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Supercapacitor reciprocity and response to linear current and voltage ramps
The focus in supercapacitor research typically falls into one of two categories: (i) the rational design and engineering of electrode materials and electrolyte formulation to achieve high performance devices at competitive costs, and (ii) the modeling of their resulting behavior in response to constant-current charging/discharging, cyclic voltammetry or impedance spectroscopy. However, less work has been dedicated to new ways for charging these devices. In this work we show that charging a supercapacitor, modeled as a constant phase element with a series resistor, using a linear voltage ramp
Multiple Pinch-Off Points in Memristive Equations: Analysis and Experiments
Pinched hysteresis behavior is considered evidence of the existence of the memristive element. Recently, the multi-lobes (more than two) behavior has been discovered in some memristive devices. In this paper, a fractional-order flux/voltage-controlled memristive model is introduced that is able to develop multiple symmetric and asymmetric pinch-off points. Generalized closed-form expressions for the necessary conditions of multiple pinch-off points existence are derived in addition to the coordinates of the pinch-off points in the I-V plane. Closed-form expressions for the minimum and maximum
Extraction of bioimpedance phase information from its magnitude using a non-uniform Kramers–Kronig transform
A novel non-uniform Kramers–Kronig Transform algorithm for bioimpedance phase extraction is proposed and tested in this work. The algorithm error is studied and compared with a previously proposed phase extraction technique, also based on the Kramers–Kronig transform. Results using simulated datasets and experimental datasets confirm the excellent performance of the algorithm. © 2020, European Biophysical Societies' Association.
Extraction of Phase Information from Magnitude-Only Bio-impedance Measurements Using a Modified Kramers–Kronig Transform
The need for portable and low-cost bio-impedance analyzers that can be deployed in field studies has significantly increased. Due to size and power constraints, reducing the hardware in these devices is crucial and most importantly is removing the need for direct phase measurement. In this paper a new magnitude-only technique based on modified Kramers–Kronig transforms is proposed and tested. Comparison with impedance measurements of fresh and aging tomato samples using a precise industry standard impedance analyzer is carried out and explained. Error and noise analysis of the proposed
Extending the double-dispersion Cole–Cole, Cole–Davidson and Havriliak–Negami electrochemical impedance spectroscopy models
Double-dispersion impedance models are important for the accurate fitting of spectral impedance measurements in Electrical Impedance Spectroscopy (EIS). While the Cole–Cole model is the most widely known, it is possible to define double-dispersion Cole–Davidson and Havriliak–Negami models as well. In this work, we show that more freedom can be exercised when these three models are combined together and that this combination can be done in various forms. Experimental results using a two-stage optimization algorithm applied on the suggested models are provided. © 2021, European Biophysical
Communication-The Ragone Plot of Supercapacitors under Different Loading Conditions
The power-energy performance of supercapacitors is usually visualized by the Ragone plot of (gravimetric or volumetric) energy density vs power density. The energy is commonly computed from E = CV2/2, and the power from P = E/Δt, which assume RCbased models. In this study, we investigate the energy-power profiles of two commercial supercapacitors discharged with three different types of loads: (i) constant current, (ii) constant power, and (iii) constant resistive load. The energy is computed as per the definition from the time-integral of its instantaneous power, i.e. E(t) = ò p(t)dt with p(t
Communication—convolution-based estimation of supercapacitor parameters under periodic voltage excitations
Supercapacitors are typically used in applications requiring frequent and continuous charging/discharging cycles, but most of the models available in the literature are designed to predict their behavior for a single sequence. In this letter, we show first that the electrical response and metrics of supercapacitors under periodic voltage excitations can generally be obtained using Fourier series analysis and convolution operations of functions derived based on any suitable impedance model. We verified our analysis procedure with simulations using particle swarm optimization, and experiments
Resonant square-wave clock generator for low power applications
Power reduction is the main challenge facing circuit designers in their quest to utilize the full performance of new process technologies. A major portion of the power consumed in today's systems is due to the clock generation and distribution. Resonant clocking has been a promising technique to reduce the clock power dramatically. In this paper, a novel resonant clock generator circuit is proposed to reduce the dynamic power used for clock generation by almost 75%. Two configurations of the circuit are presented. The merit of this generator is most obvious in the ease of its implementation
A dynamic calibration scheme for on-chip process and temperature variations
A process and temperature variation calibration scheme is proposed in this paper. The proposed system uses the supply voltage and body bias to calibrate the device parameters to match those of a certain process corner that is determined by the system designer. This scheme is characterized by its ability to dynamically change the desired mapping target according to the computational load. Moreover, the proposed system provides the ability to detect and control the n- and p-type variations independently through the use of an all-n and all-p ring oscillators. The calibration system has been
A dynamic power-aware process variation calibration scheme
In this paper, a power-aware process variation calibration scheme is proposed. The proposed calibration system provides the ability to detect and control the n- and p-type variations independently through the use of all-n and all-p ring oscillators. Calibration is then carried out through the use of the supply voltage and body bias to alter the device parameters to match those of a certain process corner that is determined by the system designer. This scheme is characterized by its ability to dynamically change the desired mapping target according to the computational load. The calibration
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