Low Frequency Impedance Measurements Research Articles

Small-signal equivalent circuit model of GaN-based nanodiodes at low temperature including trap-related low frequency dispersion

The small-signal equivalent circuit of GaN-based self-switching diodes has been obtained, which apart from the intrinsic R‖C branch, generally used to describe the diode performance, needs new elements to describe the low-frequency dispersion of the impedance originated by the presence of surface and bulk traps. The proposed model allows us to reproduce not only the high-frequency results (extracted from S-parameter measurements in the 40 MHz–43.5 GHz range) at room temperature, but also the low-frequency impedance measurements (75 kHz–30 MHz) at cryogenic temperatures down to 70 K. These new elements are a self-inductance associated to the effect of surface states (typical of a device with a high surface-to-volume ratio) and an extra series R–C branch modeling the influence of the bulk traps.

Design, Implementation, and Characterization of a Compact Lock-in Add-on for Low-Frequency Impedance Measurements

Impedance measurements are crucial in a variety of applications, from the characterization of lithium batteries, microbial fuel cells, and biosensors to the study of polymers and material degradation, where strict requirements have to be met in terms of frequency bandwidth and current level. Here, we present a cost-effective compact solution for ultra-low-frequency impedance measurements, operating in a wide range, from 1 mHz to 250 kHz. Coupled to a lock-in amplifier, the designed circuit is based on a Howland current pump cascaded by a precision current divider in order to set the conversion factor at 100 nA/V, 1 μA/V, or 100 μA/V. Therefore, it is possible to generate very low-current signals to measure resistive impedances up to 100 MΩ. In addition, a feedback network is inserted to null the voltage drift induced by leakage currents and offset voltages, thus allowing the measurement of low-capacitance loads, experimentally tested down to 10 nF. Remarkably, the feedback network allows to perform measurements also in the presence of high voltage bias of the load and experimental results performed up to 60 V demonstrate the excellent stability of the designed system, thus a high voltage compliance. The proposed circuit is particularly interesting for the conditioning of both resistive and capacitive sensors and it is likely to be an effective solution for the implementation of a portable instrument for measuring signals from biosensors.

Universal approach for diffusion quantification applied to lead halide perovskite single crystals

A universal approach to calculating diffusion coefficients in lead halide perovskite single crystals, which have ionic and mixed ionic–electronic conductivity, is proposed. Using impedance spectroscopy, it is demonstrated how to model a non-ideal Warburg element and transmission line equivalent circuit to identify ionic diffusion in the material. The proposed method is applicable to samples of any thickness and electrical properties. Additionally, it is shown how to overcome the challenges of low-frequency impedance measurement and the non-ideal behavior of the elements through extrapolative modeling and approximation.

Raspberry Pi Platform Wireless Sensor Node for Low-Frequency Impedance Responses of PZT Interface.

A wireless impedance monitoring system, called SSeL-Pi, is designed to have cheap, mobile, and handy practical features as compared to wired commercial impedance analyzers. A Raspberry Pi platform impedance sensor node is designed to measure signals at a low-frequency range of up to 100 kHz. The low-frequency impedance measurement via the proposed node has been combined with a new PZT interface technique for measuring local responses sensitive to structural damage. The new PZT interface can work as a surface-mounted or embedded sensor, and its local dynamic characteristics are numerically analyzed to pre-determine an effective impedance resonant frequency range of less than 100 kHz. Next, a software scheme was designed to visualize the input/output parameters of the proposed SSeL-Pi system (i.e., Raspberry Pi platform and PZT interface) and automate signal acquisition procedures of the impedance sensor node. The calibration for impedance signals obtained from the proposed system was performed by a series of procedures, from acquiring real and imaginary impedance to adjusting them with respect to a commercial impedance analyzer (HIOKI-3532). The feasibility of the wireless impedance monitoring system was experimentally evaluated for PZT interfaces that were subjected to various compressive loadings. The consistent results analyzed from signals measured by the SSeL-Pi and HIOKI 3532 systems were observed. Additionally, the strong relationships between impedance features (frequency shift and RMSD index) and compressive stresses of the PZT interfaces showed the potential for axial force/stress variation monitoring in real structures using the Raspberry Pi platform impedance sensor node and developed PZT interface.

