Sensitivity evolution and enhancement mechanism of porous anodic aluminum oxide humidity sensor using magnetic field

Capacitive sensors based on anodic oxide aluminum (AAO) film provide a fast and reliable means of sensing humidity. Moreover, the water molecules under a magnetic field preferentially form water clusters in which the dipole moments of the water molecules have a more orderly arrangement. In this article, we have investigated the sensitivity enhancement and its mechanism of the AAO humidity sensor by performing the sensing operation in the presence of an NbFeB magnet. The results show that the application of a magnetic field with a strength of 0.058 T yields a linear-like relationship between the capacitance and the relative humidity (RH) even under low RH of 25-45%. The sensitivity performance at low-to-high RH conditions arises because the magnetic field leads to a more orderly arrangement of the water molecules in the pores of the AAO film so as to increase the dielectric constant. Thus, the proposed method and mechanism suggest significant potential for enhancing the sensitivity and linearity of the capacitive AAO sensor from low-to-high RH.