Research On The Concrete Quality Detection By Acoustic Coded Signal

In the current water conservancy project quality detection,the detection of the defects of hydraulic structures mainly uses ultrasonic method,which is used for concrete crack depth detection,concrete strength testing,etc..With the increase of water conservancy engineering design requirements and the increase of the scale of construction,there are more requirements to long distance detection.High power acoustic source(electric spark,air gun)can increase the detection distance,but the resolution is relatively low.The source has a certain degree of destruction,so its application in water conservancy project quality detection is restrained.Pulse compression method is a new method in the field of medical ultrasound research in recent years.The method can improve the inspection resolution and detection distance.In the ultrasonic testing and imaging field,there are two differences between the pulse compression and traditional pulse echo method: Firstly,at the transmitting terminal coded modulation excitation is used.Signal is excited with large band width B and long duration,which is called coded excitation.Secondly,at receiving terminal,using decoding narrow signal is obtained,which is correspond to the 1/B.The target echo signal with high signal to noise ratio is obtained and the resolution is improved.Pulse compression method is introduced into the concrete defects in ultrasonic testing.First of all,the transducer bandwidth effect on the compression result is analyzed with experiment,which proved the limited transducer bandwidth restrict the signal excitation with arbitrary time-band product.To excite linear frequency modulation(LFM)signal with large energy,at transmitting terminal LFM signal is designed considering to the transducer respond trait.The finite difference method is used to calculate the wave field characteristics of the concrete model with defects.The results show that the LFM signal can improve the signal energy,signal to noise ratio and resolution.Concrete defect models were made.The testing results show that using pulse compression method,the reflection signal with narrow mainlobe and high amplitude can be obtained after the echo is compressed.Both LFM signal and Barker signal are used to inspect the concrete model in the paper.The testing results improve the feasibility of the ultrasonic coded signal inspecting concrete defects.Both theoretical analysis and experimental results show that the method of acoustic coded signal inspecting concrete defects has technical advantages.It is expected that the method will be applied to the concrete quality detection of water conservancy projects.