Electrical Impedance

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Electrical impedance

The measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (ac) circuit.

A generalized ac circuit may be composed of the interconnection of various types of circuit elements. The impedance of the circuit is given by Z = V/I, where Z is a complex number given by Z = R + jX. R, the real part of the impedance, is the resistance of the circuit, and X, the imaginary part of the impedance, is the reactance of the circuit. The units of impedance are ohms. See Electrical resistance, Reactance

Impedance, Electrical


a quantity characterizing the opposition presented by a circuit to an alternating current. Often called simply impedance, it is measured in ohms. In the case of a sinusoidal alternating current, the impedance is expressed by the ratio of the amplitude of the voltage applied to the circuit terminals and the amplitude of the current throught the circuit; here, the impedance is equal to Impedance, Electrical, where r is the resistance and x is the reactance. In the case of a nonsinusoidal alternating current, the impedance is determined separately for each kth har monic component: Impedance, Electrical.

electrical impedance

[i′lek·trə·kəl im′pēd·əns]
Also known as impedance.
The total opposition that a circuit presents to an alternating current, equal to the complex ratio of the voltage to the current in complex notation. Also known as complex impedance.
The ratio of the maximum voltage in an alternating-current circuit to the maximum current; equal to the magnitude of the quantity in the first definition.
References in periodicals archive ?
Electrical impedance probing of the muscle food anisotropy for meat ageing control.
Supported by non-technical appendices giving the basics on EIT and bioimpedance, the papers collected here provide comprehensive information on algorithms (the reconstruction problem), hardware (instrumentation), applications (for the thorax, brain function, breast cancer screening, gastrointestinal imagery and other applications such as hyperthermia and intra-pelvic venous congestion) and new directions such as magnetic induction tomography, magnetic resonance electrical impedance tomography, and industrial applications.
Many other new technologies, such as optical imaging, positron emission tomography, and electrical impedance imaging, are at a relatively early stage of development, and more research is needed to assess their accuracy, she added.
Called electrical impedance tomography, or EIT, the technique bears some similarity to magnetic resonance imaging (MRI).
MEMS and electrical impedance spectroscopy (EIS) for non-invasive measurement of cells
Contract notice: Modules for high resolution monitoring of electrical impedance in special conditions of high temperatures to range from 1 mhz to 3 ghz.
They are also adapting the technology to improve the early detection of breast cancer using high-resolution electrical impedance tomography and have forged a partnership with the NYU School of Medicine to design more effective cochlear implants.
Medical physicists mainly from the Institute of Cancer Research and Royal Marsden Hospital in the UK cover the origins of medical imaging, x-rays, x-ray transmission computed tomography and clinical applications in radiotherapy planning, radioisotope imaging, diagnostic ultrasound, spatially localized magnetic resonance imaging, infrared imaging, imaging of tissue electrical impedance, optical imaging, the mathematics of image formation and processing, perception and interpretation of images, and computer requirements.
As it moves, the pipette monitors a property called electrical impedance -- a measure of how difficult it is for electricity to flow out of the pipette.
The sample is first doped with a known concentration of polystyrene beads, and as beads and cells are drawn along the channel they pass between two electrodes, altering the electrical impedance.

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