Empa researchers have succeeded in making aerogels usable for microelectronics. Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation in wide frequency ranges and are unrivalled in terms of weight.
Electric motors and electronic devices generate electromagnetic fields that often need to be shielded so as not to affect neighboring electronic components or the transmission of signals. In the case of high-frequency electromagnetic fields, this is only possible with conductive sheaths that are closed on all sides. Thin metal sheets or metalized foils are often used for this purpose, but this is often not possible for weight or geometry reasons. A lightweight, flexible and durable material with an extremely high shielding effect would be ideal.
A team of researchers at Empa has now achieved a breakthrough in this area by producing a mixture of cellulose nanofibers and silver nanowires to create ultra-light fine structures that provide excellent shielding against electromagnetic radiation.
The effect of the material is impressive: with a density of just 1.7 milligrams per cubic centimeter, the silver-reinforced cellulose aerogel achieves more than 40 dB shielding in the frequency range of high-resolution radar radiation (8 to 12 GHz), i.e. almost all of the radiation in this frequency range is intercepted by the material. The decisive factor for the shielding effect is not only the correct mixture of cellulose and silver wires, but also the pore structure of the material. The electromagnetic fields are reflected back and forth within the pores and also trigger electromagnetic fields in the composite material, which counteract the radiated field.
In order to achieve pores of the optimum size and shape, the researchers pour the material into pre-cooled molds and allow it to freeze slowly. The growth of the "ice crystals" creates the optimum pore structure for attenuating the fields.
