How to keep windows clean for 5 years

Windows are continuously exposed to the elements, and contamination such as salts, bird excretions and soot from exhaust gases are often recurring contaminations. In applications such as windows on a tall building or lenses of cameras monitoring highway traffic, it is not always possible to manually clean such a window. But how do you keep them clean then?
SAW cleaning principle
For one of our customers, we have carried out an R&D project to select alternative techniques for cleaning windows or to passively keep them clean. Various smart coatings that prevent or even decompose contamination have been tested for suitability. Several mechanical cleaning techniques, such as advanced versions of car window wipers, have been designed, desk-researched and evaluated.
One of the most promising techniques was the use of so-called Surface Acoustic Waves (SAW). These are ultrasonic waves that travel on the surface of the window. Rain drops are being propelled by these surface waves thereby taking contaminants with them. This idea is not new; McLaren already proposed to use it on their car windows. The novel aspect is in the implementation of the system in such a way that fits the requirements of our customer.

Full-scale testing of these new cleaning methods will be part of the next phase of this project. The final goal is to be able to keep the windows clean for 5 years without maintenance.