# Air impedance

• posted

Hi,

I want to measure the impedance or conductance of air. How can I achieve and what is the possible value of the impedance of the air? Thank you very much!

Wayne

• posted

Use Google. I found this immediately. So, get yourself a permeability meter and a permittivity meter and go to it.

resource for permeability and permittivity.... google or a library.

You can also look for an acoustic impedance of air.

Jim

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The characteristic impedance of free space, also called the Zo of free space, is an expression of the relationship between the electric-field and magnetic-field intensities in an electromagnetic field (EM field) propagating through a vacuum. The Zo of free space, like characteristic impedance in general, is expressed in ohms, and is theoretically independent of wavelength. It is considered a physical constant.

Mathematically, the Zo of free space is equal to the square root of the ratio of the permeability of free space (µo) in henrys per meter (H/m) to the permittivity of free space (o) in farads per meter (F/m):

Zo = (µo/o)1/2

= [(1.257 x 10-6 H/m)/(8.85 x 10-12 F/m)]1/2

= 377 ohms (approximately)

The exact value of the Zo of free space is 120 pi ohms, where pi is the ratio of the circumference of a circle to its diameter.

The Zo of dry air is similar to that of free space, because dry air has little effect on permeability or permittivity. However, in environments where the air contains seawater spray, excessive humidity, heavy precipitation, or high concentrations of particulate matter, the Zo is slightly reduced. Characteristic impedance is important to wireless communications engineers involved in antenna design.

Also see Table of Physical Units and Constants.

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