# 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 ?
Before the analysis of the mechanical impedance of pantograph head, the range of the dominant frequency of contact force should be determined through the frequency analysis of the contact force.
Such obtained mechanical impedance [Z.sub.U](s), in the form of "partial fractions," could be represented as the sum of any rational functions.
The goal of this study is to show how the kinematics and kinetics of the ankle, and therefore its mechanical impedance, change in different maneuvers.
Moreover (1) defines that the attachment of PZT patch to the structure couples the mechanical impedance of the structure to the electrical impedance.
Moreover, the ambitious objectives of this project included achieving a real breakthrough in vibration control technologies creating an absolutely new kind of mechanical impedance matching device as a key tool for enhancing the effectiveness of other vibration control elements.
Briefly, the impedance-controlled anklebot (Interactive Motion Technologies; Watertown, Massachusetts) is an exoskeleton that is backdriveable, possesses intrinsically low mechanical impedance, and allows normal ROM in all three DOFs of the foot relative to the shank during walking or while seated but provides independent, active assistance or resistance in only DF-PF and INV-EV.
Measurement of the mechanical impedance of laminated glass.
A vertical smooth blade with an array of strain gauges was designed to dynamically measure mechanical impedance of soil at multiple depths.
[32, 33] proposed a method to test stiffness and damping of the isolator based on three-parameter system; an equivalent two-parameter physical system was obtained based on mechanical impedance theory.
Electrical admittance Y([omega]) (inverse function of the electrical impedance) of the piezoelectric transducer (PZT) is a combined function of the mechanical impedance of the PZT actuator [Z.sub.a] ([omega]) and that of the host structure Z([omega]) [6]:
The sensors are used during vibration testing of aerospace structures to match the mechanical impedance of shaker inputs and may be used to force limit the shaker controller to prevent damage to expensive structures.

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