Article Contents

1. Introduction
2. FM: Sweep and Dual Sweep
3. Ultrasonic Power Into a Tank
4. FM: Upsweep
5. Multiple Frequencies (1)
6. Multiple Frequencies (2)
7. Cavitation
8. Transducer Impedence (1)
9. Transducer Impedence (2)
10. Transducer Impedence (3)
11. Universal Transducer
12. Applying the Technology (1)
13. Applying the Technology (2)
14. Applying the Technology (3)
15. Conclusion

Designer Waveforms: Ultrasonic Technologies to Improve Cleaning and Eliminate Damage
(p. 9)

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Transducer Impedence (continued)

First, consider the figure 7 transducer array. Its 132 kHz transducers were built with an aluminum front driver, an aluminum oxide insulator, a piezoelectric ceramic, an aluminum back mass, a compression bolt and appropriate electrodes. It differs from the most numerously produced Langevin type transducers in that it replaces one of the piezoelectric ceramics with an insulator and it uses aluminum rather than steel for the back mass. The first change saves money and the second results in a longer transducer. Although you would expect this metal stacked construction to be similar to every other Langevin transducer, when the four design principles described above are applied to this or any other transducer array, a sharp, narrow and deep impedance versus frequency curve results at the selected harmonic frequency. Now consider driving an array of these transducers with a generator that sweeps over a rather large range and that puts out a constant voltage at each frequency in this range. Since the power generated by the transducer at each frequency in the range is voltage squared divided by the real part of the impedance at that frequency, it is clear that this transducer array generates an extremely high peak power at the 132 kHz valley in the impedance curve and a significantly lower power at the frequencies in the range that are away from this valley. Figure 9 shows a plot of this type of output characteristic.

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