Fast Impedance Measurements Research Articles

Fast impedance measurement method for large capacity batteries using chirp and filtered pseudo-random binary sequence

Fast impedance measurement with well-constructed excitation signals is crucial for battery internal states analysis and faults diagnosis. The pseudo-random binary sequence (PRBS) is a promising time-efficient excitation signal, but it lacks power content in the low-frequency range and is susceptible to high-frequency harmonics beyond the measurement limits, especially for square large-capacity batteries. Motivated by this, this paper proposes a novel parallel-connected signal derived from filtered PRBS and chirp sequence to boost low-frequency components while mitigating high-frequency effects. Meanwhile, to enhance accuracy in measuring square large-capacity batteries with low impedance, the paper introduces a differential amplification circuit to improve voltage response robustness against noise. Experimental results confirm the effectiveness of this method, achieving precise impedance measurements across the 0.1 Hz–1000 Hz range in just 10.24 s. With different states of charges, temperatures, and battery types, errors of the measurement are below 3.67 %.

Voltage Hysteresis Cancellation for Fast Impedance Measurements of Lithium-ion Batteries in Short Relaxation Process

Voltage Hysteresis Cancellation for Fast Impedance Measurements of Lithium-ion Batteries in Short Relaxation Process

Development of a battery real-time state of health diagnosis based on fast impedance measurements

The capability to assess and monitor the state of health (SOH) of lithium-based cells is a highly demanded feature for advanced battery management systems. Due to the existing relation between SOH and internal impedance, electrochemical impedance spectroscopy (EIS) methods are adopted for SOH diagnosis. Nevertheless, accurate EIS tests demand expensive facilities, long time test procedures, and algorithms with high-computational efforts, which makes them almost unsuitable for on-board systems. This paper presents a new diagnostic method aimed at detecting battery SOH using fast impedance measurements. Key factor is the application of a broadband current signal excitation on the battery; for the application here presented, a pseudo-random binary sequence (PRBS) excitation is adopted. To demonstrate the functionalities of a prototype testbed, several cells of the same manufacturer but presenting different SOHs, due to their past load history, have been subjected to the EIS test, acquiring voltage response under imposed excitation. Finally, test results have been processed: the key step being the clustering of impedance measurements (represented in Nyquist diagram) in different rectangular areas, which are related to actual SOH. The performed experimental test results showed the possibility to determine frequency points in which the impedance measurements dramatically change due to different cell SOH; as a consequence, these peculiar frequencies can be adopted as reference for cluster separation. According to the results here presented, the proposed method is sufficiently accurate and is a promising solution for real-time diagnostic of battery SOH.

A fast measurement of Warburg-like impedance spectra with Morlet wavelet transform for electrochemical energy devices

Fast impedance measurement via complex Morlet wavelet transform (CMWT) offers a valuable way for real-time diagnosis and in-situ monitoring on electrochemical energy devices. However, it normally suffers from a dilemma: how to set CMWT parameters such as sampling duration Tp, sampling frequency fs, scale factor range A, central frequency fc, and band factor fb? Especially for a fast measurement of Warburg-like impedance spectra. Thus, optimal theories are needed in order to acquire Warburg-like impedance spectra rapidly under a required precision and a given frequency range. In this paper, the optimal rules for a fast impedance measurement are developed based on the uncertainty principle: 1) 2.5/fL ≤ Tp ≤ 3.0/fL; 2) fs ≥ 20fU; 3) 1.0/fc≤fb≤1.4/fc where fL and fU are the lower-limit and upper-limit frequencies of the impedance spectra, respectively. Subsequently, measurement errors are quantitatively evaluated for the reconstructed impedance spectra via CMWT algorithm. Through the derived optimal rules, a fast measurement with Tp = 28.0 s and fs = 20.0 kHz is implemented for Warburg-like impedance spectra from 0.1 Hz to 1.0 kHz and with the average errors of 0.7% and 2.6% for magnitude and phase, respectively. The developed method creates a higher possibility for real-time diagnosis and in-situ monitoring of electrochemical energy devices in electric vehicles (EVs).

