Characterization of LC sensor structures realized by PCB and LTCC technology for determining moisture in building materials

This paper compares performances of two wireless sensors for measuring water concentration in building materials, one manufactured by the printed circuit board (PCB) technology and another one using the low temperature co-fired ceramics (LTCC) process. The fabricated sensors consist of inductive part (L) and interdigitated capacitive part (C) in one metal layer, connected in parallel. Inductance of inductive part was kept constant, whereas capacitance of capacitive part was changed by exposing the sensor to different moisture concentration, changing its resonant frequency. The variation of resonant frequency as a function of different water concentration was measured, using antenna coil and impedance analyser, in two widely used construction materials: clay brick and autoclaved aerated concrete block. Surface analysis for two sensors was performed by means of 3D profilometer. Mechanical properties of the sensors were measured for both conductive segments (copper and silver) and substrates materials (PCB and ceramics substrates) using nanoindenter. Comparative characteristics of the sensors are presented from their application point of view