Piezoceramic Transducers Research Articles

Damage Detection of a Concrete Column Subject to Blast Loads Using Embedded Piezoceramic Transducers.

Some of the most severe structural loadings come in the form of blast loads, which may be caused by severe accidents or even terrorist activities. Most commonly after exposure to explosive forces, a structure will suffer from different degrees of damage, and even progress towards a state of collapse. Therefore, damage detection of a structure subject to explosive loads is of importance. This paper proposes a new approach to damage detection of a concrete column structure subjected to blast loads using embedded piezoceramic smart aggregates (SAs). Since the sensors are embedded in the structure, the proposed active-sensing based approach is more sensitive to internal or through cracks than surface damage. In the active sensing approach, the embedded SAs act as actuators and sensors, that can respectively generate and detect stress waves. If the stress wave propagates across a crack, the energy of the wave attenuates, and the reduction of the energy compared to the healthy baseline is indicative of a damage. With a damage index matrix constructed by signals obtained from an array of SAs, cracks caused by blast loads can be detected throughout the structure. Conventional sensing methods such as the measurement of dynamic strain and acceleration were included in the experiment. Since columns are critical elements needed to prevent structural collapse, knowledge of their integrity and damage conditions is essential for safety after exposure to blast loads. In this research, a concrete column with embedded SAs was chosen as the specimen, and a series of explosive tests were conducted on the column. Experimental results reveal that surface damages, though appear severe, cause minor changes in the damage index, and through cracks result in significant increase of the damage index, demonstrating the effectiveness of the active sensing, enabled by embedded SAs, in damage monitoring of the column under blast loads, and thus providing a reliable indication of structural integrity in the event of blast loads.

Optimization of triple-ring electrodes on piezoceramic transducers using algorithmic differentiation

Data of material properties given by manufacturers of piezoelectric ceramics is often flawed due to, for example, slightly different manufacturing conditions for each production batch. Hence, the need for more reliable data arises. Recently published material parameter estimation methods are based on the solution of an inverse problem fitting impedance measurements of the piezoelectric ceramic to simulations by varying the material parameters in the simulation. However, the sensitivity of impedance with respect to some material parameters is close to zero and thus alternative measurement quantities which require expensive and error-prone measurement devices would be required. In order to assist in experiment design, the simulation software must be able to compute accurate sensitivity information. We applied the algorithmic differentiation (AD) package ADOL-C to the C++-based sophisticated simulation software CFS++ and thus are now able to compute the sensitivity of impedance with respect to material parameters without the use of finite differences. As these sensitivities depend on the geometry of the piezoelectric ceramic and the electrodes, we then use these sensitivities as a cost function for maximization. We compare the results of optimization with results of optimization previously obtained using a finite difference scheme. We document implementation issues and limits for integrating ADOL-C into CFS++. Nevertheless, we show the now much improved results of optimization using AD instead of finite differences and its potential for further optimization.

Physical fields of hydroacoustic sonar arrays with baffle and cylindrical piezoceramic radiators with radial polarization

Article describes the method for calculating physical fields of the cylindrical sonar array formed with the some certain, finite number of cylindrical piezoceramic transducer with radial polarization, of compensated or strength design, and cylindrical, acoustical soft, baffle situated in the middle of the array. To obtain the equations, that allow us to calculatephysical fields of this array we have solved the “pass-through” problem of sound radiation of this array. The main feature of the studied problem was that we described the work of the transducer beginning from its electrical input, unlike the classical method, when we set the oscillating velocity of the surface of the transducer as a constant. In addition, thismethod for calculating parameters of the studied array allows us to take into consideration the interaction of the physical fields in the transducer and in the array generally, and the interaction between transducers in the array and between transducers and the baffle. Constructed mathematical model allows us to provide investigations for huge amount of cylindrical arrays of similar design, because, it allows us to change such parameters of array as its dimension generally, dimensions of the baffle, the distance between the baffle and the transducers, the working medium of the array, quantity of transducers in the array, the position of each transducer in the array and the parameters of each transducer, such as its own dimensions, such as the central diameter and the thickness of the piezoceramic rings, the filling of each transducer and the material of each transducer. The obtained solution of this problem allows us to calculate the acoustic potential and the displacement of the surface of transducer. Using these parameters we obtained the equations for calculating physical fields of transducer, such as electrical current, that used for studying electrical field, oscillating velocity of the surface of transducer, used for studying the mechanical field, and acoustic pressure, which allow us to study acoustic parameters of the array, such as its directivity characteristics.Also, the obtained solutions allow us to study the fields in the inner cavity of transducer, that is also of big interest.Bibl. 7, fig. 1.

