Surface-bonded Piezoelectric Transducers Research Articles

Shear stress identification in plate rubber bearing using surface-bonded piezoelectric transducer: A feasibility study

This paper presented a preliminary study on the feasibility of shear stress identification in plate rubber bearings using surface-bonded piezoceramic (PZT) transducers. A PZT-rubber bearing structural dynamic interaction model was developed to analyze the shear stress effect on the electromechanical admittance (EMA, inverse of impedance) by introducing a mechanical impedance system consisting of parallel mechanical elements. 3D finite element (FE) model of a full-sized plate rubber bearing was generated to detect shear stress using the EMA signatures. Proof-of-concept experiment was finally conducted on two plate rubber bearings subjected to shearing force, during which the process was monitored by three PZT sheets arranged at different loci. Theoretical, numerical and experimental results demonstrated that identification results of PZT transducers were closely related to the PZT location, shear stress in rubber bearings were generally in linear relationship with the peak values of EMA spectrum and its statistically quantifiable indicators.

Real-time monitoring of residual strength in corroding steel reinforcement using ultrasonic-guided waves and multi-physics modelling

Corrosion-induced material strength degradation is a major threat to the service life of reinforced concrete (RC) structures. Continued mass loss and pit formation after the initiation of corrosion in reinforcing steel consequently results in strength degradation. In this study, a non-destructive structural health monitoring (SHM) approach using ultrasonic guided waves with multi-physics modelling to monitor and forecast strength degradation of corroding steel is presented. Surface-bonded piezoelectric wafer transducers (PWTs) are used for actuating and sensing of guided waves in order to correlate the group velocity and amplitude of flexural wave modes with the strength reduction. The major findings of the work are presented in the form of empirical relationships between guided wave characteristics with reduced yield, ultimate, and buckling strength of corroded steel. It is observed that for a rebar of 12 mm diameter having slenderness ratio between 8 and 10, a 10% increase in amplitude and 8.44% increase in group velocity of flexural mode for corroding steel indicates a corresponding reduction of 10.278% in yield strength, 10.277% in ultimate strength, and 4.45% in buckling strength in progression phase of corrosion. A multi-physics numerical model of corrosion in RC structures that considers the effect of local exposure and environment is then elucidated with deviation less than 6.34% from experimental results in order to forecast the mass loss. The presented data fusion strategy, which combines guided wave-based monitoring and multi-physics modelling finds valuable application in assessing the current state of degradation in structural performance and strength-based service life prediction.

An efficient Lamb wave-based virtual refined time-reversal method for damage localization in plates using broadband measurements

This study proposes a modified virtual time-reversal (VTR) algorithm for baseline signal-free damage detection in plate-like structures. The physical actuation and sensing of Lamb waves are performed using a broadband Gaussian excitation instead of the conventional narrowband modulated tone burst excitations. The forward response and the reconstructed signal due to the time-reversal process for a narrowband input signal are then constructed virtually using the broadband transfer function. The method eliminates the possibility of numerical errors encountered in the conventional VTR method based on narrowband excitations. It is also more efficient than the traditional VTR algorithm because it can probe at multiple excitation frequencies using a single measurement for each sensing path. This modified VTR algorithm is employed in the recently developed refined time-reversal method (RTRM), which uses an extended signal length of the reconstructed signal for computing damage index (DI) and probes the structure at the best reconstruction frequency. The new method is termed the virtual refined time-reversal method (VRTRM). The DIs based on the VRTRM are used in the reconstruction algorithm for probabilistic inspection of defects to achieve baseline signal-free localization of damages. The efficacy of the proposed VRTRM for damage localization is experimentally verified with the established technique RTRM. Experiments are performed in an aluminium plate equipped with a network of surface-bonded piezoelectric patch transducers to illustrate the conventional VTR’s pitfalls and the modified VTR’s accuracy for a single mass damage scenario. The results show that the proposed VRTRM is as accurate as the established technique RTRM in estimating the reconstructed signals and localizing a block mass damage. Finally, the VRTRM is shown to localize in a dual damage scenario with excellent accuracy. In contrast, the conventional main mode-based VTR method fails to localize the damages with or without single-mode tuning.

