Sensor science has been mainly driven since the beginning by the chase of sensitivity, stability and selectivity. But while sensitivity and stability are straightforward concepts, selectivity deserves to be more deeply discussed. Actually a sensor output can alwasy be considered as the result of a process of synthesis of the whole features of the environment, to which the sensor is exposed. The mechanism is evident, for instance when optical sensors are considered, in this case the whole spectral intensity of a luminous source is converted in an electrical signal through the sensor spectral responsivity. The process can be thought to take place also in chemical sensors (see Figure 1.). The environment, in this case, can be represented as a chemical pattern (discrete)< in which all the chemical species, each at a certain concentration level and contemporaneously present in the environment, are shown as a histogram. In the same way, sensor selectivity can be represented as a pattern of sensitivities.
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