Array Arrangement And Waveform Optimization For MIMO Ultrasonic Detection System

Ultrasonic detection is widely used in every profession, and plays an important role. However, the accuracy of ultrasonic detection is still need to be improved, particularly applied to range measurement with the dynamic liquid level or the fluctuated interface.In view of the conventional ultrasonic single channel measuring method in the measurement of the fluctuated interface, often to measure a point as the target distance and introduce error. So, we propose MIMO ultrasonic detection to improve the measurement accuracy by sampling multiple points of space. In combining with the channel separation and beamforming, we mainly further study ultrasonic array structure and signal optimization to improve the performance of ultrasonic detection system.First, in the ultrasonic array structure, we further study the array arrangement of MIMO radar and uniform and non-uniform array, analyze the relationship between number of virtual array and the array distribution, use virtual array technology to construct MIMO sparse ultrasonic array which can form a homogeneous distribution of non-overlapping virtual array.Then, in the transmit signal design optimization, in order to distinguish the echo signal from different sending and receiving, we use time-sharing and simultaneously emitting mode at the same time. In the time-sharing emitting mode, we investigate large time-bandwidth product signal, such as Barker code and linear frequency modulation signal. In the simultaneously emitting mode, we work over the multi-carrier frequency signal and design a balanced Gold code modulated linear frequency modulation signal (Gold-LFM). Through theoretical analysis and simulation, this paper ultimately optimizes the signal under two launch modes:the linear frequency modulation signal time-sharing emitting and balance Gold-LFM composite signal simultaneously transmitting. The simulation results show that the balance Gold-LFM composite waveforms have better correlation performance, through using different balance Gold code modulate the phase of chirp signal to give each element a unique signa, which is benefit for channel separation of echo signal and so as to improve the accuracy of measurement.Finally, forming the MIMO ultrasonic detection based on virtual array and optimized waveform, and simulating the measurement accuracy and anti-noise performance of single target detection and resolution of multiple target detection. The simulation results show that the measurement error of the two mode of MIMO ultrasonic detection is less than5mm, and can still work reliably in low SNR of lOdB. In the case of multiple target detection, the range resolution can be reached5mm. The simulations agree with that the proposed ultrasonic measurement is effective and feasible, and has broad application prospects.