Fresnel lens is a kind of widely used optical element. Its design and manufacture are designed into several technical fields, including optical engineering, macromolecule material engineering, CNC machining, diamond turning process, nickel plating process; molding, injection molding, casting And other manufacturing processes.
The Fresnel lens was invented by the French physicist Augustin Fresnel. He originally used this type of lens in 1822 to create a glass Fresnel lens system - a lighthouse lens. It is a finely-structured optical element that looks like a dart plate from the front and consists of a ring and a concentric circle.
Fresnel lens front view
The idea of making lighter and thinner lenses by mounting several independent sections on a frame is often thought to have been proposed by the cloth seal. Condorcet (1743-1794) proposed the use of a single piece of thin glass to grind such a lens. Fresnel, a French physicist and engineer, also placed high hopes on the application of this lens to lighthouses. According to the description of the Smithsonian Institution, in 1823, the first Fresnel lens was used on the Phare de Cordouan lighthouse at the mouth of the Gironde; the light emitted through it could be 20 miles (32 thousand). m) seen outside. Sir David Brewster, a Scottish physicist, was seen as a catalyst for Britain to use this lens in a lighthouse.
Its working principle is very simple: Assume that the refractive power of a lens only occurs on the optical surface (such as the lens surface), remove as much optical material as possible, and preserve the curvature of the surface.
Change from traditional lens to Fresnel lens structure
Another understanding is that the continuous surface portion of the lens "collapses" onto a plane. Pictured below:
Collapse to the plane
Viewed from the cross-section, the surface consists of a series of zigzag grooves, the central part of which is an elliptical arc. Each groove has a different angle from the adjacent groove, but it concentrates the light to form a central focus, which is the focus of the lens. Each groove can be seen as a separate lenslet that adjusts the light to parallel light or spotlight. This lens also eliminates partial spherical aberration.
There are two Fresnel lens effects：
The first is the focusing effect, that is, the pyrolysis infrared signal is refracted (reflected) on the PIR. The second function is to divide the detection area into several bright and dark areas so that the moving object entering the detection area can be changed in temperature to Frey. The lensed form produces a varying pyroelectric infrared signal on the PIR.
Fresnel lenses, simply put, have equidistant dents on one side of the lens. By using these ribs, the bandpass (reflection or refraction) of the specified spectral range can be achieved. Traditionally, the optical equipment is polished. Bandpass optical filters are expensive. Fresnel lenses can greatly reduce costs. A typical example is the PIR (Passive Infrared Detector). PIR is widely used on sirens. If you take a look, you will find a plastic hat on each PIR. This is the Fresnel lens. The interior of the little hat is engraved with teeth. This Fresnel lens can limit the peak frequency of incident light to about 10 microns (peak of human body infrared radiation). The cost is quite low.
The Fresnel lens can focus the light passing through the narrow-band interference filter on the photosensitive surface of the silicon photodiode detector. The Fresnel lens is made of plexiglass and cannot be wiped with any organic solution (such as alcohol). When you can first rinse with distilled water or ordinary water, and then wipe with cotton.
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