Resonator
Encyclopedia
A resonator is a device or system that exhibits resonance
or resonant behavior, that is, it naturally oscillates
at some frequencies
, called its resonant frequencies, with greater amplitude
than at others. The oscillations in a resonator can be either electromagnetic
or mechanical (including acoustic
). Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic
resonators that produce sound waves of specific tones.
A cavity resonator, usually used in reference to electromagnetic resonators, is one in which waves exist in a hollow space inside the device. Acoustic cavity resonators, in which sound is produced by air vibrating in a cavity with one opening, are known as Helmholtz resonators
.
; each degree of freedom can vibrate as a harmonic oscillator
. Systems with one degree of freedom, such as a mass on a spring, pendulum
s, balance wheel
s, and LC tuned circuits
have one resonant frequency. Systems with two degrees of freedom, such as coupled pendulums
and resonant transformers
can have two resonant frequencies. As the number of coupled harmonic oscillators grows, the time it takes to transfer energy from one to the next becomes significant. The vibrations in them begin to travel through the coupled harmonic oscillators in waves, from one oscillator to the next.
The term resonator is most often used for a homogeneous object in which vibrations travel as waves, at an approximately constant velocity, bouncing back and forth between the sides of the resonator. Resonators can be viewed as being made of millions of coupled moving parts (such as atoms). Therefore they can have millions of resonant frequencies, although only a few may be used in practical resonators. The oppositely moving waves interfere with each other to create a pattern of standing wave
s in the resonator. If the distance between the sides is
, the length of a round trip is 
. In order to cause resonance, the phase
of a sinusoidal wave after a round trip has to be equal to the initial phase so the waves will reinforce. So the condition for resonance in a resonator is that the round trip distance,
, be equal to an integral number of wavelengths 
of the wave:
If the velocity of a wave is
, the frequency is 
so the resonant frequencies are:
So the resonant frequencies of resonators, called normal modes, are equally spaced multiples (harmonic
s), of a lowest frequency called the fundamental frequency
. The above analysis assumes the medium inside the resonator is homogeneous, so the waves travel at a constant speed, and that the shape of the resonator is rectilinear. If the resonator is inhomogeneous or has a nonrectilinear shape, like a circular drumhead or a cylindrical microwave cavity, the resonant frequencies may not occur at equally spaced multiples of the fundamental frequency. They are then called overtone
s instead of harmonic
s. There may be several such series of resonant frequencies in a single resonator, corresponding to different modes of vibration.
and capacitor
are included. Oscillations are limited by the inclusion of a resistor
, which will be present, even if not specifically included, due to the resistance
of the inductor windings. Such resonant circuits are also called RLC circuit
s after the circuit symbols for the components.
A distributed-parameter
resonator has capacitance, inductance, and resistance that cannot be isolated into separate lumped capacitors, inductors, or resistors. An example of this, much used in filtering
, is the helical resonator
.
A single layer coil (or solenoid
) that is used as a secondary or tertiary winding in a Tesla coil
or magnifying transmitter
is also a distributed resonator.
short-circuited at both ends (see Microwave cavity
).
The cavity has interior surfaces which reflect a wave of a specific frequency. When a wave that is resonant with the cavity enters, it bounces back and forth within the cavity, with low loss (see standing wave
). As more wave energy enters the cavity, it combines with and reinforces the standing wave, increasing its intensity.
is a vacuum tube with a filament in the center of an evacuated, lobed, circular cavity resonator. A perpendicular magnetic field is imposed by a permanent magnet. The magnetic field causes the electrons, attracted to the (relatively) positive outer part of the chamber, to spiral outward in a circular path rather than moving directly to this anode. Spaced about the rim of the chamber are cylindrical cavities. The cavities are open along their length and so connect the common cavity space. As electrons sweep past these openings they induce a resonant high frequency radio field in the cavity, which in turn causes the electrons to bunch into groups. A portion of this field is extracted with a short antenna that is connected to a waveguide (a metal tube usually of rectangular cross section). The waveguide
directs the extracted RF energy to the load, which may be a cooking chamber in a microwave oven or a high gain antenna in the case of radar.
