Conventional Impedance Analysis Research Articles

Evolutionary Programming Based Approach for SOFC Cathode Characterization: A Case Study on Co-Free Mixed Conducting Perovskites

Cobalt-free perovskites were investigated in this work, in order to find more economical and chemically stable materials to serve as cathodes for intermediate temperature solid oxide fuel cells. The electrochemical performance of Ba0.5Sr0.5Fe0.91Al0.09O3-δ and Ba0.5Sr0.5Fe0.8Cu0.2O3-δ with oxide ion conducting La0.8Sr0.2Ga0.8Mg0.2O3-δ and proton conducting Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ electrolytes was studied using non-destructive electrochemical impedance spectroscopy. The measured data was analyzed by impedance spectroscopy genetic programming (ISGP), which results in a unique model that requires no a-priori knowledge of the tested system. In-depth cathode operation mechanism is shown by finding the distribution function of relaxation times (DFRT) using ISGP. By monitoring the changes in the DFRT models at different temperatures, we are able to de-convolute the oxygen reduction reaction to its several polarization processes. Using our analysis approach it is possible to gain additional information, which may be convoluted and therefore undetected in conventional impedance analysis.

A 30 ppm < 80 nJ Ring-Down-Based Readout Circuit for Resonant Sensors

This paper presents an energy-efficient readout circuit for micro-machined resonant sensors. It operates by briefly exciting the sensor at a frequency close to its resonance frequency, after which resonance frequency and quality factor are determined from a single ring-down transient. The circuit employs an inverter-based trans-impedance amplifier to sense the ring-down current, with a programmable feedback network to enable the readout of different resonant sensors. An inverter-based comparator with dynamically-adjusted threshold levels tracks the ring-down envelope to measure quality factor, and detects zero crossings to measure resonance frequency. The excitation frequency is dynamically adjusted to accommodate large resonance frequency shifts. Experimental results obtained with a prototype fabricated in 0.35 µm standard CMOS technology and three different SiN resonators are in good agreement with conventional impedance analysis. The prototype achieves a frequency resolution better than 30 ppm while consuming less than 80 nJ/meas from a 1.8 V supply, which is 7.8x less than the state-of-the-art.

Leakage current limit of time domain reflectometry in ultrathin dielectric characterization

The accurate characterization of highly leaky dielectrics has been a serious challenge in MOSFET and capacitor studies. We have shown that time domain reflectometry (TDR) can be used to measure the capacitance of ultrathin SiO2 MOS capacitors even at a leakage current density as high as ∼3000 A/cm2, which is approximately 103 times higher than the limit of a conventional impedance analyzer. The extremely short interaction time of the TDR C–V method makes the TDR capacitance measurement more immune to the leakage current. Since the TDR C–V method does not require special high-frequency test structures other than a ground-signal pad pattern, the TDR C–V method is a promising capacitance measurement method for leaky dielectrics.

Automated impedance‐manometry analysis detects esophageal motor dysfunction in patients who have non‐obstructive dysphagia with normal manometry

Automated integrated analysis of impedance and pressure signals has been reported to identify patients at risk of developing dysphagia post fundoplication. This study aimed to investigate this analysis in the evaluation of patients with non-obstructive dysphagia (NOD) and normal manometry (NOD/NM). Combined impedance-manometry was performed in 42 patients (27F : 15M; 56.2 ± 5.1 years) and compared with that of 24 healthy subjects (8F : 16M; 48.2 ± 2.9 years). Both liquid and viscous boluses were tested. MATLAB-based algorithms defined the median intrabolus pressure (IBP), IBP slope, peak pressure (PP), and timing of bolus flow relative to peak pressure (TNadImp-PP). An index of pressure and flow (PFI) in the distal esophagus was derived from these variables. Diagnoses based on conventional manometric assessment: diffuse spasm (n = 5), non-specific motor disorders (n = 19), and normal (n = 11). Patients with achalasia (n = 7) were excluded from automated impedance-manometry (AIM) analysis. Only 2/11 (18%) patients with NOD/NM had evidence of flow abnormality on conventional impedance analysis. Several variables derived by integrated impedance-pressure analysis were significantly different in patients as compared with healthy: higher PNadImp (P < 0.01), IBP (P < 0.01) and IBP slope (P < 0.05), and shorter TNadImp_PP (P = 0.01). The PFI of NOD/NM patients was significantly higher than that in healthy (liquid: 6.7 vs 1.2, P = 0.02; viscous: 27.1 vs 5.7, P < 0.001) and 9/11 NOD/NM patients had abnormal PFI. Overall, the addition of AIM analysis provided diagnoses and/or a plausible explanation in 95% (40/42) of patients who presented with NOD. Compared with conventional pressure-impedance assessment, integrated analysis is more sensitive in detecting subtle abnormalities in esophageal function in patients with NOD and normal manometry.

