Direct-spun CNT textiles for high-performance electromagnetic interference shielding in an ultra-wide bandwidth
Liron Issman, Matan Alper, S.T. Howard, Christian Karch, Shuki Yeshurun, Martin Pick, Adam Boies
Abstract
Electromagnetic interference (EMI) generated by electronic devices is disruptive to surrounding electronic components and deemed harmful to human beings. As high-speed, miniaturized mobile devices become ubiquitous, developing lightweight, thin, and flexible electromagnetic shielding materials (ESMs) to replace the common metallic ones is of utmost importance. Here we report the development of a high-efficiency standalone ESM made of a self-standing CNT mat (CNTM). This textile is electrically conductive (∼50 × 103 S m−1) and can be post-treated by chemical oxidation or thin copper metalization, increasing the conductivity by ∼10 and ∼1000 times, respectively. CNTMs were tested for shielding effectiveness (SE) in an ultra-wide bandwidth of 30 kHz–70 GHz. Maximal SE of >120 dB was measured for a 30 g m−2 CNTM (<100 μm thickness) at 70 GHz. SE normalized by thickness (SE/t) reached a value of >20,000 dB cm−1 for an HCl-oxidized CNTM. Both SE values are the highest values for non-metal-based ESMs. The CNTMs' experimental EMI shielding behavior corresponds to Schelkunoff's theory which confirms that the CNTM SE is dominated by conductivity-dependent reflection at lower frequencies (<1 GHz) and thickness-dependent absorption at higher frequencies. CNTMs (20 g m−2) were utilized as EMI gaskets and in composite EMI enclosures, tested at 10–50 GHz and 50 MHz-90 GHz, respectively. EMI CNT gaskets reached an SE of 120.9 dB at 50 GHz, surpassing the performance of high-end commercial gaskets (600 g m−2). EMI composite boxes laminated with CNTMs reached an SE of 119.9 dB at 90 GHz, outperforming the non-CNT laminated reference.