Mr. Keyu Chen and Mr. Juntong Xing, Ph.D. students of Professor Wei-Hsin Liao, won the Best Student Paper Award – Gold and Silver Awards respectively at the 32nd International Conference on Adaptive Structures and Technologies (ICAST 2022).
Best Student Paper Award – Gold Award
Title: A Gradient Auxetic Piezoelectric Energy Harvester for Increased Power Output
Authors: Keyu Chen, Shitong Fang, Wei-Hsin Liao
Vibration energy harvesters (VEHs) have received extensive attention over the past decade, which can provide alternative and sustainable power supply for low powered sensors. In this paper, we design and experimentally validate a gradient auxetic piezoelectric energy harvester for increased power output, which combines a cantilever beam with a gradient auxetic structure. Compared with the normal uniform auxetic structure, the gradient auxetic structure can contribute to a more uniform strain distribution of the piezoelectric cantilever beam; thus, the proposed gradient auxetic energy harvester can produce higher power than the uniform auxetic energy harvester without increasing the stress concentration at the same time. Finite element analysis is performed to analyze the characteristics of the gradient auxetic energy harvester, which matches well with the experimental data. In the experimental validation, under 1 m/s2 base excitation, the power output of the gradient auxetic energy harvester is increased by 254% and 46%, respectively, compared with the conventional energy harvester and uniform auxetic energy harvester.
Fig. 1. Exploded view of the proposed gradient auxetic piezoelectric energy harvester.
Fig. 2. (a) Prototypes of the energy harvesters; and (b) experimental setup.
Fig. 3. RMS power output of the energy harvesters with different load resistances under 1 m/s2 base excitation.
Best Student Paper Award – Silver Award
Title: A Rotational Hybrid Energy Harvester Utilizing Dynamic Bistability
Authors: Juntong Xing, Shitong Fang, Xinlei Fu, Wei-Hsin Liao
Rotational energy harvesting is one of the promising approaches for realizing the self-powered wireless sensor networks. Incorporation of hybrid energy sources and geometric bistable nonlinearity can be a solution to enhance the energy harvesting performance under low-frequency excitations. This paper proposes a gravity-based rotational hybrid energy harvester by using the dynamic bistable mechanism for low-frequency applications. A comprehensive theoretical model considering the newly introduced piezoelectric stack and force magnification frame is derived based on the extended Hamilton’s principle. The piezoelectric and electromagnetic coupling coefficients are explicitly expressed and analyzed. Both numerical and experimental results show that increasing the spring stiffness can amplify the scavenged energy at a higher excitation frequency, and narrowing the impact gap can broaden the effective working bandwidth. Furthermore, the maximum power usually occurs with the impact inter-well phenomenon, after which the chaotic and intra-well oscillations appear successively. Besides, amongst the studied cases, the maximum total power output of 2.98 mW is generated at 7.5 Hz with a spring stiffness of 4200 N m−1, which is at least one order of magnitude higher than the other state-of-the-art energy harvesters under the same excitation. Based on the validated theoretical model, further parametric studies are performed to investigate the effects of the proof mass and the initial prestress on the piezoelectric stack. It is found that the hybrid rotational energy harvesting system can possess high tunability and adaptability to the frequency-variant environment by adjusting multiple structural parameters.
Fig. 1. (a) Schematic of the proposed rotational hybrid energy harvester; (b) Details of the piezoelectric stack energy harvester (PST-EH) and two magnets; (c) Details of the electromagnetic energy harvester (EM-EH) (top view and cutaway view).
Fig. 2. Diagrams of: (a) Piezoelectric coupling coefficients 𝜃p for various spring stiffness; (b) Electromagnetic coupling coefficient 𝜃emI; (c) Electromagnetic coupling coefficient 𝜃emII; (d) 3D potential energy; (e) Equilibrium points.
Fig. 3. Experimental set-up of the proposed rotational hybrid energy harvester: (a) Apparatus and platform; (b) Main view of the rotary disc; (c) Details of the soft stopper.
Fig. 4. Experimental and numerical results of frequency varying response for various spring stiffness: (a) Output power of PST-EH versus rotational frequency; (b) Output power of No. 1 EM-EH versus rotational frequency; (c) Output power of No. 2 EM-EH versus rotational frequency.
Fig. 5. Experimental results of impact gap varying response under 𝑘sp = 2800 N/m: (a) Output power of PST-EH versus rotational frequency; (b) Output power of No. 1 EM-EH versus rotational frequency; (c) Output power of No. 2 EM-EH versus rotational frequency.