Micro‐Structuration of Piezoelectric Composites Using Dielectrophoresis: Toward Application in Condition Monitoring of Bearings
A piezoelectric material based on inorganic/organic composites suitable for aerospace and aeronautical monitoring sensors was fabricated. The designed piezoelectric composite was made of a lead zirconate titanate (PZT) filler embedded in a polydimethylsiloxane (PDMS) matrix. To improve the piezoelectric properties of the film, we increased the connectivity of the ceramic filler via electric field‐assisted structuration, leading to a columnar arrangement of the filler across the thickness. This structure (1–3) showed higher piezoelectricity than one with a randomly dispersed filler (0–3). Piezoelectric and dielectric activities of PZT/PDMS in 0–3 and 1–3 configurations were compared at different volume fractions. The 1–3 connectivity led to superior piezoelectric behavior. Thermal stability and high-temperature X‐ray diffraction analyses indicated that the composites were stable and maintained a good piezoelectric response even at 200 °C. Following process optimization, the piezoelectric behavior of this new class of composites approached that of fluorinated ferroelectric polymers, with the advantage that the stability of the piezoelectric properties was preserved at a higher temperature and lower poling electric field. In conclusion, there is potential for integrating the designed sensor in aircraft ball bearings for condition monitoring.
In aeronautics and aerospace, there is a growing need for new sensor materials suitable for direct health condition monitoring of complex structures. The main requirements when designing such sensors are sensibility, frequency bandwidth, and temperature drift [1,2]. For simple system integration, these sensors must also be light and non‐intrusive for the system with high mechanical resistance and easy processability.
Due to their ability to translate a mechanical impulse into an electric response, piezoelectric materials are commonly used as sensors in vibration monitoring, impact detection, and ultrasonic receiving sensors [2–5]. Different classes of piezoelectric materials exist, such as ferroelectric ceramics, piezoelectric polymers, and piezoelectric composites made of a ferroelectric ceramic filler embedded in a polymer matrix. Piezoelectric composites are most suitable for the above applications as they combine the piezoelectric properties of the filler with the flexibility of the matrix . Furthermore, they are characterized by a low poling electric field and high Curie temperature, making them more suitable than ferroelectric polymers . Being well workable, piezoelectric composites can be simply integrated into complex designs .
Phase arrangement is a key factor influencing the piezoelectric properties of a composite. Composites with 0–3 connectivity are most commonly produced because of their simple fabrication. However, they exhibit low piezoelectric sensibility until they reach large volumetric filler contents, which in turn deteriorate the mechanical properties . A solution to this problem is to align the fillers in columns within the matrix. In such anisotropic structures, called 1–3, the particles are closely aligned along the preferred direction, enhancing the piezoelectric properties of the whole material [4,5].