The Optimized Pseudorandom Digital Modulation Excitation Sequences for Multichannel Ultrasonic Ranging system

The crosstalk in multichannel simultaneously triggered ultrasonic sensors of ultrasonic ranging system may cause false measurement. This paper presents pseudorandom digital modulation excitation sequences for multichannel ultrasonic sensors to avoid crosstalk. To make full use of bandwidth of the ultrasonic sensors, the parameters of the pseudorandom digital modulation methods are configured. A genetic algorithm is applied to optimize the pseudorandom m sequences to obtain the best echo correlation characteristics (i.e., sharpest autocorrelation and flattest cross-correlation). The polarity correlation algorithm in the receiving circuit is implemented by Field Programmable Gate Array. Real experiments have been conducted using ultrasonic ranging system that consists of eight-channel SensComp 600 series instrument-grade electrostatic sensors excited with 2 ms optimized pseudorandom digital modulation sequences. Experimental results shows that the optimized pseudorandom BFSK sequence , which can make the eight-channel ultrasonic ranging system work together without crosstalk and has a maximal 4.1 cm absolute error, has the best performance of all the pseudorandom digital modulation sequences.

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