Electromagnetic simulation of flexible strain sensor based microstrip patch antenna

Passive wireless sensors have considerable advantages for strain measurement due to their simple installation and compactness without additional energy source embedded within the sensor. For this purpose, the design of the antenna is critical since the deformation due to changes of the measured quantity should be considered. In this paper, a passive wireless strain sensor using a microstrip patch antenna with feed-inset operating at IEEE C-band i.e. 5.8 GHz was designed and simulated using CST studio suite. The electromagnetic simulation was improved by implanting derived mathematical equations describing the deformation equations during strain measurement. The FR-4 flexible substrate having a thickness of 500 mm and dielectric loss (e0) of 4.3 was used to improve the strain sensitivity. The antenna characteristics such as return loss and radiation pattern were determined. Without strain, the microstrip antenna radiates at its resonance frequency. Under the applied strain, changes in the antenna dimensions i.e. patch length and width results a shift in the normalized resonance frequency. It was found that the shift in the resonance frequency of the patch antenna shows a nearly linear dependence under the applied strain. The strain sensitivity and the reflected signals are proportional to the applied strain. The results show a highly potential of microstrip patch antenna as small size, low cost and high performance passive wireless strain sensor for advanced structural health monitoring, radar and aerospace applications.