Fast blood impedance measurements as quality indicators in the pre-analytical phase to prevent laboratory errors

<p class="Abstract">In clinical laboratories the major quantity of errors regarding blood analyses occurs in the pre-analytical phase. Pre-analytical conditions are key necessary factors to maintain the high quality of specimens, to limit day-to-day and batch variations and to guarantee the absolute reliability and accuracy of clinical results and related diagnoses. The quality of the serum samples would have to be very high in order to avoid interferences due to hemolysis, preventing measurement errors. In addition, the quality of blood should be always monitored in a fast way to identify inadequacies and guarantee their complete usability in transfusion procedures. In a near future the solution could be supplying laboratories with smart and portable devices able to rapidly perform quality tests for every samples. Electrical impedance has a relevant potential in analyzing and monitoring blood quality. In this context, we propose a new simple impedance-based biosensor as a possible solution in the pre-analytical phase to efficiently perform fast impedance measurements, useful indicators to check the quality of the samples, ensuring the reliability of results and preventing laboratory errors. This sensor has been applied for the discrimination of different blood components, the identification of hemolysis in serum and the evaluation of blood consistency.</p>

Fast impedance measurements at very low frequencies using curve fitting algorithms

The method for reducing the time of impedance measurements at very low frequencies was proposed and implemented. The reduction was achieved by using impedance estimation algorithms that do not require the acquisition of the momentary voltage and current values for at least one whole period of the excitation signal. The algorithms were based on direct least squares ellipse and sine fitting to recorded waveforms. The performance of the algorithms was evaluated based on the sampling time, signal-to-noise (S/N) ratio and sampling frequency using a series of Monte Carlo experiments. An improved algorithm for the detection of the ellipse direction was implemented and compared to a voting algorithm. The sine fitting algorithm provided significantly better results. It was less sensitive to the sampling start point and measured impedance argument and did not exhibit any systematic error of impedance estimation. It allowed a significant reduction of the measurement time. A 1% standard deviation of impedance estimation was achieved using a sine fitting algorithm with a measurement time reduced to 11% of the excitation signal period.

ERT Investigation on Horizontal and Vertical Counter-gravity Slurry Flow in Pipelines

Abstract The occurrence of separation and slippage of the two phases in settling solid-liquid flow in pipelines make the flow unpredictable and time dependent. Therefore it is paramount for the operator of slurry pipelines to monitor and measure the flow continuously, particularly from the local point of view. This paper reports the laboratory experiments carried out on an open flow loop and the use of Electrical Resistance Tomography (ERT) to interrogate the internal structure of horizontal and vertical counter-gravity slurry flow. The use of high performance dual-plane ERT system, which is called Fast Impedance Camera System (FICA), is attempted for fast impedance measurement of the media with a temporal resolution up to 1000 dual-frames per second (dfps). The internal images of the pipeline are captured along with the measurement of solids volumetric concentration for both orientations, while the dualplane ERT is combined with cross-correlation technique to estimate axial solids velocity distribution. A set of experiments was carried out on coarse and medium sand-water slurry flow with 2% and 10% throughput volumetric concentration and the transport velocity range of 1.5-5 m/s. A flow diversion technique was used for validation of mean local solids concentration and solids axial velocity obtained from the ERT.

New approach for the calculation of impedance spectra out of time domain data

A technique for fast impedance measurement in the time domain is presented. It is based on the Fourier transformation and includes various improvements compared to previous work in the literature. Namely, it minimizes the influence of spectral leakage and aliasing and reduces noise. This is proved by the theoretical error estimate for different model systems. The technique is independent of the excitation signal and is demonstrated by a voltage step. Measurement results for a commercial Li-ion cell are presented and compared with results obtained by electrochemical impedance spectroscopy. Finally, a combination of the two techniques is proposed to cover a wide frequency range in minimum measurement time for the characterization of electrochemical systems.

Front end with offset-free symmetrical current source optimized for time domain impedance spectroscopy

Fast impedance measurements are often performed in time domain utilizing broad bandwidth excitation signals. Other than in frequency domain measurements harmonic distortion cannot be compensated which requires careful design of the analog front end. In order to minimize the influence of electrode polarization and noise, especially in low-frequency measurements, current injection shows several advantages compared to voltage application. Here, we show an active front end based on a voltage-controlled current source for a wide range of impedances. Using proper feedback, the majority of the parasitic capacitances are compensated. The bandwidth ranges from dc to 20 MHz for impedance magnitude below 5 kΩ. The output is a symmetric signal without dc-offset which is accomplished by combination of a current conveyor and a voltage inverter. An independent feedback loop compensates the offset arising from asymmetries within the circuitry. We focused especially on the stability of the current source for usage with small metal electrodes in aqueous solutions. At the monitor side two identical, high input impedance difference amplifiers convert the net current through the object and the voltage dropping across into a 50 Ω symmetric output. The entire circuitry is optimized for step response making it suitable for fast time domain measurements.

