Simple Equivalent Circuit Model Research Articles

Influence of photo-generated carriers on current spreading in double diode structures for electroluminescent cooling

Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables the study of EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency.

CSRR based folded monopole tri-band antenna array and its system level evaluation

In this article, a folded monopole antenna loaded with complementary split ring resonators (CSRRs) is proposed for tri-band applications. The two bands of the antenna are generated by the folding of the monopole (first band is caused due to fundamental mode and another due to higher order mode) and CSRRs have been responsible for the third band. By using four such antennas in form of an array, the gain and bandwidth have been improved. The prototype of the antenna array is developed on FR4 substrate and simulated results are experimentally validated. A simplified equivalent circuit model of the antenna has been developed and analyzed to quantify the power loss due to input impedance mismatch at each resonance frequency. By using the EM model of the proposed antenna in the Keysight ADS verification test bench its suitability to operate in the system environment has been confirmed.

Bandwidth-enhanced polarization-insensitive metamaterial absorber based on fractal structures

This paper presents a broadband polarization insensitive prefect metamaterial absorber based on fractal structures. Through the combination of fractal and circular structure, the bandwidth is extended without increasing the size of the unit cell. A simple equivalent circuit model has been proposed describing the absorption phenomenon to predict the frequency of absorption of the proposed absorber. The simulated result shows that the absorber's full width half maximum is 18.5%. With rotational symmetry structures, the absorber is insensitive to the polarization. The incident angles at which the metamaterial absorber can maintain 50% of the absorbance are up to 50°. With the geometrical scalability, the absorber can be extended to any frequencies. This absorber is fabricated and measured at X-band, and the experimental results coincide well with the simulation results.

Equivalent circuit model for array of circular loop FSS structures at oblique angles of incidence

This study aims to introduce a simple equivalent circuit model of circular loop shaped frequency selective surface (FSS), predicting the plane-wave transmission characteristics for oblique angles of incidence. The equivalent circuit model is based on a series of basic equations in order to calculate the inductance and capacitance of strip gratings. Through provided relations, the values of circuit elements can be calculated as well. The proposed relations are applied to many circular loop FSSs with different dimensions, and the results are compared with the full-wave simulations obtained from computer simulation technology microwave studio. Moreover, some comparison graphs between the simulated and analytical resonant frequency for different values of design parameters have been carried out to show the circuit model follows the trend of the simulated responses. Finally, both the FSS structures have been fabricated and measured in an anechoic chamber. A good agreement between the experimental results and the simulated responses demonstrates the validity of the circuit model.

Real-time monitoring of a microbial electrolysis cell using an electrical equivalent circuit model.

Efforts in developing microbial electrolysis cells (MECs) resulted in several novel approachesfor wastewater treatment and bioelectrosynthesis. Practical implementation of these approaches necessitates the development of an adequate system for real-time (on-line) monitoring and diagnostics of MEC performance. This study describes a simple MEC equivalent electrical circuit (EEC) model and a parameter estimation procedure, which enable such real-time monitoring. The proposed approach involves MEC voltage and current measurements during its operation with periodic power supply connection/disconnection (on/off operation) followed by parameter estimation using either numerical or analytical solution of the model. The proposed monitoring approach is demonstrated using a membraneless MEC with flow-through porous electrodes. Laboratory tests showed that changes in the influent carbon source concentration and composition significantly affect MEC total internal resistance and capacitance estimated by the model. Fast response of these EEC model parameters to changes in operating conditions enables the development of a model-based approach for real-time monitoring and fault detection.

Compact On-Chip Bandpass Filter With Improved In-Band Flatness and Stopband Attenuation in 0.13- $\mu \text{m}$ (Bi)-CMOS Technology

In this letter, an on-chip miniaturized bandpass filter (BPF) is presented, which is based on a grounded center-tapped ring resonator (CTRR) with shunt capacitive loading. To analyze the principle of this design, a simple but effective equivalent circuit model is provided. Using this model, it is easy to show that the CTRR-based approach has a potential to generate two transmission poles within the passband. Compared with the conventional single-pole-based approach, this dual-pole design not only possesses a flexibility of controlling the passband width, but also has better flatness of insertion loss in the passband. In addition, this approach is able to significantly improve the stopband performance. To further demonstrate the feasibility of this approach in practice, the structure is implemented and fabricated in a commercial 0.13- $\mu \text{m}$ (Bi)-CMOS SiGe technology. The measured results show that the BPF has a center frequency at 33 GHz with a bandwidth of 42.4%. The minimum insertion loss is 2.6 dB, while the stopband rejection is maintained to be better than 20 dB beyond 58 GHz. The chip, excluding the pads, is very compact at only 0.03 mm2 ( $0.11\times0.28$ mm $^{{2}}{)}$ .

