**2. AE as an advanced nondestructive technique**

The fundamental principle of this method is based on the phenomenon of the generation of an acoustic pulse when a shock wave is generated inside a solid [1–4].

**45**

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors*

Generally, AE stress waves disperse throughout the medium until interaction with an interface or boundary produces a reverberating field. Although this energy will be mostly absorbed by the medium, some of the energy can be detected by the use of a high-frequency piezoelectric ceramic transducer. Assuming that all mechanisms of energy loss in the structure and measurement system are constant, the measured electrical signal energy from the transducer is proportional to the AE event energy [5],

∫

<sup>2</sup>*dt* (1)

<sup>2</sup>*dt* (2)

0 T *V*(*t*)

\_\_1 *R*)∫

where EAE refers to the AE energy measured in the transducer and R is the impedance of the complete measuring circuit. The power of the acoustic emission signal of the detected event is proportional to the power of the source event. The advantage of energy measurement over ring down counting is that energy measurements can be directly related to important physical parameters without having to model the acoustic emission signal. Energy measurements also improve the acoustic emission measurement when emission signal amplitudes are low. Squaring the measured energy signal produces a simple pulse from a burst signal and leads to a

0 *T V*(*t*)

There are several well-known causes of microwave tube failure. These include:

A decrease in emission normally results in lowering of both the upper and lower mode boundaries. When this shift downward in current becomes significant, the operating point current has to be adjusted downward to avoid instability and oscillation. The operating point is adjusted periodically during the life of the tube. The tube remains operable until either its output power is low or the shift in mode boundaries due to cathode emission precludes stable operation over the frequency band. Cathode emission degradation is a long-term event that requires regular and careful monitoring.

Loss of vacuum is a catastrophic failure, which may not be determined with electrical monitors. From experience, it is known that the heater bushing is the predominant failure. Other key vacuum seals include the RF input and output

Heater failure is a catastrophic event and results in inability to start cathode emission. Shorted heaters are more typical than open heaters. The cause of this fault

where T is the time length of transient signal produced and V(t) is the transient voltage. Thus, the measured electrical signal energy is often referred to as the AE

*DOI: http://dx.doi.org/10.5772/intechopen.81652*

*AEenergy* ∝

*EAE* ∝(

energy descriptor and is written as

simplification of event counting.

**3.1 Cathode emission decrease**

**3.2 Loss of vacuum**

ceramic-to-metal seals.

cannot be determined with electrical monitors.

**3.3 Heater failure**

**3. Causes of microwave tube failures**

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors DOI: http://dx.doi.org/10.5772/intechopen.81652*

Generally, AE stress waves disperse throughout the medium until interaction with an interface or boundary produces a reverberating field. Although this energy will be mostly absorbed by the medium, some of the energy can be detected by the use of a high-frequency piezoelectric ceramic transducer. Assuming that all mechanisms of energy loss in the structure and measurement system are constant, the measured electrical signal energy from the transducer is proportional to the AE event energy [5],

$$AE\_{\text{energy}} \propto \int\_0^{\text{T}} V(t)^2 dt\tag{1}$$

where T is the time length of transient signal produced and V(t) is the transient voltage. Thus, the measured electrical signal energy is often referred to as the AE energy descriptor and is written as

$$E\_{AE} \propto \left(\frac{1}{R}\right) \int\_0^T V\left(t\right)^2 dt\tag{2}$$

where EAE refers to the AE energy measured in the transducer and R is the impedance of the complete measuring circuit. The power of the acoustic emission signal of the detected event is proportional to the power of the source event. The advantage of energy measurement over ring down counting is that energy measurements can be directly related to important physical parameters without having to model the acoustic emission signal. Energy measurements also improve the acoustic emission measurement when emission signal amplitudes are low. Squaring the measured energy signal produces a simple pulse from a burst signal and leads to a simplification of event counting.
