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The relative permittivity of air changes with temperature, humidity, and barometric pressure. [25] Sensors can be constructed to detect changes in capacitance caused by changes in the relative permittivity. Most of this change is due to effects of temperature and humidity as the barometric pressure is fairly stable.
By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at standard temperature and pressure, air has a relative permittivity of ε r air ≡ κ air ≈ 1.0006 . Relative permittivity is directly related to electric susceptibility (χ) by = otherwise written as
The ultimate low-κ material is air with a relative permittivity value of ~1.0. However, the placement of air gaps between the conducting wires compromises the mechanical stability of the integrated circuit making it impractical to build an IC consisting entirely of air as the insulating material.
Electric susceptibility. In electricity (electromagnetism), the electric susceptibility ( ; Latin: susceptibilis "receptive") is a dimensionless proportionality constant that indicates the degree of polarization of a dielectric material in response to an applied electric field. The greater the electric susceptibility, the greater the ability of ...
Clausius–Mossotti relation. In electromagnetism, the Clausius–Mossotti relation, named for O. F. Mossotti and Rudolf Clausius, expresses the dielectric constant (relative permittivity, εr) of a material in terms of the atomic polarizability, α, of the material's constituent atoms and/or molecules, or a homogeneous mixture thereof.
ε 0 ≈ 8.854 × 10 −12 F/m is the electric constant, also known as the permittivity of free space, c is the speed of light in free space, [9] [10] The reciprocal of Z 0 is sometimes referred to as the admittance of free space and represented by the symbol Y 0.
In general, capacitance is a function of frequency. At high frequencies, capacitance approaches a constant value, equal to "geometric" capacitance, determined by the terminals' geometry and dielectric content in the device. A paper by Steven Laux [27] presents a review of numerical techniques for capacitance calculation.
Relative permittivity table. Relative permittivities of some materials at room temperature under 1 kHz. Material. ε r. Vacuum. 1 (by definition) Air. 1.000 589 86 ± 0.000 000 50. (at STP, 900 kHz), [1]