Study of the ceramic capacitor dielectric for pulsed power

The discrete mapping model of current‐mode controlled buck converter with constant current load, taking account of composite output capacitors (parallel connection of two different types of capacitor branches, i.e. electrolytic capacitors and ceramic capacitors), is established. Based on the model, dynamical effects of varying output capacitance and equivalent series resistance (ESR) are investigated by bifurcation behaviours. The period of low‐frequency oscillation among coexisting fast‐slow scale instability is derived by exploring the loci of eigenvalues, while the operating regions are estimated. Time‐domain simulation and experimental waveforms are provided for verification of the theoretical analysis, indicating the existences of subharmonic oscillation and coexisting fast‐slow scale instability in the converter with variation of output capacitance and ESR. Research results reveal that the low‐frequency oscillation can be eventually eliminated due to a relatively large (or small) ESR and the capacitance in the same branch presents to identical tendency of dynamical effects on the converter. Moreover, the interaction effects between two parallel capacitor branches are demonstrated. It illustrates that the low‐frequency oscillation can be removed with smaller (or larger) ESR or capacitance in one branch of the composite output capacitors while larger (or smaller) ESR or capacitance in the other branch.

Microstructure and dielectric characteristics of Nb2O5 doped BaTiO3-Bi(Znl/2Til/2)O3 ceramics for capacitor applications

Oil spill cleanup and subsequent restoration of the environment is majorly a function of spill cleanup methods applied. Some of these methods, though efficient, are, however, very expensive and require more personnel for their application and relative deployment in the field. The study was aimed at examining the efficiency of a locally and readily available, eco-friendly and low cost agricultural waste (coconut husk coir) as sorbent materials for spilled engine oil cleanup under static and dynamic marine water conditions. The sorbent material was prepared and used in three forms: raw coconut husk coir (CHC), modified coconut husk coir (MCHC), and reused coconut husk coir (RCHC). Under static and dynamic marine water conditions, oil sorption batch equilibrium experiments were used to study the engine oil sorption capacity and efficiency of the sorbent. Effects of sorbent dosage and sorption times on the oil sorption and efficiency of CHC, MCHC, and RCHC were studied and determined. At a constant sorption time of 60 minutes and varying sorbent dosages of 2-8 /320 ml of engine oil-marine water concentration, MCHC exhibited the highest oil sorption efficiency of 61.18% and 44.33% for dynamic and static conditions, CHC had 55.61% and 38.50% for dynamic and static conditions, whereas RCHC had 41.66% and 26.04% for dynamic and static conditions, respectively. It is statistically deduced from the results that sorption times and sorbent dosages have significant effects on the sorption efficiency of experimental coir for spilled engine oil removal. Though there is a need for proper blending or modifications of the sorbent material to enhance its affinity to oil and hydrophobicity, there are enough potentials in the materials for mild marine water current spilled engine oil cleanup.

Multilayer ceramic capacitors (MLCC) have wide application in electronic due to its electrical characteristics: low equivalent series resistance (ESR) and high volume efficiency. One of the MLCC manufacturing problems is the choice of composition for the end pastes. The experimental results of the termination pastes composition influence on the quality high-voltage MLCC investigation are presented. The causes of the defects appearance in the termination are determined, the composition of the termination paste, which ensures the quality contact of the internal electrode with the external, is proposed.

An advanced capacitor using SiC as the dielectric material has been developed for high temperature, high power, and high density electronic components for aircraft and aerospace application. The conventional capacitor consists of a large number of metallized polysulfone films that are arranged in parallel and enclosed in a sealed metal case. However, problems with electrical failure, thermal failure, and dielectric flow were experienced by Air Force suppliers for the component and subsystem for lack of suitable properties of the dielectric material. The high breakdown electrical field, high thermal conductivity, and high temperature operational resistance of SiC compared to similar properties of the conventional ceramic and polymer capacitor would make it a better choice for a high temperature, and high power capacitor. The quality of the SiC film was evaluated. The electrical parameters, such as the capacitance, dissipation factor, equivalent series resistance, and dielectric withstand voltage, were evaluated. The prototypical capacitors are currently being fabricated using SiC film.