High frequency impedance spectroscopy study on Gd-doped CeO2 thin films

The gadolinia-doped ceria (GDC) thin films were deposited by pulsed laser deposition. Samples with special geometry were prepared which allowed us to characterize GDC film in across-plane direction. The electrical properties of the films were investigated by means of impedance spectroscopy in the frequency range of 10 Hz to 10 GHz and 380–600 K temperature interval. The data analysis was performed by using appropriate equivalent circuit. The equivalent circuit modeled thin GDC film itself, platinum metal connections (traces) in the dielectric medium of sapphire substrate and interfaces between the film and platinum electrodes. Hence, several factors influenced the impedance spectra, namely the properties of substrate, the oxygen-ion transport in the film, ion blocking at the interface between the film and the electrode, and metal traces. The electrical properties of GDC thin films were compared with these of bulk ceramics and showed similar conductivity and dielectric permittivity values. The study also revealed that measurement data at electrical field frequencies of up to 10 GHz were particularly important to correctly estimate electrical properties of GDC thin films, because at high temperatures the electric response of GDC film shifts to high frequencies (higher than 1 MHz at 600 K). The thin film sample preparation for high frequency measurements and fitting of impedance data by using relatively simple equivalent circuit model is presented.

Study of Cathode Catalyst Layer Parameters for HT-PEMFC Using Electrochemical Impedance Spectroscopy

We investigate the effect of platinum loading, cathode catalyst layer thickness and the phosphoric acid doping level on the performance of a polybenzimidazole based HT-PEMFC MEA. The objective is to characterize the cathode catalyst layer, which is known to be the limiting factor for PEMFC performance due to the sluggish kinetics of the oxygen reduction reaction. The range for each parameter is chosen carefully to investigate cell performance. Impedance measurements at four current densities (10, 20, 50 and 100 mA cm-2) with high cathode stoichiometry are performed. These operating conditions minimize the mass transport losses and therefore, the impedance data can be fitted with a simple equivalent circuit model to extract electrochemical parameters related predominantly to the cathode catalyst layer. These parameters are presented for eight membrane electrode assemblies and the cell performances are discussed. Finally, a comparison between the parameters is made and directions for improvement are suggested.

Inductance Extraction for PCB Prelayout Power Integrity Using PMSR Method

Proper power integrity (PI) analysis is required for printed circuit board (PCB) power distribution network (PDN) design. Top-layer interconnect inductance for PI has always been a vital concern for high-speed industry. Developing a simple physics-based equivalent circuit model for critical structures is essential for understanding the physics of the system and for intelligent designs. In this paper, a physics-based model size reduction (PMSR) method is applied to get the equivalent circuit model for the above-ground geometries. The extracted physics-based models are also based on the partial element equivalent circuit (PEEC) method, and can be used in analyzing the structure in its parts. By applying PMSR method, a physics-based equivalent circuit model can be proposed and this circuit model is related to the geometric features of the design. In this way, PMSR method can provide an intuitive guideline in designing PCB and reducing above inductances, therefore, a low-ripple dc voltage can be delivered through PDN. Taking advantage of PEEC and PMSR methods, the top-layer inductances of three different geometries are calculated and the physics-based circuit models are obtained, respectively.

Collective plasmonic oscillations in gold nanostrips arrays.

Excitation of collective plasmonic modes and their effect on optical behavior are experimentally and theoretically studied in 1D arrays of gold nanostrips in comparison with continuous gold films with periodically modulated profile. In strips, the angular dependence of the reflectivity demonstrates a peak at the resonance condition as opposed to a dip observed in continuous sine wave gratings. In addition, an extremely narrow feature in the reflection is observed in strips and tentatively ascribed to the bright Wood-Rayleigh anomaly. Theoretical calculations based on the combined transfer-matrix coupled-wave analysis and coordinate transformation method are shown to fit the experimental angular and spectral behavior of the plasmonic resonances. The effects are also discussed in terms of a simple equivalent circuit model.

A Simple Equivalent Circuit Model for Shielding Analysis of Magnetic Sheets Based on Microstrip Line Measurement

This paper presents a simple equivalent circuit model for estimating shielding performance of thin and flexible magnetic sheets or films, which are commonly used in modern mobile devices, such as smartphones. The proposed equivalent circuit model can accurately and effectively represent the measurement setup using a microstrip line and a loop probe that are typically employed to evaluate a near-field shielding effectiveness (SE) of commercial magnetic absorbing sheets or films. The calculated SEs of magnetic sheets using the proposed equivalent circuit model are validated by 3-D electromagnetic simulation and experiment, and show good agreement with measurement results in the frequency range up to 0.5 GHz.

