A retroreflector (sometimes called retroflector or cataphote ) is a device or surface that reflects light back to its source with minimum scattering. In the retroreflector, the electromagnetic wavefront is reflected back along the parallel but opposite vector of the wave source. The angle of incidence in which the device or surface reflects light in this way is greater than zero, unlike a planar mirror, which does this only if the mirror is exactly perpendicular to the front wave, has a zero angle of view.
Video Retroreflector
Jenis
There are several ways to get retroreflection:
Reflector corner
A set of three reflective surfaces perpendicular to one another, placed to form a cube angle, work as a retroreflector. Three appropriate normal vectors of angular sides form a base ( x , y , z ) to represent the direction an arbitrary entrance light, [ a , b , c ] . When the light reflects from the first side, say x, x -components of sunlight, a , reversed to - a /i> - and z -components do not change. Therefore, because the ray bounces first from the x side then the y side and finally from the side of the ray direction z go from [ a , b /i>] to [- a , , c ] - a , - b , c ] i> b , - c ] and it leaves the angle with the three components of the direction exactly upside down.
The angular reflector occurs in two varieties. In a more general form, angles are cut corners of transparent material cubes such as conventional optical glass. In this structure, the reflection is achieved either with total internal or silver reflections on the outer cube surface. The second form uses a perpendicular flat mirror that classifies air space. Both of these types have similar optical properties.
A relatively thin retroreflector can be formed by combining many small corner reflectors, using standard hexagonal tiles.
Cat Eyes
Another common retoreflector type consists of a refractive optical element with a reflective surface, arranged so that the focal surface of its bias element coincides with the reflective surface, usually a transparent ball and (optionally) a round mirror. In a partial approach, this effect can be achieved by the lowest divergence with a single transparent ball when the refractive index of the material is exactly one plus the refractive index n i of the medium where the radiation occurs (n i about 1 for air). In this case, the spherical surface serves as a concave-shaped round mirror with the curvature required for retraction. In practice, the optimum refractive index may be lower than n i 1? 2 due to several factors. For one, it is sometimes better to have an imperfect retroreflection, slightly different, as in the case of road signs, where the angle of illumination and observation is different. Due to spherical abnormality, there is also a radius from the midline where the incident rays are focused at the center of the back surface of the ball. Finally, the high index material has a higher Fresnel reflection coefficient, so the efficiency of the light clutch from the ambient to the ball decreases as the index becomes higher. Commercial retroreflective beads thus vary in an index of about 1.5 (common form of glass) to about 1.9 (generally barium titanate glass).
The problem of spherical aberration with cat's eye can be solved in many ways, one of which is a spherical symmetrical index gradient inside the ball, as in Luneburg lens design. Practically, this can be approached with a concentric ball system.
Because rear-side reflections for non-coated spheres are not perfect, it is common to add a metal layer to the back of the retoreflective balls to increase the reflectance, but this implies that the retroreflection only works when the ball is oriented on a particular. direction.
An alternative form of the cat's eye retroreflector uses a normal lens focused on a curved mirror rather than a transparent ball, although this type is much more limited in the various incidence angles that retroreflects.
The term cat comes from the resemblance of the cat's eye retraceflector to an optical system that produces the famous phenomenon of "luminous eye" or eyeshine in cats and other vertebrates (which reflect only light, rather than actually shine). The combination of the lens and the cornea forms a refractive convergent system, while the tapetum lucidum behind the retina forms a spherical concave mirror. Since the function of the eye is to form an image on the retina, eyes focused on distant objects have a focal surface which roughly follows the reflective lumidum tapetum structure, which is a necessary condition for forming a good retroreflection.
Type retroreflector can consist of many small versions of this structure incorporated in thin sheets or in paint. In the case of paint containing glass beads, the paint embraces beads to the surface where retroreflection is required and the beads stand out, their diameter being about twice the thickness of the paint.
Conjugate-phase mirror
The third less common way to generate retroreflectors is to use nonlinear optical phenomena of phase conjugation. This technique is used in advanced optical systems such as high power lasers and optical transmission lines. The phase conjugate mirrors require relatively expensive and complex apparatus, as well as large amounts of power (since nonlinear optical processes can be efficient only at high intensity). However, the conjugate-phase mirror has much greater accuracy toward the retroreflection, which in passive elements is limited by the mechanical accuracy of the construction.
Maps Retroreflector
Operation
Retroreflectors are devices that operate by returning the light back to the light source along the same light direction. The light intensity coefficient, R I , is a measure of reflector performance, defined as the ratio of the reflected light power (light intensity) to the amount of light falling on the reflector (normal lighting). A reflector looks brighter as its R I value rises.
