Lumped Capacitance Research Articles

An Ultra-Compact On-Chip Reconfigurable Bandpass Filter With Semi-Lumped Topology by Using GaAs pHEMT Technology

A semi-lumped reconfigurable on-chip bandpass filter with GaAs pHEMT technology is presented in this paper. Three order tunable bandpass filter is designed with serial lumped capacitors, parallel resonators, and reconfigurable components. The operating bands are adjusted by field effect transistors and its corresponding gate bias circuits with GaAs technology. The semi-lumped topology, intending to reduce the size of the circuit, is employed to construct the parallel resonators, which are implemented with short-ended stubs and metal-insulator-metal capacitors. The equivalent circuit model is built to interpret the mechanism of the on-chip reconfigurable bandpass filter. Compared with the traditional tunable filters, an ultra-compactness feature and low insertion loss are obtained with the proposed design. The size of the on-chip filter is only 0.8×1.07 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is equivalent to 0.08×0.11 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 10 GHz. The presented filter is reconfigurable in two frequency bands, one is centered at 10 GHz with a fraction bandwidth (FBW) of 24.94% and the other is operated at 8.8 GHz with a FBW of 13.35%. The tuning range of the FBW is 30.6%. Good agreements are observed between the simulated and measured S-parameters.

On the Minimal Loading of Sensorless Series-Series Compensated Inductive WPT Link Operating at Load Independent Voltage Output Frequency Without Feedback

It is well-known that continuous conduction mode (CCM) operation at certain frequency yields nearly load-independent voltage gain in practical series-series compensated inductive wireless power transfer links (SS-IWPTL). Such an operation is usually referred to as “load independent voltage output” (LIVO). Residual load dependence is due to the presence of non-zero equivalent series resistances in both transmitter and receiver. On the other hand, it has been shown that voltage gain remains load-dependent at the same operating frequency in discontinuous conduction mode (DCM) irrespectively of equivalent series resistances values. Consequently, the output voltage of SS-IWPTL operated at LIVO frequency resides within a range with lower bound corresponding to rated load and upper bound corresponding to zero loading for a given input voltage. The upper bound expression (typically attained in CCM) is derived using the first harmonic approximation (FHA) based equivalent circuit and is well-established by previous works. On the contrary, derivation of the lower bound (achieved in DCM) requires differential equation (DE) based analysis and was barely treated in the literature. The paper demonstrates that lumped capacitance of receiving side coil and input capacitance of receiving side rectifier must be taken into account during DE-based analysis since they impose significant receiving side voltage oscillations, which may give rise to safety issues. In order to damp these oscillations and keep the output DC voltage below a predetermined limit, minimal loading should be applied at the SS-IWPTL output, creating an RCD-snubber equivalent. Guidelines for the minimal load sizing are derived in the paper analytically. Simulations and experiments based on a 400V, 1kW SS-IWPTL operating at LIVO frequency demonstrate excellent matching, validating the proposed analysis.

Self-Curing Decoupling Technique for MIMO Antenna Arrays in Mobile Terminals

The self-curing decoupling technique is substantially extended to apply to multi-input multi-output (MIMO) antenna arrays in mobile terminals. Using this proposed technique, the mutual coupling between antennas can be reduced by inlaying lumped element capacitors on the ground plane. The decoupling method does not require any physical connection or obstruction between coupled antennas. The significance of the proposed decoupling technique is fourfold: 1) it works for inverted-F antennas (IFAs), monopole antennas, and loop antennas, the most three commonly used antenna forms for mobile terminals; 2) the inherent improvement on matching conditions after decoupling; 3) the flexibility in implementation owing to its detachment from the antenna body; and 4) the applicability to an array with more than two elements. Four demonstrating examples, including two IFAs, two monopole antennas, two loop antennas, and a MIMO array with four elements of different antenna types are studied by EM modeling, passive tests, and MIMO over-the-air (OTA) measurements. The experimental results show that significant improvements in port isolation (from 9 to 30 dB), total efficiency (from 53% to 69%), and above all, the system data throughput can be achieved. The working mechanism of the method is revealed and justified through the partial element equivalent circuit (PEEC) model in the fifth example.

