Artificial transmission lines for high sensitive microwave sensors

Two common and two new unit cells for artificial lines made of four reactive elements are studied concerning their sensitivity to capacitive changes and their applicability as capacitive sensors. It is shown that selection of the unit cell is very important and can highly influence the sensitivity. The shown principle is very powerful and can be scaled up to THz frequencies, only limited by available fabrication technology. A built planar differential microwave sensor based on artificial lines working at 2.3 GHz is presented. It features a simple output power evaluation instead of a classic but more complicated phase difference measurement. With power variation of up to 60 dB in dependence of small environmental dielectric changes it shows a very high sensitivity and dynamic range. Functional layer coatings can be applied easily due to its planarity and open wide application areas for biomedical sensing.