impedance


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impedance

 [im-pe´dans]
1. obstruction or opposition to passage or flow, as of an electric current or other form of energy.
2. the resistance in alternating current circuits, represented by the letter Z in mathematical formulas. Medical equipment is often rated according to impedance to allow for optimum performance by matching impedance ratings. A transformer can be used between components to cause the impedances of unequal systems to match.
acoustic impedance an expression of the opposition to passage of sound waves, being the product of the density of a substance and the velocity of sound in it.

im·ped·ance

(im-pē'dăns),
1. Total opposition to flow. In electricity, when flow is steady, impedance is simply the resistance, for example, the driving pressure per unit flow; when flow is changing, impedance also includes the factors that oppose changes in flow. Thus, deviations of impedance, from simple ohmic resistance because of the effects of capacitance and inductance, become more important in alternating current as the frequency of oscillations increases. In fluid analogies (for example, pulsatile flow of blood, to-and-fro flow of respiratory gas), impedance depends not only on viscous resistance but also on compressibility, compliance, inertance, and the frequency of imposed oscillations.
2. Resistance of an acoustic system to being set in motion.

impedance

/im·ped·ance/ (im-pēd´ans) obstruction or opposition to passage or flow, as of an electric current or other form of energy. Symbol Z .
acoustic impedance  an expression of the opposition to passage of sound waves, being the product of the density of a substance and the velocity of sound in it.
aortic impedance  the sum of the external factors that resist ventricular ejection.

impedance

[impē′dəns]
Etymology: L, impedire, to entangle
a form of electric resistance observed in an alternating current that is analogous to the classic electric resistance that occurs in a direct current circuit. It is expressed as a ratio of voltage applied to a circuit to the current it produces, as an alternating current oscillates ahead of or behind the voltage.

Impedance

Cardiac pacing The total opposition that a circuit presents to alternating electrical current. Cf Resistance.

im·ped·ance

(im-pē'dăns)
1. Opposition to flow of gases, liquids, or electrical current.
2. Resistance of an acoustic system to being set in motion.

impedance

any resistance to the flow of fluids moved by a series of pulses, such as blood flow.

impedance

obstruction or opposition to passage or flow, as of an electric current or other form of energy.

acoustic impedance
an expression of the opposition to passage of sound waves, being the product of the density of a substance and the velocity of sound in it.
References in periodicals archive ?
Sonoscan's laboratories often image parts on both the front and back surfaces because a substantial difference in average acoustic impedance between the two surfaces can be a sign that the part is counterfeit due to blacktopping of the top surface.
Also, in many cases there is not much concern, as the impedance signal is traveling down a through-hole to an impedance-controlled flexible layer.
The equivalent circuit in Figure 2(b) from [20] requires five capacitors and six resistors to represent this averaged impedance data.
For the impedance spectroscopy analysis, the blood was drawn with the help of 5-mL syringe and further processed for the isolation of RBCs.
On the other hand, STATCOM can be modeled as a shunt branch which is an ideal current source, without internal impedance.
Figures 2 and 3 show the relationships between the impedance ratio [rho] and frequency-ratio p, q, which clearly demonstrate that the decrease rate of [rho] is reducing with the increase of p and q.
In the four special cases presented below, the terminating impedance [Z.
The parasitic patch is used to improve impedance matching and AR bandwidth.
New IRA of reduced input impedance of 100 [ohm] is designed with full ACD plate of length 184 mm and 2 mm thickness and a 46 cm diameter parabolic reflector with focal length 18.
In EHV transmission line, as the impedance angle is close to 90[degrees], and reactance component predominates, in order to simplify computation, the reactance component can be used to judge impedance convergence, as shown by
Conclusion: Normal pregnancy causes dilatation of the pelvicalyceal system and significant reduction in renal venous impedance index values in second and third trimesters.