1. F. Laermer, A. Schilp, German Pat., DE 4 241 045 granted on 26 May 1994 (US Pat. 5 501 893 granted on 26 March 1996).
2. Technical Digest of Transducers‘95;Offenberg,1995
3. Technical Digest of Transducers‘97;Lutz,1997
4. Late News Contributions;Funk,1995