Analysis of the Thermomechanical Response of Structural Cables Subject to Fire

Cable-supported structures such as bridges and stadia are critical for the surrounding community and the consequences arising from a major fire event can be substantial. Previous computational studies into the thermal response of cables often employed simplistic heat transfer models that assumed lump capacitance or cross-sectional homogeneity without proof of validity. This paper proposes a methodology for calculating the thermal response of a cable cross-section allowing for heat transfer by conduction through each strand contact surface and radiation across inter-strand cavities. The methodology has been validated against two experiments of cables subjected to radiant heating and an input sensitivity analysis has been undertaken for the heat transfer and material parameters. The approach is compared against simple heat transfer lumped methods for a parallel-strand cable where it is shown that these lumped models are not always conservative. The model is then coupled with a two-dimensional generalised plain strain model to study the likely effect of the cross-sectional temperature gradients on the mechanical response. The study considers three qualitatively different hydrocarbon jet fire scenarios, both with and without external insulation for fire protection. It is shown that the proposed methodology can reproduce realistic cross-sectional temperature distributions with up to 50% temperature difference at the cable external surface and can capture the phenomenon of load shedding in a gradually heated cable. It is also shown that assuming a lumped thermal mass neglects the possibility of moment-inducing temperature gradients which are not considered in the ambient design of cables that is driven by tensile capacities. The proposed model and its predictions contribute towards an improved understanding and a more informed structural design of cable-supported structures in fire.

Experimental and analytical study of transient convection at film flow-wall interface using infrared thermography

The convection heat transfer of transient flow usually involves transient temperature and transient heat flux at the flow-wall interface. For experimental studies on this type of convection heat transfer problems, it is difficult to take measurement at the flow-wall interface, particularly for liquid flow. A substrate with small thickness can be used. One surface is exposed to the flow, while, on the free surface, there is a thin-skin heat source providing a constant and uniform heat flux, and the temperature at the free surface is measured using infrared thermography. Then the heat transfer coefficient of the transient flow can be obtained based on the temperature measured on the free surface. Two experimental tests of water droplets impacting a water film flow are conducted using this method. We solve a 1-D transient conduction problem, and the derived solution is used to calculate the heat transfer coefficient for the two experiments. Additionally, the lumped capacitance method (LCM) and the present analytical method are compared for calculating convection heat transfer.

Design Considerations for Radiofrequency Whole-Body and Head Coils

It is shown that the transverse-plane ${\bf{B}}_1^ + $ homogeneity in TEM whole-body and head RF coils, which is responsible for acquiring uniformly illuminated MR images, is frequency independent and solely depends on achieving high excitation purity of the fundamental $m = 1$ mode. This necessitates that the capacitive coupling introduced by the interconnecting lumped capacitors should maximize the separation between the resonance frequency of the fundamental mode and that of all other higher order modes. Alternatively, full-orthogonal excitation of the coil, if possible, would mitigate this design challenge, especially if high- Q operation cannot be guaranteed. In this contribution, a field theoretical technique for the optimization of the capacitive coupling is introduced and applied to the birdcage configuration as a representative of TEM coils. A fairly general analysis of these coils is also introduced and/or revisited, which underlies the proposed technique and offers simple analytic design equations. Simulation results are presented to validate the considered approach. The presented analysis deals with the homogeneously filled coils and therefore does not consider the ${\bf{B}}_1^ + $ inhomogeneities caused by the loading. The latter will be the subject of future publications.

