Abstract: The electrochemical detection of glucose using glucose oxidase (GOx) has been conducted by means of AC impedance measurements. In the absence of glucose, the Nyquist plots were straight line due to...

Abstract: Poly(2,2-Dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltametrically coated onto carbon fiber microelectrode (CFME) as an active functionalized microelectrode. An electrochemical impedance spectroscopic study on the prepared electrodes is reported in this paper which electropolymerization performed under different initial monomer concentrations. The electrochemical impedance data fitted to equivalent circuit model, used to find out numerical values of the proposed components. Effect of the parameters on the capacitive behavior of the (PProDOT-Me2) coated carbon fiber microelectrode and morphology of films obtained by AFM and SEM was discussed. Highly porous coating was obtained at 100 mV/s scan rate and 10 cycles. EDX and ATR-FTIR results indicated the doping of anion of electrolyte due to formation of polaronic and bipolaronic sites. The presence of surface functional groups were determined by ATR-FTIR. Nanoscale conjugated polymer modified carbon fiber microelectrodes exhibited high capacitance of approximately 90 degrees phase angle, and vertical line in Nyquist plot. The capacitive behavior of CFME was increased by this very thin film coating of PProDOT-Me2. The electroactivity of Poly 2,2-Dimethyl-3,4-propylenedioxythiophene on the carbon fiber microelectrode open the possibility of using these coated electrodes for electrochemical microsupercapacitors and biosensor electrodes.

Abstract: This paper presents the dynamic electrothermal simulation of a rectangular resistor integrated on a semiconductor substrate Due to the temperature dependence of the electrical conductivity of the resistive sheet, self heating provokes a coupling between the electrical and thermal problem and gives rise to nonlinear phenomena We introduce a time stepping iterative method to perform the calculations The electrical and thermal solvers are based on FEM and Green's functions techniques respectively An extensive dynamic analysis of the device will be presented The results include heating and cooling curves, Nyquist plot (complex locus) of the thermal impedance, time constant spectrum and structure function Comparisons with the linear case, ie a temperature independent resistor, are made and accompanied by analytical approximations if possible One key observation is that the nonlinearity may easily be overlooked: its detection is only possible in particular characteristics

Abstract: Stability is a very important property of control loop systems. For Linear Time Invariant (LTI) systems the Nyquist criterion is well known. In systems with converters, signals with different frequencies are related, these systems are not LTI. To describe them, the theory for Linear Time Periodic (LTP) systems can be used: The transfer function of the LTI systems is extended to the transfer matrix of LTP systems; the Nyquist criterion can also be extended for these systems using the eigenloci of the transfer matrix. Regarding Exponentially Modulated Periodic (EMP) signals as stationary solutions for LTI or LTP systems, an alternative approach is presented: The Nyquist criterion can be derivated using the relation between the Nyquist plot and the conformal map of the transfer function for LTI systems. With this, a transfer function of the open loop is defined also for LTP systems. As will be shown the Nyquist criterion can be applied to this transfer function for LTP systems.

Abstract: This paper presents a simple proportional-plus- integral (PI) boundary controller for an unstable parabolic systems. For an infinite-dimensional system, the characteristics of minimum-phase is not easily observed from those governing equation and boundary conditions. In this paper the method of infinite product expansion is firstly employed to identify exact locations of system zeros/poles. Furthermore, if the system parameters are given, the Nyquist plot can be used for minimum-phase check. Once the minimum-phase condition is satisfied, a simple PI output feedback boundary controller can achieve stabilizing even if there are multiple unstable modes.

Abstract: This paper presents dynamic thermal analyses of a power amplifier. All the investigations are based on the transient junction temperature measurements performed during the circuit cooling process. The presented results include the cooling curves, the structure functions, the thermal time constant distribution and the Nyquist plot of the thermal impedance. The experiments carried out demonstrated the influence of the contact resistance and the position of the entire cooling assembly on the obtained results.

