Actually, all the piezzo-alternatives I know flopped. Piezzo seems the only workable technology for refreshable braille, especially if you want acceptable refresh times. Piezzo does up to 20 Hz, which is really nice when scrolling along indented code for instance. The proposed alternatives I know of all were in the range of 1-2Hz, which is totally unusable in practice. But they were marketed like a revolution, everytime one came out. It is easy to promote something as the "new big thing" if you manage to prevent actual users telling what they think :-)