The R I value of the reflector is a function of color, size, and reflector conditions. Clear or white reflectors are the most efficient, and appear brighter than other colors. The surface area of ​​the reflector is proportional to the value of R I , which increases when the reflective surface increases.
The value of R I is also a function of spatial geometry between observer, light source, and reflector. Figures 1 and 2 show the observation angle and the angle of entry between the car's lights, the bike, and the driver. The angle of observation is the angle formed by the rays and the sight lines of the driver. The observation angle is a function of the distance between the headlights and the driver's eyes, and the distance to the reflector. The traffic engineer uses a 0.2 degree observation angle to simulate a reflector target of about 800 feet in front of the passenger car. As the angle of observation increases, the reflector performance decreases. For example, a truck has a large separation between the headlamps and the driver's eye compared to the passenger vehicle. The bike's reflector is brighter for the driver of the passenger car than the truck driver at the same distance from the vehicle to the reflector.
The reflector's normal light and axis as shown in FIG. 2 forms the angle of the entrance. The entrance angle is a function of orientation of the reflector to the light source. For example, the corner of the entrance between the car approaching the bike at a 90 degree intersection is separated larger than the corner of the entrance to the bike directly in front of the car on a straight road. The reflector is the brightest for the observer when it is directly connected to the light source.
The reflector brightness is also a function of the distance between the light source and the reflector. At a certain point of view, as the distance between the light source and the reflector decreases, the light falling on the reflector will increase. This increases the amount of light returning to the observer and the reflector is lighter.
Apps
On the road
Retroreflection (sometimes called retroflection) is used on street surfaces, road signs, vehicles, and clothing (most of the surface of special safety clothing, lacking in ordinary coats). When the car's headlights illuminate the retroreflective surface, reflected light is directed to the car and its drivers (rather than in all directions as with diffuse reflections). However, pedestrians can see retroreflective surfaces in darkness only if there is a direct light source between them and reflectors (eg, through a torch being carried) or directly behind them (for example, through an approaching car from behind). "Cat Eye" is a special type of retroreflector embedded in the road surface and is mostly used in the UK and parts of the United States.
The better reflector angle sends light back to the source over long distances, while the ball is better to send light to the receiver rather off-axis from the source, such as when the light from the headlights is reflected into the driver's eyes.
Retroreflectors can be embedded in the road (parallel to the road surface), or they can be raised above the road surface. The raised reflector may be visible for very long distances (usually 0.5-1 km or more), while the droplet reflector is only visible at very close distances because higher angles are required to reflect light properly. Raised reflectors are generally not used in areas that regularly experience snow during the winter, because passing through the snow can release them from the highway. The stress on the highway caused by cars that run over embedded objects also contributes to the acceleration of wear and pothole formation.
Retroreflective street paint is thus very popular in Canada and part of the United States, as it is unaffected by the passage of snowplows and does not affect road interiors. Where weather permits, buffers or retoreflector enhancements are preferred because they last longer than the road paint, which is blocked by elements, can be obscured by sediment or rain, and blocked by road vehicles.
For road signs
Reflecting power is the light reflected from the source to the surface and back to the original source. For traffic signs and vehicle operators, the light source is the vehicle's headlights, where light is sent to the face of the traffic sign and then returned to the vehicle operator. Traffic signs are made with reflow reloading so traffic signs are visible at night. The face of a reflective sign is made with glass beads or prismatic reflectors embedded in the tarp so that the face reflects light, thus making the mark appear brighter and visible to the vehicle operator. According to the National Highway Traffic Safety Administration (NHTSA), the publication of Traffic Safety Facts 2000 states fatal accident rates are 3-4 times more likely to occur in nighttime accidents than daytime incidents.
The misunderstanding of many people is that retroreflectivity is only important during night trips. However, in recent years, more states and agencies require headlights to be turned on in bad weather like rain and snow. According to the Federal Highway Administration (FHWA): About 24% of all vehicle accidents occur during bad weather (rain, hail, snow and fog). Rain conditions accounted for 47% of weather related accidents. These statistics are based on an average of 14 years from 1995 to 2008.
The Manual on Uniform Traffic Control Equipment requires signs to be illuminated or made with remanufactured sheets, and although most of the marks in the US are made with remanufactured sheets, they have decreased over time. Until now, there is little information available to determine the duration of retroreflectivity. MUTCD now requires that agencies maintain traffic signs to a set of minimum levels but provide various maintenance methods that agencies can use for compliance. The minimum retoreflectivity requirement does not imply that the agency should measure every sign. In contrast, the new MUTCD language describes a method that can be used by an agency to maintain traffic radar signatures at or above the minimum level.
