Sensor integration

Another important point is the integration of sensors into the microreactor. A full integration is often not economical. This section explains new ways for an appropriate technology. For optimal operation of microreactors, we need to measure 

This is necessary both for process control as well as the reliabihty of the system. The integration of sensors into the microreactor or building a multisensor module for the four functions of state is easy for a microreactor made of sUicon. For the process pressure, the piezoresistive principle is used often. With diEFerential pressure measurements, the flow rate can be determined. Alternatively, calorimetric principles are used widely. These are easy to implement technically, but a calibration is needed for eatii new medium. The most robust sensors are the Coriolis mass flow sensors. In process engineering, they are very common, but in terms of micro process engineering, there is still a need for research. In Ref. [26], sensors of this type are described. Ref [25] is a good summary of other microflow sensors. For measurement of temperature, there are many equivalent principles but will not be discussed here. Substantially, it is more difficult to measure the concentration in the reactor. In addition to optical principles, the impedance spectroscopy is often used. See Ref [27-31] for more details. 

Life of the sensors is increased when the wetted surfaces are passivated with a chemically resistant material, silicon nitride or aluminum nitride. 

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Multilayered structures play an important role in the production of, e.g., biomaterials, catalysts, corrosion protectors, detectors/diodes, gas and humidity sensors, integral circuits, optical parts, solar cells, and wear protection materials. One of the most sophisticated developments is a head-up-display (HUD) for cars, consisting of a polycarbonate substrate and a series of the layers Cr (25 nm), A1 (150 nm), SiO, (55 nm), TiO, (31 nm), and SiO, (8 nm). Such systems should be characterized by non-destructive analytical methods. 

Similar to its predecessors of the Emrys series, the operation limits for the Initiator system are 60-250 °C at a maximum pressure of 20 bar. Temperature control is achieved in the same way by means of an IR sensor perpendicular to the sample position. Thus, the temperature is measured on the outer surface of the reaction vessels, and no internal temperature measurement is available. Pressure measurement is accomplished by a non-invasive sensor integrated into the cavity lid, which measures the deformation of the Teflon seal of the vessels. Efficient cooling is accomplished by means of a pressurized air supply at a rate of approximately 60 L min-1, which enables cooling from 250 °C to 40 °C within one minute. 

Special features of the sensor integrated into damper design ... 

Fig. 5.49 Sensor integrated in damper, photo courtesy of B/S/H and SUSPA.

Figure 11. Comparison of a wearable foam sensor integrated into a shirt, and a reference airflow monitor (facemask) for monitoring breathing during treadmill experiments. The results (bottom) indicate that these types of innocuous wearable sensors can provide important information on general heath indicators such as breathing [27].

Dual-technology sensors consist of two different sensor technologies incorporated together into one sensor unit. For example, a dual technology sensor could consist of a passive infrared detector and a monostatic microwave sensor integrated into the same sensor unit. 

S. Asti, A.M. Gu, E. Scheid, and J.P. Guidemt. Design of a low power SnOa gas sensor integrated on silicon oxynitride membrane Sensors and Actuators B67 (2000), 84-88. 

Static and Dynamic Behavior and Aspects of Sensor Integration By R. Balias... 

To build an efficient and compact microreactor, the fabrication technique must allow for three-dimensional structures and the use of the appropriate materials, and the technique should be low cost. Since reactants and products must flow in and out of the device, traditional standard thin film techniques are not suitable for the reactor framework. However, thin film techniques are very useful for integration, surface preparation, sensor integration, and finishing or packaging. Fortunately, traditional thin film techniques can be modified for microreactor fabrication other techniques, which will be discussed below, are also available. 

Flow-through sensors integrating detection and a chemical or biochemical reaction rely on immobilization in the probe proper or the flow-cell (or a special housing included in it) of a species intended to take part in or catalyse the reaction by which the analyte, viz. the catalyst or reagent, is measured, according to which the sensors described in this Chapter are divided into two broad categories. 

Figure 4.1 — Classification of flow-through (bio)chemical sensors integrating separation and detection according to various criteria.

Most flow-through sensors integrating retention and detection involve placement of an inert support in the flow-cell of a non-destructive spectroscopic detector where the analytes or their retention products are retained temporarily for sensing, and then eluted. Rendering these sensors reusable entails including a regeneration step suited to the way retention is performed. 

Figure 5.3 shows the different possible ways in which the ingredients of the (bio)chemical reaction can take part in the sensing process. For example, the analyte can be retained temporarily and take part in the separation process. The reagent can be present in the solution used to immerse the sensor or immobilized in a permanent fashion on a suitable support. Also, the catalyst can be introduced directly across a membrane or be permanently immobilized. Finally, the reaction product can be the species transferred in the separation process or also be temporarily immobilized. These and other, more specific alternatives that are described below are all possible in (bio)chemical flow-through sensors integrating reaction, separation and detection. 

Figure 5.3 — Types of immobilization and species involved in (bio)chemical flow-through sensors integrating reaction, separation and detection.

There are two possible configurations for this type of flow-through sensor integrating gas diffusion, reaction and detection that differ in whether the reagent is dissolved in the acceptor solution or immobilized on a sensing microzone located near the diffusion membrane. The descriptions below are based on such a difference. 

As with sensors based on a triply integrated process involving gas diffusion, there are few reported examples of sensors integrating dialysis, reaction and detection. There follows a description of die most salient examples based on the ingredient of the (bio)chemical reaction that is dialysed at the sensing micro2one. 

Therefore, this sensor integrates a biochemical and a chemical reaction with a prior separation (dialysis) and chemiluminescence detection. The process involves the following steps (a) dialysis of the enzyme (6) enzymatic oxidation of the reagent (c) derivatization of hydrogen peroxide and d) detection of the chemiluminescence produced. Such an original approach offers several advantages over similar methodologies, namely ... 

The descriptions of sensors integrating sorption, reaction and detection provided below are classified according to the type of immobilization... 

This modern technology provides a possibility to design multi-ion sensors integrated with the reference cell (REFET). These sensors are very small, enjoy a high longevity and use only very small amounts of the necessary selective (and often relatively expensive) compounds for ion sensing, such as valinomycin. 

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

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