A prototype multifunction differential pressure-flow sensor for medical and industrial applications.

摘要

Micro-Electro-Mechanical Systems (MEMS) have been one of the key enabling technologies in the field of microelectronics. They have successfully replaced all bulk sensing systems with miniature scale sensors and are found to be suitable for many commercial and industrial applications as well. Following this trend, MEMS have now matured to a point where they will be applied in biological and chemical applications and could successfully replace the sensing systems that are currently being used. One such application is the drug delivery system for medical applications. Flow sensors are an integral part of these drug delivery systems and are one of the main devices necessary to monitor the amount of a drug that will be delivered into the human body.;Flow sensors based on different sensing principles have been published in the literature with the sensing principle based upon their intended use. The differential pressure sensing principle is one successful technique that has been published. However, it has only been explored up to the point of demonstrating the proof of concept associated with sensing the volumetric flow rate of the fluid. There are still many avenues that need exploration in order to successfully realize a flow sensor suitable for medical applications. The current situation in this competitive world calls for multiple functionalities being embedded into one system. Hence, sensors with additional sensing capabilities such as sensing fluid type, fluid pressure, flow direction, and fluid presence in addition to flow rate would be ideal for a system-in-chip configuration. Also, flow sensors that possess such multiple sensing capabilities can be applied to generic applications as well as medical applications.;The objective of this research endeavor was to successfully demonstrate a flow sensor using the differential pressure sensing principle to sense flow rates as low as 0.1 ml/hr. In addition to sensing the volumetric flow rate, the type of fluid will be sensed based on the dielectric constant of the fluid. Also, the viscosity of the fluid will be monitored. Moreover, functionalities such as fluid pressure, fluid presence, and flow direction will be sensed. Flow sensors were configured such that they can successfully demonstrate two differential pressure sensing modes, those being sensors placed in the cavity and sensors placed in the channel. Assembly and packaging was perfomed, followed by testing to study the flow sensor characteristics. Hysteresis and repeatability study of the sensors was performed as part of the initial evaluation. Each of the sensor designs was tailored for measuring low flow rates.;Surface micromachined pressure sensors were bonded with a cap embedded with flow restriction channel and sensor cavities to realize a flow sensor. This flow sensor has pressure sensors housed in the flow restriction channel in addition to the ones in the sensor cavity. This enabled us to measure the volumetric rate and viscosity of the fluid in two different sensing modes. An interdigitated structure was integrated along with the pressure sensors which enabled us to sense the permittivity of the fluid. Flow direction, fluid presence, and fluid pressure were also sensed by utilizing one or combination of the sensing structures.;In this research endeavor, a prototype model of a flow sensor with additional sensing capabilities was developed and demonstrated. Surface micromachining technology was utilized for the realization of the MEMS sensors. The majority of the processing tools and technology utilized for realizing these specific MEMS structures were borrowed and modified from current production tools to suit these requirements. Some of these processes included photo resist, etch, diffusion, bonding, screen print, and sawing. The developed flow sensor has the capability of measuring very low flow rates, as low as 0.01 ml/hr. It also possesses the capability to sense the fluid type based on viscosity or the permittivity of the fluid. Fluids successfully discerned were de-ionized water, NACL, fluorocarbon, and glucose. The input and output pressure of the fluid passing through the sensor was also measured. Fluid presence and flow direction can also be determined.