Design And Fault Diagnosis Of Piezoelectric Modal Sensors Array

Recently, the noise and vibration control techniques have been one of the research hotspots and difficulties in the fields of aerospace and aviation. It is of great practical value and economic significance to study on the active noise and vibration control technology for improving the safety and comfort of aircraft.To achieve the noise/vibration reduction over a wide frequency range, a large number of sensors are required to measure a global error information(such as vibration energy, sound power). However, increasing the number of sensors will bring significant difficulty for the design of the controller. To solve this difficulty, this thesis focuses on the piezoelectric modal sensor technology emerging in recent years. The key point of modal sensor technology is properly designing error sensors to decompose a large number of discrete vibration signals of structure into few high-quality independent orthogonal contributors, so the controller can be easy to design. The design methods, the practical application, and the fault diagnosis of piezoelectric modal sensors array are respectively studied in this thesis.First, a brief introduction about the phylogeny and the study status of piezoelectric modal sensors using in the active noise and vibration control system is given. The advantages of designing PVDF films as error sensors and some applications of piezoelectric modal sensor in the noise and vibration measurements are also analyzed.Then, with an example of vibrating beam under unknown boundary conditions, an array of rectangular PVDF patches are arranged on the surface of structure evenly. “Pseudo-inverse method” for the design of modal sensor using PVDF array is verified by numerical calculations and experiments. The main advantage of this method is there no need of the boundary condition or structural mode shape information. And the stability of the “Pseudo-inverse method” is experimentally investigated by imposing a small perturbation of the structural boundary conditions.Notice that intensive numerical calculations are required in the “Pseudo-inverse method”. In order to simplify the modal sensor design, a novel experimental method for the design of piezoelectric modal sensors by using experimental modal analysis is presented. The curvature mode shapes of structure obtained by experimental modal analysis are directly taken as weights of PVDF array. So the weighted combination of the PVDF outputs is proportional to the response of the target mode. Other modes are filtered out. Numerical simulation and experimental results show that the proposed method is effective and easy to operate. Furthermore, this method can be extended to two-dimensional structures and it has a good prospect of engineering application.Finally, a time-domain novel sensor validation method for PVDF array is proposed by using modal filtering. It is very important to effectively identify the faulty sensor of PVDF array in order to maintain the reliability of the piezoelectric modal sensor. Otherwise, error introduced by faulty sensor can cause undamaged areas to be identified as damaged. The curvature of the differences between the reconstructed and measured the responses are taken as sensitive index. The research results show that the proposed method is effective and accurate. The main advantage of proposed method is without need of health sensor informations.