Study of Impact Damage in PVA-ECC Beam under Low-Velocity Impact Loading Using Piezoceramic Transducers and PVDF Thin-Film Transducers.

Compared to conventional concrete, polyvinyl alcohol fiber reinforced engineering cementitious composite (PVA-ECC) offers high-strength, ductility, formability, and excellent fatigue resistance. However, impact-induced structural damage is a major concern and has not been previously characterized in PVA-ECC structures. We investigate the damage of PVA-ECC beams under low-velocity impact loading. A series of ball-drop impact tests were performed at different drop weights and heights to simulate various impact energies. The impact results of PVA-ECC beams were compared with mortar beams. A combination of polyvinylidene fluoride (PVDF) thin-film sensors and piezoceramic-based smart aggregate were used for impact monitoring, which included impact initiation and crack evolution. Short-time Fourier transform (STFT) of the signal received by PVDF thin-film sensors was performed to identify impact events, while active-sensing approach was utilized to detect impact-induced crack evolution by the attenuation of a propagated guided wave. Wavelet packet-based energy analysis was performed to quantify failure development under repeated impact tests.

Quantitative evaluation of compactness of concrete-filled fiber-reinforced polymer tubes using piezoceramic transducers and time difference of arrival

Owing to its light weight and corrosion resistance, the concrete-filled fiber-reinforced polymer tube (CFFT) structure has a broad application prospect; the concrete compactness is key to the strength of CFFTs. To meet the urgent requirement of compactness monitoring of CFFTs, a quantitative method, which uses an array of four equally spaced piezoceramic patches and an ultrasonic time difference of arrival (TDOA) algorithm, is developed. Since the velocity of the ultrasonic wave propagation in fiber-reinforced polymer (FRP) material is about half of that in concrete material, the compactness condition of CFFT impacts the piezoceramic-induced wave propagation in the CFFT, and differentiates the TDOA for different receivers. An important condition is the half compactness, which can be judged by the Half Compactness Indicator (HCI) based on the TDOAs. To characterize the difference of stress wave propagation durations from the emitter to different receivers, which can be utilized to calculate the concrete infill compactness, the TDOA ratio (TDOAR) is introduced. An innovative algorithm is developed in this paper to estimate the compactness of the CFFT using HCI and TDOAR values. Analytical, numerical, and experimental studies based on a CFFT with seven different states of compactness (empty, 1/10, 1/3, 1/2, 2/3, 9/10, and full) are carried out in this research. Analyses demonstrate that there is a good agreement among the analytical, numerical, and experimental results of the proposed method, which employs a piezoceramic transducer array and the TDOAR for quantitative estimating the compactness of concrete infill in a CFFT.

Connection looseness detection of steel grid structures using piezoceramic transducers

Connection looseness phenomena of steel grid structures might induce issues of lowering integrity, large deformation, even total collapse of the structures. The goal of this article is to propose an evaluation method for bolt-sphere joint looseness of steel grid structures using piezoceramic guided wave–based method through experiments and numerical simulations. A single bolt-sphere joint looseness experimental model is established and tested, considering grid member connection angles of 0°, 45°, 90°, and 180°, respectively. Then, multiple bolt-sphere joint looseness detection tests by selecting six kinds of cases for a steel grid structure model are performed. Piezoceramic patch arrays bonded on the surface of grid members are used as transducers to generate and receive detection guided waves, and external torques are applied to indirectly simulate the bolt-sphere joint looseness effect. The experimental results show that the bolt-sphere joint looseness impact on the ultrasonic wave energy attenuation has a nonlinear regularity. Based on the regularity, an evaluation method and key techniques for the bolt-sphere joint looseness detection based on guided wave energy are proposed and experimentally validated. To further clarify the bolt-sphere joint looseness detection mechanism, the ABAQUS software is used for a finite element analysis of the single bolt-sphere joint looseness evaluation. The numerical and experimental results match well, verifying the feasibility of the proposed method.