The klystron
, tube waveguide, is a beam tube including at least two apertured cavity resonators. The beam of charged particles passes through the apertures of the resonators, often tunable wave reflection grids, in succession. A collector electrode is provided to intercept the beam after passing through the resonators. The first resonator causes bunching of the particles passing through it. The bunched particles travel in a field-free region where further bunching occurs, then the bunched particles enter the second resonator giving up their energy to excite it into oscillations. It is a particle accelerator
that works in conjunction with a specifically tuned cavity by the configuration of the structures. On the beamline
of an accelerator system, there are specific sections that are cavity resonators for RF
.
The reflex klystron is a klystron utilizing only a single apertured cavity resonator through which the beam of charged particles passes, first in one direction. A repeller electrode is provided to repel (or redirect) the beam after passage through the resonator back through the resonator in the other direction and in proper phase to reinforce the oscillations set up in the resonator.
In a laser
, light is amplified in a cavity resonator which is usually composed of two or more mirrors. Thus an optical cavity
, also known as a resonator, is a cavity with walls which reflect electromagnetic waves (light
). This will allow standing wave modes to exist with little loss outside the cavity.
s to generate signals of a precise frequency
. These are called piezoelectric resonators, the most common of which is the quartz crystal. They are made of a thin plate of quartz with metal plates attached to each side, or in low frequency clock applications a tuning fork
shape. The quartz material performs two functions. Its high dimensional stability and low temperature coefficient makes it a good resonator, keeping the resonant frequency constant. Second, the quartz's piezoelectric
property converts the mechanical vibrations into an oscillating voltage
, which is picked up by the plates on its surface, which are electrically attached to the circuit. These crystal oscillator
s are used in quartz clock
s and watches, to create the clock signal
that runs computers, and to stabilize the output signal from radio transmitters. Mechanical resonators can also be used to induce a standing wave in other medium. For example a multiple degree of freedom system can be created by imposing a base excitation on a cantilever beam. In this case the standing wave
is imposed on the beam. This type of system can be used as a sensor
to track changes in frequency or phase of the resonance
of the fiber. One application is as a measurement device for dimensional metrology
.
s. Every musical instrument has resonators. Some generate the sound directly, such as the wooden bars in a xylophone
, the head of a drum
, the strings in stringed instruments, and the pipes in an organ. Some modify the sound by enhancing particular frequencies, such as the sound box of a guitar
or violin
. Organ pipe
s, the bodies of woodwinds, and the sound boxes of stringed instruments are examples of acoustic cavity resonators.
s are designed as acoustic resonators that work with the muffler
to reduce noise, by making sound waves "cancel each other out"http://auto.howstuffworks.com/muffler4.htm. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers
use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance, the resonance of the exhaust pipes is also used to 'pull' the combustion products out of the combustion chamber quicker.
, referred to simply as the resonator. The length of the tube varies according to the pitch of the note, with higher notes having shorter resonators. The tube is open at the top end and closed at the bottom end, creating a column of air which resonates
when the note is struck. This adds depth and volume to the note. In string instruments, the body of the instrument is a resonator.
The tremolo
effect of a vibraphone
is obtained by a mechanism which opens and shuts the resonators.
may also have resonators. Many five-string banjos have removable resonators, to allow the instrument to be used with resonator in bluegrass
style, or without in folk music
style. The term resonator, used by itself, may also refer to the resonator guitar
.
The modern ten-string guitar
, invented by Narciso Yepes
, adds four string resonators to the traditional classical guitar. By tuning these resonators in a very specific way (C, Bb, Ab, Gb) and making use of their strongest partials (corresponding to the octaves and fifths of the strings' fundamental tones), the bass strings of the guitar now resonate equally with any of the 12 tones of the chromatic octave. The Guitar Resonator is a device for driving guitar string harmonics by an electromagnetic field. This resonance effect is caused by a feedback loop and is applied to drive the fundamental tones, octaves, 5th, 3rd to an infinite sustain
.
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
or resonant behavior, that is, it naturally oscillates
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
at some frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, called its resonant frequencies, with greater amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
than at others. The oscillations in a resonator can be either electromagnetic
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
or mechanical (including acoustic
Acoustic music
Acoustic music comprises music that solely or primarily uses instruments which produce sound through entirely acoustic means, as opposed to electric or electronic means...
). Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic
Musical acoustics
Musical acoustics or music acoustics is the branch of acoustics concerned with researching and describing the physics of music – how sounds employed as music work...
resonators that produce sound waves of specific tones.
A cavity resonator, usually used in reference to electromagnetic resonators, is one in which waves exist in a hollow space inside the device. Acoustic cavity resonators, in which sound is produced by air vibrating in a cavity with one opening, are known as Helmholtz resonators
Helmholtz resonance
Helmholtz resonance is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle. The name comes from a device created in the 1850s by Hermann von Helmholtz, the "Helmholtz resonator", which he, the author of the classic study of acoustic science, used to...
.
Explanation
A physical system can have as many resonant frequencies as it has degrees of freedomDegrees of freedom (engineering)
In mechanics, degrees of freedom are the set of independent displacements and/or rotations that specify completely the displaced or deformed position and orientation of the body or system...
; each degree of freedom can vibrate as a harmonic oscillator
Harmonic oscillator
In classical mechanics, a harmonic oscillator is a system that, when displaced from its equilibrium position, experiences a restoring force, F, proportional to the displacement, x: \vec F = -k \vec x \, where k is a positive constant....
. Systems with one degree of freedom, such as a mass on a spring, pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
s, balance wheel
Balance wheel
The balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring...
s, and LC tuned circuits
RLC circuit
An RLC circuit is an electrical circuit consisting of a resistor, an inductor, and a capacitor, connected in series or in parallel. The RLC part of the name is due to those letters being the usual electrical symbols for resistance, inductance and capacitance respectively...
have one resonant frequency. Systems with two degrees of freedom, such as coupled pendulums
Double pendulum
In mathematics, in the area of dynamical systems, a double pendulum is a pendulum with another pendulum attached to its end, and is a simple physical system that exhibits rich dynamic behavior with a strong sensitivity to initial conditions. The motion of a double pendulum is governed by a set of...
and resonant transformers
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
can have two resonant frequencies. As the number of coupled harmonic oscillators grows, the time it takes to transfer energy from one to the next becomes significant. The vibrations in them begin to travel through the coupled harmonic oscillators in waves, from one oscillator to the next.
The term resonator is most often used for a homogeneous object in which vibrations travel as waves, at an approximately constant velocity, bouncing back and forth between the sides of the resonator. Resonators can be viewed as being made of millions of coupled moving parts (such as atoms). Therefore they can have millions of resonant frequencies, although only a few may be used in practical resonators. The oppositely moving waves interfere with each other to create a pattern of standing wave
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...
s in the resonator. If the distance between the sides is
, the length of a round trip is . In order to cause resonance, the phasePhase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
of a sinusoidal wave after a round trip has to be equal to the initial phase so the waves will reinforce. So the condition for resonance in a resonator is that the round trip distance,
, be equal to an integral number of wavelengths of the wave:If the velocity of a wave is
, the frequency is so the resonant frequencies are:So the resonant frequencies of resonators, called normal modes, are equally spaced multiples (harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
s), of a lowest frequency called the fundamental frequency
Fundamental frequency
The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the lowest frequency of a periodic waveform. In terms of a superposition of sinusoids The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the...
. The above analysis assumes the medium inside the resonator is homogeneous, so the waves travel at a constant speed, and that the shape of the resonator is rectilinear. If the resonator is inhomogeneous or has a nonrectilinear shape, like a circular drumhead or a cylindrical microwave cavity, the resonant frequencies may not occur at equally spaced multiples of the fundamental frequency. They are then called overtone
Overtone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...
s instead of harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
s. There may be several such series of resonant frequencies in a single resonator, corresponding to different modes of vibration.
Electromagnetic
An electrical circuit composed of discrete components can act as a resonator when both an inductorInductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
and capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
are included. Oscillations are limited by the inclusion of a resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
, which will be present, even if not specifically included, due to the resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
of the inductor windings. Such resonant circuits are also called RLC circuit
RLC circuit
An RLC circuit is an electrical circuit consisting of a resistor, an inductor, and a capacitor, connected in series or in parallel. The RLC part of the name is due to those letters being the usual electrical symbols for resistance, inductance and capacitance respectively...
s after the circuit symbols for the components.
