Structural health monitoring (SHM) is growing rapidly with strong demand from industrial automation, digital twins, and Internet of Things (IoT). In contrast to the manual installation of discrete ...devices, piezoelectric transducers by directly coating and patterning the piezoelectric materials on the engineering structures show the potential for achieving SHM function with improved benefits over cost. Until the recent years, high-performance lead-free piezoelectric ceramic coatings, including potassium-sodium niobate (KNN) and bismuth sodium titanate (BNT)-based coatings, are produced by thermal spray method. This article reviews the background and progresses of using thermal spray method for fabricating piezoelectric ceramic coatings and their values for SHM applications. The review shows the combination of environmentally friendly lead-free compositions, and the scalable thermal spray processing method opens substantial application opportunities. Ultrasonic SHM technology enabled by thermal-sprayed piezoelectric ceramic coatings is an important area where the lead-free piezoelectric ceramic materials can play with their technical competitiveness and commercial values over the lead-based compositions.
Shear mode guided waves are highly demanded for underwater structural health monitoring (SHM) applications due to their simplified non‐dispersive feature and minimal acoustic energy loss in the ...presence of liquid. Excitation and detection of pure shear wave are challenging using conventional piezoelectric materials used in the current ultrasonic transducers because they have complex piezoelectric responses mixed with multiple longitudinal, transverse, and shear modes. They also suffer from aging issue due to depoling. Here, conformable shear mode ultrasonic transducers are designed and made of flexible piezoelectric poly (L‐lactic acid) (PLLA) fibers on both flat and tubular structures. The electromechanical responses over a macroscopic area of the transducers are evaluated in a wide frequency range up to 500 kHz. The PLLA fiber‐based shear mode ultrasonic transducers exhibit a consistent sensitivity of detecting defects in liquid and air. In addition, the only shear mode in PLLA fibers originates from crystal structure without requiring electrical poling to render piezoelectricity, thus does not depole due to aging. The theoretical analyses including ab initio calculations and experimental results on both flat and tubular structures show the great potential of PLLA material and significant advantage of PLLA fiber‐based shear mode ultrasonic transducers for underwater SHM applications.
Pure shear mode and conformable ultrasonic transducers are designed and produced from flexible piezoelectric poly (L‐lactic acid) (PLLA) fibers with molecular chain orientation. The PLLA‐fiber transducers exhibit unique directivity for non‐dispersive shear wave, and no substantial change in the ultrasonic signals for operation in water. The theoretical analysis and experimental demonstration show great value for underwater ultrasonic structural health monitoring applications.
When raindrops impact on the surface of a piezoelectric beam, strain energy produced by the impinging raindrop will be converted to harvestable electrical energy by the piezoelectric layers in a ...cantilever beam. The novelty of this study is to investigate the performance of the harvester in actual rain and provide practical insights on implementation. The influences of rain parameters such as rain rate, rainfall depth, raindrop count, and drop size distribution (DSD) are discussed in this study. The raindrops accumulated on the surface of the piezoelectric beam will form a water layer. It is described using added mass coefficient in this study. In an actual rain experiment, a piezoelectric beam with surface area of 0.0018 m2 is able to produce 2076 μJ of energy over a duration of 301 min. The energy generation of a raindrop impact piezoelectric energy harvester is highly dependent on the rain rate. Due to the inconsistency of the energy generation, the piezoelectric energy harvester would require an integration of suitable energy storage device for continuous operation. Nevertheless, this work shows the feasibility of harvesting raindrop energy using a piezoelectric beam.
•The performance of a piezoelectric rain energy harvester is tested in actual rain.•The energy generation is highly dependent on the rain rate.•Practical insights on the implementation of the harvester are discussed.•A total energy of 2076 μJ is generated over a duration of 301 min.
Shear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when ...in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.
Direct‐write conformable shear mode ultrasonic transducers are designed and produced from lead‐free piezoelectric potassium sodium niobate (KNN) ceramic coatings. These coating transducers ensure consistent, non‐dispersive shear wave transmission and stable ultrasonic signals across various temperatures and underwater conditions. Such reliability and robustness highlight their potential for monitoring the health of submerged or subterranean structures, especially in harsh environments.
Advancements in the structural health monitoring (SHM) technology of composite materials are of paramount importance for early detection of critical damage. In this work, direct-write transducers ...(DWTs) were designed for the excitation and reception of selective ultrasonic guided waves and fabricated by spraying 25-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>-thick piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TRFE) coating with a comb-shaped electrode on carbon fiber-reinforced polymer (CFRP) plates. The characteristics and performance of the ultrasonic DWTs were benchmarked with the state-of-the-art devices, discrete lead zirconate titanate (PZT) ceramic transducers surface-mounted on the same CFRP plates. The DWTs exhibited improved Lamb wave mode excitation (A 0 or S 0 mode) relative to the discrete PZT transducers. Moreover, high signal-to-noise ratio was obtained by effectively canceling other modes and enhancing the directivity with the periodic comb-shaped electrode design of the DWTs, despite the smaller signal amplitudes. The enhanced directivity overcompensates for lower amplitude attenuation, making DWT a good candidate for locally monitoring critical stress hot spot regions in the CFRP structure prone to early damage initiation. It is shown that pairing a DWT sensor with a discrete PZT actuator could further achieve balanced performance in both wave mode selection and signal amplitudes, making this combination really attractive for ultrasonic SHM.
