12,835 research outputs found
Deep Level Transient Spectroscopy (DLTS) System And Method
A computer-based deep level transient spectroscopy (DLTS) system (10) efficiently digitizes and analyzes capacitance and conductance transients acquired from a test material (13) by conventional DLTS methods as well as by several transient methods, including a covariance method of linear predictive modeling. A unique pseudo-logarithmic data storage scheme allows each transient to be tested at more than eleven different rates, permitting three to five decades of time constants τ to be observed during each thermal scan, thereby allowing high resolution of closely spaced defect energy levels. The system (10) comprises a sensor (12) for detecting capacitance and/or conductance transients, a digitizing mechanism (14) for digitizing the capacitance and/or conductance transients, preamplifiers (16a, 16b) for filtering, amplifying, and for forwarding the transients to the digitizing mechanism (14), a pulse generator (18) for supplying a filling pulse to the test material (13) in a cryostat (24), a trigger conditioner for coordinating the timing between the digitizing mechanism (14) and the pulse generator (18), and a temperature controller (26) for changing the temperature of the cryostat (24).Georgia Tech Research Corporatio
Over-limiting Current and Control of Dendritic Growth by Surface Conduction in Nanopores
Understanding over-limiting current (faster than diffusion) is a
long-standing challenge in electrochemistry with applications in desalination
and energy storage. Known mechanisms involve either chemical or hydrodynamic
instabilities in unconfined electrolytes. Here, it is shown that over-limiting
current can be sustained by surface conduction in nano pores, without any such
instabilities, and used to control dendritic growth during electrodeposition.
Copper electrode posits are grown in anodized aluminum oxide membranes with
polyelectrolyte coatings to modify the surface charge. At low currents, uniform
electroplating occurs, unaffected by surface modification due to thin electric
double layers, but the morphology changes dramatically above the limiting
current. With negative surface charge, growth is enhanced along the nanopore
surfaces, forming surface dendrites and nanotubes behind a deionization shock.
With positive surface charge, dendrites avoid the surfaces and are either
guided along the nanopore centers or blocked from penetrating the membrane
Classical EIS and square pattern signals comparison based on a well-known reference impedance
International audienceElectrochemical impedance spectroscopy or ac impeda nce methods are popularly used for the diagnosis of electrochemical generators (batteries or fuel cell) . It is now possible to acquire and quantitatively interpret the experimental electrical impedances of such syst ems, whose evolutions indirectly reflect the modifications of the internal electrochemical proce ss. The scope of these measurement methods is to identify the frequency response function of the sys tem under test by applying a small signal perturbat ion to the system input, and measuring the corresponding r esponse. Once identified, and according to the application, frequency response functions can provi de useful information about the characteristics of the system. Classical EIS consists in applying a set of frequency-controlled sine waves to the input of th e system. However, the most difficult problem is the integration of this type of measuring device in embedded systems. In order to overcome this problem , we propose to apply squared pattern excitation signals to perform such impedance measurements. In this paper, we quantify and compare the performance of classical EIS and the proposed broadband identif ication method applied to a well-known impedance circuit
A hybrid battery parameter identification concept for lithium-ion energy storage applications
© 2016 IEEE.Persistent of excitation of the input/output signals is a necessity for any online parameter identification technique. In most real battery systems, the drive signals may not fully satisfy this condition at all times, which can lead to divergence and failure of the incorporated battery management system. Therefore, in this paper, a hybrid battery parameter identification concept is proposed whereby the parameters are initially identified using a special random signal called the pseudo random binary sequences. Thereafter, the Kalman filter algorithm is implemented online to estimate and track any 'disturbances' caused by varying operating conditions. A dynamic European drive cycle is used to experimentally verify the excellent performance of the proposed technique against a more precise electrochemical impedance spectroscopy method
Stress-dependent electrical transport and its universal scaling in granular materials
We experimentally and numerically examine stress-dependent electrical
transport in granular materials to elucidate the origins of their universal
dielectric response. The ac responses of granular systems under varied
compressive loadings consistently exhibit a transition from a resistive plateau
at low frequencies to a state of nearly constant loss at high frequencies. By
using characteristic frequencies corresponding to the onset of conductance
dispersion and measured direct-current resistance as scaling parameters to
normalize the measured impedance, results of the spectra under different stress
states collapse onto a single master curve, revealing well-defined
stress-independent universality. In order to model this electrical transport, a
contact network is constructed on the basis of prescribed packing structures,
which is then used to establish a resistor-capacitor network by considering
interactions between individual particles. In this model the
frequency-dependent network response meaningfully reproduces the experimentally
observed master curve exhibited by granular materials under various normal
stress levels indicating this universal scaling behaviour is found to be
governed by i) interfacial properties between grains and ii) the network
configuration. The findings suggest the necessity of considering contact
