EXPERIMENTAL EVALUATION OF MINIATURE IMPEDANCE CHIP FOR

STRUCTURAL HEALTH MONITORING OF PROTOTYPE STEEL/RC

STRUCTURES

Naveet Kaur

1, Suresh Bhalla

1, Ravi Shanker

1 and Ramakanta Panigrahi

2

1Department of Civil Engineering, Indian Institute of Technology Delhi,

Hauz Khas, New Delhi 110 016 (INDIA)

2Department of Civil Engineering, Centurion Institute of Technology, Jatni, Odisha, INDIA

CORRESPONDING AUTHOR: Dr. Suresh Bhalla

Associate Professor

Department of Civil Engineering

Indian Institute of Technology Delhi

Hauz Khas, New Delhi 110 016 (INDIA)

Tel: (91-11)-2659-1040

Tel: (91-11)-2659-1117

Email: sbhalla@civil.iitd.ac.in

1

ABSTRACT

The electro-mechanical impedance (EMI) technique has so far been very successful in

monitoring structural components made of both metals and nonmetals in the fields of civil,

mechanical and aerospace engineering. In the last two decades, researchers have reported fairly

good results using the EMI technique through costly conventional hardware, such as impedance

analyzer and LCR meter. This paper evaluates the performance of the low-cost miniature

impedance chip AD5933 for structural health monitoring (SHM) of prototype structures. Most

studies involving AD5933 have so far been restricted to miniature metal structures only, and in

particular, no study has so far been reported on reinforced concrete (RC) structures. In this

investigation, experiments are first conducted on a real-life sized reinforced concrete (RC) beam,

150×210×4000 mm in size, instrumented with 19 pairs of piezoelectric ceramic (PZT) patches

in embedded configuration, aiming to detect and locate incipient to severe damages.

Experimental investigations are then extended to a large mild steel plate structure, 1200×970×8

mm in size, divided into 30 equal panels and instrumented with one PZT patch at each node.

The results of the two studies confirm that the low cost miniature impedance chip is suitable for

level one damage diagnosis in large prototype structures, both steel as well as RC. It is however

not suitable for higher level analysis involving extraction of the structural impedance parameters.

Keywords: Electromechanical impedance (EMI) technique, piezoelectric-ceramic (PZT) patch,

damage, structural health monitoring (SHM), prototype structure, miniature impedance chip

2

INTRODUCTION

Structural health monitoring (SHM) is emerging as a new and vital engineering science to aid

engineers in improving the safety, performance and maintainance of critical structures. SHM

system solution offers precise information to help engineers and managers to assess the state-of-

health of their structures, and if needed, target specific regions to inspect. SHM systems add

unique value to a structure by converting it into a ‘smart’ structure with state-of-the-art sensing

technology. SHM can be formally defined as the measurement of the structure’s operating and

loading environment, as well as critical responses to track and evaluate any symptoms of

operational incidents, anomalies and deteriorations/damages, which might affect its smooth

operation, serviceability or safety reliability1. Various techniques available for SHM can be

classified as global techniques, local techniques, techniques using neural networks and

techniques using smart materials and smart system concept. With the growth of technology,

smart materials have become the centerpiece for SHM and nondestructive evaluation (NDE) of

structures. Smart piezoelectric-ceramic Lead Zirconate Titanate (PZT) materials have recently

emerged as high frequency impedance transducers for SHM and NDE after the advent of the

electro-mechanical impedance (EMI) technique2-4

. In the EMI technique, the PZT patch

bonded to the structure acts as actuator as well as sensor. It employs ultrasonic vibrations

(typically in 30-400 kHz range) to gather out a distinctive admittance ‘signature’ of the

structure. The basic principle of the EMI based SHM approach is that the occurrence of damage

in the host structure will affect its mechanical impedance, and thus the admittance (inverse of

electrical impedance) ‘signature’ of the PZT patch, which can be directly measured by an

electrical impedance analyzer or LCR meter. The impedance analyzer / LCR meter imposes an

alternating voltage signal to the bonded PZT patch over the user specified frequency range. The

3

admittance signature of the bonded PZT patch is a function of the stiffness, the mass and the

damping of the host structure, and the properties of the PZT patch. The changes in the

admittance signature relative to the baseline provide an indication of the occurrence of structural

damage, which can be thus used for damage assessment.

The EMI technique has been successfully demonstrated for damage identification and location in

a reinforced concrete (RC) frame5, monitoring of concrete hydration and damage

6, damage

assessment in aluminum truss and beam7, and monitoring rock specimen

8 using impedance

analyser/LCR meter as data acquisition system. An impedance model incorporating shear lag

effect and piezo-bond-structure interaction have also come up in the recent years9,10

.

