A Simple, Tunable, And Highly Sensitive Radio-Frequency Sensor

We report a radio frequency (RF) sensor that exploits tunable attenuators and phase shifters to achieve high-sensitivity and broad band frequency tunability. Three frequency bands are combined to enable sensor operations from similar to 20 MHz to similar to 38 GHz. The effective quality factor (Q(eff)) of the sensor is as high as similar to 3.8 x 10(6) with 200 mu l of water samples. We also demonstrate the measurement of 2-proponal-water-solution permittivity at 0.01 mole concentration level from similar to 1 GHz to similar to 10 GHz. Methanol-water solution and de-ionized water are used to calibrate the RF sensor for the quantitative measurements. (C) 2013 AIP Publishing LLC.