Definition
In an ever-developing world, where electronic devices are duplicating every other sense of perception, the sense of smell is lagging behind. Yet, recently, there has been an urgent increase in the need for detecting odours, to replace the human job of sensing and quantification.

Some of the most important applications fall in the category where human beings cannot afford to risk smelling the substance. Other important applications are continuous monitoring, medical applications, etc. These applications allow man to perform tasks that were once considered impossible.The fast paced technology has helped develop sophisticated devices that have brought the electronic nose to miniature sizes and advanced capabilities. The trend is such that there will be accurate, qualitative and quantitative measurements of odour in the near future.
Living beings interact with the surrounding environment through particular interfaces called senses, which can be divided in two groups: those detecting physical quantities and those detecting chemical quantities.

Physical interfaces (that deals with acoustic, optic, temperature and mechanic interaction mechanisms) are sufficiently well known and a wealth of successful studies to construct their artificial counterparts has been done in the past years. On the other side the chemical interfaces (bio transducers of chemical species in air: olfaction, and in solution: taste) even if well described in literature, present some aspects of their physiological working principal that are still unclear. It has also to be remarked a psychological difference, in human beings, between the two groups. Indeed the information from the physical senses can be adequately elaborated, verbally expressed, firmly memorized and fully communicated. On the contrary chemical information, coming from nose and tongue, are surrounded by vagueness and this is reflected in the poor description and memorization capacity in reporting olfactory and tasting experiences. Chemical information is of primary importance for the major part of the animals; for many of them, indeed, chemistry is the unique realm of which they are concerned, while for human beings evolution has enhanced about exclusively the physical interfaces, leaving little care of the chemical interface, if we exclude unconscious acquisition and side behaviours. For these intrinsic difficulties toward the understanding of the nature of these senses for many years only sporadic research on the possibility of fabricating artificial olfactory systems were performed. Only at the end of the eighties a new and promising approach was introduced. It was based on the assumption that an array of non-selective chemical sensors, matched with a suitable data processing method, could mimic the functions of olfaction.

In the past decade, electronic nose instrumentation has generated much interest internationally for its potential to solve a wide variety of problems in fragrance and cosmetics production, food and beverages manufacturing, chemical engineering, environmental monitoring, and more recently, medical diagnostics and bioprocesses. Several dozen companies are now designing and selling electronic nose units globally for a wide variety of expanding markets. An electronic nose is a machine that is designed to detect and discriminate among complex odours using a sensor array. The sensor array of consists of
broadly tuned (non-specific) sensors that are treated with a variety of odour-sensitive biological or chemical materials. An odour stimulus generates a characteristic fingerprint (or smell-print) from the sensor array. Patterns or fingerprints from known odours are used to construct a database and train a pattern recognition system so that unknown odours can subsequently be classified and identified. Thus, electronic nose instruments are comprised of hardware components to collect and transport odours to the sensor array - as well as electronic circuitry to digitise and stored the sensor responses for signal processing.