Talakokula et al.11

performed the corrosion assessment of RC structures using EMI

technique. The main problems with conventional LCR meter are bulkiness and exorbitant cost

(typically over US $20,000), which act as deterrent in the widespread field application of the

EMI technique. Recently, Analog Devices12

has launched the evaluation version of its impedance

measurement chip AD5933. This is not only small sized but also low cost (US $160). Its proof of

concept application has been shown by several investators13-15

. At the same time, some

discrepancies have also been reported.

All the studies conducted so far, involving AD5933, have been performed on very small

structure. No literature is currently available which covers the performance of AD5933 on large

prototype, structures including detailed comparison of performance with LCR meter. This paper

covers two detailed experimental studies involving the AD5933 impedance chip to detect

4

damage in a real life sized RC beam and a 2D prototype steel structure. The following sections of

the paper cover the theoretical background followed by experimental details and results.

THEORETICAL BACKGROUND OF EMI TECHNIQUE

In the EMI technique, a PZT patch is bonded on the structure and electrically excited by means

of an LCR meter over 30-400 kHz frequency. The constitutive relations for piezoelectric

materials under small field condition2 are

1313333 TdED T (1)

331

11 Ed

Y

TS

E (2)

where, d31 is the piezoelectric strain coefficient, 1S the Strain along the length of the PZT patch

and T1 the corresponding stress, 3D the electric charge density over the PZT patch, EY the

Young’s modulus of the PZT patch at zero eclectic field, T

33 the complex electric permittivity

of the PZT patch at zero mechanical stress and 3E the electric field in the thickness direction.

For a PZT patch of length 2l, width w and thickness h bonded on a structure, following equation

can be written for the complex electro mechanical admittance Y (inverse of electrical

impedance16

EE

a

aT Ydkl

klYd

ZZ

Z

h

wljY 2

31

2

3133

tan2 (3)

5

where, Z denotes the mechanical impedance of the structural system and aZ that of the PZT

patch, the angular frequency and k the wave number. Eq. (3) is utilized for damage detection

in the EMI technique. The mechanical impedance Z in the equation is a function of structural

parameters i.e. the stiffness, the damping and mass. Any damage to the structure will cause these

parameters to change, and hence the mechanical impedance Z, which in turn modifies Y , being a

complex quantity having conductance (G) and suceptance (B) as its real and imaginary parts,

respectively. The real part actively interacts with the structure and is therefore preferred in quick

damage assessment algorithms. A plot of G over frequency serves as a diagnostic signature of

the structure and is called the conductance signature.

The damage quantification can be preliminary or detailed. Detailed quantification requires a

computational procedure to extract the mechanical impedance (x and y) of the structure2. The

statistical approach, based on root mean square deviation (RMSD) is preliminary in nature. It is

based on variation in the conductance signature (i.e. conductance vs frequency plot). The health

of the structure can be known by visualizing the healthy signature and signature obtained after

some period, when health monitoring is needed. But to quantify changes in signature due to

damage, the index used is root mean square deviation (RMSD), which was defined4 as

100

)(

(%)

1

2

2

1

ni

i

i

ni

i

ii

u

uw

RMSD (4)

where, iu (for i = 1, 2, 3,……,n; where n is the number of readings) is a baseline signature and

iw is the signature obtained after a period of time at the time of assessment of the structure.

6

The main deterrent in widespread application of the EMI technique is that the conventional

equipment, namely impedance analyzer or the LCR meter typically costs in the range of

US $ 20,000 to US $ 40,000. Several low cost variants15,17-19

have been proposed based on

system integration of equipment such as function generator, oscilloscope and/or FFT analyzer.

Although, the cost is drastically reduced, bulkiness of the equipment still remains an issue. The

recent launch of AD5933, a miniature impedance circuit, is a step forward towards low-cost and

low power solution. The next section covers a brief technical introduction of AD5933 followed

by its evaluation on real-life RC and steel structures.

MINIATURE IMPEDANCE CHIP AD5933

In the recent past, miniature impendence chip AD5933 (which is less than US $160) has attracted

researchers actively in the field of the EMI technique. AD5933, as shown in Fig. 1, is a high

precision impedance converter system in combination with an on board frequency generator. The

frequency generator allows an external complex impedance to be excited with a known

frequency. It also contains an internal temperature sensor. This offers an additional advantage to

include thermal compensation of signatures during the signature acquisition itself. The user has

the option to power the entire circuitry from the USB port of a computer. The evaluation board is

equipped with a high performance trimmed 16 MHz surface-mount crystal to act as a system

clock to the AD5933, if required. The AD5933 is specified to a typical system accuracy of 0.5 %

(assuming the AD5933 system is calibrated correctly for the impedance range under test) within

the frequency range of 1 kHz to 100 kHz. The lower frequency limit is determined by the value

of the system clock frequency connected to the external clock pin (MCLK) of the AD5933.

