Grating
Encyclopedia
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
, elongated elements. Gratings usually consist of a single set of elongated elements, but can consist of two sets, in which case the second set is usually perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
to the first (as illustrated). When the two sets are perpendicular, this is also known as a mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
.
Grating as bridge decks
Grating can also come in 4 feet (121.9 cm) or 2 feet (61 cm) x 8 feet (243.8 cm) panels which are often used for decksDeck (bridge)
A bridge deck or road bed is the roadway, or the pedestrian walkway, surface of a bridge. It is not to be confused with any deck of a ship.The deck may be of concrete,wood which in turn may be covered with asphalt concrete or other pavement...
on bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
s, footbridge
Footbridge
A footbridge or pedestrian bridge is a bridge designed for pedestrians and in some cases cyclists, animal traffic and horse riders, rather than vehicular traffic. Footbridges complement the landscape and can be used decoratively to visually link two distinct areas or to signal a transaction...
s and catwalks. Other panel sizes may also be available. Grating can be made of different materials like steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, aluminum
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
. Fiberglass grating is also known as FRP Grating
FRP Grating
Fiberglass reinforced plastic grating is manufactured by combining a matrix of resin and fiberglass. That makes it a composite material. Fiberglass grating does not corrode like steel gratings. That is what gives them their value. They are used in corrosive environments...
.
Gratings as filters
Drain
A drain is a plumbing fixture that provides an exit-point for waste water or water that is to be re-circulatedDrain may also refer to:* Drainage, the natural or artificial removal of surface and sub-surface water from a given area...
(as illustrated) can be a collection of iron bars (the identical, elongated elements) held together (to ensure the bars are parallel and regularly spaced) by a lighter iron frame. Gratings over drains and air vents are used as filter
Filter (chemistry)
In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...
s, to block movement of large particles (such as leaves) and to allow movement of small particles (such as water or air).
Diffraction gratings
Grating can also be a diffraction gratingDiffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
: a reflecting
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
or transparent optical component on which there are many fine, parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
, equally spaced grooves.
Gratings as pictures
Diagram
A diagram is a two-dimensional geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface...
(illustrated). On the y-axis of the graph is the luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
obtained by moving a light meter
Light meter
A light meter is a device used to measure the amount of light. In photography, a light meter is often used to determine the proper exposure for a photograph...
over the grating perpendicular to the orientation
Orientation (geometry)
In geometry the orientation, angular position, or attitude of an object such as a line, plane or rigid body is part of the description of how it is placed in the space it is in....
of the grating. On the x-axis of the graph is the distance the light meter moved. The example is a square-wave
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
grating (see second panel of the illustration); the graph consists of flat, low lines (corresponding to the black bars), with abrupt corners leading to flat high lines (corresponding to the white bars). One period
Periodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...
(or cycle) of such a grating consists of one black bar and one adjacent white bar. Gratings where the black bars have a different width from the white bars are rectangular and are described by the duty cycle
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....
. The duty cycle
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....
is the ratio of width of the black bar to period (or pitch
Pitch
Pitch may refer to:* Pitch , a viscous substance produced by plants or formed from petroleum* Pitch * sales pitch** elevator pitch, a very short sales pitch such as that made during an elevator ride* Pitch accent-Music and acoustics:...
, i.e. the sum of the widths of one black and one white bar).
Gratings are usually specified by four parameter
Parameter
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....
s. Spatial frequency
Spatial frequency
In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components of the structure repeat per unit of distance. The SI unit of spatial frequency is...
is the number of cycles occupying a particular distance (e.g., 10 lines [or cycles] per millimeter). Contrast
Contrast (vision)
Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view...
is a measure of the difference in luminance between the light parts of the grating and the dark parts. It is usually expressed as Michelson contrast: the maximum luminance minus the minimum luminance divided by the maximum luminance plus the minimum luminance. Phase
Phase (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:...
is the position of the graph relative to some standard position. It is usually measured in degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
s (from 0 to 360 for one complete cycle) or in radian
Radian
Radian is the ratio between the length of an arc and its radius. The radian is the standard unit of angular measure, used in many areas of mathematics. The unit was formerly a SI supplementary unit, but this category was abolished in 1995 and the radian is now considered a SI derived unit...
s (2π for one complete cycle). Orientation
Orientation (geometry)
In geometry the orientation, angular position, or attitude of an object such as a line, plane or rigid body is part of the description of how it is placed in the space it is in....
is the angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
the grating makes with some standard orientation (such as the y-axis in a picture). It is also usually measured in degree or in radians.
Grating elements can have luminances other than that of sharp-edged bars. If the graph of a grating is sinusoidal (see top panel in the illustration), the grating looks like a set of blurry light and dark bars and it is called a sine-wave grating.
Sine-wave gratings are used extensively in optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
to determine the transfer function
Transfer function
A transfer function is a mathematical representation, in terms of spatial or temporal frequency, of the relation between the input and output of a linear time-invariant system. With optical imaging devices, for example, it is the Fourier transform of the point spread function i.e...
s of lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
. A lens will form an image of a sine-wave grating that is still sinusoidal, but with some reduction in its contrast depending on the spatial frequency and possibly some change in phase. The branch of mathematics dealing with this part of optics is Fourier analysis.
Gratings are also used extensively in research into visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
. Campbell and Robson promoted using sine-wave gratings by arguing that the human visual performs a Fourier analysis on retinal images.
See also
- Diffraction gratingDiffraction gratingIn optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
- GrateGrate*A grate is a frame of iron bars to hold fuel for a fire.*It may also refer to a covering of a drain, also called a grating.*The act of using a grater, a kitchen utensil.- People :*Don Grate US sportsman....
- GrilleGrilleA grille or grill is an opening of several slits side by side in a wall or metal sheet or other barrier, usually to let air or water enter and/or leave but keep larger objects including people and animals in or out.-Spelling:In the United States, "grille" is used to differentiate the automotive...
- FRP GratingFRP GratingFiberglass reinforced plastic grating is manufactured by combining a matrix of resin and fiberglass. That makes it a composite material. Fiberglass grating does not corrode like steel gratings. That is what gives them their value. They are used in corrosive environments...
- Manhole coverManhole coverA manhole cover is a removable plate forming the lid over the opening of a manhole, to prevent anyone from falling in and to keep unauthorized persons out....
Pedestrian infrastructure