductors. The proposed model shows excellent agreement with measured data over the whole frequency range.

Bridge circuits with frequency-independent two-terminal elements

This article substantiates the design of a group of balanced bridge circuits based on frequency-independent two-terminal elements. The number of specific design configurations that are possible is essentially limitless. The circuits are supplied with pulses of complex form and are independently balanced. Results are presented from an analysis of one of the bridge circuits.

Analytical solution and frequency extraction of iris problems in waveguide by separation of variables

The field nearby a thin iris discontinuity can be found in an exact manner by solving the wave equation in an appropriate coordinate system. To this end, it is necessary to select a coordinate system that fits the iris boundary. As an example, capacitive and inductive irises in rectangular waveguides have been solved by considering the Helmholtz equation in the elliptic-cylinder coordinate system. The presence of the waveguide environment is then enforced either by using the aperture field solution in a variational expression of the equivalent shunt susceptance or by taking images. The advantage of the new solution is that a single term solution, apart from being very accurate and numerically efficient, also contains the correct frequency dependence; thus providing results over the entire band. Moreover, wide-band equivalent circuits with frequency independent elements of the Foster's canonical form descend directly from the field analysis.

An approximate variational solution to the step discontinuity in finline

The variational method is applied to a step discontinuity in unilateral finline on the basis of a simplified description of the finite modes, as modes of a symmetrical finned waveguide. A prudent choice of the trial field in the electric and the magnetic formulations allows the derivation of economical simple equivalent circuits with frequency-independent elements over a full waveguide band for a broad range of practical step ratios. >