Using the AD5933 to frequencies past 100 kHz will introduce errors in impedance profile if the

7

sweep span is large, due to the effect of the increased roll off in the finite frequency response of

the system past 100kHz. The user interface of AD5933 software is shown in Fig. 2. Calibration

of evaluation board AD5933 is required each time the software or hardware is restarted/reset.

The calibration is done by adding calibration resistance of 200 kΩ to the circuit and running

“AD5933 Eval Software” as per the procedure prescribed in the manual.

Quinn et al.20

proposed to incorporate AD5933 into a wireless sensing device to monitor initial

curing of concrete. The feasibility of AD5933 impedance chip was explored and the results

were found comparable with HP4192 impedance analyzer. Another experimental study21

was

reported to detect corrosion in aluminum structures (widely used in aerospace, civil, and

mechanical systems) using AD5933 and a self-sensing macrofiber composite (MFC) patch.

Further verification was done involving loosening bolts in a bolt-jointed aluminum structure22

.

Na and Lee23

proposed steel wire based variant of the EMI technique to enhance the damage

detection performance on composite plates with large surface areas. The variations in the

impedance signatures were measured using the AD5933 evaluation board. Proúdekis and

Liarakos24

developed an innovative active wireless sensing system based on AD5933 to monitor

the concrete strength development at early ages and initial hydration states and a reusable

piezoelectric transducer appropriately installed in a Teflon-based enclosure. Conventional EMI

systems use wired technology, i.e. the equipment has to be installed on-site using cumbersome

cables for sensor connections and power supply. The wireless sensor networks (WSN), in

contrast, offer high flexibility due to easy deployment. Overly et al.13

tested wireless impedance

device WID2.0 in order to determine the performance as a SHM sensor node. The SHM

experiments were carried out for corrosion monitoring of aluminum plate and bolted joint of a

8

framed structure. Park et al.14

employed the AD5933 based wireless SHM technique to identify

the debonding conditions of a carbon fiber reinforced polymer (CFRP) laminated reinforced

concrete (RC) beam.

Taylor et al.25

reported using AD5933 for real-life bridge monitoring. However, no

comparison of measurements with standard LCR meter was reported. This paper

addresses this important issue involving AD 5933 on prototype structures. It presents results

of two studies on: (a) large RC beam and (b) large steel plate (typically representing a large

defence equipment), to evaluate performance of AD5933 vis-à-vis the LCR meter.

EXPERIMENTAL DETAILS OF AD5933 EVALUATION STUDY

A miniature structure (aluminum strip), as shown in Fig. 3 was used for the initial calibration

AD5933. Damage was induced in the strip by drilling a hole in it. Both healthy and damaged

conditions were assessed using AD5933 and then compared with Agilent 4980 LCR meter. The

output of the AD5933 is in form of the real part (resistance, R) and the imaginary (reactance, X)

part of impedance. In accordance with the established norms of the EMI technique2,

conductance, the real part of admittance, has been chosen as the damage indicative

parameter. This is because the conductance has higher contribution from structural

parameters than PZT patch’s own parameters. It is therefore more sensitive to damage

than susceptance, which is somewhat own drowned by PZT patch’s parameters, hence,

conductance value was determined as

22 XR

RG

(5)

9

Firstly, the repeatability of the conductance signal for undamaged state was checked. Two

readings were recorded after a gap of 24 hours to verify the repeatability of the signature. The

results are shown in Fig. 4 for both healthy and damaged conditions. It is evident that the

evaluation board AD5933 exhibits a high level of repeatability. Finally, the comparison was

done between the signature obtained in the undamaged and the damaged states as shown in

Fig. 5, from which, it is evident that RMSD index value for damage is significantly higher than

that observed during repeatability. Further, the results of evaluation board AD5933 were

compared with that of conventional EMI technique (i.e. LCR meter) as shown in Fig. 6. The

conductance values obtained from the AD5933 and LCR meter have been normalized with

their respective peak values and shown in Fig. 6(b) for better clarity. It is observed that the

trend is similar but there is difference in the values. The difference in the baseline magnitude

from the two measurement systems is on account of the different electronics involved in the

two measurement systems. Further, in view of the working of the EMI technique, where

the “change” in signature on account of damage is more important, some deviation in the

baseline from ideal one does not matter much towards damage detection.

