CIV5887/6887: Literature Review of Impedance-Based Damage Detection

This literature review provides an overview of electro-mechanical impedance (EMI)-based damage detection techniques for civil infrastructures. It discusses the application of piezoelectric transducers for monitoring changes in structural impedance related to damage, focusing on concrete structures. The review covers the theoretical background, experimental studies, and the influence of environmental factors like temperature and humidity on impedance signatures. It highlights the advantages of EMI-based methods, such as localized sensing and long-term consistency, and references studies on crack detection, concrete curing effects, and wireless monitoring systems. The review concludes by emphasizing the potential of EMI-based techniques for active monitoring of civil structures, even under varying environmental conditions, and suggests further research into thickness mode impedance changes.

ELECTRO-MECHANICAL-IMPEDANCE-BASED DAMAGE DETECTION FOR CIVIL
INFRASTRUCTURES
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Introduction
The interest and focus on the ability to check a structure as well as to detect the damages at the
earliest possible stages are extensive throughout the mechanical, civil as well as aeroscope
engineering societies and communities. Over the last two decades, numerous SHM, as well as
non-destructive evaluation methods, have been documented in the literature, depending on either
the local or even the global interrogation of structures (Chen & Liu, 2012). Impedance-based
SHM offers an interface between the conventional ultrasonic methods and global vibration
methods. This paper provides a report on the most recent technological as well as theoretical
developments that have been witnessed in the application of electro-mechanical-based damage
detection as applied in electrical structures.
Concrete structures in civil engineering are often susceptible to different kinds of damage.
During the early stages for instance during the curing of concrete, cracks are initiated as a result
of high mechanical stresses resulting from the moisture diffusion as well as temperature
fluctuation for hydration. Still, during the lifetime of such structures, the growth of crack may
result in the structures failing. It is of importance to take note that the durability of such type of
structures is linked to mechanical, chemical as well as physical deterioration, as follows:
 Concrete carbonation
 Corrosion of reinforcement fibers
 Large differences in temperature (Dziendzikowski, Niedbala, Kurnyta, Kowalczyk &
Dragan, 2018)

Hence, in the recent past years, the methods of structural health monitoring are adopted in
detection of incipient damage to enhance timely maintenance as well as the extension of
operation life of each of various structures.
Still, failures in structures may result in loss of lives as well as the destruction of property.
Furthermore, the complex as well as the large nature of civil structures renders the inspection
quite expensive and at times not reliable. Thus, new methods were developed and came out for
checking the various civil engineering structures. One of most important methods which have
been tested for the detection of damage in aeronautical, civil as well as mechanical structures is
the technique based on the electrochemical impedance. Nevertheless, this method still needs
more studies for its enhancement concerning applications involving various concrete structures
(Fan, Li & Hao, 2016).
Review of Electro-mechanical-impedance-based damage detection for civil infrastructures
The technique of structural health monitoring depending on electromechanical impedance was
initially proposed in 1994. The technique makes use of piezoelectric transducers joined to the
structure for monitoring the variations in damping, stiffness as well as mass. As a result of
difficulty in attaining the mechanical impedance of structure, the measurements of electrical
impedance are obtained through the use of piezoelectric transducers that are coupled to system.
Assuming the features of piezoelectric transducers patch do not change over time, the variation
in electrical impedance will be related directly to the variations in mechanical impedance that is
influenced by availability of damage (Feng, Dandjekpo & Zhou, 2012). The process of
measurement is described and quantified by electromechanical model shown below

