Developments In Piezoelectric Nanogenerators

Acceleration sensors play a crucial and essential role in many fields, such as large mechanical structure testing, national defense, transportation, auto industry, biomedical devices, and so on.

Usually, a commercial acceleration sensor is made with piezoelectric ceramic, owing to its eminent piezoelectric performance (piezoelectricity can transform a force signal to an electrical signal). However, the application of piezoelectric ceramic acceleration sensors is largely limited in extreme service environments because of its inherent brittleness during performance. What’s more, the subsequent polarization processing is energy-intensive and complex.

Besides, Poly (vinylidene fluoride) (PVDF), a representative piezoelectric polymer, is another good choice given its excellent impact resistance and toughness. Unfortunately, the piezoelectric performance is not strong enough, leading to low sensitivity for sensors, in addition to requiring polarization processing.

In this work, we present PVDF with high crystallinity of β-phase (piezoelectricity is mainly from β-phase crystal) in a high pressure and high temperature environment. It shows good piezoelectricity without polarization processing. Based on it, a novel acceleration sensor is prepared. The sensor shows a high sensitivity of 2.405 nA·s2·m-1 and excellent stability (97% remaining after 10000 cycles).

Integrated with three ones, the self-powered 3D acceleration sensor is developed for vector acceleration measurement in any directions, as well as the compositions in three axes respectively. In addition, a real-time 3D frequency and acceleration sensor system is developed for vehicle monitoring system to avoid casualties when there is a vehicle accident. This provides an experienced reference for solving problems in vehicle safety monitoring and automobile security systems.

In prospect, the easy process of PVDF and the high sensitivity device provides potential for commercial production in many fields, such as transportation, self-powered devices, energy harvesting and so on.

In the next study, we will focus on improving the piezoelectricity of PVDF, with the goal of obtaining a higher sensitivity. A higher sensitivity can protect us better when we are driving. Despite this, the acceleration sensor can be applied in some extreme environments. For example, it can be set on a long bridge to monitor its condition, preventing sudden collapse. This helps us to repair the bridge and protect people’s lives.

On the other hand, fabricating PVDF as a nanogenerator for energy harvesting is also part of our future work. Owing to the outstanding piezoelectricity, PVDF prepared in high pressure and high temperature environments can generate higher open-circuit voltage and short-circuit current. If we apply it in our shoes, when we walk and run, it can harvest more energy for powering small electronics, such as some small sensors, watches, and even cell phones.

In a word, the PVDF prepared by this method has many applications, and we will improve their performance and expand the application fields further.

These findings are described in the article entitled Polarization-free high-crystallization β-PVDF piezoelectric nanogenerator toward self-powered 3D acceleration sensor, recently published in the journal Nano EnergyThis work was conducted by Long Jin, Songyuan Ma, Weili Deng, Cheng Yan, Tao Yang, Xiang Chu, Guo Tian, Da Xiong, Jun Lu, and Weiqing Yang from Southwest Jiaotong University.