Zero-group-velocity (ZGV) Lamb waves are usually excited and detected using non-contact laser ultrasonic systems, as contact techniques such as using conventional bulky discrete piezoelectric ...transducer may cause interferences and errors in identifying the ZGV Lamb waves due to the large mass and stiffness introduced. Nevertheless, contact transducers have many advantages over the laser ultrasonic method, including cost, sensitivity, safety, and efficiency. Here, a contact technique is explored by using lightweight and low-profile direct-write piezoelectric ultrasonic transducer (DWT) made of piezoelectric polymer coating to generate and detect the ZGV Lamb waves. The frequency shift and wave attenuation of the ZGV Lamb waves, and their ability for monitoring adhesive bonded structure are investigated with both numerical modeling and experimental testing, with comparison between the DWT and discrete piezoelectric transducer. The potential of the DWT for generating and detecting ZGV Lamb waves for ultrasonic nondestructive evaluation is demonstrated by overcoming the drawbacks of discrete piezoelectric transducers.
The use of carbon fiber reinforced polymer (CFRP) composites is gaining popularity in various industries. Due to its anisotropic nature, the characterization of the mechanical properties of CFRP is ...challenging. The current practices for determination of the elastic properties of CFRP materials are through destructive testing methods, which is not feasible in many in-situ scenarios. This paper presents an in-situ and non-destructive method to characterize elastic properties of CFRP plates by using an ultrasonic 2D-array transducer. The ultrasonic 2D-array transducer was made of 64 piezoelectric elements and the measurement is automated by an advanced ultrasonic system. An automated time-of-flight extraction algorithm was used based on peak detection of ultrasonic signals. The elastic constants of the CFRP plates were calculated based on the Christoffel equation. This method was validated by ultrasonic through-transmission method by using two discrete ultrasonic transducers. Complete elastic constant matrix measurements for unidirectional and quasi-isotropic CFRP plates were demonstrated using the proposed method. This method has higher positional accuracy, faster testing speed, and better consistency compared to through-transmission method. This work can also be applied for in-situ structural health monitoring of elastic properties changes of materials and structures.
Conformability, lightweight, consistency and low cost due to batch fabrication in situ on host structures are the attractive advantages of ultrasonic transducers made of piezoelectric polymer ...coatings for structural health monitoring (SHM). However, knowledge about the environmental impacts of piezoelectric polymer ultrasonic transducers is lacking, limiting their widespread use for SHM in industries. The purpose of this work is to evaluate whether direct-write transducers (DWTs) fabricated from piezoelectric polymer coatings can withstand various natural environmental impacts. The ultrasonic signals of the DWTs and properties of the piezoelectric polymer coatings fabricated in situ on the test coupons were evaluated during and after exposure to various environmental conditions, including high and low temperatures, icing, rain, humidity, and the salt fog test. Our experimental results and analyses showed that it is promising for the DWTs made of piezoelectric P(VDF-TrFE) polymer coating with an appropriate protective layer to pass various operational conditions according to US standards.
While the active ultrasonic method is an attractive structural health monitoring (SHM) technology, many practical issues such as weight of transducers and cables, energy consumption, reliability and ...cost of implementation are restraining its application. To overcome these challenges, an active ultrasonic SHM technology enabled by a direct-write transducer (DWT) array and edge computing process is proposed in this work. The operation feasibility of the monitoring function is demonstrated with Lamb wave excited and detected by a linear DWT array fabricated in situ from piezoelectric P(VDF-TrFE) polymer coating on an aluminum alloy plate with a simulated defect. The DWT array features lightweight, small profile, high conformability, and implementation scalability, whilst the edge-computing circuit dedicatedly designed for the active ultrasonic SHM is able to perform signal processing at the sensor nodes before wirelessly transmitting the data to a remote host device. The successful implementation of edge-computing processes is able to greatly decrease the amount of data to be transferred by 331 times and decrease the total energy consumption for the wireless module by 224 times. The results and analyses show that the combination of the piezoelectric DWT and edge-computing process provides a promising technical solution for realizing practical wireless active ultrasonic SHM system.
This paper presents a method for measuring surface cracks based on the analysis of Rayleigh waves in the frequency domain. The Rayleigh waves were detected by a Rayleigh wave receiver array made of a ...piezoelectric polyvinylidene fluoride (PVDF) film and enhanced by a delay-and-sum algorithm. This method employs the determined reflection factors of Rayleigh waves scattered at a surface fatigue crack to calculate the crack depth. In the frequency domain, the inverse scattering problem is solved by comparing the reflection factor of the Rayleigh waves between the measured and the theoretical curves. The experimental measurement results quantitatively matched the simulated surface crack depths. The advantages of using the low-profile Rayleigh wave receiver array made of a PVDF film for detecting the incident and reflected Rayleigh waves were analyzed in contrast with those of a Rayleigh wave receiver using a laser vibrometer and a conventional lead zirconate titanate (PZT) array. It was found that the Rayleigh waves propagating across the Rayleigh wave receiver array made of the PVDF film had a lower attenuation rate of 0.15 dB/mm compared to that of 0.30 dB/mm of the PZT array. Multiple Rayleigh wave receiver arrays made of the PVDF film were applied for monitoring surface fatigue crack initiation and propagation at welded joints under cyclic mechanical loading. Cracks with a depth range of 0.36-0.94 mm were successfully monitored.
