Piezoceramic Transducers Research Articles

Intelligent prediction of rock bolt debonding employing the fractal theory and relevance vector machine (FT-RVM) with piezoceramic transducers

Intelligent prediction of rock bolt debonding employing the fractal theory and relevance vector machine (FT-RVM) with piezoceramic transducers

Mechanical Strain, Temperature, and Misalignment Effects on Data Communication between Piezoceramic Ultrasonic Transducers.

Acoustic waves can be used for wireless telemetry as an alternative to situations where electrical or optical penetrators are unsuitable. However, the response of the ultrasonic transducer can be greatly affected by temperature variations, mechanical deformations, misalignment between transducers, and multiple layers in the propagation zone. Therefore, this work sought to quantify such influences on communication between ultrasonic transducers. The experimental measurements were performed at the frequency where power transfer is maximized. Moreover, there were four experimental models, each with its own performed setup. The ultrasonic transducers are attached to both sides of a 6 mm thick stainless-steel plate for configuring just one barrier. Multiple layers of transducers are attached to the outer side of two plates immersed in an acoustic fluid with a 100 mm thick barrier. In both cases, the S21 parameter was used to quantify the influence of the physical barrier because it correlates with the power flow between ports that return after a given excitation. The results showed that when a maximum deformation of 1250 μm/m was applied, the amplitude of the S21 parameter varied around +0.7 dB. Furthermore, increasing the temperature from 30 to 100 °C slightly affected the S21 (+0.8 dB), but the signal decayed quickly for temperatures beyond 100 °C. Additionally, the ultrasonic communication with a multiple layer was found to occur under misalignment with an intersection area of up to 40%. None of the factors evaluated resulted in insufficient power transfer, except for a large misalignment between the transducers. Such results indicate that this type of communication can be a robust alternative, with a minimum alignment of 40% between transducers and electrical penetrators.

Research on wireless monitoring system and algorithms for preload force utilizing machine learning and electromechanical impedance

The root mean square deviation is a common way to measure the electromechanical impedance of piezoceramic transducers that are used for traditional preload monitoring. However, due to the impedance signal’s high sensitivity to temperature, most current research is carried out under the same temperature conditions to avoid its effects. Even so, it is impossible to ignore the temperature factor in practical engineering, which hinders the application of impedance technology. Therefore, this paper proposes a novel approach for preload monitoring in actual engineering: using a wireless impedance signal acquisition platform to collect long-distance impedance signals and then establishing a predicted model based on machine learning (ML) considering the temperature. The wireless impedance signal acquisition platform includes a smart washer, a piezoelectric impedance wireless sensing device, and the host computer software. This test established a dataset under various operating conditions and developed a machine-learning-based predictive model. After comparing five typical ML algorithms, it was discovered that XGBoost performed better in prediction accuracy and generalization ability. Moreover, the Shapley additive explanation method is utilized to further analyze and interpret the XGBoost model. It indicates that ML primarily relies on numerical features (such as the area of each subinterval) to identify the impedance signal and predict the prestress, whereas information features (such as temperature value, peak, etc.) have little influence on the model’s output. Finally, the results above demonstrate that the ML-based models can predict the preload at different temperatures, effectively reducing temperature interference.

SHM System Architecture based on Ultrasonic Guided Waves for Aircraft Application Scenarios

Structural health monitoring (SHM) based on ultrasonic guided waves is a novel technology using permanently attached actuator and sensor networks, data acquisition and data evaluation systems to enable in-service inspection of aircraft structures. A modular and decentralized SHM system is presented that can be adapted to various aircraft application scenarios. The central element of the SHM system is a robust sensor array based on piezocomposite technology that can be efficiently integrated into the manufacturing process of CFRP structures (via co-bonding). The sensor array consists of integrated piezoceramic transducers, temperature sensors, electrical cables and integrated electronic components. The decentralized system architecture of the individual electronic components reduces the installation and cabling effort during the assembly of aircraft structures as well as the system weight. Integration and installation aspects as well as various system architectures are discussed using an Airbus A350 door surround structure. Furthermore, an outlook of damage detection under representative flight loads is given.

