FPGA-based Signal Processing Algorithms Research And Implementation Of Parametric Array

According to the parametric acoustic array theory, the parametric loudspeaker is away to make consumers having the independent speech spaces. Compared with theconventional speaker system which has the full range directions, the sound generated bythe parametric loudspeaker system have the high directivity characteristics because ofthe self-demodulated role of the air. This thesis summarizes the nonlinear acousticformula derivations and solves the second-order wave equations by the method offundamental solution. This thesis also presents a improved AM square wave modulation,the modified DSB square wave modulations and the modified SSB square wavemodulation.According to various methods to get the nonlinear acoustics equations, this thesissummarizes two typical derivation methods: one is called Aanonson method; the otheris called Westervelt method. According to the wave equation obtained and sound sourcewhich is broadband amplitude modulation wave input, the physical problems changeinto the mathematical equations. This thesis uses the fundamental solution from themethods of mathematical physics to solve the wave equation. In the progress of thesolving, this thesis convertes the multivariable differential equation to the singlevariable differential equation by Fourier transform and Hankel transform. Finally, themiddle axis and far-field analytical solution of the wave equation is got by someappropriate estimates. The obtained analytical solution can be characterized as follows:the far-field acoustic wave is proportional to the time derivative of the square of theamplitude of the source acoustic. The analytical solution is the basic for the far-fieldaudible sound distortion analysis.On the basic of the existing DSB square wave modulation and SSB square wavemodulation, this thesis presents some modified DSB square wave modulations and amodified SSB square wave modulation, and also verifies the reasonableness of theoutput waves from the above square wave modulations by the Fourier series expansionand Matlab simulation. The thesis also rechanges the output of the modified AMmodulation bought out at2008to the square wave with low frequency, and also verifies the reasonableness of the output waves by the Fourier series expansion and Matlabsimulation. The author designes the FPGA-oriented hardware system which is suitablefor the square wave modulation. In order to reduce the power consumption of the wholesystem, the power amplifier uses the full-bridge circuit. The above mentioned squarewave modulations are achieved in the FPGA hardware system. By the compare of theresults of the DSB square wave modulation, the modified DSB square wave modulationand the modified SSB square wave modulation, the second modulation is better than thefirst modulation at the way of harmonic distortion; The third modulation has lowharmonic distortion, but has a higher inter-modulation distortion.