Cells sense and respond to scaffold pore geometry and mechanical stimuli. Many fabrication methods used in bone tissue engineering render structures with poorly controlled pore geometries. Given that cell-scaffold interactions are complex, drawing a conclusion on how cells sense and respond to uncontrolled scaffold features under mechanical loading is difficult. In this study, monodisperse templated scaffolds (MTSC) were fabricated and used as well-defined porous scaffolds to study the effect of dynamic culture conditions on bone-like tissue formation. Human bone marrow-derived stromal cells were cultured on MTSC or conventional salt-leached scaffolds (SLSC) for up to 7 weeks, either under static or dynamic conditions (wall shear stress [WSS] using spinner flask bioreactors). The influence of controlled spherical pore geometry of MTSC subjected to static or dynamic conditions on osteoblast cell differentiation, bone-like tissue formation, structure, and distribution was investigated. WSS generated within the two idealized geometrical scaffold features was assessed. Distinct response to fluid flow in osteoblast cell differentiation were shown to be dependent on scaffold pore geometry. As revealed by collagen staining and microcomputed tomography images, dynamic conditions promoted a more regular extracellular matrix (ECM) formation and mineral distribution in both scaffold types compared with static conditions. The results showed that regulation of bone-related genes and the amount and the structure of mineralized ECM were dependent on scaffold pore geometry and the mechanical cues provided by the two different culture conditions. Under dynamic conditions, SLSC favored osteoblast cell differentiation and ECM formation, whereas MTSC enhanced ECM mineralization. The spherical pore shape in MTSC supported a more trabecular bone-like structure under dynamic conditions compared with MTSC statically cultured or to SLSC under either static or dynamic conditions. These results suggest that cell activity and bone-like tissue formation is driven not only by the pore geometry but also by the mechanical environment. This should be taken into account in the future design of complex scaffolds, which should favor cell differentiation while guiding the formation, structure, and distribution of the engineered bone tissue. This could help to mimic the anatomical complexity of the bone tissue structure and to adapt to each bone defect needs. Impact statement Aging of the human population leads to an increasing need for medical implants with high success rate. We provide evidence that cell activity and the amount and structure of bone-like tissue formation is dependent on the scaffold pore geometry and on the mechanical environment. Fabrication of complex scaffolds comprising concave and planar pore geometries might represent a promising direction toward the tunability and mimicry the structural complexity of the bone tissue. Moreover, the use of fabrication methods that allow a systematic fabrication of reproducible and geometrically controlled structures would simplify scaffold design optimization.

This paper describes an automated test configuration that is used for rapid characterization of the equivalent series resistance (ESR) of ceramic multilayer capacitors. The primary components in this system are a coaxial resonant line, an HP 8753D vector network analyzer, and a personal computer. Sample measurements are provided for several 1206 style capacitors, and the trends in ESR versus the internal capacitor architecture are presented.

With population growth, increasing world energy demand and depletion of conventional oil resources, exploiting heavy and extra-heavy oil reservoirs seems one of the promising options in supplying world oil request. However, there are several barriers to the rapid growth of production from such reservoirs. CO2-based enhanced oil recovery (CO2-EOR) techniques are among processes utilized to enhance heavy oil and bitumen production. The design and modeling of CO2-EOR require extensive knowledge about the solubility and diffusivity of CO2 in heavy oil. Hence the primary objective of this research was to identify the main mechanisms involved in the static and dynamic mass transfer of CO2 into the heavy oil systems. This experimental study commenced by allowing CO2 to be in contact at static condition with two different types of heavy oil having viscosities of 5000 and 20000 cP at 298 K. Experiments were conducted at three different initial pressures (1.73, 3.10, 4.49 mPa) and pressure decay concept was used to determine the CO2 solubility for each individual case. The experiments then were extended using a Mini-bench top reactor (PARR-4560) from Parr Instrument Company to repeat similar tests in dynamic condition. Using the reactor's stirrer, the oil was agitated at the velocity of 30 rpm; thereby a semi-flowing condition was generated leading a convection effect in the oil bulk phase. For both dynamic and static conditions, the proper mathematical model were proposed and solved numerically to determine the diffusion coefficient value at each specific operating condition. Results showed that the solubility of CO2 at initial pressure of 1.73 mPa for 5000cP oil is 0.04015, and 0.04195 g/100cc for static and dynamic conditions, respectively. The diffusion coefficient value at static and dynamic condition for the same experimental condition is 4.531×10-10 m/s2 and 4.852×10-10 m/s2. Experimental and mathematical interpretations of other cases showed similar behaviour. From the results at both conditions it can be obtained that the initial pressure has significant effect on reaching the stability condition and longer time is required for higher pressures. Moreover, diffusion coefficient is more sensitive to oil viscosity rather than ultimate solubility value.

