Skip to Main content Skip to Navigation
Theses

CONCEPTION, RÉALISATION ET CARACTÉRISATION D'UN HAUT-PARLEUR ULTRA-DIRECTIF BASÉ SUR L'AUTO-DÉMODULATION NON LINÉAIRE

Abstract : Non-linearities associated with the propagation of a strong level acoustic wave result in an amplitude self-demodulation phenomenon: when an ultrasonic carrier wave (primary wave) is amplitude modulated by an audio signal, the audio signal (secondary waves) grows along the ultrasounds emission lobe. The parametric array obtained in this way has a narrow directivity compared to usual sound reproduction systems of comparable size.
This thesis aims at improving the existing systems. With this intention, a design tool and a demonstration prototype are developed.
First, fundamental principles of nonlinear acoustics are reminded in order to understand the self-demodulation phenomenon. This makes possible to conclude on the influence from the primary waves field on the secondary waves field and to determine the primary waves field properties necessary for a use as directive loudspeaker. The distortions induced by the self-demodulation are also highlighted. Then usual distortions reduction preprocessings are detailed and evaluated using a simulation algorithm in order to conclude on their advantages and their use conditions.
In order to obtain a very narrow directivity and a strong level at the ultrasonic frequencies, a transducers array is used. We choose to work with PVDF film transducers. Second, a physical model of the PVDF film transducers coupled to a cavity is proposed. This one is used to predict the acoustic pressure radiated by an elementary cell according to parameters like the cavity dimensions and the film properties. Then, an array radiation model is used to define a cells array fulfilling the application requirements.
Finally, a prototype of directive loudspeaker is made. It is characterized in linear mode (without self-demodulation) and in directive loudspeaker mode in order to do an experimental assessment of this study.
Complete list of metadatas

Cited literature [38 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-00201456
Contributor : Alexandre Ritty <>
Submitted on : Saturday, December 29, 2007 - 1:56:23 PM
Last modification on : Tuesday, March 31, 2020 - 3:20:47 PM
Long-term archiving on: : Tuesday, April 13, 2010 - 3:50:00 PM

Identifiers

  • HAL Id : tel-00201456, version 1

Citation

Alexandre Ritty. CONCEPTION, RÉALISATION ET CARACTÉRISATION D'UN HAUT-PARLEUR ULTRA-DIRECTIF BASÉ SUR L'AUTO-DÉMODULATION NON LINÉAIRE. Acoustique [physics.class-ph]. Université du Maine, 2007. Français. ⟨tel-00201456⟩

Share

Metrics

Record views

1259

Files downloads

19412