On The Moon
Astronauts at Apollo 11 , 14 , and 15 missions leave the retroreflectors on the Moon as part of the Lunar Laser Ranging Experiment. The Soviet Lunokhod 1 and Lunokhod 2 rovers also carry smaller arrays. The reflected signal was initially received from Lunokhod 1 , but no detectable signal was detected from 1971 to 2010, at least in part due to some uncertainty in its location on the Moon. In 2010, it was found in photos of Lunar Reconnaissance Orbiter and retroreflectors have been used again. Lunokhod 2 array continues to return signal to Earth. Even in good display conditions, only one reflected photon is received every few seconds. This makes the job of filtering laser-generated photons from challenging natural photons.
On satellite
Many artificial satellites carry retroreflectors so they can be traced from earth stations. Some satellites are built solely for starting lasers. Other satellites include retroreflectors for orbital calibration, such as satellite navigation (for example, most GLONASS satellites and some GPS satellites) as well as in satellite altimetry (eg, TOPEX/Poseidon). Retroreflectors can also be used for the laser range between satellites (eg, GRACE-FO).
Satellite start laser
LAGEOS, or Laser Geodynamics Satellites, is a series of scientific research satellites designed to provide orbiting orbiting laser benchmarks for Earth geodynamic studies. There are two LAGEOS spacecraft: LAGEOS-1 (launched in 1976), and LAGEOS-2 (launched in 1992). They use an angle-cube retraceflectors made of fused silica glass. In 2004, both LAGEOS spacecraft were still operating. Three STARSHINE satellites equipped with retroreflectors were launched starting in 1999. The LARES satellite was launched on February 13, 2012. (See also List of passive satellites)
BLITS
The BLITS (Ball Lens In The Space) satellite ball retracedflector was placed into orbit as part of the September 2009 Soyuz launch by the Russian Federal Space Agency with assistance from the International Laser Ranging Service, an independent body initially hosted by the International Association. Geodesy, International Astronomical Union, and international committee. The ILRS Central Bureau is located at the Goddard Space Flight Center of the United States.
The reflector, a type of Luneburg lens, was developed and manufactured by the Institute for Precision Instrument Engineering (IPIE) in Moscow.
The purpose of this mission is to validate the concept of a round glass retoreflector satellite and obtain SLR (Satellite Laser Ranging) data for solutions to scientific problems in geophysics, geodynamics, and relativity. BLITS allows measurement of millimeter and submillimeter SLR measurement accuracy, since the "target error" (uncertainty of the center of reflection relative to the center of mass) is less than 0.1 mm. An added advantage is that the Earth's magnetic field does not affect satellite orbits and rotation parameters, unlike retroreflectors that are inserted into active satellites. BLITS allows the most accurate measurements of any SLR satellite, with the same accuracy as the ground target.
The actual satellite is a solid ball about 17 cm, weighs 7.63 kg. It is made with two hemispheres (outer radius 85.16 mm) of low refractive index glass ( n Ã, = 1.47), and an inner ball or spherical lens (radius 53.52 mm) made of high refractive index glass ( n Ã, = 1.76). The hemisphere is attached to the spherical lens with all concentric sphere surfaces; The outer surface of one hemisphere is coated with aluminum and protected by a layer of varnish. It's designed to start with a green laser (532 m). When used to start, the phase center is 85.16 mm behind the center of the ball, with correction of the 196.94 mm range taking into account the refractive index. A smaller round ball retroreflector of the same type but a 6 cm diameter tied to a Meteor-3M spacecraft and tested during a space flight in 2001-2006.
Before the collision with space debris, the satellites were in a synchronous, circular sun-orbit, 832 km high, with a slope of 98.77 degrees, a 101.3 minute orbital period, and a spin period of 5.6 seconds alone. In early 2013, the satellite was found to have a new orbit 120 m lower, a faster spin period of 2.1 seconds, and a different rotation axis. The change was traced back to the events that occurred January 22, 2013 at 07:57 UTC; data from the US Space Control Network showed that within 10 seconds BLITS was close to the predicted path of the former Chinese Fengyun-1C satellite fragment, at a relative speed of 9.6 km/sec between them. The Chinese government destroyed Fengyun-1C, at an altitude of 865 km, on January 11, 2007 as an anti-satellite missile test, causing 2,300 to 15,000 pieces of debris.
