Understanding Smart Sensors - Nomads.usp

206 Understanding Smart SensorsTop viewRotorStatorsA A 1PolysiliconFixed axleSilicon nitrideSilicon dioxideCross sectionFigure 9.2 Electrostatic micromotor. (After: [4].)9.2.3 MicropumpsA miniature peristaltic pump has been designed, fabricated, and tested. Thepump consists of three silicon wafers bonded together, as shown in Figure 9.5,to produce a flow channel, membrane, and heater [8]. Silicon fusion bondingwas used to bond the wafers containing those elements. The heaters are suspendedin a thermopneumatic fluid and sequentially activated from left toright. The flow channel is fabricated by a proprietary etching technique toclosely match the contour of the bulging silicon nitride membrane. Heating thefluid deflects the membrane that displaces the liquid. The deflected membraneseals the channel to prevent backflow. Performance of the micropump has beenpredicted to be 7 mL per minute at 15 psi. Pumps that can displace preciseamounts of liquid have applications in medicine for automatic insulin dispensing,as well as in manufacturing for precise process control and reduced materialcost.