Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

RF Generator System for Surgical Vessel Sealing

Abstract: Systems, methods, and apparatus for providing power to an electrosurgical instrument. In particular, a power supply is disclosed in which non-sinusoidal (e.g., pulsed) constant frequency voltage having a variable amplitude is passed to an LC circuit to produce a quasi-sinusoidal current in the LC circuit. The constant driving frequency can be one half the resonant frequency of the LC circuit allowing the LC circuit to operate as an impedance, and thus limit current spikes and arcing. The frequency and phasing of the driving voltage also enables the LC circuit to discharge energy back into a power provider of the power supply so that energy does not build up in the LC circuit. These features result in less severe current spikes and arcing, as well as reduced cutoff times.

Dielectric spectroscopy in a micromachined flow cytometer: theoretical and practical considerations

Abstract: We propose a model to determine the influence of different cell properties, such as size, membrane capacitance and cytoplasm conductivity, on the impedance spectrum as measured in a microfabricated cytometer. A dielectric sphere of equivalent complex permittivity is used as a simplified model to describe a biological cell. The measurement takes place between a pair of facing microelectrodes in a microchannel filled with a saline solution. The model incorporates various cell parameters, such as dielectric properties, size and position in the channel. A 3D finite element model is used to evaluate the magnitude of the electric field in the channel and the resultant changes in charge densities at the measurement electrode boundaries as a cell flows past. The charge density is integrated on the electrode surface to determine the displacement current and the channel impedance for the computed frequency range. The complete impedance model combines the finite element model, the electrode-electrolyte interface impedance and stray impedance, which are measured from a real device. The modeled dielectric complex spectra for various cell parameters are discussed and a measurement strategy for cell discrimination with such a system is proposed. We finally discuss the amount of noise and measurement fluctuations of the sensor.

High frequency surgical apparatus with tracking of impedance measurement

Abstract: The HF surgical instrument (21) with a HF generator (11), is connectable with at least one active electrode (12) output (13) and at least one neutral electrode (14) - output (15), at which at least one part neutral electrode (14a) of a neutral electrode pair (14a,14b) can be connected. The individual electrodes (14a,14b) of which are connected at an auxiliary voltage with a marked lower frequency than the HF. A monitoring circuit from the auxiliary voltage and the auxiliary current flowing between the part neutral electrodes produces an impedance signal (19) representative for the impedance between the part neutral electrodes. With the exceeding of the first fixed upper alarm threshold (17) and/or a lower second upper alarm threshold (20) matchable to the actual value of the impedance signal, for the impedance signal (19) delivers a HF generator blocking signal (22) and/or an alarm signal (23). The matching of the second alarm threshold (20) is carried out by pressing a SET push button (24).

Polarization Resistance Method for Determination of Instantaneous Corrosion Rates

Abstract: The polarization resistance method for the determination of instantaneous corrosion rates of metals were reviewed. The assumptions in electrode kinetics that govern the connection between the slope of steady-state applied electrochemical potential-applied current density (Eapp-iapp) measurements (i.e., the polarization resistance) and the corrosion rate were restated. Electrochemical impedance, as well as statistical and spectral electrochemical noise methods for obtaining polarization resistance, also were discussed. Traditional sources of error such as high excitation voltage amplitudes, insufficiently slow voltage ramp rates, high alternating current (AC) frequencies, inadequate polarization hold periods, high solution resistance, presence of parallel reduction-oxidation reactions, and nonuniform current and potential distributions were examined with the goal of defining some of the conditions and circumstances where these complicating factors are important. Other complicating factors such as ...