The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel.

Stress-induced surface acoustic wave velocity shifts are analyzed for langasite (LGS) SAW resonators. The analytical methodology has been verified by comparing experimental results and analytical results for quartz resonators. LGS SAW resonators with Euler angles which are most sensitive and least sensitive to diametrical forces are determined and their applications in force sensors and resonators with minimum acceleration sensitivity are discussed. Sensitivity of the analytical results to different groups of nonlinear material constants is discussed; it was found that for specific configurations, failure to include the third-order piezoelectric constants, dielectric constants and electrostrictive constants may lead to a significant calculation error. Surface acoustic waves propagating on an LGS square plate subject to bending moment along the propagation direction and normal to the propagation direction are analyzed; it was found that the average momentinduced velocity shift of LGS resonators are comparable to quartz resonators. Analyses of the sensitivity of the results to different groups of nonlinear material constants shows that for some specific wave propagation directions, failure to include the third-order piezoelectric constants, dielectric constants, and electrostrictive constants may lead to large errors.

In the present work, we have demonstrated a highly sensitive H₂ gas sensor using a lanthanum doped ZnO (La_ZnO) thin film operated at 300 °C. Also, a p-type to n-type carrier reversal activity is revealed in the presence of H₂ gas species, which predominantly depends on the operating temperature and doping concentration of lanthanum. Pure and La_ZnO (1–10 at. %) thin films were successfully synthesized using a sol-gel route, where a 5 at. % lanthanum doped ZnO thin film shows an outstanding H₂ gas sensitivity (400%) among all other samples with an optimized temperature of 300 °C. Moreover, this sensor actively responds to a wide H₂ gas concentration (10–500 ppm) with a sensitivity of 0.9 (∼n). Additionally, H₂ gas sensing selectivity and mixed gas sensing performance were investigated in the presence of CO and CO₂ gas species at optimized temperature (300 °C). Results show that the pure and 1–3 at. % La_ZnO thin films exhibited n-type H₂ gas sensing, while p-type sensing behavior was observed for 5% and 10% La_ZnO thin films at 300 °C. It is further observed that O⁻ species are extremely active to CO gas species operating at a high operating temperature (>250 °C). Therefore, despite the emerging p-type behavior of the sensor, the ejected electrons are expected to dominantly reduce the sensor resistance in the presence of CO gas species at 350 °C. The improvement of H₂ sensing is further interrelated with the defect levels using Raman spectroscopy.