Impedance Analyzer Design Based on EMI and Lamb Wave

Yu-xiang Zhang1, a, Xin Zhang1,b, Shi-yi Chen1,c, Jia-Zhao Chen1,d

1 Xi’an Research Inst of Hi-Tech, Xi’an 710025, China

ayuxiangz@tom.com, b,c,d15109111712@163.com

Keywords: EMI, Lamb Wave, Health monitoring

Abstract. 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.

Introduction

EMI 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 design

1.1 The system hardware design and implementation

System 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:

Applied Mechanics and Materials Vol. 529 (2014) pp 506-510Online available since 2014/Jun/30 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.529.506

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.207.50.37, Georgia Tech Library, Atlanta, USA-11/11/14,17:20:39)

STM32

Lamb Wave Signal

Incentive Module

EMI Incentive

Acquisition Module

Mobile Power

Lamb Data Acquiring Module

PZT PZT

Figure 1 Health monitor experimental block diagram

1.2 The design and implementation of system software

Software 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 structure

This experiment was carried out on the thin plate structure. Plate size is 500 mm * 300 mm * 1

mm, PZT1, PZT2, PZT3 paste positions 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 cracks in 5 mm long.

500mm

300mm

100mm 100mm100mm

PZT3 PZT1PZT2

Figure 2 Contains crack plate structure test specimen figure

Contrast 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 admittance spectroscopy 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

Applied Mechanics and Materials Vol. 529 507

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 condition

508 Mechanical Automation and Materials Engineering II

S0

A0

S0 A0

(g) PZT1 on nondestructive condition (h) PZT1 on damage condition

Figure 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 fewer than 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 Conclusions

In 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.

AKNOWLEDGEMENT

This work was financially supported by the National Natural Science Foundation of China

(51275517，51105346).

Applied Mechanics and Materials Vol. 529 509

References

[1] H. Lamb. On the Waves in an Elastic Plate. The Proceeding of the Royal Society of London,

1997:293-312.

[2] I A Vietorov. Rayleigh and lamb waves [M]. New York: Plenum Press, 1967.

[3] Saravanos D A, P R Heyliger. The Coupled Layerwise Analysis of Composite Beams 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 in Composite 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 in Applications And

Science of Computation Intelligence. III Proceedings of SPIE. 2000. Vol. 4055:350-361.

510 Mechanical Automation and Materials Engineering II

Mechanical Automation and Materials Engineering II 10.4028/www.scientific.net/AMM.529 Impedance Analyzer Design Based on EMI and Lamb Wave 10.4028/www.scientific.net/AMM.529.506