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This paper presents the performance of three different micro-electro mechanical systems (MEMS)-based surface acoustic wave (SAW) devices for sensing hydrogen gas. All three devices, namely, Device 1, Device 2 and Device 3, were constructed with the same dimensions but with varying geometries. The devices were simulated using COMSOL Multiphysics and various analyses such as deflection, electric potential, frequency shift with respect to the concentration of hydrogen gas, total capacitance of interdigital transducers (IDTs) and sensitivity were performed using finite element modeling. The devices were constructed with a lithium-niobate piezoelectric substrate and a ZnO sensing layer. The performance of MEMS-based SAW devices can be improved by doping with nanomaterials. The devices were tested with hydrogen gas at concentration from 10ppm to 100ppm. Owing to the mass loading effect, Device 3 exhibited maximum sensitivity and a close approximation of the simulated results with the theoretical results.

This study describes an easy and cheap inkjet printing method for producing a paper-based gas sensor consisting of a composite film made of graphene oxide and poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate) (PEDOT:PSS). A glossy paper substrate is an inkjet printed with ink made by dispersing graphene oxide in a PEDOT:PSS conducting polymer solution to test its ability to detect ammonia (${\text{NH}}_3)$ at ambient temperature. The presence of few-layer graphene oxide in the PEDOT:PSS copolymer and the existence of $\pi$–$\pi$ interactions between graphene oxide and PEDOT:PSS are confirmed by Fourier transform infrared spectroscopy, UV–Visible spectrophotometer, and X-ray diffraction. In a small concentration range of 1–100 ppm at ambient temperature, the ink-jet printed graphene oxide-PEDOT:PSS gas sensor displays strong responsiveness and good selectivity to NH₃. The study found that ${\mathrm{\text{NH}}}_4$ is a strong donor in the ammonia gas produced by a bubble system of ammonia water, with ${\mathrm{\text{NH}}}_4$ molecules being ideal candidates for molecular doping of graphene. The ${\mathrm{\text{H}}}_2\mathrm{\text{O}}$ molecule can facilitate quick desorption by converting ${\mathrm{\text{NH}}}_3$ to ${\mathrm{\text{NH}}}_4$. The interaction between graphene oxide and ${\mathrm{\text{NH}}}_3$ molecules is weak. The attained gas-sensing performance may be attributed to the increased specific surface area of graphene oxide and enhanced interactions between the sensing film and ${\mathrm{\text{NH}}}_3$ molecules via $\pi$ and lone pair electron network. The ${\mathrm{\text{NH}}}_3$-sensing mechanisms of the flexible printed gas sensor are based on the competitive interaction of ammonia on the sensor, adsorption and dissociate ionization on the sensor surface.