Immunity of the second harmonic shear horizontal waves to adhesive nonlinearity for breathing crack detection

High-order harmonic guided waves are sensitive to micro-scale damage in thin-walled structures, thus, conducive to its early detection. In typical autonomous structural health monitoring (SHM) systems activated by surface-bonded piezoelectric wafer transducers, adhesive nonlinearity (AN) is a non-negligible adverse nonlinear source that can overwhelm the damage-induced nonlinear signals and jeopardize the diagnosis if not adequately mitigated. This paper first establishes that the second harmonic shear horizontal (second SH) waves are immune to AN while exhibiting strong sensitivity to cracks in a plate. Capitalizing on this feature, the feasibility of using second SH waves for crack detection is investigated. Finite element (FE) simulations are conducted to shed light on the physical mechanism governing the second SH wave generation and their interaction with the contact acoustic nonlinearity (CAN). Theoretical and numerical results are validated by experiments in which the level of the AN is tactically adjusted. Results show that the commonly used second harmonic S0 (second S0) mode Lamb waves are prone to AN variation. By contrast, the second SH0 waves show high robustness to the same degree of AN changes while preserving a reasonable sensitivity to breathing cracks, demonstrating their superiority for SHM applications.

A machine learning framework for guided wave-based damage detection of rail head using surface-bonded piezo-electric wafer transducers

Due to repeated heavy loads, environmental conditions and non-frequent monitoring, the rail is subjected to heavy damage resulting in sudden failure. Hence, a frequent, faster, and efficient monitoring strategy is required. This paper attempts to investigate the application of guided wave (GW) generated through surface-bonded piezo-electric wafer transducer (PWT) to detect damages in rail at high frequencies. Firstly, a combined experimental and simulation study is presented in an effort to understand the dispersion characteristics of guided wave and its interaction with head damages in a relatively small rail specimen. The numerical simulation results are validated with those obtained from the experiments showing a good agreement between them. Secondly, a framework based on the machine learning algorithm is proposed to efficiently detect damage in rail head. Numerous inseparable guided wave modes are observed at higher frequencies implying the inability to detect damage through specific mode. Therefore, a machine learning framework is trained using time, frequency, and time–frequency domain features of the signal. Total 672 numerical simulations of different types of damage with different severity and location in the rail head are carried out to train and validate the model. It is found that GW generated through surface bonded PWTs is able to detect minimum defect size of 5% of head area with 1 mm thickness. Finally, the proposed framework is tested using simulation and experiment results of arbitrary damage in the rail head. The error in estimating severity was found to be in the range from 2.00% to 16.67%.

Cracking Diagnosis in Fibre Reinforced Concrete Cubes and Cylinders with Synthetic Fibres using a PZT-based Health Monitoring System

This paper carried out experimental research of concrete specimens with synthetic fibres under repeated splitting tension and uniaxial compression to investigate the efficiency of a proposed health monitoring methodology that implements surface-bonded piezoelectric transducers. The developed technique uses small-sized custom-made devices for diagnosing damage due to concrete cracking caused by the imposed repeated loading at various load levels. A test program of standard 150/300 mm cylinders and 150 mm cubes made of plain and fibre reinforced concrete subjected to splitting tensile and compressive repeated loading is presented and discussed. The proposed method utilises the frequency response measurements of a network of small-sized piezoelectric patches mounted to the surface of the tested specimens in order to detect the onset of damage since cracking has probably been developed in the inner concrete, whereas no visible cracks appeared on their surface. The objectives of this study also include development of a quantitative assessment procedure of damage using the statistical index values distribution at various points of measurements. The influence of distance, type of material (plain or fibrous concrete) and damage level triggers changes in the measurements of the piezoelectric transducers and the adopted statistical index seems to be a reliable assessment tool for damage quantification. Further, for the first time, a wireless and portable structural health monitoring system display feasible detection of premature cracks for damage prognosis in fibre reinforced concrete structural members.

Transfer matrix modeling on a longitudinal-bending coupled piezoelectric transducer with single-phase excitation: Analysis and verification.

