Flow sensor using micromachined pressure sensor

A flow sensor capable of measuring flow rate, fluid type, fluid pressure, fluid presence, and flow direction has been demonstrated. This research activity demonstrates a very simple cap fabrication and assembly process that enabled the realization of a flow sensor with multiple sensing capabilities. A surface micromachined process is employed to fabricate the pressure sensors as well as the cap that defines the fluid channel. The sensor was configured in a way to successfully demonstrate two differential pressure sensing modes (i.e. sensors within the cavity and sensors in the flow channel). Both flow rate and viscosity measurements are based on the differential pressure sensing principle. Fluid presence is determined using an interdigitated structure which can also sense the fluid type based on permittivity of the fluid. The flow rate measured successfully has been as low as 0.01 ml/hr and showed very good linearity when compared to the theoretical model. The diameter of the pressure sensor diaphragm utilized was as low as 100 microns and depended on the flow rate required to measure.