After the above repeatability check, experiments were extended to a prototype reinforced

concrete (RC) structure. A real life size RC beam of span 4 m, part of a related energy harvesting

study26

, was considered for experimentation. The beam confirmed to a self-compacting M40

grade with 30% fly ash. PZT patches were embedded inside the beam in the form of Concrete

Vibration Sensor (CVS). CVS, shown in Fig. 7(a), is a packaged sensor, designed especially for

monitoring RC structures. CVS is composite in nature and has better compatibility with

surrounding concrete and can withstand the harsh conditions encountered during casting. It is a

10

proprietary product developed by Bhalla and Gupta27

in the Smart Structures and Dynamics

Laboratory (SSDL), IIT Delhi28

. It consists of a PZT sensor patch encapsulated in a proprietary

configuration suitable for casting along with the structure, thereby permanently embedding the

patch in the RC structures. The packing provides an additional advantage of protection of the

embedded sensor against ambient environmental conditions, hence, enhancing the life of the

sensor. The beam consisted of two layers of 19 CVS each at top and bottom, flushing with the

surface. Controlled damage was induced by chipping off the concrete at a specific location (one

third length of the beam, between CVS location 7 and 8) where a notch was created at the time

of casting [see Fig. 7(a)]. The damage was induced in three levels as explained using Fig. 7(a).

State 1 represents an undamaged condition, and in State 2, concrete was chipped off from the

notch, which was specifically designed to create damage between CVS locations 7 and 8. For

damaged states 3 and 4, 50% and 100% of the bottom reinforcement was curtailed, respectively.

The experimental setup used for acquiring the EMI signature using AD5933 is shown in

Fig. 7(b). The EMI signature of the 19 embedded CVS at top and 19 at bottom in the RC beam

was acquired using the AD5933. For the operation of AD5933, the frequency range chosen was

80 kHz to 100 kHz at a voltage of 1 V, in order to compare26

the results with the impedance

analyser, LCR meter. A typical plot of the real part of the EMI signature (conductance) for

undamaged and damaged states using AD5933 is shown in Fig. 8(a). The difference in the

conductance values for undamaged and damaged state 1 is maximum. The signatures of higher

level of damages became less and less distinguishable from one another, as apparent in the

figure. For locating the damage, RMSD value for each sensor node was calculated. RMSD value

for ith

element (between nth

and (n+1)th

sensor node location) for three different damage states

for the 19 CVS at top and bottom was calculated each using

11

2

1 nn

i

RMSDRMSDRMSD (6)

RMSD values were determined for three different damage states for the 19 CVS at top and

bottom each and plotted for bottom 19 CVS sensors for AD5933 in Fig. 8(b). It can be observed

from the figure that the damage in all the three stages has been effectively located. However, the

difference in the magnitudes of the RMSD index corresponding to State 3 and State 4 is not

high. This is a well accepted fact for the EMI technique.

In order to carry out a higher level of damage analysis, the equivalent stiffness of the beam was

determined from the admittance signatures of the CVS based on the method proposed by

Bhalla2. It is based on the trend of the real and the imaginary components of the mechanical

impedance x and y, respectively. The variation of x and y for typical CVS is shown in Fig. 8(c).

It is observed that the ‘x’ values are somewhat negative which is not an acceptable fact2,5

from

mechanics point of view. Hence, it can be mentioned that though the conductance (G) and

susceptance (B) signature acquired using AD5933 is sufficient for detecting and locating

damage, however, extracting the correct equivalent parameters from G and B for higher level of

damage assessment is not achievable using AD5933. This can be recognized as a drawback of

AD5933.

In the second study, a large plate of size 1200×970×8 mm, emulating typical defence

structural/mechanical component, was used as specimen for the experiment, as shown in Fig. 9.

The structural steel belonged to grade Fe 410 as per IS 2062. There were 42 nodes in the steel

plate and at each node a PZT patch of 10×10 mm with thickness of 0.3 mm was attached. PZT

patches were of grade PIC 151 manufactured by PI Ceramic. There were holes in the plate (panel

12

no. 6, 15 and 26) which were covered by the small plates. Damage scenarios were created by

removing the cover plates. Healthy baseline condition was created by fixing all the cover plates

and tightening the bolts with a torque of 35 N-m by using a torque wrench. Then, the damage

was induced by loosening the bolts of the cover plate of panel number 15 by reducing the torque

at an interval of 5 N-m. The signatures were acquired by the impedance chip AD5933. The

torque was reduced up to 25 N-m as it is the minimum value that can be applied by the torque

wrench. Finally, the cover plate was fully removed and the signatures were acquired. The RMSD

values were computed for various degrees of damages induced in the steel plate. Fig. 10 shows

the RMSD values with change in torque applied. It is clearly evident that even a minor incipient

damage such as loosening of the bolts can be easily identified by AD5933, very much like LCR

meter. In the next step, moderate damages were introduced by removing the cover plates by

using nut and bolt system. The signature was obtained in healthy and damaged condition in

frequency range of 74 kHz – 76 kHz, which was selected by trial. After selecting the frequency

range, two damage scenarios were considered – single damage and multiple damage. A single

damage was induced in the steel plate by removing one cover plate, one at a time as shown in