Surface-bonded type piezoelectric transducers have the advantages of simple structure, easy miniaturization, and flexible designand have been widely employed as the stator of ultrasonic motors. In order to simplify the control system, a surface-bonded type single-phase excited piezoelectric transducer operating in the longitudinal-bending coupling vibration is proposed, modeled, and validated in this study. Using the asymmetrical excitation effect, the longitudinal-bending coupled vibration is generated in the proposed piezoelectric transducer only applied with a single-phase electrical signal, leading to the production of the elliptical motion at its driving tip. The proposed transducer holds the advantages of compact structure, simple control system, and low manufacturing costs. The transfer matrix method, which is an efficient and fast semi-analytic computation solution, is employed to develop a dynamic model for the proposed transducer in this study in order to provide a general modeling method for surface-bonded type piezoelectric transducers operating with the longitudinal-bending coupled vibration. A novel longitudinal-bending coupled vibration transfer matrix is created first for surface-bonded type piezoelectric composite element. Then, a general semi-analytical electromechanical coupling model is developed to analyze dynamic behaviors of the proposed piezoelectric transducer. Finally, experimental validation is carried out on the prototype of the proposed piezoelectric transducer and compared with the calculation results using the developed transfer matrix model. Experimental results matched well with the calculation results, which confirmed the correctness of the transducer designand verified the feasibility of the developed transfer matrix model. The proposed piezoelectric transducer presents the potential application for linear ultrasonic motors.

Role of transducer inertia in generation, sensing, and time-reversal process of Lamb waves in thin plates with surface-bonded piezoelectric transducers

An analytical model is presented for the generation, sensing, and time-reversible process of Lamb waves in thin isotropic plates with surface-bonded piezoelectric wafer transducers, incorporating the shear-lag effect of the bonding layer and inertia effects of the system in transducer modeling. A one-dimensional dynamic shear-lag model for the actuator-plate interaction is used to obtain the shear stress distribution at the actuator-plate interface. The Lamb wave solution for the plate under this shear traction excitation is obtained using the two-dimensional (2D) elasticity equations. A consistent sensor-plate interaction model incorporating the shear-lag and inertia effects is developed to determine the induced sensor voltage from the Lamb strain at the plate surface. The model is validated by comparing it with the 2D coupled piezoelasticity-based finite element simulation and experimental data. Detailed parametric studies are conducted to illustrate the effect of inclusion of inertia of actuator, sensor, adhesive, and plate in the transducer modeling on the Lamb wave generation, sensing, time reversibility, and the system’s best reconstruction frequency, and to ascertain how various geometrical and material parameters of the system influence the same. The developed closed-form solution will be immensely useful for the design of Lamb wave based structural health monitoring systems.

Monitoring corrosion-induced thickness loss of stainless steel plates using the electromechanical impedance technique

Stainless steel plates are widely used in steel structures. Corrosion damage of a stainless steel plate can induce the thickness and mass loss of the stainless steel plate. The corrosion-induced thickness loss (CITL) is one of the main reasons for the degradation of the stiffness and bearing capacity of the stainless steel plate, which endangers the safety of the structure and causes economic losses. Therefore, effective monitoring of the CITL of the stainless steel plate can help to ensure the safety of steel structures. In this study, a novel monitoring method for the CITL of the stainless steel plate based on the electromechanical impedance (EMI) technique is presented. The effective mechanical admittance (EMA) of a simply supported thin stainless steel plate under the excitation of a single surface-bonded piezoelectric transducer is derived theoretically; the resonance frequency shift () of the bending vibration mode in the admittance signature is extracted as the CITL-sensitive feature to identify the CITL of the stainless steel plate. The quantitative relationship between and CITL, based on the EMA, is established theoretically for monitoring the CITL of the stainless steel plate. The effectiveness of the proposed method is verified by experiments. The experimental results demonstrate that the proposed method can sensitively identify, accurately quantify and predict the CITL of the stainless steel plate, and has excellent stability and reliability. This method can not only overcome the limitation of the existing statistics-based EMI methods that cannot quantify the CITL, but also compensate for the weakness of commonly-used non-destructive testing methods that cannot quantitatively predict CITL in an on-line monitoring manner. The proposed method provides an effective monitoring and tracking tool for the CITL of the stainless steel plate.

Time reversibility of Lamb waves in thin plates with surface-bonded piezoelectric transducers is temperature invariant at the best reconstruction frequency

The Lamb wave time-reversal method has been widely proposed as a baseline-free method for damage detection in thin-walled structures. Under varying thermal environments, it would require that the time reversibility of Lamb waves is temperature invariant. In this study, we examine the temperature dependence of Lamb waves and its time reversibility using experiments and finite element simulations on isotropic plates with surface-bonded piezoelectric wafer transducers for actuation and sensing. The study is conducted at three different temperatures of the system from 25°C to 75°C for a wide range of excitation frequency. The results indicate that the time reversibility can undergo significant changes due to temperature variations depending on the excitation frequency. However, at the best reconstruction frequency corresponding to the maximum similarity of the reconstructed signal with the original input signal (proposed recently as the probing frequency), the change in the percent similarity with temperature is insignificant. The results also demonstrate that changes in the physical properties of both adhesive layers and piezoelectric transducers with temperature play a dominant role in influencing Lamb wave amplitudes. However, only the change in the characteristics of the adhesive layers is responsible for the temperature dependence of the time reversibility of Lamb waves.

