Ultrahigh FOM Microwave Sensing Based on the Fano-Resonant Spiral Dipole Antenna

Microwave sensors with low cost and high compatibility show great potential in the areas of environmental monitoring, food safety, and biomedical diagnostics. However, small microwave sensors using asymmetric antenna structures exhibit large fabrication difficulties or low figure of merits (FOMs). Here, we propose the Fano-resonant spiral dipole antenna (∼
λ
₀
/13). In the antenna, a Fano resonance with a narrow bandwidth (∼
f
₀
/640) and high spectral contrast (
C
≈ 1.0) is supported. In particular, an antenna array is used to improve the transmission efficiency (5-fold enhancement). Based on the Fano-resonant spiral dipole antenna, ultrahigh FOM microwave sensors are successfully realized. The Sensing FOM of the sensors can reach up to 252 RIU
⁻¹
and 172 RIU
⁻¹
, respectively, which are more than nine times those of the other sensors.