Fig. 11. Damage 1, 2 and 3 correspond to the removal of cover plate in panels 15, 26 and 6,

respectively. The RMSD value for all the panels for damage case 1 are shown in Fig. 12(a),

which clearly indicates that there is damage in the panel number 15 of the steel plate. Similarly,

damage 2 and 3 are also correctly detected, as shown in Figs. 12(b) and (c). In general, for an

array of PZT patches as in the present case of the plate structure, the occurrence of

damage alters the signatures of a particular PZT patch in inverse proportion to its distance

from the damage location. This implies that the nearest PZT patch is most affected and the

farther ones less. A plot of RMSD indices forms a sort of “umbrella” structure, with the

13

RMSD peak occurring at damage location and the magnitude going down as we recede

away from it. The damage location can be identified as the PZT patch with maximum

RMSD value. The trend can be somewhat offset by applying a minimum threshold, as in

Figures 12 and 14, but still, some peaks may exceed this threshold.

The multiple damage scenario was introduced in the plate by removing more than one cover

plates at a time. The various multiple damages are shown in Fig. 13. The damages 1 and 2 were

induced in the panel number 15 and 26 of steel plate as shown in Fig. 13(a). Then, the damages 1

and 3 were induced in the panel number 15 and 6 of steel plate as shown in Fig. 13(b). Finally

the damages 1, 2 and 3 were induced in the panel number 6, 15 and 26 of steel plate, as shown in

Fig. 13(c). The results are shown in Fig. 14. All cases of multiple damages are clearly identified.

From analysis of the above results, it can be concluded that the miniature impedance chip

AD5933 can be successfully used for single as well as multiple damage detection similar to the

expensive LCR meter.

CONCLUSIONS

This paper has successfully demonstrated low cost EMI technique for health monitoring of

prototype structures using miniature impedance chip AD5933. Both incipient as well as severe

damages, including multiple damages were successfully detected and located, both in RC as well

s steel structures considered in the study. The hard ware solution costs only US $160 only, much

lower than any other conventional hardware used for EMI technique. The conductance acquired

using AD5933 follow the same trend as that of the conventional EMI technique. However, the

absolute magnitude obtained from AD5933 differs from the conventional. This may be due to the

14

electronics involved in AD5933 is different from the LCR meter as it does not use pure

sinusoidal sweep as LCR meter. However, this problem is not important as far as health

monitoring is concerned as the difference in magnitude of signals is important rather than the

absolute magnitude of the signals in structural health monitoring. In addition AD5933 is also

equipped with instantaneous temperature measurement, which is important for real life

applications where damage is generally mixed with temperature.

The evaluation board AD5933 exhibits a high level of repeatability. Single location as well as

multiple locations damages on prototype structure can be easily detected by miniature impedance

chip. Even an incipient damage induced in the prototype structure such as loosening of bolts can

also be easily detected. Hence, AD5933 hardware can be used for single and multiple damage

detection and damage quantification. Hence, AD5933 is fully capable of level 1 damage

diagnosis in any real-life RC or steel structure. The correct extraction of equivalent parameters,

however via AD5933 cannot done, which can be attributed as its drawback. It is therefore, not

suitable for level ‘2’ diagnosis, which is possibly due to the fact that the AD5933 measurements

differ in their absolute value to the LCR meter acquired signature.

15

REFERENCES

1. Aktan, A. E., Catbas, F. N., Grimmelsman, K. A. and Tsikos, C. J., “Issues in

infrastructure health monitoring for management,” Journal of Engineering Mechanics

ASCE 126: 711–724 (2000).

2. Bhalla, S., “A mechanical impedance approach for structural identification, health

monitoring and non-destructive evaluation using piezo-impedance transducers,” PhD

Thesis Nanyang Technological University Singapore (2004).

3. Park, G., Cudney, H. H. and Inman, D. J., “Impedance-Based Health Monitoring of Civil

Structural Components”, Journal of Infrastructure Systems, ASCE, 6(4): 53-160 (2000).

4. Giurgiutiu, V., Redmond, J., Roach, D. and Rackow, K., “Active sensors for health

monitoring of ageing aerospace structures”, Proceedings of the SPIE Conference on

Smart Structures and Integrated Systems, edited by N. M. Wereley, SPIE 985: 294-305

(2000).

5. Bhalla, S. and Soh, C. K., “Structural impedance based damage diagnosis by piezo-

transducers,” Eartquake Engineering Structural Dynamics 32: 1897-1916 (2003).

6. Soh, C. K. and Bhalla, S., “Calibration of Piezo-Impedance Transducers for Strength

Prediction and Damage Assessment of Concrete,” Smart Materials and Structures 14(4):

671-684 (2005).