Portable and Highly Versatile Impedance Meter for Very Low Frequency Measurements

Electrical Impedance Spectroscopy (EIS) is a characterization technique that is gaining more and more importance in various fields of research and applications. The frequency range of investigation varies according to the type of application. In some fields (biology, medicine, energy) it is useful to be able to perform measurements at very low frequency values (down to a few mHz or even below). While impedance meters operating at frequencies in the range from a few tens of Hz up to a few MHz can be regarded as quite standard pieces of instrumentation commonly available in many laboratories, instrumentation for measurements at very low frequencies, although commercially available, is less common. The subject of this work is the design, realization and testing of a low frequency impedance measurement platform that has the advantage of being portable, rather inexpensive, and yet highly versatile. In our approach, we exploit a personal computer and a soundboard as a powerful system for digital signal generation and analysis that, with the help of low complexity and low-cost external hardware and a public domain software for the implementation of the core system, allow to tailor the platform for targeting specific applications with minimal effort. As an example, we will demonstrate the application of the system to the investigation of polypyrrole-based supercapacitor structures.

On the inverse relaxation approach to supercapacitors characterization

[Display omitted] A novel inverse relaxation technique for supercapacitor characterization is developed, modeled numerically, and experimentally tested on a number of commercial supercapacitors. It consists in shorting a supercapacitor for a short time τ, then switching to the open circuit regime and measuring an initial rebound and long-time relaxation. The results obtained are: the ratio of “easy” and “hard” to access capacitance and the dependence C(τ), that determines what the capacitance the system responds at time-scale τ; it can be viewed as an alternative to used by some manufacturers approach to characterize a supercapacitor by fixed capacitance and time-scale dependent internal resistance. Among the advantages of proposed technique is that it does not require a source of fixed current, what simplifies the setup and allows a high discharge current regime. The approach can be used as a replacement of low-frequency impedance measurements and the ones of IEC 62391 type, it can be effectively applied to characterization of supercapacitors and other relaxation type systems with porous internal structure. The technique can be completely automated by a microcontroller to measure, analyze, and output the results.

On The Inverse Relaxation Approach To Supercapacitors Characterization

A novel inverse relaxation technique for supercapacitor characterization is developed, modeled numerically, and experimentally tested on a number of commercial supercapacitors. It consists in shorting a supercapacitor for a short time τ, then switching to the open circuit regime and measuring an initial rebound and long–time relaxation. The results obtained are: the ratio of “easy” and “hard” to access capacitance and the dependence C(τ), that determines what the capacitance the system responds at time–scale τ; it can be viewed as an alternative to used by some manufacturers approach to characterize a supercapacitor by fixed capacitance and time–scale dependent internal resistance. Among the advantages of proposed technique is that it does not require a source of fixed current, what simplifies the setup and allows a high discharge current regime. The approach can be used as a replacement of low–frequency impedance measurements and the ones of IEC 62391 type, it can be effectively applied to characterization of supercapacitors and other relaxation type systems with porous internal structure. The technique can be completely automated by a microcontroller to measure, analyze, and output the results.

Finding the effective structure parameters for suspensions of nano-sized insulating particles from low-frequency impedance measurements

Based on the method of compact groups of inhomogeneities, we formulate new mixing rules for suspensions of charged insulating particles. They express the quasistatic conductivity and permittivity of a suspension in terms of the effective geometric and dielectric parameters of the particles, electric double layers (EDLs), and suspending liquid. Also, we present our low-frequency impedance measurements of the conductivity and permittivity of Al2O3-isopropyl alcohol nanofluids as functions of Al2O3-particle volume concentration. Our rules give good fits for most of these data and allow us to estimate, among other things, the effective thickness, conductivity, and permittivity of the EDLs. The experimentally-recovered values agree well with elementary theoretical estimates suggesting the charging of the particles through preferential adsorption of contaminant ions. The possible effects of other mechanisms on the effective conductivity and permittivity of suspensions are also discussed.

