Theory Of Active Noise Absorption And Methods Of Designing The Control System

Active noise absorption has great application prospects in areas such as shipping,vehicle and so on. It has great theoretical and practical importance to research on themechanics of active noise absorption and the designing methods of practical controllingsystem.First, the theory and method of active noise absorption are researched by this thesis.Impedance matching method and pressure release method are both studied for a particularhybrid absorption system. From the acoustic theory, the absorption coefficient is relatedwith the impedance of the media and the surface, and when it matches, all of the soundwill go though the interface without reflection. The velocity of the controlling surface canbe controlled to modify the impedance of the surface, so that a impedance matchingcondition is realized and the maximum absorption is achieved. The pressure releasemethod follows a different rule, and it comes from the view of energy loss. When thepressure of the back surface of the absorbing material is reduced to zeroes due to the effectof the controlling surface, the particle velocity will increase, which will increase theenergy loss of the system and thus improves the absorption coefficient. The relationshipbetween the absorption coefficient and the thickness of absorbing material and thedistance between absorbing material and controlling surface is researched. Thin platepiezoelectric actuator has the advantage of being simple and good frequency response andit has great prospect in the future. The finite element modeling method is researched forthis piezoelectric actuator, and placement optimization of the piezoelectric patches isperformed using generic algorithm.The active noise absorption system can be realized using feedback method or feedforward method. However, they have different properties. Feedback control systemdoesn’t use reference signal and has the advantage of being simple. But due to thedynamic property of the actuator system, it can’t reach satisfactory absorption in abroadband range, or the system will be unstable. It’s generally suited for narrowbandproblem. Feed forward method has the advantage of being suitable for broadband problem. However, it needs a reference signal which will increase the complexion of the system,and even for some cases the reference signal will be difficult to get. The two methods willbe both discussed by this thesis and the simulation based on MATLAB/SIMULINK isperformed.Based on the theoretical analysis, the control system is set up using DSP, audio chipaic23b, Signal Conditioner and power amplifying device to validate the result. Theexperiment result agrees well with the theoretical analysis.