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

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • compliance audit

    A compliance audit is a comprehensive review of an organization's adherence to regulatory guidelines.

  • regulatory compliance

    Regulatory compliance is an organization's adherence to laws, regulations, guidelines and specifications relevant to its business...

  • Whistleblower Protection Act

    The Whistleblower Protection Act of 1989 is a law that protects federal government employees in the United States from ...

SearchSecurity

  • reverse brute-force attack

    A reverse brute-force attack is a type of brute-force attack in which an attacker uses a common password against multiple ...

  • orphan account

    An orphan account, also referred to as an orphaned account, is a user account that can provide access to corporate systems, ...

  • voice squatting (skill squatting)

    Voice squatting is an attack vector for voice user interfaces (VUIs) that exploits homonyms (words that sound the same but are ...

SearchHealthIT

SearchDisasterRecovery

  • business continuity policy

    Business continuity policy is the set of standards and guidelines an organization enforces to ensure resilience and proper risk ...

  • business continuity and disaster recovery (BCDR)

    Business continuity and disaster recovery (BCDR) are closely related practices that describe an organization's preparation for ...

  • warm site

    A warm site is a type of facility an organization uses to recover its technology infrastructure when its primary data center goes...

SearchStorage

  • RAM (Random Access Memory)

    RAM (Random Access Memory) is the hardware in a computing device where the operating system (OS), application programs and data ...

  • primary storage (main storage)

    Primary storage is the collective methods and technologies used to capture and retain digital information that is in active use ...

  • cache memory

    Cache memory, also called CPU memory, is high-speed static random access memory (SRAM) that a computer microprocessor can access ...

Close