Three-Dimensional Frequency-Dependent Thermal Model for Planar Transformers in LLC Resonant Converters

In this paper, a thorough thermal analysis is carried out in order to find an analytical three-dimensional (3-D) frequency-dependent thermal model of planar transformers (PTs) used in high-frequency power converters. Because of the tendency of having higher power density as well as miniaturization of power converters, the components have to work near their thermal limit margins. This issue is more critical for planar magnetics in LLC converters due to their variable high-frequency operation, making thermal modeling and heat transfer analysis tools necessary. The proposed 3-D frequency thermal model is obtained based on the lumped parameters network (LPN) according to different thermal resistances of the PT including convection, conduction, and radiation heat exchanges. It should be noted that not only the 3-D geometry effect of the core is applied to the proposed model, but thermal surface resistances are also considered to model the high-frequency operation effect. Moreover, the lumped capacitance thermal model is used to analyze the transient thermal variation of the transformer. The LLC resonant converter with two PTs, including EE58/11/38 and ER51/10/38 planar cores, is considered to show the compatibility of the proposed 3-D-frequency LPN model. In addition, the temperature distribution of different parts of the transformers is evaluated using finite element method modeling and compared with the proposed 3-D frequency-dependent LPN model. Experimental results confirm the improved accuracy of the proposed LPN model and show the proposed model predicts the temperature distribution in PTs with an error of less than 3%. Considering the improved accuracy and low computational time of the method, the proposed 3-D frequency-dependent model is a powerful and fast design tool to evaluate the temperature distribution for different designs, and so can be used to effectively optimize the transformer from thermal point of view.

On the comparison between computational fluid dynamics (CFD) and lumped capacitance modeling for the simulation of transient heat transfer in solar dryers

In this paper transient heat transfer in a solar food drier is modeled by using both computational fluid dynamics (CFD) and lumped capacitance modeling techniques. The CFD model is used to simulate the air flow and transient heat transfer within the dryer. A lumped capacitance model, developed from energy exchanges between various components of the drying chamber, is extensively compared with the results of the CFD model. The two models predict both a 40 °C rise in steady-state temperature within the drying chamber. Before reaching this temperature, there is about 8 °C RMS deviation between the transient temperature prediction of the two models. This deviation is mainly caused by the heat transfer coefficient around the food rack shelfs. Fitting these coefficients give rise to a minimal RMS deviation between the two models of 1.8 °C and 0.9 °C on the lower and upper rack shelfs respectively. The transient heat transfer phenomenon from CFD modeling also showed that the spatial distribution of temperature after 30 min is uniform thus validating the very assumption of lumped capacitance modeling. This demonstrates that the lumped capacitance model can supplant the computationally demanding CFD modeling technique in predicting transient heat transfer phenomenon in solar food dryers.

Common-Mode Noise Modeling and Reduction for 1-MHz eGaN Multioutput DC–DC Converters

Enhancement-mode gallium nitride (eGaN) high-electron-mobility transistors (HEMTs) are promising to increase the switching frequency into multimegahertz for the high power density. However, it is a serious challenge to identify the equivalent lumped capacitances of megahertz multiwinding planar transformers for common-mode (CM) noise analysis to optimize the electromagnetic interference filters. The couple turn with its one-capacitor model is proposed to quantify the total CM noise current via the high-frequency transformer. With the modeled total CM noise current, the equivalent lumped interwinding capacitance model of the transformer can be derived conveniently and accurately. A complete CM noise path model is built for a GaN-based active clamp forward with a self-driven synchronous rectification multioutput converter. Then, a CM noise cancelation capacitance is applied and optimized to generate a reverse extraction current to cancel the CM noise current. Compared with other methods, the proposed modeling technique can build the equivalent lumped interwinding capacitance model of the multiwinding planar transformer in the printed circuit board layout stage before it is fabricated physically. The proposed model is verified by the experimental results with a 1-MHz GaN prototype with 100-V input, 5-V/6-A, and ±12-V/ 0.83-A outputs. The CM noise spectrum is well predicted. The CM noise is reduced by around 15 dB (a reduction of 12.6%) below 9 MHz.

