Design Of Wide Band Ultrasonic Tomography

Ultrasonic tomography(UT)utilizes the transmission and reflection characteristics of ultrasonic waves when propagating in different media.By applying ultrasonic excitation to the measurement field,we can obtain field boundary signals,extract the information such as characteristic acoustic attenuation in the measurement field,and then reconstruct the medium distribution image in the measurement field.With the advantages of non-invasive,non-radiation,and visualization,ultrasonic tomography has a wide range of application prospects in the fields of multiphase flow measurement,medical imaging,and non-destructive testing.The existing ultrasonic tomography systems have some shortcomings such as single measurement frequency,low integration,leading to problems such as small application range,poor portability,and low reconstruction accuracy.In order to improve the accuracy of image reconstruction of the complex flow of multiphase flow,a set of 32-channel wide band ultrasonic tomography system is designed in this paper.The completed work is as follows:(1)Design and implement a digital wide band ultrasonic tomography system.The system uses FPGA(Field Programmable Gate Array)as the main control unit,includes wideband ultrasonic sensor array,wideband excitation source module,switch module,data preprocessing and analog front-end module,data processing module and CPCI bus module.The system realizes the generation of arbitrary waveform excitation signals in1-5MHz frequency band,the excitation voltage amplitude can be adjusted within200 Vpp.The acquisition part realizes 32-channel parallel data acquisition and processing,the sampling rate is up to 80 MSPS,with the channel average signal-to-noise ratio is 51.7d B.Based on the above design,the system acquisition rate can reach up to104 frame/sec.(2)Aiming at the problem of online demodulation of time-frequency domain information of wideband ultrasonic signals,the FPGA-based wideband echo signal spectrum demodulation method and the DSP-based single-frequency echo signal amplitude extraction method are designed,which achieves the purpose of multi-channel parallel data demodulation under multiple excitation states in a wide frequency band.(3)Combining the characteristics of wideband ultrasound tomography,a multifrequency ultrasound fusion imaging method is designed.The experiment uses liquidsolid,gas-water,oil-water two-phase media and oil-gas-water,oil-water-sand threephase media as the measured objects,compares the single-frequency imaging results of the system and the multi-frequency fusion imaging results.Among them,the accuracy of multi-frequency ultrasound imaging is greatly improved relative to single-frequency,and the three-phase medium distribution can be reconstructed by the multi-frequency fusion imaging,which reflects the advantages of this wideband system.In summary,the designed wide band ultrasonic tomography system measures the modulation information under different excitation frequencies,which makes the amount of information acquired by ultrasonic tomography richer,broadens the application range of the system.It is of great significance to the application of ultrasonic tomography in the measurement of complex flow conditions.