Figure 1: Electromechanical model of SHM technique (Feng, Dandjekpo & Zhou, 2012)
Structural health monitoring based on the electro-mechanical impedance is simple as well as a
straightforward approach. The basic concept of technique is to establish the changes in the
mechanical impedance of structure that is monitored as the scenario compared with against
without damage. The measurement of mechanical impedance is conducted indirectly via the
measurement of electrical impedance with the help of piezoelectric transducers that are coupled
to the structure being monitored or incorporated to the same (Lim & Soh, 2012).
The measurements are conducted both for the pristine condition as well as during the structure
lifetime. Taking into consideration the coupling features between the piezoelectric transducers
patch and the structure, the presence of damage may be verified by taking note of changes in the
electrical impedance signal. This change may be quantified with help of an adequately defined
metrics of damage.
Among the initially published findings on this subject for the civil structures demonstrated that
the electrochemical impedance technique was successful in the detection of cracks within the
context of unloading and loading of a prototype form by a bridge segment. The structure was
made using reinforced concrete. Other researches have generated relatively reliable outcomes for

instance in the detection of damage in the concrete plates in which the damage was generated
from a cutting blade.
In yet another study, the effect of a concrete cure on the signals of impedance was taken into
consideration. For such an aim, there was the introduction of a piezoelectric transducer in the
concrete plate during the process of manufacturing. The study established that the impedance
signals varied when the samples were subjected to compression, nevertheless, the authors did not
carry out more elaborate studies in the presence of incipient damage when the tests were being
conducted. A study regarding the influence of signals of impedance of detachment of
piezoelectric transducers was as well carried out (Martowicz, Sendecki, Salamon, Rosiek & Uhl,
2016). In such a case, bonding of sensors was done to the steel fibers that were used in
reinforcing the concrete structures. The effect of loading as well as temperature on signals of
impedance of a piezoelectric sensor coated with a structure of protection with epoxy and cement
was as well investigated.
A wireless monitoring system pegged on impedance signals was developed in a study conducted
recently. The admittance signal module was used for damage prognosis in a reinforced concrete
structure. A network of sensors was included in the pouter as well as inner parts of structure in
this regard, nevertheless, when adopting the admittance module, consideration should be made
that the impedance signals include the imaginary segment of impedance signal as it depends on
the variation of temperature.
Under high ranges of frequency deployed in the impedance-based technique, the sensing region
of piezoelectric transducer is confined to an area close to piezoelectric transducer sensor. The
localized nature of sensing area offers advantages in the sense the impedance sensor tends to be

less sensitive to the changes in the condition boundary or even any other operational vibrations
that often affect the lower-order global modes (Park, Kim, Hong, Mascarenas & Lynch, 2010).
Elaborate experimental studies were reported by Raju on the dimensions that influence the
impedance-based techniques, for instance, the levels of actuator excitation, length of test wire,
multiplexing as well as changes in the boundary conditions. Raju concluded that the changes in
such parameters do not have any significant effect on signatures of impedance. Zhou, Ha &
Inman (2010) studied numerous issues associated with the practical implementation of method of
impedance. The long-term consistency of impedance signature within two months has been
studied and prefect repeatability has been noted (Zhou, Ha & Inman, 2010). Their investigation
as well as inclusive of protection of piezoelectric sensor against the effects of a humid
surrounding with the use of silica gel layer, multiplexing an avalanche of piezoelectric
transducers in the optimization of time of sensor interrogation and probable adoption of double-
sided adhesive tapes in the bonding of piezoelectric transducer sensors.
The effects of changes in temperature on dynamic interaction between a patch of piezoelectric
transducers and host structure were investigated by Park et al. (2012). In as much as the study
reported that changes in the temperature would result in a variation in the impedance signatures,
such effects were minimal in comparison with variations as a result of structural damages (Park,
Chang, Kim, Yun & Inman, 2010). In other words, the thermal effects do not have an effect on
significant levels on the resonant frequency estimation of measurement of impedance. Hence, the
researchers suggested that the effects of variation in temperature could be ignored to
acknowledge the vertical as well as horizontal changes of points of resonant frequency in
measurement of impedance.