The role of particle dopant to the thermal conductivities of PCM coconut oil by means of the T-history method

We described in this paper the role of chemical dopant to the thermal conductivity of organic phase change material (PCM) of coconut oil (co_oil) based on T-history method. We used the nanoparticle dopant, namely graphite, CuO, and ZnO. Each kind of dopant was added to co_oil in a certain amount of 1 wt% and 2 wt%. For comparison, the data of pure co_oil was also taken and compared to the data from direct measurement. Because of the smaller diameter to height ratio, the lumped capacitance method is applicable here. Hence, the heat transfer between PCM and water during solidification or melting process is one dimensional, so that the one-dimensional transient heat diffusion equation for cylindrical geometry is applicable. Analysis of the data for solidification and melting processes led to the values of solid and liquid thermal conductivities. We note that in general 1 wt% dopants have effectively increased the thermal conductivities of co_oil, which is important for the effective heat transport of the material in response to the heat from the environment. More increase of dopant concentration has resulted in the reduction of thermal conductivities, which might be due to the agglomeration of particle dopant due to van der Waals interaction between particles.

New EBG of CSRR with lumped capacitors applied to oscillator harmonics suppression

In this article, a compact electromagnetic band-gap (EBG) structure is presented to reject harmonics of a crystal oscillator in the power distribution network. Compared to traditional EBG structures of complementary split ring resonator (CSRR), the proposed CSRR adding lumped capacitors (LC-CSRR) provides a higher rejection-performance at the series self-resonant frequency of the lumped capacitors. A four-layer printed circuit board is designed and fabricated to measure the S-parameters of the proposed EBG structure, and a harmonics power testing board is presented to measure rejection performance of the proposed EBG structure. The measured results show that the proposed EBG obtains an attenuation of 60 dB over the whole range of global navigation satellite system band. By inserting the proposed EBG structure of LC-CSRR, we measure that the harmonics powers can be decreased by 28.8 dB between the input and output of the EBG.

Transient temperature distribution in pre-tensioned anchors of cable-supported structures under ISO834 fire

Anchors of steel cables consist of steel wires and filling materials, which provide wedge effect when the connected steel cable is in tension. The performance of steel cables and cable-supported structures significantly depends on the behavior of anchors, which becomes more serious when subjecting to fire. This paper investigates the transient temperature distribution in anchors exposed to ISO834 fire to provide references for predicting the mechanical behavior of anchors and steel cables at elevated temperatures. Firstly, experiments are conducted to determine the specific heat and thermal conductivity of filling materials such as zinc copper alloy for hot-cast anchors and mixture of epoxy resin and steel shot for cold-cast anchors. These measured thermal properties are then used for analytical calculation and numerical simulation. A formula to calculate the transient temperature distribution of fillers in hot-cast anchors is derived based on lump capacitance equilibrium and verified against numerical results. Numerical analyses of heat transfer in hot-cast and cold-cast anchors show that the heating rate of fillers is significantly lower than that of the socket wall. The temperature decreases along the longitudinal axis of anchors. The cross section of socket wall of hot-cast anchors has a non-uniform temperature distribution, while the filler part has a uniform temperature distribution. For cold-cast anchors, the socket wall has a uniform temperature distribution, while the filling materials have a significantly non-uniform temperature distribution. The geometry size of anchors has a minor effect on the heating rate of hot-cast anchors but significantly affects that of cold-cast anchors. The filling material of unprotected hot-cast and cold-cast anchors will reach its melting point less than 30 min when exposing to ISO834 fire.

A simplified analytical approach for concrete sensible thermal energy storages simulation

A simple lumped capacitance based computing model was developed and here presented. The code permits the thermal and energetic analysis of concrete thermal energy storages (TESs) during time. The simulated system consists of a parallelepiped concrete module that can be heated (charging phase) and cooled (discharging phase) by a single-phase working fluid flowing in a tube embedded in the concrete. The modules can be piled up in different configurations to build any desired TES. The new simulation code was validated against the experimental data carried out by ENEA with two different concrete mixtures, during both the heating and cooling processes using mineral oil as working fluid. Furthermore, on the basis of the energetic analysis, two different TES thermal efficiencies were proposed to evaluate the charge or discharge progresses over time. This simple and easy-to-use model allows for a drastic reduction of the computational time needed to simulate the TES and it can be easily integrated, in various arrangements, to any concentrated solar power plant (CSP) and associated energy conversion plant simulation models to have a quick evaluation of the whole system performance.