Assessment of wave modulus of elasticity of concrete with surface-bonded piezoelectric transducers

Measurement of the modulus of elasticity of concrete based on wave propagation technique is a critical method to assess condition and performance of concrete materials and structures. In this study, a combined numerical and experimental study is conducted for assessment of wave modulus of elasticity (WMoE) of the fully-cured concrete using surface-bonded PZT (lead zirconate titanate) transducers, also so called smart piezoelectric modules (SPMs). Rayleigh wave (R-wave) acquired from the surface-bonded PZT transducers is selected as the main target signal, and the explicit physical relationship between R-wave and WMoE is applied in signal processing. Piezoelectric solid element and electric load are applied to model the PZT transducers and actuate stress waves in numerical simulation, respectively. The numerical analysis provides a better understanding of surface wave propagation in concrete and sheds light on physical experiment. Effects of excitation frequency, excitation waveform, and size of PZT transducers are first examined in numerical simulation and then validated by physical experiment. Good agreements between the numerical and experimental results show that the Hanning windowed 5-peak or 7-peak sinusoidal tone burst at the frequency range of 40 kHz to 100 kHz is recommended as the excitation signals; while the width-to-thickness ratio of square transducers ranging from 10 to 15 is suggested for selection and design of surface-bonded PZT transducers. Effective measurement of WMoE using the surface-bonded PZT transducers shows great potential for nondestructive evaluation of concrete, and it can be used for condition assessment and health monitoring of concrete structures.

Monitoring of Fiber-Reinforced Composite Single-Lap Joint with Electromechanical Impedance of Piezoelectric Transducer.

The single-lap joint of fiber-reinforced composites is a common structure in the field of structure repair, which has excellent mechanical properties. To study and monitor its quasi-static response behavior under external load, two methodologies called effective structural mechanical impedance (ESMI) and reduced-ESMI (R-ESMI) are presented in this article. A two-dimensional electromechanical impedance (EMI) model for a surface-bonded square piezoelectric transducer (PZT) is adopted to extract more sensitive signatures from the measured raw signatures. There are two major advantages of the monitoring scheme based on ESMI and R-ESMI signatures: (1) excellent monitoring results with less signatures to process, (2) the ability to monitor the quasi-static behavior of a single-lap joint with previously ignored susceptance signatures. Combining the extracted ESMI signatures with the index of root-mean-square deviation, the quasi-static behavior of single-lap joints can be effectively quantified. To test the effectiveness of ESMI methodology, verifying experiments were conducted. The experimental results convincingly demonstrated that the presented ESMI and R-ESMI methodologies have good feasibility in monitoring the quasi-static behavior of a fiber-reinforced composite single-lap joint. The proposed method has potential application in the field of structural health monitoring (SHM).

A novel electromechanical impedance model for surface-bonded circular piezoelectric transducer

The electromechanical impedance (EMI) technique is one of common used methods for damage diagnosis. However, the mechanism of EMI-based damage diagnosing is usually complicated and difficult to be comprehensively described. To solve this problem to a certain extent, a novel EMI model for describing the interaction between piezoelectric transducer (PZT) and host structure is developed in this paper. The developed EMI model has advantages of simplicity in formula and excellent precision in signatures prediction. An efficaciously equivalent SMD (Spring-Mass-Damping) system is adopted to obtain the local structural mechanical impedance (LSMI) and to calculate the equivalent parameters ( ) in the vicinity of PZT. To verify the effectiveness of the novel model, a series of experiments are separately conducted on the specimen under healthy condition and damage condition. Through comparing the predicted curves with the experimental ones, the effectiveness of the developed model is demonstrated when used for predicting signatures, especially for resistance signatures. The developed EMI model has shown the potential application in the field of structural health monitoring and damage diagnosis.

