Design And Experimental Research Of Piezoelectric Volume Displacement Sensor Array

The active noise and vibration control(ANVC) technology is a persistent research topic in the fields of aviation and aerospace. It is of great economic value and practical significance to reduce noise, improve flight comfort and fatigue life of the aircraft. The ANVC can mainly be divided into three categories, such as active vibration control(AVC) system, active noise control(ANC) system and active structural acoustic control(ASAC) system. ASAC system is the combination of AVC and ANC. In ASAC system, the minimization of sound radiation is achieved by modifying the response of the structure through structural inputs. It often produces global far-field attenuation with relatively few actuators as compared to AVC or ANC. It means that ASAC system is more effective than AVC and ANC for the structual-borne sound control problems.One of the primary concerns in ASAC approaches is to choose the appropriate sensor. Appropriately configured error sensors in ASAC system should be able to provide signals that are only related to the radiating part of the out-of-plane vibration and filter out the others.. Piezoelectric volume displacement sensor used in ASAC system can filter out the vibration information without contributing to far-field sound radiation, only obtain the vibration information related to sound radiation outward.Through this error sensing strategy, the controller can be easy to be designed. Because of the superiority of using piezoelectric sensor as ASAC system error sensor, this thesis study on designing displacement sensor with an array of PVDF(polyvinylidene fluoride). The modal method as well as the pseudo-inverse method combined with Tikhonov regularization method are used to design the sensor array. And experimental results are also presented to show the feasibility of the proposed PVDF volume displacement sensor.The thesis outline is organized as follows:Firstly, a brief introduction about active structural acoustic control technology is illustrated. The advantages and characteristics of the PVDF used as error sensor in ASAC system are analyzed. The method of designing piezoelectric volume displacement sensor and the regularization method adopted in this paper are also briefly introduced.Secondly, in the wave-number domain, the relationship between volumedisplacement and far field sound pressure are deduced. It is shown that the far field sound pressure can be significantly reduced by cancellation of the volume displacement of the vibrating structures.Thirdly, using modal method and the pseudo inverse method, the piezoelectric volume displacement sensor array of uniform beam and the multiple-step beam are designed. A numerical analysis results show that the sensor array designed by pseudo inverse method can accurately measure displacement. Notice that, modal method need more complex numerical calculation to gain modal information of the structure.Pseudo-inverse method is suitable for the unknown boundary conditions and modal information. It has good anti-noise performance and better engineering application prospects.Finally, experimental work is presented to measure volume displacement of multiple-step beam with piezoelectric displacement sensor array designed by pseudoinverse method. The output signals of the PVDF volume displacement sensor array agree well with the volume displacement measured by accelerometer. It means that the pseudo-inverse method is feasible to design the PVDF volume displacement sensors..