Exploiting Sensitivity Enhancement in Micro-wave Planar Sensors Using Intermodulation Products With Phase Noise Analysis

In this paper, a new technique to enhance the sensitivity of microwave resonators is introduced. Double split ring resonators are implemented as the core of a loss-compensated resonator. It is illustrated that regenerative oscillators when mixed together can produce higher order intermodulation products (IMP) at the output. The variations in sensing tone are multiplied and exhibit considerably higher sensitivities at 3(rd), 5(th), and 7(th) IMP components compared to the main resonant frequency. The sensor is also integrated into wireless platform with ultra-wideband bowtie antennas. Common fluids such as Toluene, n-Heptane, IPA, Ethanol, Methanol, Acetone, and Water are tested in fluidic channel and demonstrated that the sensitivity for intermodulation products are significantly increased proportional to the order of IMP. The proposed sensor is also examined with glucose concentration sensing for the range of 0- 600 mg/dL and significant variation for 7(th) IMP sensor is observed as opposed to saturation of conventional sensor. Also, asphaltene concentrations down to 6 ppm are recognizable when precipitated from toluene solution using the proposed sensor. Moreover, a rigorous analytical study is presented for phase noise of the IMP originated from reference signals.