Simple Equivalent Circuit Model Research Articles

Two-pole digitally tunable evanescent-mode waveguide narrow-band filter with radio frequency micro-electromechanical systems switches

A two-pole evanescent-mode waveguide narrow-band filter digitally tunable with micro-electromechanical system (MEMS) switches is demonstrated. A design approach for a prescribed frequency shift and tuning range is elaborated using a simple equivalent circuit model. The validity of the proposed frequency tuning concept is proved through simulation and measurement of a prototype. The measured tunable filter achieves three resonant states around 3 GHz, with an average frequency tuning of 20 MHz between each state, a fractional 1-dB bandwidth of 1.2-1.5% and better than 2.1 dB insertion loss. The measured unloaded quality factor (Q) of the filter varies from 315 to 460 over the frequency tuning range.

Cycling behaviour of Li/Li4Ti5O12 cells studied by electrochemical impedance spectroscopy

We studied the behaviour of Li/Li(4)Ti(5)O(12) cells by electrochemical impedance spectroscopy to gain insight into the changes at the electrode/electrolyte interfaces during extensive cycling. A simple equivalent-circuit model is able to describe the impedance of the complete battery as a function of both state-of-charge and state-of-degradation. The formation of the solid-electrolyte interface and dendrite growth at the Li metal electrode have a strong influence on the impedance measurements although the battery performance is not significantly affected.

Diffusion and Gas Conversion Analysis of Solid Oxide Fuel Cells at Loads via AC Impedance

Impedance measurements were conducted under practical load conditions in solid oxide fuel cells of differing sizes. For a 2 cm2button cell, impedance spectra data were separately measured for the anode, cathode, and total cell. Improved equivalent circuit models are proposed and applied to simulate each of measured impedance data. Circuit elements related to the chemical and physical processes have been added to the total-cell model to account for an extra relaxation process in the spectra not measured at either electrode. The processes to which elements are attributed have been deduced by varying cell temperature, load current, and hydrogen concentration. Spectra data were also obtained for a planar stack of five 61 cm2cells and the individual cells therein, which were fitted to a simplified equivalent circuit model of the total button cell. Similar to the button cell, the planar cells and stack exhibit a pronounced low-frequency relaxation process, which has been attributed to concentration losses, that is, the combined effects of diffusion and gas conversion. The simplified total-cell model approximates well the dynamic behavior of the SOFC cells and the whole stack.

Induction Magnetometer with a Metal Shielded Pickup Coil for MHz Range Operation

This paper presents an induction magnetometer with a metal shielded pickup coil for MHz range operation. The validity of two simple equivalent circuit models for voltage detection and current detection is also confirmed by experimental results. From the measured frequency response for a calibrated magnetic field of 10 nT, we successfully demonstrate the ability of the magnetometer. The experimental results reveal the quantitative data of the equivalent resistance and inductance. When the resistance of the pickup coil is quite low, the equivalent resistance can be regarded as the resistance of the BNC connector (50 Ω). With the equivalent resistance, the absolute error of the output voltage between measurement and estimation is less than ±1 dBμV between 0.3 MHz and 2 MHz. In contrast, it is found that the existence of the metal shielded layer affects the estimated equivalent inductance. If the pickup coil has no metal shielded layer, the estimated value of the equivalent inductance is 56.3 times the inductance of the pickup coil. This value is verified by the estimated and measured results. However, this phenomenon is not found if the pickup coil has the metal shielded layer.

Electrochemical behaviour of chalcopyrite (CuFeS2) in FeCl3 solution at room temperature under differential stress

The electrochemical behaviour of chalcopyrite (CuFeS2) was studied by polarisation curve and electrochemical impedance spectroscopy (EIS) in FeCl3 solution at room temperature under differential stress. Experimental results showed the relation between chalcopyrite potential difference and elastic stress is ΔφHCuFeS2=−VdPZF. The corrosion current density and charge transfer electrical resistance increased distinctly, whereas double-layer capacitance decreased and the corrosion potential became more negative with increasing differential stress. The EIS data have been analyzed and discussed in the simple equivalent circuit model, the Randles equivalent electrical circuit model and the point defect model, respectively. The experimental results are significant for mineral processing and hydrometallurgy.