Smart concrete slabs with embedded tubular PZT transducers for damage detection

The objective of this study is to develop a new concept and methodology of smart concrete slab (SCS) with embedded tubular lead zirconate titanate transducer array for image based damage detection. Stress waves, as the detecting signals, are generated by the embedded tubular piezoceramic transducers in the SCS. Tubular piezoceramic transducers are used due to their capacity of generating radially uniform stress waves in a two-dimensional concrete slab (such as bridge decks and walls), increasing the monitoring range. A circular type delay-and-sum (DAS) imaging algorithm is developed to image the active acoustic sources based on the direct response received by each sensor. After the scattering signals from the damage are obtained by subtracting the baseline response of the concrete structures from those of the defective ones, the elliptical type DAS imaging algorithm is employed to process the scattering signals and reconstruct the image of the damage. Finally, two experiments, including active acoustic source monitoring and damage imaging for concrete structures, are carried out to illustrate and demonstrate the effectiveness of the proposed method.

Monitoring concept for structural integration of PZT-fiber arrays in metal sheets: a numerical and experimental study

ABSTRACTThe technique joining by forming allows the structural integration of piezoceramic fibers into locally microstructured metal sheets without any elastic interlayers. A high-volume production of the joining partners causes in statistical deviations from the nominal dimensions. A numerical simulation on geometric process sensitivity shows that the deviations have a high significant influence on the resulting fiber stresses after the joining by forming operation and demonstrate the necessity of a monitoring concept. On this basis, the electromechanical behavior of piezoceramic array transducers is investigated experimentally before, during and after the joining process. The piezoceramic array transducer consists of an arrangement of five electrical interconnected piezoceramic fibers. The findings show that the impedance spectrum depends on the fiber stresses and can be used for in-process monitoring during the joining process. Based on the impedance values the preload state of the interconnected piezoceramic fibers can be specifically controlled and a fiber overload.

Electromechanical Admittance Signature Analysis of Piezo-ceramic Transducers for NDE

Of the multiple applications of the piezoelectric ceramics transducers such as Lead-Zirconate-Titanate (PZT), one prominent one is in the field of non-destructive evaluation (NDE) using the Electromechanical Impedance method (EMI). In this method a piezo-ceramic transducer (PZT) is bonded on to the structure and actuated using a harmonic voltage at ultrasonic frequency ranges. The dynamics of the PZT-structure interaction is captured in the frequency response of the electrical admittance of the PZT, popularly called as the admittance signature. A mechanical damage in the structure alters the mass, stiffness and damping properties locally, which in turn alters the admittance signature. Many analytical and semi-analytical models of the EMI method that have been used are limited in application to simple systems. The coupled-field finite element modeling has been demonstrated to quite accurately predict the admittance signatures as obtained by the experimental EMI technique. This paper presents the results of identification and quantification studies of damage using the analysis of admittance signatures obtained by coupled-field FE model of a simple cantilever type plate in ANSYSTM.

A Time Reversal Based Pipeline Leakage Localization Method With the Adjustable Resolution

Due to the diffraction limit, the systems to localize signal sources used to suffer from the low resolution issue, which also occurs in the pipeline leakage localization. For a pressurized pipeline that carries gas, a leakage will generate a negative pressure wave (NPW) that propagates along the pipeline. The NPW can be detected by piezoceramic transducers that are bonded on the surface of the pipeline. Via processing NPW signals, the locations of the leakages can be obtained. However, since the wavelengths of the NPW signals are several meters, the resolution is meter sized. In this paper, a novel pipeline leakage localization method which can adjust the resolution is developed to improve the localization resolution. The proposed method includes a formula to adjust the localization resolution based on the time reversal technique. Via adjusting the parameter of the formula, various localization resolutions can be obtained. We investigated the performance of the proposed method in an experiment with a 55.8 m PVC pipeline equipped with two manually controllable leakage points. With the help of the piezoceramic transducers, the experimental results show that the proposed method can deliver the resolutions which represent a significant improvement, as compared with that of the conventional time reversal localization method. Furthermore, the proposed method can be used for other passive detection.