A distributed-parameter
Distributed element model
In electrical engineering, the distributed element model or transmission line model of electrical circuits assumes that the attributes of the circuit are distributed continuously throughout the material of the circuit...
resonator has capacitance, inductance, and resistance that cannot be isolated into separate lumped capacitors, inductors, or resistors. An example of this, much used in filtering
Filter (signal processing)
In signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
, is the helical resonator
Helical resonator
A helical resonator is a passive electrical component that can be used as a filter. Physically, a helical resonator is a wire helix surrounded by a square or cylindrical conductive shield. Like cavity resonators, helical resonators can achieve Q factors in the 1000s...
.
A single layer coil (or solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
) that is used as a secondary or tertiary winding in a Tesla coil
Tesla coil
A Tesla coil is a type of resonant transformer circuit invented by Nikola Tesla around 1891. It is used to produce high voltage, low current, high frequency alternating current electricity. Tesla coils produce higher current than the other source of high voltage discharges, electrostatic machines...
or magnifying transmitter
Magnifying transmitter
The magnifying transmitter is an advanced version of Tesla coil transmitter. It is a high power harmonic oscillator that Nikola Tesla intended for the wireless transmission of electrical energy...
is also a distributed resonator.
Cavity resonators
A cavity resonator is a hollow conductor blocked at both ends and along which an electromagnetic wave can be supported. It can be viewed as a waveguideWaveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
short-circuited at both ends (see Microwave cavity
Microwave cavity
A microwave cavity is a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. Such cavities act as resonant circuits with extremely low loss at their frequency of operation...
).
The cavity has interior surfaces which reflect a wave of a specific frequency. When a wave that is resonant with the cavity enters, it bounces back and forth within the cavity, with low loss (see standing wave
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...
). As more wave energy enters the cavity, it combines with and reinforces the standing wave, increasing its intensity.
Examples
The cavity magnetronCavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
is a vacuum tube with a filament in the center of an evacuated, lobed, circular cavity resonator. A perpendicular magnetic field is imposed by a permanent magnet. The magnetic field causes the electrons, attracted to the (relatively) positive outer part of the chamber, to spiral outward in a circular path rather than moving directly to this anode. Spaced about the rim of the chamber are cylindrical cavities. The cavities are open along their length and so connect the common cavity space. As electrons sweep past these openings they induce a resonant high frequency radio field in the cavity, which in turn causes the electrons to bunch into groups. A portion of this field is extracted with a short antenna that is connected to a waveguide (a metal tube usually of rectangular cross section). The waveguide
Waveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
directs the extracted RF energy to the load, which may be a cooking chamber in a microwave oven or a high gain antenna in the case of radar.
The klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...
, tube waveguide, is a beam tube including at least two apertured cavity resonators. The beam of charged particles passes through the apertures of the resonators, often tunable wave reflection grids, in succession. A collector electrode is provided to intercept the beam after passing through the resonators. The first resonator causes bunching of the particles passing through it. The bunched particles travel in a field-free region where further bunching occurs, then the bunched particles enter the second resonator giving up their energy to excite it into oscillations. It is a particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
that works in conjunction with a specifically tuned cavity by the configuration of the structures. On the beamline
Beamline
In particle physics, a beamline is the line in a linear accelerator along which a beam of particles travels. It may also refer to the line of travel within a bending section such as a storage ring or cyclotron, or an external beam extracted from a cyclic accelerator.In materials science, physics,...
of an accelerator system, there are specific sections that are cavity resonators for RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
.
The reflex klystron is a klystron utilizing only a single apertured cavity resonator through which the beam of charged particles passes, first in one direction. A repeller electrode is provided to repel (or redirect) the beam after passage through the resonator back through the resonator in the other direction and in proper phase to reinforce the oscillations set up in the resonator.
In a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
, light is amplified in a cavity resonator which is usually composed of two or more mirrors. Thus an optical cavity
Optical cavity
An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric...
, also known as a resonator, is a cavity with walls which reflect electromagnetic waves (light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
). This will allow standing wave modes to exist with little loss outside the cavity.