Inverse Spin-Hall Effect Induced by Spin Pumping in Different Thickness Pt Films

The inverse spin-Hall effect, conversion of spin currents into electromotive force, has been investigated in Pt thin films with changing the thickness of the Pt films. We measured the electric voltage due to the inverse spin-Hall effect induced by the spin pumping in Ni81Fe19/Pt bilayer systems with different Pt thickness films (d N=10, 30, 50, and 75 nm) at room temperature. The experimental results show that the signal induced by the inverse spin-Hall effect V ISHE is inversely proportional to the Pt thickness d N, which is well reproduced by a simple equivalent circuit model.

Analysis of Inductive Coupling and Design of Rectifier Circuit for Inter-Chip Wireless Power Link

A wireless power link utilizing inductive coupling is developed between stacked chips. In this paper, we discuss inductor layout optimization and rectifier circuit design. The inductive-coupling power link is analyzed using simple equivalent circuit models. On the basis of the analytic models, the inductor size is minimized for the given required power on the receiver chip. Two kinds of full-wave rectifiers are discussed and compared. Various low-power circuit design techniques for rectifiers are employed to decrease the substrate leakage current, reduce the possibility of latch-up, and improve the power transmission efficiency and the high-frequency performance of the rectifier block. Test chips are fabricated in a 0.18µm CMOS process. With a pair of 700 × 700µm2 on-chip inductors, the test chips achieve 10% peak efficiency and 36mW power transmission. Compared with the previous work the received power is 13 times larger for the same inductor size [7].

Simple Equivalent Circuit Model of a Stripline in Inhomogeneous Dielectric Media

Equivalent circuit models of a stripline have been proposed previously but most of them are either in a very complex form or are only able to model striplines in homogeneous media. In this work, modal decomposition technique is applied and a simple equivalent circuit model for a stripline in inhomogeneous substrate is proposed. Comparison with other models is also presented.

Spatial Variation of Negative Oxygen Ion Energy Distribution in RF Magnetron Plasma with Oxide Target

The energy distribution of negative oxygen (O-) ions and its spatial variation was measured in an RF magnetron plasma using a mass analyzer with an energy analyzer. O- ions with kinetic energies higher than 50 eV were observed during the sputtering of MgO. Spatial variation of the O- energy distribution was observed and was explained using a simple equivalent circuit model.

Reference module selection criteria for accurate testing of photovoltaic (PV) panels

It is shown that for accurate testing of PV panels the correct selection of reference modules is important. A detailed description of the test methodology is given. Three different types of reference modules, having different I SC (short circuit current) and power (in Wp) have been used for this study. These reference modules have been calibrated from NREL. It has been found that for accurate testing, both I SC and power of the reference module must be either similar or exceed to that of modules under test. In case corresponding values of the test modules are less than a particular limit, the measurements may not be accurate. The experimental results obtained have been modeled by using simple equivalent circuit model and associated I– V equations.

On the Equivalent Circuit Models of Piezoelectric Ceramics

The use of piezoelectric ceramics as actuators and/or sensors is prevalent. This paper is aimed to explore simple but useful equivalent circuit models of piezoelectric ceramics with the consideration of energy dissipation. Based on the electrical impedance, the equivalent circuit models of piezoelectric ceramics are investigated under unloaded and loaded conditions. The characteristics and physical meanings of the circuit models are discussed by considering the frequency range of interest. The circuit models and discussions in this paper can provide a good understanding on the behaviors of the piezoelectric ceramics when designing and analyzing the piezo-based systems and structures.

Boolean Logic Gates Utilizing GaAs Three-Branch Nanowire Junctions Controlled by Schottky Wrap Gates

A GaAs-based three-branch nanowire junction (TBJ) with Schottky wrap gates (WPGs) is investigated to realize novel Boolean logic gates. The WPG-controlled TBJ shows a bell-shaped voltage input–output curve and is controlled by gate voltage on the WPGs. The observed characteristics are explained using a simple equivalent circuit model. AND gate operation is realized in the WPG-controlled TBJ and its output voltage swing is controlled using WPGs. It can also operate as a NOT gate by changing the measurement circuit. A NAND gate is fabricated by integrating two WPG-controlled TBJs, and correct operation with a voltage transfer gain of 2.2 is realized.

