Dictionary:Impedance

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(im pēd’ ∂ns)

1. The apparent resistance to the flow of alternating current, analogous to resistance in a dc circuit. Impedance is (in general) complex, of magnitude Z with a phase angle Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \gamma} . These can be expressed in terms of resistance R (in ohms), inductive reactance Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle X_L=2\pi fL} , and capacitive reactance Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle X_C=\frac{1}{2\pi fC}} :


Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle Z=\sqrt{R^2+\left(X_L-X_C\right)^2}} ,


Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \gamma=\tan^{-1} \left( \frac{X_L-X_C}{R} \right) } .


Z is in ohms when frequency f is in hertz, L is inductance in henrys, and C is capacitance in farads.

2. Acoustic impedance, the product of density and velocity, the ratio of the pressure to the volume displacement at a given surface in a sound-transmitting medium. Because reflection coefficients change with angle, elastic impedance is sometimes used for non-normal incidence.

3. In magnetotelluric exploration, if Ex is the electric-field component in an arbitrary horizontal direction and Hy is the associated magnetic-field (in the orthogonal horizontal direction), the wave impedance (Cagniard impedance, field impedance, or surface impedance) ZS is:


Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle Z_S= \frac{E_x}{H_y} } .


The surface impedance is a complex number because of phase differences between Ex and Hy. Measurements of surface impedance versus frequency can be interpreted in terms of the electrical properties of the subsurface. The surface impedance is a tensor if the conductivity structure is nonlayered. The reciprocal of impedance is called admittance.



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Impedance
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