Mechanical
Mechanical resonators are used in electronic circuitElectronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
s to generate signals of a precise frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. These are called piezoelectric resonators, the most common of which is the quartz crystal. They are made of a thin plate of quartz with metal plates attached to each side, or in low frequency clock applications a tuning fork
Tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal . It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a...
shape. The quartz material performs two functions. Its high dimensional stability and low temperature coefficient makes it a good resonator, keeping the resonant frequency constant. Second, the quartz's piezoelectric
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
property converts the mechanical vibrations into an oscillating voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, which is picked up by the plates on its surface, which are electrically attached to the circuit. These crystal oscillator
Crystal oscillator
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
s are used in quartz clock
Quartz clock
A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...
s and watches, to create the clock signal
Clock signal
In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...
that runs computers, and to stabilize the output signal from radio transmitters. Mechanical resonators can also be used to induce a standing wave in other medium. For example a multiple degree of freedom system can be created by imposing a base excitation on a cantilever beam. In this case the standing wave
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...
is imposed on the beam. This type of system can be used as a sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
to track changes in frequency or phase of the resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
of the fiber. One application is as a measurement device for dimensional metrology
Dimensional metrology
Dimensional Metrology is the science of calibrating and using physical measurement equipment to quantify the physical size of or distance from any given object. Inspection is a critical step in product development and quality control...
.
Acoustic
The most familiar examples of acoustic resonators are in musical instrumentMusical instrument
A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...
s. Every musical instrument has resonators. Some generate the sound directly, such as the wooden bars in a xylophone
Xylophone
The xylophone is a musical instrument in the percussion family that consists of wooden bars struck by mallets...
, the head of a drum
Drum
The drum is a member of the percussion group of musical instruments, which is technically classified as the membranophones. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a shell and struck, either directly with the player's hands, or with a...
, the strings in stringed instruments, and the pipes in an organ. Some modify the sound by enhancing particular frequencies, such as the sound box of a guitar
Guitar
The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...
or violin
Violin
The violin is a string instrument, usually with four strings tuned in perfect fifths. It is the smallest, highest-pitched member of the violin family of string instruments, which includes the viola and cello....
. Organ pipe
Organ pipe
An organ pipe is a sound-producing element of the pipe organ that resonates at a specific pitch when pressurized air is driven through it. Each pipe is tuned to a specific note of the musical scale...
s, the bodies of woodwinds, and the sound boxes of stringed instruments are examples of acoustic cavity resonators.
Automobiles
The exhaust pipes in automobile exhaust systemExhaust system
An exhaust system is usually tubing used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes...
s are designed as acoustic resonators that work with the muffler
Muffler
A muffler is a device for reducing the amount of noise emitted by the exhaust of an internal combustion engine. A US Patent for an Exhaust muffler for engines was granted to Milton and Marshall Reeves in 1897....
to reduce noise, by making sound waves "cancel each other out"http://auto.howstuffworks.com/muffler4.htm. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers
Aftermarket (automotive)
The automotive aftermarket is the secondary market of the automotive industry, concerned with the manufacturing, remanufacturing, distribution, retailing, and installation of all vehicle parts, chemicals, tools, equipment and accessories for light and heavy vehicles, after the sale of the...
use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance, the resonance of the exhaust pipes is also used to 'pull' the combustion products out of the combustion chamber quicker.
Percussion instruments
In many keyboard percussion instruments, below the centre of each note is a tube, which is an acoustic cavity resonatorAcoustic resonance
Acoustic resonance is the tendency of an acoustic system to absorb more energy when it is forced or driven at a frequency that matches one of its own natural frequencies of vibration than it does at other frequencies....
, referred to simply as the resonator. The length of the tube varies according to the pitch of the note, with higher notes having shorter resonators. The tube is open at the top end and closed at the bottom end, creating a column of air which resonates
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
when the note is struck. This adds depth and volume to the note. In string instruments, the body of the instrument is a resonator.
The tremolo
Tremolo
Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...
effect of a vibraphone
Vibraphone
The vibraphone, sometimes called the vibraharp or simply the vibes, is a musical instrument in the struck idiophone subfamily of the percussion family....
is obtained by a mechanism which opens and shuts the resonators.