Effect of cavity radiation on transient temperature distribution in steel cables under ISO834 fire

This paper theoretically and numerically investigates the transient temperature distribution of steel cables. The effect of cavity radiation on the heat transfer through the air gap between steel wires of cables is taken into account. A simple calculation method is proposed based on the lump capacitance equilibrium to determine the temperature history in the center of steel cables. An equivalent parallel thermal resistance considering the cavity radiation and conduction is used to determine the total thermal resistance of wires. The accuracy of the proposed method is verified against numerical results from two-dimensional heat transfer analyses on cables with realistic cross sections under ISO834 fire. Parametric studies are conducted to investigate the effect of sectional dimension and cavity radiation on the temperature distribution of steel cables. The results show that the cavity radiation accelerates the heating rate of steel cables compared to round steel bar models. This indicates that it is not safe to directly use the traditional equivalent steel bar model to determine the temperature history of steel cables. It is found that the transient temperature distribution of steel cables is non-uniform. A higher central temperature of steel cables is achieved due to the cavity radiation effect compared to that of round steel bars. This temperature difference is also not monotonic and increases with increasing sectional dimension of cables.

A Comparison of Widespread Flexible Residential Electric Heating and Energy Efficiency in a Future Nordic Power System

Integrating ever-increasing amounts of variable renewable energy (VRE) into the power system could benefit from harnessing widespread residential demand-side management. This paper presents case studies on the potential benefits of power-to-heat (P2H) flexibility and energy efficiency improvements in a hypothetical future Finnish detached housing stock in the year 2030, both as a part of the larger Nordic power system and in an isolated Finnish power system. The housing stock was depicted using two archetype houses modeled using a simple lumped capacitance approach, integrally optimized as a part of a stochastic linear programming unit commitment model of the power system. With sufficient amounts of VRE, residential P2H with thermal storage was found to yield more system cost savings than simple energy efficiency improvements. However, energy efficiency improvements remained more beneficial for house owners, as excessive use of residential P2H for assisting the power system could result in increased heating costs.

Evaluation of convective heat transfer coefficient and specific heat capacity of a lithium-ion battery using infrared camera and lumped capacitance method

The electrochemical performance of lithium-ion batteries is highly temperature dependent. An accurate determination of battery thermal parameters is crucial for research including cell thermal analysis, safety design, and multiphysics simulations. This work explores the possibility to use a lumped capacitance model based experimental approach to measure the battery convective heat transfer coefficient and specific heat capacity. In this approach, the transient temperature of the battery and its can (by removing the jellyroll) is measured with an infrared radiation camera. When the Biot number of the battery Bi ≪1, the lumped capacitance model can be used to determine cell specific heat capacity through the measured battery surface temperature, where the convective heat transfer coefficients of both the can and the battery are the same and the specific heat capacity of the can is known. As an example, the specific heat capacity of LG G5 smartphone batteries is measured to demonstrate the proposed approach. The specimens are tested under both natural and forced convection conditions. The measured cell specific heat capacity is very consistent between these two convection conditions.

Effects of Transient Heat Transfer on Compressor Stability

The effects of heat transfer between the compressor structure and the primary gas path flow on compressor stability are investigated during hot engine re-acceleration transients. A mean line analysis of an advanced, high-pressure ratio compressor is extended to include the effects of heat transfer on both stage matching and blade row flow angle deviation. A lumped capacitance model is used to compute the heat transfer of the compressor blades, hub, and casing to the primary gas path. The inputs to the compressor model with heat transfer are based on a combination of full engine data, compressor test rig measurements, and detailed heat transfer computations. Nonadiabatic transient calculations show a 8.0 point reduction in stall margin from the adiabatic case, with heat transfer predominantly altering the transient stall line. 3.4 points of the total stall margin reduction are attributed to the effect of heat transfer on blade row deviation, with the remainder attributed to stage rematching. Heat transfer increases loading in the front stages and destabilizes the front block. Sensitivity studies show a strong dependence of stall margin to heat transfer magnitude and flow angle deviation at low speed, due to the effects of compressibility. Computations for the same transient using current cycle models with bulk heat transfer effects only capture 1.2 points of the 8.0 point stall margin reduction. Based on this new capability, opportunities exist early in the design process to address potential stability issues due to transient heat transfer.

