TABLE OF CONTENTS Dr. Thomas Kenny, Department of Mechanical Engineering, Stanford University
Chemical sensors are used to detect the presence of specific chemical compounds or elements, and their concentrations. This chapter covers some basic concepts for sensing of chemical quantities and some important applications.
The human nasal sensing apparatus contains a remarkably flexible and sensitive detection capability. Humans are capable of detecting and distinguishing thousands of different smells with almost instantaneous recognition. Odor detection is made very complicated because of the lack of uniqueness in the chemical basis of most smells. There is no garlic molecule that is distinct from the enchilada molecule, yet a person can easily distinguish these smells.
All biological odor detection systems are based on a fairly small number of distinguishable sensors. The smell recognition system is based on pattern-matching of the response of the different chemical sensors in the nose to various odors. Garlic and enchiladas produce a slightly different collective response in the entire set of sensors in your nose, and your brain has stored an extensive collection of these patterns which are used for comparisons. Psychologists have found that these odor patterns can be among the strongest of memories, and smells are often used to aid in the reconstruction of memories.
Chemical sensing system designers need to draw lessons from these biological systems. An important lesson is that a multifunctional system will probably need to use a small set of distinct sensors and a pattern-matching algorithm...
