Printed Microwave Frequency Humidity Sensor Operating With Phase Shifting Scheme

Abstract

This paper investigates a shifting sensing scheme combining slots, transmission lines, and printing technologies. This sensing scheme translates the electrical sensitivity of a transmission line conductor to the insertion phase as a measurement variable. A coplanar waveguide (CPW) based structure was designed, screen-printed, and tested on relative humidity (RH) conditions ranging from 22.8 -75.3 %RH. For the first time, a composite material made of poly-pyrrole and TEMPO Oxidized Cellulose Nanofibers (TOCN/PPy) was integrated to the structure and studied as a humidity sensitive conductor in microwave frequencies. The measured sensitivity was 0.154°/%RH at 5.870 GHz, while insertion losses decreased by 1.26 dB. The effects of sensing layers thickness as well as trade-off considerations between phase sensitivity and signal attenuation were analyzed by simulation.

Terahertz Humidity Sensing Based on Surface-Modified Polymer Mesh Membranes with Photografting PEGMA Brush

“…The experiment result in Figure 3 expresses that the duration of UV exposure time should not be less than 10 min for a complete graft polymerization process of P(PEGMA- co -BPA) copolymer brush. In addition, to detect immobilization of P(PEGMA- co -BPA), the sensing method based on intensity interrogation of the THz transmitted signals is better than the proposed phase interrogation method [ 5 , 9 ] because the measured phase variation of the transmitted THz pulse from the ultra-thin immobilized layer during the photograft polymerization is extremely small and ignored.…”

“…However, it only works at low humidity levels within a small linear response range from 10.5% to 21.0% RH [ 6 ]. Another microwave RH sensor works on the basis of incorporating a sensing layer TOCN/PPy, i.e., conductive polymer-doped cellulose nanofibers, into a coplanar waveguide structure, demonstrating a proportional phase response to different RH levels from 22.8% to 75.3% [ 9 ]. The sensitivity of the phase-sensitive RH sensor, approximately 0.154°/% RH, was measured at 5.870 GHz but with a relatively high insertion loss of 1.26 dB [ 9 ].…”