Browse Definitions :
Definition

characteristic impedance of free space

The characteristic impedance of free space , also called the Z o 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 Z o of free space, like characteristic impedance in general, is expressed in ohm s, and is theoretically independent of wavelength . It is considered a physical constant.

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

Z o = (µ o / 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 Z o of free space is 120 pi ohms, where pi is the ratio of the circumference of a circle to its diameter.

The Z o 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 Z o is slightly reduced. Characteristic impedance is important to wireless communications engineers involved in antenna design.

Also see Table of Physical Units and Constants.

This was last updated in September 2005

SearchCompliance

  • information governance

    Information governance is a holistic approach to managing corporate information by implementing processes, roles, controls and ...

  • enterprise document management (EDM)

    Enterprise document management (EDM) is a strategy for overseeing an organization's paper and electronic documents so they can be...

  • risk assessment

    Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

SearchSecurity

  • spam trap

    A spam trap is an email address that is used to identify and monitor spam email.

  • honeypot (computing)

    A honeypot is a network-attached system set up as a decoy to lure cyber attackers and detect, deflect and study hacking attempts ...

  • cracker

    A cracker is someone who breaks into someone else's computer system, often on a network; bypasses passwords or licenses in ...

SearchHealthIT

SearchDisasterRecovery

  • risk mitigation

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a business.

  • call tree

    A call tree is a layered hierarchical communication model that is used to notify specific individuals of an event and coordinate ...

  • Disaster Recovery as a Service (DRaaS)

    Disaster recovery as a service (DRaaS) is the replication and hosting of physical or virtual servers by a third party to provide ...

SearchStorage

  • cloud storage

    Cloud storage is a service model in which data is transmitted and stored on remote storage systems, where it is maintained, ...

  • cloud testing

    Cloud testing is the process of using the cloud computing resources of a third-party service provider to test software ...

  • storage virtualization

    Storage virtualization is the pooling of physical storage from multiple storage devices into what appears to be a single storage ...

Close