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

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.
References in periodicals archive ?
This then raises the question whether the assumption of a rectangular cross-section for an impedance calculation is accurate enough, or will signal integrity be compromised by this imperfectly shaped cross-section?
As mentioned in part 1, to ensure a reflection-free signal, high-speed nets require impedance matching.
Compared with (8) and (9), the impedance ratio based on current source mode is [T.sub.m] = [Z.sub.g] / [Z.sub.s].
The response and recovery times for the sensors that presented the best linearity of impedance response were measured.
Elastic impedance inversion with different K values gives different values of Poisson's ratio estimation, which shows that it is sensitive to the choice of K (Mallick, 2001).
When a MPP is backed with a cavity (air gap) of depth D, impedance of the cavity ([z.sub.CAV]) is added to the MPP impedance ([z.sub.MPP]):
Again, as the response of bioimpedance changes with frequency, a multifrequency impedance analysis can offer better insight into plant physiology and better understanding to plant tissue status.
In impedance control, the end-effector behaves as a damped spring-mass system, which is represented in a single DoF system as
From the relationship in Figure 3, it can be observed that the resonator length ([[theta].sub.0]) can be shortened by selecting a smaller impedance ratio value K (or bigger impedance difference), enabling a compact-size resonator.
Equations (1), (2), (3), (4), (5), and (6) link the ECS impedance with applied stress for understanding the operation principle of eddy current-based elastic and plastic deformation evaluation method.
Applying the surface electric impedance definition J = [Y.sub.e]E to Eqs.
Figure 1 shows a non-contact measurement setup for the impedance of a load [Z.sub.L] connected to an end of a wire.