Sai Rayasam, Applied Science, Summer 2020
Caption: Though it looks like a hologram with a ghostly appearance, this aerogel is actually a solid. It has a very low density and is extremely porous, making it the lightest material known to man and the best conductor in the world. (Source: Wikimedia Commons)
All of the electronic devices used on an everyday basis generate electromagnetic fields. Most of the fields created by these devices (like phones and other small electronics) are weak and have no effect on their environment. But there are some large devices out there that create electromagnetic fields strong enough to affect neighboring electronic components, and, in some cases, destroy them.1 In order to prevent this interference from happening, a conductive shell is needed in order to enclose the magnetic field and shield it away from other devices in the vicinity. Most commonly, thin metal sheets or metallized foils are used as the shielding material. But, for many applications, such materials are too heavy for the device, making those materials inapplicable. To address this problem, a light, flexible, and durable material with a high shielding effectiveness is needed.2
That type of material has now been made by a team of researchers led by Zhihui Zeng and Gustav Nyström. The researchers used nanofibers of cellulose (the material found in the cell walls of plants) obtained from wood. The researchers chose cellulose because its chemical structure can enable a wide range of chemical modifications.2
The researchers created a composite material by combining the cellulose nanofiber with silver nanowires. Furthermore, they combined these materials based on aerogels, an extremely light and sparse material, with the end product being a material with the density of 1.7 milligrams per cubic centimeter. However, the mass of the object does not downplay the power of its shielding. It is so effective that the silver-reinforced cellulose aerogel shields more than 40 decibels (dB) in the frequency range of high-resolution radar. This means that all radiation in the high-resolution frequency will be intercepted by this material, which makes it very effective.2
Ultimately, the effectiveness of the design stems from its mimicry of aerogels. Aerogels are extremely porous materials, and to mimic this property of aerogels, the researchers had to conduct specific and meticulous steps. First, the researchers poured the composite material into pre-cooled molds and allowed it to freeze out slowly. Eventually, ice crystals grew on the material, which created the optimum pore structure for damping the fields. Within these newly made pores, the electromagnetic field that the composite material insulates is reflected back and forth. This in turn creates an additional magnetic field in the composite material, which counteracts the original field. Additionally, with their pore-making process, the researchers can also specify the damping effect of the field in certain spatial dimensions. For example, if the material is frozen out in the mold in the vertical direction, the damping effect is optimized in the horizontal direction, and vice versa.2
In another experiment, the same researchers tried out a different composite material by exchanging the silver nanowires with two-dimensional nanoplates of titanium carbide. The cellulose fibers underwent the same process as before to create the desired pores. They were then combined with the nanoplates to achieve a similar shielding effectiveness. In relation to its density, no other material in the world can achieve this effectiveness, making this material the lightest electromagnetic shield in the world.2
The creation of both these configurations promise astonishing innovations in the future. Aerogels have already been used as effective materials for thermal insulation, but it can now be the most common material used as a conductive shell in certain electronic devices. The previous use of heavy materials such as metal can now be replaced by the ultra-light materials that the researchers created. With some more research and innovation, aerogel-like cellulose fibers could usher in a new era of shielding material.
Sources:
- EMF Explained 2.0. (n.d). What is EMF? – L2. Retrieved from http://www.emfexplained.info/?ID=25192
- Swiss Federal Laboratories for Materials Science and Technology (EMPA). (2020, July 2). The lightest shielding material in the world: Protection against electromagnetic interference. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2020/07/200702113703.htm
- Klose, R. (2020, July 2). The world’s lightest shielding material: Protection against electromagnetic interference. EMPA. Retrieved from https://www.empa.ch/web/s604/cellulose-emi-shielding?inheritRedirect=true