OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 4.5 seconds, and the recovery time was 6.9 seconds, reflecting efficient adsorption-desorption kinetics. As shown in Fig. 7, a, the capacitance-RH curve confirms moderate sensitivity and reliable humidity tracking at lower frequency ranges. The 4% ZnO–NGM sensor exhibited well-balanced performance in sensitivity, response time, and recovery time. The capacitance rose steeply in the range of 10% to 60% RH and gradually at higher RH, with a good correlation between RH and capacitance. At lower frequencies (10–80 kHz), the sensor showed increased sensitivity as a result of improved dipole relaxation and ionic conduction, whereas at 1 MHz, the capacitance response became flattened as a result of polarization response time limitations. The response time was 4.0 s, and recovery time was 6.2 s, both of which were among the shortest recorded at all doping levels. As shown in Fig. 7, b, the capacitance-RH curve confirms moderate sensitivity and reliable humidity tracking at lower frequency ranges. The 1% ZnO–NGM sensor had moderate capacitance sensitivity, response time, and recovery time. Capacitance increased with RH because of the dielectric polarization due to adsorbed water molecules. At lower frequencies (10 kHz and 50 kHz), the sensor was more sensitive, whereas at higher frequencies (1 MHz), the polarization response was restricted, leading to a flat capacitance curve. The response time was 4.8 seconds, and recovery time was 6.9 seconds, which provided a moderate improvement compared to the pure ZnO. As shown in Fig. 7, c, the capacitance-RH curve confirms moderate sensitivity and reliable humidity tracking at lower frequency ranges. The 5% ZnO–NGM sensor exhibited high sensitivity to changing humidity levels, and the sensitivity was 53.9 pF/%RH. The capacitance rose sharply between 10% and 60% RH and gradually at higher RH. Although the sensor showed much higher sensitivity than with lower doping concentrations, the response and recovery times (4.2 and 6.6 seconds) were marginally slower as a result of partial agglomeration of the NGM, which lowered the number of active adsorption sites available. Despite the reduced kinetics, the sensor showed high sensitivity and was therefore appropriate for applications where sensitivity is more important than rapid response times. As shown in Fig. 7, d, the capacitance-RH curve confirms moderate sensitivity and reliable humidity tracking at lower frequency ranges. The 10% ZnO–NGM sensor showed the highest capacitance sensitivity (62.1 pF/%RH) of all the doping levels, but its response time (6.0 s) and recovery time (8.0 s) were slower than those of the other sensors. The slower kinetics were mainly caused by the agglomeration of the NGM at this higher doping level, which restricted water molecule adsorption and desorption and also ionic mobility. Despite these limitations, the 10% doping level showed better sensitivity, and this is beneficial in many applications where sensitivity is important even at the cost of reduced response speed. As shown in Fig. 7, e, the capacitance-RH curve confirms moderate sensitivity and reliable humidity tracking at lower frequency ranges [31]. Fig. 6. Experimental setup for humidity sensing using an LCR meter and a controlled chamber
RkJQdWJsaXNoZXIy MTk0ODM1