Low drift micro-flowsensors (TET.6634)

Research
The general trend in miniaturisation systems in chemistry, pharmacy and biology asks for the miniaturisation of the instruments for the control. In these fields, the accurate and reliable measurement of the amount of fluid (liquids and gases) flowing through pipes is one of the key issues. Basically, in these micro flowsensors the fluid is locally heated and the temperature distribution at and around the heater(s) is measured. Any flow will change the temperature distribution, and its measurement provides information on the flow. The elements for sensing in current microflow sensors are made by thin films of metal. These films have the notorious problem of drift of their properties. This causes unreliable measurement results, which is extremely problematic if the sensors need to be very sensitive. In this project we propose a solution to this problem by combining two innovations. One innovation is related to the measurement of the temperature by using thermocouples. The other one is related to a control scheme of the sensors. The idea is to control the heaters so that their temperature difference is zero, and the control power provides the information on the flow. The importance of thermo elements lays in the fact the only temperature difference cause any signals. According to simple models of this sensors system the drift can be eliminated completely.
The research program consists of micro fabrication of the sensor elements, modelling of their interaction (heat transfer) with the flowing medium, and an in-depth study of the performance of the sensors. A successful project will result in demonstrators ready for industrial tests.

Utilization
Flow sensors are required in all situations where liquid and gases must be transported in a controlled way. There are applications emerging for the consumer market, in particular in the motorcar industry, but currently the bulk of flow sensors are purchased for industrial, medical and laboratory applications. Flow controllers are indispensable for the IC industry. Examples for industrial applications are in the food, process, (fine) chemical and pharmaceutical industry. Laboratory applications are in the same fields and in others such as environmental monitoring, meteorology. We mention chemical analysis systems such as flow injection and chromatography. Quite often, the flow sensor is part of a control system, e.g. of a flow controller or a dosage system.
In many applications small flow sensors are required. Small systems may be more costeffective, perform better and are more convenient to use. Therefore there is a great trend for miniaturization. When miniaturizing flow sensors one has to face the problem that automatically the quantity of flow to be measured becomes smaller. On the other hand, the market demands flow sensors capable of measuring ultra small debits (?gr/min). Automatically, the sensors for these small debits must be small. Currently there are no reliable sensors of the required sensitivity and precision. It follows that more sensitive and more reliable flow sensors are needed. This research program is intended to fill the gap.