A New Impedance Measurement System for PZT-Based Structural Health Monitoring

Recent research has shown that electromechanical (E/M) impedance-based techniques are an efficient strategy for damage sensing in the context of structural health monitoring (SHM). The basic principle is to excite the lead zirconate titanate (PZT) sensors attached to the structure and to measure the corresponding electrical impedance. A variation in the electrical impedance indicates a variation in the mechanical impedance and, consequently, structural damage. To measure the electrical impedance, most universities and research centers use expensive, bulky, heavy, and high-powered impedance analyzers, which limit new developments and practical applications. To overcome these issues, this paper presents an efficient and inexpensive methodology for electrical impedance measurement. To verify the efficiency and accuracy of the new methodology, practical tests were carried out, and the results were compared with those obtained using a conventional impedance analyzer.

Studies of giant magnetoimpedance effect of Co‐rich microwires in wide frequency range

AbstractThe GMI effect in Co‐rich amorphous microwires with nearly‐zero and negative magnetostriction constant has been investigated in the frequency range from a few MHz up to 10 GHz using conventional impedance analyzer based technique and microwave waveguide method. The GMI response of the order of 200% has been observed for all samples at MHz frequencies, while only one samples demonstrated considerable GMI ratio of about 60% at GHz frequencies. This can be explained by the fact that impedance dependence on external magnetic field in the microwaves range is affected not only by the magnetic softness of the wire material but also by the magnetic resonance conditions in the not saturated sample. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Development of an impedance-based wireless sensor node for structural healthmonitoring

This paper presents the development and application of a miniaturized impedance sensornode for structural health monitoring (SHM). A large amount of research has beenfocused on utilizing the impedance method for structural health monitoring. Thevast majority of this research, however, has required the use of expensive andbulky impedance analyzers that are not suitable for field deployment. In thisstudy, we developed a wireless impedance sensor node equipped with a low-costintegrated circuit chip that can measure and record the electrical impedance of apiezoelectric transducer, a microcontroller that performs local computing and a wirelesstelemetry module that transmits the structural information to a base station.The performance of this miniaturized and portable device has been compared toresults obtained with a conventional impedance analyzer and its effectiveness hasbeen demonstrated in an experiment to detect loss of preload in a bolted joint.Furthermore, for the first time, we also consider the problem of wireless powering of suchSHM sensor nodes, where we use radio-frequency wireless energy transmission to deliverelectrical energy to power the sensor node. In this way, the sensor node doesnot have to rely on an on-board power source, and the required energy can bewirelessly delivered as needed by human or a remotely controlled robotic device.

Real-Time Measurement of PMA-Induced Cellular Alterations by Microelectrode Array-Based Impedance Spectroscopy

For a feasible and cost-effective impedance measurement of cellular alterations in real-time, we combined commercially available microelectrode arrays (MEAs), consisting of 60 microelectrodes, with a conventional impedance analyzer. For proof of principle, a breast carcinoma cell line (MCF-7) was cultured on MEAs, and cellular alterations were measured by impedance spectroscopy at a frequency ranging from 10 Hz to 1 MHz. Cells were stimulated with phorbol 12-myristate 13-acetate (PMA) at different concentrations to activate protein kinase C (PKC)-mediated extra- and intracellular changes. By addition of 0.03 microM PMA, an increase of the relative impedance (Z(rel)) was observed after 10 min with a maximum at 1 kHz. Moreover a gradual elevation of the impedance was measured 60 min after stimulation with PMA. If 0.3 microM PMA was applied, the maximal amplitude of the relative impedance after 60 min shifted from 1 kHz (0.03 microM PMA) to 150 Hz. Subsequently, the impedance was further increased up to 90 min after PMA application, after which the impedance reduced after 240 min. Since we could use MEAs for at least 10 times without affecting the sensitivity, our study revealed that commercially available MEAs comprising nanocolumnar titanium nitrite electrodes are suitable microstructures for a highly reproducible and cost-effective multisite measurement of intracellular processes by impedance spectroscopy.

Theoretical analysis and experimental measurement for resonant vibration of piezoceramic circular plates.