Reliability Assessment of Damage Localization Techniques for Guided Wave-based Structural Health Monitoring Systems in Composite Stiffened Structures

In Guided Wave-based Structural Health Monitoring (GWSHM) systems, the reliability assessment is of utmost importance. The primary focus is the smallest damage that can be detected with 90 percent probability and 95 percent confidence. However, the probability of correct damage localization is equally crucial as the probability of detection. In this view, defining the smallest damage that can be localized accurately in a statistically meaningful way is quite challenging. Several localization techniques have been developed in the literature to localize damage resorting to a GW sensor network, like SAFT and RAPID. This article investigates the reliability of such SHM systems with these localization techniques using an experimental data set from the Open Guided Waves (OGW) platform and compares it with predictions obtained via a simulation model using the EFIT method. A carbon fibre-reinforced plate-like structure reinforced by an omega stringer and a GWSHM system employing twelve piezoceramic transducers bonded over the surface to excite and receive guided waves are used. Pseudo damage of thirteen different sizes are attached to three different locations using a damping tacky tape. Moreover, the EFIT modelling tool is used to simulate the experiment with an extensive number of damage scenarios at the defined three damage locations with a high degree of consistency with the experimental data, facilitating a more robust analysis. The Outcome concerning the influence and correlation between damage size on localization accuracy, considering various localization techniques, were explored and discussed. In addition, the reliability assessment allowed to establish the performance of the localization approaches in a rigorous way.

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.

Diagnostic imaging of debonding in FRP-strengthened reinforced concrete structures using combinational harmonics generated by Rayleigh waves

A debonding location imaging technique (DLIT) utilising mixed-frequency Rayleigh waves is reported in this paper to predict the location of debonding in fibre-reinforced polymer (FRP) composite strengthened concrete structures. In the proposed methodology, a piezoceramic transducer network is employed to sequentially scan the FRP-concrete interface. One of the transducers serves as an actuator while the remainder serve as sensors. The incident waves which are sent by the actuator consist of two different fundamental frequencies. After the incident waves interact with debonding, additional signals are generated that coincide with the sum of the fundamental frequencies (i.e., sum frequency). The received wave component at the sum frequency is in accordance with theoretical predictions. In order to apply the DLIT, a time-frequency analysis is then applied to process the data collected by each actuator-sensor transducer pair in order to determine the signal energy density amplitudes (i.e., signal envelopes) at the fundamental frequencies and the sum frequency. Based on cross-correlation analysis between the signal envelopes of the fundamental frequencies and the sum frequency, an image can be constructed that reveals the centroid of the debonding region. Following the presentation of the proposed DLIT, numerical and experimental studies are then reported that compare the predicted centroid of debonding with the actual centroid of debonding as incorporated into the numerical model and the experimental specimens, respectively. The results demonstrate that the proposed DLIT based on the Rayleigh wave features at sum frequency can satisfactorily predict the location of debonding.

Directivity and Excitability of Ultrasonic Shear Waves Using Piezoceramic Transducers-Numerical Modeling and Experimental Investigations.

In this paper, piezoceramic-based excitation of shear horizontal waves is investigated. A thickness-shear d15 piezoceramic transducer is modeled using the finite-element method. The major focus is on the directivity and excitability of the shear horizontal fundamental mode with respect to the maximization of excited shear and minimization of Lamb wave modes. The results show that the geometry of the transducer has more effect on the directivity than on the excitability of the analyzed actuator. Numerically simulated results are validated experimentally. The experimental results show that transducer bonding significantly affects the directivity and amplitude of the excited modes. In conclusion, when the selected actuator is used for shear excitation, the best solution is to tailor the transducer in such a way that at the resonant frequency the desired directivity is achieved.

Coupled Axisymmetric Thermoelectroelasticity Problem for a Round Rigidly Fixed Plate

