Sensors interrogation

Fig. 9.13 Mach Zehnder interferometer (MZI) sensor interrogation circuit using (a) conventional linear waveguide geometry and (b) folded spiral waveguide geometry. The dashed line in (b) indicates the sensor window boundaries in this infra red camera image...

Fig. 9.15 A ring resonator sensor interrogation circuits with (a) one bus waveguide, and (b) two bus waveguides. The plots give a qualitative indication of the typical intensity spectrum that would be observed at the respective output ports...

The four sensor interrogation steps of pulse application, conductivity measurement, float period, and open circuit potential measurement are repeated for a user-defined number of cycles to produce a sensor response curve. Each set of four such steps produces a single-datum point of conductivity and open circuit potential data. Several such points obtained over a period of time produces a response curve. The response curve captures the change in conductivity of the transducer as a function of time following initialization. 

Microfabricated Array Electrodes Electroactive Polymer Sensor Interrogation System for Conductimetric Response and Impedimetric Response Microcantilevers Biocompatiblity... 

The development of new and novel sensor interrogation systems and data processing techniques ... 

The absorption-based platforms described previously employed evanescent wave interrogation of a thin sensing layer coated onto a planar waveguide. A sensitivity enhancement strategy for optical absorption-based sensors based on planar, multimode waveguides was developed recently by us18. The objective was to apply this theory to the development of low-cost, robust and potentially mass-producible sensor platforms and the following section outlines the assumptions and predictions of this theoretical model. 

Figure 6 illustrates the platform under consideration in this analysis. The principle of sensor operation is as described previously for absorption-based optical sensors employing evanescent wave interrogation of the sensing layer. 

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

The MZI interrogation circuit of Fig. 9.13b offers a simple method to eliminate sensor drift due to changes in temperature or other common mode variables. 

The MCLW sensor has been exploited by several groups for a wide range of experiments. However, both the design of the sensor and the detection scheme used in connection with the monitoring vary. This section reports on experiments using angular interrogation, absorbance detection and fluorescence detection. 

The potential for MR sensors to interrogate on-line/in-line processes in the Food Processing industry is reiterated on an almost annual basis. Nevertheless there are a number of significant technical hurdles to be... 

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