3-D Printing Microfluidic Channels With Embedded Planar Microwave Resonators for RFID and Liquid Detection

In this letter, we present a novel sensor based on a planar resonator embedded within a 3-D printed fluidic channel for liquid sensing applications with a maximum detectable resolution of 1000 ppm (0.1 V%) ethanol in water. The fabricated sensor operates between 5.3 and 5.8 GHz with a quality factor of 116 and a resonant amplitude of -15 dB. The resonator sensor embedded within the fluidic channel enables 50-μm proximity between the resonator and liquid material inside the channel. The encapsulating polymer material also protects the resonator's ring from positional drift, allowing consistent measurements to be made easily without the need for complex fabrication processes. The sensor measured ethanol and water mixtures with a sensitivity of 2.5 MHz per ethanol volume percentage with a resolution of 0.1% ethanol. In addition to improved accuracy and sensitivity, the sensor device is affordable, easy to design and fabricate for a range of frequencies, and environmentally friendly with the continuous reusability.