FAQ on Reflectors and Reflector Foils
A reflector reflects light or, in more general terms, an electro-magnetic wave in a particular preferred direction according to the laws of physics.
The reflector foil is a reflector in foil form and is therefore flexible and usually self-adhesive. The reflective surface is arranged under a transparent top layer for protection against environmental influences.
With retro-reflection, the light beam is reflected back in the direction of incidence. “Retro” comes from Latin and means “backwards”. The light waves are rotated by the reflection.
A retro-reflector is a reflector that reflects the incident light back parallel to the light source, regardless of the angle of incidence. The lit surface (reflector structure) typically has a particularly fine angular structure with many small triple mirrors, which enables retro-reflection.
The light waves oscillate in different vertical and horizontal directions. The polarization of light describes the direction of oscillation. If the light has no preferred direction, it is known as non-polarized light.
A linear polarizer is a filter that allows the light to pass through in a certain direction of oscillation (for example, vertically polarized), while blocking light in the direction of oscillation perpendicular to it (in the example, horizontally polarized light).
The functional principle of a retro-reflex sensor uses the properties of the polarizer in combination with the properties of the retro-reflector. The light from the emitter is emitted in a certain direction of oscillation. The polarization filter built into the retro-reflector rotates the light waves so that the receiver can receive the rotated light waves. When an object comes in between, the light waves are not rotated and the sensor has no signal so that it “switches”.
Where reflectors and reflector foils are concerned, structure describes the shape of the elements (triple, cube corners) on the reflective surface (retro-reflective system).
There are reflector structures ranging from very small elements (cube corners) located on the microstructure and continuous structure, through to large cube corners (with several cm) on the macrostructure and honeycomb structure.
With LED light (red light) or long ranges, macro or honeycomb structures are suitable.
A reflector with a micro or continuous structure is better suited for light beams with a low beam divergence and a small beam diameter, with a laser beam, for example.
Because the laser beam is very fine, down to less than one millimeter, a retro-reflective system with very small triangles, located on the microstructure and continuous structure, is ideal.
Red light has a larger light spot diameter (several cm), meaning that large triple structures such as macro or honeycomb structures are suitable.
A reflector with macrostructure should be used for long-distance alignment. The advantage of a large triple structure is the degree of reflection, because the larger the triple, the better the degree of reflection and the greater the range.
An aperture angle is incorporated into the triple structure. The triples are not exactly vertical, but are arranged at 90° to each other, so that the light is reflected back wider. The larger the triple, the larger the aperture angle.
With two-lens optics, the reflector must reflect the light back into the receiver with a slight offset. With an aperture angle of more than 90°, this effect is also achieved in the close range, as the light is reflected back wider and thus also hits the receiver.
The reference reflector is the reflector to which the sensor’s range is referenced.
Yes, it is important to pay attention to the positioning, especially with two-lens devices. The minimum distance to the reflector and the maximum range must be observed depending on the structure of the reflector.
The reflector must be placed at a specified distance from the sensor so that the receiver can detect sufficient light beams. If the range specifications state, for example: “0.07…8 m”, the minimum distance of the reflector to the sensor must be 7 cm. The object can still be detected in the minimum distance range, however!
Each reflector has a maximum range, which describes the maximum distance between sensor and reflector. If the range specifications state “0.07…8 m”, for example, the reflector cannot be mounted at a distance greater than approx. 8 m, as the reflected light is otherwise so weak that the receiver no longer recognizes it.
The size of the reflector should be adapted to the light spot of the incident light beam. Particularly at maximum range, it is important to remember that the larger the light spot diameter is, the larger the reflector must be. Small reflectors can be used in close range and where space is limited.
There are mounting holes, screws, fixing plugs, and self-adhesive foil.
This refers to a slight damping of the signal by the object. In the case of transparent materials, the signal is only slightly damped by the object and the undamped signal must therefore be as stable as possible for the sensor to function reliably.
An anti-fog coating helps to prevent temperature-related fogging on the reflector. The fine droplets disappear at lightning speed, ensuring retro-reflection.
