Active sensing for measuring contact of thin film gecko-inspired adhesives

Active sensing provides a way to assess whether a thin film of gecko-inspired adhesive has made good contact with a surface. This knowledge is useful for applications like gripping objects in space where a failed grasp could lead to loss of the object. Our active sensing approach uses Lamb waves in thin bilayers, excited, and detected by piezoelectric strips. From the theory, we describe how attenuation increases with contact boundary condition changes. We validated the theory using frustrated total internal reflection imaging, showing that attenuation increases as the contact area grows. Pull tests on different textures of acrylic plate show that the slope change of the signal can predict the maximum adhesion limit with a 10 N window and predict impending failure with a detection rate >80%. Lifting a cylindrical object shows that the sensor can signal different types of failures with a detection rate >85%, associated with unstable grasping.