Signal Synthesis And Digital Separarion Of Ultrasonic Array Based On Frequency Division Multiplexing

Traditional ultrasonic sensor arrays often use independent electrical channels to receive and process ultrasonic echoes.However,with the increasing numbers of array elements,the number of receiving channels are also increased,which leads to the increase of the circuit scale of detection system,complexity and cost.To solve this problem,this paper proposes a method of multi-channel ultrasonic signal synthesis and echo parameter separation based on frequency division multiplexing,so as to realize the multi-channel ultrasonic signal sharing the receiving channel and effectively separating the parameters of each channel.Based on the analysis of the existing signal synthesis and separation methods,according to the characteristics of ultrasonic signals and the requirements of nondestructive testing,in full consideration of the bandwidth of synthetic signals restricted by devices,the theoretical model and parameter separation rules of multi-channel ultrasonic signal frequency division multiplexing synthesis method are established.The modulation sequence is generated by digital devices.After D/A circuit conversion,the sensor analog signal is modulated,and with the help of the digital sequence,the parameters of the digital end are accurately separated.Compared with the method based on time domain synthesis,the method is more convenient to use.Compared with the method based on orthogonal synthesis,more channel signals can be synthesized under a certain frequency band width.The proposed method belongs to the frequency domain synthesis method of multi-channel ultrasonic signals.The modulated signals allow overlapping in the frequency band.At the same time,the demodulation signals and modulated signals are not synchronized due to the circuit phase change in the traditional demodulation process.The main research work and conclusions of this paper are as follows:(1)First of all,the research status of ultrasonic array detection and multi-channel signal transmission with preprocessing technology is analyzed,and several common multi-channel signal multiplexing technologies in communication fields are listed.On this basis,the research status of ultrasonic signal multiplexing technology is analyzed,as well as the characteristics of different kinds of signal separation methods,and the overall idea and scheme of this paper is determined.(2)A multi-channel signal synthesis method of ultrasonic array based on frequency division multiplexing is proposed,the pre-processing method of ultrasonic echo signal is analyzed,the modulated signal sequence is generated by digital devices,the theoretical framework of the multi-channel array signal synthesis is established,and the relationship between the sensor center frequency,the number of channels of the synthesized signal and the total bandwidth of the synthesized signal is analyzed through simulation experiments.(3)The method of parameter separation of ultrasonic synthesized signal is analyzed by using wavelet transform,and the signal is decomposed by using wavelet packet,and Meyer wavelet is selected as the basis function.The parameters of synthetic signal are determined by simulation.The synthesized signal is decomposed and reconstructed,and the echo delay and amplitude accuracy of each channel obtained after separation are analyzed.Finally,according to the parameter separation performance and device bandwidth requirements,the number of synthesized channels is determined to be eight.(4)The synthesis circuit is designed and produced,including signal generation,excitation booster circuit,modulation signal generation circuit,preprocessing circuit,multiplication circuit and addition circuit.The eight-channel signal synthesis is realized according to the characteristics of analog end components,and the functions and characteristics of the circuit are analyzed.(5)The test platform of signal synthesis and digital separation system was built,and the defects of the standard test block were tested by ultrasonic detection.In the test,the analog end synthesis and digital end demodulation of eight ultrasonic array signals were carried out.The amplitude and delay parameters of each channel echo signal were estimated from the demodulated signal,and the maximum relative error of delay was0.21 %.The maximum amplitude relative error is 19.61%.It realizes the purpose of eight-channel signal sharing single-channel signal receiving and processing analog channel,improves the utilization rate of the frequency band,and effectively reduces the complexity of the receiving circuit.At the same time,the amount of data collected is significantly reduced compared with the independent receiving mode.