Direction sensitive deformation measurement by circular microstrip sensor

The feasibility of applying circular microstrip antennas for deformation measurement is studied. For this purpose the frequency dependent reflection coefficient S₁₁ is analyzed. Deformation of the sample influences sensor geometry and causes a change of patch current distribution and resonant frequency shift. This effect is utilized to deformation evaluation. So far, microstrip sensors were utilized only if the direction of external force was known. In some applications this condition is not fulfilled, thus directional properties of sensors should be considered. In order to analyze this problem FEM simulations were carried out. Directional characteristics for selected resonant frequencies of designed sensor have been determined. It enables deformation and stress direction evaluation.