Honoring Professor Gerhard M. Sessler on his 80th Birthday (15th of February 2011) [Editorial]

The authors of the following twelve papers would like to present their contributions to honor Gerhard Sessler, the main inventor of the electret condenser microphone, as a small token of appreciation for his friendship, guidance and leadership over so many years. A similar "Festschrift", incidentally with the same number of contributions, was dedicated to Professor Sessler at his 60th birthday in 1991 [1]. A special tribute to Gerhard Sessler with a list of most of his publications up to 1990 opened that issue. Over the last 20 years, Gerhard Sessler has remained very active in science and has again published a large number of seminal papers that are easily accessible via the relevant databases. A few of his present research topics become visible from the special issue papers by some of his friends, collaborators and former students.