Introduction. To describe the operation of temperature piezoceramic structures, the theory of thermoelectroelasticity is used, in which the mathematical model is formulated as a system of nonself-adjoint differential equations. The complexity of its integration in general leads to the study of problems in an unrelated formulation. This does not allow us to evaluate the effect of electroelastic fields on temperature. The literature does not present studies on these problems in a three-dimensional coupled formulation in which closed solutions would be constructed. At the same time, conducting such studies allows us to understand the interaction picture of mechanical, thermal and electric fields in a structure. To solve this problem, a new closed solution of a coupled problem for a piezoceramic round rigidly fixed plate has been constructed in this research. It provides for qualitative assessment of the cross impact of thermoelectroelastic fields in this electroelastic system.Materials and Methods. The object of the study is a piezoceramic plate. The case of unsteady temperature change on its upper front surface is considered, taking into account the convection heat exchange of the lower plane with the environment (boundary conditions of the 1st and 3rd kind). The electric field induced as a result of the thermal strain generation is fixed by connecting the electrodated surfaces to the measuring device. The thermoelectroelasticity problem includes the equations of equilibrium, electrostatics, and the unsteady hyperbolic heat equation. It is solved by the generalized method of finite biorthogonal transformation, which makes it possible to construct a closed solution of a nonself-adjoint system of equations.Results. A new closed solution of the coupled axisymmetric thermoelectroelasticity problem for a round plate made of piezoceramic material was constructed.Discussion and Conclusion. The obtained solution to the initial boundary value problem made it possible to determine the temperature, electric and elastic fields induced in a piezoceramic element under arbitrary temperature axisymmetric external action. The calculations performed provided determining the dimensions of solid electrodes, which made it possible to increase the functionality of piezoceramic transducers. Numerical analysis of the results enabled us to identify new connections between the nature of external temperature action, the deformation process, and the value of the electric field in a piezoceramic structure. This can validate a proper program of experiments under their designing and significantly reduce the volume of field studies.

Dual-Use Strain Sensors for Acoustic Emission and Quasi-Static Bending Measurements.

In this paper, a MEMS piezoresistive ultrathin silicon membrane-based strain sensor is presented. The sensor's ability to capture an acoustic emission signal is demonstrated using a Hsu-Nielsen source, and shows comparable frequency content to a commercial piezoceramic ultrasonic transducer. To the authors' knowledge, this makes the developed sensor the first known piezoresistive strain sensor which is capable of recording low-energy acoustic emissions. The improvements to the nondestructive evaluation and structural health monitoring arise from the sensor's low minimum detectable strain and wide-frequency bandwidth, which are generated from the improved fabrication process that permits crystalline semiconductor membranes and advanced polymers to be co-processed, thus enabling a dual-use application of both acoustic emission and static strain sensing. The sensor's ability to document quasi-static bending is also demonstrated and compared with an ultrasonic transducer, which provides no significant response. This dual-use application is proposed to effectively combine the uses of both strain and ultrasonic transducer sensor types within one sensor, making it a novel and useful method for nondestructive evaluations. The potential benefits include an enhanced sensitivity, a reduced sensor size, a lower cost, and a reduced instrumentation complexity.

Ultrasound jetting and atomization of sessile and impacting droplets

We present the results of our experimental and theoretical study of the jetting and atomization of a sessile and an impacting droplet subject to an ultrasonic surface vibration with a frequency of 2.5 MHz and piezoceramic transducer (PZT) surface velocity of 0.2–1.5 ms−1. Such high-frequency vibrations result in the formation of a liquid jet shooting outwardly from the surface of the droplet, which eventually breaks up into droplets. Part of the liquid remains on the surface, which eventually goes through ultrasonic atomization. We have divided this process into three categories of (i) jetting, (ii) jet breakup and liquid layer formation, and (iii) liquid layer atomization, and characterized jetting and jet breakup separately. For impacting droplets, jetting occurs immediately and at relatively low surface vibration velocities as compared to those for sessile droplets. We have developed a model to predict the PZT surface velocity for the onset of jetting, the jet diameter, jet velocity, and spreading diameter based on momentum, force, and energy balances. The liquid jet may break up into droplets due to Rayleigh–Plateau breakup (ejecting droplets on the order of jet diameter, λa) and acoustic breakup of the jet (ejecting both few hundred micrometer and few micrometer droplets).

Multidomain modeling of acoustical transducers and arrays using electrical network theory

Modeling of piezoceramic acoustic transducers involves the transformation of energy in the electrical, mechanical, acoustical radiation domains. By using generalized coordinates and Lagrangian mechanics, in which principle of least action is applied in each domain, the electrical, piezoelectric, mechanical and sound radiation problems can be solved separately and then combined in a multi-contour equivalent electro-mechanical circuit with each mechanical vibrational resonant modes representing separate degrees of freedom in the coupled electrical circuit. This energy approach involves the calculation of the potential and kinetic energies of each practical mode of vibration, which can be determined analytically, experimentally, or by finite-element-analysis. This is an alternative to the use of Newtonian mechanics which requires an accurate description of the real boundary conditions in the device and is common in many FEA modeling approaches. The availability of software (e.g., Matlab, Python, LTSpice, etc.) to model electrical circuits (networks in the case of multi-resonant devices) makes for a powerful and efficient modeling approach. The historical emergence of this approach stems from adapting the Rayleigh-Ritz method for mechanical and electrical domains with the advent of piezoelectric and magnetostrictive bodies. Several example of piezoceramic transducers are presented.