Compact coplanar waveguide bandpass filter using loaded split‐ring resonator

AbstractA compact coplanar waveguide (CPW) band‐pass filter using a cross‐coupled λ/4 resonator with loaded split‐ring resonators (SRRs) is introduced in this letter. The proposed filter exhibits a quasi‐elliptic function response and its circuit size occupies only 12 × 11.8 mm2 (≈0.21λg × 0.20λg). Also, a simple equivalent circuit model is set up. A good agreement between simulations and measurements verify the proposed filter and the validity of design methodology. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1565–1568, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24396

High-Power High-Linearity InGaAs/InP Photodiodes

The third-order intermodulation distortions of an InGaAs/InP modified uni-traveling carrier photodiode (MUTC-PD) are characterized using a two-tone setup. At 0.3 GHz modulation frequency and photocurrents above 40 mA the third order local intercept point (IP3) reaches 52 dBm and remains above 35 dBm up to the photodiode's 3 dB bandwidth. A simple equivalent circuit model is used to explain the frequency characteristics of the intermodulation distortions. Based on experimental data, we find that the frequency characteristics of the IP3 can be attributed to the change of both the responsivity and device capacitance induced by the photocurrent and the transient voltage drop at the load and series resistors. Further investigations of the non-linear phenomena suggest that the Franz-Keldysh effect and impact ionization are the primary reasons for voltage-dependent responsivity, while low doping concentration in the p-type InGaAs absorber and space charge screening are responsible for the voltage dependent capacitance and photocurrent dependent capacitance, respectively.

The Frequency Behavior of the Intermodulation Distortions of Modified Uni-Traveling Carrier Photodiodes Based on Modulated Voltage Measurements

The effect of modulated voltage on the nonlinear response of an InGaAs-InP charge-compensated modified uni-traveling carrier photodiode is characterized using a modulated bias measurement setup. Based on experimental results for the dependence of responsivity and photodetector capacitance on bias voltage, we use a simple equivalent circuit model to explain the frequency characteristics of the intermodulation distortions caused by the modulated bias. Good agreement has been achieved between the simulation and measurement.

인덕턴스 변화 모델을 이용한 EMGF 출력 분석

Explosive Magnetic Generator of Frequency(EMGF)는 고폭화약의 폭발을 이용하여 화약의 폭발 에너지를 전자기 에너지로 변환 시키면서 초고주파의 강한 전자파를 발생시키는 효율적인 방법으로 연구되고 있다. 이 때 발생하는 전자파의 물리적 원인은 현재까지 명확하게 규명되어 있지 않은데, 단순한 시변 등가회로 해석만으로는 이러한 고주파 발진을 설명하기 어려운 것으로 알려져 있다. 이 논문에서는 기존에 널리 받아 들여 지고 있는 지수 감소적인 시변 인덕턴스 변화 모델에 대해서 자장압축효과를 고려한 유한요소 해석을 통해 문제점을 분석하고 보다 정확한 인덕턴스 변화 모델의 경향성에 대해서 제시하고자 한다. 그리고 이렇게 제시된 새로운 인덕턴스 변화 모델을 사용한 EMGF 출력 시뮬레이션을 통해 새로운 인덕턴스 변화 모델이 출력에 미치는 영향을 분석한다. The Explosive Magnetic Generator of Frequency (EMGF) has been studied as a method to generate a strong microwave effectively through converting the explosion powder energy into the electromagnetic energy. However, the generated high frequency electromagnetic wave has not been explained clearly yet, for it is known to be difficult to analyze the high frequency electromagnetic wave oscillation using a simple time-varying equivalent circuit model. In this paper, we analyze the problems of the widely used inductance model with an exponential decreasing pattern and investigate the tendency of a more accurate inductance variation model using the finite element method of EMGF inductance by considering the magnetic compression effect. And we have shown via an EMGF output simulation that the new inductance variation model proposed here has an negative effect on EMGF output.