In the traditional Constant-On-Time (COT) control mode, the output bypass capacitor mostly uses ceramic capacitors, and its equivalent series resistance (ESR) is small, the phase of output voltage ripple lags behind the inductor current, causing system instability. For this reason, this paper adopts the ripple compensation technology. By injecting the external ramp and the internal inductor current ramp, a virtual resistance is introduced for the ESR, and the resistance value of the ESR is increased to meet the stability conditions. The chip is designed based on 18V 0.1Sum BCD process. The simulation results show that when the input voltage is 12V and the temperature is 27°C, the system conversion efficiency can reach 97%, and the system output voltage ripple is about 3.4mV.

Nonlinear transmission lines -NLTLs are promising as a high-power RF source in radars, battlefield communication disruption, satellites, biomedical instrumentation, and other communication systems [1–2]. Another way to produce the RF signals on NLTL is using nonlinear components such as ceramic capacitors. In this work, we synthesized and characterized a barium zirconium titanate ceramic for use in nonlinear dielectrics. Its application is in NLTLs due to their high permittivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&gt; 5000$</tex> in the phase temperature transition with low tangent loss <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&lt; 0.07$</tex> . The electrical characterization investigated in this work is in temperature, frequency, and DC voltage sweep, which give the nonlinearity factor of ceramic, a key parameter to produce RF in NLTL, and the dielectric strength to know the breakdown voltage in the pulsed power systems.

Arc spray method has been widely used as contact layer forming method for lead welding in metallized film capacitor. The materials used as contact layer are Zn and Zn-Sn alloy etc. Metallized film capacitor show the change of electrical properties, particularly, equivalent series resistance (E.S.R) and dissipation factor (tan /spl delta/) with spray conditions of spray air pressure, material feeding speed and applied voltage. In this study, morphology, size and temperature of sprayed particles were measured and their effects on electrical properties were investigated. The size of particles is about 50 /spl mu/m to 80 /spl mu/m and the shapes of many particles is irregular form. The uniform small particles sprayed at 4bar were deposited densely, therefore, the capacitors made of these particles had low equivalent series resistance and low dissipation factor. After withstand current test, the capacitors with contact layer of smaller particle size show the smaller change of capacitance and dissipation factor.

The aim of this paper is to present two very simple, cheap, and practical experimental techniques that are able to estimate the capacitor equivalent circuit for a wide range of frequencies and temperatures. The capacitor equivalent circuit considerably changes with temperature, aging, and frequency. Therefore, knowledge of their equivalent circuit at their operating conditions can lead to better design proposals. In addition, knowledge of the evolution of the equivalent series resistance (ESR) with temperature is essential for the development of reliable online fault diagnosis techniques. This issue is particularly important for aluminum electrolytic capacitors, since they are the preferred capacitor type in power electronics applications and simultaneously one of the most critical components in such applications. To implement the first technique, it is necessary to put the capacitor under test in series with a resistor and connect it to a sinusoidal voltage. The second technique requires a simple charge-discharge circuit. After acquiring both capacitors' current and voltage through an oscilloscope, which is connected to a PC with Matlab software, it is possible to compute both capacitor capacitance and resistance using the least mean square (LMS) algorithm. To simulate the variation of capacitor case temperature, a very simple prototype was used. Several experimental results were obtained to evaluate the accuracy and precision of the two experimental techniques.

Due to their substantial energy density and economical pricing, switching-mode power supplies (SMPSs) often utilize electrolytic capacitors. However, their ability to function at low temperatures is essential for dependable operation in several sectors, including telecommunications, automotive, and aerospace. This study includes an experimental evaluation of how well standard SMPS electrolytic capacitors operate at low temperatures. This paper investigates the suitability of standard electrolytic capacitors used in switched-mode power supplies (SMPSs) for low-temperature applications. The experimental evaluation exposed the capacitors to temperatures ranging from −5 °C to −40 °C, assessing capacitance (Cp), impedance (Z), dissipation factor (DF), and equivalent series resistance (ESR) at each temperature. The capacitor’s time-domain electrical signals were analyzed using the Pearson correlation coefficient to extract discriminative features. These features were input into an artificial neural network (ANN) for training and testing. The results indicated a significant impact of low temperatures on capacitor performance. Capacitance decreased with lower temperatures, while the ESR and leakage current increased, affecting stability and efficiency. Impedance was a valuable diagnostic tool for identifying potential capacitor failure, showing a 98.44% accuracy drop at −5 °C and 88.75% at the peak temperature, indicating proximity to the manufacturer’s specified limit. The study suggests further research and development to improve the performance of electrolytic capacitors in SMPS systems under cold conditions, aiming to boost efficiency and reliability.