Comparative analysis of signal processing techniques for impedance-based SHM applications in noisy environments

Structural health monitoring (SHM) systems have been extensively studied in recent decades to determine the health statuses of mechanical, naval and aerospace engineering components. Currently, one of the most promising non-destructive tests for the detection of structural damage is the electromechanical impedance (EMI) technique, which uses low-cost, surface-bonded piezoelectric transducers operating both as sensors and actuators. Although many studies have reported the effectiveness of the EMI method, numerous practical issues, such as signal noise effects caused by environmental conditions, may severely affect the detection and quantification of damage. Therefore, this paper presents a comparative analysis of three signal processing techniques used in the context of the EMI method, which have the potential to enhance the detection of structural damage under environmental signal noise effects. These signal analysis methods include (i) damage indices, such as the correlation coefficient deviation metric, computed directly on impedance signatures; (ii) the wavelet transform computed on transducer response signals in the time domain; and (iii) a novel approach of damage feature extraction in the EMI method based on the Hinkley criterion. Experimental tests were carried out to analyse the three signal processing techniques on a damaged aerospace composite carbon fibre structure subjected to various signal noise levels. The experimental results revealed that conventional damage indices and wavelet transform were significantly affected by noise, whereas the proposed approach based on the Hinkley criterion was more effective for detecting damage in noisy environments.

Impact source localisation in aerospace composite structures

The most commonly encountered type of damage in aircraft composite structures is caused by low-velocity impacts due to foreign objects such as hail stones, tool drops and bird strikes. Often these events can cause severe internal material damage that is difficult to detect and may lead to a significant reduction of the structure’s strength and fatigue life. For this reason there is an urgent need to develop structural health monitoring systems able to localise low-velocity impacts in both metallic and composite components as they occur. This article proposes a novel monitoring system for impact localisation in aluminium and composite structures, which is able to determine the impact location in real-time without a-priori knowledge of the mechanical properties of the material. This method relies on an optimal configuration of receiving sensors, which allows linearization of well-known nonlinear systems of equations for the estimation of the impact location. The proposed algorithm is based on the time of arrival identification of the elastic waves generated by the impact source using the Akaike Information Criterion. The proposed approach was demonstrated successfully on both isotropic and orthotropic materials by using a network of closely spaced surface-bonded piezoelectric transducers. The results obtained show the validity of the proposed algorithm, since the impact sources were detected with a high level of accuracy. The proposed impact detection system overcomes current limitations of other methods and can be retrofitted easily on existing aerospace structures allowing timely detection of an impact event.

SHM of single lap adhesive joints using subharmonic frequencies

The increased usage of adhesive bonding as a joining method in modern aerospace components has led to developing reliable ultrasonic health monitoring systems for detection of regions of poor adhesion. Nonlinear acousto-ultrasonic techniques based on higher harmonics and subharmonic frequencies have shown to be sensitive to the detection of micro-voids and disbonds. Nonlinear resonance properties of disbonds generate various nonlinear phenomena such as self-modulation, subharmonics, hysteresis and so on. By exploiting the local natures of these phenomena, this paper demonstrates the use of subharmonics for detection and imaging of flaws in bonded structures. To optimise the experimental testing a two-dimensional analytical model and a three-dimensional finite element analysis simulation were developed for understanding the generation of nonlinear elastic effects with emphasis on subharmonic frequency components. The proposed analytical model qualitatively described the generation of subharmonics but also higher harmonics due to the nonlinear intermodulation of the driving and resonance frequencies associated with the disbonded region. The numerical model was developed by modifying the user defined cohesive element formulation with a bi-linear traction-displacement relationship in order to simulate the interaction of elastic waves with the structural disbond. Whilst the analytical model supported the selection of the driving frequency, the numerical one successfully predicted the generation of subharmonic frequencies originating in the disbonded area. Experimental tests were conducted on a disbonded single lap joint structure using surface-bonded piezoelectric transducers and a laser-Doppler vibrometer, and allowed to validate the analytical and numerical results. It was clearly demonstrated that the nonlinear resonance effects in the form of subharmonics could be used to discriminate reliably regions of poor adhesion in bonded structures. This work can lead to new in situ nonlinear acoustic based health monitoring system for locating and imaging defects in critical aerospace components.

