Strain measurement based on microstrip patch antennas

The strain sensors based on microstrip patch antennas have shown great potential for structural health monitoring (SHM) in aerospace and civil industries. This paper will introduce a novel method of strain measurement in which the shift in antenna resonant frequency can be utilized to measure strain. The patch antenna sensor with a rectangular patch radiates at two fundamental modes (TM₁₀ and TM₀₁) and their resonant frequencies (f₁₀ and f₀₁) are determined by the corresponding electrical length of the current flow. An applied strain changes the dimensions of the microstrip patch antenna, resulting in the electrical length change, which has different influences on the electricity flow as well. Therefore, the structural strain information can be collected by the change of antenna resonant frequencies. Four categories of proposed sensors with different dimensions were designed and manufactured to measure the strain applied to the cantilever beam, and the experimental results show that there is a strong linear relationship between the resonant frequency shift and the applied strain. Besides, antenna sensors have more sensitivity at higher initial resonant frequencies, which is in good agreement with the theoretical analysis. The investigation can provide a preliminary theoretical basis for the application of this innovative measuring strain technology in the wireless SHM system.