Sensing of liquid droplets with a scanning near-field microwave microscope

We demonstrate a scanning near-field microwave microscope based on an interferometric technique for dielectric characterization in liquid media. The instrumentation combines a vector network analyzer, an interferometry-based matching network and an evanescent microwave coaxial probe. The measurement sensitivity of the measured microwave signals can be enhanced at the desired frequency in the range 1–26 GHz. Other advantages such as simplicity of operation and high spatial resolution are also achieved. As a demonstration, we have observed a high electromagnetic coupling between the probe tip and liquid droplets featuring emergent applications in biological and chemical researches.