**5. Application of the AE technique to magnetron tubes**

This section presents the effects on AE during normal and abnormal functioning of a magnetron. The experiment was conducted at the SPAWAR Systems Center, San Diego microwave radar tube laboratory [7]. The proper operation of a magnetron device depends upon the amplitude of the pulsed voltage applied, the temperature, the filament voltage, and the proper loading of the magnetron by the RF system. The normal operating parameters of the magnetron tube (2J55) utilized for this experiment were intentionally changed in order to stress the magnetron tube and induce abnormal functioning. **Table 1** shows the magnetron parameters for the experiments described below.

It was observed that when the tube was stressed, it typically produced an anomalous current pulse with a resulting anomalous RF pulse. The pulses were captured utilizing the masking feature of a 500-MHz digital LeCroy 9354AM oscilloscope, where a mask is defined based on a normal pulse shape, and pulses which lie outside the mask are captured. A fast Fourier transform was performed on the captured AE signal.

**Figures 8** and **9** were obtained by using a type S9208 AE transducer, and they show the normal and abnormal pulses, respectively. In both cases, the pulse rate was adjusted to 100 pps, and the oscillator filament primary voltage was set at the normal value of 115 V. Channel 3 on the oscilloscope was connected to the output of the acoustic emission post amplifier and is shown in the upper trace. Channel B was connected to the current sensor of the magnetron, and it shows a zoom trace of the current pulse (see lower curve in figures). The mask was set on channel D


**Table 1.**

*Magnetron parameters.*

**Figure 8.** *Magnetron under normal operation with pulse voltage of 15 kV.*

#### **Figure 9.**

*Magnetron under abnormal operation with pulse voltage of 19.5 kV.*

(zoom trace) and is shown superimposed on the current pulse. Channel A shows the magnitude FFT of the acoustic emission signal from channel 3. The amplitude of the AE signal decreased considerably during the detection of an anomalous pulse when compared with the AE under normal operation.

**51**

**Figure 11.**

**Figure 10.**

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors*

Further details of the experiments can be found in Ref. [7].

*Magnetron under normal operation with filament voltage of 115 V.*

*Magnetron under abnormal operation with filament voltage of 0 V.*

The experiment was repeated again using a type S9208A AE transducer. All parameters were initially set to normal values (filament primary at 115 V, pulse voltage at 15 kV, pulse rate at 1000 pps, and all RF power delivered to the matched load). Abnormal conditions were then obtained by gradually reducing the oscillator filament primary voltage from 115 V to zero. **Figures 10** and **11** show the results of this experiment under normal and abnormal conditions,

Once again, the amplitude of the acoustic emission signal decreased considerably during the detection of an anomalous pulse. Similar behavior was observed when the magnetron was stressed under different conditions. The system demonstrated the ability to detect anomalous pulses under different stress conditions.

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

respectively.

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

The experiment was repeated again using a type S9208A AE transducer. All parameters were initially set to normal values (filament primary at 115 V, pulse voltage at 15 kV, pulse rate at 1000 pps, and all RF power delivered to the matched load). Abnormal conditions were then obtained by gradually reducing the oscillator filament primary voltage from 115 V to zero. **Figures 10** and **11** show the results of this experiment under normal and abnormal conditions, respectively.

Once again, the amplitude of the acoustic emission signal decreased considerably during the detection of an anomalous pulse. Similar behavior was observed when the magnetron was stressed under different conditions. The system demonstrated the ability to detect anomalous pulses under different stress conditions. Further details of the experiments can be found in Ref. [7].

**Figure 10.**

*Acoustics of Materials*

**50**

**Figure 9.**

**Figure 8.**

**Table 1.**

*Magnetron parameters.*

(zoom trace) and is shown superimposed on the current pulse. Channel A shows the magnitude FFT of the acoustic emission signal from channel 3. The amplitude of the AE signal decreased considerably during the detection of an anomalous pulse

when compared with the AE under normal operation.

*Magnetron under abnormal operation with pulse voltage of 19.5 kV.*

*Magnetron under normal operation with pulse voltage of 15 kV.*

**Parameter Typical values Stressed condition** Filament voltage 6.3 V AC 3.2 V AC Pulse rate 1000 pps 1000–10,000 pps

Reflected power 0% 100% Pulse voltage 15 kV 15–21 kV

Case temperature 95°F Cooling fan shut off, temperature increased to over 150°F.

*Magnetron under normal operation with filament voltage of 115 V.*

**Figure 11.** *Magnetron under abnormal operation with filament voltage of 0 V.*
