Two-dimensional sensor array

The basis of RAFA is the direct eigenvalue solution of the mixture matrix of responses based on a singular-value decomposition. Let N represent a data matrix of the pure component response of analyte k from the two-dimensional sensor array and M represent the sample response of the same instrument to the analyte of interest and all interfering components the solution of the rank annihilation problem can be stated as follows ... 

Figure 11.7 An illustration of the process used in two-dimensional sensor arrays with both GRAM and TLD. The left-hand side of the figure shows the two-dimensional response patterns used in calibration, and the right-hand side of the figure shows the resulting information from the second-order techniques. (Reprinted with permission from Elsevier Science BV.)...

Pang L, Hwang GM, Slutsky B, Eainman Y (2007) Spectral sensitivity of two-dimensional nanohole array surface plasmon polariton resonance sensor. Appl Phys Lett 91 123112... 

Charge coupled detectors These devices are not yet commonly available in commercial instrumentation for analytical spectrophotometry although they are used in applications in inductively coupled plasma atomic emission spectrometry. However, they have found extensive application in imaging and astronomical applications. Essentially they are two-dimensional photodiode arrays which allow many spectra to be acquired in one readout. A typical array sensor is shown in Figure 9. 

Fig. 16.2 Nanoscale optofluidic sensor arrays (NOSA). (a) 3D illustration of a NOSA sensing element. It consists of a ID photonic crystal microcavity, which is evanescently coupled to a Si waveguide, (b) The electric field profile for the fundamental TE mode propagating through an air clad Si waveguide on SiOi. (c) SEM of a NOSA device array. It illustrates how this architecture is capable of two dimensional multiplexing, thus affording a large degree of parallelism, (d) Actual NOSA chip with an aligned PDMS fluidic layer on top. Reprinted from Ref. 37 with permission. 2008 Optical Society of America...

In this sheet image scanner, two-dimensional array of sensor cells cover the large area entirely and the data are read electrically, avoiding mechanical scans. We believe that the electronic scan method would be practical, because the manufacturing costs of organic transistors are expected low even for large-areas. 

In a number of different bioreactor cultivations with bacteria, yeasts, molds and mammalian cells, it was shown how the electronic nose can serve to visualize the course of the processes. The pattern recognition method that best manages to mirror the complex sensor array responses during extended cultivations is two- or three-dimensional PCA. Examples from such electronic nose applications are given below. 

Fig. 10.21. Diagram showing the structure of a two-dimensional matrix-addressed array. The pixel designs for a liquid crystal and for an image sensor are shown.

Instrument Design for a Passive Sensor Based on Adaptive Speetral Imager with a Two-Dimensional Foeal Plane Array... 

Figure 1. Current Nanoscale Optofluidic Sensor Arrays, (a) 3D rendering of the NOSA device, (b) 3D rendering after association of the corresponding antibody to the antigen immobilized resonator, (c) Experimental data illustrating the successful detection of 45 pg/ml of anti-streptavidin antibody. The blue trace shows the initial baseline spectrum corresponding to Fig. la where the first resonator is immobilized with streptavidin. The red trace shows the test spectra after the association of anti-streptavidin. (d) Finite difference time domain (FDTD) simulation of the steady state electric field distribution within the 1-D photonic crystal resonator at the resonant wavelength, (e) SEM image demonstrating the two-dimensional multiplexing capability of the NOSA architecture.

The application of chemical sensors now and in the future will be oriented around real time monitoring of chemical and environmental processes [3, 4]. These processes are complex systems where a variety of chemicals are present. From a calibration point of view, sensor systems for these applications will either have to be fully selective or be able to handle multicomponent samples. Since the perfectly selective sensor is difficult to almost impossible to develop, sensors in the array or two-dimensional array format have certain advantages. 

The linear algebra approaches used in first-order methods for pattern recognition are simple mathematical distance measurements in a multidimensional space. By using some examples of data plotted in a two-dimensional space resulting from an array of two sensors, simple relationships can be established that are identical in higher-dimensional spaces. In figure 11.3, the uppermost plot contains the responses of two sensors for pure samples with constant concentrations of three analytes denoted by circles, squares, and triangles. The two sensors have differential selectivity to the three analytes. The locations in this two-dimensional space of the analytes are physically separated from each other. The distribution of each cluster is caused by the combination of the measurement error of the two sensors. 

The pairs of the related parameters, such as time constant r, and weight coefficient a, are supposed as the co-ordinates of a point in a two-dimensional plot. Reciprocal time constant was assumed to be the length of the vector while the weigh coefficient defined the sine of the rotation angle (j) for the vector. The points of separate sensors from an array are displayed in individual segments of the circular plot. 

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