M. Kropp

Pressure stable thermoelectric flow sensors by means of membrane perforation

A commonly used method for measurements of small liquid flows are membrane based thermoelectric flow sensors. High temperature stable flow sensors have been developed and fabricated at IMSAS. A pressure stable version of these sensors has been developed by creating a membrane with perforation. Thereby a backpressure compensation is achieved. Here we present the fabrication process, first measurements and simulation results showing pressure stability to at least 8 bar.

Inline chemical process analysis in micro-plants based on thermoelectric flow and impedimetric sensors

In micro-plants, as used in chemical micro-process engineering, an integrated inline analytics is regarded as an important factor for the development and optimization of chemical processes. Up to now, there is a lack of sensitive, robust and low-priced micro-sensors for monitoring mixing and chemical conversion in micro-fluidic channels. In this paper a novel sensor system combining an impedimetric sensor and a novel pressure stable thermoelectric flow sensor for monitoring chemical reactions in micro-plants is presented. The CMOS-technology-based impedimetric sensor mainly consists of two capacitively coupled interdigital electrodes on a silicon chip. The thermoelectric flow sensor consists of a heater in between two thermopiles on a perforated membrane. The pulsed and constant current feeds of the heater were analyzed. Both sensors enable the analysis of chemical conversion by means of changes in the thermal and electrical properties of the liquid. The homogeneously catalyzed synthesis of n-butyl acetate as a chemical model system was studied. Experimental results revealed that in an overpressure regime, relative changes of less than 1% in terms of thermal and electrical properties can be detected. Furthermore, the transition from one to two liquid phases accompanied by the change in slug flow conditions could be reproducibly detected.

Miniaturized thermal flow sensors with through silicon vias for flip-chip packaging

We present the first miniaturized, high temperature stable thermal flow sensor with through silicon vias for electrical connection on the back of the silicon chip. The electrical and mechanical connections are done by standard flip-chip bonding to a printed circuit board which leads to a simpler packaging as compared to wire bonding. Moreover, the chip size could be further reduced without any loss of performance.

Bend sensor based on fibreoptics and concept for a compact evaluation unit

A concept study for a bend sensor based on a fibre Bragg grating (FBG) and a compact evaluation unit for the investigated type of sensor is presented. For this, two independent measurands, one well known and one novel, are considered. The fibreoptic sensor principle is capable of resolving the radius and the direction of the bend. The measurement data evaluation principle is capable of resolving multiple distributed FBG sensors, which are present in a single fibre at different positions.

In-process parameter calibration of thermoelectrical flow sensors with monolithic integrated channel

A time consuming and expensive part of sensor fabrication, especially for flow sensors, is the calibration of each fabricated sensor. This is necessary because of inaccuracy in sensor fabrication and assembly. With the help of an analytical model containing some important sensor parameters, which are obtained in-process during the fabrication, we show that it is possible to calibrate the sensor with respect to the flow rate within a deviation of µ5% for thermoelectrical flow sensors with monolithic integrated channels. An expensive single sensor calibration is thereby prevented. The model based calibration is possible due to the accurate acquisition of geometries of the monolithic integrated channel design compared e.g. to attaching a channel formed by injection molding. Solving technological issues will increase the accuracy of resulting calibrated systems.

Novel impedimetric and perforated thermal flow sensor for inline chemical process analysis in micro residence time reactors

A novel impedimetric and thermal flow sensor chip with perforated membrane for the inline chemical process analysis in micro residence time reactors were developed. Sensors were optimized for reactors made of stainless steel with a hydraulic diameter in the range of ∼1 mm. The impedimetric sensor chip consists of capacitively coupled interdigital electrodes made of MoSi2 on a silicon substrate. The thermal flow sensor consists of a heater in between two thermocouples on a thin membrane containing small holes for pressure compensation. CFD simulations were conducted to study the influence of medium flow in the cavity below the membrane. A micro fluidic flow cell with sensor electronics was developed for the characterization of both sensors. Experimental results revealed that changes of less than 1% in the thermal and electrical properties of the liquid can be detected. Insofar, the combination of the impedimetric and thermal flow sensor chip enables the analysis of reactive mixtures in overpressure regime by means of 4 independent physical parameters.