Based on the electroelastic theory for piezoelectric plates, the vibration characteristics of piezoceramic disks with free-boundary conditions are investigated in this work by theoretical analysis, numerical simulation, and experimental measurement. The resonance of thin piezoceramic disks is classified into three types of vibration modes: transverse, tangential, and radial extensional modes. All of these modes are investigated in detail. Two optical techniques, amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometer (LDV), are used to validate the theoretical analysis. Because the clear fringe patterns are shown only at resonant frequencies, both the resonant frequencies and the corresponding mode shapes are obtained experimentally at the same time by the proposed AF-ESPI method. Good quality of the interferometric fringe patterns for both the transverse and extensional vibration mode shapes are demonstrated. The resonant frequencies of the piezoceramic disk also are measured by the conventional impedance analysis. Both theoretical and experimental results indicate that the transverse and tangential vibration modes cannot be measured by the impedance analysis, and only the resonant frequencies of extensional vibration modes can be obtained. Numerical calculations based on the finite element method also are performed, and the results are compared with the theoretical analysis and experimental measurements. It is shown that the finite element method (FEM) calculations and the experimental results agree fairly well for the resonant frequencies and mode shapes. The resonant frequencies and mode shapes predicted by theoretical analysis and calculated by finite element method are in good agreement, and the difference of resonant frequencies for both results with the thickness-to-diameter (h/D) ratios, ranging from 0.01 to 0.1, are presented.

Experimental and numerical investigations of resonant vibration characteristics for piezoceramic plates.

Electronic speckle pattern interferometry (ESPI) is a full field, non-contact technique for measuring the surface displacement of a structure subjected to static loading or, especially, to dynamic vibration. In this article we employ an optical system called the amplitude-fluctuation ESPI with out-of-plane and in-plane measurements to investigate the vibration characteristics of piezoceramic plates. Two different configurations of piezoceramic plates, namely the rectangular and the circular plates, are discussed in detail. As compared with the film recording and optical reconstruction procedures used for holographic interferometry, the interferometric fringes of AF-ESPI are produced instantly by a video recording system. Because the clear fringe patterns will be shown only at resonant frequencies, both the resonant frequencies and the corresponding mode shapes are obtained experimentally at the same time by the proposed AF-ESPI method. Excellent quality of the interferometric fringe patterns for both the in-plane and out-of-plane vibration mode shapes is demonstrated. The resonant frequencies of the piezoceramic plates are also measured by the conventional impedance analysis. From experimental results, we find that the out-of-plane vibration modes (type A) with lower resonant frequencies cannot be measured by the impedance analysis and only the in-plane vibration modes (type B) will be shown. However, both the out-of-plane (bending) and in-plane (extensional) vibration modes of piezoceramic plates are obtained by the AF-ESPI method. Finally, the numerical finite element calculations are also performed, and the results are compared with the experimental measurements. It is shown that the numerical calculations and the experimental results agree fairly well for both the resonant frequencies and the mode shapes.

A New Way of Using ac Voltammetry To Study Redox Kinetics in Electroactive Monolayers

A new protocol for analyzing variable-frequency ac voltammetry (acv) data to obtain electron-transfer rate constants for redox-active groups immobilized in monolayer films on electrodes is described. The protocol involves plotting the ratio of the peak current to the background current as a function of the log of frequency and then fitting the plot to a calculated curve obtained using the Randles equivalent circuit model. The fitting procedure is particularly straightforward since it involves just two adjustable fitting parameters and can usually be performed manually in a spreadsheet. Advantages of the new method include the following: (1) it requires fewer adjustable fitting parameters than the conventional impedance analysis performed in the complex-plane format; (2) because there are fewer fitting parameters, there is less chance of the fit yielding a false convergence; (3) nonideal effects associated with a distribution of rate constants are apparently revealed in a particularly intuitive and easily...

A new penetration impedance technique

To study the electrical properties of solid ionic conductors with a spatial resolution we developed a novel variant of the impedance technique based on the two-dimensionality of the cell-electrodes arrangement and resulting frequency dependent penetration depth of the excitation signal, ie the electrical signals spread deeper into the ionic conductor the lower the frequency. The technique was quantitatively verified by detecting the position of an additional Ag strip added to the ionic conductor. Using the advantage that at high frequencies only the region close to the working electrode is probed, the technique was used to study parent metal/ionic conductor contacts. In this context resistance and capacitance of the Ag AgCl interface were measured and analysed in the light of ionic space charge effects. The difference of the described technique, when compared with the conventional impedance analysis, consists in the fact that the measured decay rate of electrical relaxation now includes also the information about the position in space at which the relaxation occurs.