Tham khảo tài liệu 'systems, structure and control 2012 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fouling Detection Based on Parameter Estimation 133 in the material. The pulse displays an amplitude and a phase according to the impedance size and orientation of the reflecting surface. This model is used for parameter estimation in combination with tests that use the pulse-echo method and a transducer that operates as both a pulser and receiver. Considering the effect of the noise in the estimation a noise process can be included to the model Dermile Saniie 2001 Dermile Saniie 2001b . Thus the ultrasonic pulse can be modeled by equation 2 x t 5 0 t e t 2 Where S B t denotes the model of the ultrasonic pulse and e t denotes the additive white Gaussian noise. This model can be extended to consider multiple ultrasonic pulses by equation 3 M y t E 5 0m t e t 3 m 1 Each parametric vector Bm defines the form and location of the corresponding pulse completely. For computer programming purposes the observation model expressed by equation 2 for an ultrasonic pulse can be written in the discrete form Dermile Saniie 2001 Dermile Saniie 2001b Silva et al. 2007 . The Gaussian pulse model has been chosen as the algorithm for parameter estimation since this model is more accurate and the parameters resemble the ultrasonic pulse in a more complete approach. The Gaussian pulse model is thus appropriate to determine the parameters of the guided waves method and the analysis of the fouling process is achieved by observing the variation of the estimated parameters. The estimation problem relies on the determination of the parameters of the model and modifications of these parameters in presence of fouling. Here the non-linear estimation approach is employed using programs developed with the MATLAB code Hansenlman Littlefield 1996 . 3. Proposed system The proposed system for fouling monitoring using ultrasonic transducers is illustrated by the block diagram presented in Fig. 4. This system is composed by the ultrasonic pulser and receiver which are connected to the transducers and .