Impedance Measurements as a Simple Tool to Control the Quality of Conjugated Polymers Designed for Photovoltaic Applications

AbstractThe problem of batch‐to‐batch variation of electronic properties and purity of conjugated polymers used as electron donor and photon harvesting materials in organic solar cells is addressed. A simple method is developed for rapid analysis of electronic quality of polymer‐based materials. It is shown that appearance of impurities capable of charge trapping changes electrophysical properties of conjugated polymers. In particular, a clear correlation between the effective relaxation time τeff and relative photovoltaic performance (η/ηmax) is revealed for samples of poly(3‐hexylthiophene) intentionally polluted with a palladium catalyst. This dependence is also valid for all other investigated samples of conjugated polymers. Therefore, fast impedance measurements at three different frequencies allow one to draw conclusions about the purity of the analyzed polymer sample and even estimate its photovoltaic performance. The developed method might find extensive applications as a simple tool for product quality control in the laboratory and industrial‐scale production of conjugated polymers for electronic applications.

Characterizing aging effects of lithium ion batteries by impedance spectroscopy

Impedance spectroscopy is one of the most promising methods for characterizing aging effects of portable secondary batteries online because it provides information about different aging mechanisms. However, application of impedance spectroscopy “in the field” has some higher requirements than for laboratory experiments. It requires a fast impedance measurement process, an accurate model applicable with several batteries and a robust method for model parameter estimation. In this paper, we present a method measuring impedance at different frequencies simultaneously. We propose to use a composite electrode model, capable to describe porous composite electrode materials. A hybrid method for parameter estimation based on a combination of evolution strategy and Levenberg–Marquardt method allowed a robust and fast parameter calculation. Based on this approach, an experimental investigation of aging effects of a lithium ion battery was carried out. After 230 discharge/charge cycles, the battery showed a 14% decreased capacity. Modeling results show that series resistance, charge transfer resistance and Warburg coefficient changed thereby their values by approximately 60%. A single frequency impedance measurement, usually carried out at 1 kHz, delivers only information about series resistance. Impedance spectroscopy allows additionally the estimation of charge transfer resistance and Warburg coefficient. This fact and the high sensitivity of model parameters to capacity change prove that impedance spectroscopy together with an accurate modeling deliver information that significantly improve characterization of aging effects.

Detecting endocrine-disrupting compounds by fast impedance measurements.

The increasing concern worldwide over the adverse effects of endocrine disruptors on human health has created a need for screening systems to detect xenoestrogens, a diverse group of environmental chemicals that mimic estrogenic actions and are hypothesized to decrease male fertility. Here, we describe a novel, class-selective detector that uses fast impedance measurements to monitor the binding of estrogen and xenoestrogens to a native estrogen receptor. We embedded the receptor in synthetic lipid bilayers attached to gold electrodes. The lipid bilayers serve as electrical circuits constructed of resistors and capacitors. Estrogen binding to the receptor-modified electrode is immediately followed by conformational changes in the lipid layer, leading to alterations of the electrical circuit components that are detected by fast impedance measurements. The electrochemical system enabled characterization of changes in the bilayer structure and quantification of estrogen binding to the receptor. To assess the effectiveness of the method for detecting environmental estrogenic chemicals, we chose two classes of xenoestrogens: bisphenol A, a synthetic xenoestrogen, and genistein, a phytoestrogen. This system is highly sensitive and amenable to use in the field, providing an efficient and economic tool for measuring minuscule amounts of endocrine-disrupting chemicals in environmental or human samples.

Fast Impedance Analysis of a Surface Microstructure during Anodic Oxidation of a Copper/Gold Alloy

The anodic oxidation of ordered Cu/Au alloys was studied by quartz crystal microbalance measurements and quartz crystal impedance spectroscopy. A fast impedance measurement technique is presented, which allows us to monitor the surface microstructure during the selective dissolution. We learn that the state of the alloy surface characterized by impedance measurements after the oxidation is not necessarily equal to that during the oxidation.