1 - Introduction

Sensors are conventionally classified according to the quantity to be measured into the groups for the measurement of:

• mechanical quantities (position, displacement, force, acceleration, pressure, flow rate, acoustic waves, etc.)
• thermal quantities (temperature, heat flow, etc.)
• electrostatic and magnetic fields and fluxes
• radiation intensity (electromagnetic, nuclear, etc.)
• chemical quantities (concentration of humidity, gas components, ions, etc.)
• biological quantities (concentration of enzyme substrates, antigens, antibodies, etc.)

Another classification is possible according to the nature of interaction giving the basis of operation in the groups of physical sensors, chemical sensors, and biosensors. Generator-type sensors operate without external excitation, while modulator-type sensors need an external source from nature.