Figure 5.

Relative humidity sensors: main elements composing the measuring chain (sensor, analog electronics, data acquisition, post-processing or signal analysis stage) to estimate $f_R$. Analog electronic stages vary between different sensors since the output quantities are different. $C(RH)$, $R(RH)$, $\lambda (RH)$, $I(RH)$ are capacitance, resistance, wavelength, and light intensity changes caused by the RH, respectively. $V(RH)$ is the voltage output, $i(RH)$ is the current output. The capacitive sensors picture is adapted from [112]; the resistive sensors picture is from [113]; the nanocrystals and nanoparticles sensors image is from [114]; the fiber-optic humidity sensors picture is adapted from [115].