7. Lim, Y. Y., Bhalla, S. and Soh, C. K., “Structural identification and damage diagnosis

using self-sensing piezo-impedance transducers,” Smart Materials and Structures 15:

987-995 (2006).

8. Yang, Y. W., Bhalla, S., Wang, C., Soh, C. K. and Zhao, J., “Monitoring of rocks using

smart sensors,” Tunneling and Underground Space Technology 22: 206-221 (2007).

16

9. Bhalla, S. and Moharana, S., “A refined shear lag model for adhesively bonded piezo-

impedance transducers,” Journal of Intelligent Material Systems and Structures, 24(1):

33-48 (2012).

10. Moharana, S. and Bhalla, S., “Numerical investigation of shear lag effect on PZT –

Structure integration: Review and applications,” Current Science, 103(6): 685-696

(2012).

11. Talakokula, V., Bhalla, S., and Gupta, A., “Corrosion assessment of RC structures based

on equivalent structural parameters using EMI technique,” Journal of Intelligent

Materials System and Structures, 25: 484-500 (2014).

12. Analog Devices, “1 MSPS, 12 Bit Impedance Converter Network Analyzer”,

http://www.analog.com/en/index.html (2014).

13. Overly, T. G., Park, G., Farinholt, K. M. and Farrar, C. R. “Development of an extremely

compact impedance-based wireless sensing device,” Smart Materials and Structures

17(6): 1-9 (2008).

14. Park, S., Kim, J. W., Lee, C. and Park, S. K., “Impedance-based wireless debonding

condition monitoring of CFRP laminated concrete structures” NDTE International 44:

232-238 (2011).

15. Xu, B. and Giurgiutiu, V., “A low-cost and field portable electromechanical (E/M)

impedance analyzer for active structural health monitoring,” In: Proc. 5th International

Workshop on Structural Health Monitoring Stanford University September 15–17(2005).

16. Liang, C., Sun, F.P. and Rogers, C.A., “Coupled Electro-Mechanical Analysis of

Adaptive Material Systems-Determination of the actuator power consumption and system

energy transfer,” Journal of Intelligent Material Systems and Structures l5:12-20 (1994).

17

17. Peairs, D. M., Park, G. and Inman, D. J., “Improving accessibility of the impedance-

based structural health monitoring method” Journal of Intelligent Material Systems and

Structures 15(2):129–139 (2004).

18. Panigrahi, R., Bhalla, S. and Gupta, A., “A cost-effective variant of electromechanical

impedance technique for structural health monitoring,” Experimental Techniques 34(2):

25-29 (2009).

19. Bhalla, S., Gupta, A., Bansal, S. and Garg, T., “Ultra low-cost adaptions of electro-

mechanical impedance technique for structural health monitoring,” Journal of Intelligent

Material Systems and Structures 20: 991-999 (2009).

20. Quinn, W., Kelly, G., and Barrett, J., “Development of an embedded wireless sensing

system for the monitoring of concrete,” Structural Health Monitoring- An International

Journal 11(4):381-392(2012).

21. Park, S., Grisso, B. L. and Inman, D. J., “MFC-based structural health monitoring using a

miniaturized impedance measuring chip for corrosion detection,” Research in

Nondestructive Evaluation 18(2): 139-150 (2007).

22. Park, S., Lee, J. J. and Yun, C. B., “Electro-mechanical impedance-based wireless

structural health monitoring using PCA-data compression and k-means clustering

algorithm,” Journal of Intelligent Material Systems and Structures 19 (4): 509-520

(2008).

23. Na, S. and Lee, H. K., “Resonant frequency range utilized electro-mechanical impedance

method for damage detection performance enhancement on composite structures,”

Composite Structures 94: 2383-2389 (2012).

18

24. Providakis, C. and Liarakos, E., “T-WiEYE: An early-age concrete strength development

monitoring and miniaturized wireless impedance sensing system,” Procedia Engineering

10: 484–489 (2011).

25. Taylor, S. G., Farinholt, K. M., Park, G., Farrar, C. R. and Todd, M. D., “Multi-scale

wireless sensor node for impedance-based SHM and long-term civil infrastructure

monitoring” Smart Structures and Systems 6(5): 661-673 (2010).

26. Kaur, N. and Bhalla, S., “Combined Energy Harvesting and Structural Health Monitoring

Potential of Embedded Piezo Concrete Vibration Sensors”, Journal of Energy

Engineering, American Society of Civil Engineers-ASCE (published online, DOI:

10.1061/(ASCE)EY.1943-7897.0000224 , (2014).

27. Bhalla, S. and Gupta, A., “A novel vibration sensor for concrete structures.” Invention

disclosure (FT/IPR/CE/SB/2007/0570), Foundation for Innovation and Technology

Transfer (FITT), IIT Delhi, Patent application no. 1011/DEL/2011 (2007).

