Piezoelectric devices are used for energy harvesting, pressure sensors, microphones, and medical imaging, among other applications. Still, they have limitations in energy efficiency and reliability, and most devices are made from lead-based materials. In recent years, flexoelectric technology has garnered interest as a lead-free alternative.

Flexoelectricity is driven by strain gradients in the material to induce electrical polarization. Although flexoelectricity is a universal phenomenon in all insulating materials and is understood fundamentally, device development for practical applications is rare.

Hahn et al. built a hydrophone prototype to study how such a device, used to hear and record underwater sounds, might measure up to its piezoelectric counterpart. They used barium strontium titanate (BST), a ceramic material demonstrated to have the best flexoelectric coefficients.

Knowing the flexoelectric effect is sensitive to bending deformation, the researchers built a single-bending point prototype, using a BST beam measuring 10 millimeters wide and 77 millimeters long. Finite element analysis (FEA) was employed to study the single-bending point and three-bending point configurations.

The FEA modeling showed that the three-bending point design outperformed the single-bending point one by 43%, despite an average strain decrease. The greater number of flexural points enables harvesting in more areas, because the strain gradient decays horizontally from the bending points. Therefore, increasing the collection area in the single-bending point design does not significantly increase power generation.

“The ideal situation for flexoelectric materials is to collect the maximum strain gradient, which is at the flexural points,” author Michael Hahn said. “The multi-bending point experiments evaluated in FEA should be further investigated and confirmed by prototyping experiments.”

Source: “Flexoelectric barium strontium titanate (BST) hydrophones,” by Michael Hahn, Susan Trolier-McKinstry, and Richard J. Meyer Jr., Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0038756.

This paper is part of the open Trends in Flexoelectricity Collection, learn more here. Submission Deadline: February 28, 2021.