The negative-differential-resistance (NDR) mechanism of a hydroelastic microfluidic oscillator

A microfluidic oscillator is of interest because it converts a stable laminar flow to oscillatory flow, especially in view of the fact that turbulence is typically absent in miniaturized fluidic devices. One important design approach is to utilize hydroelastic effect-induced autonomous oscillations to modify the flow, so to reduce the reliance on external controllers. However, as complex fluid-structure interactions are involved, the prediction of its mechanism is rather challenging. Here, we present a simple equivalent circuit model and investigate the negative-differential-resistance (NDR) mechanism of a hydroelastic microfluidic oscillator. We show that a variety of complex flow behaviors including the onset of oscillation, formation of different oscillation patterns, collapse of the channel, etc can be well explained by this model. It provides a generic approach for construction of microfluidic NDR oscillators, following which a new design is also proposed. Relevant findings give more insights into the hydroelastic instability problems in microfluidics, and enrich the study of microfluidic flow control devices based on the electric circuit theory.

Investigation of temperature-dependent small-signal performances of TB SOI MOSFETs**Project supported by the National Natural Science Foundation of China (No. 61331006) and the National Defense Pre-Research Foundation of China (No. 9140A11040114DZ04152).

This paper investigated the temperature dependence of the cryogenic small-signal ac performances of multi-finger partially depleted (PD) silicon-on-insulator (SOI) metal oxide semiconductor field effect transistors (MOSFETs), with T-gate body contact (TB) structure. The measurement results show that the cut-off frequency increases from 78 GHz at 300 K to 120 GHz at 77 K and the maximum oscillation frequency increases from 54 GHz at 300 K to 80 GHz at 77 K, and these are mainly due to the effect of negative temperature dependence of threshold voltage and transconductance. By using a simple equivalent circuit model, the temperature-dependent small-signal parameters are discussed in detail. The understanding of cryogenic small-signal performance is beneficial to develop the PD SOI MOSFETs integrated circuits for ultra-low temperature applications.

Electromagnetic Analysis and Steady-State Performance of Double-Sided Flat Linear Motor Using Soft Magnetic Composite

The applicability of a soft magnetic composite (SMC) material to a new double-sided buried-type interior permanent-magnet flat linear brushless motor (IPM-FLBM) with slot-phase shift is presented through the steady-state performance improvement in this paper. The IPM-FLBM using a conventional electrical solid steel is used as a base model prototype for the performance comparison. The analytic models for armature resistance, inductances of series-connected asymmetric dual three-phase windings, no-load flux linkages, and back electromotive forces (back EMFs) are investigated to derive a closed-form equation for the thrust force. The magnetic field capability due to the design parameter changes of the new SMC prototype is analyzed using two simplified nonlinear magnetic equivalent circuit (MEC) models, comparing with the base model prototype. The iron and copper losses of the SMC prototype also are investigated in terms of the thermal limitation. The steady-state performance enhanced by the reduced air-gap size is experimentally validated through the comparison of the static thrust force with that of the base model prototype.

Anomalous DC and RF behavior of virgin AlGaN/AlN/GaN HEMTs

The performance of gallium nitride transistors is still limited by technological problems often related to defects and traps. In this work, virgin AlGaN/AlN/GaN HEMTs exhibiting an anomalous DC behavior accompanied by frequency dispersion in the microwave range, both in the transconductance and output conductance, are analyzed. This anomalous response, which is mitigated by high-bias conditions, is attributed to the presence of traps and defects both in the volume of the GaN channel and in the source and drain contacts. A simple equivalent circuit model is proposed to replicate the dispersive response of the transistor, achieving an excellent agreement with the measured S–parameters and thus providing relevant information about its characteristic frequency.

Magneto-Electric Effect Modeled in a Nonlinear Experiment

This letter presents a nonlinear model and experimental assessment of a magneto-electric (ME) device fabricated using a hexaferrite film and a spiral coil. In both the model and experiment, two sources are applied to the ME film and the spiral coil. The ME effect is modeled by two equation-based sources for generating the ME effect from the ME film to the spiral coil (and vice versa). A simple equivalent circuit model is used. In the nonlinear experiment, the two different sources are applied in a frequency range of 1-40 MHz. The voltage across the coil is measured as a function of the two sources with coupled frequencies and amplitude. In the simulation, the voltage on the spiral coil is a combination of the two sources modulated in the frequency domain; moreover, they are in agreement with experimental results showing that the output voltage of the spiral coil is a function of not only its direct source, but also the source on the ME film (so arising from the ME coupling). Between the experiment and simulation, the average amplitude difference is approximately 20%, whereas the resonance peaks are in agreement.