Design, calibration and tests of versatile low frequency impedance analyser based on ARM microcontroller

Numerous simple impedance analysers based on the microcontroller (μC) and dedicated impedance converter integrated circuits (IC) were reported recently. In many applications sophisticated analogue circuitry has to be appended to enhance the measurement possibilities or to circumvent the limitations. In this paper the impedance analyser IMP-STM32 based solely on the μC and general purpose operational and instrumentation amplifiers is presented. It uses the internal DAC and ADCs in the μC to generate the excitation and to measure the response of the measured object. It also uses the external analogue circuits to condition the excitation signal and measure voltage and current. The magnitudes and phase shifts of voltage and current are evaluated using the three parameter sine fitting algorithm allowing for fast low-frequency impedance measurements. The calibration procedure of completed device is presented as well as the tests of its accuracy. The device allowed for measurements at frequency range between 1mHz and 100kHz in 1Ω to 1GΩ impedance range with 1% accuracy. IMP-STM32 was also compared to the Agilent 4294A precision impedance analyser. In the middle of the impedance ranges (1Ω to 300kΩ) the discrepancies between the two were less than 0.2%.

Transient measurements of carrier relaxation time and density in the P3HT:PCBM organic photovoltaic cell

The authors have used transient photovoltage measurements to evaluate carrier relaxation times (τ) in P3HT:PCBM based photocells over a wide range of open circuit voltages. Satisfactory agreement is found with data obtained by low frequency impedance measurements. The authors find the differential capacitance measurements yield data consistent with the theoretical value expected based on Langevin recombination. The Langevin coefficient is three orders of magnitude smaller than the theoretical one. For the low light levels, the relaxation time variation is determined by the RC time constant behavior of the photodiode.

Differences between direct current and alternating current capacitance nonlinearities in high-k dielectrics and their relation to hopping conduction

Capacitance nonlinearities were studied in atomic layer deposited HfO2 films using two types of signals: a pure ac voltage of large magnitude (ac nonlinearities) and a small ac voltage superimposed to a large dc voltage (dc nonlinearities). In theory, ac and dc nonlinearities should be of the same order of magnitude. However, in practice, ac nonlinearities are found to be an order of magnitude higher than dc nonlinearities. Besides capacitance nonlinearities, hopping conduction is studied using low-frequency impedance measurements and is discussed through the correlated barrier hopping model. The link between hopping and nonlinearity is established. The ac nonlinearities are ascribed to the polarization of isolated defect pairs, while dc nonlinearities are attributed to electrode polarization which originates from defect percolation paths. Both the ac and dc capacitance nonlinearities display an exponential variation with voltage, which results from field-induced lowering of the hopping barrier energy.

Proliferation Monitoring of Immunocytes Using Low Frequency Impedance Measurement

1. Introduction We previously performed a study of the fine behaviors in the differentiation of THP-1 (a human myeloid leukemia cell line) into macrophages1). In this study, using a combination of an incubator and an impedance analyzer, we first drew a Nyquist plot of the natural proliferation process non-invasively. We then plotted the impedance at the low frequency of 25 mHz temporally, and compared it with the proliferation curve (profile) of THP-1. 2. Experiments 2-1. Measurement system Fig. 1 shows a schematic diagram of the immunocyte differentiation monitoring system used in this study. The system consists of an impedance analyzer, potentiostats (1255, 1287, Solartron), and an incubator (4020, Asahi Life Science). For the measurement cell in the incubator, we installed a pair of platinum electrodes (5mm x 5 mm x 0.05 mm; inter-electrode distance 8 mm) in a petri dish (φ8 mm).2-2. Proliferation curve of THP-1 To determine the number of THP-1 cells, starting with 2.7x105cells/mL, we cultured the cells in a RPMI1640 culture medium in an incubator, counted the number of cells each day, and plotted a proliferation curve.2-3 Impedance measurement relative to proliferation of THP-1 The measurement solution was 200mL of a solution obtained by adding 11.4 mM glucose to phosphate buffer. 10 μL of THP-1 cultured in Section 2-2 was introduced into this solution, and the impedance was measured at an applied voltage of 10 mVrms and frequency of 25 mHz - 5 kHz each day. 3. Results and discussion Fig. 2 shows the proliferation curve of THP-1. It was found that Day 1 was the lag phase from the day of initiation of culture, Day 2 to Day 4 was the log phase, and Day 4 to Day 6 was the stationary phase. Fig. 3 shows the Nyquist plot of the impedance in the phase of the proliferation curve of THP-1. In the lag phase on Day 1 at 25 mHz, the impedance was less than 5 kΩ, but in the log phase, it increased to approximately 15 kΩ, while in the stationary phase, the impedance slightly decreased, but still exceeded 12 kΩ. In the death phase, the impedance decreased rapidly, and fell below 8 kΩ. Table 1 summarizes the absolute values (lag phase, stationary phase) of impedance at 25 mHz, and the changes (log phase, death phase) per day in the absolute values of impedance. The impedance in each period mostly coincided with the proliferation curve. This suggests that it is possible to estimate the proliferation of floating cells from the impedance in the low-frequency region. In future, we aim to draw up a calibration curve, and study the proportion of living cell counts and dead cell counts together with morphological changes. Reference [1] S.Kasai, K.Shoji, M.Tada, H.Kiriu, R.Ishii, H.Kodama, 222ndECS Meeting, (2012) Table 1 Magnitude |Z| of impedance at 25mHz in each phase of the THP-1 proliferation curve Period|Z|Lag phaseDay 1-22.2 x103 Ω, effectively constantLog phaseDay 2-44.6 x103 Ω/dayStationary phaseDay 4-62.3 x104 Ω, slight decreaseDeath phaseDay 6-92.7 x103 Ω/day

