Study And Realization On Chaotic Signal Based Ultrasonic Ranging System

The detection technology is used in lots of aspects. Our nation attaches greatimportance to it by providing a large sum of money for related research. However,sometimes there are needs to tackle the problem of weak signal, because the signalenergy dissipates when being transmitted, and the noise in the environment can’t beeliminated completely. The performance will degrade on low signal-to-noise-ratio(SNR) conditions. Therefore we need a ranging method with the ability of weaksignal detection to improve the performance on low SNR conditions, thus increase theeffective ranging distance.In this thesis, a chaotic signal based ranging method is proposed exploiting thechaotic oscillator of the initial condition sensitivity and the immunity to disturbing. Inthis work, the Duffing oscillator is chosen to cancel the influence of noise, becausethere is a sine item in its expression equation, which is similar to the ultrasonic wave,and plays an important role in the dynamics of the chaotic oscillator. The mappingrelationship between the driving force of the Duffing oscillator and the GeneralFloquet Exponent (GFE) is depicted. The proposed method introduces the detectionsignal into the oscillator and uses the mapping relation to recover the signal, reducingthe influence of noise, thus improving the ranging accuracy and distance. Accordingto the different observation model, the theoretical limitation of conventional rangingmethod and the proposed method are derived. It shows that under the same SNR, theproposed method can achieve better accuracy than the conventional method.Simulations of these ranging methods have the same results.To further prove the effectiveness of the proposed method, an ultrasonic rangingexperiment system is built, using the Field Programmable Gate Array (FPGA), a D/Aconverter, a power amplifier, transducers, an oscilloscope and so on. The collecteddata are processed on a computer. In the experiment, the proposed method iscompared with the conventional hard threshold method and the soft threshold method.The results show that the proposed chaotic signal based ranging method is superior tothe conventional methods in terms of both accuracy and effective distance.