A PZT active sensing method for monitoring prestressing force based on the ultrasonic reflection coefficient

Prestress monitoring is key to ensuring the safety and longevity of post-tensioned prestressed structures. A new method of prestress monitoring, based on piezoceramic transducers, is proposed. Compared to traditional ultrasonic detection, we utilize piezoelectric (PZT) active sensing monitoring, eliminating the need for a specialized ultrasonic probe. First, a relationship model between the signal received energy and loading force is established based on the principle of ultrasonic reflection coefficient at the contact interface. On this basis, we overcome the low signal-to-noise ratio issue associated with the traditional method by employing the time reversal (TR) method. Next, the model parameters were fitted using experimental data. The values of the fitting evaluation metrics, SSE and RMSE, tend to be close to 0, while the R-squared value tends to be close to 1. This indicates the reliability of the model. Finally, the prestressing force validation tests are conducted through unloading tests. The average relative error between the measured and actual values across different paths ranges from 6.85% at the minimum to 15.61% at the maximum. Since the method is related to the proximity of the interface contact, it can be applied in other areas of civil engineering, such as assessing the adhesive strength of composite structures, crack development, and detecting axial stress.

Radial vibration analysis for piezoceramic shell-stacked spherical transducer with thick walls

With the development of ultrasonic transducers, spherical piezoelectric transducers have attracted tremendous attention in a variety of application fields due to their ability to resist higher pressures and produce omnidirectional radiation. However, the wall thickness of piezoceramic spherical shells is usually thin due to the limitations of polarization technology and operating voltage, leading to the limited vibration performance and power capacity of the spherical transducer. We present a piezoceramic shell-stacked spherical transducer (PSST) capable of addressing the problem of difficult excitation caused by the thick wall of the piezoceramic shell. The resulting device consists of a two-layered piezoceramic shell interposed between the inner and outer concentric spherical metal shells. By removing the equivalent mechanical transformers, a novel electromechanical equivalent circuit of the PSST is established to simplify the theoretical analysis of the designed PSST. The electromechanical characteristics of the resulting device are experimentally verified, and the measured results are in good agreement with the theoretical predictions and simulation results. Our design opens up possibilities for designing spherical transducers with high-vibration performance and may offer potential for a wide range of applications such as underwater detection and structural health monitoring.

On the strength of the piezoceramic transducer in the system of structural health monitoring

The aim of the presented paper is the more detailed investigation and improvement of pre-stressing technology for the piezoelectrical transducer (PET) protection from degradation at action of extreme overload and longtime variable load in operation. Earlier developed 1D model of embedded PET is verified by the finite element analysis. Using this model, the parametrical assessment of stress state and strength of conventional transducer is done. It is shown that there is specific class of PET for which satisfying solution cannot always be obtained by optimization of parameters of the conventional piezoelectrical transducer (CPET). Therefore, further analysis is focused on the stress state and strength of the pre-stressed piezoelectrical transducer (PPET) it comparison with CPET. The electromechanical impedance (EMI) and its integral indicis are used for assessment of PET operability. Numerical simulation of EMI response to possible damages of PET and the outcome of static and fatigue tests are shown the significantly higher resistance of PPET against operational degradation in comparison with CPET.

Defect Detection in Solid Timber Panels Using Air-Coupled Ultrasonic Imaging Techniques

This paper reports on investigations of the air-coupled ultrasonic (ACU) method to detect common defects in solid timber panels made of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.). The ACU technology is a non-contact method for nondestructive timber testing with quicker scanning rates compared to contact methods. A testbed was set up consisting of commercially available piezo-ceramic ACU transducers and in-house manufactured signal processing circuits. To demonstrate the suitability of the ACU technique, through-transmission measurement results are presented for samples with defects such as knots, wormholes, and cracks. Pulse compression methods (Barker-coded method) were used to improve the power of received signals based on cross-correction algorithms. Results showed defects of timber panels made of Chinese fir can be detected with a thickness of less than 40 mm. Defects larger than 3 mm in diameter could be detected with high precision. Applying the pulse compression method showed better results than using common sine signals as excitation signals since it increased the signal-to-noise ratio, which is especially important for air-coupled measurement of high-attenuation materials like timber materials. The measurement results on reference samples demonstrated that ACU technology is a promising method for timber defect detection, especially for the quality assessment of engineered wood products.

