About the Authors

Esa Räsänen

esa.rasanen@tut.fi

Affiliations Department of Physics, Tampere University of Technology, FI-33101 Tampere, Finland, Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

Otto Pulkkinen

Affiliation Department of Physics, Tampere University of Technology, FI-33101 Tampere, Finland

Tuomas Virtanen

Affiliation Department of Signal Processing, Tampere University of Technology, FI-33101 Tampere, Finland

Manfred Zollner

Affiliation Electro-Acoustic Laboratory, Regensburg University of Applied Sciences, D-93025 Regensburg, Germany

Holger Hennig

Affiliations Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA, Max Planck Institute for Dynamics and Self-Organization (MPI DS) Göttingen, Am Fassberg 17, D-37077 Göttingen, Germany

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: ER HH. Performed the experiments: ER OP TV. Analyzed the data: ER OP HH. Contributed reagents/materials/analysis tools: ER OP TV MZ HH. Wrote the paper: ER OP TV HH.