PhD Thesis Defense: Huan Zhao

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"Design and Manufacturing of Multifunctional Piezoelectric Composites"

Abstract

Piezoelectric materials possess a unique ability to convert mechanical energy into electrical signals and have broad industrial applications. However, monolithic piezoelectric materials such as piezoceramics and piezopolymers often suffer from inherent trade-offs among mechanical strength, elasticity, and durability. Piezoelectric composites, typically consisting of a polymer matrix with ceramic reinforcements, offer a solution by combining the advantages of each constituent. Nevertheless, maintaining stable mechanical performance in high-temperature environments remains a significant challenge as conventional polymer matrices usually experience structural degradation.
 
In this thesis, a novel piezoelectric composite is developed using a preceramic polymer (PCP) matrix with barium titanate (BTO) inclusions. PCPs are silicone-based polymers that undergo a unique polymer-to-ceramic phase transition upon heating. The Digital Light Processing (DLP) 3D printing technique is employed to fabricate the composites. The resulting piezocomposites can withstand compressive stress up to 30 MPa and strain up to 20% without structural failure, even at 500 °C. Moreover, repeated thermal cycling enhances the longitudinal piezoelectric coefficient (d33) to 6.98 pC/N, a 2.36-fold improvement over single-cycle processing.

To enhance the piezoelectric response beyond the inherent limits of bulk materials, this thesis explores advanced architectural designs. Studies of piezoelectric energy harvesters (PEH) and metastructure-based pressure sensors (MBPS) indicate that controlling strain distribution and deformation mechanisms through architectural design is crucial for improving electro-mechanical performance.

Guided by these insights, a multifunctional compressible piezocomposite sensor (CPS) is developed. Its unique geometry enables high-performance acceleration sensing and dynamic force sensing within a single device – capabilities that are typically incompatible in sensors made from bulk materials. As a low-frequency, triaxial accelerometer, the CPS achieves a sensitivity up to 5023.5 mV/g with a resonant frequency up to 23 Hz. As a dynamic force sensor, it demonstrates a sensitivity of 11.53 V/N over a force range up to 4 kN. Its extensive strain range (over 600%) also suggests potential for strain sensing. This dual-mode sensor overcomes the inherent sensitivity-range trade-off of conventional devices through its optimized geometry. In addition, its advanced material composition enables reliable performance at high temperatures. Together, these complementary attributes open new avenues for applications in robotics, aerospace, and biomedical technologies.

Thesis Committee

• Yan Li (Chair)
• Jifeng Liu
• William J. Scheideler
• Stewart Sherrit (NASA JPL)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.