Rapid Impedance Spectrum Measurements for State-of-Health Assessment of Energy Storage Devices

Harmonic compensated synchronous detection (HCSD) is a technique that can be used to measure wideband impedance spectra within seconds based on an input sum-of-sines signal having a frequency spread separated by harmonics. The battery (or other energy storage device) is excited with a sum-of-sines current signal that has a duration of at least one period of the lowest frequency. The voltage response is then captured and synchronously detected at each frequency of interest to determine the impedance spectra. This technique was successfully simulated using a simplified battery model and then verified with commercially available Sanyo lithium-ion cells. Simulations revealed the presence of a start-up transient effect when only one period of the lowest frequency is included in the excitation signal. This transient effect appears to only influence the low-frequency impedance measurements and can be reduced when a longer input signal is used. Furthermore, lithium-ion cell testing has indicated that the transient effect does not seem to impact the charge transfer resistance in the mid-frequency region. The degradation rates for the charge transfer resistance measured from the HCSD technique were very similar to the changes observed from standardized impedance spectroscopy methods. Results from these studies, therefore, indicate that HCSD is amore » viable, rapid alternative approach to acquiring impedance spectra.« less

Quantitative Non-Destructive Evaluation of Steel Microstructure Using Elastic Wave Perturbation

The purpose of this investigation is to develop the nondestructive tools for microstructure assessments in carbon alloyed steels. The role of carbon in steel and its effects on electromagnetic property and also the free electron model have been reviewed. The fundamental electromagnetic principle behind low frequency impedance measurements has been included. The systematic analysis of phonon vibration and ultrasonic resonance spectroscopy for elastic wave perturbation in T22 Cr-Mo steel has been presented. A brief examination of nondestructive microstructure evaluation techniques has been described. The induced microstructure variations in Grade T22 Cr-Mo steel, including the correlations of changes in physical (microstructure) and mechanical (hardness data) properties during annealing have been measured. The explanations of aged carbide precipitates, martensitic and pearlitic nucleation and growth have been illustrated. The possibility of simultaneous use of two nondestructive wave techniques is discussed. The electron model and electron interactions are associated and are shown to support the results of low frequency impedance measurements enhanced elastic wave perturbations.

Interfaces and traps in pentacene field-effect transistor

The equivalent circuit parameters for a pentacene organic field-effect transistor are determined from low frequency impedance measurements in the dark as well as under light illumination. The source-drain channel impedance parameters are obtained from Bode plot analysis and the deviations at low frequency are mainly due to the contact impedance. The charge accumulation at organic semiconductor–metal interface and dielectric–semiconductor interface is monitored from the response to light as an additional parameter to find out the contributions arising from photovoltaic and photoconductive effects. The shift in threshold voltage is due to the accumulation of photogenerated carriers under source-drain electrodes and at dielectric–semiconductor interface, and also this dominates the carrier transport. The charge carrier trapping at various interfaces and in the semiconductor is estimated from the dc and ac impedance measurements under illumination.

