The Research Of Ultrasonic Signals Demodulation Technology In The Laser Heterodyne Interference

Laser ultrasonic has a great application prospect in non-destructive testing. Laser pulse will generate ultrasonic in the analyte. The analyte’s characteristic can be obtained by analyzing the ultrasonic signals. In the laser heterodyne interference detection technology, the ultrasonic signals under test can be obtained by processing and analyzing the interference signals.In this paper, the main work is demodulating the phase-modulation interference signals to get the ultrasonic signals. The hardware demodulation system and software demodulation algorithm are put forward after analyzing the characteristics of ultrasonic signals and heterodyne interference signals.The research issues are listed as following:1. Based on the method of phase demodulation with AD8302, the design of PLL is to maintain frequency consistency of carrier signals and reference signals. The demodulation system mainly includes the high-frequency amplifier, PLL and phase discriminator AD8302. The high-frequency amplifier can enlarge or reduce high frequency signals. PLL AD8302 can measure the phase difference between interference signals and reference signals. PLL can eliminate the difference frequency signals of carrier signals and reference signals in the demodulation results.2. By improving the PGC based on the arctangent arithmetic, a new kind of software demodulation algorithm based on PGC is proposed. Through simulation and experiment research, the algorithm principle is simple. But the demodulation results may appear distortion. And the software demodulation algorithm has certain limitations in practical application.3. The effectiveness and innovation of hardware demodulation system are verified by the experiments. Firstly the hardware demodulation system is verified in the static and dynamic phase demodulation experiments. The contrast experiments show that compared with the software demodulation and phase demodulation with AD8302, the hardware demodulation system works well and it can improve SNR. Finally the demodulation system is applied to the laser ultrasonic detection experiment and it succeeded in the demodulation of ultrasonic signals.