The design concepts and fabrication processes of flexible electrets with ultrahigh equivalent piezoelectric effect.

Electromechanical coupling devices play a crucial role in high-precision actuation and high-sensitivity mechanical sensing. With a continuous increase in the required precision of actuation and sensing, coupled with the complexity of service environments, especially in mechanical conditions, a key scientific challenge is to enable these devices to simultaneously achieve ultra-high electromechanical coupling efficiency and robust environmental adaptability.

To address this challenge, Professor Xu Minglong's team at Xi'an Jiaotong University (XJTU) proposed a novel design and fabrication method for thin films based on flexible electret materials, exhibiting ultra-high equivalent piezoelectric effects.

The team created a sandwich-structured piezoelectric-electret composite film using two layers of fluorinated ethylene propylene (FEP) encasing a middle layer of poly (vinylidene fluoride-trifluoroethylene) copolymer (PVDF-TrFE).

They patterned the middle layer to form porous structures at macroscopic scales, and further utilized thermal stress processing to generate microscale wrinkles at the interfaces. This multi-scale design significantly increased the effective area for net charge storage. Subsequent electrode polarization embedded opposite charges on either side of these wrinkles, creating equivalent oriented dipoles. Consequently, when subjected to mechanical loads, deformation of the electret material alters the equivalent dipole moments, inducing local electric field changes that generate an ultra-high equivalent piezoelectric effect in the external circuit.

This research, titled ‌Ultra-sensitive piezoelectric-like film with designed cross-scale pores‌, was published in Science Advances.