Dual‐band circular polarised square‐ring patch antenna loaded lumped capacitors

Herein, a dual-band circularly polarised (CP) antenna for adjustable frequency ratio is proposed. The proposed antenna consists of two square-ring patches with a gap on the stacked substrates. A capacitor is inserted within the gap of each square-ring patch. The two square-ring patches have two resonant frequencies, because the additional resonant frequency is generated by the gap. The two first resonant frequencies of each square-ring patch combine to form the low band and two second resonant frequencies combine to make the high band. In the low band, as the gaps of the two square-ring patches are located on different diagonals, the two first resonant frequencies are orthogonal to each other. In the high band, as the second resonant frequency is perpendicular to the first resonant frequency, the two second resonant frequencies are also orthogonal to each other. In the measurement results, the low and high bands achieve -10 dB bandwidths (BWs) of 3.75 and 2.49%, 3 dB axial ratio BWs of 0.99 and 0.53%, and gains of 1.89 dBi and 0.64 dBi, respectively. By appropriately changing the values of two capacitors, frequency ratio has an available range from 1.065 to 1.336.

Signal Integrity Design and Analysis of Silicon Interposer for GPU-Memory Channels in High-Bandwidth Memory Interface

In this paper, for the first time, we designed and analyzed channels between a graphic processing unit and memory in a silicon interposer for a 3-D stacked high bandwidth memory (HBM). We thoroughly analyzed and verified the electrical characteristics of the silicon interposer considering various design parameters, such as the channel width and space, redistribution layer via, and under bump metallurgy pads. In particular, we also considered the meshed ground planes used for the proposed transmission lines, which are microstrip and strip lines. Signal integrity (SI) of the proposed channels in the silicon interposer was successfully analyzed and verified using a full 3-D electromagnetic solver and circuit simulations. Based on the extracted lumped circuit resistance, inductance, conductance and capacitance parameters, we thoroughly analyzed the channel characteristics and identified the parameters that dominantly affect SI in relation to each frequency range. From the analyzed insertion loss and far end crosstalk, we verified SI of the silicon interposer by eye-diagram simulations in terms of eye-height voltage and timing jitter in the time domain. In the worst case, the eye-height voltage and timing jitter of the proposed microstrip lines are 0.911 V and 36.8 ps, respectively, with 72 mV of signal coupling. The eye-height voltage and timing jitter of the proposed strip line are 0.887 V and 42.1 ps with 34 mV of single couplings. We show that the proposed channels of the silicon interposer can successfully transfer data at a 2-Gb/s data rate. Finally, we propose concepts and solutions for the next-generation HBM interface with higher data rates up to 8 Gb/s.

Insertion Loss Characterization of Impedance Matching Networks for Low-Power Rectennas

An impedance matching network inserted between an antenna and a rectifier is essential for rectennas, but few studies have characterized the insertion loss of the matching network if nonideal matching elements are considered. In general, the matching elements, including lumped capacitors, lumped inductors, and transmission lines, are approximated as lossless; if the overall conversion efficiency decreases, the underlying reason seldom attributes to the loss of the matching network. In this paper, we derive the insertion loss of the matching network comprising actual lumped elements and transmission lines. The loss is quantified using the operating power gain of a two-port network, which varies with different levels of input power. When the input power ranges between −30 and 0 dBm, more than 95%, 90%, and 75% of power dissipates at 900 MHz, 1.8 GHz, and 2.4 GHz, respectively, due to the use of actual matching elements. The numerical results are verified by experimental data, and all the analyses demonstrate that the loss of the matching network becomes very serious as the input power is low. These observations are explained using the contour plot of operating power gain. Accordingly, this study provides a theoretical development for rectenna designers.