Polymer composite films containing fillers comprising quasi‐1D van der Waals materials, specifically transition metal trichalcogenides with 1D structural motifs that enable their exfoliation into bundles of atomic threads, are reported. These nanostructures are characterized by extremely large aspect ratios of up to ≈106. The polymer composites with low loadings of quasi‐1D TaSe3 fillers (<3 vol%) reveal excellent electromagnetic interference shielding in the X‐band GHz and extremely high frequency sub‐THz frequency ranges, while remaining DC electrically insulating. The unique electromagnetic shielding characteristics of these films are attributed to effective coupling of the electromagnetic waves to the high‐aspect‐ratio electrically conductive TaSe3 atomic‐thread bundles even when the filler concentration is below the electrical percolation threshold. These novel films are promising for high‐frequency communication technologies, which require electromagnetic shielding films that are flexible, lightweight, corrosion resistant, inexpensive, and electrically insulating.
We
report on the synthesis of the epoxy-based composites with graphene
fillers and test their electromagnetic shielding efficiency by the
quasi-optic free-space method in the extremely high-frequency (EHF)
band (220–325 GHz). The curing adhesive composites were produced
by a scalable technique with a mixture of single-layer and few-layer
graphene layers of few-micrometer lateral dimensions. It was found
that the electromagnetic transmission, T, is low
even at small concentrations of graphene fillers: T<1% at a frequency of 300 GHz for a composite with only ϕ
= 1 wt% graphene. The main shielding mechanism in composites with
the low graphene loading is absorption. The composites of 1 mm in
thickness and a graphene loading of 8 wt% provide an excellent electromagnetic
shielding of 70 dB in the sub-terahertz EHF frequency band with negligible
energy reflection to the environment. The developed lightweight adhesive
composites with graphene fillers can be used as electromagnetic absorbers
in the high-frequency microwave radio relays, microwave remote sensors,
millimeter wave scanners, and wireless local area networks.
The aim of this study was to evaluate the absorption in a user’s head of an electromagnetic field (EMF) emitted by the Wi-Fi and/or Bluetooth module of a wearable small Internet of Things (IoT) electronic device (emitting EMF of up to 100 mW), in order to test the hypothesis that EMF has an insignificant influence on humans, and to compare the levels of such EMF absorption in various scenarios when using this device. The modelled EMF source was a meandered inverted-F antenna (MIFA)-type antenna of the ESP32-WROOM-32 radio module used in wearable devices developed within the reported study. To quantify the EMF absorption, the specific energy absorption rate (SAR) values were calculated in a multi-layer ellipsoidal model of the human head (involving skin, fat, skull bones and brain layers). The obtained results show up to 10 times higher values of SAR from the MIFA located in the headband, in comparison to its location on the helmet. Only wearable IoT devices (similar in construction and way of use to the investigated device) emitting at below 3 mW equivalent isotropically radiated power (EIRP) from Wi-Fi/Bluetooth communications modules may be considered environmentally insignificant EMF sources.
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