Abstract
We propose rectangular asymmetric double split resonators with field confining tips for use as thin-film sensors. In contrast to frequency selective surfaces, which consist of two-dimensional, periodic resonator arrays, only a single unit cell placed inside a rectangular waveguide is sufficient for sensing. Compared to circular structures, the rectangular design offers a miniaturization. Furthermore, the tips at the end of the resonator arms concentrate the field components into a small area, increasing the volumetric sensitivity of the device.