Cantilever Array for Chemical Sensing: Development of a Moisture-Independent Sensor with Possible Application in Explosive Detection

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2 – Fundamentals of Chemical Detection artificial sensing organs that would enable machines to orient themselves independently in the environment. Robots, it was believed, should not execute a program blindly. They should be able to detect barriers and adapt their actions to the existing environment. In this respect, sensors first represented technical sensing organs , i.e. eyes, ears, and tentacles of automatic machines. With our senses we can not only see, hear and feel, but also smell and taste. The latter sensations are the results of some kind of chemical analysis of our environment, either of the surrounding air or of liquids and solids in contact with us. Consequently, chemical sensors can be considered artificial noses or artificial tongues. Nowadays, it would be not be sufficient to see chemical sensors merely as some kind of technical sensing organs. They can be used in many other fields besides just intelligent machines. The official definition was given by IUPAC (International Union of Pure and Applied Chemistry) in 1991 [14]: A chemical sensor is a device that transforms chemical information, ranging from concentration of a specific sample component to total composition anal- ysis, into analytically useful signal. Another good pragmatic desciption taken from the literature is the following [15]: Chemical sensors are small-sized devices comprising a recognition element, a transduction element, and a signal processor capable of continuously and reversibly reporting a chemical concentration. 2.2 Elements of Chemical Sensors Accodingly to IUPAC [16], chemical sensors usually contain two basic components con- nected in series: a chemical (molecular) recognition system (receptor) and a physicochem- ical transducer. In other documents, additional elements are considered to be necessary, in particular units for signal amplification and for signal conditioning (see Figure 2.1). Figure 2.2 shows the working principle of a general chemical sensor. When the molec- ular analytes like explosives, biochemical warfare agents, and hazardous gases are intro- duced into the sensor chamber by a chemical delivery system, those analytes react with the receptor coating layer, and an electrical, optical, or mechanical response signal due to the molecular interaction is generated by the transducer. 2.2.1 Classification of Sensors Today, signals are processed nearly exclusively by means of electrical instrumentation. Accordingly, every sensor should include a transducing function, i.e. the actual concentra- tion value, a non-electric quantity, must be transformed into an electric quantity voltage, current or resistance. Classification of sensors is accomplished in different ways. Prevalent is a classification following the principles of signal transduction [14] . The following sensor groups result. • Optical sensors, following absorbance, reflectance, luminescence, fluorescence, re- fractive index, optothermal effect and light scattering. 6

Anteprima della Tesi di Stefano Fissolo

Anteprima della tesi: Cantilever Array for Chemical Sensing: Development of a Moisture-Independent Sensor with Possible Application in Explosive Detection, Pagina 6

Laurea liv.II (specialistica)

Facoltà: Ingegneria

Autore: Stefano Fissolo Contatta »

Composta da 104 pagine.

 

Questa tesi ha raggiunto 209 click dal 20/10/2008.

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