acoustic impedance

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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.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

a·cous·tic im·ped·ance

the resistance that a material offers to the passage of a sound wave (colloquial); a property of a medium computed as the product of density and sound propagation speed (characteristic acoustic impedance). Discontinuities in acoustic impedance are responsible for the echoes on which ultrasound imaging is based. Unit: the rayl.
Farlex Partner Medical Dictionary © Farlex 2012

a·cous·tic im·ped·ance

(ă-kūstik im-pēdăns)
Resistance that a material offers to the passage of a sound wave (colloquial).
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
A second characteristic of ultrasound waves is that their rate of propagation is inversely proportional to the acoustical impedance of the material through which they are transmitted.
From the experimental values a number of thermodynamic parameters, namely ultrasonic velocity, adiabatic compressibility, acoustical impedance, relaxation time, free length, free volume, internal pressure, Rao's constant, ultrasonic attenuation, cohesive energy, molar volume, and Wada's constant have been calculated.
At very low frequencies, the results are sensitive to the value of the acoustical impedance since it is difficult to measure impedance accurately below 50 Hz using ASTM E1050.