A Nonlinear Least Squares Fit procedure for analysis of immittance data of electrochemical systems

A Nonlinear Least Squares Fit (NLLSF) program is described, with which frequency dispersion data of electrochemical systems can be analyzed in terms of an equivalent circuit. The NLLSF procedure uses a combination of an analytical and gradient search according to the Marquardt algorithm. Through the use of an unique Circuit Description Code (CDC) different equivalent circuits may be used with the program. The use of an analytical derivatives routine enhances the execution speed. The power of such a fit procedure is demonstrated in multi parameter fits, on synthetic and real data, performed by the program “EQIVCT”

Design of a CMOS closed-loop system with applications to bio-impedance measurements

This paper proposes a method for impedance measurements based on a closed-loop implementation of CMOS circuits. The proposed system has been conceived for alternate current excited systems, performing simultaneously driving and measuring functions, thanks to feedback. The system delivers magnitude and phase signals independently, which can be optimized separately, and can be applied to any kind of load (resistive and capacitive). Design specifications for CMOS circuit blocks and trade-offs for system accuracy and loop stability have been derived. Electrical simulation results obtained for several loads agree with the theory, enabling the proposed method to any impedance measurement problem, in special, to bio-setups including electrodes.Ministerio de Ciencia e Innovación TEC2007-6807

Measurement Procedures for the Electrical Characterization of Oxide Thin Films

This paper describes a measurement system for the electrical characterization of oxide thin films. Such films can be produced using plasma-sputtering processes and permit the realization of a large set of high-performance components, such as capacitors, active devices, sensors, and protective coatings. The electrical properties of the oxide films, which have a thickness of less than 1 μm, are difficult to measure since very high resistances (on the order of gigaohms) and small capacitances (on the order of picofarads) are expected for contact areas smaller than 1 mm2. The measurement system and the procedures described in this paper represent an alternative solution to the commercial devices, which usually employ a mercury probe for performing the contact with the specimen under characterization. Furthermore, the proposed system can be used not only to estimate the electrical properties of a single point but to evaluate the uniformity of oxide films on large specimens as well. The experimental results reported refer to valve-metal-based oxide films deposited in a lab-scale capacitively coupled parallel-plate reactor and show the effectiveness of the proposed procedure

Kalman-variant estimators for state of charge in lithium-sulfur batteries

Lithium-sulfur batteries are now commercially available, offering high specific energy density, low production costs and high safety. However, there is no commercially-available battery management system for them, and there are no published methods for determining state of charge in situ. This paper describes a study to address this gap. The properties and behaviours of lithium-sulfur are briefly introduced, and the applicability of ‘standard’ lithium-ion state-of-charge estimation methods is explored. Open-circuit voltage methods and ‘Coulomb counting’ are found to have a poor fit for lithium-sulfur, and model-based methods, particularly recursive Bayesian filters, are identified as showing strong promise. Three recursive Bayesian filters are implemented: an extended Kalman filter (EKF), an unscented Kalman filter (UKF) and a particle filter (PF). These estimators are tested through practical experimentation, considering both a pulse-discharge test and a test based on the New European Driving Cycle (NEDC). Experimentation is carried out at a constant temperature, mirroring the environment expected in the authors' target automotive application. It is shown that the estimators, which are based on a relatively simple equivalent-circuit–network model, can deliver useful results. If the three estimators implemented, the unscented Kalman filter gives the most robust and accurate performance, with an acceptable computational effort

Influence of X-ray Irradiation on the Properties of the Hamamatsu Silicon Photomultiplier S10362-11-050C

We have investigated the effects of X-ray irradiation to doses of 0, 200 Gy, 20 kGy, 2 MGy, and 20 MGy on the Hamamatsu silicon-photomultiplier (SiPM) S10362-11-050C. The SiPMs were irradiated without applied bias voltage. From current-voltage, capacitance/conductance-voltage, -frequency, pulse-shape, and pulse-area measurements, the SiPM characteristics below and above breakdown voltage were determined. Significant changes of some SiPM parameters are observed. Up to a dose of 20 kGy the performance of the SiPMs is hardly affected by X-ray radiation damage. For doses of 2 and 20 MGy the SiPMs operate with hardly any change in gain, but with a significant increase in dark-count rate and cross-talk probability.Comment: 21 pages,30 figure

Techniques for improving the accuracy of cyrogenic temperature measurement in ground test programs

The performance of a sensor is often evaluated by determining to what degree of accuracy a measurement can be made using this sensor. The absolute accuracy of a sensor is an important parameter considered when choosing the type of sensor to use in research experiments. Tests were performed to improve the accuracy of cryogenic temperature measurements by calibration of the temperature sensors when installed in their experimental operating environment. The calibration information was then used to correct for temperature sensor measurement errors by adjusting the data acquisition system software. This paper describes a method to improve the accuracy of cryogenic temperature measurements using corrections in the data acquisition system software such that the uncertainty of an individual temperature sensor is improved from plus or minus 0.90 deg R to plus or minus 0.20 deg R over a specified range

Behavioral modeling of digital IC input and output ports

This paper addresses the development of accurate and efficient behavioral models of digital integrated circuit input and output ports for signal integrity simulations and timing analyses. The modeling process is described and applied to the characterization of actual device