TEMPO-oxidized cellulose nanofibre (TOCN) films and composites with PVOH as sensitive dielectrics for microwave humidity sensing

This paper investigates TEMPO oxidized cellulose nanofibers (so-called TOCN)films as sensitive dielectrics for humidity detection in microwave frequencies. TOCN is used either as a sensitive material or as a host-matrix enclosing polyvinyl alcohol (PVOH)to achieve highly sensitive humidity sensing. A resonator in coplanar waveguide grounded (CPWG)technology was designed and fabricated. TOCN and TOCN/PVOH gels were dropped in the area of the resonator where the analysis showed the electromagnetic field to be maximum at the resonance. Gels became thin films after drying. Experimental humidity tests were then conducted within the 21.9–89.3%RH range, using the resonant frequency and the transmission phase as measurement variables. The best sensitivity with TOCN was 2.67 MHz/%RH regarding the resonant frequency, and 0.523°/%RH regarding the transmission phase. The effects of PVOH were visible starting from 55%RH, where the sensitivity was raised to 6.000 MHz/%RH and 0.785°/%RH respectively. © 2019 Elsevier B.V

Environmentally-friendly cellulose nanofibre sheets for humidity sensing in microwave frequencies

This paper investigates environment friendly cellulose nanofibres (CNF) as new and sensitive material for humidity sensing in RF/microwave frequencies. CNF sheets were fabricated by sonocatalyzed TEMPO process and physically characterized. Humidity sensing investigation was performed with CNF sheets taped on the top of circuits in coplanar waveguide (CPW) technology. This investigation includes sensitivity and dynamic range analysis with reflected waves along the CPW circuit through resonant frequency shift, and transmitted waves through S21 phase shift. Moreover, sheets with various amounts of CNF were used to study the influence of CNF weight on humidity sensing performances. Regarding the resonant frequency shift, the best sensitivity was measured with the weightier CNF film (71 g/m2), that is 2.82 MHz/%RH from 55%RH to 100%RH. Regarding the phase shift, the same film sensitivity is 0.7°/%RH from 70%RH to 100%RH, with a figure of merit of 7.43°/dB as a phase shifter. © 2017 Elsevier B.V