EMI检测研究

Impedance Analyzer Design Based on EMI and Lamb Wave Yu-xiang Zhang1, a, Xin Zhang1,b, Shi-yi Chen1,c, Jia-Zhao Chen1,d 1Xi’an Research Inst of Hi-Tech, Xi’an 710025, Chinaa yuxiangz@, b,c,d151********@Keywords: EMI, Lamb Wave, Health monitoringAbstract. EMI and the Lamb Wave technology are two kinds of mainstream active detection method in health monitoring , which have a long-term development. Health monitoring based on the combination of the EMI technology and Lamb wave, can be either a single method to conduct monitoring and analysis of specific structure ,or two methods together to conduct more comprehensive damage monitoring.IntroductionEMI technology is based on the global vibration method to detect structural local damage, sensitivity to the initial small damage of some large structure. PZT is sensitive to its sensing range of injury, but with less sensitivity to the area of far away. In a large structure, often take the form of the PZT array to realize health monitoring. EMI technology can qualitatively react the damage conditiont commonly, also can determine the basic damage location.Effect of Lamb wave technology on the far field damage recognition is obvious, commonly used to monitor in motor shell, pipe, plate structure, the structure of the aviation wing skin and transmission line, but because of its limitations, it can only be used to monitor in the thickness and the excitation wave length in the structure of the same order of magnitude. Having the dispersive and multi-mode characteristics, its signal contains more information than the traditional stress wave, so that it can in the limited frequency range produce a large amount of data points[1-5].The health monitoring system based on PZT is studied. Meanwhile, on the basis of EMI and Lamb wave, giving full play to their respective advantages and overcoming the limitations of a single monitoring, health monitor was designed. Monitoring in the sheet structure containing crack illustrates the validity and reliability of health monitor higher.1 System overall scheme design1.1 The system hardware design and implementationSystem used STM32 development board as the core controller, respectively controlling AD5933 and AD9833 to realize signal incentives, whose waveform is sine wave and sine wave after modulation. And it acquires data by controlling AD5933 and ADS930, and communicating respectively on the IIC and SPI, uses KEY0, KEY1 on the development board as EMI and Lamb wave monitoring switch button respectively.Specific EMI and Lamb wave parts hardware is the same as the third and fourth chapter. The hardware block diagram is shown in figure 1:STM32Lamb Wave Signal Incentive Module EMIIncentiveAcquisitionModule Mobile PowerLamb Data Acquiring ModulePZTPZTFigure 1 health monitor experimental block diagram1.2 The design and implementation of system softwareSoftware is compiled by RVMDK, mainly complying the communication and display of AD5933, AD9833, ADS930, IIC, SPI. By compiling the enable of KEY0, KEY1, swaps between EMI technology and the Lamb wave technology are conducted.2 Sheet containing crack monitoring analysis of composite structureThis experiment was carried out on the thin plate structure. Plate size is 500 mm * 300 mm * 1 mm, PZT1, PZT2, PZT3 paste position are shown in figure2. The distance between PZT1 and PZT2, PZT3 is 200 mm and 300 mm respectively. 1 for non-destructive, between PZT1, PZT2 on plate2 is there a line crack in 5 mm long.500mm 300mm100mm 100mm100mm PZT3PZT1PZT2Figure 2 contains crack plate structure test specimen figureContrast between plate1 and 2 reacts admittance modulus values change of with and without damage. During the EMI test PZT piezoelectric patches is excited by peak of 10V sine voltage, to measure frequency between 10-100 kHz admittancespectroscopy of bolt looseness. X axis as the frequency, is divided into an average of 200 points, and the step frequency of it is 4.5 kHz; meanwhile Y axis is for the admittance values. Solid lines represent the nondestructive curve plate, and dotted lines represent the damage curve plate. Lamb wave experiment selects frequency whose thickness is 1 MHz/mm. By composite monitoring of EMI technology and the Lamb wave technology, specific contrast between EMI and Lamb wave experiment is presented in figures(a)-(d). As is shown in figure3:(a) PZT2 contrast at 10-100 kHz (b) PZT1 contrast at 10-100 kHz(c) PZT2 contrast at 40-50 kHz (d) PZT2 contrast at 40-50 kHz(e) PZT2 on nondestructive condition (f) PZT2 on damage conditionS0S0A0A0(g) PZT1 on nondestructive condition (h) PZT1 on damage conditionFigure 3 composite plate structure containing crack monitoring figure Comprehensive analysis of EMI and Lamb wave experiment figure, can draw the following conclusion:(1) By EMI technology health monitoring for PZT1 and PZT2 under 10 kHz to 100 kHz frequency is conducted. As can be seen from the admittance chart, PTZ2 change before and after damage is greater than the PZT1, particularly in 20 kHz to 60 kHz frequency, among which the peak has obvious changes and many other peaks is presented. So the experiment proved the fact that EMI technology could be effective for health monitoring, and is sensitive of damage in a certain range, the farther the distance, the lower the sensitivity.(2) From 20 to 30 mm in Lamb wave charts, signal amplitude of A0 mode and S0 obviously observed has obvious changes before and after damage, and at the rear end of waveform, there will be some other new models, such as S1, S2 and A1. Propagation mode changes, by which can judge the existence of structure damage.3 ConclusionIn this paper, based on PZT composite structure health monitoring system is designed. For hardware design, the STM32 act as hardware core, with AD5933, AD9833, ADS930 as incentives and acquisition chip; for software design, KEY0, KEY1 serve as conversion button, using RVMDK software to compile. The system fuses EMI technology and Lamb wave technology, to conduct health monitoring of sheet structure containing the damage. Through the analysis of waveform curve and impedance spectroscopy, The fact that the damage exists and damage location is between PZT1 and 3, and between PZT2 and 3, is qualitatively analysed by Lamb wave charts; then by EMI technology damage existence can be demonstrated, and the damage position can be more accurately located in close distance from PZT2, far from PZT1, and between PTZ2 and PTZ3. The effect is good, so as to lay a foundation for the next step accurate location.AKNOWLEDGEMENTThis work was financially supported by the National Natural Science Foundation of China (51275517，51105346).References[1] H. Lamb. On the Waves in an Elastic Plate. The Proceeding of the Royal Societyof London, 1997:293-312.[2] I A Vietorov. Rayleigh and lamb waves [M]. New Y ork: Plenum Press, 1967.[3] Saravanos D A, P R Heyliger. The Coupled Layerwise Analysis of CompositeBeams with Embedded Piezoelectrie Sensors and Actuators [J].Journal of Intelligent Material SystemsandStruetures. 1995, (6) : 350-362.[4] Saravanos D A, BirmanV, D.A.H opkins. Detection of Delaminations inComposite Beams Using Piezoelectric Sensors [C]. Proceedings of the 35 th Structure, Structural Dyamics and Materials Conference of the AIAA.1994:181-191.[5] Kereel, Klein. Separation of Lamb Waves in Laser Ultrasonics [J]. J inApplications And Science of Computation Intelligence. III Proceedings of SPIE.2000. V ol. 4055:350-361.。