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This paper demonstrates the first-of-its-kind additively manufactured microfluidics-based flexible RF sensor, combining microfluidics, inkjet-printing technology, and soft lithography, which could potentially enable the first “real-world” wearable “smart skin” applications. A low-cost, rapid, low-temperature, and zero-waste fabrication process is introduced, which can be used to realize complex microfluidic channel networks with virtually any type of sensing element embedded. For proof-of-concept purposes, a reusable and flexible microfluidics sensor was prototyped using this process, which only requires 0.6- \mu \text L fluid volume to produce a 44% frequency shift between an empty ( \epsilon r=1 ) and a water-filled channel ( \epsilon r=73 ), demonstrating a sensitivity that is higher than most previously reported microfluidics-based microwave sensors. Seven different fluids were used to measure the sensitivity of the prototype and an overall sensitivity of 24\%/ \log (\epsilon r) was observed. The “peel-and-replace” capability of the presented sensor not only facilitates the cleaning process for sensor reusability, but it also enables sensitivity tunability. For bent/conformed configurations, the sensor’s functionality is good even for a bending radius down to 7 mm, demonstrating its great flexibility. After bending multiple times, the sensor still exhibits a very good performance repeatability, which verifies its reusability feature. The introduced additively manufactured RF microfluidics-based sensor would be well suited for numerous wearable and conformal fluid sensing applications (e.g., bodily fluids analyzing and food monitoring), while it could also be utilized in a variety of microfluidics-reconfigurable microwave components. [ABSTRACT FROM AUTHOR]

This paper introduces the first-of-its-kind wireless passive sensing platform combining radio frequency identification (RFID), microfluidics, and inkjet printing technology that enables remote fluid analysis and requires as little as 3 \muL of fluid. The demonstrated variable microfluidic capacitors, resonators, and RFID tags are fabricated using a novel rapid, low-cost, and low-temperature additive inkjet process, making them disposable. However, even with their disposable nature, the RF microfluidic devices exhibit repeatability and long-term reusability for accurately detecting water, various alcohols, and % content of water/alcohol mixtures down to 1% water in ethanol. While the main discussion is on fluid sensing, the demonstrated components can also be used in fluid-tunable RF applications. [ABSTRACT FROM AUTHOR]