28. SSDL “Smart Structures and Dynamic Laboratory” Department of Civil Engineering, IIT

Delhi (2014). <http://ssdl.iitd.ac.in/>

LIST OF FIGURES

Figure 1: Evaluation board AD5933.

Figure 2: User interface of AD5933.

Figure 3: Aluminum strip specimen for repeatability check.

Figure 4: Repeatability signatures of structure in (a) healthy condition and (b) damaged

condition.

Figure 5: Comparison between healthy and damaged condition for aluminum strip

19

Figure 6: Comparison between AD5933 and LCR meter signature for (a) actual values and

(b) normalized with respective peak values.

Figure 7(a): RC beam showing CVS location, notch for damage and different damaged states.

Figure 7(b): Experimental setup for acquiring the EMI signature.

Figure 8(a): Comparison of typical conductance (G) signature acquired using AD5933.

Figure 8(b): Variation of typical equivalent parameters (x and y) for undamaged state.

Figure 8(c): RMSD of conductance plots acquired using AD5933 for undamaged and different

states of damage.

Figure 8(d): RMSD of conductance plots acquired using LCR meter for undamaged and

different states of damage.

Figure 9(a): Experimental set up for 2D plate structure.

Figure 9(b): Steel plates with cover plates and PZTs showing panel numbers.

Figure 10: RMSD vs Change in torque.

Figure 11: Damages in the steel plate showing (a) Damage-1 in panel number 15 (b) Damage-

2 in panel number 26 (c) Damage-3 in panel number 6.

Figure 12(a): RMSD values of 30 panels for damage-1 by AD5933.

Figure 12(b): RMSD values of 30 panels for damage-2 by AD5933.

Figure 12(c): RMSD values of 30 panels for damage-3 by AD5933.

Figure 13: Multiple damage scenario in steel plates showing (a) Damage 1 and 2 in panel no.

15 and 26 (b) Damage 1 and 3 in panel no. 15 and 6 (c) Damage in 1, 2 and 3 in

panel no. 15, 26 and 6.

Figure 14: RMSD values of 30 panels under multiple damage scenarios for damage (a) 1 & 2

(b) 1 &3 (c) 1, 2 & 3.

20

Figure 1: Evaluation board AD5933.

21

Figure 2: User interface of AD5933.

22

Figure 3: Aluminum strip specimen for repeatability check.

PZT Patch covered with

adhesive layer

Damage (Hole)

23

(a)

(b)

Figure 4: Repeatability signatures of structure in (a) healthy condition and (b) damaged

condition.

0.850

0.854

0.858

0.862

0.866

0.870

0.874

0.878

0.882

64.0 64.4 64.8 65.2 65.6 66.0 66.4 66.8 67.2

Co

nd

uct

ance

(S

)

Frequency (kHz)

G2

G1

RMSD = 0.031 %

0.862

0.864

0.866

0.868

0.870

0.872

0.874

0.876

0.878

0.880

65 65.1 65.2 65.3 65.4 65.5 65.6 65.7 65.8 65.9 66

Co

nd

uct

ance

(S

)

Frequency (kHz)

G2

G1

RMSD = 0.025 %

24

Figure 5: Comparison between healthy and damaged condition for aluminum strip.

0.850

0.854

0.858

0.862

0.866

0.870

0.874

0.878

0.882

64.0 64.5 65.0 65.5 66.0 66.5 67.0

Co

nd

uct

ance

(S

)

Frequency (kHz)

Undamaged

condition

Damaged

condition

RMSD = 19.6 %

25

(a)

(b)

Figure 6: Comparison between AD5933 and LCR meter signature for (a) actual values and (b)

normalized with respective peak values.

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

64.0 64.5 65.0 65.5 66.0 66.5 67.0

Co

nd

uct

ance

(S

)

Frequency (kHz)

LCR Meter

AD5933

0.00

0.20

0.40

0.60

0.80

1.00

1.20

64.0 64.5 65.0 65.5 66.0 66.5 67.0

Co

nd

uct

ance

(S

)

Frequency (kHz)

LCR Meter

AD5933

26

(a)

(b)

Figure 7: (a) RC beam showing CVS location, notch for damage and different

damaged states.

(b) Experimental setup for acquiring the EMI signature.

Damaged: State 2 Damaged: State 3 Damaged: State 4 Undamaged: State 1

1 2 3 4 5 6 7 8 9

11-19 10

15 mm 25 mm

Embedded CVS (typ.)

at location 1

Notch for damage

Laptop AD5933

RC Beam

27

(a) (b)

(c) (d)

Figure 8: (a) Comparison of typical conductance (G) signature acquired using AD5933.

