Sensitivity Optimization in SRRs Using Interferometry Phase Cancellation

In this paper, an optimization technique is introduced for microwave planar sensing that employs split ring resonators (SRRs) in an interferometer structure. A phase shifter provides a second path parallel to SRR with additional 180-degree phase that results in their destructive summation at the output and a sharp notch in transmission is produced. The notch is designed adjacent to the resonator ~ 4 GHz and the sensing parameter is the amplitude variation of the notch. It is shown that the notch can be created with arbitrary material loading only using proper phase shifting. The dynamic range of sensing is improved from Δf/f
₀
≅ 1% in conventional frequency tracking of the SRR to as high as Δ|S
₂₁
|/|S
_21-0
| = 40% in the proposed notch-depth tracking. This helps detecting methanol in ethanol to be improved at the limit of detection by 14 times using the proposed technique.