Electrical Odor Sensors

These chemosensors represent the simplest of gas sensors in that their chemical reactivity is directly transduced into an electrical signal. Changes in resistance, capacitance, voltage, or current indicate the presence of a particular analyte. These types of sensors are widely used for gas and odor measurements in commercial e-nose sensor arrays. 

Chemiresistors represent the most common and simple type of sensor that incorporates organic materials. Generally speaking, the chemiresistor consists of a pair of electrodes that form contacts with the chemosensing material, which is deposited onto an insulating mechanical support (Fig. 5.2). 

Recently, organic conducting polymers have become the focus of much of the materials research in chemosensing devices. Synthetic flexibility allows the chemical and physical properties of polymers to be tailored over a broad range of values for any given application. In addition, polymers exhibit tunable specificity to volatile organic compounds, which makes them ideal candidates for replacing canonical sensor materials such as metal oxide semiconductors. 

Recent work done in this class of sensors has incorporated nonpolymeric materials to bind the carbon black particles, such as monomeric, low-vapor 

In general, carbon black composites demonstrate fast response times, good reversibility, reproducibility, and stability. However, they lack the ability to react selectively to different gaseous analytes, making them better suited for a sensor array application where pattern recognition algorithms can be used to identify analytes. 

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K., Electric responses of odor sensor using vapor-deposited copper-phthalocyanine film, Jpn... 

Saito M., Koyano T., Miyamoto Y., and Kaifn K., Electric responses of odor sensor using vapor-deposited copper-phthalocyanine film, Jpn J. Appl. Phys., 34, 3271-3272, 1995. 

When gaseous odor molecules are absorbed by the polymer, the electrical conductivity of the polymer changes. Different gases affect conductivity in different ways. Other sensor coatings are polymers containing conductive particles of silver or graphite. 

The information is initially encoded as electrical unit, but are immediately captured and digitized in order to be numerically translated by a computer system. In practice, an odorant is described by the electronic nose, based on the responses of individual sensors, as a point or a region of a multidimensional space. 

Each odor is, according to the twelve sensors, represented by 12 graphs showing a characteristic profile ( fingerprint ). These sensor-specific, time-dependent, series of electric conductivity data, which are produced by the presence of the odorous substances provide the data for the evaluation. They are processed by means of neiuonal networks. 

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