Flexoelectric barium strontium titanate (BST) hydrophones

Flexoelectric hydrophones offer the possibility of reasonable sensitivity in lead-free systems. Flexoelectricity utilizes strain gradients, rathan the strain, in the case of a piezoelectric. As a fourth rank tensor, flexoelectricity is shown by all solids; the magnitude of the flexoelectric coefficient scales with the relative permittivity, In this work, a Ba0.7Sr0.3TiO3 ceramic with an effective flexoelectric coefficient, ∼μ12, of 105.6 ± 0.6 μC/m at room temperature was utilized in a prototype three-point bending hydrophone. Tap testing with a calibrated acoustic hammer showed a resonant frequency of 250 Hz and a maximum sensitivity of 80 pC/N. Finite element analysis (FEA) was employed to compare single and three bending point hydrophone designs. The results showed a 43% increase in charge output in the three bending point design versus the single bending point design despite an average strain decrease of 48% in each electrode pair. This design would lower the voltage output by 48% in a voltage-based design unless the voltages could be added in series.