A metamaterial-inspired miniaturized wide-band microwave interferometry sensor for liquid chemical detection

This paper presents a miniature wide-band interferometry sensor for dielectric spectroscopy and detection of liquid chemicals based on utilizing two composite right/left-handed (CRLH) transmission lines (TLs) in a zero-IF mixing configuration. The equivalent series capacitance of the CRLH TLs, constructed by using microstrip interdigital capacitors, is loaded with microfluidic channels, and exposed to the material under test (MUT) to act as the sensing element. Due to the nonlinear dispersion relation of the artificial TLs with respect to the sensing capacitor, higher sensitivity over a frequency band as wide as 4-8 GHz is achieved, compared to the previously-reported resonator- or capacitor-based sensors. The final fabricated system prototype is 4 cm×8 cm. Moreover, a calibration method is presented based on measurement results, which shows an rms error less than ~1.5% for liquid-chemical permittivity detection. To the best of author's knowledge, this is the first disclosure of wide-band and highly-sensitive microwave interferometry sensor suitable for portable lab-on-board applications.