Volume 134, Issue 6, December 2013
Index of content:
- TRANSDUCTION 
134(2013); http://dx.doi.org/10.1121/1.4824815View Description Hide Description
A microelectromechnical-loudspeaker based on the magnetostrictive effect is presented. The membrane consists of a comb structure of monomorph bending cantilevers with an area of about 16 . Prototypes generate a sound pressure level (SPL) of up to 102 dB at 450 Hz with a total harmonic distortion of 2% inside a 2 measurement volume. The fabrication process of the device as well as a coupled simulation model to calculate its sound pressure is introduced. The model reproduces the measurements and is employed to further optimize the loudspeaker membrane. As a result, a computed maximum SPL of 106 dB has been achieved with a −6 dB frequency range extending from 100 Hz to 2.6 kHz.
Acoustic beam steering by light refraction: Illustration with directivity patterns of a tilted volume photoacoustic source134(2013); http://dx.doi.org/10.1121/1.4828825View Description Hide Description
The symmetry of a thermoelastic source resulting from laser absorption can be broken when the direction of light propagation in an elastic half-space is inclined relatively to the surface. This leads to an asymmetry of the directivity patterns of both compressional and shear acoustic waves. In contrast to classical surface acoustic sources, the tunable volume source allows one to take advantage of the mode conversion at the surface to control the directivity of specific modes. Physical interpretations of the evolution of the directivity patterns with the increasing light angle of incidence and of the relations between the preferential directions of compressional- and shear-wave emission are proposed. In order to compare calculated directivity patterns with measurements of normal displacement amplitudes performed on plates, a procedure is proposed to transform the directivity patterns into pseudo-directivity patterns representative of the experimental conditions. The comparison of the theoretical with measured pseudo-directivity patterns demonstrates the ability to enhance bulk-wave amplitudes and to steer specific bulk acoustic modes by adequately tuning light refraction.