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.

Differential signal transmission circuit

Abstract: Differential signal transmission circuit for transmitting a high speed signal through a differential transmission line with: a CMOS (complementary metal oxide semiconductor) differential driver for receiving a transmitted from an LSI for high speed signal and passing the signal to a differential transmission cable; and an impedance matching circuit provided between an output of the CMOS differential driver and ground to reduce an output impedance of the CMOS differential driver; wherein said impedance matching circuit comprises a series termination circuit which is provided between the output of the CMOS differential driver and the differential transmission cable, and a pair of parallel resistors, which are provided between the output of the CMOS differential driver and mass which, with the sum of the resistance of series termination circuit and an overall impedance is adjusted at the output of the CMOS differential driver to a characteristic impedance of the differential transmission cable, and wherein the total impedance at the output of the CMOS differential driver is set by the parallel resistors.

Quantification of membrane properties of trigeminal root ganglion neurons in guinea pigs.

Abstract: Passive and active (voltage- and time-dependent) membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. The complex impedance functions of trigeminal ganglion neurons were computed from the ratios of the fast Fourier transforms of the intracellularly recorded voltage response from the neuron and of the input current, which had a defined oscillatory waveform. The impedance magnitude functions and corresponding impedance locus diagrams were fitted with various membrane models such that the passive and active properties were quantified. The complex impedances of less than one-quarter of the 105 neurons which were investigated extensively could be described by the complex impedance function for a simple RC-electrical circuit. In such neurons, the voltage responses to constant-current pulses, using conventional bridge-balance techniques, could be fitted with single exponential curves, also suggesting passive membrane behavior. A nonlinear least-squares fit of the complex impedance function for the simple model to the experimentally observed complex impedance yielded estimates of the resistance of the electrode, and of input capacitance (range, 56 to 490 pF) and input resistance (range, 0.8 to 30 M omega) of the neurons. The majority of trigeminal ganglion neurons were characterized by a resonance in the 50- to 250-Hz bandwidth of their impedance magnitude functions. Such neurons when injected with "large" hyperpolarizing current pulses using bridge-balance techniques showed membrane voltage responses that "sagged" (time-dependent rectification). Also, repetitive firing commonly occurred with depolarizing current pulses; this characteristic of neurons with resonance in their impedance magnitude functions was not observed in neurons with "purely" passive membrane behavior. A nonlinear least-squares fit of a five-parameter impedance fitting function based on a membrane model to the impedance locus diagram of a neuron with resonance yielded estimates of its membrane properties: input capacitance, the time-invariant part of the conductance, the conductance activated by the small oscillatory input current, and the relaxation time constant for this conductance. The ranges of the estimates for input capacitance and input resistance were comparable to the ranges of corresponding properties derived for neurons exhibiting "purely" passive behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Impedance spectra of tumour tissue in comparison with normal tissue; a possible clinical application for electrical impedance tomography

Abstract: Electrical characteristics of living tissues have been investigated for a long time in the search for further methods to complement the traditional investigations of pathology and physiology. Tumour tissue has been shown to exhibit a larger permittivity and conductivity than normal tissues. This might be associated with the fact that tumour cells have a higher water content and sodium concentration than normal cells, as well as different electrochemical properties of their cell membranes. To our knowledge only a few contributions on this subject have been published. This study describes an additional application on measurements of the complex impedance of tumour and normal tissues, in order to compare the impedance features of the two tissue types. The tissue sample is placed in a measuring cell in which the temperature is controlled. The measuring cell is connected to an impedance meter able to measure the complex impedance in terms of real and imaginary part curves for frequencies from 1.5 kHz to 700 kHz. The four-electrode principle is used with the current injected by the outer electrodes and the voltage difference measured between the inner electrodes. The current can be altered up to 1 mA. The instrument can be calibrated with known resistance and capacitance networks connected to the input of the instrument in order to minimize the measurement errors. The calibration routine uses a polynomial adaptation and can be applied interactively. Measurements performed by the instrument show promising results. Preliminary results show that this method can be extended to a new application for detection of tumour tissue by electrical impedance tomography (EIT).

Design of a High-Efficiency Wireless Power Transfer System With Intermediate Coils for the On-Board Chargers of Electric Vehicles

Abstract: In this paper, a high efficiency inductive wireless power transfer system for the on-board chargers of electric vehicles is proposed. In order to improve the power transfer efficiency, the proposed system adopts two additional intermediate coils with resonant capacitors, which increases the effective magnetizing impedance between the transmitter and receiver coils with no ferrites. The resonant tank of the proposed system is designed to operate the converter as a current source and as a voltage source at two different frequencies to implement the constant current (CC) mode charge and constant voltage (CV) charge, respectively. Since the proposed converter operates at a fixed frequency in each mode of charge operation, full soft switching of all the switching devices is possible and the zero phase angle condition can be achieved in both the CC and CV mode operations. A theoretical analysis based on a Thevenin model to come up with a suitable design for the battery charger and its closed-loop controller is presented and its superior performance is demonstrated by experimental results. A 6.6 kW prototype is implemented with a 200 mm air gap to demonstrate the validity of the proposed method. Experimental results show that the dc to dc conversion efficiency of the proposed system is 97.08% at 3.7 kW of output power in the CV mode charge.