Research on planar frequency selective fabrics with Jerusalem-shaped units

Planar frequency selective fabrics (FSFs) with Jerusalem-shaped units were proposed in this paper. In accordance with the previous work, the design process was specifically for 10 GHz. Through simulation and optimization procedures, the ideal structure parameters were obtained, and the proposed FSFs with optimized parameters showed good stability to differential and integral algorithms, transmission modes and incidence angles of electromagnetic (EM) waves. To further explore the internal EM transmission mechanism of FSFs, the surface currents at 4, 10 and 14 GHz were analyzed comparatively. Based on the simulated results, 10 samples with the polyester fabric substrate were fabricated through the computer-based carving method and the transmission characteristics were tested using the Shielding Room Method. The fabricated FSFs indeed showed good frequency response characteristics, as expected, and the comparison of measured and simulated results verified the validity of the design procedures. The influence rules of structure parameters ( p, a, b, c) were further studied in detail by changing their values properly, and the simplified equivalent circuit model was proposed to explore the corresponding physical mechanism, which could provide physical insight into the performance of the FSFs.

Ultra‐wideband grid array antenna for automotive radar sensors

This study presents the design of an ultra-wideband (UWB) grid array antenna (GAA) for automotive radar sensors. The GAA is constructed using long transmission lines and short radiating lines loaded with reactive circular disc elements to improve the bandwidth performance. The reactance loading provides more number of zeros in the antenna's reactance and hence provides a wider impedance bandwidth. A simplified equivalent circuit model is provided to understand the fundamental operation of the proposed GAA. The GAA is composed of 33 elements arranged in two rows to obtain narrow beam along one plane and relatively wider beam along the other plane. The proposed GAA is characterised by low profile, large bandwidth, high gain and fan beam radiation pattern. The prototype antenna is fabricated and experimental results are presented. From the experimental results, it is evident that the proposed GAA is suitable for UWB short range automotive radar systems to efficiently detect and prevent collision.

Coupled equivalent circuit models for fluid flow and heat transfer in large connected microchannel networks – The case of oblique fin heat exchangers

This paper presents a simplified equivalent circuit model, which exploits the electric–hydraulic analogy and electric–thermal analogy, to predict the mass flow distribution and temperature distribution in an oblique fin array used in enhanced heat transfer applications. Methods to obtain accurate correlations for calculation of flow-dependent hydraulic ‘resistances’ are outlined and developed for both primary and secondary channels in the oblique fin array. Appropriate Nusselt number correlations and thermal resistance models are also employed to predict the temperature distribution associated with the mass flow distribution. Detailed full-domain numerical (CFD) simulations are performed to obtain parameters for the hydraulic resistance correlations, and also to serve as benchmarks for the proposed equivalent circuit model. Detailed comparisons between the results of simplified model and numerical simulation showed that the simplified model can accurately predict the mass flow distribution and temperature distribution, within ±5%, for varying fin number, aspect ratio, fin pitch, fin length, oblique angle and inlet velocity. Slightly higher deviations of mass flow prediction are observed for high inlet velocities as a result of the presence of vortices close to the trailing edge of the oblique fin region.

A Simplified Equivalent Circuit Model of Series Resonant Converter

Equivalent circuit models are useful design tools for control and have already well served their purposes in pulse width modulation dc–dc converters. However, no simple equivalent circuit model is available yet for resonant-type dc–dc converters. Up to now, the most successful equivalent circuit model of series resonant converter (SRC) is based on extended describing function concept, which was proposed by Yang et al. [30]. However, the equivalent circuit is a complicated fifth order with the cross-coupling effect and no analytical solution is provided for transfer functions. This paper proposes a simple third-order equivalent circuit model of SRC. The equivalent circuit model is derived by simplification of the original fifth-order equivalent circuit, based on the fact that the resonant capacitor behaves like an equivalent resonant inductor with respect to the modulation frequency. The equivalent circuit model can predict the dynamic behavior very well when the switching frequency is below, close to, or above the resonant frequency. Furthermore, for the first time, analytical expressions of all transfer functions, i.e., control-to-output, input-to-output, output impedance, and input impedance are provided. These analytical transfer functions will serve as a useful tool for the feedback design. The equivalent circuit model is verified by Simplis simulation and experimental results.