A curvature sensor based on flexoelectricity using Ba0.64Sr0.36TiO3 (BST) material is proposed and developed in this paper. The working principle of the sensor is based on the flexoelectricity, exhibiting coupling between mechanical strain gradient and electric polarization. A BST curvature sensor is lab prepared using a conventional solid state processing method. The curvature sensing is demonstrated in four point bending tests of the beam under harmonic loads. BST sensors are attached on both side surfaces of an aluminum beam, located symmetrically with respect to its neutral axis. Analyses have shown that the epoxy bonding layer plays a critical role for curvature transfer. Consequently a shear lag effect is taken into account for extracting actual curvature from the sensor measurement. Experimental results demonstrated good linearity from the charge outputs under the frequencies tests and showed a sensor sensitivity of 30.78pC•m in comparison with 32.48pC•m from theoretical prediction. The BST sensor provides a direct curvature measure instead of using traditional strain gage through interpolation and may offer an optional avenue for on-line and in-situ structural health monitoring.
In this paper, a method to focus flexural Lamb waves to a local area by mounting elastic metamaterials (EMMs) on the
surface of the plate is proposed. The EMM consists of silicon rubber and lead connected in series bonded vertically on
an aluminum plate. A simplified effective mass-“spring”-mass model is used to study the EMM plate. The frequency-dependent
effective mass density of the EMM plate is determined with the aid of the numerically based effective
medium method. By making use of the low locally resonant frequency of the EMM plate, the EMM plate is carefully
designed with different dimensions to attain high effective mass densities. The effective mass density can be assumed to
dominate the change of wave velocity and propagation direction in the EMM plate. An effective mass density profile is
then employed along the transverse direction of wave propagation to achieve focusing. Finally, numerical simulation
with finite element method (FEM) is utilized to investigate the focusing phenomenon of the A0 mode Lamb waves at 30
kHz and the out-of-plane displacement response beyond the EMM region. Numerical simulation results have shown that
focusing the low frequency A0 mode Lamb waves using EMMs is feasible. The focusing may have potential applications
in structural health monitoring by manipulating Lamb waves through controlling and focusing Lamb waves to any
arbitrary location of the plate with amplified displacement and yet largely retained five-peaked toneburst waveform.