Theoretical model and experimental verification of flexoelectric response of porous plate under impact load and its application as passive and protective impact sensor

Porous materials are widely used as protecting devices against low-velocity impacts due to their excellent energy absorption and dissipation capabilities. Thus, monitoring low-velocity impacts on porous materials is vital for safety assessment of humans and structures in industry. It is advantageous and cost-effective to enable porous materials to have the function of in-situ sensing without extra sensors. In this work, we propose to use polymeric foams as in-situ impact sensors by utilizing their intrinsic flexoelectric effect. We first establish a theoretical model for the flexoelectric output of a porous plate under impacts. Then, we validate the model by measuring the flexoelectric response of porous polydimethylsiloxane (PDMS) plates under low-velocity impacts. We show that the porous plates can accurately sense the information of the impacts including the velocity, the masses and sizes of the impacting spheres. Finally, we demonstrate an application of the porous material as an impact sensor-and-protector that senses the impact and keeps the integrity of a dropping egg. This work opens a promising avenue to develop a new type of monitoring technology for low-velocity impacts based on the flexoelectric effects of porous materials by integrating a sensing function with their conventional protecting role.