Damage detection of fatigue cracks under nonlinear boundary condition using subharmonic resonance

In recent years, the nonlinear ultrasonic technique has been widely utilized for detecting fatigue crack, one of the most common forms of damage. However, one of limitations associated with this technique is that nonlinearities can be produced not only by damage but also by various intrinsic effects such as boundary conditions. The objective of this paper is to demonstrate the application of a nonlinear ultrasonic subharmonic method for detecting fatigue cracks with nonlinear boundary conditions. The fatigue crack was qualitatively modeled as two elastic, frictionless half spaces that enter into contact during vibration and where the contact obeys the basic Hertz contact law. The nonlinear ordinary differential equation drawn from the developed model was solved with the method of multiple scales. The threshold of subharmonic generation was studied. Different threshold behaviors between the nonlinear boundary condition and the fatigue crack were found that can be used to distinguish the source of nonlinear subharmonic features. To evaluate the proposed method, experiments using an aluminum plate with a fatigue crack were conducted to quantitatively verify the subharmonic resonance range. Two surface-bonded piezoelectric transducers were used to generate and receive ultrasonic wave signals. The experimental results demonstrated that the subharmonic component of the sensing signal could be used to detect the fatigue crack and further to distinguish it from inherent nonlinear boundary conditions.

Application of subharmonic resonance for the detection of bolted joint looseness

Bolted joint structures are prone to bolt loosening under environmental and operational vibrations, which may severely affect the structural integrity. This paper presents a bolt looseness recognition method based on the subharmonic resonance analysis. The bolted joint structure was simplified to a two-degree-of-freedom nonlinear model, and a multiple timescale method was used to explain the phenomenon of the subharmonic resonance and conditions for the generation of subharmonics. Numerical simulation predictions for the generation of the subharmonics and conditions for the subharmonics can be found with respect to the excitation frequency and the excitation amplitude. Experiments were performed on a bolt-joint aluminum beam, where the damage was simulated by loosening the bolts. Two surface-bonded piezoelectric transducers were utilized to generate continuous sinusoidal excitation and to receive corresponding sensing signals. The experimental results demonstrated that subharmonic components would appear in the response spectrum when the bolted structure was subjected to the excitation of twice its natural frequency. This subharmonic resonance method was found to be effective on bolt looseness detection.

Ultrasonic guided wave propagation and disbond identification in a honeycomb composite sandwich structure using bonded piezoelectric wafer transducers

A coordinated theoretical, numerical, and experimental study is carried out in an effort to understand ultrasonic guided wave propagation and interaction with disbond, as well as, to identify disbond in a honeycomb composite sandwich structure using surface-bonded piezoelectric wafer transducers. In contrast to most of the work done previously, a fast and efficient two-dimensional semi-analytical model based on global matrix method is used to study dispersion characteristics as well as transient response of the healthy honeycomb composite sandwich structure subjected to relatively high-frequency piezoelectric wafer transducer excitations. Numerical simulations are then conducted using commercially available finite element package, ABAQUS, in order to explore guided wave propagation mechanisms due to the presence of disbond. Numerical simulations are further broadened to investigate the effect of disbond size on the amplitudes and group velocities of propagating guided wave modes. A good agreement is observed between the theoretical, numerical and experimental results in all cases studied. It is noticed that the presence of disbond, in particular, amplifies the first anti-symmetric (A0) mode and increases its group velocity. Finally, based on these modal behaviors, the location of an unknown disbond, within the piezoelectric wafer transducer array is experimentally determined by applying a probability-based damage detection algorithm.

Guided wave propagation in a honeycomb composite sandwich structure in presence of a high density core

A coordinated theoretical, numerical and experimental study is carried out in an effort to interpret the characteristics of propagating guided Lamb wave modes in presence of a high-density (HD) core region in a honeycomb composite sandwich structure (HCSS). Initially, a two-dimensional (2D) semi-analytical model based on the global matrix method is used to study the response and dispersion characteristics of the HCSS with a soft core. Due to the complex structural characteristics, the study of guided wave (GW) propagation in HCSS with HD-core region inherently poses many challenges. Therefore, a numerical simulation of GW propagation in the HCSS with and without the HD-core region is carried out, using surface-bonded piezoelectric wafer transducer (PWT) network. From the numerical results, it is observed that the presence of HD-core significantly decreases both the group velocity and the amplitude of the received GW signal. Laboratory experiments are then conducted in order to verify the theoretical and numerical results. A good agreement between the theoretical, numerical and experimental results is observed in all the cases studied. An extensive parametric study is also carried out for a range of HD-core sizes and densities in order to study the effect due to the change in size and density of the HD zone on the characteristics of propagating GW modes. It is found that the amplitudes and group velocities of the GW modes decrease with the increase in HD-core width and density.