6. Conclusion

Converters based on piezoelectric standing-wave transformers are used in applications of less than a few tens of watts, where a very small footprint and planar topology are required; they have been used extensively for flat-screen backlighting. Today, their use corresponds to niche applications, such as plasma surface treatment. The use of GaN semiconductors enables them to operate at very high frequencies (1 to 10 MHz) in thickness mode, with very good efficiencies (> 90%) and power densities. It has been demonstrated that the travelling-wave operating regime enables the design of universal converters capable of delivering a wide variety of power waveforms, both continuous and alternating, of any shape; research is continuing in this promising field.