Flow sensor using micromachined pressure sensor

Abstract

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.

Flowmetering for microfluidics

“…4). 55,56 In the first case, when the pressure increases, the diaphragm deforms, resulting in a variation of the piezoresistive resistance. The resistance variation can be obtained from either current or voltage measurements.…”

“…Although much progress has been made to increase the flow rate measurement ranges (up to 3 orders of magnitude 54,56 ), this technology remains, to our knowledge, a proof-of-concept. Its limitations seem to have so far prevented attempts for its industrialization and commercialization.…”

Fully front-side bulk-micromachined single-chip micro flow sensors for bare-chipSMT(surface mounting technology) packaging

“…For 'type A' sensor design, the two differential pressure sensors are placed in serial connection with the flow channel, rather than placed on top of the channel that was previously published in [11][12][13]. While for the 'type B' sensor, the two pressure sensors are laid at one side of the channel.…”

“…In contrast to the traditional fabrication techniques for piezoresistive flow sensors where silicon-silicon (or siliconglass) bonding was normally used to form the flow-channel structure [11][12][13], the herein proposed fabrication technique monolithically integrates the pressure reference cavity and the flow channel in a single-silicon substrate. Therefore, the proposed sensor should be advantageous in saving fabrication cost.…”

Integrated throughflow mechanical microfluidic sensors

“…As mentioned above, the Coriolis component has a 90°phase shift. Thus, it can be expressed as: 47) withĈ cor the Coriolis mode component. The two capacitive output signals can now be written as:…”