Acoustic Transducer of Turbulent Pressure Fluctuations in a Temperature-Stratified Medium

The operation of an acoustic transducer in a temperature-stratified medium is investigated. The formation of a response of piezoceramic transducers of pressure fluctuations under the action of temperature fluctuations in a working medium on the sensor element is considered. The attenuation of the temperature signal of a pressure transducer in a turbulent boundary layer is calculated numerically. The effect of distortions of the spectral levels of pressure fluctuations detected by a sound transducer in the field of temperature inhomogeneities is investigated for the example of measurements of turbulent pressure fluctuations in a boundary layer during vertical ascent of the device to the surface from a specified depth in a deep sea.

Real-Time Monitoring of Soil Compaction Using Piezoceramic-Based Embeddable Transducers and Wavelet Packet Analysis

Quantitative assessment of soil compaction is of great importance to construction work, precision agriculture, and geotechnical research. Currently, measurement of soil compaction is mainly performed through field measurements, and the accuracy is highly influenced by personnel experience. In addition, most of the current methods for soil compaction measurement are capable of real-time monitoring. This paper presents an exploratory study of using a piezoceramic-based active sensing approach coupled with wavelet packet analysis to quantitatively monitor soil compaction in real time. In the active sensing approach, a pair of smart aggregates (SA) consisting of piezoceramic transducers embedded inside a host material are embedded into soil. In the pair, one SA acts as transmitter to transmit a modulated stress wave towards the other SA, which acts as receiver. The attenuation ratio of the stress wave propagating energy in soil is governed by the degree of soil compaction, so that the received wave properties of the smart aggregate sensor can be further characterized by using wavelet packet as an index to evaluate the soil compaction in real time. Integrated with remote sensing technologies, the proposed method has potential to be utilized as a real-time remote-sensing technology, which can offer a solution in the monitoring the degree of soil compaction.

Analysis of forced vibration of piezoceramic transducers at a non-uniform electric loading

Analysis of forced vibration of piezoceramic transducers at a non-uniform electric loading

An Embedded Tubular PZT Transducer Based Damage Imaging Method for Two-Dimensional Concrete Structures

In this paper, a damage imaging method for 2-D concrete structures is proposed by employing embedded tubular piezoceramic transducers. The proposed method can image the damages when few numbers of transducers are used or less experimental data is collected. First, the time difference of arrival-based delay and sum (DAS) imaging method is adopted to improve the damage localization accuracy for concrete structural health monitoring. Compared with the conventional DAS imaging algorithm, the proposed method increases the potential number of combinations between the response signals induced by the damage in each transmitter and sensor pair, improving the signal to noise ratio of the imaging map and enhancing the performance of the defect detection and location. Second, to enable the proposed method applicable to a 2-D concrete structure (such as cement concrete pavement and shear walls), embeddable tubular lead zirconate titanate (PZT) transducers rather than conventional PZT patches are used. The new tubular PZT transducers are able to generate radially uniform stress waves in a planar concrete structure. Due to the special construction of the tubular PZT transducers, the detection aperture is significantly improved. Therefore, a few transducers are needed in contrast with the conventional PZT patches. The experimental results conducted on a concrete slab with eight embedded tubular PZT transducers demonstrate that the proposed method can predict the defect accurately and efficiently even with few transducers and less experimental data.

