Research On Photoacoustic Signal Detection Technology In Strong Noise Environment

Additive manufacturing is a new processing mode in recent years.Compared with the traditional “subtracted material” processing,additive manufacturing has the advantages of integrated complex structure and reduced material waste.Currently,the additive manufacturing for metal materials is mainly used in the fields where aerospace,military and other fields which have high requirements for processing components.For this reason,an effective detection method is urgently needed for defect detection of components in additive manufacturing."Research on photoacoustic signal detection technology under strong noise environment" is mainly for defect detection in the noisy environment of additive manufacturing process,combined with photoacoustic effect piezoelectric theory,photoacoustic imaging theory and other technologies.Detection of subsurface defects in simulated additive manufacturing samples.In the research of this subject,there are many difficulties:(1)There are a lot of interference noise in the powder-based selective laser melting technology(SLM)environment,including instrument vibration noise,electromagnetic noise,and environmental noise.Etc.How to detect the required photoacoustic signal under the strong noise becomes a difficult point;(2)The pulse echo detection method in the most widely used laser ultrasonic technology in photoacoustic technology is difficult to detect small defects under the surface..Therefore,this subject uses the photoacoustic effect at low frequencies to detect defects and achieves superior results.The main work in this paper is as follows:(1)The analysis of the theory of detection technology such as photoacoustic piezoelectric theory and photoacoustic imaging theory was completed,and the relevant detection system was built based on the above theory.(2)Scanning studies of subsurface defects were performed:(a)multi-point scanning studies of defects;(b)single-line sweep studies of defects;and(c)two-dimensional imaging studies of defects.(3)According to the multi-point sweeping study of defects,the signal variation law of defect center and defect-free position is obtained.(4)According to the single-line frequency sweep study of the defect,the signal variation law of the excitation laser sweeping the defect at different modulation frequencies is obtained,and the detection of the defect with a minimum width of 0.2 mm is realized.(5)According to the research results of(3)and(4),the two-dimensional imaging of the defects results in a better quality imaging result.Through the work of this paper,the contact detection of the subsurface defects of the simulated additive manufacturing samples is realized,and a large amount of data foundation and detection possibility are provided for the system to realize photoacoustic space coupling defect detection,which has certain significance.