Abstract: A drawback of the circle criterion for controller design for systems with memory-less nonlinearities is that it employs the Nyquist plot, for which frequency is an implicit variable. This paper presents a method for translating the circle criterion into allowable and forbidden regions on the Bode plot of a single-input/single-output system. This circle criterion-bode plot facilitates controller synthesis with loop shaping. The design concept is to shape the open loop response to avoid intersections between the forbidden regions and the magnitude and phase graphs. An application to the design of the controller for a lateral tape motion compensation system shows the utility of the plot.

Abstract: Electrical and electrochemical processes in a bioactive soda-lime phosphosilicate glasses and in a bioabsorbable soda-lime phosphate glass during thermal poling were studied by means of thermally stimulated depolarization current measurements, ac impedance spectroscopy, and SEM/EDX analyses. The thermal poling was done by sputtering thin Pt electrode films onto the faces of the glass samples and by applying voltages up to 1 kV to the electrodes at temperatures up to 513 K. The poling leads to the formation of interfacial layers under the electrodes which are responsible for two depolarization current peaks and for one additional semicircle in a Nyquist plot of the ac impedance. The SEM/EDX profiles suggest that redox and transport processes of Na+ ions are responsible for the formation of the interfacial layers and that Ca2+ ions are immobile under the poling conditions. The sodium depletion layer under the anode leads to a negative surface charge of the glass samples which may enhance their bioactivity.

Abstract: The regularities of motion of a point on the plane (in the space) of adjustable controller parameters at variations of the phase margin under a fixed crossover frequency were analyzed. The problem of decomposition of the stability domain into the zones with simple and complex Nyquist plots and subsequent construction of the point subset where all points satisfying the requirements on the system frequency characteristics was solved. Examples were presented.

Abstract: This series of papers presents details of numerical studies of the nature of the impedance of solid oxide fuel cell (SOFC) anodes caused by gas-phase transport processes. The present part treats channel geometries where gases are transported parallel to the electrode surface. Two cases are investigated: (i) channel flow by forced convection, a typical situation in planar stack segments; and (ii) channel diffusion without convective flow, a typical situation in laboratory-scale single-chamber experiments using symmetrical cells. Current/voltage curves and electrochemical impedance spectra are simulated based on the Navier-Stokes transport equations and nonlinear electrochemistry models. Both channel flow and channel diffusion cause a capacitive behavior in the form of an resistance-capacitive (RC)-type semicircle in the Nyquist diagram. Its resistance and relaxation frequency strongly depend on operation parameters (gas concentration, flow rate, temperature, electrochemical polarization) and geometry (channel length and cross-sectional area). The model predictions are in good quantitative agreement with four different experimental studies published in the literature. The simulation approach thus allows a physically based assignment of observed gas concentration impedance processes.

Abstract: The storage behavior and process of the first delithiation-lithiation of LiCoO2 cathode were investigated by electrochemical impedance spectroscopy (EIS). The electronic and ionic transport properties of LiCoO2 cathode along with variation of electrode potential were obtained in 1 mol·L−1 LiPF6-EC:DMC: DEC electrolyte solution. It was found that after 9 h storage of the LiCoO2 cathode in electrolyte solutions, a new arc appears in the medium frequency range in Nyquist plots of EIS, which increases with increasing the storage time. In the charge/discharge processes, the diameter of the new arc is reversibly changed with electrode potential. Such variation coincides well with the electrode potential dependence of electronic conductivity of the LiCoO2. Thus this new EIS feature is attributed to the change of electronic conductivity of Li x CoO2 during storage of the LiCoO2 cathode in electrolyte solutions, as well as in processes of intercalation-deintercalationtion of lithium ions. It has been revealed that the reversible increase and decrease of the resistance of SEI film in charge-discharge processes can be also ascribed to the variation of electronic conductance of active materials of the LiCoO2 cathode