title: Converting sunlight into audible sound by means of the photoacoustic effect: The Heliophone.
abstract: One hundred and thirty-five years after Alexander Graham Bell and his assistant Charles Sumner Tainter explored the photoacoustic effect, and about 40 years after Rosencwaig and Gersho modeled the effect in a photoacoustic cell configuration, the phenomenon is revisited in a "Heliophone" device that converts sunlight into sound. The light is focused on a carbon blackened copper coated Kapton foil in an acoustic cell by means of a compound parabolic collimator, and its intensity is modulated by a mechanical chopper. A horn is employed to make the sound audible without electronic amplification. The description of the photoacoustic effect that was introduced by Rosencwaig and Gersho is extended to a cell-horn configuration, in which the periodically heated air above the foil acts as an oscillating piston, driving acoustic waves in the horn. The pressure in the cavity-horn assembly is calculated by considering the air layer piston as an equivalent volume velocity source. The importance of the carbon black (soot) layer to enhance light absorption, but above all to enhance the photothermal excitation efficiency, is elucidated by means of an experimentally supported physical model.
authors.affiliation: Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium.
authors.forename: N B
authors.initials: NB
authors.lastname: Roozen
authors.affiliation: Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Glorieux
authors.affiliation: Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.affiliation: STU Bratislava, Faculty of Civil Engineering, Department of Building Structures, Radlinskeho 11, Bratislava, 810 05, Slovak Republic.
authors.forename: M
authors.initials: M
authors.lastname: Rychtáriková
authors.affiliation: Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium.
authors.forename: T
authors.initials: T
authors.lastname: Van der Donck
authors.affiliation: Overtoon, Platform for Sound Art, Luchtvaartsquare 19, 1070, Brussels, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Jacobs