When it comes to mobile phones and passenger trains, there's something of an engineering paradox at work. To help insulate the cars, the double-glazed windows are often equipped with an ultra-thin metal coating that lets light through, but reflects heat away, so the car interior maintains the desired temperature using minimal energy. These coated, doubled-glazed windows have four times the energy efficiency of regular, untreated windows.
Unfortunately, the coating not only reflects heat, it also blocks telecommunication signals. Since railway cars are made out of metal, the metal coating in the windows effectively turns them into Faraday cages, earthed metal screens that enclose a space to cut it off from electromagnetic radiation.
The standard solution to this problem is to equip the cars with electronic boosters and repeaters, but this means using more energy as well as more money on installation and maintenance. The alternative solution is to alter the metal coating to make the windows more selective as to what exactly can pass through.
The design makes use of the fact that electromagnetic waves of mobile phones, which are centimetric in size, are different to heat waves (which are micrometric in size), which are different again to light waves (nanometric in size). The team used a high-precision laser to remove about 2.5 percent of the metal coating and inscribe a special pattern into the surface that is invisible to the naked eye, but lets the electromagnetic waves and light waves through, but still blocks the heat waves and therefore doesn't affect insulation.
Source: newatlas.comAdded: 31 August 2016