Excitation Method And Fpga Based Design And Implementation Of Non-crosstalk Ultrasonic Ranging System

A single ultrasound transducer cannot detect the panorama information of the environment. If multiple transducers are used simultaneously, and the ultrasound emited by ultrasonic transducers cannot be distinguished, it is sure that the crosstalk will occer. The solution to this problem is that each transcuer is given a unique identity, and then the receiver can distinguish between echoes using correlation-matching method. To realize a non-crosstalk ultrasonic ranging system, the following research has been done in this thesis.The carrier is modulated using signal with a unique identity, and the modulated signal is used as the excitation signal. In order to make the implementation of the hardware much simpler, the pulse position modulation is adopted. The ultrasonic echoes are directly correlated for identification instead of demodulation. Normally the numerical or experimental methods are used to obtain the excitation signal which has good correlation characteristic (i.e. sharp autocorrelation and flat corss-correaltion) and high energy efficiency. The theoretic conditions of the excitation signals with better performance are derived in this thesis by using the principle of mathmatic and the basic characteristics of ultrasonic transducer. The conditions can help guide constructing excitation signals.The front-end module of ultrasonic-signal-processing hardware is built, which has the features such as compactness, low power-consumption, integration of ultrasonic receiving and sending as well as automatic gain with large range of dynamic amplitude. The back-end module of digital signal processing system based on field programming gate array (FPGA) is designed. The cross-zero polarity correlation method is used in order to save hardware resources and accelerate processing speed. The core of the cross-zero polarity correlation is that the simple logic operation instead of complex multiplication is applied under the promise of not influencing the result. The RS-232 interface between the ultrasonic ranging system and host computer is designed, which realizes the communication between the ranging system and the host computer.Experiments are performed with the ultrasonic ranging system, and the results show that the ranging system has high accuracy, wide measuring range, stable performance, and can reject crosstalk signal as well. The experimental results also demonstrate the feasibility, effectivity and practability of the proposed excitation method and the FPGA based ultrasonic ranging hardwere system.