A new type of MEMS flow sensor has been designed, analyzed, fabricated, and tested. This sensor consists of a surface micromachined switch with a complex cantilever shape. A portion of the sensor is bent at a right angle to the substrate and to the flow direction. The fluid flow produces a pressure on the sensor; sufficient pressure causes the switch to close at the designed flow rate. These flow sensors have been developed for a large multi-university project for the design and construction of a biomimetic underwater lobster robot to be used to search for and destroy mines. However, we envision a variety of other uses for these flow sensors, including biomedical applications such as blood flow measurement.
The fabrication process is based on the Northeastern University Metal Micromachining (NUMEM) technology . The NUMEM process has been used to fabricate various surface micromachined metallic structures such as microrelays, microinterferometers, micromirrors, and microaccelerometers.
The analysis of these devices consists of using incompressible fluid mechanics to determine the pressure acting on the sensor and beam theory to model the resulting deflection of the switch. The first set of flow sensors was designed to close at flow velocities of 0.5, 1.0, 3.4, and 5.4 m/s. The area of the paddle, which lies in the flow, is varied in order to obtain sensors that close at different flow rates. The results of testing agree well with the analytical predictions. Although these flow sensors are unidirectional, an array of four sensors at each point can be used to determine the flow velocity and direction.