(b) Variation of typical equivalent parameters (x and y) for undamaged state.

(c) RMSD of conductance plots acquired using AD5933 for undamaged and

different states of damage.

(d) RMSD of conductance plots acquired using LCR meter for undamaged and

different states of damage.

(a) (b)

(c)

Figure 8: Comparison of (a) typical conductance (G) signature and (b) RMSD of conductance

plots acquired using AD5933 for undamaged and different states of damage.

(c) Variation of typical equivalent parameters (x and y) for undamaged state.

0.045

0.046

0.047

0.048

0.049

85 86 87 88 89 90

Co

nd

uct

ance

(G

, m

S)

Frequency (kHz)

1.5

1.7

1.9

2.1

2.3

2.5

1 2 3 4 5 6 7 8 9 10111213141516171819R

MS

D (

%)

Element

Damaged-State 2

Damaged-State 3

Damaged-State 4

Damage

Location

-100

-50

0

50

100

150

-10

-8

-6

-4

-2

0

2

4

6

8

10

80 85 90 95 100

y(u

nit

)

x(u

nit

)

Frequency (kHz)

x (unit)

y (unit)

Undamaged (State 1)

Damaged (State 2)

Damaged (State 3)

Damaged (State 4)

-100

-50

0

50

100

150

-10

-8

-6

-4

-2

0

2

4

6

8

10

80 85 90 95 100

y (u

nit

)

x (u

nit

) Frequency (kHz)

x (unit)

y (unit)

1.5

1.7

1.9

2.1

2.3

2.5

1 3 5 7 9 11 13 15 17 19

RM

SD

(%

)

Element

Damaged (State 2)

Damaged (State 3)

Damaged (State 4)

Damage

Location

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

1 3 5 7 9 11 13 15 17 19

RM

SD

(%

)

Element

Damaged (State 2)

Damaged (State 3)

Damaged (State 4) Damage

Location

28

Figure 9: (a) Experimental set up for 2D plate structure.

(b) Steel plate with cover plates and PZT patches showing panel numbers.

(a)

(b)

Figure 9: (a) Experimental set up for 2D plate structure.

(b) Steel plate with cover plates and PZT patches showing panel numbers.

Local PC AD5933 Remote PC

Cover Plates

PZT Patch

(typical)

29

Figure 10: RMSD vs Change in torque.

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40

RM

SD

val

ues

(%

)

Change in torque ∆T (N-m)

30

Figure 11: Damages in the steel plate showing

(a) Damage-1 in panel number 15

(b) Damage-2 in panel number 26

(c) Damage-3 in panel number 6.

(a) (b)

(c)

Figure 11: Damages in the steel plate showing

(a) Damage-1 in panel number 15

(b) Damage-2 in panel number 26

(c) Damage-3 in panel number 6.

Damage-3

(Panel no. 6)

Damage-1

(Panel no. 15) Damage-2

(Panel no. 26)

31

(a)

(b)

(c)

Figure 12: (a) RMSD values of 30 panels for damage-1 by AD5933.

(b) RMSD values of 30 panels for damage-2 by AD5933.

(c) RMSD values of 30 panels for damage-3 by AD5933.

31

32

33

34

35

36

RM

SD

Val

ues

(%

)

Panels along Plate Length

Damaged panel no. 15

31

32

33

34

35

36

RM

SD

Val

ues

(%

)

Panels along Plate Length

Damaged panel no. 26

31

32

33

34

35

36

RM

SD

Val

ues

(%

)

Panels along Plate Length

Damaged panel no. 6

32

Figure 13: Multiple damage scenario in steel plates showing

(a) Damage 1 and 2 in panel no. 15 and 26

(b) Damage 1 and 3 in panel no. 15 and 6

(c) Damage in 1, 2 and 3 in panel no. 15, 26 and 6.

(a) (b)

(c)

Figure 13: Multiple damage scenario in steel plates showing

(a) Damage 1 and 2 in panel no. 15 and 26

(b) Damage 1 and 3 in panel no. 15 and 6

(c) Damage in 1, 2 and 3 in panel no. 15, 26 and 6.

Damage 1, 2 & 3

Damage 1 & 2

Damage 1 & 3

33

(a)

(b)

(c)

Figure 14: RMSD values of 30 panels under multiple damage scenarios for damage (a) 1

& 2 (b) 1 &3 (c) 1, 2 & 3.

20

25

30

35

40

RM

SD

Val

ue

(%)

Panels along Plate Length

Damaged 2 and 1

20

22

24

26

28

30

RM

SD

Val

ue

(%)

Panels along Plate Length

Damaged 1 and 3

25

29

33

37

41

RM

SD

Val

ue

(%)

Panels along Plate Length

Damaged 1, 2 and 3