1.1. Introduction

Together with temperature, pressure is one of the most important physical quantities in our environment. Pressure is a significant parameter in such varied disciplines as thermodynamics, aerodynamics, acoustics, fluid mechanics, soil mechanics and biophysics. As an example of important industrial applications of pressure measurement we may consider power engineering. Hydroelectric, thermal, nuclear, wind and other plants generating mechanical, thermal or electrical energy require the constant monitoring and control of pressures: overpressure could cause the deterioration of enclosures or drains and cause very significant damage.

As a significant parameter, pressure enters into the control and operation of manufacturing units that are automated or operated by human operators. Pressure measurement is also used in robotics, either directly in controls or indirectly as a substitute for touch (artificial skin for example), for pattern recognition or for determining strength of grip. All these activities require instrument chains in which the first element is the pressure sensor, delivering data relating to the pressure of compressed air, gas, vapor, oil or other fluids, determining the correct operation of machines or systems.

The variety of mentioned applications demands a great diversity of sensors. This diversity also derives from the fact that pressure covers a very wide range from ultra-high vacuums to ultra-high pressures. It can be expressed as an absolute value (compared to vacuum) or as a relative value (compared to atmospheric pressure); it can also represent a difference between two pressures or relate to various media...