High accuracy and resolution damage detection for concrete based on novel virtual correlation imaging method and embedded piezoelectric sensing technology

This paper presents a novel virtual correlation imaging (VCI) method to reduce the adverse effects of stress wave distortion and realize high accuracy and resolution damage imaging based on the sparse stress wave data collected by embedded piezoceramic transducers. Specifically, a compensation function is first constructed in the VCI method based on the frequency response characteristic of damage-induced scattering signals. Then, the constructed compensation function is emitted as the virtual excitation signal in the simulation space via virtual channels. To automatically compensate for the effect of waveform distortion, a virtual correlation operator is developed based on the scattering signal and its corresponding virtual received signal to design the imaging function. Finally, the practicability of the proposed VCI method is investigated on a concrete specimen with two successively drilling holes under laboratory conditions. The results indicate that, compared with the conventional damage imaging methods, the proposed VCI method can effectively decrease the adverse effect of distorted probing stress waves on damage localization accuracy and spatial resolution during the imaging process.

Phase/frequency analysis of diffuse Lamb-wave field for fatigue-crack detection in an aluminium multi-riveted strap joint aircraft panel

A diffuse Lamb-wave field is utilised for fatigue-crack detection in a multi-riveted strap-joint aircraft panel. The work involves an extensive experimental programme of fatigue testing. Ultrasonic Lamb-wave responses are captured using a network of low-profile, surface-bonded piezoceramic transducers. Various phase/frequency characteristics of Lamb waves are used to detect and monitor fatigue cracks. An outlier statistical analysis – based on these characteristics - is also performed for damage detection. The results show that phase analysis can be used successfully for damage detection in such structures. In contrast, frequency analysis does not offer reliable damage detection. The results demonstrate the potential and limitations of the method for reliable fatigue-crack detection in complex aircraft structures.

NON-LINEAR MODEL OF A RECUPERATIVE SHOCK ABSORBER

This article examines the rationale for using a shock absorber with the function of recuperating mechanical energy into electrical energy. Current trends in the transport industry, regarding the need to use autonomous power sources in the transport infrastructure, are considered. This direction is promising due to the replacement of vehicles with internal combustion engines by electric transport, as well as the need for autonomous power supply of individual nodes and aggregates. The need for autonomy emerges acutely in the conditions of the energy crisis, and at the same time, the lack of energy resources. Special attention is paid to energy recovery using the direct and conversepiezoelectric effect. The structure, chemical and physical properties, principle of operation and practical application of piezoceramic transducers, and the possibility of their use as energy harvesters (generators) are considered. The considered scientific and technical problem, which consists in determining the nature of the negative impact of various types of external oscillations on the functioning of structural elements of vehicles, to reduce which various shock absorbers or dampers are used. This work considers the use of a recuperative shock absorber of vibration loads with the use of a piezoelectricenergy harvester as a converter of mechanical energy of vibrations into electrical energy. Piezoceramic inserts are used as an energy collector in the design of an automobile hydraulic shock absorber. An assessment of the efficiency of recuperation and conclusions regarding the feasibility of use and implementation are provided. The shock absorbers which are installed to absorb vibrations consume a large amount of mechanical energy, converting it into heat which is dissipated into the atmosphere. This energy, without reducing the efficiency of functioning, can be beneficially used by using a piezoelectric generator with piezoelectric ceramics to convert mechanical energy into electrical energy.

Effect of high temperature on nonlinear guided wave in reinforced concrete structures

There are some ations that reinforced concrete (RC) structures may be subjected high temperatures, e.g., building fires, rocket and jet aircraft engine blasts, and nuclear power reactors. It is crucial to ensure the integrity and safety of these RC structures. This study investigates the effects of high temperature on the behavior of nonlinear guided wave, which can potentially be used for non-destructive evaluation, in reinforced concrete structures. In this study, the reinforced concrete specimens are heated from 100 to 800°C. Two sets of experimental studies are considered. At temperatures 100–300°C, piezoceramic transducers are embedded at the rebars in the reinforced concrete specimens to generate and measure the longitudinal wave. At temperatures 300–800°C, the longitudinal transducers are installed at the rebars exposed outside the reinforced concrete specimens. The results show that the high temperature induces the debonding between the rebar and the concrete, which causes the generation of the second harmonic when the longitudinal wave interacts with the debonding. A nonlinear parameter is defined to monitor the effects of the heat damage caused by the increasing temperature on the reinforced concrete structures.