Characteristics and use of a nonlinear end-fired array for acoustics in air

Download
Author
Akar, Ali Onur
Date
2007-03Advisor
Larraza, Andres
Denardo, Bruce C.
Metadata
Show full item recordAbstract
The parametric array exploits two highly collimated ultrasound beams interacting in a given volume producing a single beam with very high directivity and almost no side lobes. The high directivity of the difference frequency signal of the parametric array is due to the interaction of the waves in the volume effectively producing a virtual endfired array boosting pressure levels along the interaction region which is limited by the absorption coefficient. This thesis focuses on experiments conducted in an anechoic room using AS-18-B Audio Spotlight system from HolosonicTM. Furthermore, nonlinear theory was modeled by a linear discrete array. The beam pattern of the parametric loudspeaker, range dependence of primary and secondary signals and total harmonic distortion (THD) were measured and then compared to theory. Experimental data for the beam pattern of the parametric loudspeaker agreed with the theory. It was all shown that the parametric array had a very narrow beam width and almost no side lobes as opposed to conventional loudspeakers. Both primary waves and difference wave frequency signals were examined for their range dependence. Due to the complicated interference of the primary waves, it was impossible to compare experimental results with theoretical predictions. For the difference wave signals, experimental data was verified by theory, which was modified in order to accommodate both wave generation and spreading region. Finally, THD of the parametric loudspeaker was measured for different amplitude modulation depths. Experimental results showed that preprocessing should be applied in order to decrease THD and achieve clean audio signal reproduction.
Collections
Related items
Showing items related by title, author, creator and subject.
-
Design and application of an underwater acoustic parametric source
Khosla, Ranvir C. (Monterey, California. Naval Postgraduate School, 1973-12);Parametric sound generation has been an active area of applied research for the last ten years. The acoustic parametric source takes advantage of the non-linearity of the medium to generate energy at the difference of ... -
Nonlinear oscillations of a triatomic molecule
Wilson, Sean Odell (Monterey California. Naval Postgraduate School, 2002-06);ude decreases if the difference of the frequency of the two modes is reduced. We consider the simplest case of a symmetric rectilinear molecule where the coupling has a cubic nonlinearity in addition to a linear restoring ... -
Investigations of parametric excitation in physical systems
Janssen, Michael T. (Monterey, California. Naval Postgraduate School, 2005-06);Parametric excitation can occur when the value of a parameter of an oscillator is modulated at twice the natural frequency of the oscillator. The response grows exponentially and is only limited by a nonlinearity of the ...