A study of ceramic addition in end termination of multilayer ceramics capacitors with cofiring process

Paolo Nora Paolo Nora, co-author of the paper “A novel sufficient condition to avoid sub-harmonic oscillations for Buck converters with constant on-time control” talks to us about their work page 305. I am part of the Architecture Definition Team of the Analogue Power and Interface Division (APID) of Microchip Technology Inc., and I collaborated with Profs. Bizzarri and Brambilla of the Politecnico di Milano on the topic of stable operation of Constant-ON-Time (COT) control, which is one of the most common control methods for analogue point-of-load (POL) Buck regulators. Indeed, my main area of interest is the architectural definition of analogue switch-mode regulators. A few years ago, I became aware of the topic of power integrity for my field of work. Both areas are very closely related, since POL regulators are often deployed in applications where power integrity considerations become increasingly critical for a successful power system design. The topic of Constant-ON-Time (COT) control, and – more generally – of ripple-based control of Buck converters has been a major focus for many power electronics researchers in the last few years, and different analysis methods have been used to determine its stability conditions. The importance of COT control (and its variations) of Buck POL converters is huge, due to the popularity of this control method in the industry. The reasons for such a wide popularity mainly stem from its superior load-transient performance over fixed-frequency architectures, and in the apparently simple design process it takes to develop the application. Simply put, the key design aspect is the phase relationship between the output voltage ripple fed to the controller and the Buck inductor current ripple. In addition, the total magnitude of the ripple seen by the controller plays an important role and must be adequate to ensure jitter-free operation. However, over many application cases encountered in practice, we've only seen a few of them being affected by confirmed instability issues (pulse-bursting operation) despite all recommended design practices being followed. This pushed us to consider different analysis methods to assess stability conditions, and here is where the nonlinear dynamical systems analysis expertise of profs. Bizzarri and Brambilla came to the fore. By using the state-variables methodology and state-plane graphical representations, and by leveraging nonlinear dynamical systems theory results, a new and more articulated sufficient condition for stable operation of the COT Buck converter was derived. This condition includes both circuit parameters and operating conditions. We have also shown that the well-known output capacitor time constant stability criterion is encompassed by the new sufficient condition. State-space analysis is a powerful method; however, its complexity rapidly explodes as the number of state variables increases. For the sake of manageability, the source of ripple fed to the COT control engine had to be limited to the resistor Re in series with the output capacitor, neglecting other well-known methods of ripple self-generation which would have added more state variables (i.e. more capacitors). The big question was then whether the simplified configuration would still be relevant from the practical perspective. Here is where some power integrity concepts, such as flat-impedance design of the POL stage and the power distribution network (PDN), played a key role. Indeed, resistor Re in series with the output capacitor may not just be a poorly controlled parasitic element – such as the equivalent series resistance (ESR) of an ordinary multi-layer ceramic capacitor (MLCC). In power-integrity-aware POL and PDN designs, the value of Re is intentionally controlled and – in some cases – it could even be implemented with a physical resistor. Also, if the POL stage is dedicated to some digital loads which are not particularly sensitive, the magnitude of the output voltage ripple generated by Re could also be adequate for a real-world application. We can conclude that the analysis of the simplified configuration presented in this Letter will become increasingly relevant as power integrity considerations will affect more and more POL/PDN designs. Another major challenge was experimental verification, whose description unfortunately exceeds the scope of the Letter. The state-variables method and the state-plane representation lend themselves very well to model rapid load transients and can predict the maximum load step that can be applied without saturating the COT control engine (i.e. engaging the minimum OFF time). This is also a new result and it is of utmost practical importance. Simply put, the outcome is that it should only take a very small load step to saturate the COT engine. If this does not happen, then it means that the design – for some reason – is not exploiting the full potential of COT control, and this should raise a red flag to the designer. As previously mentioned, this topic has attracted the attention of many researchers in power electronics over the last 10–15 years and there is a wealth of excellent, highly technical literature out there. I have to say that the perception of COT control is too simplistic for many practicing engineers: just make sure the controller is seeing enough voltage ripple, and that voltage ripple is in-phase with the inductor current ripple, and you're done! Unfortunately, experience reveals that the situation is not so simple. The challenge is how to convey all the highly technical results to a large community of users who simply do not have the time to dig into the fine details of POL design. The focus of many practicing engineers is not analogue design, not to mention POL design. Therefore, in the future, I see the highly technical analysis methods and results becoming available from the websites of many semiconductor vendors in the form of software tools as an extra aid for POL design verification, beyond the simple sets of equations provided by most datasheets. I also believe that the topic of digital implementation of COT-control and ripple-based control and their modeling will also grow exponentially.