Applications
Structural Health Monitoring (SHM)
SHM is a technology that involves permanently attaching or embedding sensors into critical infrastructure and structures—such as bridges, buildings, aircraft, and pipelines—to evaluate their condition in real-time, detect damage at an early stage, and predict their remaining lifespan. Real-time monitoring offers enormous economic and social benefits by enhancing safety and reducing maintenance costs.
P(VDF-TrFE) Copolymers for SHM Applications
Traditionally, piezoelectric ceramic sensors like PZT (lead zirconate titanate) have been used in SHM, but they come with several limitations. P(VDF-TrFE) polymer sensors offer unique advantages that overcome these challenges.
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Superior Flexibility and Conformability:
PZT is a ceramic and is inherently brittle, making it difficult to apply to curved or complex-shaped structures. In contrast, P(VDF-TrFE) is highly flexible in film or fiber form and can perfectly conform to any complex surface, such as pipes, aircraft fuselages, or bridge cables. This is a critical factor for maximizing the coupling between the sensor and the structure, thereby enhancing signal transfer efficiency.
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Lightweight and Non-Invasive:
Polymer sensors are extremely lightweight and have a negligible effect on the intrinsic dynamic properties (e.g., vibration frequencies) of the structure being monitored. This is crucial for accurate structural state analysis.
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Excellent Durability and Environmental Resistance:
P(VDF-TrFE) is chemically very stable and exhibits outstanding resistance to external environmental factors such as moisture, UV radiation, and temperature fluctuations. Accelerated aging tests have demonstrated that these sensors can reliably measure changes in a structure's condition without significant performance degradation. This is an essential characteristic for infrastructure monitoring, which requires a service life of several decades.
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Long-Term Reliability and Fatigue Resistance:
SHM sensors must withstand millions of cycles of repetitive loading (e.g., from vehicle traffic or wind). The P(VDF-TrFE) polymer itself shows excellent fatigue resistance, with almost no degradation in piezoelectric performance even after more than 10 million mechanical strain cycles. Previously reported performance degradation was largely due to the failure of rigid metal electrodes, a problem that has recently been solved by using flexible electrodes (e.g., silver paste).
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Cost-Effectiveness and Scalability:
The ease of manufacturing large-area films, combined with wireless sensor networks, can eliminate the high costs associated with installing extensive cabling, making it advantageous for monitoring large-scale structures cost-effectively.
Working Principle
P(VDF-TrFE) sensors detect structural damage using both passive and active methods.
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Passive Sensing:
It can detect the faint acoustic emissions (AE) released when a crack forms or the vibrations caused by an external impact. This method is simple as it requires no separate signal generator, but it can only detect a signal after damage has already occurred.
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Active Sensing:
This is the core technology of SHM. A part of the sensor network acts as an actuator, intentionally propagating signals like ultrasonic guided waves through the structure. Other sensors then receive these signals. A signal from the structure in a healthy state (the baseline) is stored in advance. Over time, if damage such as cracks, delamination, or corrosion occurs within the structure, the guided waves will be scattered or attenuated by the damaged area. This causes the waveform, amplitude, and arrival time of the received signal to differ from the baseline. By analyzing these changes in the signal, it is possible to determine the existence (detection), location (localization), and severity (classification) of the damage. By integrating data from multiple sensors, the location of the damage can be pinpointed with high precision.
Application Fields
1. Aerospace
Modern aircraft increasingly rely on carbon fiber reinforced composites (CFRP) for their lightweight and high-strength properties. However, these composites are highly susceptible to "Barely Visible Impact Damage" (BVID), where low-velocity impacts (e.g., a dropped tool) cause severe internal cracking or delamination with little to no visible surface damage. This internal damage can reduce the material's compressive strength by up to 60% and can grow under flight-induced fatigue loads, potentially leading to catastrophic structural failure. Traditional non-destructive testing (NDT) is time-consuming, expensive, and requires grounding the aircraft, significantly reducing operational efficiency.
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Implementing Smart Structures: P(VDF-TrFE) sensors are thin and flexible, allowing them to conform perfectly to the complex curved surfaces of fuselages and wings. They can also be embedded directly between composite layers during manufacturing. This transforms the aircraft structure itself into a vast "nervous system" that monitors its own health in real-time.
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Active Damage Detection: A network of sensors acts as both actuators, generating ultrasonic guided Lamb waves, and sensors, receiving these waves. By comparing the received signals to a baseline (healthy state) dataset, any changes in the wave caused by BVID or fatigue cracks can be detected. Artificial intelligence algorithms analyze these minute signal changes to precisely identify the location and severity of the damage.
2. Civil/Architectural Engineering
Large-scale civil infrastructure such as bridges, high-rise buildings, and tunnels are constantly subjected to stresses from traffic loads, wind pressure, temperature variations, and unpredictable events like earthquakes. This leads to fatigue accumulation, concrete cracking, and steel corrosion over time. Such damage often occurs gradually and may not be visible until structural performance is already significantly compromised, requiring costly and extensive repairs.
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Large-Scale Distributed Sensing: P(VDF-TrFE) sensors are cost-effective and durable, making them economically viable for deployment in large numbers across vast areas like bridge decks, main cables, and building beam-column joints. They can be embedded in concrete during construction or bonded to existing steel frames to monitor stress and vibration distribution across the entire structure in real-time.
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Fatigue Monitoring: By continuously measuring vibrations and strain caused by heavy vehicles, the system can assess the fatigue accumulation at critical points and predict the structure's remaining service life.
3. Energy/Industrial Plants
Various components in the energy/industrial fields, for example, wind turbine blades, gas pipelines, and hydrogen tank, can be exposed to harsh pressure, temperature, environmental conditions. This leads to frequent damage such as surface erosion, adhesive bond fatigue, and internal cracking, which reduces power generation efficiency and can lead to failure of components. Monitoring the condition of wind turbine blades, gas pipelines, and hydrogen tank to prevent major accidents.