Pore size optimisation of humidity sensor—a probabilistic approach

Strontium-Doped Hematite as a Possible Humidity Sensing Material for Soil Water Content Determination

“…Moreover, at 20 °C and under atmospheric pressure, the mean free path of water vapor molecules decreases from 85.44 to 84.82 nm in dry air containing humidity traces and up to the water vapor saturation. The molecular entry into the pore is possible if the free path of the incident vapor molecule is less than the pore size [44]. The desired pore size should be comparable to the molecular free path of vapor at all humidity conditions, so that the molecules can impinge and adsorb on the pore wall [44].…”

“…The molecular entry into the pore is possible if the free path of the incident vapor molecule is less than the pore size [44]. The desired pore size should be comparable to the molecular free path of vapor at all humidity conditions, so that the molecules can impinge and adsorb on the pore wall [44]. Finally, in addition to the protonic conduction in the adsorbed layers, electrolytic conduction occurs in the liquid layer of water condensed within capillary pores, thereby resulting in an enhancement of conductivity.…”

“…The loss of porosity and of specific surface area because of the higher firing temperatures at 1,000 °C (Table 4) could be responsible for the reduced sensitivity to humidity, as specific surface area is the principal microstructure feature for sensing humidity under low RH conditions, while mesopore volume dominates under high RH conditions [9,44]. This can be confirmed by the fact that the response to humidity of this last sample is close to the one of the thick-film fired at 900 °C (Figure 11).…”

A micro interdigitated thin film metal oxide capacitive sensor for measuring moisture in the range of 175–625 ppm

“…It has been investigated that keeping pore morphology of nanostructured thin film identical, the sensitivity can be increased by simply optimizing the configurations of both bulk parallel plate or membrane type interdigitated capacitors [18,24]. However, if the electrode area increases, the size of the device will increase and it will create problems when packaging the sensor in the small sample chamber.…”

Hybrid polymer/cobalt chloride humidity sensors based on optical diffraction

“…Materials sensitivity is thus dependent on the surface morphology, pore size and distribution, which further affect the stability, the response time and the operational range [8]. Polymeric sensors have mostly been investigated as bulk materials with respect to changes of their dielectric constant, or their specific volume and mass upon interaction with water, in applications involving surface acoustic wave (SAW) devices and resistive or capacitive-type sensors.…”