Communications
Modulated retroreflectors, in which reflectance changes over time in several ways, are the subject of research and development for free-space optical communication networks. The basic concept of the system is that a low-power remote system, such as a mote sensor, can receive an optical signal from the base station and reflect the modulated signal back to the base station. Since the base station supplies optical power, it allows the remote system to communicate without excessive power consumption. Modulated retroreflectors also exist in the form of modulated phase-conjugate mirrors (PCMs). In the latter case, the "time-reversed" wave is generated by PCM with the temporal encoding of the phase conjugate waves (see, eg, SciAm, Oct. 1990, "The Photorefractive Effect," David M. Pepper, et al. >).
Refereflectors aim at cheap corners used in user-controlled technology as optical datalink devices. The briefing is done at night, and the required retroreflector area depends on the intended distance and ambient lighting of the streetlights. The optical receiver itself behaves as a weak retroreflector because it contains a large, precisely focused lens that detects the illuminated object in its focal plane. It allows shooting without retroreflector for short range.
In the fish
This single biological example is known: in the Anomalopidae family flashlight (see Tapetum lucidum).
Ship, ship, emergency kit
Retroflective bands are recognized and recommended by the International Convention for the Safety of Life at Sea (SOLAS) because of their high reflectivity of light and radar signals. Applications for life rafts, personal flotation devices, and other safety equipment make it easy to find people and objects in the water at night. When applied to the surface of the ship, it creates a larger radar signature - especially for fiberglass vessels, which generate little radar reflection on their own. This is in accordance with the rules of the International Maritime Organization, IMO Res. A.658 (16) and meets the specifications of US Coast Guard 46 CFR Part 164, Subpart 164.018/5/0. Examples of commercially available products are 3M 3150A and 6750I component numbers.
Other uses
Retroreflectors are used in the following sample applications:
- In a survey with total station or robot, the human or robotic instrument directs the laser beam at the angle cube retrace that is held by the rodman. This instrument measures the time of light propagation and turns it into the distance.
- In Canada, aerodrome lighting can be replaced with the right colored retroreflectors, the most important being the white retraces that illustrate the runway edge, and should be seen by planes equipped with landing lights up to 2 nautical miles away.
- A common digital camera (non-SLR), sensor systems are often retroreflective. Researchers have used this property to demonstrate the system to prevent unauthorized photos by detecting digital cameras and emitting highly focused light rays to the lens.
- On the movie screen to allow for high brightness in dark conditions.
- The digital compositing program and chroma key environment use retroreflection to replace traditional litative backgrounds in composite work as it provides a more solid color without requiring the background to be turned on separately.
- In Longpath-DOAS systems, retroreflectors are used to reflect light emitted from light sources back to the telescope. It was then analyzed spectrally to obtain information about the air trace gas content between the telescope and the retro reflector.
- Barcode labels can be printed on a retroreflective material to increase scan coverage by up to 50 feet.
- In 3D view; in which the retro-reflective sheet and a set of projectors are used to project a stereoscopic image back into the user's eyes. Use of mobile & amp; Position tracking installed on the user's eyeglass frame enables the hologram illusion to be created for computer-generated imagery.
See also
- Reflector angle
- Free-space optical communication
- Repair Block III GPS Satellite
- Heiligenschein
- High visibility clothing
- Square optics
- Modulate retro-reflector
- Reflective prism
- Retroreflective sheeting and tape
- Safety Reflector
Note
References
- Optical Letter , Vol. 4 , pp.Ã, 190-192 (1979), "Retroreflective Arrays as Conjugate Estimated Phase," by H.H. Barrett and S.F. Jacobs.
- Optical Engineering , Vol. 21 , pp.Ã, 281-283 (March/April 1982), "Experiments with Retrodirective Circuits," by Stephen F. Jacobs.
- Scientific American , December 1985, "Phase Conjugation," by Vladimir Shkunov and Boris Zel'dovich.
- Scientific American , January 1986, "Optical Phase Conjunction Application," by David M. Pepper.
- Scientific American , April 1986, "The Amateur Scientist" ('Wonders with the Retroreflector'), by Jearl Walker.
- Scientific American , October 1990, "The Photorefractive Effect," by David M. Pepper, Jack Feinberg, and Nicolai V. Kukhtarev.
External links
- Apollo 15 Laser Start Retroreflector Experiment
- Manual Traffic Signal - Retroreflective Sheetings Used for Face Signs
- Motor retroreflective Sheeting
- Lunar retroflector
- The howstuffworks article on the invisibility cloak based on the retroreflector
- The Law of Traffic Signs Reflective
Source of the article : Wikipedia
0 Comments