Raw and analysed filter data for SHM

RF based sensors are an attractive option for structural health monitoring applications due to the ease of access of interrogating such sensors. However, in most work, only scalar quantities are measured giving no indication of direction of strain or displacements. In this paper, a novel approach to displacement sensing is presented in which relative displacements are tracked in all three degrees of freedom. The sensor design is based on a pair of coupled line element filters whose frequency dependent forward power transfer is sensitivity to relative positions between the two filters. Multiple features in the S21 parameter are used to differentiate displacement direction. Gold based devices were fabricated on quartz substrates and characterized through vector network analyzer measurements. Results demonstrate uncoupled sensitivities of -1.41 MHz/mm, -1.74 MHz/mm and 12.23 MHz/mm for x, y and z displacements respectively.