The lightest shielding material in the world
Protection against electromagnetic interference

Date:
July 2, 2020
Source:
Swiss Federal Laboratories for Materials Science and Technology
(EMPA)
Summary:
Researchers have succeeded in applying aerogels to microelectronics:
Aerogels based on cellulose nanofibers can effectively shield
electromagnetic radiation over a wide frequency range - and they
are unrivaled in terms of weight.



FULL STORY ========================================================================== Electric motors and electronic devices generate electromagnetic fields
that sometimes have to be shielded in order not to affect neighboring electronic components or the transmission of signals. High-frequency electromagnetic fields can only be shielded with conductive shells that
are closed on all sides. Often thin metal sheets or metallized foils
are used for this purpose.

However, for many applications such a shield is too heavy or too poorly adaptable to the given geometry. The ideal solution would be a light,
flexible and durable material with extremely high shielding effectiveness.


========================================================================== Aerogels against electromagnetic radiation A breakthrough in this area
has now been achieved by a research team led by Zhihui Zeng and Gustav Nystro"m. The researchers are using nanofibers of cellulose as the basis
for an aerogel, which is a light, highly porous material. Cellulose
fibres are obtained from wood and, due to their chemical structure,
enable a wide range of chemical modifications. They are therefore a
highly popular research object. The crucial factor in the processing
and modification of these cellulose nanofibres is to be able to produce
certain microstructures in a defined way and to interpret the effects
achieved. These relationships between structure and properties are the
very field of research of Nystro"m's team at Empa.

The researchers have succeeded in producing a composite of cellulose
nanofibers and silver nanowires, and thereby created ultra-light fine structures which provide excellent shielding against electromagnetic
radiation. The effect of the material is impressive: with a density of
only 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) -- in other words: Virtually
all radiation in this frequency range is intercepted by the material.

Ice crystals control the shape Not only the correct composition of
cellulose and silver wires is decisive for the shielding effect,
but also the pore structure of the material. Within the pores, the electromagnetic fields are reflected back and forth and additionally
trigger electromagnetic fields in the composite material, which counteract
the incident field. To create pores of optimum size and shape, the
researchers pour the material into pre-cooled moulds and allow it to
freeze out slowly. The growth of the ice crystals creates the optimum
pore structure for damping the fields.

With this production method, the damping effect can even be specified in different spatial directions: If the material freezes out in the mould
from bottom to top, the electromagnetic damping effect is weaker in the vertical direction. In the horizontal direction -- i.e. perpendicular
to the freezing direction -- the damping effect is optimized. Shielding structures cast in this way are highly flexible: even after being bent
back and forth a thousand times, the damping effect is practically the
same as with the original material. The desired absorption can even be
easily adjusted by adding more or less silver nanowires to the composite,
as well as by the porosity of the cast aerogel and the thickness of the
cast layer.

The lightest electromagnetic shield in the world In another
experiment, the researchers removed the silver nanowires from the
composite material and connected their cellulose nanofibres with two- dimensional nanoplates of titanium carbide, which were produced using a
special etching process. The nanoplates act like hard "bricks" that are
joined together with flexible "mortar" made of cellulose fibers. This formulation was also frozen in cooled forms in a targeted manner. In
relation to the weight of the material, no other material can achieve
such shielding. This ranks the titanium carbide nanocellulose aerogel
as by far the lightest electromagnetic shielding material in the world.


========================================================================== Story Source: Materials provided by Swiss_Federal_Laboratories_for_Materials_Science_and
Technology_(EMPA). Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Zhihui Zeng, Changxian Wang, Gilberto Siqueira, Daxin Han,
Anja Huch,
Sina Abdolhosseinzadeh, Jakob Heier, Frank Nu"esch, Chuanfang
(John) Zhang, Gustav Nystro"m. Nanocellulose‐MXene Biomimetic
Aerogels with Orientation‐Tunable Electromagnetic Interference
Shielding Performance. Advanced Science, 2020; 2000979 DOI:
10.1002/advs.202000979 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200702113703.htm

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