Part 3 looked at how Fresnel enhanced to the performance of his lens in the lighthouse application; this part looks at how the lens itself has been extended by new materials and manufacturing techniques and found modern applications even though lighthouses are obsolete.
Fresnel’s legacy lives on, in unrelated ways
There no argument: lighthouses are no longer needed, and it might also seem that Fresnel and his lenses are no longer needed. But that is not the case at all. Due to poor health, Fresnel passed away in 1827 at the age of 39. Unlike many innovators, he lived to see the acceptance and adoption of his lens, as well as the industrial improvements in glassmaking, illumination, and more for which his lens was directly and indirectly responsible.
If all Fresnel did was develop a special lens for lighthouses, and enhance glass-making technology, he would be a historical note but perhaps not much else. However, his theoretical and experimental legacy is very much with us. His equations on waves and reflectivity are used in the rendering of computer-graphics images where there are complex reflective surfaces (water, for example). His diffraction analysis is relevant to our understanding of limits on optical microscopy, IC lithography, and even some RF imaging (radar, MRI).
Despite the demise of lighthouses as critical maritime infrastructure, his lenses are still used but for very different classes of applications. Since they are relatively flat, lightweight, and low cost, they are used as concentrators for solar energy impinging on photovoltaic arrays. They can be molded easily and cheaply in plastic, in sizes up to several feet across yet only a fraction of an inch thick. The Fresnel lens’ low resolution compared to a conventional lens is not acceptable for most image applications, but that is not a factor in the solar application or a lower-resolution magnification situation.
You can buy large but inexpensive (a few dollars) molded-plastic “flat” magnifiers with 2× or 3× power to help read printed documents (Figure 1).
Fresnel lenses are used in many infrared detection systems (think heat, fire, and burglar alarms/security systems and their PIR function) as well as applications with a wide field of view. There is also some research investigation use of precision micromachining or chemical etching to create these lenses. Still, at present, the benefits are not viable compared to plastic moldings at a much lower cost.
Highly engineered versions, precision-molded in advanced plastics with a resolution of about 100-200 lines/inch, are also used in optical devices such as bar-code scanners. In contrast, a quality glass lens has a resolution of ten times that figure but much greater thickness, weight, and cost. Their sources also offer detailed optical and material specifications as would be provided for any other technical component (Figure 2) and Table.
Where efficient light collection or distribution is the objective rather than image quality and high resolution, a Fresnel lens is often an attractive option with many advantages over conventional glass or even high-quality plastic lens implementation.
Innovations often serve a distinct role as they address problems in a specific time frame and setting, but may themselves become unneeded, obsolete, or even forgotten as new developments and technologies arise and dramatically shift the problem/need/solution environment. Sometimes, however, an innovation tightly focused on a specific problem – here, lighthouses – finds a new and very different role for applications not envisioned at the time. For the Fresnel lens, while their lighthouse use is indeed gone, they have found important new roles in solar panels, scanners, and many other electro-optical uses. When combined with other new technologies such as low-cost plastic molding, they have an important position in many new applications.
EE World Online References
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Related Content and References:
- “A Short Bright Flash: Augustin Fresnel and the Birth of the Modern Lighthouse,” Theresa Levitt, W.W. Norton & Co., 2013
- “Fundamentals of Physics,” Halliday and Resnick, John Wiley & Sons, Inc.
- Encyclopædia Britannica , “Augustin-Jean Fresnel”
- Wikipedia, “Fresnel lens”
- “Fresnel Lens
- Hyperphysics/Georgia State University, ” Fresnel Lens”