2.1. Acoustic EmissionAE refers to the generation of transient elastic or stress waves during the rapid release ofenergy from localized sources within a material. The source of these emissions in metals isclosely related to the dislocation movement accompanying plastic deformation and theinitiation and extension of cracks in a structure under stress.AE systems are comprised of an AE sensor, preamplifier, amplifier and filter, an acquisitionand a data display. In the corrosion process, an AE parameter is extracted and then therelation with corrosion grading is determined. The parameters commonly used in corrosionapplications include AE HIT, Even and AE energy.2.1.1. AE sensor? The heart of the AE system is the sensor? The function of the sensor is to convert the acoustic wave energy emitted by thesource into usable electrical signal typically voltage time signal. This voltage timesignal is used for all subsequent steps in the AE technique.? Acoustic emission sensors can be based on different physical principles.? The signals can be generated by electromagnetic devices such as phonograph pickupby capacitive microphones, by magneto restrictive devices or by piezo electricdevices.? The requirements of an AE sensor are 😕 High sensitivity? Ruggedness? Wide bandwidth in the case of broad band sensor and narrow bandwidth in thecase of resonant sensor.? Fidelity.2.1.2. Preamplifiers? The preamplifier enhance the signal level against noise? The preamplifier must be located close to the sensor.? The preamplifier provides required filtering, gain and cable drive capability.? Uses of preamplifiers? To amplify the small sensor signals so that they can be transmitted over longsignal cables? To match high impedance of sensors to low impedance of signal cable.? To provide a means of common mode rejection to reduce electrical pick upfrom sensor cable.2.1.3. Filters? Filters plays an important role in allowing the amplified signal from sensor andattenuating unwanted noise.? Filter with flat frequency response for desired frequencies and sharp cut off forunwanted noise is required.? Typically low pass, band pass or high pass filters can be used.