Stringed instruments
String instruments such as the bluegrass banjoBanjo
In the 1830s Sweeney became the first white man to play the banjo on stage. His version of the instrument replaced the gourd with a drum-like sound box and included four full-length strings alongside a short fifth-string. There is no proof, however, that Sweeney invented either innovation. This new...
may also have resonators. Many five-string banjos have removable resonators, to allow the instrument to be used with resonator in bluegrass
Bluegrass music
Bluegrass music is a form of American roots music, and a sub-genre of country music. It has mixed roots in Scottish, English, Welsh and Irish traditional music...
style, or without in folk music
Folk music
Folk music is an English term encompassing both traditional folk music and contemporary folk music. The term originated in the 19th century. Traditional folk music has been defined in several ways: as music transmitted by mouth, as music of the lower classes, and as music with unknown composers....
style. The term resonator, used by itself, may also refer to the resonator guitar
Resonator guitar
A resonator guitar or resophonic guitar is an acoustic guitar whose sound is produced by one or more spun metal cones instead of the wooden sound board . Resonator guitars were originally designed to be louder than conventional acoustic guitars which were overwhelmed by horns and percussion...
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The modern ten-string guitar
Ten-string guitar
There are many varieties of ten-string guitar, including:* Both electric and acoustic guitars.* Instruments used principally for classical, folk and popular music.* Both coursed and uncoursed instruments.-Ten-stringed harp guitars:...
, invented by Narciso Yepes
Narciso Yepes
Narciso Yepes was a Spanish guitarist.-Biography:Yepes was born into a family of humble origin in Lorca, Region of Murcia. His father gave him his first guitar when he was four years old. He took his first lessons from Jesus Guevara, in Lorca...
, adds four string resonators to the traditional classical guitar. By tuning these resonators in a very specific way (C, Bb, Ab, Gb) and making use of their strongest partials (corresponding to the octaves and fifths of the strings' fundamental tones), the bass strings of the guitar now resonate equally with any of the 12 tones of the chromatic octave. The Guitar Resonator is a device for driving guitar string harmonics by an electromagnetic field. This resonance effect is caused by a feedback loop and is applied to drive the fundamental tones, octaves, 5th, 3rd to an infinite sustain
Sustain
In music, sustain is a parameter of musical sound over time. As its name implies, it denotes the period of time during which the sound remains before it becomes inaudible, or silent.Additionally, sustain is the third of the four segments in an ADSR envelope...
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See also
- Acoustic resonanceAcoustic resonanceAcoustic resonance is the tendency of an acoustic system to absorb more energy when it is forced or driven at a frequency that matches one of its own natural frequencies of vibration than it does at other frequencies....
- Crab cavityCrab CavityCrab cavities are a form of electromagnetic cavity used in particle accelerators to provide a transverse deflection to particle bunches. They can be used to provide rotation to a charged particle bunch by applying a time varying magnetic field...
- Electrical resonanceElectrical resonanceElectrical resonance occurs in an electric circuit at a particular resonance frequency where the imaginary parts of circuit element impedances or admittances cancel each other...
- Helical resonatorHelical resonatorA helical resonator is a passive electrical component that can be used as a filter. Physically, a helical resonator is a wire helix surrounded by a square or cylindrical conductive shield. Like cavity resonators, helical resonators can achieve Q factors in the 1000s...
- Magnetic resonanceMagnetic resonanceMagnetic resonance can mean:*Nuclear magnetic resonance*Electron spin resonance*Magnetic resonance imaging *Functional magnetic resonance imaging *Muon spin spectroscopy...
- Mechanical resonanceMechanical resonanceMechanical resonance is the tendency of a mechanical system to absorb more energy when the frequency of its oscillations matches the system's natural frequency of vibration than it does at other frequencies...
- Microwave cavityMicrowave cavityA microwave cavity is a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. Such cavities act as resonant circuits with extremely low loss at their frequency of operation...
- Optical ring resonatorsOptical ring resonatorsAn optical ring resonator is a set of three or more waveguides in which at least one is a closed loop coupled to one input waveguide and one output waveguides...
- OscillationOscillationOscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
- ResonanceResonanceIn physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
- Superconducting RF
- Standing waves