Browse Definitions:
Definition

# harmonic

A harmonic is a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of some reference signal or wave. The term can also refer to the ratio of the frequency of such a signal or wave to the frequency of the reference signal or wave.

Let f represent the main, or fundamental, frequency of an alternating current ( AC ) signal, electromagnetic field , or sound wave. This frequency, usually expressed in hertz , is the frequency at which most of the energy is contained, or at which the signal is defined to occur. If the signal is displayed on an oscilloscope, the waveform will appear to repeat at a rate corresponding to f Hz.

For a signal whose fundamental frequency is f , the second harmonic has a frequency 2 f , the third harmonic has a frequency of 3 f , and so on. Let w represent the wavelength of the signal or wave in a specified medium. The second harmonic has a wavelength of w /2, the third harmonic has a wavelength of w /3, and so on. Signals occurring at frequencies of 2 f , 4 f , 6 f , etc. are called even harmonics; the signals at frequencies of 3 f , 5 f , 7 f , etc. are called odd harmonics. A signal can, in theory, have infinitely many harmonics.

Nearly all signals contain energy at harmonic frequencies, in addition to the energy at the fundamental frequency. If all the energy in a signal is contained at the fundamental frequency, then that signal is a perfect sine wave. If the signal is not a perfect sine wave, then some energy is contained in the harmonics. Some waveforms contain large amounts of energy at harmonic frequencies. Examples are square waves, sawtooth waves, and triangular waves.

In wireless communications and broadcasting, transmitters are designed so they emit a minimum of energy at harmonic frequencies. Normally, a wireless device is intended for use at only one frequency. Signal output at harmonic frequencies can cause interference to other communications or broadcasting. For example, a broadcast signal at 90.5 MHz (in the standard FM band) would have a second harmonic at 181 MHz, a third harmonic at 271.5 MHz, a fourth harmonic at 362 MHz, and so on. Some or all of these harmonic signals could, if strong, disrupt activities in other wireless services.

This was last updated in September 2005

#### Join the conversation

Send me notifications when other members comment.
Thank you for this...This has been a very clear description of harmonics relating to signals!
Cancel
May you have harmonics that are lower than the fundamental frequency? Example: A 20KHz sine wave would have a 10KHz and 5KHz and 2.5KHz etc....
Cancel
This really helped me with my science project.
Cancel
To go deeper in your visualisation and ear of harmonic on very didactic and pedagogic way is to visit http://www.bachmonic.com
Seeing and earing harmonic on a piano!
Cancel

Joseph
<a href="http://www.c2bpromo.com">http://www.c2bpromo.com</a>
Cancel

## SearchCompliance

• ### risk map (risk heat map)

A risk map, also known as a risk heat map, is a data visualization tool for communicating specific risks an organization faces. A...

• ### internal audit (IA)

An internal audit (IA) is an organizational initiative to monitor and analyze its own business operations in order to determine ...

• ### pure risk (absolute risk)

Pure risk, also called absolute risk, is a category of threat that is beyond human control and has only one possible outcome if ...

## SearchSecurity

• ### federated identity management (FIM)

Federated identity management (FIM) is an arrangement that can be made among multiple enterprises to let subscribers use the same...

• ### cross-site scripting (XSS)

Cross-site scripting (XSS) is a type of injection security attack in which an attacker injects data, such as a malicious script, ...

• ### firewall

In computing, a firewall is software or firmware that enforces a set of rules about what data packets will be allowed to enter or...

## SearchHealthIT

• ### 21st Century Cures Act

The 21st Century Cures Act is a wide-ranging healthcare bill that funds medical research and development, medical device ...

• ### vendor neutral archive (VNA)

A vendor neutral archive (VNA) is a technology that stores medical images in a standard format and interface, making them ...

• ### HITECH (Health Information Technology for Economic and Clinical Health) Act of 2009

The HITECH (Health Information Technology for Economic and Clinical Health) Act of 2009 is legislation that was created to ...

## SearchDisasterRecovery

• ### business continuity and disaster recovery (BCDR)

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

• ### business continuity plan (BCP)

A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

• ### call tree

A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

## SearchStorage

• ### all-flash array (AFA)

An all-flash array (AFA), also known as a solid-state storage disk system, is an external storage array that uses only flash ...

• ### volume manager

A volume manager is software within an operating system (OS) that controls capacity allocation for storage arrays.

• ### external storage device

An external storage device, also referred to as auxiliary storage and secondary storage, is a device that contains all the ...

## SearchSolidStateStorage

• ### hybrid hard disk drive (HDD)

A hybrid hard disk drive is an electromechanical spinning hard disk that contains some amount of NAND Flash memory.

Close