Effects of an attached functionally graded layer on the electromechanical behaviors of piezoelectric semiconductor fibers

In this paper,we propose a specific two-layer model consisting of a functionally graded(FG)layer and a piezoelectric semiconductor(PS)layer.Based on the macroscopic theory of PS materials,the effects brought about by the attached FG layer on the piezotronic behaviors of homogeneous n-type PS fibers and PN junctions are investigated.The semi-analytical solutions of the electromechanical fields are obtained by expanding the displacement and carrier concentration variation into power series.Results show that the antisymmetry of the potential and electron concentration distributions in homogeneous n-type PS fibers is destroyed due to the material inhomogeneity of the attached FG layer.In addition,by creating jump discontinuities in the material properties of the FG layer,potential barriers/wells can be produced in the middle of the fiber.Similarly,the potential barrier configuration near the interface of a homogeneous PS PN junction can also be manipulated in this way,which offers a new choice for the design of PN junction based devices.

A Neural Coordination Strategy for Attachment and Detachment of a Climbing Robot Inspired by Gecko Locomotion

Climbing behavior is a superior motion skill that animals have evolved to obtain a more beneficial position in complex natural environments.Compared to animals,current bionic climbing robots are less agile,stable,and energy-efficient.Further,they locomote at a low speed and have poor adaptation to the substrate.One of the key elements that can improve their locomotion efficiency is the active and flexible feet or toes observed in climbing animals.Inspired by the active attachment-detachment behavior of geckos,a hybrid pneumatic-electric-driven climbing robot with active attachment-detachment bionic flexible feet(toes)was developed.Although the introduction of bionic flexible toes can effectively improve the robot’s adaptability to the environment,it also poses control challenges,specifically,the realization of attachment-detachment behavior by the mechanics of the feet,the realization of hybrid drive control with different response characteristics,and the interlimb collaboration and limb-foot coordination with a hysteresis effect.Through the analysis of geckos’limbs and foot kinematic behavior during climbing,rhythmic attachment-detachment strategies and coordination behavior between toes and limbs at different inclines were identified.To enable the robot to achieve similar foot attachment-detachment behavior for climbing ability enhancement,we propose a modular neural control framework comprising a central pattern generator module,a post-processing central pattern generation module,a hysteresis delay line module,and an actuator signal conditioning module.Among them,the hysteresis adaptation module helps the bionic flexible toes to achieve variable phase relationships with the motorized joint,thus enabling proper limb-to-foot coordination and interlimb collaboration.The experiments demonstrated that the robot with neural control achieved proper coordination,resulting in a foot with a 285%larger adhesion area than that of a conventional algorithm.In addition,in the plane/arc climbing scenario,the robot with coordination behavior increased by as much as 150%,compared to the incoordinated one owing to its higher adhesion reliability.