Research On Imaging Method By Using Ultrasonic Arrays For Concrete Structures

Synthetic aperture focusing technique (SAFT), which made a breakthrough inclassical concept of ultrasonic imaging system concerning lateral resolution, can be usedto detect and observe the remote object with high lateral resolution by means of actualelement transducers with small aperture and low operating frequency.Smaller theelement transducer aperture D is, higher the lateral resolution is. Some mutuallycontradictory requirements about systematic parameter design in the direct imagingtechnique can be solved by using this method.In this work, for satisfying the need of quick detection to the internal defects andembedded objects in concrete structures, a detect method combining linear array probesand SAFT has been presented to reach high resolution detection in concrete byultrasonic arrays. Traditional SAFT algorithm has been improved to adapt to this newdetection method according to the structural characteristics of linear array probes, wherethe geometrical relationship of echo sound path through reflection point is discussed indetail by different situations. Numerical simulations and ultrasonic array data fusion areconducted to form cross section figures by using the finite element software WAVE3000and mathematical software MATLAB in the subject.In array SAFT algorithm, the scanning signals between interval transducers inarray are used to increase array dimension maximum to amalgamate detecting data forhigher imaging resolution compared with traditional SAFT. As frequency componentsof the pulse signal is rich, the grain scattering is serious in concrete material, then therewill be oscillation signal at the position of echo wave height in imaging figures. Thispaper also presents a new method based on cross-correlation to filter oscillation signalas well better suppression effect to lateral wave magnitude.Numerical simulations have accomplished in two ways, single point reflection andthe finite element simulations. Single point reflection is to verify the effectiveness ofarray SAFT algorithm. Imaging quality is tested and discussed after using array SAFTalgorithm through finite element simulations, and it is demonstrated that the linear arrayprobe combined with array SAFT algorithm can achieve high resolution in detection of concrete theoretically.A ultrasonic array detection system to complete the probes data fusion isestablished for effective detection within concrete structures in the experiment.Provided that actual concrete test blocks be complicated, experimental effects are lessobvious and typical than simulation results, but it does not matter that imaging figuresreveal the effectiveness of the linear array probes.