As a result, the above works of literature explicitly illustrate the impedance-based damage
detection methods may be used in the active monitoring of civil structures even as with the
availability of significant changes of factors of environment for instance temperature or
humidity.
The basic principle of impedance-based technique is to check on the electrical point impedance
of a piezoelectric transducer patch that is bonded to a structure (Park, Chang, Kim, Yun &
Inman, 2010). The physical variations in the structure result in variations in the structural
mechanical impedance that may, in turn, initiate variations in electrical impedance of
piezoelectric transducer. The applications of piezoelectric transducers to civil structures started
relatively in the recent past. The use of piezoelectric transducers was reported by Zheng et al.,
(2019) for the detection of damage on the laboratory sized truss structure alongside a prototype
truss joint. The successful applications of method were reported by Tseng et al. and Bhalla on
concrete as well as other civil-related infrastructures. In as much as the previous studies have
been taken into consideration the variations of a lateral mode-impedance of piezoelectric
transducers, a new study are suggested in which the changes in the thickness of mode impedance
are suggested (Zheng et al., 2019).

References
Chen, B., & Liu, W. (2012). A high computational power wireless sensor network for distributed
structural health monitoring. International Journal of Sensor Networks, 11(3), 137-147
Dziendzikowski, M., Niedbala, P., Kurnyta, A., Kowalczyk, K., & Dragan, K. (2018). Structural
health monitoring of a composite panel based on pzt sensors and a transfer impedance
framework. Sensors, 18(5), 1521
Fan, X., Li, J., & Hao, H. (2016). Piezoelectric impedance-based damage detection in truss
bridges based on time-frequency ARMA model. Smart Struct. Syst, 18(3), 501-523
Feng, X., Dandjekpo, E. T., & Zhou, J. (2012). Post-Earthquake Damage Detection Using
Embedded Electro-Mechanical Impedance Sensors for Concrete Dams. In The 15 th
World Conference on Earthquake Engineering (pp. 24-28) Li, J. C., Lin, L., Wu, D., Li,
X. M., & Lei, M. K. (2016). Elevated excitation voltage electrical impedance
measurement system of electro-mechanical impedance-based structural health
monitoring. Experimental Techniques, 40(1), 381-390
Lim, Y. Y., & Soh, C. K. (2012). Effect of varying axial load under fixed boundary condition on
admittance signatures of electromechanical impedance technique. Journal of Intelligent
Material Systems and Structures, 23(7), 815-826
Martowicz, A., Sendecki, A., Salamon, M., Rosiek, M., & Uhl, T. (2016). Application of
electromechanical impedance-based SHM for damage detection in bolted pipeline
connection. Nondestructive Testing and Evaluation, 31(1), 17-44

Park, J. H., Kim, J. T., Hong, D. S., Mascarenas, D., & Lynch, J. P. (2010). Autonomous smart
sensor nodes for global and local damage detection of prestressed concrete bridges based
on accelerations and impedance measurements. Smart Structures and Systems, 6(5-6),
711-730
Park, S., Chang, H., Kim, J. W., Yun, C. B., & Inman, D. (2010). Wireless structural health
monitoring and early-stage damage detection using piezoelectric impedance sensors.
In Earth and Space 2010: Engineering, Science, Construction, and Operations in
Challenging Environments (pp. 3853-3862)
Park, S., Park, S., Kim, J., & Chang, H. (2010, May). Debonding condition monitoring of a
CFRP laminated concrete beam using piezoelectric impedance sensor nodes.
In Proceedings for FraMCos-7—7th International Conference on Fracture Mechanics of
Concrete and Concrete Structures, Jeju, Korea (pp. 23-28)
Zheng, Y., Liu, K., Wu, Z., Gao, D., Gorgin, R., Ma, S., & Lei, Z. (2019). Lamb waves and
electro-mechanical impedance based damage detection using a mobile PZT transducer
set. Ultrasonics, 92, 13-20
Zhou, D., Ha, D. S., & Inman, D. J. (2010). Ultra-low-power active wireless sensor for structural
health monitoring. Smart Structures and Systems, 6(5-6), 675-687