Mechanical fields of the piezoceramic radiator of strength design situated near acoustical baffle

Article describes the mechanical fields of the cylindrical piezoceramic transducer of the strength design, with circular polarization located near cylindrical acoustical soft baffle. As an investigated parameter of the mechanical field of transducer chosen the oscillating velocity of the surface of transducer, because, studying of this parameter has huge interest in practical applications, because on the construction stage of the creating of sonar array we have to know the maximum mechanical loads that arise in the transducer during its operation, and in the classical methods for calculating oscillating velocity of the surface of transducer is set to the constant value, so it can’t identify the changes in the characteristics of the oscillating velocity on the surface of transducer, caused by the interaction between the elements of the array. Unlike the classical methods, oscillating velocity on the surface of transducer is not constant value, and numerical calculations of the physical fields provided, beginning from the electrical input of transducer. Equations, used for calculating numerical values of the oscillating velocity, obtained, using the results of solution of the “pass-through” problem of sound radiation of the cylindrical sonar array formed with cylindrical piezoceramic transducers with circular polarization and cylindrical acoustic soft baffle located in the middle of the array. This solution allows us to take into consideration interaction of the fields in the transducer itself and into array entirely. The numerical analysis of the dependencies of oscillating velocity of the surface of the transducer provided both, for frequency dependence and angle dependence. The analysis provided both, for amplitude and phase characteristics of the velocity. For the frequency dependencies we studied the oscillating velocity in the point on the surface of transducer, that lays in the opposite direction to the baffle, and for angular dependencies we chosen some interesting frequencies to provide the investigations. This frequency and angular characteristics were compared between themselves and with characteristics of transducer itself, without baffle, for situations, when we changed the distance between the transducer and the baffle and the dimensions of the baffle were constant and when we changed the dimensions of the baffle without changing the distance between baffle and the transducer. As a result of investigations we have determined physical causes of the changes in the oscillating velocity of the surface of cylindrical piezoceramic transducer as a part of the system “radiator – baffle”.Ref. 6, fig. 4.

Novel poling method for piezoelectric 0–3 composites and transfer to series production

Integration of piezoceramic particles into polymers is considered to meet current and future challenges of function integration in lightweight engineering. Especially composites with integrated piezoceramic transducers for sensory tasks such as condition or structural health monitoring are gaining importance. A possible, mass production compatible manufacturing approach is the direct formation of a piezoceramic particle-electrode-assembly during the processing by integrating the ceramic and its electrodes into the polymer matrix. The piezoelectric particles are then fully surrounded by the polymer matrix, forming a so-called 0–3 composite (Newnham et al., 1978). However, it is unpoled and inactive and thus requires poling to activate the piezoelectric properties. It is known that poling of piezoelectric particles in a polymer matrix is difficult due to the misfit in dielectric constants of polymer and ceramic. To overcome this obstacle, a poling process that is conducted during the uncured stage of the polymer matrix is introduced in the present paper, making use of the relatively low electrical resistance of the selected polymer in the uncured state. In a first step, the method is modelled and experimentally verified using specimen made of PZT pearls embedded in epoxy resin. In these preliminary experiments, effective piezoelectric charge coefficients up to 28.6 pC/N were achieved. The method is transferred and integrated into the production of fibre-reinforced polyurethane composites. Effective piezoelectric charge coefficients of 5.5 pC/N are obtained for the polyurethane based composites.

Water-molecular emission from cavitation bubbles affected by electric fields

Orange emission was observed during multibubble sonoluminescence at 1 MHz in water saturated with noble gas. The emission arose in the vicinity of the peeled ground electrode of a piezoceramic transducer exposed to water, suggesting that cavitation bubbles were affected by the electric fields that leaked from the transducer. The spectrum of the emission exhibited a broad component whose intensity increased towards the near-infrared region with peaks at 713 and 813 nm. The spectral shape was independent of the saturation gas of He, Ne, or Kr. The broad component was attributed to the superposition of lines due to vibration-rotation transitions of water molecules, each of which was broadened by the high pressure and electric fields at bubble collapse. An emission mechanism based on charge induction by electric fields and the charged droplet model is proposed.

Dynamic Modelling of Embeddable Piezoceramic Transducers.

