An auxetic based geometric tuning approach in microwave sensors for enhanced sensitivity in strain measurements

Reducing sensor size without compromising the antenna’s characteristics is quite a challenge in radio frequency (RF) sensors for strain measurement, due to the dependence of sensor size on wavelength. This paper explores the possibility of utilising an auxetic structure in a patch antenna to enhance the strain sensitivity at lower strains. A new design concept of auxetic-microstrip patch antenna (AMSPA) sensor is introduced for the first time in strain measurements. The radiating element of a microstrip patch antenna is modified with a hexagonal re-entrant auxetic (negative Poisson’s ratio) cluster without altering the resonant frequency. The structural and electromagnetic co-simulations are performed to investigate the strain sensitivity under tensile loads. The simulation and experiment results indicate that the AMSPA sensor is suitable for detecting lower strains without deteriorating the antenna characteristics. The results show that the proposed sensor has a higher sensitivity of −4.157 ± 0.5 kHz /µε at lower strains with an enhanced gain (+12.2 %) in comparison with conventional microstrip antenna. The auxetic architecture enable sensor miniaturization by introducing additional surface current paths without degrading the antenna performance.