Non-contact, nondestructive hydrogen and microstructural assessment of steel welds

Nondestructive low-frequency impedance has been developed to determine hydrogen content in operating pipeline steel and weldments through a structural coating. A low frequency impedance measurement is similar to a resistivity measurement with a depth function due to the sensor coil reactance. Resistivity introduces variability in impedance measurements because resistivity is a function of the conductivity of the material, the depth of the measurement, and the alloy content. The conductivity, based on the free electron model, is a function of the electronic effective mass, the electron concentration, and the dominating scattering mechanisms, which is altered by such factors as inclusions, microstructure, temperature, and strain. Each of these variables must be separated out to obtain a hydrogen content measurement in operating pipelines (with a structural coating) using low frequency impedance. Techniques used to separate out the variables associated with operating pipeline steels are presented. The use of real-time low frequency impedance measurements to monitor hydrogen content as it diffuses out of a steel weldment is presented and discussed.

A High Measurement Channel Density Impedance Array Analyzer: Instrumentation and Implementation Approaches

The development of impedance-based array devices is hindered by a lack of robust platforms and methods upon which to evaluate and interrogate sensors. One aspect to be addressed is the development of measurement-time efficient techniques for broadband impedance spectroscopy of large electrode arrays. The objective of this work was to substantially increase the throughput capability of low frequency impedance measurement of a large channel-count array analyzer by developing true parallel measurement methods. The goal was achieved by Fourier transform based analysis of simultaneously-acquired, multi-channel, time-based, current and voltage data. Efficacy and quantitative analysis of the parallel approach is demonstrated through complex impedance measurement of dummy cell arrays consisting of up to 100 elements to sub-Hertz frequencies. The accuracy and measurement-time efficiency of the standard sequential measurement method, and a hybrid standard + parallel approach, are evaluated.

Development and Demonstration of Measurement-Time Efficient Methods for Impedance Spectroscopy of Electrode and Sensor Arrays.

The development of impedance-based array devices is hindered by a lack ofrobust platforms and methods upon which to evaluate and interrogate sensors. One aspectto be addressed is the development of measurement-time efficient techniques forbroadband impedance spectroscopy of large electrode arrays. The objective of this workwas to substantially increase the low frequency impedance measurement throughputcapability of a large channel count array analyzer by developing true parallel measurementmethods. The goal was achieved by Fourier transform-based analysis of simultaneouslyacquiredmulti-channel time-based current and voltage data. Efficacy and quantitativeanalysis of the parallel approach at frequencies less than ca. 10 Hz as well as a combinedsequential parallel approach for efficient broadband impedance spectroscopy over 5-orders of magnitude in frequency is demonstrated through complex impedancemeasurement of arrays consisting of up to 100 elements.

Four-Qubit Device with Mixed Couplings

We present the first experimental results on a device with more than two superconducting qubits. The circuit consists of four three-junction flux qubits, with simultaneous ferro- and antiferromagnetic coupling implemented using shared Josephson junctions. Its response, which is dominated by the ground state, is characterized using low-frequency impedance measurement with a superconducting tank circuit coupled to the qubits. The results are found to be in excellent agreement with the quantum-mechanical predictions.

Low frequency impedance measurement using sine-fitting

This paper describes an impedance measurement technique based on the use of a personal computer, two digitizing channels and the application of four-parameter sine-fitting algorithms to estimate amplitude, phase, offset and frequency of the voltages across the impedance under measurement and of a reference impedance. This simple and inexpensive setup leads to experimental results with accuracy comparable to those obtained with sophisticated high cost dedicated impedance measurement equipment. The results here presented, obtained using a low cost 12 bit PC data acquisition board, for impedances with amplitudes ranging from 100 Ω to 1 kΩ at 1 kHz, show relative standard deviations of the amplitude below 0.002% and standard deviations of the phase under 0.001°.