Flexible and biocompatible polyvinyl alcohol/nitrogen-doped porous carbon film with weakly negative permittivity in radio frequency for wearable devices

Abstract

Metacomposites with negative permittivity have attracted widespread attention due to their great application prospects in electromagnetic wave absorption, biosensors, electronic devices, and other fields. In this work, by designing nitrogen-doped porous carbon (NPC) and preparing film with polyvinyl alcohol (PVA), weakly negative permittivity in the radio frequency band is obtained when NPC content reaches 20 wt%. In NPC, the electrons around the doped nitrogen atoms are highly localized, reducing the carrier concentration. In addition, the doped nitrogen makes the band structure flatter, resulting in an increase in the effective electron mass. These two strategies reduce the plasma frequency, thereby achieving weakly negative permittivity (about − 40) from 10 kHz to 1 MHz. Moreover, the porous structure is conducive to electron transfer, achieving high carrier mobility and thus obtaining low dielectric dispersion, so that the negative permittivity is maintained at around − 40 in the range of 10 kHz to 1 MHz, which is almost unaffected by frequency. Furthermore, the film exhibits sensitive sensing performance to human motion and can be used as a wearable sensor to detect human motion. It also shows great application potential in wearable medical electronic devices, wearable invisible cloaks, and other fields.

Graphical abstract

Here, metacomposite with weakly negative permittivity at radio frequency is designed, via fabricating polyvinyl alcohol/nitrogen-doped porous carbon (PVA/NPC) film. Theory calculations demonstrate that doped-N atoms reduce carrier concentration and enhance effective electrons mass, through introducing localized electrons around N atoms and flatting band structure, respectively. Moreover, this film exhibits excellent capacitive sensing performance and is used in wearable devices