Subthreshold parameters of radio-frequency multi-finger nanometer MOS transistors

The subthreshold radio-frequency (RF) characteristics of multi-finger nanoscale MOS transistors were studied by using the measured scattering (s) parameters. Small-signal circuit parameters were determined based on a simplified small-signal equivalent circuit model. We found that besides the source and gate resistances, most of the parameters such as the channel resistance, drain inductance and intrinsic capacitance are found to be significantly different to those in the saturation mode of operation. The subthreshold channel resistance increases and the drain inductance decreases as the finger number increases because of the more significant charge transport along the finger boundaries. In addition, the channel resistance can be governed by the drain-induced barrier lowering in a transistor with very short gate length. The equivalent intrinsic capacitance of the small-signal equivalent circuit is governed by the substrate resistance and capacitance which make the parameter extraction more difficult.

Generalized serial dilution module for monotonic and arbitrary microfluidic gradient generators

In this paper, we propose a generalized serial dilution module for universal microfluidic concentration gradient generators including N cascaded-mixing stages in a stepwise manner. Desired concentrations were generated by means of controlled volumetric mixing ratios of two merging solutions in each stage. The flow rates were adjusted by controlling channel length, which is proportional to fluidic resistance in each channel. A generalized mathematical model for generating any complex concentration and output flow rate gradients is presented based on the fact that there is an analogy between microfluidic circuits and electrical circuits. The pressure drop corresponds to a voltage drop, the flow rate to an electrical current, and the flow resistance to an electrical resistance. A simple equivalent electrical circuit model was generalized, and in the model each channel segment was represented by an electrical resistance. As a result of the mathematical modelling, the only variable parameter in the generalized serial dilution module was the channel length. By the use of the generalized serial dilution module with N = 4, three types of microfluidic gradient generators for linear, logarithmic and Gaussian gradients were successfully designed and tested. The proposed strategy is capable of generating universal monotonic gradients with a single module or arbitrary gradients with multiple modules ranging from linear to complex non-linear shapes of concentration gradients as well as arbitrary output flow rate gradients in a stepwise manner. The simple universal gradient generation technology using the generalized serial dilution module will find widespread use in the greater chemical and biological community, and address many challenges of gradient-dependent phenomena.

Time-domain electrostatic force spectroscopy on nanostructured lithium-ion conducting glass ceramics: analysis and interpretation of relaxation times

The nanoscopic electrical properties of LiAlSiO(4) glass ceramics with different degrees of crystallinity chi were studied by means of time-domain electrostatic force spectroscopy (TDEFS). Thereby, a faster relaxation process due to lithium ion movements in the glassy phase and a slower process due to lithium ion movements in the crystallites could be distinguished. Over a broad range of crystallinity values, the TDEFS relaxation times of both processes are Arrhenius activated, with an activation energy being essentially independent of chi and with a pre-exponential factor depending in a systematic fashion on chi. With increasing crystallinity, the pre-exponential factor of the faster process (glassy phase) increases, while that of the slower process (crystallites) decreases. In order to explain this observation, we consider simple equivalent circuit models for the capacitance relaxation of the system AFM tip/gap/sample.

Electrical Properties of Metal–Silicon Nitride–Hydrogenated Amorphous Silicon Capacitor Elucidated Using Admittance Spectroscopy

Detailed admittance spectroscopy was performed on a metal–silicon nitride–hydrogenated amorphous silicon (MIAS) structure. On the basis of the properties of hydrogenated amorphous silicon (a-Si:H), three simplified equivalent circuit models under various operating conditions (accumulation, depletion and full depletion) are presented along with an alternative direct measurement method at room temperature. Admittance spectroscopy shows that the interface states density between silicon nitride (SiNx) and a-Si:H can be determined from the depletion equivalent circuit model. The resisivity and activation energy of a-Si:H can also be obtained using the accumulation and depletion equivalent circuit models. These models can be employed easily to monitor the fabrication parameters of thin-films transistors (TFTs) and to accurately and directly obtain the capacitance model parameters of TFTs.