morphologies and packing structures in modelling electrical responses using
network-based approaches.Comment: 12 pages, 4 figure
Binary Sequences for Online Electrochemical Impedance Spectroscopy of Battery Cells
Online diagnostic of lithium-ion battery (LIB) cells may have significant impact on chemical energy storage systems. Electrochemical impedance spectroscopy (EIS) is widely used for the characterization of LIBs and could be the most appropriate technique for online diagnostic, but its response time should be shortened. This work investigates the usage of multisine excitation to shorten the measurement time and simplify the hardware implementation for EIS of battery cells. Two types of multisine binary sequences are considered: sigma-delta modulated multisine sequences (SDMSs) and maximum length binary sequences (MLBSs). Their applicability to online and in situ EIS monitoring is evaluated by designing a measurement architecture also suitable to be implemented in a system-on-chip. The calibrated measurement system is compared with a benchtop reference instrument, reporting an RMSE deviation smaller than 5% in the frequency range of interest 1-200 Hz. The realized system is then used for online monitoring of the discharge process of a commercial 18650 LIB cell. The two proposed sequences are compared in terms of accuracy using a digital battery emulator circuit. Both the sequences demonstrated to be suitable for fast measurement and simple hardware integration, enabling online in situ EIS monitoring at cell level
Energy-Efficient PRBS Impedance Spectroscopy on a Digital Versatile Platform
partially_open6siThis research has been partially funded by the Italian Ministry of University and Research (MUR) through the program “Dipartimenti di Eccellenza” (2018-2022). The research has also received partial support from the Italian Ministry of University and Research (MUR) and the Eranet FLAG ERA initiative within CONVERGENCE project (CUP B84I16000030005) through the IUNET Consortium.This paper presents the digital design of a versatile and low-power broadband impedance spectroscopy (IS) system based on pseudo-random binary sequence (PRBS) excitation. The PRBS technique allows fast, and low-power estimation of the impedance spectrum over a wide bandwidth with adequate accuracy, proving to be a good candidate for portable medical devices, especially. This paper covers the low-power design of the firmware algorithms and implements them on a versatile and reconfigurable digital platform that can be easily adjusted to the specific application. It will analyze the digital platform with the aim of reducing power consumption while maintaining adequate accuracy of the estimated spectrum. The paper studies two main algorithms (time-domain and frequency-domain) used for PRBS-based IS and implements both of them on the ultra-low-power GAP-8 digital platform. They are compared in terms of accuracy, measurement time, and power budget, while general design trade-offs are drawn out. The time-domain algorithm demonstrated the best accuracy while the frequency-domain one contributes more to save power and energy. However, analysis of the energy-per-error FOM revealed that the time-domain algorithm outperforms the frequency-domain algorithm offering better accuracy for the same energy consumption. Numerical methods and microprocessor resources are exploited to optimize the implementation of both algorithms achieving 27 ms in processing time, power consumption as low as 1.4 mW and a minimum energy consumption per measurement of 0.5 mJ, for a dense impedance spectrum estimation of 214 points.embargoed_20210525Luciani G.; Crescentini M.; Romani A.; Chiani M.; Benini L.; Tartagni M.Luciani G.; Crescentini M.; Romani A.; Chiani M.; Benini L.; Tartagni M
Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors
This work reports on the experimental investigation of the wide band gap
compounds LiMgZ (Z = P, As, Sb), which are promising candidates for
opto-electronics and anode materials for Lithium batteries. The compounds
crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The
polycrystalline samples were synthesized by solid state reaction methods. X-ray
and neutron diffraction measurements show a homogeneous, single-phased samples.
The electronic properties were studied using the direct current (DC) method.
Additionally UV-VIS diffuse reflectance spectra were recorded in order to
investigate the band gap nature. The measurements show that all compounds
exhibit semiconducting behavior with direct band gaps of 1.0 eV to 2.3 eV
depending on the Z element. A decrease of the peak widths in the static 7Li
nuclear magnetic resonance (NMR) spectra with increasing temperature was
observed, which can directly be related to an increase of Li ion mobility.Comment: 8 page
A 177 ppm RMS Error-Integrated Interface for Time-Based Impedance Spectroscopy of Sensors
This paper presents an integrated circuit for time-based electrical impedance spectroscopy (EIS) of sensors. The circuit exploits maximum-length sequences (MLS) in order to perform a broadband excitation of the sensors under test. Therefore, the measured time-domain EIS is obtained by cross-correlating the input with the output of the analog front end (AFE). Unlike the conventional digital approach, the cross-correlation operation is performed in the analog domain. This leads to a lower RMS error in the measured time-domain EIS since the signal processing is not affected by the quantization noise of the analog-to-digital converter (ADC). It also relaxes the sampling frequency of the ADC leading, along with the lack of random access memory (RAM) usage, to a reduced circuit complexity. Theoretical concepts about the circuit’s design and operation are presented, with an emphasis on the thermal noise phenomenon. The simulated performances are shown by testing a sensor’s equivalent model composed of a 50 kΩ resistor in parallel with a 100 (Formula presented.) (Formula presented.) capacitor. A time-based EIS output of 255 points was obtained with a maximum tested frequency of 500 (Formula presented.) (Formula presented.) and a simulated RMS error of 0.0177% (or 177 ppm)
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