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SEPTEMBER 2019 I DESIGN007 MAGAZINE 71 If you feel like breaking out the papyrus and doing the math yourself, Figure 2 shows one of the simpler equations. Otherwise, you can just use a calculator (Figure 3). Conclusion Your documentation should not be a con- fusing ambiguity. When you design for con- trolled impedance, the documentation instead becomes a double-check that can help speed your design through the manufacturing pro- cess. If you design your board to hit the exact impedance number that would otherwise be called out in the documentation, you should be well within the manufacturer's tolerance range. I recognize that testing is important in many instances, such as when there are high perfor- mance or special materials requirements. In any case, tests are far more enjoyable when you know the answers to the questions beforehand. When you integrate impedance math into your design process, you get quality boards faster and more efficiently. DESIGN007 Bob Tise is an engineer at Sunstone Circuits. To read past columns or contact Tise, click here. Microfluidics is the manipulation and study of sub-mi- croscopic liters of fluids. The current gold standard for the fabrication of microfluidic devices is soft lithography where elastomeric materials are casted on a mold fabri- cated in a cleanroom. 3D printing emerged as an attractive alternative to soft lithography. 3D printers turn a design into working proto- types in the order of hours, and the recent introduction of low-cost 3D printers make 3D printing more accessible in general to researchers. Current 3D printing technologies for the fabrication of microfluidic devices have a few limi- tations: available materials for 3D printing, achievable di- mensions of microchannels by commercial 3D printers, and integration of 3D-printed microfluidics with functional materials or substrates. To overcome these challenges, researchers from the Singapore University of Technology and Design's (SUTD's) Soft Fluidics Lab have developed an alternative method to apply 3D printing for the fabrication of microchannels. The researchers applied direct ink writing (DIW) 3D print- ing of fast-curing silicone sealant to fabricate microfluidic devices rapidly on various substrates. The design of fluid- ic channels is determined by the patterned silicone seal- ant while the top and bottom transparent substrates seal the channels. "Our approach to apply DIW 3D printing allows direct patterning of microchannels essentially on any flat sub- strate," said Assistant Professor Michinao Hashimoto, the principal investigator of the project. The team also dem- onstrated the ease of patterning of silicone barriers di- rectly on an off-the-shelf PCB, immediately integrating electrodes into the microchannels that would function as real-time flow sensors. (Source: SUTD) Researchers Develop Rapid, Low-cost Method to 3D Print Microfluidic Devices Figure 3. The same equation, using a calculator. (Source: EEWeb)