Embedded Lead Zirconate Titanate (PZT) transducers have been widely used in research related to monitoring the health status of concrete structures. This paper presents a dynamic model of an embeddable PZT transducer with a waterproof layer and a protecting layer. The proposed model is verified by finite-element method (FEM). Based on the proposed model, the factors influencing the dynamic property of the embeddable PZT transducers, which include the material and thickness of the protecting layer, the material and thickness of the waterproof layer, and the thickness of the PZT, are analyzed. These analyses are further validated by a series of dynamic stress transfer experiments on embeddable PZT transducers. The results show that the excitation frequency can significantly affect the stress transfer of the PZT transducer in terms of both amplitude and signal phase. The natural frequency in the poling direction for the PZT transducer is affected by the material properties and the thickness of the waterproof and protecting layers. The studies in this paper will provide a scientific basis to design embeddable PZT transducers with special functions.

Characterization of Ultrasound Energy Diffusion Due to Small-Size Damage on an Aluminum Plate Using Piezoceramic Transducers.

During the propagation of ultrasonic waves in structures, there is usually energy loss due to ultrasound energy diffusion and dissipation. The aim of this research is to characterize the ultrasound energy diffusion that occurs due to small-size damage on an aluminum plate using piezoceramic transducers, for the future purpose of developing a damage detection algorithm. The ultrasonic energy diffusion coefficient is related to the damage distributed in the medium. Meanwhile, the ultrasonic energy dissipation coefficient is related to the inhomogeneity of the medium. Both are usually employed to describe the characteristics of ultrasound energy diffusion. The existence of multimodes of Lamb waves in metallic plate structures results in the asynchronous energy transport of different modes. The mode of Lamb waves has a great influence on ultrasound energy diffusion as a result, and thus has to be chosen appropriately. In order to study the characteristics of ultrasound energy diffusion in metallic plate structures, an experimental setup of an aluminum plate with a through-hole, whose diameter varies from 0.6 mm to 1.2 mm, is used as the test specimen with the help of piezoceramic transducers. The experimental results of two categories of damages at different locations reveal that the existence of damage changes the energy transport between the actuator and the sensor. Also, when there is only one dominate mode of Lamb wave excited in the structure, the ultrasound energy diffusion coefficient decreases approximately linearly with the diameter of the simulated damage. Meanwhile, the ultrasonic energy dissipation coefficient increases approximately linearly with the diameter of the simulated damage. However, when two or more modes of Lamb waves are excited, due to the existence of different group velocities between the different modes, the energy transport of the different modes is asynchronous, and the ultrasonic energy diffusion is not strictly linear with the size of the damage. Therefore, it is recommended that only one dominant mode of Lamb wave should be excited during the characterization process, in order to ensure that the linear relationship between the damage size and the characteristic parameters is maintained. In addition, the findings from this paper demonstrate the potential of developing future damage detection algorithms using the linear relationships between damage size and the ultrasound energy diffusion coefficient or ultrasonic energy dissipation coefficient when a single dominant mode is excited.

Experimental Investigation on the Detection of Multiple Surface Cracks Using Vibrothermography with a Low-Power Piezoceramic Actuator.

Vibrothermography often employs a high-power actuator to generate heat on a specimen to reveal damage, however, the high-power actuator brings inconvenience to the application and possibly introduces additional damage to the inspected objects. This study uses a low-power piezoceramic transducer as the actuator of vibrothermography and explores its ability to detect multiple surface cracks in a metal part. Experiments were conducted on a thin aluminum beam with three cracks in different orientations. Detailed analyses of both thermograms and temperature data are presented to validate the proposed vibrothermography method. To further investigate the performance of the proposed vibrothermography method, we experimentally studied the effects of several critical factors, including the amplitude of excitation signal, specimen constraints, relative position between the transducer and cracks (the transducer is mounted on the same or the opposite side with the cracks). The results demonstrate that all cracks can be detected conveniently and simultaneously by using the proposed low-power vibrothermography. We also found that the magnitude of excitation signal and the specimen constraints have a great influence on detection results. Combined with effective data processing methods, such as Fourier transformation employed in this study, the proposed method provides a promising potential to detect multiple cracks on a metal surface in a safe and effective manner.