Dual-band antennas for frequency-doubler-based wireless strain sensing

In this letter, two dual-band antennas operating at 2.9 and 5.8 GHz are proposed and investigated in terms of the strain dependency of their resonances. They are designed to operate as strain-sensing and communicating devices at the same time in a frequency-doubling strain sensor that is interrogated wirelessly by a reader. An integration of transmit and receive antennas into one dual-band structure offers a compact sensor solution. The antennas' resonance frequencies shift if strain is applied, which in the case of the proposed antennas can be used to characterize the strain not only in terms of amplitude, but also direction. A very small size is achieved for an optimized one-feed design, which leads to high strain sensitivity values along one axis. A novel two-feed concept is designed to ease integration with the frequency doubler and detect strain in two directions with equal sensitivity. Return loss and radiation patterns of both designs are presented. Due to the wide beamwidths of both antennas, interrogation is possible from a wide range of angles.